Polymer Engineering TE 1123 - WordPress.com · Bulk polymerization •Mass or block polymerization: Polymerization of the undiluted monomer. •carried out by adding a soluble initiator

Different Polymerisation

Techniques

Polymer Engineering

TE 1123

Farhana Momotaz, Dept. of TE, KUET

Polymerisation Techniques

The method/ technique by which monomer is converted to

polymer is called polymerisation method / polymerisation

technique.

The following three conditions must be considered for

polymerisation techniques:

Polymerisation process.

Purification of raw materials.

Reaction vessel.


(II ) Purification of raw materials:

we can purify the raw material of different polymerisation process by the following process

a. Solid raw material-

We can purity solid raw material by two ways. such as-

Re-crystallisation.

Re- precipitation.

b. Liquid raw material:

We can purify liquid raw material by two ways, such as-

Distillation at atmosphere pressure.

Distillation at under reduced pressure.

c. Gas raw material

We can purify gas raw material by absorption process. The gases are usually purified by passing absorption tower containing suitable liquids and solids.


(III)Reaction vessel


(III)Reaction vessel contd…..

For laboratory preparation of polymers, glass flasks with

multiple necks are used.

Through this necks, the contents of the flask are stirred with

mechanical /magnetic stirrer and inert gas is flowed.

The temperature is measured with thermometer and

refluxing is done with a condenser.

Some times the contents are agitated by magnetic stirrer

instead of a mechanical stirrer.

The flask has flange in the middle to easy the removal of the

polymer from the flask.


(I) Polymerisation process

Mainly Three types of polymerisation process. Such as –

Solid phase polymerisation.

Gas phase polymerisation.

Liquid phase polymerisation. Bulk or mass polymerization.

Solution polymerization.

Suspension polymerization.

Emulsion polymerization.

Interfacial polymerization.

Melt polymerization.

Dispersion polymerization.


Solid phase polymerization:

Solid phase polymerisation is mostly restricted to chain

polymerisation.

The polymer build up in this process is slow because molecular

mobility in the solid state is completely restricted.

The thermal activation of the reaction is quite difficult.

The photo or radiation activation technique is restricted.


Gas phase polymerisation:

It is known in the case of very few olefinic monomers.

It has a very poor heat transfer.

Two methods used in the gas phase polymerization are-

a) Spraying the catalyst into the gaseous monomer.

b) Feeding the gaseous monomer into a fluidised bed made up of

the catalyst particles.

In both (a) and (b)cases the polymer is obtained as a free flowing

powder.


Liquid phase polymerisation Bulk or mass polymerization.

Solution polymerization.

Suspension polymerization.

Emulsion polymerization.

Interfacial polymerization.

Melt polymerization.

Dispersion polymerization


1. Bulk or mass polymerisation:

Techniques: Liquid monomer +Initiator+ C.T.A.→ Polymer.

Examples: It is usually adopted to produce polystyrene, polyvinyl

chloride, polymethyl methacrylate and low density polyethylene.


Bulk polymerization• Mass or block polymerization: Polymerization of the undiluted

monomer.

• carried out by adding a soluble initiator to pure monomer (in

liquid state).

• The mixture is constantly agitated & heated to polymerization

temperature.

• Once the reaction starts, heating is stopped as the reaction is

exothermic.

• The heat generated is dissipated by circulating water jacket.

• Viscosity increases dramatically during conversion.

• The method is used for the polymerization of liquid state

monomers.



Advantages Disadvantages

• The system is simple and requires thermal insulation.

• The polymer is obtained pure.

• Large castings may be prepared directly.

• Molecular weight distribution can be easily changed with the use of a chain transfer agent.

• Heat transfer and mixing

become difficult as the

viscosity of reaction mass

increases.

• Highly exothermic.

• The polymerization is

obtained with a

broad molecular weight

distribution due to the

high viscosity and lack of

good heat transfer.

• Very low molecular weights

are obtained.Farhana Momotaz, Dept. of TE, KUET

2. Solution polymerisation:

Techniques:

Monomer + Inert + Solvent + Catalyst +C.T.A

Polymer.

Examples:

It is used for the production of Polyacrylonitrile,

PVC, Polyacrylic acid, Polyacrylamide, Polyvinyl

alcohol, PMMA, Polybutadiene, etc.


Solution polymerization

Some disadvantages of bulk polymerization are

eliminated in solution polymerization.

Monomer along with initiator dissolved in solvent,

formed polymer stays dissolved.

