PVC autoclave model

Abstract

The batch reaction of polyvinyl chloride (PVC) in a pressure autoclave is modelled by considering the various mechanisms for conversion from vinyl chloride monomer (VCM) to the polymer during the middle phase of the industrial process. A key step is to determine at what stage the droplets of VCM stop contracting because of the density difference between VCM and PVC - this is known as the 'freeze point'. A model is proposed that locates the freeze point as that point where the unfavourable energy due to wetting of the PVC by water is dominated by the energy required to compress the gel network inside the droplets. Preliminary investigations support this explanation and suggest avenues for further work. A corollary of this model is an explanation of the role of 'secondary granulating agents' in controlling the porosity of the final product.