Polymer Process Engineering

Prof. Shishir Sinha

Hello friends, welcome to the polymer applications in building materials under the edges of polymer
process engineering. Here we are going to cover about the brief introduction, then historical
background and we will discuss about the principle of polymer modification for various cement
composites. I will discuss about the latex modification system and then the process technology apart
from this we will discuss the different properties.

Now mortar and concrete made with the Portland cement they have been widely used in the
construction industry for over 200 years. However, they have a disadvantage including decay
hardening, low tensile strength, large drying shrinkage and low chemical resistance. The polymer
additives they have been introduced to mitigate these drawbacks in a technique called polymer
modified or polymer cement, mortar or concrete.
 The polymer additives this included the latexes, re dispersible polymer powders, water soluble
polymers, liquid resins and monomers. The polymer modified mortars and concretes they have a
monolithic co-matrix where the organic polymer matrix and cement gel matrices are blended together
and the properties of the polymer modified mortar and concrete are determined by this co-matrix
structure. In systems modified with the latexes, re dispersible polymer powders and water-soluble
polymers, water drainage during cement hydration leads to the formation of a film or membrane. A
system modified with the liquid resins and monomers the addition of water triggers cement hydration
and polymerization of the liquid resin or monomers.
 Let us talk about the brief history. In 1923 the natural rubber latex being used and the first patent for
a polymer hydraulic cement system is issued to christen involving the paving materials with natural
rubber latexes and cement as filler. In the very next year in 1924 again the natural rubber latex and
Liffber published a patent introducing the concept of a polymer latex modified mortar and concrete
using natural rubber latex. Again in 1925 pertaining to the natural rubber latex Kirkpatrick patented a
similar idea. In between 1920 and 1930 the development of polymer modified mortars and concretes
using natural rubber latex being carried out.

In 1932 the synthetic rubber latex came into existence and Bond's patent suggested the use of
synthetic rubber latexes for the polymer modified system. In the similar year pertaining to the
synthetic resin latex the polyvinyl acetate latex being produced and Rodwell's patent claimed that the
application of synthetic resin latex to modified system. In 1940s the synthetic latex the chloroprene
rubber poly acrylic esters latex being developed and the patent published on polymer modified system
using the synthetic latexes. In the similar arena the polyvinyl acetate modified mortar and concrete
been developed and active development of polyvinyl acetate modified mortar and concrete. In the
late 1940s onward, there are various polymers being developed and increased use of polymer
modified mortar and concrete in various applications.
 In 1953 polyvinyl acetate modified mortar was developed and Geist they have reported a detailed
study on polyvinyl acetate modified mortar. This provides a valuable suggestion for later research. In
the 1960s the styrene-butadiene rubber poly acrylic ester polyvinylidene chlorine vinyl increase the
use of this polymer in practical applications. In the 1960s the unsaturated polyester resins they are
within prominent use and they developed the the ester create system modified with the unsaturated
polyester resin. In 1965 and 1973, people widely used epoxy resins and finally, they patented a system
based on epoxy resin.

In 1959 the urethane pre-polymer was developed and the system was modified with the urethane
pre-polymer patented. Early 60s methyl cellulose found a very prominent role and methyl cellulose is
used as a water-soluble polymer modifier and adhesive polymer-modified mortars for ceramic tiles.
In 1974 the polymer-modified system was reviewed and Relay and Reis they wrote a summarized
review of the polymer-modified system. In the 1970s the polymer modified mortar and concrete
research and development being carried out and the development pertaining to the extensive
research and development conducted worldwide. In the 80s polymer modified mortar and concrete
dominance being there and polymer-modified mortar and concrete became the dominant material in
the construction industries.