The mixture is kept at polymerizaion temperature &

constantly agitated.

Depending on concentration of monomer the viscosity

of solution does not increase.



After the reaction is over, the polymer is used as such

in the form of polymer solution or the polymer is

isolated by evaporating the solvent.

Polymer so formed can be used for surface coating.



After the reaction is over, the polymer is used as such

in the form of polymer solution or the polymer is

isolated by evaporating the solvent.

Polymer so formed can be used for surface coating.

It is used for the production of Polyacrylonitrile, PVC,

Polyacrylic acid, Polyacrylamide, Polyvinyl alcohol,

PMMA, Polybutadiene, etc



Farhana Momotaz,

Dept. of TE, KUET

• The solvent acts as a diluent & helps in facilitating

continuous transfer of heat of polymerization.

Therefore temperature control is easy.

• The solvent allows easy stirring as it decreases the

viscosity of reaction mixture.

• Solvent also facilitates the ease of removal of polymer

from the reactor.

• Viscosity build up is negligible.

Advantages


• To get pure polymer, evaporation of solvent is required

additional technology, so it is essential to separate &

recover the solvent.

• The method is costly since it uses costly solvents.

• Polymers of high molecular weight polymers cannot be

formed as the solvent molecules may act as chain

terminators.

• The technique gives a smaller yield of polymer per

reactor volume, as the solvent waste the reactor space.

• The purity of product is also not as high as that of bulk

polymerization. Removal of last traces of solvent is

difficult.

Disadvantages


3. Suspesion polymerisation:

Techniques: Monomer +water (an heat transfer system) +

Emulsifier + Initiator (monomer soluble) + Catalyst (protective

colloids) Polymer ( beads / pearls).

i.e. Monomer + protective colloids + surface active agent +

initiator. polymer

Example: This technique is used to form PVC, Polyvinyl

acetate, Polystyrene, Styrene-divinyl benzene copolymer beads

(used for ion exchange) etc.


Suspension polymerization

Liquid or dissolved monomer suspended in liquid

phase like water.

Initiators used are monomer soluble e.g. dibenzoyl

peroxide.

Thus, polymer is produced in heterogeneous medium.

Initiator

The size of monomer droplets is 50-200 µm in

diameter.

The dispersion is maintained by continuous agitation

and the droplets are prevented to coalesce (unite or

merge) by adding small quantity of stabilizers.



The stabilizers used are PVA, gelatin, cellulose are

used along with inorganic stabilizers such as kaolin,

magnesium silicate, aluminum hydroxide,

calcium/magnesium phosphate, etc if necessary.

As it concerns with droplets, each droplet is tiny bulk

reactor. The polymerization takes place inside the

droplet & product formed being insoluble in water.

The product separated out in the form of spherical

pearls or beads of polymer.

Hence the technique is also known as Pearl

polymerization / Granular polymerization / Bead

polymerization.Farhana Momotaz, Dept. of TE, KUET


The products are small uniform spheres. They can be

used directly for some applications as precursors of

ion exchange resins otherwise they can be extruded &

chopped to form larger, easily moulded pallets.

They can be dissolved in a suitable medium for use as

adhesives & coatings.




• The process is comparatively cheap as it involves only

water instead of solvents.

• Viscosity increase is negligible.

• Agitation & temperature control is easy.

• Product isolation is easy since the product is insoluble

in water.

Advantages


• The method can be adopted only for water insoluble

monomers.

• It is difficult to control polymer size.

• Polymer purity is low due to the presence of suspending

& stabilizing additives that are difficult to remove

completely.

• Suspension polymerization reaction is highly agitation

sensitive.

• Larger volume of reactor is taken up by water.

• The method cannot be used for tacky polymers such as

elastomers because of the tendency for agglomeration of

polymer particles.

Disadvantages


4. Emulsion Polymerisation :

Techniques: Water insoluble monomer + Initiator (insoluble

in monomer) + Water + Emulsifier (made of Two parts – a

long non-polar Hydrocarbon chain with a polar group, such

as – COONa, -OSO3Na) Polymer.


Emulsion polymerization

The technique is used for the production of large

number of commercial plastics & elastomers.

The system consists of water insoluble monomer,

dispersion medium & emulsifying agents or

surfactants (soaps and detergents) and a water soluble

initiator (potassium persulphate / H2O2, etc).

The monomer is dispersed in the aqueous phase, not

as a discrete droplets, but as a uniform emulsion.

