Polyesterien

Polyesterien, the Finnish plural noun for polyesters, refers to a family of polymers that contain ester linkages in their main chain. The best-known member is polyethylene terephthalate (PET), but the class also includes other polymers formed from diols and dicarboxylic acids, such as polybutylene terephthalate (PBT) and polytrimethylene terephthalate (PTT).

Polyesters are produced by condensation polymerization, joining a diol with a dicarboxylic acid to form ester linkages and releasing a small molecule, typically water. PET is commonly made from ethylene glycol and terephthalic acid (or dimethyl terephthalate) and then polymerized to high molecular weight. Processing conditions, catalysts, and monomer purity influence molecular weight, crystallinity, and material properties; catalysts such as antimony compounds and titanium compounds are often used.

Properties of polyesters include thermoplasticity, good tensile strength, abrasion resistance, and dimensional stability. The degree of crystallinity affects transparency, stiffness, and barrier properties to gases. PET, for example, is clear and has a relatively good gas barrier, which makes it suitable for beverage bottles and packaging. Polyester fibers, produced by melt-spinning, are widely used in textiles for their resilience, wrinkle resistance, and ease of care.

Applications span fibers for clothing and home furnishings, bottles and food packaging, films, and various engineering parts. Environmental considerations include the non-biodegradability of most polyesters and the importance of recycling. PET, in particular, is widely recycled through mechanical and chemical recycling routes, contributing to a circular economy despite energy use and potential microplastic concerns. Advances continue in bio-based monomers and improved recycling technologies.