Plastic materials

PLASTIC FABRICATION
PROCESSES
• Spectrum of forming processes for the
thermoplastic materials
• Injection Molding:

• A process in which granular polymer, usually thermoplastic is fed from

hopper into a heated barrel where it is melted, after which a screw or ram
forces the material into a mold. Pressure is maintained until the part is
solidified.
• Blow Molding:
• Calendering
The process of forming thermoplastic or thermosetting sheet or film by
passing the material through a series of heated rolls. The gap between
the last pair of heated rolls determines the sheet thickness. The mold is
only blended and plasticized on separate equipment. Elastomer sheets,
gaskets, vinyl flooring tiles are often formed
• Rotational Molding
• Solid Phase Forming:
• Thermoforming:

Thermoforming is ideal for low volume production of containers,

machines guards, and other parts with suitable shapes,
• Extrusion:
 Thermoplastic Materials
(Commodity Plastics)

Thermoplastics materials used in high-volume, widely

recognized applications known as commodity thermoplastics.

1. Polyethylene (PE):
Polyethylene (PE) is simplest of all polymers, it is relatively
insensitive to most solvents. This is an advantage that PE use for
applications such as chemical reaction vessels or pipes, where
inertness of the container is critical. PE is also highly
electrically resistant and good thermal insulator.
• Low-Density Polyethylene (LDPE)
• High-Density Polyethylene (LDPE)
• Linear Low-Density Polyethylene (LLDPE)
• Ultra Low-Density Polyethylene (ULDPE)

PolyVinyl Chloride (PVC):

a) Rigid PVC (unmodified PVC)
b) Plasticized PVC or Vinyl (solvent modified)
c) Plastisol (vinyl dispersion)

Polyvinylidene Chloride (PVDC):

It is made from trichloroethane, a common solvent. In domestic it is
used for the packaging. In industrial application it is used for the
same types of applications as PVC. However it has better strength,
temperature resistance and solvent resistance than PVC.
Acrylonitrile butadiene styrene (ABS):
This material is the combination of Impact-resistant
polystyrene (IPS) and styrene acrylonitrile (SAN) to obtain best
properties as according to weatherability, heat distortion,
barrier properties and impact toughness.
Applications include golf carts, luggage with ABS sides,
refrigerator liners and ABS tabletops. ABS can be
electroplated and is used for metalized knobs, handles for radios
and televisions.
Polyetheretherketone (PEEK) – Strong, chemical- and heat-
resistant thermoplastic, biocompatibility allows for use in
medical implant applications, aerospace moldings. One of the
most expensive commercial polymers.
Styrene Acrylonitrile (SAN):
Styrene and acrylonitrile are copolymerized to form a
random, amorphous copolymer that has improved
weatherability, stress crack resistance and barrier properties.
Applications for SAN includes dishwasher-safe container, oil
resistant container, packaging for food stuffs,
pharmaceuticals, and cosmetics where oil resistance is needed
and bottles with barrier properties
 Engineering Plastics
Cellulosics:

Cellulose acetate (CA)

CA is the most common of the cellulosics. It is notable for its
attractive appearance (gloss & clarity), toughness and high impact
resistance. It is used for tool handles and packaging film where
moisture passage is desired as for fruits and vegetables.
Cellulose acetate butyrates (CAB)
CAB are tough, transparent and water resistant. Some typical uses
include data keyboards, transparent dial covers, light covers and
blister packaging.
Cellulose nitrates (CN):
They were originally used for billiard balls, mens’s shirt collars.
• Aramids (aromatic polyamide)
This material contains the amide groups with benzene rings
between them. The aramids are non-burning, solvent resistant and
very high melting. Due to that properties it is mostly used in safety
helmets. When made into a fiber, the material is called KEVLAR and
is widely used in making bulletproof vests and as a reinforcement in
composites.
If the polymer is changed chemically, a molding plastic resin is
called NOMEX is used as a coating to strengthened and add flame
retardance to many other materials such as fire protecting clothes.
• Polyoxymethylenes (POM):
POM consists of high degree of crystallinity produces
excellent strength, stiffness, surface hardness, barrier properties,
solvent resistance and a sharp melting point. Mostly used in valve
bodies, non-lubricated bearings, mounting brackets.
• Polycarbonate (PC):
Polycarbonate is formed by a condensation polymerization.
Superior mechanical and physical properties have created a strong
application capability for polycarbonate. Uses includes small tool
housing, pump impellers and safety helmets and recreational
vehicle bodies.
Due to the combination of high optical clarity and toughness, this
material used in bulletproof windows, break resistant lenses,
headlights and tail-lights.
• Polymethylmethacrylate (PMMA):
The most important property of PMMA is its optical clarity.
This plastic has as high as 92% light transmittance. It is also lowest
sensitive to UV light, excellent weather resistance and also very high
gloss. Due to that properties PMMA used in windshields (especially
for planes and helicopters), skylights, automobile taillights.
• Polyphenylene ether:
The mobility of polyphenylene ether is improved by
blending with high-impact polystyrene. The impact strength of these
polymers causes them to more widely used in pump impellers, valve
components, electrical sockets, flow meters, wheel covers and
window frames.