So the polymer modified mortars and concrete various types of polymer modified mortar and
concrete they are available nowadays. This includes the latex, re dispersible polymer powder, water
soluble polymer, liquid resin and monomer modified mortars and concrete. So among these options
the latex modified mortar and concrete are the most commonly used cement modifiers. There are
various type of things like polymer latex, elastomeric latex, thermoplastic latex, thermosetting latex,
bituminous latex, mixed latex, then re dispersible polymer powders, water soluble polymers, liquid
resins, monomers. In polymer cement co-matrix formation let us talk about the mechanism.
 There are three-step procedures this can be described like first step polymer particles are uniformly
dispersed in the cement paste phase when mixed with the fresh cement mortar or concrete. This is a
cement hydration and flocculation and these are polymer particles. This is the polymer latex. Now
cement gel is gradually formed by cement hydration while polymer particles deposit partially on the
surface of the cement gel un-hydrated cement particle mixtures. The calcium hydroxide reacts with
the silica surface of aggregates to form a calcium silicate layer and the calcium hydroxide crystals are
formed at the contact zone between the cement hydrates and aggregates in presence of polymer
latex.

In the second step the polymer particles they are confined in capillary pores due to drainage and
development of cement gel structure. The polymer particles flocculate and form a continuous close
packed layer on the surface of cement gel un-hydrated cement particle mixture and adhere to the
mixture and aggregate surface. The larger pores in the mixture are filled by adhesive and auto
adhesive polymer particles. The chemical reaction may occur between the reactive polymer particle
surfaces and calcium ions and calcium hydroxide crystals or silicate surfaces. Let us talk about the third
step.

The polymer particle coalescence takes place into the continuous film or membrane as water is
withdrawn by the cement hydration. Now drainage of the water between the polymer particles and
coalescence of the polymer particles. Now film or membranes bind cement hydrates together and
form a monolithic network where the polymer phase interpenetrates throughout the cement
hydrates.
Now the structure acts as a matrix phase for latex modified mortar and concrete binding aggregates
to the hardened material. Now let us talk about the latex modification.

The latex modification greatly improves the properties of ordinary cement mortar and concrete. The
hardened cement paste typically has an agglomerate structure leading to micro cracks and poor
tensile strength. The latex-modified mortar and concrete bridge micro cracks with polymer films
preventing cracks propagation and developing a strong cement hydrate aggregate bond. Increasing
the polymer content or polymer cement ratio enhances the effect increasing tensile strength and
fracture toughness. The excess air entrainment and the polymer inclusion disrupts the monolithic
network structure and reduce the strength despite some effective chemical reactions.
 The polymer film or membrane this improve the waterproofness resistance to chloride ion
penetration moisture transmission carbonation and oxygen diffusion chemical resistance and freeze
durability. The specific surface area of cement gel an indicator of hydration this can be accelerated or
retarded by latex addition at the initial stage. Say after 28 days cure the specific surface area of all
paste is comparable. This suggesting the polymer modification does not significantly affect the cement
hydration. The pore structure of latex modified system is influenced by the type of polymer and
polymer cement ratio.

Increasing the polymer cement ratio decreases the total porosity or pore volume improving the
impermeability resistance to carbonation and freeze thaw durability. Modification of cement mortar
using re-dispersible polymers. Now, modification of cement mortar and concrete with re-dispersible
polymer powder follows the same principle as per the latest modification. Re-dispersible polymer
powder they are added to the dry mix of cement and aggregates. The mixture is then wetted with the
help of water causing the re-dispersible polymer powder to re-emulsify.

The re-emulsified re-dispersible polymer powder behave in a similar manner as latex in the modifying
the mortar and concrete. Let us talk about the modification using water soluble polymers. Water
soluble polymers like cellulose, derivatives and a polyvinyl alcohol they are used for modification of
cement mortar and concrete. Now, these polymers are added in a small amount as powder or aqueous
solution during mixing. The main benefit of this modification is improved workability and prevention
of dry out phenomena.
 The water soluble polymer increase the viscosity of the water phase in the modified cement mortar
and concrete. The formation of thin water impervious film provides a sealing effect and water soluble
polymers generally do not significantly improve the strength of the modified system. Let us talk about
the modification using liquid resin. Liquid thermosetting resins are used for modification of cement
mortar and concrete. Polymerizable low molecular weight polymers or pre-polymer they are added in
liquid form during mixing.

