TABLE OF CONTENTS There are two main classes of plastics. About 80% of the millions of tons of plastics used in the world every year are thermoplastic and the remaining 20% are thermosetting . Thermosetting polymers are those that undergo an irreversible change during moulding - as happens to an egg when it is boiled. Thermoplastics, on the other hand, can go through a continual cycle of softening when they are heated and solidifying when they are cooled like candle wax. The vast majority of the plastics used in rotational moulding are thermoplastics, but some moulders use materials with thermosetting characteristics for example, crosslinked polyethylene.
Polyethylene and polypropylene are thermoplastics that are part of the same polyolefin family. Along with polystyrene and polyvinyl chloride they are the most common thermoplastic polymers, and are frequently called the commodity plastics. Engineering plastics have higher performance criteria and are generally more expensive than commodity materials. Nylon, acrylonitrile-butadiene-styrene terpolymer (ABS) and polycarbonate are typical engineering plastics. High-performance plastics generally have properties superior to engineering plastics and are even more expensive. Fluoroethylene (FEP) and polyether etherketone (PEEK) are typical high-performance plastics.
Thermoplastics, by their nature, are amenable to reuse and recycling. Although their properties deteriorate each time they go through a cycle of heating and cooling, thermoplastics are relatively easy to work with during moulding, and waste material need not be totally discarded. At the end of its useful life, a thermoplastic part could be melted and moulded into a different...
