80 What is a molecule? Try to define it in your own words. The terms rubber and elastomer are often used interchangeably, even though rubber refers to the natural gum rubber produced from the sap of the Hevea tree. POLYMERS, PLASTICS, CERAMICS, AND COMPOSITES Other materials which we commonly use in our everyday life are polymers, plastics, ceramics, and composites. Polymers Polymers are materials produced by a process called polymerisation, a chemical reaction in which small molecules combine together to form long molecular chains. They have a good resistance to corrosion and are usually used as thermal and electrical insulators. They have many applications, including adhesives and electronic devices. They are divided into two categories: thermoplastic polymers, which are very ductile because their molecular chains are not rigidly connected; thermosetting polymers, which are strong but brittle because their molecular chains are rigidly linked. Elastomers are polymers with elastic properties that, at room temperature, can be stretched and, when released, return to within 90% of their original dimension and shape, e.g. rubber. They can be both thermoplastic or thermosetting, depending on their type and formulation. Plastics Plastics are synthetic polymers that are specifically designed to be moulded and used in a variety of products and industries. These materials are versatile, malleable, and can be easily shaped into various forms when heated. Plastics are made primarily from petroleum-based chemicals but can also be derived from renewable resources like plants. Ceramics Ceramics are inorganic, non-metallic substances produced using clay and other minerals from earth (for example beach sand) or chemically processed 190 MeCHaNiCs powders. Naturally occurring ceramics are commonly used for pottery, bricks, tableware, etc., whereas chemically prepared ceramics find applications in engineering and electronics, having excellent mechanical and physical properties, such as strength, hardness, and a very high melting point. Ceramics are also typically used as electrical insulators having extremely low electrical conductivity. Composites Composite materials are the combination of two or more materials having significantly different properties that, once combined together, produce a composite with unique characteristics. The advantage is that with the combination of various properties, the resulting material can be very strong but lightweight, or thermal insulating and corrosion-resistant at the same time. Composites are usually made up of two parts: the matrix, which is the external covering usually made of metal, polymers, or ceramics; the reinforcement, which is a cluster of fibres usually made of a stronger material such as carbon. The most common composites are fibreglass, Kevlar, and carbon fibre. clay: argilla cluster: ammasso to mould: stampare pottery: terracotta reinforcement: rinforzo sap: linfa