Raw materials
PVC
Almost a century elapsed from the synthesis of vinyl chloride, realised in laboratory by the French scientist V.H. Regnault in 1835, to the production of the first PVC objects.
The polymerisation of vinyl chloride had already been carried out in laboratories in the years immediately preceding WWI, but the real production of PVC objects began in America in 1927, and has been realised on an industrial scale only since 1939.
Today, 70 years after its first appearance on the market, PVC is one of the most widely spread plastic materials.
The monomer vinyl chloride, called MVC, easily polymerises thus forming PVC. Polymerisation is that chemical process through which a substance is obtained, made by two or more molecules, called monomers, of the same compound. The word polymer (from Greek poli = many and mera = part) indicates a substance made of many fundamental units which occur several times in the structure, like a wall made of many identical bricks.
Polymerisation is obtained as follows: MVC are put into the autoclave together with water and additives, such as "catalysts" or reaction accelerators, emulsifying agents, dispersants, etc.; under the combined action of heat and mechanical movements polymerisation actually takes place. Most of MVC molecules combine thus forming large PVC chain molecules that, after they are dried and purified, take the form of white powder. Raw materials from which PVC is obtained are oil and sodium chloride, commonly known as rock salt or more simply as salt. Considering that there are large quantities of salt all over the planet and that it is not an energy source, it can be asserted that PVC production depletes natural resources less than other mass polymers which entirely derive from oil. With electrolysis chlorine and sodium are obtained from salt in fixed percentage.
The chloride obtained through electrolysis replaces part of the hydrogen contained in ethylene, an unsaturated hydrocarbon that can be found in cracking gases of oil products, thus creating mono-vinyl chloride, whose empirical formula is CH2 = CHCl, and hydrochloric acid (H-Cl). Objects made with polyvinyl chloride are smooth, bright oil-, fat- and aroma-repellent; they can be transparent or opaque; they are self-extinguishing and do not propagate fire; they are generally stiff and abrasionproof.
These positive features derive from the presence of chlorine in PVC; chlorine is a toxic gas when let free, but when it is fixed into polyvinyl chloride becomes inert and therefore is not dangerous.
