Download - CORPORATE TRAINING AND PLANNING Styrene Based Polymers (Styrenics) Introduction of polystyrene Monomer preparation Polymerization -Mass polymerization

CORPORATE TRAINING AND PLANNING

Styrene Based Polymers (Styrenics) Introduction of polystyrene Monomer preparation Polymerization

- Mass polymerization- Suspension polymerization- Solution polymerization

Available grades Properties related to structure General properties Processing behaviour Processing techniques Applications


High impact Polystyrene (HIPS) Introduction

General properties

Applications

Acrylonitrile butadiene styrene (ABS) Introduction

Preparation of ABS

Properties of ABS

Processing behaviour

Processing techniques

Applications

Styrene acrylonitile (SAN) Introduction

Properties of SAN

Applications


Polystyrene

Introduction

Polystyrene was first produced commercially by Dow chemical company in 1937.

Polystyrene was first initially used for its excellent dielectric and optical properties.

CH2=CH

Polymerization

CH2-CH

Styrene Monomer Polystyrene

nn


Monomer Preparation

Styrene is produced from the ethyl-benzene by a process of dehydrogenation at 630°C.

+ C2H4

C2H5

MgO 630°C

Dehydrogenation -H2

CH=CH2


Styrene at room temperature is a liquid with boiling point at 145.2°C.

Like many aromatic compounds, it has pleasant smell in pure form but looses the same due to traces of

ketones and aldehydes if allowed to oxidize by exposure to air.

It is a solvent for polystyrene and many synthetic rubbers, including SBR, but has only a very limited mutual solubility in water.

It has a strong tendency to polymerize on heating or on exposure to UV light.


Polymerization

Polymerization methods

Mass Suspension Solution


Mass Polymerization (Tower Process)

Styrene is pre-polymerized by heating (without initiators) at 80°C for two days in pre-polymerization kettle.

Monomer-polymer mixture is then run into a tower which is fitted with heating and cooling jackets and the top of the tower is maintained at temperature of 110°C, the temperature of about 150°C in between and bottom temperature at 180°C.

High temperature at bottom ensures a high conversion.

Base of the tower forms the hopper of an extruder from which melt emerges as filament which are cooled, disintegrated and packed.


Solution Polymerization

Styrene and solvent are blended together and pumped through number of reactors with different heating zones.

From the last reactor the polymer is run into devolitilising vessel.

At a temperature of 225°C, the solvent and the polymer are removed, condensed and polymer is fed into extruder units, extruded as filaments, granulated, and stored.

Polymerization in solution reduces the exotherm but may lead to problem of solvent recovery and solvent hazards.


Suspension Polymerization

In this process the monomer is suspended in droplets.

The reaction is initiated by monomer soluble initiators such as Benzoyl peroxide.

It is necessary to coat the droplets effectively with some suspension agents e.g. Poly (vinyl alcohol),talc to prevent them cohering.

The resulting particle size depends on the quantity of suspension agent and speed of agitation.

Following polymerization, unreacted monomer may be removed by steam distillation and the polymer is washed and dried.


Structure Property Relationship

PS is linear hydrocarbon polymer.

Due to steric hindrance of benzene ring causing stiffening effect, the Tg. of commercial polymer is 90° to 110°C. Consequence of this Tg value and amorphous nature of material make it hard and transparent at room temperature.

It is soluble in benzene, styrene, toluene. The presence of benzene ring in polystyrene having greater reactivity than Polyethylene.

Due to phenyl group Polystyrene is having limited chemical resistance.

CH2-CH

Polystyrene

n


General properties of PSGeneral properties of Polystyrene are,

Hard, rigid and transparent thermoplastic.

Low cost, good mouldability.

Low water absorption, good dimensional stability.

Good electrical insulation properties, colourability.

Incorporation of 1% of saturated aliphatic amines, cyclic amines or aminoalcohols has been found to improve greatly the resistance to weathering.

It is brittle in nature.

It is enable to withstand the temperature of boiling water.

It is having mediocre oil resistance.


Properties of Polystyrene Name Value Unit

Specific gravity 1.05 --

Tensile Strength 32.4-56.5 MPa

Tensile modulus 3103-3276 MPa

Flexural modulus 3103-3448 MPa

Elongation at break 1.2-3.6 %

Impact Strength (Izod ) 13.3-24 J/m

Hardness M 60-84 ---

HDT (under 1.82 MPa load.) 76-108 °C

Glass transition temperature 74-110 °C

Dielectric Strength 19.7 KV/mm


Processing Considerations

Unmodified grades have negligible water absorption.

Specific heat of PS is less, therefore higher plasticizing capacity machines should be used. Melts have good stability at processing temperatures.

Generally no need to purge while shutting down.

Recycling percentage should not be more than 15-20% in injection moulding.

Due to amorphous innature, polymer gives low mould shrinkage.

Polystyrene melts are of medium viscosity but highly pseudo plastic.


Processing Techniques

Injection Moulding

Plastic temperature in the process range from 200° C to 250°C for GPPS and 180° to 250°C for HIPS grades.