The polymer content in modified mortar and concrete is generally higher than latex modified system
and the polymerization occurs in presence of water resulting in the formulation of polymer phase and
simultaneously cement hydration occurs. The modified system this forms a co-matrix phase with a
network structure of interpenetrating polymer and cement hydrate phase. The co-matrix phase
strongly binds aggregates. We can have improved strength and other properties as per the observed
in the modified mortar and concrete that may be similar to the latex modified system. Let us talk about
the modification using monomers.
 The modification of cement composites with monomer is similar to liquid resin modification but
involves the addition of monomer instead of liquid resin. Monomers are mixed with cement mortar
and concrete in significant quantities and polymerization in the cement hydration occurs
simultaneously during or after curing. The aim is to create a monolithic matrix that binds aggregates.
Generally this modification approach has not been successful due to poor properties of the modified
system. There are various challenges attributed to this one.

These challenges include interference with the cement hydration, degradation of monomers by
cement alkalis and difficulty in achieving uniform dispersion during mixing. Let us talk about the
materials used in the latex modified system. The materials used in the latex modified mortar and
concrete are the same as those in the ordinary cement mortar concrete. First and foremost is the
cement. We can use the ordinary Portland cement which is being widely used.
 The other types such as high early strength ultra high early strength sulphate resisting moderate heat,
white cement, blended cement, high alumina and ultra rapid hardening cement they are also
employed. Ear-entraining cement should not be used due to the latex addition. Then talk about the
polymer latexes. The polymer latexes consists of small polymer particles maybe say 0.05 to 5 p.m.
They are dispersed in water. They are usually produced by emulsion polymerization, reaction reactor
agitation and heating with initiator they can cause the chain polymerization and unreacted monomer
they are removed by stripping. Latexes may be concentrated or diluted and additives like preservatives
and stabilizers are being added. Ultra rubber latex and epoxy latex have different production
processes. The polymer latex this can be cationic, anionic, non-ionic based on the electrical charges
on the particles and they are copolymer system with the total solid content of 40 to 50 percent by
weight.
 Most commercially available latexes for cement modifiers are based on elastomeric and
thermoplastic polymers. Polyvinyl acetate latex and polyvinylidene chloride polyvinyl chloride latex
they are generally not recommended as cement modifier in Japan due to poor water resistance and
chloride ion liberation respectively. There are general requirements for polymer latexed as a cement
modifier. One is that high chemical stability towards active cation Ca++ or Al3++ they are released
during the cement hydration. High mechanical stability under severe condition including mixing and
pumping.

Low air entraining action with appropriate anti-foaming agent during the mixing and there should be
no negative impact on cement hydration. The formation of continuous polymer film in mortar or
concrete achieved by lower minimum film forming temperature and strong addition to cement
hydrates and aggregates. Excellent water resistance, alkali resistance, weatherability of the polymer
films formed in mortar and concrete and thermal stability to withstand the temperature variation
during the transportation and storage like free throw stability in cold climates or high temperature
storage ability in hot climate. The commonly used commercial latexes for the cement modifier this
includes styrene butadiene rubber, polychloroprene rubber, polyacrylates esters, polyethylene vinyl
acetate EVA copolymers. These latexes typically come with a suitable anti-foaming agent eliminating
the need of additional anti-foaming agent during mixing.

The latex modified mortar and concrete use the same type of aggregate as ordinary cement mortar
and concrete. This includes the river sand and gravels, crushed sand and stones, silica sands, artificial
lightweight aggregates. The silica sands and siliceous crushed stones these can be used for corrosion
resistance purposes. Aggregates with the excessive water content should be avoided to achieve the
desired polymer cement ratio. The aggregate should be clean, sound and have a proper grading and
the selection of aggregate depends on the factors such as application, thickness, cover in reinforced
concrete and type of and density of reinforcement.
𝛼 = (Vc + Vp)/(Va +Vw)

Φ = Vp + VW (l/m3 )
Vc, Vp, Va, VW, Vs, Vg: Volumes of cement, polymer, air, water, sand, and gravel per unit volume of latex

modified concrete, respectively (l/m3)

