Polyethenic or vinyl resins

Transcription

1 Polyethenic or vinyl resins Obtained by the polymerization of monomers containing the ethylenic bond (-c =c-) Important members of this type of resins are given below. (i) polyethylene (or) polythene: ( P E) P E is a versatile plastic made from polymerization of ethylene gas. Preparation of PE : It is obtained by the polymerization of ethylene. The ethylene gas is first liquefied under high pressures (up to 1500 atm) and then pumped into a heated pressure vessel, maintained at to 250 o C. By catalytic effect of traces of Oxygen present ethylene is polymerized into PE It is waxy solid, comes out from the perforation in the bottom of the vessel. n (H 2 C = CH 2 ) Ethylene Polymerization [ H 2 C CH 2 ] n Polyethylene (PE)

2 By using free radical initiator, low density polythe (LDPE) is obtained While by using ionic catalysts, high density polyethylene (HDPE) is obtained. Properties : (1) Polyethylene is a rigid, waxy, white, non-polar material, exhibiting considerable chemical resistance to strong acids, alkalis and salt solutions at room temperature. (2) It is good insulator of electricity (3) But it is swollen and permeable to most oils and organic solvents, particularly Kerosene. (4) The high density Polythene (HDPE), which is completely linear, has better chemical resistance, particularly to organic solvents, a higher softening point (125 0 to C) and greater rigidity than the low density polythene (LDPE), but it has a low impact strength and is relatively brittle. Example: HDPE polymer Uses : (1) It is used as films and sheets for packaging applications, including bags and wrappings, table clothes etc.

3 (2) It is also used for making high frequency insulator parts, bottle caps, flexible bottles, Kitchen and domestic appliances, toys etc. (3) It is used for production of house wares and cable insulation, for coating paper, for preparing bottles, industrial containers, pipes for water supply, etc. (II) Polyvinyl Chloride : (PVC) It is prepared from the monomer, vinyl chloride. Vinyl chloride, so needed is generally prepared by treating acetylene at 1 to 1.5 atm with hydrogen chloride at C, in presence of metal chloride as catalyst. HC = CH + HCl Acetylene H 2 C = CH Cl Vinyl chloride PVC is obtained by heating a water emulsion of vinyl chloride in presence of a small amount of benzyl peroxide or hydrogen peroxide in an autoclave under pressure. Cl Cl Polymerization H 2 C = CH [- H 2 C CH- ] n Vinyl chloride Polyvinyl Chloride (PVC)

4 Properties: (1) PVC is colourless odourless, non inflammable and chemically inert powder, resistant to light, atmospheric oxygen, inorganic acids and alkalis, but soluble in hot chlorinated hydrocarbons such as ethyl chloride. (2) Pure resins possess a high softening point (148 0 C) and a greater stiffness and rigidity compared to polyethylene, but is brittle. Uses : (1) Regid PVC or unplasticized PVC have superior chemical resistance and high rigidity, but is brittle. It is used for making sheets, which are employed for tank linings, light filtings, safety helmets, refrigerator components, tyres, cycle and motor cycle mudguards. (2) Plasticized PVC is used for making continuous sheets. Employed for packing rain coats, table cloths and curtains, electrical insulation like covering of electric cables, toys, tool handles, toiled goods, radio components, plastic coated cloth chemical containers, thermal insulating foam (used in buildings, cinemas and aircrafts), conveyor belts (used in coal mines), etc.

5 (III) Polystyrene (PS) : It is prepared by polymerization of styrene monomers. The monomer, styrene is prepared from benzene and ethylene under pressure at 90 0 C in presence of a catalyst (Alcl 3 ). The resulting ethyl benzene is dehydrogenated to slyrene by passing over an iron oxide or magnesium oxide or aluminium oxide catalyst at about C. The styrene is then refined by distillation. Poly styrene (PS) is prepared by polymerization of styrene in presence of benzoyl peroxide catalyst.

6 Properties : (1) Poly Styrene is transparent and excellent moisture resistant. Its high refractive index (1.60) renders it useful for plastic optical components. (2) It is highly electric insulating, highly resistant to acids and good chemical resistant. (3) It has the unique property of transmitting light through curved sections. Uses : It is used in moulding of articles like toys, combs, buttons, radio and television parts, refrigerator parts, battery cases, high frequency electric insulators, lenses, indoor lighting panels, etc.