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

2. THERMOPLASTICS & THERMOSETTING PLASTICS

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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