Rubber, plastics and polymer–metal joints

Rubber can be natural or synthetic. Vulcanised rubber and rubber articles are made by adding to the rubber a vulcaniser (sulphur), activators that speed vulcanisation, softeners and substances that slow ageing. By the amount of sulphur added, vulcanisation produces soft, medium-soft or hard rubber (ebonite): soft rubber contains a few per cent sulphur, ebonite far more, up to about half. Soft rubbers line apparatus and equipment, while ebonite is made into pipes, plates and tubes. Rubbers are made acid-resistant, heat-resistant, cold-resistant and resistant to oil and petrol. About 50 000 kinds of article are made of rubber; the most important are tyres for various vehicles, plus clothing, footwear, belts and porous materials. Because rubber resists aggressive media, it is important in the chemical industry too. Burning old tyres and rubber gives toxic smoke, so rubber waste is never burned but handed in for recycling. At school, rubber is cut with scissors rather than a sharp knife, under adult supervision; some people are allergic to latex.