Types of plastic

Elastomers

Elastomers (rubbers) are special polymers that are very elastic. They are lightly cross-linked and amorphous with a glass transition temperature well below room temperature. They can be envisaged as one very large molecule of macroscopic size.

Elastomers can be classified into three broad groups: diene, non-diene, and thermoplastic elastomers. Diene elastomers are polymerized from monomers containing two sequential double bonds. Typical examples are polyisoprene, polybutadiene, and polychloroprene. Nondiene elastomers include butyl rubber (polyisobutylene), polysiloxanes (silicone rubber), polyurethane (spandex), and fluoro-elastomers. Non-diene elastomers have no double bonds in the structure, and thus, crosslinking requires other methods than vulcanization such as an addition of trifunctional monomers (condensation polymers), or addition of divinyl monomers (free radical polymerization), or copolymerization with small amounts of diene monomers like butadiene.

Thermostables

Thermosets are hard and have a very tight-meshed, branched molecular structure. Curing proceeds during shaping, after which it is no longer possible to shape the material by heating. Further shaping may then only be performed by machining. Thermosets are used, for example, to make light switches.

The starting material for producing thermosets is normally malleable or fluid earlier to curing and is oftentimes meant to be formed into the final shape. It may also be used as an adhesive. Once hardened, a thermoset cannot be melted for reshaping, in contrast to thermoplastic polymers which are generally fabricated and distributed in form of grains, and shaped into the final product form by melting, pressing, or injection molding.

Thermosetting plastics are generally stronger than thermoplastic materials due to the three-dimensional network of bonds (crosslinking). The higher the crosslink density and aromatic content of a thermoset polymer, the higher the resistance to heat degradation and chemical attack. Mechanical strength and hardness also improve with crosslink density, although at the expense of brittleness. They normally decompose before melting.

Thermoplastics

Thermoplastics have a linear or branched molecular structure which determines their strength and thermal behavior; they are flexible at ordinary temperatures. At approx. 120 - 180°C, thermoplastics become a pasty/liquid mass. The service temperature range for thermoplastics is considerably lower than that for thermosets 

Thermoplastics are determined as polymers that can be melted and recast almost indefinitely. They are melted when heated and harden upon cooling. When frozen, however, a thermoplastic becomes glass-like and subject to fracture. These characteristics, which lend the material its name, are reversible so the material can be reheated, reshaped, and frozen repeatedly. As a result, thermoplastics are mechanically recyclable. Some of the most common types of thermoplastic are polypropylene, polyethylene, polyvinylchloride, polystyrene, and polycarbonate.