Plastics Plan Plastics Amorphous plastics and crystalline plastics Production Plastics

Thermoplastics and thermosetting polymers

This plastic handle from a kitchen utensil has been deformed by heat and partially melted
One important classification of plastics is the degree to which the chemical processes used to make them are reversible or not.
Thermoplastics do not undergo chemical change in their composition when heated and thus can be molded repeatedly. Examples include polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC).^[13]
Thermosets, or thermosetting polymers, can melt and take shape only once: after they have solidified, they stay solid.^[14] If reheated, thermosets decompose rather than melt. In the thermosetting process, an irreversible chemical reaction occurs. The vulcanization of rubber is an example of this process. Before heating in the presence of sulfur, natural rubber (polyisoprene) is a sticky, slightly runny material; after vulcanization, the product is dry and rigid.
Amorphous plastics and crystalline plastics
Many plastics are completely amorphous (without a highly ordered molecular structure),^[15] including thermosets, polystyrene, and methyl methacrylate (PMMA). Crystalline plastics exhibit a pattern of more regularly spaced atoms, such as high-density polyethylene (HDPE), polybutylene terephthalate (PBT), and polyether ether ketone (PEEK). However, some plastics are partially amorphous and partially crystalline in molecular structure, giving them both a melting point and one or more glass transitions (the temperature above which the extent of localized molecular flexibility is substantially increased). These so-called semi-crystalline plastics include polyethylene, polypropylene, polyvinyl chloride, polyamides (nylons), polyesters and some polyurethanes.
Conductive polymers
Main article: Conductive polymer
Intrinsically Conducting Polymers (ICP) are organic polymers that conduct electricity. While a conductivity of up to 80 kS/cm in stretch-oriented polyacetylene,^[16] has been achieved, it does not approach that of most metals. For example, copper has a conductivity of several hundred kS/cm.^[17]