• Polysulfones:
The polysulfones are more dimensionally stable and tougher
then the polyphenylenes. Creep is very low in these materials over a
wide range of temperature allowing them to be used for hot water
pipes, chemical resistance parts, circuit breakers, automobile
applications near the engine. Since these materials are solvent craze
and physical and optical properties could be reduced.
 Thermoset Material
• Amino Plastics
1. urea formaldehyde
2. Melamine formaldehyde
• Phenolics
• Vinyl Esters
• Epoxies
• Polyurethanes
 urea formaldehyde

• Urea-formaldehyde, also known as urea-methanal,

so named for its common synthesis pathway and
overall structure,[1] is a non-transparent thermosetting
resin or polymer. It is produced from urea and
formaldehyde. These resins are used in adhesives,
finishes, particle board, MDF, and molded objects. UF
and related amino resins are a class of
thermosetting resins of which urea-formaldehyde
resins make up 80% produced globally. Examples of
amino resins use include in automobile tires to
improve the bonding of rubber to tire cord, in paper for
improving tear strength, in molding electrical devices,
jar caps, etc.
 Melamine formaldehyde

• Melamine resin or melamine

formaldehyde (also shortened to melamine)
is a hard, thermosetting plastic material made
from melamine and formaldehyde by
polymerization.[1]
• In its butylated form, it is dissolved in n-butanol
and xylene. It is then used to cross-link with
alkyd, epoxy, acrylic, and polyester resins, used
in surface coatings. There are many types,
varying from very slow to very fast curing.Use
in Kitchen utensils ,cabinet making etc.
 Phenolics

• Phenol formaldehyde resins (PF)

or phenolic resins are synthetic
polymers obtained by the reaction of
phenol or substituted phenol with
formaldehyde. Used as the basis for
Bakelite, PFs were the first
commercial synthetic resins
(plastics). They have been widely
used for the production of molded
products including billiard balls,
 Vinyl Esters

