Thermosets & thermoplastics

8102019 Thermosets amp thermoplastics

httpslidepdfcomreaderfullthermosets-thermoplastics 17

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PLASTICS

Dr K SIVAKUMAR

Dept of Chemistry SCSVMV University

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Syllabus Plastics

Thermoplastics

Thermosetting plastics

Processingof plasticsInjection moulding

Blow moulding

Extrusion processes

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THERMOPLASTICS

amp

THERMOSETTING PLASTICS



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Thermoplastics (resins) Thermoplastics soften when

heated and subsequently melt When cooled theybecome hard and rigid once again

Example Polyethylene PVC Nylon

Uses Bags Mugs Toys

Thermosetting plastics (resins) Thermosetting resins

do not become softy on heating amp they never melt

once set

Example Bakelite

Uses Electric switches Telephone parts Cookerhandles

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Moulding constituents of plastic

Higher polymer material is mixed with 4 to 10ingredients each of which imparts some useful

property to the moulded products

Some are

Resins Holds the different constituents together

Example Linear polymers with low molecular

weights

Resins form 40-50 of moulding mixture

Plasticisers To increase the plasticity and flexibility

Example Castor oil Dibutylphthalate Alkyl amp Aryl

Phosphate etc



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Fillers To impart valuable service properties such as

strength resistance finish and workability

Reducing cost shrinkage on setting and brittlenessExample Wood flour asbestos china clay talc

gypsum saw dust

Fillers form 60 of plastics

Lubricants To facilitate the moulding operations

Gives glossy finish

Example Waxes soaps Oleates stearates

Catalystaccelerators To accelerate the

polymerisation (added only in thermosetting resins)Example Hydrogen peroxide Benzoyl peroxide

Metals (Ag Cu amp Pb)

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Difference between Thermoplastics amp Thermosetting plastics

SNo THERMOPLASTICS THERMOSETTING PLASTICS

1 Formed by addition Polymn Formed by condensation Polymn

2 Long chain linear polymers Three dimensional network

structure joined by strong covalent

bonds

3 Soften on heating and stiffen on

cooling

Do not soften on heating

4 Can be remoulded Cannot be remoulded

5 Usually soft weak amp less brittle Usually hard strong amp more brittle

6 Can be reclaimed from wastes Cannot be reclaimed from wastes

7 Soluble in organic solvents Insoluble in organic solvents



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INJECTION MOULDING (for Thermoplastics)bullMaterials of definite quantity at Hi Temp is injected into a cold mould under P

bullIn cold mould the polymer solidifies

bullPolymer is fed as granules pellets powder through hopperbullPolymer get softened in horizontal cylinder

bullHydraulic piston pushes the molten material into mould

bullUniform spreading inside the hot cylinder is ensured by torpedo

bullMolten plastic is injected through a nozzle into moulded cavity

Mould

bullConsists of movable amp stationary parts

bullMolten plastic is injected at a P of

15000kgcm2

bullProper flow of material is ensured by

preheating the mould to appropriate T

bullMould is cooled by circulating water

and then opened to eject the moulded

article

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BLOW MOULDING (for thermoplastics) [for hollow plastic articles]bullTo produce soft drink bottles containers using Polyethylene PVC Polystyrene

bullPARISON ndash hot softened thermoplastic made by injection extrusion moulding

bullParison is placed inside a two piece hollow mould (as 2 halves)

bullParison kept between two halves encloses a blowing pin at one end

bullOther end pinches and closes

bullParison is blown using pressurized air through the blow pin



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BLOWMOULDING ContinuedhelliphellipbullParison kept under hot condition is inflated and expands until it comes in

contact with inner area of the cold hollow mould

bullUnder pressure

bullParison acquires the shape of hallow cavity of mould

bullMould is cooled and the thermoplastic article is removed from the mould by

opening the mould

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EXTRUSION MOULDING

bullFor producing common plastic materials

bulleg films filaments hoses sheets amp coating wires and cables with PVCbullPlastic material as powder granules is fed into a cylinder thru hopper

bullCylinder is with the provision for heating

bullHot plastic is pushed thru cylinder by helically revolving screw

bullDue to friction the Temperature increases



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EXTRUSION MOULDING (Continueshellip)

bull Plastic material passes through three zones

1 Feed zone2 Compression zone

3 Metering zone

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bull In compression zone powder charge is melted by heating element

bull It is compressed by revolving screw

bull Polymer flows at a constant rate due to helical movement of screwbull Pressure in this zone enables plastic to be in melted stage amp enters the die



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bull From die moulded plastic is coming out in desired profile

bull Extrudated material from die is hot and hence it is cooled rapidly to

avoid any deshaping

bull Cooling by passing extrudate over a conveyor belt through which

tubes of cold watercold air are passed



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Thermoplastics (resins) Thermoplastics soften when

heated and subsequently melt When cooled theybecome hard and rigid once again

Example Polyethylene PVC Nylon

Uses Bags Mugs Toys

Thermosetting plastics (resins) Thermosetting resins

do not become softy on heating amp they never melt

once set

Example Bakelite

Uses Electric switches Telephone parts Cookerhandles

4

Moulding constituents of plastic

Higher polymer material is mixed with 4 to 10ingredients each of which imparts some useful

property to the moulded products

Some are

Resins Holds the different constituents together

Example Linear polymers with low molecular

weights

Resins form 40-50 of moulding mixture

Plasticisers To increase the plasticity and flexibility

Example Castor oil Dibutylphthalate Alkyl amp Aryl

Phosphate etc



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gypsum saw dust



Gives glossy finish





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bonds


cooling








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Mould



15000kgcm2





article

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bullUnder pressure



opening the mould

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EXTRUSION MOULDING








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3 Metering zone

12







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avoid any deshaping





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gypsum saw dust



Gives glossy finish





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bonds


cooling








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Mould



15000kgcm2





article

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bullUnder pressure



opening the mould

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EXTRUSION MOULDING








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3 Metering zone

12







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avoid any deshaping





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Mould



15000kgcm2





article

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bullUnder pressure



opening the mould

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EXTRUSION MOULDING








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3 Metering zone

12







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avoid any deshaping





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bullUnder pressure



opening the mould

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EXTRUSION MOULDING








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3 Metering zone

12







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avoid any deshaping





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3 Metering zone

12







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avoid any deshaping





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avoid any deshaping



Documents

Thermosets & thermoplastics