The size of monomer droplet is around 0.5 to 10 μm

in diameter depending upon the polymerization

temperature & rate of agitation.Farhana Momotaz, Dept. of TE, KUET


The emulsion of monomer in water is stabilized by a

surfactant.

A surfactant has a hydrophilic and hydrophobic end in

its structure.

When it is put into a water, the surfactant molecules

gather together into aggregates called micelles.

The hydrocarbon tails (hydrophobic) orient inwards &

heads (hydrophilic) orient outwards into water.

The monomer molecules diffuse from monomer

droplets to water & from water to the hydrocarbon

centre of micelles.Farhana Momotaz, Dept. of TE, KUET






• Water

• Monomer

• Surfactant

Examples:

• Synthetic rubber-styrene-butadiene (SBR), Polybutadiene,

Polychloroprene.

• Plastics-PVC, polystyrene, Acrylonitrile-butadiene-styrene

terpolymer (ABS).

• Dispersions-polyvinyl acetate, polyvinyl acetate copolymers,

latexacrylic paint, Styrene-butadiene, VAE


High molecular

weight polymers

fast polymerization rates.

allows removal of heat from

the system.

viscosity remains close to

that of water and is not

dependent on molecular

weight.

The final product can be used

as such ,does not need to be

altered or processed

Surfactants and polymerization

adjuvants -difficult to remove

For dry (isolated) polymers,

water removal is an energy-

intensive process

Designed to operate at high

conversion of monomer to

polymer. This can result in

significant chain transfer to

polymer.

Can not be used for

condensation, ionic or Ziegler-

Natta polymerization.

Advantages Disadvantages


5. Interfacial condensation

Techniques:This is a modern method of condensation

polymerisation. By this method, we can produce polymer or

polyesters which are widely used in textile industries. In this

technique, polymerisation is allowed to proceed at the

interface between an aqueous and an organic medium.

Reactants having highly reactive functional group.

Aqueous + Organic medium → polymer.

Since the polymer formation at the interface is a diffusion

controlled process, very high molecular weight products can

be achieved by this technique.


Example:

ClOC COCl H2N NH2

OC CONH NHCl H (2n-1) HCl

n

+

n + n


Interfacial condensation contd…..

Merits:

Simple instrument.

Easy separation of polymer.

Demerits:

Limited in use.

Required highly reactive monomer.


6. Melt poly condensation:

PolymerHigh temperature

Inert atmosphere

(N2/CO2)

Monomer

(at least one solid component and not

decomposed in its melting point)

Technique:

Example: Polyethylene, Ethylene glycol, Nylon 6,6.


Homogeneous system.

Requires longer duration.

No exotherm, but proper heat transfer within the medium

becomes difficult.

Viscosity of the medium increases very rapidly.

Suitable for producing medium to high molecular weight

products.

Suitable for poly condensation polymerisation.

Polymer is less contaminated and freeing from monomer and

byproduct is difficult.

Features:


7. Dispersion polycondensation:

Monomer + Inert solvent Polymer + Bi-product.Polymerisation

Technique:

Example: Many of the liquid polyester resins based on glycols andunsaturated di-carboxylic acid are prepared using high boiling aromatichydrocarbons as solvents.


Features:

Homogeneous system.

Viscosity of the medium increases slowly.

Requires longer duration.

No exotherm, heat transfer is uniform.

Suitable for producing medium to high molecular weight products.

Suitable for polycondensation polymerisation.

polymer usually contaminated with solvent.


Why suspension polymerisation is called

bead or pearl polymerisation?:

This polymerisation proceeds to 100% conversion and the

product is obtained as spherical beads or pearls. For this

reason, this technique is known as bead or pearl

polymerisation.


Feature upon which polymerisation technique

depend:

Nature of polymer.

The type of polymerisation mechanism chosen.

The required physical form.

Viability of the process for industrial production.


Properties required for Fibre forming polymer:

Molecular weight should be high.

Crystallinity – high not suitable.

Resistance to different chemical.

Orientation – Physical and chemical symmetry.

- Straight chain structure.

Glass Transition Temperature (Tg) – Should be near to Room Temp.

Crystalline Melting Point Tm- 2000 – 3000 C is suitable.

Polymer should be soluble in some solvent from which it can be spun.

Hygroscopic nature – Should be hydrophobic.

Chain length – should be hydrophobic.

Should have Linearity.


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Polymer Engineering TE 1123 - WordPress.com · Bulk polymerization •Mass or block polymerization: Polymerization of the undiluted monomer. •carried out by adding a soluble initiator