PBT plastic

PBT, short for polybutylene terephthalate, is a hard, tough plastic from the polyester family, a close cousin of the PET used for drink bottles. It shrugs off heat, absorbs very little water, insulates well and holds its shape precisely, which makes it a favorite for electrical parts.

It is made from two building blocks. Terephthalic acid, or a close relative of it, is heated with butanediol. The acid ends of one molecule react with the alcohol ends of the other, linking them and releasing water each time. Repeated thousands of times, this builds long chains, a process called polycondensation. The molten plastic is pushed out, cooled and chopped into pellets, often with chopped glass fiber and flame retardants mixed in.

The pellets are melted and injection molded into small, exact shapes. In a TV, PBT forms the bodies of many connectors, which must survive the heat of soldering without warping, and the bobbin that a transformer's wire is wound on. Some makers use other heat-resistant plastics, such as nylon or liquid-crystal polymer, for the same jobs.