When particularly good dispersion is required, a better option for incorporating these

additives is to produce an additive concentrate. To obtain the necessary dispersion in the final
product, the concentrate is produced utilizing a fluxed melt mixer such as a Banbury prior to
extrusion. The extruded concentrate may then be blended with the polymer matrix during a
final compounding stage or may be added during the final moulding or extrusion step. Colour
concentrates are a well-known example, but lubricants. UV/light stabilizers may also be
incorporated in this manner.

• High Add Levels

• Single screw extrusion
The addition of higher-add-levels of fillers and reinforcements may be done on a single screw
or a twin-screw extruder. The choice is determined by the type of filler/reinforcement. In
general, the single screw use is limited to low-aspect-ratio additives such as Ca CO3 and talc.

The production of CaCO3 filled and talc filled materials may be accomplished using only a
dry-solid mixer and a two-stage vented extruder. An Auger-type hopper stuffer assists
feeding. As the filler level increases, melt fluxing mixers, such as Farrel Continuous Mixer
(Figures 2) may be used to optimize mixing and distribution. The Farrel Continuous Mixer is
a counter rotating, non-intermeshing twin-rotor mixer. It can be divided into 3 zones: (a) Feed
zone (b) Mixing zone (c) Discharge zone. The feed zone of the mixer is designed to optimize
ingestion and delivery of feed m material (s) into the mixing zone. Upon entering the mixing
zone, the feed material is melted and then continuously fluxed, pumped, back mixed and it
exits through the discharge zone. The maximum achievable loading will depend, to some
extent, on the melt viscosity of the polymer, but primarily on the type of filler. For example,
specialized Ca CO3 concentrates have been produced with filler levels upto 80%, while it is
difficult to reach a 50% loading with mica.

At high filler loadings, intensive mixing may not be necessary, as long as the filler is
uniformly distributed. Over-mixing can cause separation. In general, both batch (Banbury)
and continuous (FCM type) mixers are suitable.

Metered feeding is necessary for all high filler-level systems. Fillers such as CaCO3 are
liable to bridge in the hopper. In addition, there is a potential for separation and build-up of
the filler on vertical metal surfaces. The critical design features of the feeders are the agitator
and the feed screw and their relationship with each other. The agitator should sweep the
hopper walls as closely as possible to prevent filler build-up. The hopper should be equipped
with a level control feeder.

SECTIONAL VIEW OF TYPICAL FCM IN OPERATION

The compounding extruder should have relatively shallow flights. A compression ratio of
2.5:1 is preferred and no additional mixing devices are generally required.

Mineral fillers tend to be hygroscopic. Therefore, a vacuum vent is utilized during the
extrusion step. When a cold-cut pelletizing system is used, the emerging strands from the die
face is taken into water bath and taken out quickly, taking care to ensure integrity of the
strands. A blower assists water removal from the strands prior to chopping.

ReciprocatingExtruders
In these types of machines, both rotational and reciprocating action of the screw occur
simultaneously and are continuous. These machines are specifically designed to enhance
mixing performance and are usually referred to as Ko-Kneaders.

A schematic sketch of a Ko-Kneader is shown in Figure (3). The Kneader is a single screw
extruder with interrupted screw flights and stationary pins or teeth in the barrel. The screw
flights can be continuous in the feed section and vent section to improve forward conveying.
In this section, no pins are located in the barrel. The mixing section of the screw is typically
double-fighted with a small helix angle of 13 degree. The interruptions in the screw flights
leave flight segments that look like vanes. There are three rows of pins or teeth along the
length of the barrel. The barrel has a clamshell design, which facilitates cleaning of the barrel.
Modern kneaders have a typical L/D ratio of about 11.

PP can be compounded with CaCO3, talc and glass fibres on Ko-Kneaders,

Twin screw extruders

The compounding of fillers, reinforcements, flame retardants (solids/liquids) can be achieved
with a twin-screw extruder. Twin-screw extruders are designed to allow flexibility in the
method of component introduction, in addition to the ability to change screw configuration.
The extruder comes configures with multiple feed ports, allowing the polymer components to
be added as specified by the compounder. For example, the resin is generally added at the
beginning of the extruder to ensure melting, mixing and uniformity of melt temperature,
while fillers/reinforcing agents or liquid additives are added further downstream.

Twin-screw extruders make use of starve feeding systems as opposed to flood feeding system
utilized with single-screw extruders. Side feeders for filler addition are also employed.
Venting, pelletizing and downstream handling requirements are all similar for systems
described in section 3.2-1.
Feed alternatives (depending on formulation)

Flame Retardant PP
A schematic sketch of a typical twin-screw set up for introducing liquid flame retardant into
PP is shown in Figure (4). The extruder set up requires two feeding ports, one for PP and one
injection port for additive located downstream. The first section of the extruder creates a melt
pool before the liquid is injected. The viscosities of the polymer melt and liquid are matched
near the injection port and then the mass is allowed to homogenize in the latter part of the
extruder. The factors which govern the quality of the final product are the temperature profile
in the extruder, screw design and extruder geometry.

Filled PP
Filled PP grades can be compounded with twin screw extruders. Dispersion requirements for
talc and CaCO3 vary according to the final product application. The primary objectives are
uniform incorporation and mixing. A schematic diagram of mixing elements which make up
a configurations shown in Figure (5).

Fillers are added downstream t a melt to isolate their abrasive effects. A melt seal is formed
upsteam where large pitch screws are used. The downstream section is configured for low
shear mixing for low performance applications. Applications requiring high degree of
dispersion are compounded using a high shear intensive mixing section.

GlassFibreFilledPP
Compounding technique for incorporating glass fibre into PP requires isolation of high and
low shear sections along the screw length. Chopped fibres or continuous rovings can be used.
The design of the screw determines the final fibre length in PP. PP in powder/pellet form is
metered into the feed zone with stabilizers and lubricants. The additives can be pre blended or
metered individually. A relatively high shear plasticizing and mixing section is used to
generate a homogeneous melt. Fibres are introduced into the melt via second feed opening
located downstream (figure 6.) Metering equipment is required for chopped strands.
Continuous rovings are continuously unwound from the core, drawn in by the turning screw.
One inside the barrel, the continuous rovings are chopped to length by the kneading elements
located downstream of the feed opening. A less intensive mixing section is needed for
chopped fibre, since the fibres have only to be wetted out and dispersed. Degassing and die
extrusion follows the compounding step.

Table (14) shows the effect of compounding technique on physical properties of glass fibre
filled PP product. It is, therefore, important to select the correct compounding machine to
obtain reinforced products with desired mechanical properties.
Table – 14 Effects of Compounding Technique on 20% glass reinforced-PP
Property Standard twin screw Intensive twin screw Fluxed melt mixer
Melt flow rate, condition L.g/10 min. 4 5 9
Tensile strength (yield) MPa 79 70 49
Yield elongation, % 2.8 3.1 5.1
Flexural modulus (1% secant), MPa 4071 3726 26.22
Heat deflection temp. (264 psi), deg. C. 134 134 104
Fibre length (average), um 550 550 300

Twin screw-extruder for introducing liquid FR into PP

Twin screw Extruder

Continuous Twin Screw
 Typical configuration for glass fibre incorporation into PP

Schematic view of a Banbury Type Internal Mixer

 PP Compounding Problems
https://www.linkedin.com/pulse/plastic-injection-molding-defects-series-flow-marks-flow-stebro-
mold/

Plastic Injection Molding Defects series-

Flow Marks or Flow Lines

Grace Zhang
August 23, 2019

Flow marks, also known as flow lines, are surface defects in which circular
ripples or wavelets appear near the gate. It also appears as a wavy
pattern often a slightly different color than the surrounding area and
generally on narrower sections of the injection molded components. They
may also appear as ring-shaped bands on the product’s surface near the
entry point of the mold or gate, which the molten material flows through.
Ripples, a similar defect, appear as small fingerprint-like waves near the
edge or at the end of the flow, which indicate the direction of material
flow within the cavity of the mold. These are molding defects that can
occur in the manufacturing process of plastic injection molding.
Flow marks are most commonly caused by resin cooling too quickly or
improper gate location. They are supposed to be made by a sudden
change of the flow front speed. The sudden change of the flow speed
causes the difference in the cooling condition of the surface. Differences
in wall thickness can also cause the material too cool at different rates,
leaving behind flow lines. You can see the causes of flow lines from below
fishbone diagram.

Sometimes, flow marks can be eliminated by adjusting the injection

molding parameter such as increasing injection speed and pressure, which
will help to ensure uniform filling and cooling. You can see the solution
from below table.

If you like it, please kindly share it:)

If I can answer any questions you may have on optimizing the plastic part
design, CNC plastic prototype, mold manufacturing, and injection
molding or if I can be of any other help, please feel free to connect. My
email address is grace@stebro-mold.com Wechat, WhatsApp and phone
number is 86-18938202488

What are Flow Marks in Injection Molding

and How to Prevent Them
Understanding injection molding flow marks and what causes them.

Injection molding is one of the fastest, most efficient methods of creating high-quality
plastic parts—but it is not without its limitations. Designers often find defects in their
parts that add lengthy delays to the manufacturing process. While frustrating, these
defects are solvable given an understanding of their causes and how to implement
key adjustments to the injection molding process. This article will explore one
common defect known as flow marks, what they are, what causes them, and how to
prevent them from occurring in your plastic injection molding capabilities.

What is a Flow Mark?

A plastic injection molded part shows the presence of flow lines.

Image Credit: Ryan Wickre on Twitter: "Ain't no harm in injection molding flow lines. Good on
@askdyson / @dysonjames for showing them off! http://t.co/D8kPh8Wo" / Twitter
Flow marks (also known as flow lines) show as a wavy pattern or ripple on a molded
part’s surface. While not detrimental to the structural integrity of a part per-se, they
indicate an uneven material flow and can reduce aesthetic qualities. Flow marks
occur near the plastic injection nozzle (also known as the gate) and radiate outwards
through the part. As shown in the above picture, they generally appear as circles,
lines, and/or repeated patterns.
What Causes Flow Marks in Injection Molding?
There are many reasons for flow marks in injection molding—but generally they are
the result of the plastic material cooling at an uneven rate. There are many causes
for this non-uniform cooling, so the below sections will explore material, machine,
and mold/mold design causes that lead to flow marks. Note the below sections cover
the most common reasons but may not cover all the possible sources.

Material Causes
Slide 1 of 1

Plastic injection molding resins in pellet form.

Image Credit: Selecting the Right Injection Molding Material (xometry.com)

Keeping track of material temperature through the injection molding machine is

incredibly helpful when reducing flow marks. Thermoplastics have a Melt Flow Index
(MFI) that indicates the flow characteristics of a melted plastic; plastics with a low
MFI are more prone to flow marks while higher MFIs work better. This specification is
closely tied to temperature, and temperature is notoriously squirrely with plastics.
Too hot and the plastic will start to degrade, but too low and flow marks increase.

An improper flow rate and injection speed also cause flow marks. The injection
speed should remain consistent as the plastic enters the mold, otherwise, it will slow
down, cool, and cause flow marks. The flow rate should ensure the material does not
lose its stored heat before entering the mold, otherwise, it will drop in temperature
before molding and cause flow marks.
Machine Causes

An injection molding machine.

Image Credit: Injection molding machine - Wikipedia
Machine parameters are common sources of flow marks. If the machine injection
pressure is too low, the material will not melt uniformly through the mold and cause
uneven cooling. Similarly, low nozzle and barrel temperatures will not sufficiently
heat plastic, resulting in flow issues. Improper timing also contributes to flow marks,
where short residence and cycling times can cause uneven cooling and flow marks.
Mold/Mold Design Causes

An injection mold use to create a fan blade.

Image Credit: Steel Fan Blade Plastic Injection Mould, For To Make Blade Of Fan, | ID:
21225430612 (indiamart.com)
Poorly designed molds are another significant source of flow marks. Molds with poor
venting, non-uniform wall thicknesses, and inadequate lubricant will lead to bad
results. Sprue/gate/runner design will also dictate flow mark frequency.
Gates/runners that are too small or thin will reduce material flow, temperature, and
pressure, causing a litany of issues including flow marks.

Another critical design consideration is a cold slug well; a cold slug is the small bit of
solid plastic that cools inside the nozzle tip during cooling phases. The cold slug
prevents plastic drooling during the injection process, but the slug still ends up in the
molded part. Some designers will either not include a well for the cold slug to go to
during injection or poorly design a cold slug well. Either case results in poor material
flow and even complete blockages, causing a variety of defects.
How do I prevent flow marks?

Illustration of an Injection Molding Machine Components.

Image Credit: Injection moulding - Injection moulding - Wikipedia
Preventing flow marks will entail some tuning, trial-and-error, and intelligent design.
Below are the best ways to minimize flow marks in an injection mold, but it is vital to
first isolate the cause of the flow marks before changing things up. The below
sections will reference components from the above diagram.

