Polyvinyl Chloride PVC and its Variants

The world capacity for PVC is now around 25 million tonnes of which European capacity is 6 million tonnes. Much of the growth of capacity in recent years has been in the Asia-Pacific region. European capacity has grown only slowly in the past 20 years with mature market demand in many sectors. As a result, developments have largely been directed at cost reduction and rationalisation of production plant. The trading and merging of assets between major petrochemical companies is a feature of the current supply industry. 

Liquid plasticisers can be added to increase flexibility and reinforcing fillers can be added to increase stiffness. For applications where high strength is not needed PVC will tolerate relatively high loadings of low cost filler such as calcium carbonate. 

Raw PVC polymer has a particulate structure with size and shape determined by the polymerisation conditions. During processes, such as pipe extrusion, sufficient heat and work, as shear mixing, must be applied to the molten polymer to break down and then fully fuse the particle structure. This heat and work must be limited to a level which does not breakdown the polymer structure nor degrade the physical properties. PVC processing must therefore be carefully controlled within optimum conditions with the addition of appropriate additives to protect the polymer chain from thermal and oxidative degradation. 

As a result of pipe failures that were identified as having inadequate gelation , or fusion of the polymer particle structure, a simple test involving the immersion of a sample in methylene chloride was introduced. The solvent action quickly breaks down an inadequately processed sample by destroying the interface between sintered particles. If 

By far the greatest part of PVC production across the world is now made by the suspension process. Vinyl chloride monomer (derived from a reaction between ethylene (derived from oil) and chlorine (derived from common salt) is dispersed in deionised water with the help of small quantities of chemical dispersants and polymerisation initiators (typically peroxide compounds). At moderately raised temperature (50 C) and pressure (0.7 MPa) polymerisation proceeds and the polymer can be removed from the resulting slurry by de-watering and steam stripping the unconverted vinyl chloride monomer. 

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