Injection pressures are of 30 to 275 MPa depends on the grade of the material.

Typical mould temperature is 10-80°C.


Extrusion Typical extrusion conditions

Temperature profile 150-200°C

Recommended screw L/D ratio 25:1 to 30:1

Recommended compression ratio 2:1 to 3:1


Grading of Polystyrene General purpose polystyrene (GPPS)

Good balance is maintained to have good heat resistance, reasonably high setting-up temperature, good flow

properties and moderate impact strength.

High molecular weight polystyrene (HMPS)

HMPS gives impact strength without the loss of clarity.

Heat resistant grade

By reducing monomer content from 5% to 0%, softening point may raised from 70°C to 100°C.

Easy flow grade

It can be obtained by using low molecular material, by using internal lubricant , by using external lubricant and by controlling size and shape of granules.


Trade names Supreme, India – Suprene

Dow Chemical, US – Pelaspan

Arco chemical , US – Dylene

Kanegafuchi chemical, Japan - Kanelite


Expanded Polystyrene

Bead (Suspension )Polymerization is generally used for manufacturing expanded polystyrene.

Blowing agents may be incorporated before polymerization or used to impregnate the bead under

heat and pressure in a post-polymerization operation.

The impregnated beads may then be processed by two basically different techniques.

Steam moulding process. Direct injection moulding or

extrusion.

The beads can be expanded to about 40 times their previous size with densities as low as 16 kg / cm3.


Applications of PSHousehold

Items like power boxes, combs, toys, bangles, decorative gift articles, ball pen, water jug, mugs, plates, trays, racks, boxes, jar, etc.

Automobile In automobile industries automatic parts like reflector,

doom lights, display signs and automotive penal covers.

Electrical/Electronics Many electrical and electronic items like light diffusers

battery cases, electrical coil forms,TV and transistor cabinets, refrigerator, door and body liners, floppy

storage boxes.


Medical Medical applications like disposable syringe.

Packaging Thin walled packaging, containers, disposable transparent containers, bottles, utility boxes, packaging of fish, bottle caps.

Industrial Battery cases, filling cabinets, quick dry emulsion paints, blade dispenser, foot rules and lay flat produce boxes.

Building Bathroom accessories like toilet seats, Flooring & ceiling channels and profiles, wall tiles, towel racks, window envelop and building


Applications

PS Room Partitioner PS Bathroom cell

PS Door fittings CD cover


High Impact Polystyrene (HIPS)

HIPS is manufactured by dissolving unsaturated rubber in styrene monomer and polymerizing the monomer in a solution or mass-suspension process.

The rubber is generally polybutadiene.

In this process the resultant blend will contain not only rubber and polystyrene but also a graft polymer where short styrene side chains have been attached to the rubber molecules and this enhances the impact strength.

The rubber content in solution polymerization can go up to 14% by weight.

HIPS obtained by this process are having impact strength 7 times greater than GPPS.


General Properties

Good dimensional stability even at low temperature and high impact strength than the general purpose

polystyrene.

Good toughness, ease of processing, higher resistance to stress cracking.

High elongation at break, less resistance to ageing than GPPS.

Lower hardness and rigidity than GPPS and dissolved by alcohols, ketones, ethers etc.


Properties of HIPS Name Value UnitSpecific gravity 1.05 --Tensile Strength 16.0-41.3 MpaTensile modulus 1653-2549 MpaFlexural modulus 1791-2687 MpaElongation at break 1.0-1.5 %Impact Strength (Izod ) 48.1-219 J/mHardness M 63-88 ---HDT (under 1.82 MPa load.) 69-76 °CGlass transition temperature 93-105 °CDielectric Strength 11.8-19.7 KV/mm


Processing of HIPS

Thermoforming

HIPS is one of the major thermoforming materials. Solid sheet of HIPS is extruded and shaped by a variety of forming methods.

The most common method is in-line vacuum forming.

In this process, vacuum is drawn between sheet and mold or pressure is applied to the mold plug while

air is drawn out from the space the sheet and mold.

Typical forming temperature range is around 130° to 180°C and temperature at which forming may be

removed from the mould is at 85°C.


Applications of HIPS

Household HIPS is used in jugs, dishes, beakers, butter dishes, hair brushes, pens, disposable cups, air cooler body.

Packaging Venting and portion cup lid, plates and bowls, dairy containers.

Industrial Helmets, textile and marine parts, neck pieces for pen, air coolers, rotary drums, machine housing .

Electrical and Electronics Portable TV cabinets, transistor cabinets, knobs and lining, air conditioner and air cooler front grills, television cabinets, PCB covers.


Applications

HIPS Television Cabinet HIPS Floppy Storage Box

HIPS Instrument body HIPS Solid shape


Acrylonitrile Butadiene Styrene (ABS) Copolymer

These materials are complex blends and copolymers of Acrylonitrile, butadiene and styrene.

In most types, Acrylonitrile and styrene are grafted onto a polybutadiene backbone. The product also contain unreacted polybutadiene and some acrylonitrile styrene copolymer. The reasons for its widespread acceptance are high impact resistance, good stiffness, excellent surface quality, high dimensional stability at elevated temperatures.

