Poly propylene: Polypropylene (PP) is a linear polymer, composed of repeating units of isopropane. These resins are not hygroscopic and may be used as received without need for drying. At temperatures above 220ºC, EVA resins can evolve toxic fumes.
The main attractive features of PP are: =>
- Exceptional flex life,
- Good surface hardness,
- High chemical resistance,
- Good stability in boiling water,
- Excellent electrical property
- Long-life integral hinge application.
1. Atactic PP is a low melting, gooey material
2. Isoatactic PP is high melting (176º), crystalline, tough material that is industrially useful
3. Syndiotactic PP has similar properties, but is harder to synthesize.
Preparation of Poly propylene: PP is prepared by using Ziegler type catalyst – titanium tri chloride with aluminium tri ethyl, aluminium tri butyl, or aluminium di ethyl chloride in naphtha under nitrogen atmosphere to form slurry consisting of 10% catalyst and 90% naphtha. The molecular weight can be controlled by using hydrogen as a chain transfer agent. In suspension process, propylene is charged into the polymerization vessel under pressure while the catalyst and the reaction diluent are metered in separately. Polypropylene (PP) also known as polypropene is a thermoplastic polymer used in a wide variety of applications including packaging, textiles (e.g., ropes, thermal underwear and carpets), stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. An addition polymer made from the monomer propylene, it is rugged and unusually resistant to many chemical solvents, bases and acids.
Injection moulding:
1. Melt temperature : 180 - 300°C
2. Mold temperature : 20 - 60°C. Higher the mold temperature then better the surface gloss.
3. High injection pressure and speed are recommended.
Extrusion moulding:
1. A three-zone screw with a total L/D ratio of 20-25 is generally recommended.
2. Melt temperature is, generally, in the overall range of 240-270ºC .
Blow moulding:
1. Melt temperature should lie between 190 and 220°C.
2. Mold temperature should lie between 20 and 40°C.
APPLICATIONS OF PP
Electrical/Electronics
Radio and TV housing capacitors, coil forms, control knobs, transformer housing,switch gears
Packaging
BOPP films used as goods wrapping, garment packaging
Appliances
Agitators, housing for coffee maker, mixies, vacuum cleaner and washing machine parts
Automotive
Car bumpers, dash board, steering wheel covers, radiator grills, air filter parts
Medical
Disposable syringes, tubes and blow moulded bottles, trays
Household
Coffee makers, hair dryers, air-conditioner parts, microwave oven trays, babyfeeding bottles, thermoflask cases and chains, ropes, tapes and hinged property applications
Strengths:
1. Good chemical resistance against most inorganic acids, alkalis, and salts
2. Good resistance to environmental stress cracking when in contact with alcohols, esters, detergents, or polar hydrocarbons
3. Very good fatigue resistance
4. Very low density
5. Excellent dielectric properties
6. More rigid than PE and retains mechanical
properties at elevated temperatures
7. Mechanical and electrical properties unaffected by submersion in water
8. Good resistance to steam sterilization
9. Excellent hinge characteristics
10. Can be joined by hot-gas, hot-tool, induction, or friction welding.
Limitations:
1. Poor resistance to UV, need to be stabilized
2. Embrittles below -20°C
3. Low upper service temperature, 90℃-120℃
4. Attacked by highly oxidizing acids, swell rapidly in chlorinated solvents and aromatics
5. Heat-ageing stability is adversely affected by contact with metals.
6. Post moulding dimensional changes due to crystallinity effects.
7. Limited impact resistance
8. Low scratch resistance
9. Poor paint adhesion.
Properties
1. Stiffer than PE
2. Higher glass transition temperature and melting point
3. Possesses integral hinge property
4. Low specific gravity than polyethylene
5. Chemical resistance is similar to polyethylene
6. Very low water absorption
7. Excellent dielectric properties
8. Can be sterlised with steam and ethylene oxide
9. Copolymers have more impact strength and high gloss than homopolymers
10. Good tensile strength
11. Good abrasion resistance
12. Low UV resistance
13. Brittle at lower temperatures
14. Less resistance to oxidation
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