2.2.1 Production, structure and properties of PVC

PVC, with chemical formula C2H3Cl, is a vinyl polymer composed of repeating vinyl groups (ethenyls), having one hydrogen atom replaced by chlorine on alternate carbon atoms per repeat unit:

PVC production and processing consists of five major steps (Titow, 1984):

VCM is polymerized into the polymer product by an exothermic free-radical reaction at 40–70°C in the liquid state under pressure (in batch reactors) with continual mixing of the ‘suspension’ to obtain a uniform particle size. After degassing, stripping, centrifuging and drying of the resulting slurry, it is sieved to obtain the powdered ‘suspension PVC’ product with sizes of 120–150 μm. There are other production methods for PVC as well, e.g. the ‘emulsion’ technique, which produces smaller sizes (e.g., 10 μm). Suspension and emulsion type PVCs have somewhat different properties and are used for different applications, suspension being the more commonly used. Normally, any PVC product is expected to have less than 1 ppm (parts per million) of monomer (VCM) content left unreacted:

[2.1]

PVC is a white, amorphous, odorless powder, which is stable under normal temperatures and pressures up to 70–80°C, after which it begins to decompose with evolution of hydrochloric acid (HCl) gas and discoloration (yellowing).

PVC was first made in 1872 by the German chemist Eugen Baumann, who did not apply for any patent. In 1912, the German chemist Fritz Klatte working for Greisheim-Electron, Germany, decided to try to react acetylene with HCl (which apparently produced the monomer VCM), and he left the product on the shelf, where it apparently polymerized over time by sunlight. Hence Klatte was the first inventor to receive a patent for PVC (in 1913), using mercuric chloride as a catalyst; this patent expired in 1925. This original method was widely used during the 1930s and 1940s, but has since been superseded by more economical advanced processes, at least in the Western hemisphere.

The importance of PVC and its use was not realized until 1926 when Waldo Semon, an American chemist working at B.F. Goodrich, invented PVC independently. Semon quickly understood that this new material would have a big potential to produce brand-new objects, and he first produced a shower curtain.Semon and B.F. Goodrich immediately patented PVC for the USA (Semon, 1926a, 1926b). Later, Semon tried to produce golf balls and shoe heels from PVC. A great many new uses for this wonderful waterproof material then followed, and PVC was a real success in the world.

Being a thermoplastic, PVC softens if heated and hardens as it cools; and it can be processed by the use of any conventional plastics processing techniques, such as extrusion (specifically for complex-shaped extrusion profiling for housing materials), calendering (wide films and sheets such as agricultural films and PVC leather), injection and blow molding (except injection molding, because its melt viscosity is high). PVC materials have rather low densities, hence they offer relatively low material costs on a volume basis and hence are cost-effective. PVC is one of the major low-cost, high-volume commodity resins used today due to its economy and the excellent chemical and mechanical properties it provides.

Two main types of PVC resins are produced and processed:

When plasticizers are added, flexible plasticized PVC (pPVC) is obtained with rubber-like elasticity, high tensile and fatigue strengths, which can be used specifically for industrial hoses, gaskets, elastic automotive parts and electrical cable covers, where elasticity is a must. pPVC also finds applications in film and sheets, flooring, shower curtains and synthetic leather products. In the 1970s pPVC was often used to make ‘vinyl car tops’, and it was also used to make vinyl records. PVC-based materials also have a key role in the production of medical and clinical devices; however, similar arguments are arising with regard to its safety issues (Latini et al., 2010). Table 2.1 summarizes some characteristics of PVC.