Changes to Pressure Parameters

One of the easiest remedies is to increase the back and holding pressure of the
injection molding machine. Larger back pressure will help push the fluid throughout
the runners/mold, enhancing compaction. Increasing the holding pressure (or the
static pressure once the plastic is injected) will improve surface quality as the plastic
better conforms to the mold cavity’s finish. Note that excessive injection pressure
will lead to jetting (another defect), so find a balance using other parameters.

Changes to Temperature Parameters

Temperature is not as simple—both the machine and the mold are sources of heat,
and radical changes to one or the other can lead to worse defects. Temperature is
also tightly related to pressure, where low melt temperatures can seem like a
pressure problem at first, so take your measurements!

First, verify that the barrel temperature is to material specifications. Most

thermoplastics intended for injection molding will come with recommended barrel
temperatures, but operators can very slightly deviate from the recommended if
needed. Also, note that there are four separate heating bands/zones: rear, center,
front, and nozzle (shown in the above diagram as the three heaters around the barrel
and the nozzle itself). The material temperature should be set to gradually rise as the
plastic is pushed through the barrel, with a general rule of +6°C per zone.

Raising the nozzle temperature is where more trial-and-error occurs. Nozzle

temperatures are ideally the same as the melt temperature, but will realistically be
less due to the nozzle touching the cold mold. Raising the nozzle temperature to
slightly above the melt temperature will reduce this cooling and keep the material
fluid through the injection process. Again, the general rule is 6°C higher than the
previous zone (the barrel front).

Finally, a too-cold mold hinders any progress with the previous temperature tweaks.
Most material will come with recommended values for mold temperature but
remember that cooling will naturally occur as the plastic moves further from heat
sources.

For temperature in general, it is best to start with the recommended barrel, nozzle,
and mold temperature, test 10 or so mold samples, examine the results, and adjust
from there.

Injection Speed
Injection speed is closely tied to injection pressure—the higher the pressure, the
faster the flow rate of the material. Speed is important in injection molding because,
at low speeds, the molten material has more time to cool, increasing flow lines. If
necessary, nozzle diameter can be increased to allow for more flow and to prevent
early cooling.

Injection speed is also related to material, where a too-stiff molten polymer will slow
down regardless of pressure or speed. If the molten plastic is thick and the gate is
small, the filling speed will slow and cause uneven cooling. Find a material with the
stiffest flow possible without causing non-fill (unfilled areas of the mold, also known
as short shot), and use its recommended flow rate to ensure faster flow.

Gate, Sprue, & Runner Design

Gate, sprue, and runner design is vital—thin/small gates and runners will restrict
material flow, reducing pressure, injection speed, and ultimately temperature.
Luckily, simulation tools (such as C-MOLD) will calculate the ideal gate, sprue, and
runner sizes for your mold to optimize the process. Gate location is also important,
where gates closer to cooler or thinner areas of the mold will decrease cooling time
and increase flow line frequency. Note that certain components (gears, for example)
have set gate locations to improve filling, so only change entry points when there are
no set rules.

Venting
Venting allows trapped air in the mold cavity to escape once the molten plastic
enters the mold. Place vents at the end of each runner section and consider adding
vents opposite the gate. The viscosity of the plastic will determine the vent depth, but
generally, stiffer materials need deeper vents. Another benefit of computer
simulations is that they will show where the melt will fill last, keying you in on where
to put optimal ventilation.

Mold Design
Sharp edges/corners in cavity designs will lead to non-uniform flow and uneven
cooling. Designing molds with fillet edges and round corners will improve material
flow (especially to thicker areas) and reduce flow marks. Also, keep in mind the
effect of wall thickness on cooling. Molds with uniform wall thickness will not have to
worry about this effect, but those with variable wall thickness will experience more
uneven cooling. As a rule, wall thickness should change smoothly through the part,
and thicker areas should contain more fillets and round corners. A cold slug well
should also be added at the end of the primary runner, preventing clogs and cooling
issues.

Operator Knowledge
The last method for reducing flow marks in injection molding is to educate operators
on proper procedures and on the injection molding process. If the injection molding
machine is not automatically cycled, operators must understand the appropriate
cycling time to prevent inconsistent molding cycles. Proper application of mold
lubricant should also be taught, where large flow length-to-wall thickness ratio
sections should receive more lubricant (in accordance with material specifications).
Work shifting also helps reduce errors due to complacency or exhaustion, but many
of the above problems can be eliminated simply by using robotics/control systems
instead of human control.

Summary
This article presented an understanding of what flow marks are, what causes them,
and how to prevent them in your injection molding process. If still having difficulties
or not achieving the results you’d like, contact our injection molding experts at
Xometry for assistance.

Xometry provides quotes on injection molding services. Visit our plastic injection
molding capabilities page to get a free, no-obligation quote or to learn more about
our material capabilities, finishes, and injection mold classes. Also, be sure to review
our Ultimate Guide to Injection Molding, where you can learn more about
optimizing your design for the injection molding process.

Sources:

1. Plastic Injection Molding Defects series-Flow Marks or Flow Lines

(linkedin.com)
2. HOW TO IMPROVE FLOW MARK IN INJECTION MOLDING - Plastic Injection
Molding and Mold Maker Manufacturing (cavitymold.com)
3. Flow Lines Defect in Injection Molding Process (uninko-plastics.com)
4. #023 Measures to Solve Molding Defects (Flow Marks) | Technical Tutorial -
MISUMI (misumi-techcentral.com)
5. Flow marks Plastic injection molding defect -ECO MOLDING
(injectionmould.org)
6. Cold slug well design | HSmold Plastic Injection Mold for Parts in automotive,
medical, industrial Mould custom Manufacturer (hsmolds.net)
7. Injection Mold Flaws & How to Prevent Them: Flow Lines, Knit Lines, & Blush
(chem-pak.com)
8. What Causes Flow Lines in Plastic Injection Molding? - Ecomolding.com
9. Don’t Forget the Cold Slug Well | Plastics Technology (ptonline.com)
What Causes Flow Lines in
Plastic Injection Molding?
Definition of Flow Lines:
Flow lines, also known as flow marks Linear marks on the surface of a molded
product, which indicates the flow direction of the molten plastic.

Injection molding process

1．Insufficient Pressure / Holding Pressure
The injection pressure and the holding pressure are not high enough to press
the solidified layer against the mold surface, thus leaving flow lines along the
melt flow direction.
Increase the injection pressure and the holding pressure, to press the
solidified layer against the mold surface until the product is molded, so as to
prevent the occurrence of flow lines.

2．Improper Residence Time

the plastic material stays in the barrel for a too short period of time, while the
melt temperature is low. Even if the cavity is barely filled, the plastic cannot be
compacted during pressure holding, thus leaving flow lines along the melt flow
direction.

The Shot-to-Barrel Ratio should be kept between 1/1.5 and 1/4.

3．Improper Cycle Time

When the cycle time is too short, the plastic is not sufficiently heated in the
material barrel, and the temperature of the melt is low. Even though the cavity
is barely filled, the plastic cannot be compacted during pressure holding, thus
leaving flow lines along the melt flow direction

The cycle time is extended until the plastic is fully melted, and the temperature
of the melt is high enough to prevent flow lines along the melt flow direction.

4．Barrel Temperature Too Low

When the barrel temperature is too low, the melt temperature will be low, and
the injection pressure and holding pressure will not be high enough to press
the solidified layer against the mold surface, thus leaving flow lines along the
melt flow direction.
Increase the material temperature, injection pressure and holding pressure to
press the solidified layer against the mold surface until the product is molded,
so as to prevent the occurrence of flow lines. The material temperature can be
set by reference to material supplier’s recommendations.

The material barrel is divided into four zones: Rear, Center, Front and Nozzle.
The material temperature settings should be gradually raised as it moves
forward. Increase by 6°C with every zone forward.

When necessary, the temperature of the Nozzle and/or the Front are
sometimes set to be the same as the Center temperature.

5．Nozzle Temperature Too Low

After absorbing the heat released by the heating band, as well as the frictional
heat generated by the relative movement of the plastic molecules caused by
the rotation of the screw, the plastic in the barrel undergoes gradual
temperature rises.

The last heating zone in the barrel is the Nozzle, where the melt should reach
the desired temperature, but it must be moderately heated to maintain the
optimal conditions.

If the nozzle temperature is not set high enough, due to too much heat is
taken away through the contact between the nozzle and the mold, the material
temperature will decrease, so that the injection pressure and the holding
pressure will not be high enough to press the solidified layer against the mold
surface, thus leaving flow lines along the melt flow direction.

Raise the Nozzle temperature. The nozzle temperature is usually set to be

6°C higher than the Front temperature.

Mold
1 ． Mold Temperature Too Low
If the mold temperature is too low, the material temperature will drop very fast,
so the injection pressure and the holding pressure will not be high enough to
press the solidified layer against the mold surface, thus leaving flow lines
along the melt flow direction.
Raise the mold temperature, maintain a high material temperature, as well as
high injection pressure and holding pressure to press the solidified layer
against the mold surface until the product is molded, so as to prevent the
occurrence of flow lines.
The mold temperature can be set from the recommended values of the
material supplier, with an increment of 6°C at each adjustment. Then perform
10 shots, and after the injection molding is stable, decide whether further
adjustment is necessary according to the result.

2． Sizes of the Sprue, the Runner and/or the Gate

If the sprue, the runner, and/or the gate are too small, the flow resistance will
be increased. And, if the injection pressure is not high enough, the
advancement of the melt front will become slower and slower, and the plastic
will become colder and colder, so that the insufficient injection pressure and
holding pressure will not be able to press the solidified layer against the mold
surface, thus leaving flow lines along the melt flow direction.

It is a feasible way to simulate and analyze the filling status of the different
melt transfer systems (including the sprue, the runner and the gate) on a
computer with CAE (such as, C-MOLD), to find out the ideal sprue, runner,
and gate sizes (including length and section related dimensions, such as
diameter, etc.)

3． Insufficient Venting

Insufficient venting will cause the melt filling to be blocked, and the melt front
will not be able to press the solidified layer against the mold surface, thus
leaving flow lines along the melt flow direction.

Start venting at the end of each runner section, which removes a large amount
of gas before filling the cavity.

The cavity venting should not be neglected. Consider adding vents on the
parting surface opposite to the gate. Correspondingly, consider adding venting
ejector pins at the end of the product blind hole.
Simulate melt filling through CAE (such as, C-MOLD), which helps us quickly
find out all possible last filled areas, i.e., the areas where vents must be
added. The addition of a vacuum system for air extracting before and during
filling is an effective venting method.

For some textured products, this may be the only way of venting.

Plastic Material
1．Poor Fluidity
 The mold cavity with a large flow length to thickness ratio must be filled with
the plastic that features great fluidity. If the fluidity of the plastic is not good
enough, the melt will be flowing slower and slower, colder and colder, so that
the injection pressure and the holding pressure are not high enough to press
the solidified layer against the mold surface, thus leaving flow lines along the
melt flow direction. Material suppliers are able to offer professional
recommendations according to specific designs:
The most flowable plastic is selected on condition that no flashing is caused.

2．Improper Application of Molding Lubricant

Usually, the lubricant content is below 1%. When the flow length to wall
thickness ratio is large, the lubricant content must be moderately increased to
ensure that the solidified layer is pressed against the mold surface until the
product is molded, so as to prevent the occurrence of flow lines. The lubricant
must be increased upon agreement with the material supplier.

Operator
1． Bad Habits

Inconsistent molding result will occur if the operator switches the door of the
injection molding machine too early or too late. When the barrel heater tries to
replenish heat in time due to irregular heat loss, the plastic temperature will
not be uniform, thus causing the cold spot. It is not easy for the injection
pressure and the holding pressure to press the solidified layer around the cold
spot against the mold surface, thus leaving flow lines along the melt flow
direction. Usually, the operator should be constantly educated to let everyone
know the troubles caused by inconsistent molding cycles and recognize the
importance of maintaining best molding practices. Appropriate work shifts are
able to prevent operators from making mistakes due to exhaustless or
distraction. Automated production with robots or the like is a way to maintain a
consistent molding cycle.

 By Jerry.w
 Last updated January 15, 2021

Table of Contents

When the injection molding process runs well, it can all seem so
straight forward. In reality, to ensure that every product comes
out of the process a success takes a lot of skill and knowledge.
When in the hands of inadequate expertise, a lot can go wrong.
Many defects can occur in injection molding. Minimizing the
occurrence of these defects is key to getting the best out of your
machine. The plastic product market is becoming more
competitive. Consumers today are more informed and have
more options. They demand spotless products which are no
short of aesthetic perfection. Defects in plastic products are not
acceptable. Other than aesthetics these defects can also affect
product functionality. For example, a plastic material used as
gear needs to have perfect smoothness. These defects occur as
a result of improper processing conditions and settings. Defects
such as flow marks are undesirable in injection molding. This
article gives you an insight into the precautions taken to prevent
such.

What is a Flow Mark?

