1.3 NON-METALS 18 What difference is there between the two terms malleability and plasticity? See unit 1.1. Before the invention of plastic, the only substances that could be moulded were clay and glass. Hardened clay and glass were used for storage, but they were heavy and brittle. The world s first fully synthetic plastic was Bakelite, invented in New York in 1907, by Leo Baekeland, who used the term plastics for the first time. POLYMERS, PLASTIC MATERIALS In this unit we are going to examine the properties and applications of nonmetallic materials which have become widely used in every sector of our life. The term plastic The term plastic originated from the Greek word plastikos, meaning fit for moulding . It refers to the material s malleability or plasticity during manufacturing, which allows it to be cast, pressed, or extruded into a variety of shapes. What is plastic? Plastic is any synthetic or semi-synthetic organic polymer. A polymer is a chemical compound with very small molecules (monomers) bonded together in long repeating chains. Polymers can be both: natural, such as cellulose and rubber, or synthetic substances, which are generally derived from oil and are usually referred to as plastic materials. ONLINE RESOURCES The exciting world of synthetic polymers bond: legame clay: argilla to extrude: estrudere, espellere to harden: indurirsi helmet: casco to mould: forgiare to reheat: scaldare di nuovo rubber: gomma to soften: ammorbidirsi stiff: forte tyre: pneumatico to undergo: sopportare 42 Any polymer used to make plastic is almost always mixed with additives (colourants, stabilisers, fillers, and reinforcement) that affect its properties. Features and applications Plastics have a lot of different applications: from optical components to telecommunication equipment, from food storage to adhesives, from architectural elements to car parts, clothing, ski boots and safety helmets. Moreover, plastics are perfect insulators as they do not allow electricity or heat to flow through them and this high resistance to the flow of electric current makes them well-suited to electrical applications. Types of plastics According to their chemical and structural bonds, plastics are usually classified as: Thermoplastics, which soften or melt when heated and harden when cooled: in particular, they can undergo reheating processes in order to be reshaped into a new form; Thermosettings, which cannot undergo reheating processes and become permanently hard and rigid when heated. Elastomers There exist some special polymers called elastomers which are very elastic because the intermolecular forces between the polymer chains are rather weak. They can be both natural and synthetic and their main quality is that of returning to their original shape after deformation. Most of them are synthetic, derived from sub-products of petroleum and natural gas. They are the basic material for any rubber products and adhesives, and their high resilience, elasticity and toughness make them fundamental for the production of tyres, for example. Materials MechPower.indb 42 30/01/24 17:07