• Vinyl Ester, or Vinylester, is a resin produced by the

esterification of an epoxy resin with an unsaturated
monocarboxylic acid. The reaction product is then
dissolved in a reactive solvent, such as styrene, to
approximately 35–45 percent content by weight.
• This thermoset material can be used as an alternative
to polyester and epoxy materials as the
thermoset polymer matrix in composite materials, where
its characteristics, strengths, and bulk cost are
intermediate between polyester and epoxy.
• In homebuilt airplanes, the Glasair and Glastar kit planes
made extensive use of vinylester fiberglass-reinforced
structures.
 CREEP
• In materials science, creep (sometimes
called cold flow) is the tendency of a solid
material to move slowly or deform
permanently under the influence of
mechanical stresses. It can occur as a result of
long-term exposure to high levels of stress
that are still below the yield strength of the
material. Creep is more severe in materials
that are subjected to heat for long periods,
and generally increases as they near their
melting point.
 Recycling of Plastics
• A major concern about the use of plastics for packaging and
disposable items is the environmental effect of these materials
lasting for centuries in landfills or other places of disposal
• There are two significant reasons for the poor plastics recycling
record: (1) some plastics are thermosetting and they cannot be
recycled (they cannot be remelted), and (2) there are thousands
of grades of thermoplastic materials, and they cannot be mixed
when they are remelted.
• There are a great many types of plastics, but almost 90% of the
volume of thermoplastics manufactured is made up of only six:
polyethylene (high and low density), polystyrene, polyvinyl
chloride, polypropylene, and polyethylene terephthalate.
• The system is very simple. The SPI is recommending that all 8-oz
and larger containers and all 16-oz and larger bottles (up to and
including 5/gal) have a symbol molded on the bottom to indicate the
type of plastic that they were made from.
Material Coatings
 Steps Before Coating The
Materials:
• Surface Preparation/Pretreatment (remove oily soils, corrosion
products, and loose particulates)
Metal Surface Cleaning
i. Abrasive cleaning (surfaces are abrasive cleaned to remove rust and
corrosion by media blasting, hand or power sanding, and hand or power
brushing).
ii. Alkaline cleaning (To remove oily soils, aqueous solutions of
alkaline phosphates, borates, and hydroxides are applied to metals by
immersion or spray.)
iii. Detergent cleaning
iv. Emulsion cleaning (Heavy oily soils and greases are
removed by aqueous emulsions of organic solvents such as mineral spirits
and kerosene)
 Coating materials
Coatings can be classified by their resins types:
Common Coating Resin
1. Acrylics
Acrylics are noted for color and gloss retention in outdoor exposure. Gloss is
the capacity of surfaces to reflect directed light and it is a
very significant feature in coating durability. When a coating
degrades, the surface becomes rough and the gloss
reduces. Their outstanding weather resistance allowed them to replace
nitrocellulose lacquers in automotive finishes for many years. These medium-
priced resins can be formulated to have excellent hardness, abrasion, chemical, and
mar resistance.
2. Epoxies
Epoxy resins can be formulated with a wide range of properties. These medium- to
high-priced resins are noted for their adhesion, make excellent primers, and are
used widely in the appliance and automotive industries. Epoxy coatings provide
excellent chemical and corrosion resistance. They are used as electrical
insulating coatings because of their high electric strength at elevated temperatures.
3. Polyesters There are basically two types of polyesters: two-
component and single-package. Two- component polyesters are
cured using peroxides that initiate free-radical polymerization, while
single-package polyesters, sometimes called oil-free alkyds, usually at
elevated temperatures.
Two-component polyesters are well known as gel coats for glass
reinforced and ceramic materials and automobiles.
High-quality one-package polyester finishes are used on
automobiles, magnet wire, and industrial products.

4. Polyurethane Polyurethane resin-based coatings are extremely

versatile. These type of coatings are abrasion resistant, flexible,
resilient, tough, chemical resistant, and weather resistant. Owing to
their chemical resistance and ease of decontamination from chemical,
biological, and radiological warfare agents, they are widely used for
painting military land vehicles, ships, and aircraft.
• 5. Fluorocarbon They are noted for their lubricity or nonstick
properties due to low coefficients of friction, and also for
weatherability. Fluorocarbons are used as chemical-resistant
coatings for processing equipments. They are also used as nonstick
coatings for cookware, friction-reducing coatings for tools, and
as dry lubricated surfaces in many other industrial products.

• 6. Polyimides Polyimide coatings have excellent long-term

thermal stability, wear, mar and moisture resistance. Polyimide
coatings are used in electrical applications as insulating varnishes
and magnet wire enamels in high-temperature, higher liability
applications.

• 7. Silicones They are noted for their high temperature resistance,

moisture resistance, and weatherability. Silicones are used in high-
temperature coatings for exhaust stacks, ovens, and heaters.
Elastomers
 Elastomers
• For convenience of classification, polymers that have more
than 200% elastic elongation are grouped together as
elastomers.
• Elastomers are materials that can be repeatedly stretched to
over their normal length and then immediately return to their
original length when released.
• All materials have some elastic elongation, but for many
materials, especially ceramics and metals, the elastic
elongation is very small, typically less than 2%. Whereas
others, such as polyethylene can have elastic elongation up to
50%.
 Thermoset Elastomers
• Natural rubber
Natural rubber is obtained by drying the sap of certain
plants, chiefly the rubber tree. The sap is emulsion or suspension of
non-soluble component in water solution. Such emulsion is called a
latex.
Natural rubber has excellent fatigue, excellent resilience and low
energy loss.
Crude natural rubber
Applications are to coat fabric made into water proof
coats, as water proof coating for shoes.
• Some serious limitations are the tendency of the crude
rubber material to soften and creep at elevated
temperatures.

