Polyesterresiner

Polyesterresiner, or polyester resins, are a family of thermosetting polymers used in fiberglass-reinforced plastics and castings. They are unsaturated polyester resins (UPR) formed by the condensation of diols with dicarboxylic acids or anhydrides, creating a backbone that is crosslinked by an unsaturated monomer such as styrene. During curing, free-radical polymerization occurs, typically initiated by an organic peroxide catalyst like benzoyl peroxide, under heat or ambient temperature depending on formulation. Styrene also acts as a reactive diluent, reducing viscosity for molding and wetting.

Processing methods include hand lay-up, spray-up, and resin transfer molding, with reinforcements such as glass fibers to form fiber-reinforced plastics. Variants based on the diacid component include orthophthalic and isophthalic resins, where isophthalic resins generally offer improved chemical resistance and weathering. Additives, fillers, pigments, and stabilizers tailor properties for marine, auto, and construction applications. Vinyl ester resins are a related class with generally higher chemical resistance but still subject to a similar cure mechanism.

Properties: Polyester resins are inexpensive and provide good adhesion to glass fibers, moderate mechanical strength, and ease of processing. They exhibit shrinkage and can develop exothermic heat during curing. They have relatively limited heat and UV resistance unless stabilized, and their performance depends on formulation and curing conditions. They emit volatile organic compounds, notably styrene, during processing, requiring adequate ventilation and protective equipment.

Applications include boat hulls and components, automotive body fillers, architectural panels, and various consumer casts and art objects. Safety and environmental considerations emphasize handling styrene-containing products, proper waste disposal, and occupational exposure controls.