Poly vinyl chloride (PVC)
Poly vinyl chloride (PVC): Introduction: Polyvinyl chloride is obtained by heating a water emulsion of the vinyl chloride in an autoclave under pressure in the presence of benzoyl peroxide or hydrogen peroxide.
- PVC is a colourless and adourless powder.
- It is chemically inert and non-inflammable and exhibits high resistance to light, atmospheric oxygen, acids and alkalis.
- It is soluble in chlorinated hydrocarbons, tetrahydrofuran (THF) and cyclohexanone.
- Pure resin possesses a high softening point (148oC) and a greater stiffness and rigidity compared to polyethylene, but is brittle.
- It is the most widely used synthetic plastic.
- Rigid PVC unplasticized PVC have superior chemical resistance and high rigidity but is brittle. It is used for making sheets that are employed for tank– linings, light-fittings, safety, helmets, refrigerator components, tyres, cycle and motor cycle mudguards. It is also extruded in strip and tube form for use in the place of non-ferrous metals.
- Platicized PVC is used for making continuous sheets of different thicknesses from 0.1mm to 8mm. It is employed for packing rain coats, table-clothes and curtains, electrical insulation like coverings of electric cables, injection moulding of articles like toys, tool-handles, toiled-goods, radio-components, plastic-coated cloth, chemical containers, thermal insulating foam, conveyor belts etc.
Plasticized PVC is obtained by adding plasticizers like dibutyl phthalate, dioctyl phthalate, tricresyl phosphate etc.
Polyvinyl chloride (PVC):
PVC is made by addition polymerization. It is of two types.
- Rigid PVC : (Unplasticized PVC):
Preparation: Rigid PVC is made by heating vinyl chloride (in the form of emulsion of it in water) in the presence of small amount of benzoyl peroxide or H2O2 as catalyst under pressure in an autoclave.
- Presence of chlorine atoms on the alternate carbon atoms of PVC causes an increase in the interchange attraction. This increases the hardness and stiffness of polymer. Its softening point is also high (148oC)
- The Cl-Cl dipole makes PVC a polymeric polar molecule, but because of the immobility of the dipole at room temperature, power factor of PVC is comparatively low.
- PVC is colourless, odourless and non-inflammable.
- It has superior chemical resistance but is soluble in ethyl chloride and tetrahydrofuran (THF).
- It has excellent oil resistance and resistance to weathering.
- It is used in acid recovery plants and in plants for handling hydrocarbons, many of which adversely affect the polyolefins. This is due to its very good resistance to chemicals.
- Rigid PVC has great potential importance to building industry since it has excellent resistance to weathering. When considered regarding initial cost, installation and maintenance cost, it is found to be very economical. Hence, it is used for making pipes for drainage and guttering. It is also replacing wood for making window frames that neither corrodes or not.
- Rigid PVC is also used for making bottles –
- For consumable liquids (like edible oils, fruit squashes, table wine and vinegar).
- For liquids of household use (like bislery mineral water, cosmetics and detergents)
Preparation: plasticized PVC is obtained by adding plasticizers such as DOP (dioctyl phthalate), dibutyl phthalate, tricresyl phosphate etc., to rigid PVC.
Plasticized PVC is a very good insulator for direct current and low frequency AC current.
- Plasticized PVC is completely replaced rubber insulated wire for domestic flex and is used widely industrially.
- It is used for sheathing in cables where polyethylene is employed as insulators.
- Plasticized PVC is used for making leather cloth which is used in
- Car applications in upholstery and trim,
- Kitchen upholstery
- Bathroom curtaining
- Ladies handbags.
Compared to leather, PVC-leather cloth has greater abrasion resistance, flex resistance and washability. Its cost is very low.