• This limitation is overcome by cooking crude, natural

rubber with sulphur. The use of heat and sulphur led to
the name of this process vulcanization. After this
process, the polymeric material gets harder and the
amount of elongation decreases.

• This hard rubber is widely used in combs making,

insulation and bowling balls.
Isoprene Rubber (IR)
The synthetic polyisoprene is a mixture of
cis and trans molecular forms. This synthetic rubber is mostly
used for light weight tires for vehicles.
Butyl rubber:
Butyl rubber has high damping capability, low gas
permeability and good UV radiation and oxidation resistance.
The principal applications are as vibration damping pads, inner
tubes in tires, high temperature hoses and gas masks.
Oil-resistance elastomers:
Nitrile butadiene rubber
NBR used where oil resistance required. NBR has
good abrasion resistance. Typical applications include oil and fuel
line, gaskets, seals, conveyor belts and coating for printer rolls.
Chloroprene rubber or Neoprene:
The addition of chlorine improve its oil resistance properties.
The thermal resistance, stiffness and strength of neoprene is also
better. The presence of chlorine makes neoprene non-flammable.
The applications are fuel hoses, boots, shoe soles and coating for
fabrics where oil resistance and non-flammability are important.

Styrene Butadiene Rubber (SBR):

SBR is copolymer of polystyrene and polybutadiene. The significant

use of this rubber is largely due to its low cost. It is used for hoses,
belts, gaskets, shock mounts and most automobile tires.
 Thermoplastic elastomers
• Styrene based materials
These elastomers are least expensive and most common
of the thermoplastic elastomers. One of the most common brand
name is kraton. These elastomers are used for footwear, molded
and extruded goods and modification of other plastics and
adhesives.
• Urethane based materials
These elastomers are also very common and are used extensively
as spandex and elastane fibre and for biomedical implant
materials. These materials have excellent abrasion resistance, are
oil resistant, and have very high fatigue resistance.
• Fluoro-Elastomers
The high cost of fluro-elastomers limit their applications
to only those that require the special properties, but these
applications are still numerous. They include gaskets, oil seals,
diaphragms, pump and valve lining. Fluro-elastomers are coated
onto fabric for chemical and petrochemical handling equipments.

• Silicones
The application for silicon elastomers are molding resins
include sealant, caulks, elastomeric coating for waterproofing,
flexible molding materials, encapsulating gels.
 Corrosion Engineering
Materials

Engineering
Materials

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 Corrosi Engineering
on Materials

Corros
ion

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 Corrosi Engineering
on Materials

Corrosion Engineering:
It is the application of science and art to prevent or control corrosion
economically and safely. So therefore corrosion Engineers must have
knowledge about corrosion principles, its control and the properties of
materials.

Corrosion:
“Corrosion is the chemical reaction of material with its surrounding
environment.”
“Destruction or deterioration of a material by chemical, electrochemical,
or metallurgical interaction between the environment and the material.”
Common Example: Rust- the reddish compound referred to as rust is actually
Iron Oxide, as a result of reaction between oxygen and Iron.
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 Corrosi Engineering
on Materials

Why Metal Corrode:

The driving force that causes metals to corrode is a natural consequence of their
temporary existence in metallic form. It is therefore only natural that when these
metals are exposed to their environments they would revert back to the original state in
which they were found.
The primary corrosion product of iron, for example, is Fe(OH)2 (or more
likely FeO.nH2O), but the action of oxygen and water can yield other products having
different colors:
• Fe2O3·H2O or hydrous ferrous oxide, sometimes written as Fe(OH)3, is the
principal component of red-brown rust. It can form a mineral called hematite, the
most common iron ore.
• Fe3O4·H2O or hydrated magnetite, also called ferrous ferrite (Fe2O3·FeO), is most
often green but can be deep blue in the presence of organic complexants.
• Fe3O4 or magnetite is black.
Corrosion Rate Expression

corrosion rate can be expressed as

• The mass of metal turned into corrosion product per unit area of surface per unit
time.
• An increase in corrosion depth (penetration rate) per unit time.
• Corrosion penetration rare (CPR) or Mils penetration per year

This expression is the most desirable way of expressing corrosion rates. It expresses
corrosion in terms of penetration.
W = weight loss in milligram
A = area in square inches
t = exposure time in hours.