Flow marks occur as circles or lines that occur around the gate.
These marks remain and are visible in the cooled product. They
are evidence of nonuniformity in flow pattern upon entry into the
mold. This nonuniformity in the flow is a result of the temperature
gradient within the melt. The slight difference in the colour tone
of these flow marks is due in part to light refraction. It is also a
result of pigment redistribution. In the ideal case, such defects
occur during the trial runs. Once the engineer notices such a
defect, the right measures get put in place to address it. This of
course gets prevented in the first place by a well-designed
process and mold system. The ability to recognize the flow mark
early can save a lot of trouble and expenses down the line. You
can recognize flow marks by the following characteristics:

 Occurs near the gate

 Sometimes has a little different color tone from the rest of
the part
  Occurs as circles or lines or patterns
How to Fix Flow Mark on Plastic Parts
Unfortunately, there is nothing that you can do after the problem
occurs. The part must get rejected and sent to recycle. It is
important to ensure that measures are in place to detect such
problems. The best thing is to detect the flow mark early.
Chances are this is not only a one-off occurrence and will
happen in the next cycle. So the earlier it gets detected the less
the damage done. So process engineers must ensure that
measures are in place for defect detection. In the ideal case, the
defect gets detected before it occurs. This is possible by knowing
the parameters which lead to this defect occurring. By detecting
the error before it occurs you can save time and resources.
Parameters such as temperatures and melt flow rate can be
indicators for defects.

What Leads to Flow Marks

There is a combination of factors that lead to flow marks.
Although it occurs at the gate. The cause can be a result of the
machine settings originating from before the gate. Causes of flow
mark can be any or all the following:
Image illustrating flow marks in injection molding

Melt temperature is too low

The melt temperature is a key factor in controlling the melt
viscosity. The main purpose of heating the plastic is to allow it to
deform and flow. When you notice flow marks, chances are you
are running at sub-optimal temperature. Heat requires some sort
of fuel input and this is running cost. So the operator needs to
run the process at an optimal temperature. But caution is
necessary to run well below the degradation temperature. Have
temperature sensors to track temperatures at different points of
the injection molding. This ensures the melt gets to the mold at
the right temperature to prevent a flow mark. Control systems
and alarms can get installed. These give warnings where the
temperatures fall below the set values. This way the problem of
flow mark gets alerted before it happens.

The temperature inside the mold is too low

The mold is not heated as this is where cooling occurs. Some
molds get precooled. But if the temperature in the mold is too low
it causes problems. When the melt gets into the mold and upon
entry premature cooling may occur. If parts of the mold cols too
early around the gate, this leads to flow marks. The hotter fluid
flows over the cooled melt. This leads to the formation of flow
marks.

Melt injection speed is not high enough

The speed at which the melt gets injected should sustain it till it
gets to the mold. The melt should also get to the mold fast
enough before it loses all it’s stored heat. If the temperature is
too low, by the time the melt reaches the mold part of it has
begun to solidify. This occurs as it gets forced through the gate.
This difference in flow pattern registers as a flow mark.

Melt injection pressure is too low

The melting speed relates to the pressure. If the pressure is not
high enough then it does not have enough compaction.
Compaction contributes to melting uniformity. With enough
injection pressure-flow patterns get evened out.

Wrong size of runner and/or gate

If the runner and gates are too narrow this restricts flow.
Restriction of flow slows down the melt. It also exposes more
areas of the melt to temperature loss. The shorter flow diameter
means the center of the melt is closer to the walls of the runner.
This is particular in cold runner systems.

If you have any of the above situations in your injection molding

machine. The chances of flow marks are higher. The following
section looks at how to prevent flow marks from occurring.

How to Prevent Flow Mark Problems

There are two approaches to prevent flow marks from occurring.
Or occurring in the next cycles. One approach is to change the
mold design. The other approaches involve modifying the
injection molding conditions. The following sections discuss the
different measures taken to remedy the flow mark.

Cold Sludge Well

The flow irregularity that leads to the flow mark is sometimes
caused by a cold sludge. This gets caught in the melt. This
mixes with the hot meld and only about melts enough to get
through the gate. The thermal energy of this cooler plastic results
in a lowering of the temperature of the melt around it. The lower
temperature of this part of melt gives it higher viscosity. This
increased resistance to flow slows down the melt. Incoming
hotter melt flows past it to fill the other parts of the mold. This
uneven temperature and viscosity results in the flow mark seen
in the formed part. So a cold sludge well can solve this problem.
The cold sludge well gets placed right before the gate. This
collects any cooled or frozen plastic and prevents it from getting
into the mold. The sludge drops in the well by gravity before the
next shot gets into the mold.

Use Gates and Runners that are wide enough

If the gate and runner diameter are too small, this restricts melt
flow. Also the smaller the channel the faster it cools. This
premature cooling prevents the optimal volume of fluid from
getting in the mold. Having more fluid entering the fluid helps
build up pressure hence turbulence. This helps prevent flow
marks from developing. So to address flow marks. Widening of
the gate is an option.

Reduce distance from the hot nozzle to mold

The longer the melt has to travel, the more chances of premature
cooling. You don’t want the melt cooling before entering the
mold. Where the distance cannot be any shorter, another option
is to use a hot runner. This way the melt remains hot until it gets
into the mold.
Increase Back Pressure
Increasing the back pressure can help improve melt uniformity
within the injection chamber. This pressure then melt gets held at
is too transferred as it gets injected. This back pressure gives the
fluid added pressure as it travels through the runners. The
backpressure also ensures good compaction of the melt. This
contributes to minimizing the chances of uneven flow pattern
build-up.

Increase Temperature
Always be careful before going for the option of increasing the
temperature of the melt. This is achieved by changing the
temperature settings on the barrel. Temperature relates to many
of the parameters in injection molding. In particular pressure and
viscosity. When you increase the temperature the melt flows
better. But be mindful that you don’t want to get too close to the
degradation temperature of the plastic. The increasing
temperature where there are problems in flow uniformity can
have detrimental impacts. If there is poor mixing, this can lead to
hot spots and parts overheating. Such overheating leads to
degradation and this causes other defects. You don’t want to
solve one problem and then create another in the process. Other
than the barrel temperature the temperature of the mold can also
get increased. Usually, a pre-cooled mold gets used to help with
the cooling of the part. But if this causes premature cooling then
increase the mold temperature.

Increase injection speed

The speed of injection gets related to the pressure of injection.
So if you increase the pressure applied to the screw as the melt,
speed is also increased as a result. Increased injection speed
helps get the melt into the mold before cooling occurs. So where
you can’t have a hot runner, you want the melt to get in the mold
as fast as possible. But at the same time, excessive speed can
cause other problems like jetting. So keep injection speed within
reasonable limits.

Fillet Edges and Corners

Sharp edges in the mold design can contribute to non-uniform
flow patterns. These contribute to flow marks developing. To
address this fillet or round these corners. This reduces the
impact of the change of flow direction. It also prevents the
generation of uneven flow patterns. This also prevents another
problem in mold release.

Gate Location
The location of the gate is an important factor. Although for some
products there are set rules for where to locate the gate. For
example in the injection molding of gears. Here the gate gets
located at the center of the gear for optimal filling. But where
there are no clear rules then locate the gate at the side of the
mold where the wall is thinnest. The thinner walls mean a lower
temperature drop. This prevents the disruption of flow patterns in
the mold. As the melt goes from the thinnest to the thicker walls,
the temperature difference evens.

Conclusion
The flow mark in injection molding is a preventable problem. But
once it occurs on a product, such a product is most often not
acceptable. While it may not affect the functionality of the
product, it has a significant impact on appeal. Maintaining the
right conditions and having a mold, gate, and runner system fit to
purpose. This helps prevent the occurrence of flow marks.

#023 Measures to Solve Molding Defects (Flow Marks)

Category : Molding Defect Countermeasures
December11, 2009
Flow marks are a phenomenon in which a pattern of the flow tracks of the
molten plastic remains on the surface of the molded product. Depending
on the extent, these can become defects in the case of molded products
in which their external appearance is an important aspect of quality, such
as in the case of home electrical appliances, containers for cosmetics, etc.

Flow marks are caused because there is a difference in the extent to

which the cooling takes place upon contact with the surface of the mold at
the front end of the plastic when the molten plastic is flowing inside the
cavity of the mold.

The following countermeasures can be considered in order to avoid flow

marks.

(1) Countermeasures related to molds

1.Set the cavity surface temperature a little higher.

2.Widen the gate.
3.Widen the runner.
4.Acquire sufficient cold slag.

(2) Countermeasures related to the injection molding conditions

1.Increase the injection pressure.

2.Increase the injection speed.
3.Acquire sufficient volume and increase the cushion amount.
4.Increase the dwell time.
5.Increase the dwell time.
6.Increase the plastic temperature.

(3) Countermeasures related to the design of the molded product

1.Make variations in the wall thickness of the molded product small.

Injection Mold Flaws & How to Prevent Them: Flow

Lines, Knit Lines, & Blush
May 24th, 2019
Posted in Injection Molding Flaw Repair
Preventing Flow Lines, Knit Lines, &
Blush
Injection molding isn’t an exact science, and there is a lot that can go wrong in getting your
plastic pieces ready for market.
While frustrating and sometimes costly, injection molding flaws can’t be fully avoided. However,
you can make small changes to your injection equipment and processes to help you decrease
the number of flaws that result from the injection molding process.
Here are 3 common injection molding flaws and how to prevent them from happening in the
future:
Flow Lines
Flow lines appear as a wavy pattern on the surface of your plastic parts. They usually are a
slightly different color than the rest of the piece, and typically occur on more narrow sections of
the molded item.
They also can appear as ring-shaped patterns near the entry points of the mold.
Most flow lines don’t impact the functionality or integrity of the molded item, but they can be
unsightly and impact your ability to resell the piece to a client.
What Causes Flow Lines?
Flow lines are often the result of variations in the cooling speed of the plastic as it flows in
different directions through the mold. They also can occur when you’re creating pieces of
differing thicknesses, as the thinner areas cool before thicker areas are fully filled, causing flow
lines.
Molten plastic cools very quickly, and flow lines often occur as more hot plastic flows past parts
that have already become cool and gummy.
How to Prevent Flow Lines
There are a few adjustments that you can make to your injection molding process to prevent flow
lines, including:
 Increase the injection speed, pressure, or material temperature: Slow-moving molten
plastic is more likely to cool quickly and cause flow lines. Increasing one of the variables on
the material you’re using helps the product move more quickly, fully filling the mold before it
begins to cool.
 Round the corners of the mold where wall thickness increases: This helps keep flow
rate consistent to the thicker sections and prevents flow lines.
 Relocate mold gates farther from the mold coolant: Providing further separation
between the injection point and the cooling apparatus will increase cooling time and
decrease flow lines.
 Increase nozzle diameter: This increases flow speed and prevents early cooling.
Knit Lines
A knit line is the spot where two flows meet. When these areas are visible, it can pose no
problem at all to the piece, be nothing more than a cosmetic flaw, or can be a source of major
structural problems for your piece.
Knit lines often occur when two flows meet and are held at different temperatures, leaving a line
between.
How to Prevent Knit Lines
If you’re creating large pieces, knit lines can cost you a great deal of money in lost parts. Here
are a few ways to prevent knit lines in your plastic parts:
 Increase material temperature: Higher temperatures on both materials prevent one
section from cooling too quickly.
 Increase injection speed and pressure: Faster-moving materials will meet more quickly
so one doesn’t cool too soon.
 Redesign the mold: Redesigning the mold to eliminate partitions between sections will
remove knit lines altogether.
  Switch materials: Materials with lower melting temperatures or viscosity allows for faster
flow and slower cooling.
Blush
Blush is a cloudy discoloration usually found around an injection gate. However, blushing can be
found throughout the surface of a molded plastic piece.
A molded piece with blushing is often very structurally weak due to the loose molecular structure.
This can be caused by an improperly sized gate hole, a high injection speed, low injection
pressure, improper melt temperature, too-small nozzle diameter, or incorrectly located gates.
How to Prevent Blushing
If you can find the cause of your injection molding blushing, you can adjust your equipment or
process to prevent it, including:
 Fix gate hole sizing: A gate hole that is too small or the wrong size for the material will
cause blushing, check your gate’s hole size against the type of material you use and the
relative thickness of your finished product and see if that fixes the problem.
 Decrease injection speed: If the mold is filled too quickly by a high injection speed, it can
have a negative impact on the material at the gate hole. Adjusting the injection speed so
your mold fills more slowly allows the material to fill the space with less pooling.
 Adjust melt temperature: Check the temperature of your material against the
specifications to see if that takes care of the issue.
 Increase nozzle diameter: If your injection nozzle is too narrow, the material doesn’t flow
out at a fast enough rate, causing pooling. Widening your nozzle diameter allows material to
flow freely and properly fill your mold.
 Relocate gate holes: If your gates are positioned closer to more narrow sections of your
piece, they will begin to harden first and cause less material to flow to the thicker areas.
Moving your gates to areas with more thickness should alleviate this issue.
Plastics Coatings for Injection Molding Flaw Repairs
No matter how careful you are and how much you adjust your equipment and processes, some
injection molding flaws are unavoidable. Save time, money, and frustration using high-quality
plastics coatings from Chem-Pak. You get more useable pieces, increasing profitability for your
business. Learn more!

Compounding is defined as the process of incorporating additives, modifiers into PP for achieving uniformity on a
scale appropriate to the quality of the articles subsequently made from the compound. It is also known as hot or
melt blending.