Let us talk about the determining the mixed properties. There are several notations being used and
these some of the symbols used in the mixed design system like theta c that is the compressive
strength of latex modified concrete and the units are kilogram force per centimeter square. Then SL
slump then the units are in centimeter. Then alpha that is a binder wide ratio by volume that is a v c
plus v p over v a v w phi that is a slump control factor this is by volume that is v p plus v w. Now v c, v
p, v a, v w, v s, v g these are the volumes of the cement, the polymer, the air, the water, the sand and
the gravels per unit volume of the latex modified concrete respectively.
 Then C, P, W, S, G weight of cement, weight of polymer, weight of water, weight of a sand and weight
of gravel per unit volume of the latex modified concrete respectively that is in kilogram per meter
cube. The unit of the cement content, unit polymer content and unit water content and unit sand
content and unit gravel content. P over C the polymer cement ratio by weight, W over C water cement
ratio by weight, A the air content by volume, S over A that is the sand aggregate ratio or the sand
percentage by volume, A is a unit aggregate content by volume that is equal to v s plus v g. Now the
calculation of slump S cell is equal to J phi minus k into 1 minus S over A where J and k are the empirical
constant. Now if we try to calculate the strength prediction that regardless of polymer type the
compressive strength theta c of latex modified concrete can be predicted by the polymer cement ratio
of 5, 10, 15 and 20 percent by using the binder void ratio alpha as per the following like polymer
cement ratio 5 percent theta c is equal to 675 alpha minus 40, 10 percent theta c is equal to 595 alpha
minus 88, 15 percent theta c is equal to 474 alpha minus 63 and 20 percent theta c is equal to 423
alpha minus 88.
 Now preparation of nomographs the water cement ratio and the unit cement content of the latex
modified concrete can be represented as a function of the binder void ratio A for each polymer type
and polymer cement ratio. So, the equation can be W over C is equal to minus m alpha plus n and C is
equal to q alpha plus r here m and q and r are empirical constants. Now this particular figure provides
the example of nomographs that utilize these equation to estimate W over C and C values. Now the
procedure for determining the mixed properties of the latex modified concrete involves different
steps like determining the required workability and the primary secondary performance of the
concrete based on its application, measure the required slump and determine the compressive
strength theta c and secondary properties such as flexural strength, waterproofing, adhesion, etc.
Now determination of the polymer cement ratio P over C based on the manufacturer's information
and technical data of polymer latexes for cement modifiers.
𝑺
𝑺𝒍 = 𝒋𝝓 − 𝒌 (𝟏 − )
𝒂
𝑊/𝐶 = − 𝑚𝛼 + 𝑛
𝐶 = 𝑞𝛼 + 𝑟
Here, m, n, q, and ‘r’ are empirical constants.

Simultaneously determine the binder void ratio alpha using an equation of compressive strength
prediction. Estimate the water cement ratio W over C and a unit cement content using nomograph
and determine the value of A. We calculate the unit polymer content P and a unit water content W by
applying the estimated C to the determination of P over C and W over C, respectively and determine
the slump control factor phi using the sum of, say V P and V W derived from P W and the specific
gravities of the polymer and water. So determine the sand aggregate ratio S over A using the equation
of for slump prediction and next step is to estimate the air content A using the estimated values of C
P W and these specific gravities of cement polymer and water according to the this particular equation
that is alpha is equal to V C plus V P over V A over V W.
 𝑽𝑪 + 𝑽𝑷
𝜶=
𝑽𝒂 + 𝑽𝒘
𝑨 = 𝟎. 𝟏𝑽𝒂 = (𝑽𝑪 + 𝑽𝑷 − 𝜶𝑽𝒘 )/𝟏𝟎𝜶
𝒂 = 𝑽𝑺 + 𝑽𝒈 = 𝟏𝟎𝟎𝟎 − (𝑽𝒘 + 𝑽𝑪 + 𝑽𝑷 + 𝑽𝒂 )

Therefore, A is equal to 0.1 V A is equal to V C plus V P plus minus alpha V W over tan alpha. Also we
need to calculate the aggregate content by balancing equation of material the concrete as alpha is
equal to V S plus V G is equal to 1000 minus V W plus V C plus V P plus V A. Then next step is to estimate
the unit sand content S and the unit gravel content G by applying the determined S over A and A and
A specific gravities of the sand and gravel.
 So dear friends in this particular segment we discussed about the application of polymers specifically
in the building aspects and for convenience we have included several references which you can utilize
as and when required. Thank you very much.