Its main disadvantages are lack of transparency, poor weathering resistance, poor flame resistance.

CH2-CH-CH2-CH=CH-CH2-CH2-CH

CNn


ABS Preparation Styrene and Acrylonitrile are added to polybutadiene latex and

the mixture is warmed to about 50°C to allow absorption of the monomers.

Water soluble initiator is added to polymerize styrene and Acrylonitrile.

The resultant materials will be a mixture of Polybutadiene, polybutadiene grafted with Acrylonitrile and Styrene, and Styrene-Acrylonitrile copolymer.


General Properties Chemical and Solvent resistance Generally resistant to alkalis and acids but not concentrated

oxidizing acids. Dissolved by many aromatic and chlorinated hydrocarbons,

esters and ketones.

Maximum Service temperature UL temperature index 60-75°C. Alloy with Polycarbonate may be as high as 95°C.

Flammability Standard grades are considered as slow burning and usually

meet the UL HB requirement. The material burns with a smoky yellow flame emitting a pungent gas.


Properties of ABS

Properties Value Unit

Specific gravity 1.03-1.06 --

Tensile Strength 30-52 MPa




Impact Strength (Izod ) 134-320 J/m

Hardness R 105-112 ---


Glass transition temperature 105-115 °C

Dielectric Strength 16-31 KV/mm


Processing Considerations

May absorb upto 0.3% moisture and therefore must be stored under dry condition.

Greater tendency to degradation than PS during processing so important not to overheat. Avoid too high screw speed and back pressure during moulding.

Generally less free flowing than PS particularly with heat resistance grades.

Being an amorphous, the materials have a low moulding shrinkage.


Processing Techniques

Injection Moulding

Typical Injection Moulding conditions Recommended melt temperatures 220-280 °C. Typical mould temperature is 40–90 °C. Injection pressures of 69-138 MPa. L/D ratio is 20:1 and Compression ratio of 2:1 to 3:1.


Extrusion

Typical extrusion conditions Melt temperatures 205-250 °C. Temperature profile 192-250°C. Recommended screw L/D ratio 20:1 to 36:1. Recommended Compression ratio 2.5:1 to 3:1.


Thermoforming

ABS can be thermoformed over a temperature range of 130 to 190°C.

The optimum conditions depend on material grade,part design, draw ratio, sheet thickness and forming technique.


Electroplating

ABS is the best material for electroplating.

The polymer is treated by an acid etching process which

dissolves out some of the rubber particles at or near the polymer surface. After sensitization and activation

electroless metal deposition processes are carried out .


Trade names

GE, India - Cycolac

Bhansali polymers , India - Abstron

Kanegafuchi chemical, Japan - Kane Ace

Bayer , DE - Novodur

Polychemical co, Taiwan - Polylac


Applications of ABS

Automobile Radiator grills, head light housing, seat belt, head lamp fixtures, door knobs, two wheeler front noise, water panel, helmet, electroplated parts, mirror housing and wheel covers. In the vehicle construction industry.

Agriculture Drinking water system, water vent systems and irrigation systems.


Household Plumbing fixtures, table edging, sliding doors, window

trucks, refrigerators liners, refrigerator door handles, pipe fittings, ventilator system components, picnic boxes, food processors, coffee maker leads, microwave oven tops.

Medical IV fluid monitoring controllers, blood glucose meter,

surgical clips, emergency intravenous infusion pump, scanner body, ECG / EEG body frames, cabinets for medical kit, breathing exerciser.


Applications

ABS Car Dashboard ABS car interiors

ABS Car bumper ABS meter box


Blends of ABS ABS/PC

Increase in HDT up to 130°C.

ABS/PVC (80:20)

Fire retarding ABS type material.

ABS/PVC (10:90)

Impact modified form of unplasticised PVC.

ABS/Acrylic material

A reasonable transparent ABS-type polymer.


Styrene Acrylonitrile Copolymer (SAN)

SAN is a copolymer of styrene and acrylonitrile.

H2C C CH2 CH C HC CH2 CH CH2 CH

CN

CN

H

H

H

Styrene Acrylonitrile (SAN)

n


The main features of SAN are, Excellent dimensional stability. Very good tensile and flexural strength. Good abrasion resistance and impact strength. High chemical resistance, better resistance to stress

cracking and crazing. Resistance to water, acid and alkalis is greater than

PS.


Grading of SAN

- UV stabilized grade

- Antistatic grade

- Glass reinforced grade


Properties of Styrene acrylonitrile Name Value Unit

Specific gravity 1.07 --

Tensile Strength 57-75 MPa




Impact Strength (Izod ) 13-24 J/m

Hardness M 80-83 ---


Glass transition temperature 115 °C

Dielectric Strength 12-16 KV/mm


Applications

SAN cassette casing SAN speedometer cover

Download - CORPORATE TRAINING AND PLANNING Styrene Based Polymers (Styrenics) Introduction of polystyrene Monomer preparation Polymerization -Mass polymerization

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