Unsaturated Polyester Resins, Blends, Interpenetrating Polymer Networks, Composites, and Nanocomposites: State of the Art and New Challenges (original) (raw)

Unsaturated Polyester Resins

The fact that some natural oils besides alkyd resins can be dried by certain additives and employed as coatings was realized long ago. This results from a polymerization reaction of the unsaturated moieties in ester molecules (Fig. 6.1). Carleton Ellis' original patents with regard to polyester resins egressesed in the 1930s. While profit-making production started in 1941 by now reinforced with glass fiber for radar domes, also known to as radomes. Unsaturated polyester resins (UPRs) consist of two polymers, that is, a short-chain polyester bearing, polymerizable double bonds and a vinyl monomer. The curing reaction involves the copolymerization of the vinyl monomer with the double bonds of the polyester. During the process of curing, a threedimensional network is formed. UPR is yielded in this process, belonging to the thermoset class. UPRs have interesting applications in compression molding (sheet molding compounds), injection molding (bulk molding compounds), filament winding, resin transfer molding (RTM), pultrusion, and the hand lay-up process [1]. 85% of fiber-reinforced polymer (FRP) products such as aircraft parts, motor covers, belt guards, water-cooling towers, boats, architectural parts, chairs in ducts and other process equipment in chemical plants and paper mills, water pipes, and chemical containers are manufactured using polyesters, and they are used in offshore applications, construction, and the paint industry [2,3]. The determination of the gel time and curing time is a very significant step in the processing of UPRs while manufacturing composite products. The curing reaction should be accomplished in a governable manner to attain a high-quality product [4]. On account of the enormous amount of applications where flammability does not matter, such as underground mine bolts, pipes, and in many marine applications, the percentage of flame-retardant resins relative to all UPRs is less than 153 Unsaturated Polyester Resins.