Polypropylene (PP) sold for commercial consumption has some types of additive. We will define 'unmodified' PP
as representing only those additives without which PP could not be viably processed in commercial extruders,
moulding machines and the like. Accordingly, we will define 'modified' PP as that which has additives designed to
provide special environmental, processing or physical properties. Typical additives to unmodified PP include
antacids such as calcium stearate, calcium pelargonate, zinc oxide or hydrocalcite. These compounds are
required to neutralize catalyst residues that could otherwise form acids detrimental to the converter's equipment.
The second basic additive to PP is antioxidant. This is required, as a minimum to protect the polymer from chain
scission during processing and ageing. Typical process stabilizer antioxidants are hindered phenols.

Most additional additives and modifiers such as clarifiers, flame retardants etc. are targeted to affect a certain
class of properties. Further, fillers and reinforcements are incorporated to impart "Value Addition" to PP. High
value added PP products can be made by "Modifying PP with elastomers such as EPM/EPDM.

Value added PP products

* Low-level additives
* Environmental Property Enhancement

In addition to process stabilizers, additional heat stabilizers are used to improve the long term heat ageing of PP.
Several antioxidants will afford improvements, with the choice dependant on the environment requires. An
important parameter is the continuous use temperature. Typical PP Homopolymer with moderate stabilization
has a continuous use temperature of 105 °C. Special stabilization can increase that temperature to 125 deg. C.
Thioethers can act as long term heat stabilizers.

The UV resistance of unmodified PP is poor. However, stabilization can improve its performance significantly.
Typically, hindered amines-can be used in combination with other appropriate additives to deliver service life or
more than 5 years outdoors in both pigmented and non-pigmented products. This can be done without affecting
the appearance of a component. In addition, if a black appearance is acceptable, special grades of carbon black
at levels above 2% can provide a service life of more than 20 years.

In addition to the stabilized applications listed above, there are many specialized uses of PP that require low
levels of stabilizers. Among the applications for these stabilizers are the protection of PP components in radiation
sterilizing environments, the prevention of colour development in various environments and the stabilization of
wire-coating resin against the effects of copper. Each of these unique applications requires specific additive
packages.

Processing Property Enhancements

In addition to the need for application heat stabilizers, some manufacturing processes require exceptional melt
stability. For example, if products will be reprocessed repeatedly, if high levels of scrap are used or if extruded
sheet subsequently will be exposed to high temperatures, as in a thermoforming application, the goal would be to
minimize degradation in the extrusion process. In these cases, additional melt stabilizers are required. Phosphite-
based products are used for this purpose.

In film resins, slip agents and antiblocks are added to improve the processing and performance characteristics of
the film. Slip agents are typically amides, with the particular selection depending on the characteristics being
sought. Typical antiblocks are utilized to prevent the film from sticking to itself, while slip agents are utilized to
prevent the film from sticking to other surfaces, such as the converting equipment. Also used in film for
processing and application performance are antistats. These products act to minimize static build-up as the film
passes over the downstream equipment, as well as to minimize the dust pick up inherent in packaged products.
For the latter applications, antistats are sometimes incorporated into PP used in sheets, bottles and moulded
articles. Monoglycerides and/or diglycerides are typical PP antistats.

Injection moulding products may utilize additives to adjust processing performance in the form of lubricants
and/or mould release additives. These additives may interfere with decorating.

Physical Property Enhancements

as crystallinity is responsible for many of the characteristics of PP, his ability to control it allows one to influence
the physical properties of the resin. Nucleators are employed that provide sites for the initiation of crystals. The
choice of nucleator will determine which properties are affected most significantly. The target properties are
usually stiffness and heat deflection temperature, contact clarity and/or see-through clarity. Nucleators may also
affect processing performance owing to their effect on the rate of polymer crystallization.

High Level additives (Fillers and Reinforcements for PP

With the exception of the carbon black at more than 2% level, all the additives mentioned in Section 2.1 are
utilized at very low levels. Typically, the total add level of these types of additives will remain below 2%. The
properties that are most significantly affected by these type of additives are processing and environmental
characteristics. To achieve significant differences in properties, fillers and reinforcements are used at much
higher levels. Fillers and reinforcements are generally distinguished by the resulting differences in properties that
they provide to PP.

Fillers are defined as additives in solid form that differ from polymer matrix with respect to their composition and
structure. They are generally inorganic in nature and less frequently organic and are used at levels of 10% and
above. Different types of fillers can be classified as under:
Inert or Extender Fillers: These fillers occupy space in the polymer increase bulk density and lower cost and
thereby extend the polymer. |
Active Fillers: These produce specific improvements in physical and/or mechanical properties.
Reinforcements: These are specific type of active fillers. They increase tensile strength and flexural modulus of
PP.

PP has the capability of accepting large amounts of mineral fillers (upto 70% by weight are marketed as
masterbatches). These include various forms of cellulose, hydrated oxides, clays, glass, metal powder, carbon
fibre, wollastonite, asbestos, talc, calcium carbonate, mica and combinations of these. Each has certain
characteristics that it imparts to a PP compound and will be discussed in detail elsewhere.
One of the original aims of introducing fillers was to decrease the cost of polymer by use of inexpensive fillers.
However, it soon became apparent that improved properties were possible. This allowed use of high cost fillers,
i.e. higher-purity, better colour and special surface treatments to improve adhesion at the dispersed phase
interface. The most important fillers for PP are calcium carbonate, talc and mica. Glass fibre is used to reinforce
PP.

Therefore, the aim today in compounding fillers and reinforcements in PP is selective modification of properties
for specified end-use or in other words "Tailor-Making" of properties.

Selection criteria for fillers and reinforcements in PP

when incorporating fillers and reinforcements into PP, a number of factors have to be considered. These are
summarized below:
* Particle shape, mean particle size and particle size distribution of the fillers
* Dispersability and adhesion (linkage) with the PP matrix
* Abrasive action of the filler on the processing machines
* Properties of the filler/reinforcement such as specific gravity, intrinsic strength, inorganic impurities.
* Problems associated with dust when handling fine powders
* Cost of the filler/reinforcement

Reinforcement is justified only when a distinct improvement of properties/cost reduction compared to

unreinforced PP is found or when a specific combination of properties is not achievable by other means.

Some general rules for selecting fillers and reinforcements in PP are summarized below:
Property Improvement Sought Choice of Filler/Reinforcement

Improved surface finish Calcium carbonate, talc, glass beads

Improved tensile strength and Glass fibres, wollastonite, carbon fibres
flexural modulus
Increased conductivity Carbon powder, A1 flakes, Ni-coated mica, stainless steel fibre

Properties of filled and reinforced plastics

The main difference between inactive and active or reinforcing fillers is their influence on physical and
mechanical properties. Modulus of elasticity and stiffness are increased to some extent by all fillers, even the
spherical types such as CaCO3 and glass spheres. On the other hand, tensile strength can only be improved by
fibre reinforcement. Also the temperature of deflection under load (HDT) cannot be increased to the same extent
as by fibre reinforcement. Fillers in platelet form, such as talc or mica, produced a marked improvement in these
properties.

The use of extender fillers can result in the following changes in the properties of thermoplastics
* Increase in density
* Increase in modulus of elasticity, as well as in compressive and flexural strength (stiffening)
* Lower shrinkage
* Increase in hardness and improvement in surface quality
* Increase in HDT
* Less temperature dependence of mechanical and physical properties
* Cost reduction

Reinforcing fillers produce the following improvements in thermoplastics:

* Increase in Tensile strength at break and compressive, shear and flexural strength
* Increase in modulus of elasticity and stiffness of the composite material
* Increase in HDT and decreasing temperature dependence of mechanical properties
* Lower shrinkage

Two discrete phases are always present in reinforced plastics. The discontinuous filler phases should exhibit
higher tensile strength and higher modulus of elasticity than the polymer matrix, whereas the continuous polymer
phase should possess higher elongation at break than the fibre. For this reason, fibres are suitable as reinforcing
agents.

When the fibre reinforced material is subjected to a tensile load, local tensile stresses are transferred to the
polymer/fibre interface by shear forces and distributed over the fibre surface. For this purpose, the fibre must
adhere well to the polymer and possess a specific length, since otherwise it slips out of the matrix material. The
higher the modulus of elasticity of the matrix polymer, the smaller can be the minimum length of the fibre.
Adhesion can be considerably improved by coupling mechanism between the filler and the plastic.

Calcium Carbonate Filled PP

Calcium Carbonate (CaCO3) can be classified as

* Mineral ground or natural

* Precipitated or synthetic

Naturally occurring calcium carbonate is found as chalk, limestone, marble and is the preferred variety for filler
incorporation into PP.
A typical composition of filler grade calcium carbonate is shown below

CaCo3 : 98.5-99.5%
MgCO3: Upto 0.5%
Fe2O3 : Upto 0.2%

Other impurities include silica, alumina and aluminium silicate, depending on location, source of the ore.
Typical mineral properties are
Density : 2.70 g/cc
Moh;s hardness : 3
Degree of whiteness : 85-95%
Oil absorption : 9-21 g/100 g. powder
Specific surface area : 1-15 m2/gm

Loadings of calcium carbonate in PP typically run from 10 to 50%, although concentrations as high as 80% have
been produced. The filler is available in a variety of particle sizes and size distributions can be coated or
uncoated. Generally speaking, large particle size, greater than 5 um CaCO 3 are less expansive, but they
reduce the impact strength of the PP compound. Smaller particle sizes (less than 1 um) cost more and
are more difficult to compound, but provide superior impact strength and improved surface appearance.
CaCO3 is usually selected as a filler when a moderate increase in stiffness is desired. Minimal sacrifice in impact
strength can be tolerated.

Other effects of the mineral filler are to increase the density of the PP compound, reduce shrinkage which can be
helpful in terms of part distortion and the ability to mould in tools designed for other polymers. At typical levels
10-50%, the viscosity of the compound is not significantly affected by the CaCO 3. The main secondary
additive employed in CaCO3 formulations is a stearate. The stearate acts as a processing aid, helping to disperse
the finer-particle size CaCO3. It also helps to prevent the absorption of stabilizers into the filler. Finally, as an
added benefit, it acts to cushion the system, resulting in improved impact. (Figure 1.)

Figure 1. (a) Effect of filler level on falling weight impact strength of PP at 23 deg. C.
(b) Effect of filler level on notched izod impact strength PP at 23 deg. C.

Table (1) illustrates several properties available based on CaCO3 formulations. Applications of this product range
are in furniture, flush tanks, fan regulator covers, textile bobbins, and refrigerator parts. It is an inexpensive
substitute for polystyrene and ABS co-polymer. IN PP films, incorporation of CaCO 3 improves drawing properties.
In PP tapes, use of CaCO3, upto 5-6% greatly reduces tendency of PP to fibrillate.

Table -1: Typical Product Properties of CaCO3, Filled-PP a No break, flex.

Homopolymer standard CaCO3 Copolymer standard CaCO3 Alternate
Property CaCO3
Unfilled 20% 40% Unfilled 20% 40% 20% 40%
Melt flow rate, condition 4 3 2 4 3 2 3 2
L,g/10 min.
Density, g/cc 0.903 1.05 1.22 0.899 1.03 1.2 1.04 1.22
Tensile strength (yield) 36 32 26 28 25 21 22 19
MPa.
Flexural modulus(1% 1656 2311 2725 1311 1794 2242 1414 1725
secant), MPa
Rockwell R hardness 99 98 97 82 86 87 82 82
Heat deflection 97 117 120 85 86 94 83 83
temperature (deg. C)
Notched izod (23C), 42 48 42 133 69 42 NBFa NBFa
J/m

Talc Filled PP
Talc, chemically is hydrated magnesium silicate and can be represented at 3 MgO.4SiO2-H2O. Naturally
occurring talc can exist in various forms like fibrous lamellar, needle, modular etc.
A typical composition of talc is as under:
SiO2 :40-62%
Al2O3 :0.2-11%
Fe2O3 :0.1-0.5%
FeO :0.1-6.0%
CaO :0.3-1.0%
MgO :30-33%
H2O :16-17%

Typical Mineral properties are

Density :2.90 g/cc
Oil absorption :28-51 g/100 g. powder
Moh's Hardness :1

Talc is generally selected to achieve higher stiffness than is possible with CaCO3, although at the cost of
reduced impact strength and greater sensitivity to moisture. It helps to decrease shrinkage and warpage and
increases thermal conductivity of the PP compound. Additional effects are higher HDT's and higher tensile
strength as compared to CaCO3 formulations.

Table (2) summarizes typical physical properties of talc filled PP.

