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Dept. of Chemistry, SCSVMV University

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1 Dept. of Chemistry, SCSVMV University
Course: B.E (EEE) – Part Time Subject: APPLIED SCIENCE Unit: V PLASTICS Dr. K. SIVAKUMAR Dept. of Chemistry, SCSVMV University Syllabus: Plastics Thermoplastics Thermosetting plastics Processing of plastics Injection moulding Blow moulding Extrusion processes


3 Thermoplastics (resins): Thermoplastics soften when heated and subsequently melt. When cooled they become hard and rigid once again. Example: Polyethylene, PVC, Nylon Uses: Bags, Mugs, Toys Thermosetting plastics (resins): Thermosetting resins do not become softy on heating & they never melt once set. Example: Bakelite Uses: Electric switches, Telephone parts, Cooker handles

4 Moulding constituents of plastic:
Higher polymer material is mixed with 4 to 10 ingredients 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 & Aryl Phosphate etc.,

5 Fillers: To impart valuable service properties such as strength, resistance, finish and workability.
Reducing cost, shrinkage on setting and brittleness. Example: 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 Catalyst/accelerators: To accelerate the polymerisation (added only in thermosetting resins) Example: Hydrogen peroxide, Benzoyl peroxide, Metals (Ag, Cu & Pb)

6 Difference between Thermoplastics & Thermosetting plastics
S.No. 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 & less brittle Usually hard, strong & more brittle 6. Can be reclaimed from wastes Cannot be reclaimed from wastes 7. Soluble in organic solvents Insoluble in organic solvents

7 INJECTION MOULDING (for Thermoplastics):
Materials of definite quantity at Hi Temp. is injected into a cold mould under P In cold mould, the polymer solidifies Polymer is fed as granules, pellets / powder through hopper Polymer get softened in horizontal cylinder Hydraulic piston pushes the molten material into mould Uniform spreading inside the hot cylinder is ensured by torpedo Molten plastic is injected through a nozzle into moulded cavity Mould: Consists of movable & stationary parts Molten plastic is injected at a P of 15000kg/cm2 Proper flow of material is ensured by preheating the mould to appropriate T Mould is cooled by circulating water and then opened to eject the moulded article

8 BLOW MOULDING (for thermoplastics); [for hollow plastic articles]
To produce soft drink bottles, containers using Polyethylene, PVC, Polystyrene PARISON – hot softened thermoplastic made by injection / extrusion moulding Parison is placed inside a two piece hollow mould (as 2 halves) Parison kept between two halves encloses a blowing pin at one end Other end pinches and closes Parison is blown using pressurized air through the blow pin

9 BLOW MOULDING: Continued……
Parison kept under hot condition is inflated and expands until it comes in contact with inner area of the cold hollow mould Under pressure Parison acquires the shape of hallow cavity of mould Mould is cooled and the thermoplastic article is removed from the mould by opening the mould

10 EXTRUSION MOULDING: For producing common plastic materials eg: films, filaments, hoses, sheets & coating wires and cables with PVC Plastic material as powder / granules is fed into a cylinder thru hopper Cylinder is with the provision for heating Hot plastic is pushed thru cylinder by helically revolving screw Due to friction the Temperature increases

11 EXTRUSION MOULDING: (Continues….)
Plastic material passes through three zones Feed zone Compression zone Metering zone

12 EXTRUSION MOULDING: (Continues….)
In compression zone, powder charge is melted by heating element It is compressed by revolving screw Polymer flows at a constant rate due to helical movement of screw Pressure in this zone enables plastic to be in melted stage & enters the die

13 EXTRUSION MOULDING: (Continues….)
From die moulded plastic is coming out in desired profile Extrudated material from die is hot and hence it is cooled rapidly to avoid any deshaping Cooling by passing extrudate over a conveyor belt through which tubes of cold water/cold air are passed

14 Department of Chemistry
Good Luck! The End Dr. K. SIVAKUMAR Department of Chemistry SCSVMV University

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