ABSTRACT
Polyethylene is a translucent material often fabricated into clear, thin films. Thicker sections are more translucent than thinner ones, and the addition of colorants and other additives greatly enhances polyethylene’s commercial importance. Polyethylenes are partially crystalline and partly amorphous and have very wide molecular weight ranges. Low-density (LDPE) is made via three processes: low-pressure, high-pressure tubular and a high-pressure stirred-autoclave polymerization. The excellent properties of isotactic polypropylene have helped it become one of the fastest-growing commodity thermoplastics. Polypropylene may be processed via injection molding, thermo-forming or extrusion. Polypropylene has outstanding combinations of heat resistance, tensile strength, abrasion resistance, clarity, optical gloss as well as relatively low specific density. Propylene block copolymers are important commercial products prepared from propylene either following homopolymerization followed by copolymerization with ethylene, propylene or by blending polypropylene with ethylene-propylene rubber.
