Polyesterharsen

Polyesterharsen, known in English as polyester resins, are a family of thermosetting polymers produced by the condensation of diols with diacids (or their derivatives) and subsequent crosslinking with vinyl monomers such as styrene. They are widely used as a resin matrix in fibre-reinforced plastics (FRP) and castings due to their good mechanical properties, processing ease, and relatively low cost.

Most unsaturated polyester resins (UPR) are based on diols such as ethylene glycol or diethylene glycol and diacids such as phthalic anhydride and maleic anhydride; isophthalic or terephthalic variants improve chemical resistance and weatherability. The resins contain unsaturation sites that allow free-radical polymerization when mixed with a vinyl monomer, typically styrene, and initiated by organic peroxides or similar initiators. Curing yields a crosslinked network; inhibitors control gelation and processing stability.

Key varieties include unsaturated polyester resins (UPR) and saturated polyester resins (SPR). UP resins use unsaturation for crosslinking and are common in FRP laminates; SPRs employ alternative crosslinking chemistries and tend to offer different performance profiles. Orthophthalic and isophthalic-based UP resins are common, while terephthalic-based resins offer improved UV resistance.

Processing and properties are balanced: resins are usually liquids that can be hand-laminated, sprayed, or cast and then cured at ambient or elevated temperatures. After curing, they provide good strength and modulus, decent chemical resistance, but relatively low heat resistance and potential UV yellowing. Shrinkage during cure and styrene emissions require ventilation and proper handling. Fillers like glass fibers improve mechanical properties and reduce shrinkage.

Applications include FRP boat hulls, automotive body parts, chemical storage tanks, piping, flooring, and tooling for composites. Safety concerns include exposure to styrene and initiators, emphasized by ventilation and protective equipment. End-of-life disposal and recycling remain challenging considerations.