Table 2 : Typical product properties of talc filled - PP

Property Homopolymer Copolymer
Unfilled Unfilled 20% 40% Unfilled 20% 40%
Melt flow rate, condition L, g/10 min. 4 3.5 2.8 4 3.5 2.8
Density, g/cc 0.903 1.05 1.22 0.899 1.04 1.22
Tensile strength (yield) MPa. 35 34 31 27 28 26
Flexural modulus(1% secant), MPa 1656 2484 3278 752 2208 2898

Rockwell R hardness 99 98 95 82 87 85
Heat deflection temperature (°C) 88 110 118 77 105 114

Notched izod (23C), J/m 42 32 21 133 53.38 32

In addition to structural and thermal property improvements, talc contributes to better dimensional stability,
enhanced thermoforming opacity and depending on talc grade, white colour. The purity of talc is particularly
important to the thermal properties. The presence of metal ions can catalyse the degradation of PP, which will
decrease the long-term thermal stability of the composite. Small amounts of stabilizer packages are often used in
combination with talc, as in under- the hood applications. Surface treated talc do not affect the thermal properties
of PP adversely.

Talc-filled masterbatches are available at loading upto 75%. Dark talc is often used for exterior and interior
automotive engineering applications where colour is not so critical Although the reinforcement properties of dark
talc are lower than those of white-talc grades, the dark talc provides acceptable performance and costs less.
Often compounds for such applications contain both talc and CaCO3. White talc are used in PP garden furniture
and domestic appliances such as washers, dryers etc. PP is the largest volume plastic usage for talc. Talc
provides the structural strength (stiffness) and high temperature resistance needed for automotive and
appliances.

Mica Filled PP
Mica as a filler is not quite as popular as CaCO3 or talc, but it does offer some unique characteristics.
Mica occurs as complex structures of potassium and/or aluminium silicates namely, Typical mineral properties
are: Density : 2.80 g/cc
Moh's Hardness: 4
Oil absorption : 48 - 500 g/100 g powder

Following the trends that have been established, mica is the next step up in the stiffness/HDT ladder. Likewise, it
results in further decreased impact. Mica is found in a platelet form rather than in the more particular form of
CaCO3. As the fillers pass from the particulate form through the platelet form on their way to a fibrous-type form,
the changes in physical properties correspond. From another viewpoint, as the aspect ratio, or length-to-
diameter (or thickness) ratio of the filler increases, strength tends to increase and impact to decrease.
Mica offers outstanding stiffness as well as increased HDT. These properties are further enhanced by the
addition of a coupling agent. Table (3a) summarizes data on some mica-filled PP.
Table 3 a : TYPICAL PRODUCT PROPERTIES OF MICA FILLED -PP
Property Unfille 40% 40% Coupled 50% 50% Coupled
d
Melt flow rate, condition L,g/10 min. 4 2 2 1.5 2
Density, g/cc 0.903 1.23 1.23 1.36 1.36
Tensile strength (yield) MPa. 35 43 46 45 50
Flexural modulus(1% secant), MPa 1656 5796 6555 7245 8211
Rockwell R hardness 99 88 82 85 887
Heat deflection temperature (66 psi), °C 88 136 138 138 138

Heat deflection temperature (264 psi), °C 96 111 114 118 118

Mica-PP composites can be as stiff as steel sheet, but weight only 45% as such. Mica filled PP products
are considered inexpensive substitute for glass fibre filled PP (Table 3b). An interesting use of mica is in PP-PE
copolymer foam for loud speakers and musical instruments due to excellent acoustic properties of mica mineral.
The higher speed of sound in mica allows for a more compact speaker cone.
Table 3 b : Mechanical Properties of Mica & Glass - PP
Property Unfilled 20% 40%
Tensile strength, MPa 34 42 43
Flexural modulus, MPa 1311 6417 7176
Izod impact, J/m 24 42 35

Notched at 220 °C No Break 501 235

Unnotched at 22 °C
heat deflection temperature °C at 264 psi 58 125 108
Mould shrinkage, % lengthwise 2.0 0.3 0.8

Glass -Fibre Reinforced PP

Glass fibre reinforced PP is a high growth segment of the market. These products have high tensile strength and
HDT. Applications include those areas requiring the chemical resistance of PP with the strength of engineering
resins. A drawback of these materials had been their tendency to distort in the final product. Recent advances
have resulted in easy-flow grades that significantly reduce this tendency to warp. Other developments
include the production of higher impact grades. These improvements have opened new applications in the
appliance and industrial markets.

Typical fibre lengths of glass are1/8 to 3/16 inch, although longer fibres are available for specialty applications.
The standard glass diameter for PP applications is 13 microns. The factors influencing properties are the
base resin, the starting glass-fibre geometry, the compounding and processing techniques, the presence
or absence and type of a coupling agent. Table (4) lists typical properties of glass filled PP. Table (5) illustrates
the effect of polymer type and melt flow rate of physical properties using standard 3/16 inch starting fibre length
and a coupling agent. As can be seen the property balances available compare favourably with many other
engineering materials.
Table 4 : Typical Product Properties of Glass filled-PP
Units Base – PP 20% glass 30% glass 40% glass filled PP
Property Homo filled PP filled PP
polymer
Density g/cc 0.90 1.06-1.08 1.15-1.17 1.19-1.21
Tensile strength at yield MPa 35 35.5 36.0 37.0
Tensile strength at break MPa 23 32.5 35.0 36.0
Elongation at break % 60 30 20 30
Flexural strength MPa 330 440 450 450
HDT 66 psi °C. 75 90 97 112

Table 5 : Typical Product Properties of Glass Reinforced, Coupled Material

Homopolymer Copolymer
Property
20% 40% 20% 40% 20% 40%
Melt flow rate, condition L, g/10 min. 3 2 18 12 1.8 1.5
Density, g/cc 1.04 1.22 1.04 1.22 1.05 1.14
Tensile Strength (yield) MPa 83 103 77 99 61 86
Flexural modulus (1% secant), MPa 4209 6831 4071 7590 3450 4830
Heat Deflection temperature 141 144 144 145 141 143
(66 psi) °C.
Heat deflection temperature 234 136 134 137 141 143
Notched Izod (23 °C) J/m 85 112 75 96 149 192
Applications of glass filled PP are in fan blades, head lamp housing, chemical process equipment, washing
machine tanks etc.

Table (6) demonstrates the effect of the type of coupling agent on PP. As can be seen, the coupling agent
provides a considerable increase in tensile strength. In addition, other properties, such as creep
resistance are also improved. The mechanism of the coupling agent is to form a bond between the sizing
agent on the glass fibre and the specially treated PP resin.

Table- 6 : Effect Coupling Agent on a 30% Glass-Reinforced PP

No. of Coupling Agent Coupling Agent A Coupling Agent B
Property
Melt flow rate, condition L, g/10 min. 15 12 12
tensile Strength (yield)MPa 71 88 100
Yield Elongation (%) 1.8 2.1 2..9
Flexural modulus(1% secant), MPa 6141 6279 6348
Heat deflection temperature (264 psi) ° C. 143 146 146
Notched Izod (23°C) J/m 69 85 96

Table (7) shows a comparison of properties of filled PP Homopolymer

Units Base PP 20% CaCO3 20% talc 20% glass 20% glass
Property Homopolymer filled filled filled reinforced
MFI g/10 min. 4 3 3.5 3.5 3.5
Density g/cc 0.9 1.06-1.08 1.06-1.08 1.06-1.08 1.06-1.08
Mould Shrinkage % 2.1-2.3 1.6-1.8 1.5-1.7 0.8-1.0 0.8-1.0
Tensile strength at break MPa 23 18 25 32.5 80.0
Elongation at break % 60 70 50 30 -
Flexural strength MPa 33 35 47 44 61
Heat deflection temperature °C 75 75 99 90 141
Other fillers and Reinforcements
Many other fillers and reinforcements also can be used with PP, including wood flour, ground corn stalks and
other cellulose containing substances. The cellulosic based products provide low-cost opportunities for achieving
high stiffness, but their applications is limited owing to their tendency to char and generate water at processing
temperatures.

For the achievement of conductivity and/or static dissipation properties, metal powders, silver coated glass
spheres, metal wires and conductive carbons have been used. TO reduce the coefficient of friction and to
improve wear characteristics. Teflon R and Silicone are used. These systems are highly specialized and
designed for particular applications.

Colour Systems
The production of precoloured PP can be accomplished through the use of previously selected pigment systems
that have been distributed uniformly in the polymer. For successful colour matching, the viscosity of the resin, the
ease of pigment dispersion, the compounding equipment used and the selection of dispersing aids must be
considered. In order to ensure adequate dispersion, pigment systems are often predispersed in a masterbatch.
When utilizing a masterbatch, the carrier must be compatible with PP matrix. In addition, the possible nucleating
effect of certain pigments, heat stability of pigments which could affect processing and physical properties of PP
respectively must also be considered.

Flame Retardant PP
Materials used as flame retardants can be broadly classified as inorganic fillers and organic compounds.
 However, for making polypropylene flame retardant most of the conventional inorganic fillers cannot be used.
This is because of high processing temperatures of polypropylene. At times, to achieve desired level of flame
retardance substantial quantities of inorganic fillers are required to be used. This affects the properties of end
product drastically. Hence, polypropylene is made flame retardant by using organic flame retardants.

There are three broad categories of flame retardant polypropylene

• Chlorine based systems
• Bromine based systems
• Non-Halogenated systems

There are a number of flame retardants available all over the world in each of the above system. The right choice
among them depends on the end application and the cost. Another important inorganic filler is antimony trioxide
which acts as a synergist with halogen i.e. mainly chlorine and bromine containing flame retardants. The halogen
liberated from these during burning reacts with antimony trioxide to form volatile antimony halides and
oxyhalides. These enter the gaseous part of the flame and help quench reaction occurring, thereby neutralizing
free radicals. The antimony trioxide also reacts directly with the polymer to give water which cools and dilutes the
flame.

Manufacture of flame retardant polypropylene

In order to achieve uniform flame retardancy in the end product, compounding of polypropylene with all flame
retardant additives becomes extremely important. Some applications also require many other additives and fillers
to be incorporated in polypropylene along with flame retardants. This demands sophisticated compounding
equipment and quality control.

To manufacture high quality flame retardant polypropylene sophisticated machinery and technology are required.
Investment in machinery is very high even for medium sized manufacturing unit. These overheads, together with
the high rate of power consumption per unit weight of material manufactured, substantially add to the cost of the
finished product. However, this increase can be compensated by adding fillers, which increases the complexity of
compounds. Higher safety standards required by applications normally justify higher cost of flame retardant
materials.

UL Classification
Following is the basics of Underwriters Laboratory specifications:

This is a flammability test devised by Underwriters Laboratories for plastic materials used in electrical devices
and appliances. In this test, specimens are exposed for two successive 10 seconds ignitions from 3/4" burner
flame. They are classified according to the time it takes the flame to extinguish and the length of time any"after
glow" persists.

Rating are as follows:

94 V-O
Extinguishment time 0.5 seconds
After glow time 0.30 seconds
94 V-1
Extinguishment time 6-25 seconds
After glow time
No. flaming drips 0-60 seconds
94 V-2
Extinguishment time 0.25 seconds
After glow time
Flaming drips permitted 0-62 seconds
Chlorine based systems:
This is the most economical way to make Flame Retardant Polypropylene although recently highly advanced and
expensive systems are also available suitable not only for polypropylene but also for nylon, PBT etc.

Table 8 shows properties of flame retardant polypropylene made out of polypropylene Homopolymer.

Table 8 : Flame retardant polypropylene- Homopolymer chlorinated system

Units PP-FR
Property
Density gm/cc 1.15-1.17
Mould shrinkage % 1.5-1.1.6
Mechanical properties kg/cm2 340

Tensile strength at yield

Tensile strength at break kg/cm2 270
Elongation % 20
Flexural strength kg.cm2 450
Izod Impact kg.cm/cm2 2.0

Notched 20.0
Unnotched kg.cm/cm2
Thermal Properties deg. C 60

Heat Distortion temp. at 18.5 kgs.load

Flammability UL 94 V-0
Similarly Table 9 shows properties of flame retardant polypropylene copolymer. These are only typical examples
of data sheet properties. However, enough scope exists to further modify the properties as per the demands of
applications. It is also necessary to understand the limitations of this most economic system. The thermal
stability and heat resistance of flame retardant poly propylene is greatly reduced. Flame retardants also
plasticise polypropylene is mouldable at lower temperature. This reduces the heat distortion temperature and
sets a limit to the applications which need higher performance temperature. Chlorine based systems find
application in small injection moulded parts and is not recommended for any of the extrusion applications as it
poses greater degree of damage to screw, barrel, dies etc.
Table 9 : Flame retardant polypropylene- copolymer chlorinated system

Table 10 : Flame retardant polypropylene- Homopolymer brominated system

Units PPFRV-1, Unfilled PPH

Property
Density gm/cc 1.24
Mould shrinkage % 1.8-2.0
Mechanical properties kg/cm2 330

Tensile strength at yield kg/cm2 275

Tensile strength at break

elongation % 40
Flexural strength kg. cm2 460
Izod Impact kg.cm/cm2 3.0

Notched kg.cm/cm2 33.0

Unnotched
Thermal Properties °C. 96.0

Heat Distortion temp. @ 18.5 kgs. load

Flammability 1mm UL 94 V-1
Table 11
Non-halogenated Flame retardant polypropylene-Homopolymer

Non-halogen based systems

Smoke density and toxicity regulations limit the use of halogen based flame retardant polypropylene. Acidic
halogen based gases evolved during burning also damage expensive electronic circuitary. The development of
non-halogenated systems took place considering these aspects. However, it is the most expensive system today
for injection moulding applications. It is widely used for extrusion applications mainly polyethylene based cables.

