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Thermosetting resins, tehrmosets, are a network of long chain molecules that are crosslinked which gives the polymer a three dimensional, infusible structure. They polymerize unreversibly under heat or pressure to form hard, rigid masses. This is the basic difference between thermoplastic polymers and thermosetting polymers. Scrap from molding and from reject parts made of thermosetting polymers can not be remolded.

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Thermosetting resins

Thermosetting resins, tehrmosets, are a network of long chain molecules that are crosslinked which gives the polymer a three dimensional, infusible structure. They polymerize unreversibly under heat or pressure to form hard, rigid masses. This is the basic difference between thermoplastic polymers and thermosetting polymers. Scrap from molding and from reject parts made of thermosetting polymers can not be remolded.

The srosslinking usually occurs during the curing reaction, or during the polymerization reaction or after polymerization between the linear polymers. Crosslinking concurrent with polymer formation is the ease with phenol formaldehyde resins. Crosslinking also may be obtained by the use of crosslinking agents as are used in the production of epoxy resins. The consumption of thermosetting resins is much less than of thermoplastics and represents about 19 % of plastic market. Thermosets hold specific market, like urea and melamine resin which are used in bonding and as adhesives for granulated wood. Reinforcement of thermosets improve their physical properties. 90 % of reinforced plastics RP, is of the thermosets type made from polyester resins. Other thermosets that are reinforced are urethanes, phenolics, melamines and epoxy. One of the largest use of reinforced plastics is for chemical process equipment. Plastic reinforcement has been practiced for more than thirty years, and the most widely used material for reinforcement is fiber glass in varying proportions ranging between 20 to 30 %. The development in the reinforcement processing technique like in sheet molding compounds SMC are made that allow the resin, glass reinforcement, pigment fillers and thickeners to be sandwiched between two sheets of the plastic.

Engineering thermoplastics

These resins include polymers with special properties such as high thermal stability, good chemical and weather resistance, transparency, good electrical properties and other useful characteristics. Among this group are nylon, polycarbonates, polyvynil acetates, polyethersulfones, polyacetals and thermoplastic polyesters. A major portion of engineering plastics is processed by injection molding and is used for replacement of die cast metals (Zinc, magnesium and aluminum). Nylon is considered the number one engineering resin and accounted for 39 % of engineering resins.

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