Corrosion rate <0.005 ipy (<0.012 cm/year) such metal are known as good corrosion
resistance materials. And are suitable for critical part. E.g Pump shafts valve seats,
springs and impellers.
Corrosion rate >0.005 ipy (>0.012 cm/year to 0.12 cm/years) such metal are known as
low corrosion resistance materials. And are used for tanks, piping, valve bodies etc.
Corrosion rate >0.05 ipy (>0.12 cm/year) such metal are unsuitable as material of
construction.

According to available data 33% of world annual total metal production is lost because of
corrosion and 66% of the corroded metal is recoverable by re-melting the scrap. Thus
approximately 10% of metal production of the world is completely lost due to corrosion per
year.
 Corrosi Engineering
on Materials

Materials:
Metal is the material. The basic cause of corrosion is the instability of metals
in their refined (pure) form.

Environment:
Environment is the surrounding. It can be anything like Air, Oxygen, water,
acidic medium, basic medium, gases that can cause corrosion.

Forms of Corrosion:
There are following forms of corrosions.

 Dry Corrosion. ( includes gases)

 Wet Corrosion. (Includes water or any other wet material in surrounding)

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 Corrosi Engineering
on Materials

Types of Corrosions:
 Atmospheric Corrosion:
The metal reacts with atmospheric oxygen in the presence of
moisture to form oxides. It also depends upon the gaseous
impurities,2M + contents
dust → 2M. n+ + → M2
nO2 Gases like
Besides oxygen, 2No 2-
On react with metals.
Cl2, CO2, and F2 also

 Liquid metal Corrosion:

It takes place when a liquid metal flows over a solid metal at high
temperature. Eg. In nuclear reactor sodium metals corrodes the
cadmium rods.

 Galvanic corrosion:
When we joined two different metals directly or by a conductor and
exposed it to a conducting solution. The more electro-positive metal
will act as anode and the metal which is less electro-positive acts as
cathode. Due to flow of current the metal which is
acting as anode liberates its free electrons and its corrosion begins.
The corrosion is more if the potential difference between the metals is
more. Page 8 of
11
For example, stainless steel and copper base alloys are frequently
 Corrosi Engineering
on Materials

 Pitting Corrosion:
When a metal is covered by some water or dirt, the part which is
covered has low oxygen concentration acts as an anode. The part which
is exposed to oxygen acts as cathode. The covered area gets corroded
and small pits are formed on it.
Fe2+ + → Fe (Oxidation)
(OH)2 → Fe
2OH- (OH)3
 Crevice Corrosion:
This type of corrosion is caused by Corrosion deposits and dirt
deposits. This can be noticed near the rivets, bolts etc.
Used welded butt joints, vessels are designed for complete drainage
and sharp corners are used for controlling the crevice corrosion.

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Nabeel Corrosi Engineering
Ahmad on Materials

 Inter granular Corrosion:

This type of corrosion generally occurs in alloys (due to crystalline
structure). This type of corrosion occurs along the grain boundaries. It
is due to the fact that the grain boundaries shows higher electrode
potential than the grains at the center. The material along the grain
boundaries is more sensitive to corrosion.

 Erosion Corrosion:
This type of corrosion occurs when the streams of gases, liquids strikes
the surface of metal. The striking gases and liquids remove the
protective films of metal surface. It occurs when the gases and liquids
strike at high velocity.

 Wet or Immersed Corrosion:

This type of corrosion occurs when a metal is immersed in a liquidPage
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long time. In this type the liquid slowly penetrates into the surface of
 Corrosi Engineering
on Materials

 Fretting Corrosion:
In this type the surface damages because of vibrations which results in
striking or rubbing at the interface of close fitting, highly loaded
surfaces. Usually occurs in pipe fittings.

 Stress Corrosion:
When the metal undergoes processes like bending, rolling etc. we
apply stress on it. The areas of the metal under stress acts as an
anode and the remaining areas act as
cathode. Due to the potential difference set up between the two areas
the corrosion takes place in the strained portion.

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 Corrosi Engineering
on Materials

Methods for Combating

corrosion:

 Use of highly – purity

metals.
 Use of alloy addition.
 Use of special heat
treatments.
 Proper design.
 Cathodic protection.
 Use of Inhibitors.
 Surface coatings.

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