Table 11 gives properties of polypropylene Homopolymer based product. Similarly compounds based on
co-polymer fillers and other additives can be made.
Units Unfilled PPH
Property
Density gm/cc 1.04
Mould shrinkage % 1.8-2.0
Mechanical properties kg/cm2 315

Tensile strength at yield kg/cm2 270

Tensile strength at break

elongation % 38
Flexural strength kg/cm2 430

Izod Impact kg.cm/cm2 2.3

Notched kg.cm/cm2 31.0

Unnotched
Thermal Properties °C. 87.0

Heat Distortion temp. @ 18.5 kgs. load

Flammability 1mm UL 94 V-0
• Elastomer Modified PP products
One of the most common reasons to utilize a rubber/elastomer "modifier" in PP is to improve its low
temperature impact resistance. Originally, the first impact PP products were formulated from blends of PP
Homopolymer with butyl rubber. Subsequently, it was discovered that ethylene-propylene (EPM) rubber offered
greater toughening power and was easier to disperse and compound into PP. The industry then evolved towards
fine tuning of the EPM materials with the closely related ethylene-propylene-diameter polymers (EPDM).

When EPM/EPDM rubbers are thoroughly blended with either PP Homopolymer or copolymer to an extent of 10-
40% by weight, a new family of thermoplastic materials called rubber or toughened PP is produced. They have
flexural modulus of elasticity within 600-1200 MPa, together with an exceptional impact resistance down to - 50
deg. C according to the grade and percentage of EPDM used. Such a combination has been the main reason for
the success of these materials in the automobile industry.

The three properties, elastic modulus in flexural mode, impact strength and brittle/tough transition temperature
represent the most important indicators for end-use behaviour of elastomer modified PP technical articles.

A single rubber particle acts as a centre of absorption and elastic redistribution in the surrounding area of the
shock wave caused in the material when a local impact is applied. The impact energy is, therefore distributed
across a large volume of material, decreasing local intensity when the finely dispersed elastomeric particles are
numerous. Table (12) lists some properties of EPDM modified PP vs EPDM content.
Table 12 Properties of Elastomer Modified Polypropylene:
Property Test Method Units Blend I Blend II Blend III Blend IV Blend V
Density D 1505 gm/cc 0.9-1.0 0.9-1.0 0.9-1.0 0.9-1.0 0.9-1.0
Tensile strength at yield D 638 kg/cm2 45 100 150 200 220
Elongation D 638 % 500 500 500 350 100

kg/cm2 1000
Flexural Modulus D790 % 7500 7500 10000 15000

Izod Impact D256 kg. cm/cm N.B N.B N.B 60 30

-Notched D256 kg.cm/cm N.B N.B N.B NB NB

-Unnotched
Shore Hardness D2240 Shore 85A 90A 70D 77D 85D
Applications O riungs, Automobile Bumpers Dashboards,
hoses, mats trims, toys, internal panels
and mud flaps, refrigerator
bellows liners, window
profiles

Modification by Other Components

Elastomer modified PP grades require greater stiffness at elevated temperatures, better HDT and shape
stability. Filler can be added to improve these properties. Talc is generally used in 15 to 40% by weight of
finished products. EPDM-PP Talc compositions permit a wide range of possible proportions and
corresponding broad performance area for the commercial products.

I II III IV V
PP: 50 60 70 80 90
EPDM: 50 40 30 20 10

Applications:
In the recent past, the most important uses of PP-EPDM blends has been in the automobile industry.
Comparative lightness, low cost and a wide range of mechanical properties are the main factors responsible for
the continuous growth of these materials since 1975. Their main use in car bumpers using either PP-EPDM
flexible shapes mounted on a rigid steel framework or fabricated self-supporting finished articles such as
complete car front masks.

Suitable blends contain from 10 to 35% by weight of EPDM, according to flexibility and impact requirements.
EPDM-PP talc ternary blends find their biggest outlet as interment panel dash boards in many models of low to
medium cost cars. For this application stiffness and shape stability, coupled with an impact resistance high
enough to avoid splintering failures or dangerous sharp fragments in medium speed crashes provide these
blends with an ideal application.

According to an estimate 90% of the OO-EPDM blends used are for the automotive industry at present. A
summary of filled and reinforced-PP products in the automobile industry is given in Table 13.

Table 13 Plastic Components in Maruti Esteem

Material Wt. in gms. No. of parts Wt. per car
Part Name (grams.)
Instrument Panel Filled PP 4000 1 4000
Glove box Filled PP 350 1 350
Glove box lid Filled PP 200 1 200
Garnish cowl ventilator Filled PP 210 2 420
Oil filer housing assembly Filled PP 650 1 650
Fan blade 80 W Filled PP 180 1 180
Fan Blade 120 W Filled PP 236 1 236
AC blower Filled PP 160 1 160
 Air filter assembly Filled PP 800 1 800
Trim rear pillar Filled PP 150 2 300
Air ventilator assembly Filled PP 1275 1 1275
AC case and cover cooling Filled PP 550 1 550
Boot component Filled PP 500 2 1000
Bumper (Front upper) PP modified 780 1 780
Bumper (Front lower) PP modified 2600 1 2600
Bumper (Rear upper) PP modified 730 1 730
Bumper (Rear lower) PP modified 3200 1 3200
• Compounding Machinery
Compounding of PP with additives, fillers and reinforcements can be achieved using various types of machines
depending on cost and quality of mixing desired. A few of these are discussed in the section.

• Compounding low add levels

PP is generally an easily compounded material and the compounding of low-add-level products usually requires
nothing more than a dry solids mixer for pre blending and a single-screw extruder for pelletizing. Extrusion
temperatures will depend primarily on the viscosity or melt flow rate of the PP Homopolymer or copolymer
component. With melt temperatures typically falling between 190 deg. c. and 2245 deg. c. Depending on the
equipment, PP may give lower output rates on extruders than other polymers as a result of both its low density
and its rheological properties.

At high melt flow rates, pelletizing may present some problems owing to the low melt strength. With specialized
equipment, melt flow rates as high as 1000 have been pelletized. Both hot-cut and cold-cut pelletizing systems
are suitable for PP. The choice usually depends on the equipment available as well as downstream processing
considerations. In some subsequent extrusion and injection moulding processes, the shape and size of the
pellets will influence the products processing behaviour. For example, the flat, thin wafer configuration
characteristic of the hot cut has been reported to cause slipping problem in the extrusion of thin film.

When particularly good dispersion is required, a better option for incorporating these additives is to produce an
additive concentrate. To obtain the necessary dispersion in the final product, the concentrate is produced utilizing
a fluxed melt mixer such as a Banbury prior to extrusion. The extruded concentrate may then be blended with the
polymer matrix during a final compounding stage or may be added during the final moulding or extrusion step.
Colour concentrates are a well-known example, but lubricants. UV/light stabilizers may also be incorporated in
this manner.

• High Add Levels

• Single screw extrusion
The addition of higher-add-levels of fillers and reinforcements may be done on a single screw or a twin-screw
extruder. The choice is determined by the type of filler/reinforcement. In general, the single screw use is limited to
low-aspect-ratio additives such as CaCO3 and talc.

The production of CaCO3 filled and talc filled materials may be accomplished using only a dry-solid mixer and a
two-stage vented extruder. An Auger-type hopper stuffer assists feeding. As the filler level increases, melt fluxing
mixers, such as Farrel Continuous Mixer (Figures 2) may be used to optimize mixing and distribution. The Farrel
Continuous Mixer is a counter rotating, non-intermeshing twin-rotor mixer. It can be divided into 3 zones: (a)
Feed zone (b) Mixing zone (c) Discharge zone. The feed zone of the mixer is designed to optimize ingestion and
delivery of feed m material (s) into the mixing zone. Upon entering the mixing zone, the feed material is melted
and then continuously fluxed, pumped, backmixed and it exits through the discharge zone. The maximum
achievable loading will depend, to some extent, on the melt viscosity of the polymer, but primarily on the type of
filler. For example, specialized CaCO3 concentrates have been produced with filler levels upto 80%, while it is
difficult to reach a 50% loading with mica.

At high filler loadings, intensive mixing may not be necessary, as long as the filler is uniformly distributed. Over-
mixing can cause separation. In general, both batch (Banbury) and continuous (FCM type) mixers are suitable.

Metered feeding is necessary for all high filler-level systems. Fillers such as CaCO3 are liable to bridge in the
hopper. In addition, there is a potential for separation and build-up of the filler on vertical metal surfaces. The
critical design features of the feeders are the agitator and the feed screw and their relationship with each other.
The agitator should sweep the hopper walls as closely as possible to prevent filler build-up. The hopper should
be equipped with a level control feeder.

SECTIONAL VIEW OF TYPICAL FCM IN OPERATION

The compounding extruder should have relatively shallow flights. A compression ratio of 2.5:1 is preferred and no
additional mixing devices are generally required.

Mineral fillers tend to be hygroscopic. Therefore, a vacuum vent is utilized during the extrusion step. When a
cold-cut pelletizing system is used, the emerging strands from the die face is taken into water bath and taken out
quickly, taking care to ensure integrity of the strands. A blower assists water removal from the strands prior to
chopping.

Reciprocating Extruders
In these types of machines, both rotational and reciprocating action of the screw occur simultaneously and are
continuous. These machines are specifically designed to enhance mixing performance and are usually referred
to as Ko-Kneaders.

A schematic sketch of a Ko-Kneader is shown in Figure (3). The Kneader is a single screw extruder with
interrupted screw flights and stationary pins or teeth in the barrel. The screw flights can be continuous in the feed
section and vent section to improve forward conveying. In this section, no pins are located in the barrel. The
mixing sectionof the screw is typically double-fighted with a small helix angle of 13 degree. The interruptions in
the screw flights leave flight segments that look like vanes. There are three rows of pins or teetha along the
length of the barrel. The barrel has a clamshell design, which facilitates cleaning of the barrel. Modern kneaders
have a typical L/D ratio of about 11.

PP can be compounded with CaCO3, talc and glassfibres on Ko-Kneaders,

Twin screw extruders

The compounding of fillers, reinforcements, flame retardants (solids/liquids) can be achieved with a twin-screw
extruder. Twin-screw extruders are designed to allow flexibility in the method of component introduction, in
addition to the ability to change screw configuration. The extruder comes configures with multiple feed ports,
allowing the polymer components to be added as specified by the compounder. For example, the resin is
generally added at the beginning of the extruder to ensure melting, mixing and uniformity of melt temperature,
while fillers/reinforcing agents or liquid additives are added further downstream.
Twin-screw extruders make use of starve feeding systems as opposed to flood feeding system utilized with
single-screw extruders. Side feeders for filler addition are also employed. Venting, pelletizing and downstream
handling requirements are all similar for systems described in section 3.2-1.
Feed alternatives (depending on formulation)

Flame Retardant PP
A schematic sketch of a typical twin-screw set up for introducing liquid flame retardant into PP is shown in Figure
(4). The extruder set up requires two feeding ports, one for PP and one injection port for additive located
downstream. The first section of the extruder creates a melt pool before the liquid is injected. The viscosities of
the polymer melt and liquid are matched near the injection port and then the mass is allowed to homogenize in
the latter part of the extruder. The factors which govern the quality of the final product are the temperature profile
in the extruder, screw design and extruder geometry.

Filled PP
Filled PP grades can be compounded with twin screw extruders. Dispersion requirements for talc and CaCO3
vary according to the final product application. The primary objectives are uniform incorporation and mixing.
A schematic diagram of mixing elements which make up a configurations shown in Figure (5).

Fillers are added downstream t a melt to isolate their abrasive effects. A melt seal is formed upsteam where large
pitch screws are used. The downstream section is configured for low shear mixing for low performance
applications. Applications requiring high degree of dispersion are compounded using a high shear intensive
mixing section.

Glass Fibre Filled PP

Compounding technique for incorporating glass fibre into PP requires isolation of high and low shear sections
along the screw length. Chopped fibres or continuous rovings can be used. The design of the screw determines
the final fibre length in PP. PP in powder/pellet form is metered into the feed zone with stabilizers and lubricants.
The additives can be preblended or metered individually. A relatively high shear plasticizing and mixing section is
used to generate a homogeneous melt. Fibres are introduced into the melt via second feed opening located
downstream (figure 6.) Metering equipment is required for chopped strands. Continuous rovings are continuously
unwound from the core, drawn in by the turning screw. One inside the barrel, the continuous rovings are chopped
to length by the kneading elements located downstream of the feed opening. A less intensive mixing section is
needed for chopped fibre, since the fibres have only to be wetted out and dispersed. Degassing and die extrusion
follows the compounding step.

