Some of this plastic is used in PET soft drink bottles and other blow molded containers, although sheet applications are increasing. Cleaned, recycled PET flakes and pellets are in great demand for spinning fiber for carpet yarns and producing fiberfill and geotextiles. Other applications include strapping, molding compounds and both food and non-food containers. Synthetic polymers are formed by addition or condensation polymerization of monomers . If two or more different monomers are involved, a copolymer is obtained.
Some polymers are elastomers, some plastics.
Polypropylene has excellent chemical resistance, is strong and has the lowest density of the plastics used in packaging. It has a high melting point, making it ideal for hot-fill liquids. PP is found in everything from flexible and rigid packaging to fibers and large molded parts for automotive and consumer products. Polystyrene is a very versatile plastic that can be rigid or foamed. General purpose polystyrene is clear, hard and brittle.