Table (14) shows the effect of compounding technique on physical properties of glass fibre filled PP product. It is,
therefore, important to select the correct compounding machine to obtain reinforced products with desired
mechanical properties.
Table - 14
Effects of Compounding Technique on 20% glass reinforced-PP
Property Standard Intensive twin screw Fluxed melt
twin screw mixer
Melt flow rate, condition L.g/10 min. 4 5 9
Tensile strength (yield) MPa 79 70 49
Yield elongation, % 2.8 3.1 5.1
Flexural modulus (1% secant), MPa 4071 3726 26.22
Heat deflection temp. (264 psi), °C. 134 134 104
Fibre length (average), um 550 550 300

Twin screw-extruder for introducing liquid FR into PP

Twin screw Extruder

Continuous Twin Screw

Typical configuration for glass fibre incorporation into PP

Schematic view of a Banbury Type Internal Mixer

 (Contributed by Reliance Industries Limited- Product Application & Research Center)

Polypropylene (PP) - Types, Properties, Uses & Structure (specialchem.com)

Comprehensive Guide on Polypropylene (PP)

Polypropylene (PP) is a tough, rigid, and crystalline thermoplastic. It is made from
propene (or propylene) monomer. This linear hydrocarbon resin is the lightest
polymer among all commodity plastics. PP comes either as a homopolymer or as a
copolymer and can be greatly boosted with additives.

PP has become a material of choice when you are looking for:

o Superior strength in engineering applications (vs. Polyamide)

o Cost advantage in blow molding bottles (vs. PET)

>> Browse among more than 13 000 commercial grades by 300+ suppliers to
find your perfect PP plastic.
 Overview
o What is PP?
o How is PP produced?
o What are the properties of PP?
o What are the types of PP?
o How to decide between PP homopolymer vs. PP copolymer?
o How to compare between the main PP types?
o What are the disadvantages of PP?
o How additives help improve PP properties?
o How to compare between PP derivatives?
o What are the forms of PP films?
o How to process PP?
o Is PP recyclable?
o Is PP safe?
o How PP differs from PE?
o How PP challenges PET?
o How PA differs from PP?
o What are the commercially available PP grades?
 Key Applications
 Key Properties
 PP Suppliers
 Polypropylene Brands
What is polypropylene?
Polypropylene (PP) is a type of polyolefin that is slightly harder than polyethylene. It is a
commodity plastic with low density and high heat resistance. Its chemical formula is
(C H )n.
3 6

Molecular Structure of PP

It finds application in packaging, automotive, consumer good, medical, cast films, etc.
Depending on how it is produced and formulated, PP can be:
o hard or soft,
o opaque or transparent,
o light or heavy,
o insulating or conductive,
o Neat or reinforced with cheap mineral fillers, short or long glass fibers, and natural
fibers or even self-reinforced.

How is PP produced?
It is made from the polymerization of propene monomer. There are two main
syntheses to produce polypropylene:
o Ziegler-Natta polymerization or
o Metallocene catalysis polymerization

Upon polymerization, PP can form three basic chain structures. They depend on the
position of the methyl groups:

o Atactic (aPP) – Irregular methyl group (CH ) arrangement

3

o Isotactic (iPP) – Methyl groups (CH ) arranged on one side of the carbon chain
3

o Syndiotactic (sPP) – Alternating methyl group (CH ) arrangement

3
 Basic Chain Structures of PP

What are the properties of PP?

Keeping information about the properties of a thermoplastic beforehand is always
beneficial. This helps in selecting the right thermoplastic for an application. It also assists
in evaluating if the end-use requirement would be fulfilled or not. Here are some key
properties and benefits of polypropylene:

1. Melting Point - The melting point of PP occurs at a range.

o Homopolymer: 160 - 165°C
o Copolymer: 135 - 159°C

2. Density - PP is one of the lightest polymers among all commodity plastics.

This feature makes it a suitable option for lightweight\weight saving
applications.
o Homopolymer: 0.904 - 0.908 g/cm 3

o Random Copolymer: 0.904 - 0.908 g/cm 3

o Impact Copolymer: 0.898 - 0.900 g/cm 3

3. Chemical Resistance
o Excellent resistance to diluted and concentrated acids, alcohols and bases
o Good resistance to aldehydes, esters, aliphatic hydrocarbons, ketones
o Limited resistance to aromatic and halogenated hydrocarbons and oxidizing
agents

4. Flammability: PP is a highly flammable material.

5. PP retains mechanical & electrical properties at elevated temperatures. This

occurs in humid conditions and when submerged in water. It is a water-
repellent plastic.

6. PP has good resistance to environmental stress cracking.

 7. It is sensitive to microbial attacks, such as bacteria and mold.

8. It exhibits good resistance to steam sterilization.

Learn more about all polypropylene properties and their values - ranging from
mechanical and electrical to chemical properties; and make the right selection for your
application.

What are the types of PP?

The major types of polypropylene available in the market are as follows:

Polypropylene Homopolymer

PP Homopolymer is the most widely utilized general-purpose grade. It contains only

propylene monomer in a semi-crystalline solid form. Main applications include
packaging, textiles, healthcare, pipes, automotive and electrical applications.

Polypropylene Copolymer

This family is produced by polymerizing propene and ethane. It is further divided into
random copolymers and block copolymers.

1. PP Random Copolymer is produced by polymerizing ethene and propene

together. It usually features ethene units up to 6% by mass. These units are
randomly incorporated into the polypropylene chains. These polymers
are flexible and optically clear. This makes them suitable for applications
requiring transparency. Also, suitable for products requiring an excellent
appearance

2. While in PP Block Copolymer, ethene content is larger. It ranges between 5

and 15%. It has co-monomer units arranged in regular patterns or blocks.
The regular pattern makes thermoplastic tougher and less brittle than the
random copolymer. These polymers are suitable for applications requiring
high strength, such as industrial usage.

Polypropylene, Impact Copolymer

Propylene Homopolymer contains a co-mixed PP Random Copolymer phase. It has an

ethylene content of 45-65%. It is useful in parts that require good impact
resistance. Impact copolymers are mainly used in packaging, housewares, film, and pipe
applications. They are also used in the automotive and electrical segments.
Expanded Polypropylene

EPP is a closed-cell bead foam with ultra-low density. It produces three-dimensional

polymer foam products. EPP bead foam has:

o higher strength-to-weight ratio,

o excellent impact resistance,
o thermal insulation,
o Chemical and water resistance.

EPP is used in automobiles, packaging, construction products, consumer goods, and

more.

Polypropylene Terpolymer

PP Terpolymer is composed of propylene segments joined by monomers ethylene and

butane (co-monomer). These monomers appear randomly throughout the polymer chain.
PP terpolymer has better transparency than PP homopolymer. Also, the incorporation of
co-monomers reduces crystalline uniformity in the polymer. This makes it suitable for
sealing film applications.

Polypropylene, High Melt Strength

It is a long chain-branched material. It combines both high melt strength and extensibility
in the melt phase. The key features of PP HMS grades include:

o wide mechanical property range,

o high heat stability, and
o Good chemical resistance.

HMS PP is widely used to produce soft, low-density foams for food packaging
applications. Also used in the automotive and construction industries.

Bio-based Polypropylene

It is a bio-based version of PP. Its monomer propylene is derived from renewable

feedstocks. The bio-based content can vary anywhere between 30-100%. There are
several suppliers offering pure PP bio-based grades such as:

o PolyFibra® & Trifilon BioLite®

o PP/PE blend - Terralene® PP 2509 and
o In biocomposite form like Terratek®, Sappi Symbio PP, etc.
How to decide between PP homopolymer vs. PP copolymer?
PP Homopolymer PP Copolymer

High strength to weight ratio and stiffer & Bit softer but has better impact strength;
stronger than copolymer tougher and more durable than
Good chemical resistance and weldability homopolymer
Good processability Better stress crack resistance and low
Good impact resistance temperature toughness
Good stiffness High processability
Food contact acceptable High impact resistance
Suitable for corrosion resistant structures High toughness
Not preferable for food contact
applications

The potential applications for PP homopolymer and PP copolymer are nearly

identical

Because of their extensively shared properties, the choice between these two materials
is often made based on non-technical criteria.

How to compare between the main PP types?

PP, Impact
Property PP Copolymer PP Homopolymer
Copolymer

Density, g/cm3 0.9 0.9 0.9

Shore hardness,
45-55 70-80 70-83
D

Stress at yield,
11-28 20-35 35-40
MPa

Elongation at
20-700 200-600 15-600
break, %

Tensile modulus,
0.4-1 1-1.2 1.1-1.6
GPa

Notched impact 110-No Break 60-500 20-60

strength ASTM
 D256, J/m

HDT A(1.8 MPa),

46-57 50-60 50-60
°C

Minimum service
-40 to -20 -20 to -10 -20 to -10
temperature, °C

UL94 fire rating HB HB HB

Get more information about polymer properties here »

Detailed Property Comparision: PP Impact Copolymer, PP Copolymer and PP Homopolymer

What are the disadvantages of PP?

o Poor resistance to UV, impact and scratches
o Embrittles below -20°C
o Low upper service temperature, 90 - 120°C
o Attacked by highly oxidizing acids, swell rapidly in chlorinated solvents and
aromatics
o Heat-aging stability is adversely affected by contact with metals
o Post molding dimensional changes due to crystallinity effects – this can be solved
with nucleating agents Watch Video Here »
o Poor paint adhesion

However, polypropylene is gradually optimized for its performance by improving its

properties using different additives.

How additives help improve PP properties?

The addition of polymer additives can overcome the above-listed disadvantages. They
can also improve PP's physical and/or mechanical properties.

For example, PP has poor resistance to UV. The addition of hindered amines to PP
provides light stabilization. This enhances the service life as compared to unmodified
PP. Looking for UV stabilized grade? Here’s the complete list for you »

Some additives include:

Clarifiers Conductive fillers Flame retardants

Minerals Lubricants Pigments, and others
Further, fillers and reinforcers achieve significant properties related to processing and
end-use application. Check out filled or reinforced options to choose the grade of your
choice:

o Glass-fiber reinforced PP grades

o Mineral-filled PP grades
o Calcium Carbonate-Filled PP grades
o Carbon-fiber reinforced PP grades

Moreover, self-reinforced polypropylene composites benefit from several general

advantages such as:

o monomaterial concept,
o low density,
o good mechanical properties,
o high impact resistance, and
o weight savings.

Thanks to the combination of low densities and good mechanical properties. It results in
up to 50% potential weight savings over glass-reinforced parts. It is easy to recycle.

There have been significant developments seen for self-reinforced PP. These advances
bridge the gap between isotropic polymers and glass-reinforced materials. The self-
reinforced PP offers a unique combination of processing and performance
features. Learn more about the benefits and applications scope now »

Natural fiber-reinforced polypropylene options are an interesting step toward cheap

sustainable composites. Low densities lead to noticeable cost savings and weight
savings. This is up to 27% over glass fiber or talc-reinforced polypropylene. Looking for
grades reinforced with Biofillers? Here’s the complete list for you »

The use of new additives, polymerization processes and blending solutions significantly
increases PP performance. Hence, today PP is less seen as a low-cost solution but
much more as a high-performance material. It competes with traditional engineering
plastics and metals.

How to compare between PP derivatives?

Self-
Talc Glass Long Fiber
Thermoplastic Reinforced
Property Filled Filled Reinforced
Polyolefin PP
PP PP Thermoplastic
 0.97- 0.97-
Density, g/cm3 0.9-1 1.2 0.8-0.9
1.25 1.25

Shore
10-99 75-85 70-88 - -
hardness, D

Rockwell
- 10-45 - - -
hardness, M

Stress at yield,
- 22-28 19-70 - -
MPa

Elongation at
450-850 20-30 2-30 2 -
break, %

Tensile
- 1.5-3.5 1-10 4-8 4-14
modulus, GPa

Notched
impact
110-No Break 30-200 38-160 - -
strength ASTM
D256, J/m

HDT A(1.8
- 56-75 50-140 160 -
MPa), °C

Minimum
service -20 to - -30 to -
-40 to -20 - -
temperature, 5 5
°C

UL94 fire rating HB HB HB HB HB

Get more information about polymer properties here »

What are the forms of PP films?

PP film is among the leading materials today. Used for flexible packaging as well as
industrial applications. Two important forms of polypropylene films include:

Cast Polypropylene Film (CPP)

CPP is widely known for its versatility.

 o Super resistance to tears & puncture
o Greater transparency
o Better heat resistance at high temperatures
o Excellent moisture and atmospheric barriers
o High permeability to water vapor

Biaxially Oriented Polypropylene Film (BOPP)

BOPP is stretched in both transversal and longitudinal directions, producing molecular

chain orientation in two directions.

o Orientation increases tensile strength and stiffness

o Good puncture and flex crack resistance over wide range of temperatures
o Have excellent gloss, high transparency
o Can be glossy, clear, opaque, matte or metalized
o Efficient barrier against oxygen and moisture

How to process PP?

Polypropylene can be processed virtually by all processing methods. The most typical
processing methods include:

Injection Molding with PP

The processing conditions for PP injection molding include:

1. Melt temperature: 200-300°C

2. Mold temperature: 10-80°C
3. Drying is not necessary if stored properly
4. High mold temperature will improve brilliance and appearance of the part
5. Mold shrinkage lies between 1.5 and 3%. It depends on:
o processing conditions,
o rheology of the polymer, and
o thickness of the final piece

Watch free video tutorial to improve PP cycle time and limit part shrinkage
Expanded Polypropylene (EPP) may be molded in a specialized process. EPP is an
ideal material for injection molding process. It is majorly used for batch and continuous
production.

View all PP Grades Suitable for Injection Molding »

Extrusion with PP

PP can be extruded into tubes, blow and cast films, cables, etc. The processing
conditions for PP extrusion include:

1. Melt temperature: 200-300°C

2. Compression Ratio: 3:1
3. Cylinder Temperatures: 180-205°C
4. Pre-Drying: No, 3 hours at 105-110°C (221-230°F) for regrind

View all PP Grades Suitable for Extrusion »

3D Printing with PP

As a tough, fatigue-resistant and durable polymer, PP is ideal for low-strength

applications. It is currently difficult to use PP for 3D Printing processes due to its:

o semi-crystalline structure and

o heavy warping

Several manufacturers have optimized PP properties or even created blends with

improved toughness. This makes it suitable for 3D Printing applications. Hence, it is
recommended to thoroughly refer to the documentation provided by the supplier for
printing temperature, printing bed, etc.

Polypropylene is suitable for:

o Complex models
o Prototypes
o Small series of components, and
o Functional models

View all PP Grades Suitable for 3D Printing »

Other processing methods for PP

o Blow molding
o Compression molding
o Rotational molding
o Injection blow molding
o Extrusion Blow Molding
o Injection stretch blow molding
o General-Purpose Extrusion

Some grades are designed for your specific conversion mode like blow molding,
compression molding, thermoforming, etc. Check out PP grades with various conversion
mode here »

TIP: To meet specific requirements, try using the “Conversion mode” facet to narrow
down your search.

Is PP recyclable?

All plastics have a ‘Resin Identification Code/ Plastic Recycling Code’ based on the type
of resin used. PP’s resin identification code is 5. PP is 100% recyclable.

Polypropylene recycling process

The PP recycling process includes:

o Melting waste plastic to 250°C to get rid of contaminants.

o Removal of residual molecules under vacuum and solidification at approximately
140°C.

This recycled PP can be blended with virgin PP at a rate of 50%.

PP recycling – The main challenge

The main challenge in PP recycling is related to the amount consumed. Currently, 1% of

PP bottles are recycled as compared to the 98% recycling rate of PET & HDPE bottles
together.
Uses of recycled polypropylene (rPP)

A few applications of rPP include:

o Automobile battery cases,

o Signal lights,
o Battery cables,
o Brooms,
o Brushes,
o Ice scrapers, etc.

Meet the urgent demands for greener polypropylene products (lighter, recyclable, high-
performance PCR grades...) with beta nucleation to gain an edge over your competition.
Take this exclusive course by Industry Expert Dr. Philip Jacoby.

Is PP safe?
The use of PP is considered safe. This is because it does not have any remarkable
effect from an occupational health and safety point of view, in terms of chemical toxicity.

How PP differs from polyethylene (PE)?

Both PP and PE are very similar, but they also have characteristics that are unique to
each other. These features can be maximized depending on:

o how they are made and

o which application they are used for.
PP is the second most used plastic after polyethylene. They both can be designed to be
durable and lightweight. These polymers are used in many applications such as bottles
and gloves. But PP has crystal-clear transparency than PE. PP has excellent
mechanical properties. It has high resistance to fatigue, impact, heat and, freezing.

PE is tough yet light, with good resistance to impact and abrasion. PP is harder and can
be used for mechanical and structural applications.

They both are highly malleable and have relatively similar impact resistance. This means
strength does not have to be a concern when these plastics are in use. Density is
another key factor that differentiates PE from PP. Polypropylene’s density is fixed and
only varies when it is filled. Polyethylene selection is highly dependent on the varying
densities of multiple versions. PE is available in low, medium, and high-density grades.
High Density Polyethylene is known for its big strength-to-density ratio. HDPE is
considered more rigid than PP.

Here is a quick wrap-up of their main differences:

Polypropylene Polyethylene

Propylene monomers make PP Ethylene monomer make PE

It can be produced optically clear It can only be made translucent like a
PP exhibits a high resistance to milk jug
cracking, acids, organic solvents and PE stand up better in cold temperatures
electrolytes It is a good electrical insulator and
It has high melting point and good offers good tracking resistance
dielectric properties PE is sturdy as compared to PP
PP is more rigid than polyethylene

PP Grades PE Grades

If PE is more suited for your needs, find out more about the polymer here »

How PP challenges polyethylene terephthalate (PET)?

In blow-molded bottle applications, PP has emerged as a strong competitor to PET.
Compared to PET, the key features of PP include:

o Less expensive,
o Lighter in weight,
o More resistant to the high temperatures of hot filling, and
 o Less permeable to moisture.

PP bottles can be hot-filled at temperatures up to 100°C. While PET cannot withstand

filling temperatures above 76°C.

In its pure state, PP is less clear than PET. Also, the gas barrier properties of PP are not
as high as PET, and PP also falls below PET in stiffness. PP has about five times the
moisture barrier properties of PET. But PP is about 30 times more permeable than PET
to gases such as oxygen and carbon dioxide.

The production cycles of PP bottles have generally been longer than PET bottles. PP
also has a narrower range of processing temperatures than PET.

But producers of PP resins and the additives that go into them are making important
strides in overcoming these deficits, such as:

o Inserting clarifiers into PP enables it to match PET's transparency. Clarified

grades of PP have a clarity and gloss comparable to PET.

o Nucleators can speed up crystal formation in PP during cooling. This thereby

shortens cycle times, and sometimes also improves clarity as well. Explore
several nucleated PP grades here »

o Barrier layers (EVOH sandwich, coatings, etc.) enable PP to compete on a cost

basis with both glass and PET containers in many food and beverage applications
while offering good barrier properties.

The above steps make PP competitive with PET and can narrow that cost advantage
considerably. But PP still comes out as the more economical packaging choice than PET
for many applications.

Learn more about PET before you make final decision on material »

How nylon differs from PP?

Polyamide and polypropylene vary in their individual structures. Both these polymers
offer superior strength to the final parts. There are some significant distinctions you
should consider choosing any of them.

The key benefit of PP is its low melt viscosity, and it offers strength and elasticity. A low
melt viscosity enables materials to be easily used in injection molding. It also opens
more opportunities and capabilities.
 While Nylon is more heat-resistant than PP. And nylon is more malleable than PP. It can
offer designers greater design flexibility i.e., easy bending than breaking.

From the end application perspective, both polymers have poor UV stability
performance. They require suitable additives to mitigate UV damage risk.

If Nylon is more suitable for your needs, find out more about the polymer here »

Key Areas of Applications of Polypropylene

Polypropylene is widely used in various applications. It offers good chemical resistance and
weldability. Today, it is at the point of junction between cheap commodity plastics and more or
less performing engineering plastics.

Some of the popular applications showcasing PP versatility are listed below.

 O verview
 K ey A pplications
 K ey P roperties
 S uppliers
 B rands
1. Packaging Industry: Good barrier properties, high strength, good surface
finish and low cost make Polypropylene ideal for several packaging
applications. They perform well in blow molded and sheet thermoformed
products for food, personal care, health, medical and labware, household
chemicals and beauty aid products.

o Flexible Packaging: PP films’ excellent optical clarity and low moisture-

vapor transmission make it suitable for use in food packaging. Other markets
shrink-film overwrap, electronic industry films, graphic arts, disposable
diaper tabs and closures, etc. PP grades are used to produce oriented, bi-
oriented and cast films and foils.
o Rigid Packaging: PP is blow molded to produce crates, bottles, and pots.
PP thin-walled containers are commonly used for food packaging.

2. Consumer Goods: PP is used in several household products and consumer

goods applications including translucent parts, housewares, furniture,
appliances, luggage, toys etc.

3. Automotive Industy: Due to its low cost, outstanding mechanical properties

and moldability, PP is widely used in automotive parts. Used in battery cases
and trays, bumpers, fender liners, interior trim, instrumental panels and door
trims. Other key features of PP include low coefficient of linear thermal
 expansion and specific gravity, high chemical resistance and good
weatherability, processability and impact/stiffness balance.

4. Fibers and Fabrics: A large volume of PP utilized in the market segment

known as fibers and fabrics. PP fiber is used in raffia/slit-film, tape,
strapping, bulk continuous filament, staple fibers, spun bond and continuous
filament. PP rope and twine are very strong and moisture resistant that are
suitable for marine uses.

5. Medical Industry: PP is used in various medical applications due to high

chemical and bacterial resistance. Also, the medical grade PP exhibits good
resistance to steam sterilization. Disposable syringes is the most common
medical application of PP. Other uses include medical vials, diagnostic
devices, petri dishes, intravenous bottles, specimen bottles, food trays, pans,
pill containers, etc.

6. Industrial Uses: PP sheets are widely used in industrial sector to produce

acid and chemical tanks, sheets, pipes, Returnable Transport Packaging
(RTP), etc. because of its properties like high tensile strength, resistance to
high temperatures and corrosion resistance.

Polypropylene Properties and Their Values

Polypropylene is one of the versatile polymers used and exhibits excellent mechanical
properties. Polypropylene also offers good chemical and heat resistance. Some of these
characteristics have enabled it to replace polyethylene for several applications. Learn more about
all polypropylene properties and their values - ranging from mechanical to electrical to chemical
properties, to make right selection for your application.

 O verview
 K ey A pplications
 K ey P roperties
 S uppliers
 B rands

Property POLYPROPYLENE

Chemical Resistance

Acetone @ 100%, 20°C Satisfactory

Ammonium hydroxide @ 30%, 20°C Satisfactory

Ammonium hydroxide @ diluted, 20°C Satisfactory

Aromatic hydrocarbons @ 20°C Non Satisfactory

Aromatic hydrocarbons @ hot conditions Non Satisfactory

Benzene @ 100%, 20°C Limited

Butylacetate @ 100%, 60°C Non Satisfactory

Butylacetate @ 100%, 20°C Limited

Chlorinated solvents @ 20°C Non Satisfactory

Chloroform @ 20°C Limited

Dioctylphtalate @ 100%, 20°C Satisfactory

Dioctylphtalate @ 100%, 60°C Limited

Ethanol @ 96%, 20°C Satisfactory

Ethyleneglycol (Ethane diol) @ 100%, 100°C Satisfactory

Ethyleneglycol (Ethane diol) @ 100%, 20°C Satisfactory

Ethyleneglycol (Ethane diol) @ 100%, 50°C Satisfactory

Glycerol @ 100%, 20°C Satisfactory

Hydrogen peroxide @ 30%, 60°C Limited

Kerosene @ 20°C Limited

Methanol @ 100%, 20°C Satisfactory

Methylethyl ketone @ 100%, 20°C Satisfactory

Mineral oil @ 20°C Satisfactory

Phenol @ 20°C Satisfactory

Silicone oil @ 20°C Satisfactory

Sodium hydroxide @ <40%, 60°C Satisfactory

Sodium hydroxide @ 10%, 20°C Satisfactory

Sodium hydroxide @ 10%, 60°C Satisfactory

Sodium hypochlorite @ 20%, 20°C Satisfactory

Strong acids @ concentrated, 20°C Satisfactory

Toluene @ 20°C Limited

Toluene @ 60°C Non Satisfactory

Xylene @ 20°C Non Satisfactory

Electrical

Arc Resistance, sec 135 - 180

Dielectric Constant 2.3

Dielectric Strength, kV/mm 20 - 28

Dissipation Factor x 10-4 3-5

Volume Resistivity x 1015, Ohm.cm 16 - 18

Mechanical

Elongation at Break, % 150 - 600

Flexural Modulus (Stiffness), Gpa 1.2 - 1.6

Hardness Rockwell M 1 - 30
Hardness Shore D 70 - 83

Tensile Strength at Break, MPa 20 - 40

Tensile Strength at Yield, MPa 35 - 40

Toughness at Low Temperature, J/m 27 - 107

Toughness, J/m 20 - 60

Young's Modulus, GPa 1.1 - 1.6

Optical

Gloss, % 75 - 90

Haze, % 11

Transparency (Visible Light Transmission), % 85 - 90

Physical

Density, g/cm3 0.9 - 0.91

Gamma Radiation Resistance Poor

Glass Transition Temperature, °C -10

Shrinkage, % 1-3

Sterilization Resistance (Repeated) Poor

UV Light Resistance Fair

Water Absorption 24 hours, % 0.01 - 0.1

Service Temperature
Ductile / Brittle Transition Temperature, °C -20 - -10

HDT @0.46 Mpa (67 psi), °C 100 - 120

HDT @1.8 Mpa (264 psi), °C 50 - 60

Max Continuous Service Temperature, °C 100 - 130

Min Continuous Service Temperature, °C -20 - -10

Thermal

Coefficient of Linear Thermal Expansion x 10-5, /°C 6 - 17

Fire Resistance (LOI) 17 - 18

Flammability, UL94 HB

Thermal Insulation, W/m.K 0.15 - 0.21