ABSTRACT
Of the five established processes for the polymerisation of vinyl chloride monomer (VCM) two, the emulsion and microsuspension processes, can be grouped together for the purposes of discussing isolation of the polymer. Both require the removal, normally by hot air drying, of a large quantity of water, to produce a saleable product. The water to be removed may be as much as 2·5 times the weight of dry PVC produced. A third process, suspension polymerisation, produces a slurry of high water content from the reactor but the particle size and type is such that 60-80% of the water can be removed mechanically before hot air drying. A fourth process, solution polymerisation, as the name suggests, requires that an organic solvent be removed in order to isolate the PVC. This process is operated industrially only on a limited scale and is not dealt with here. In the fifth process, the mass or bulk process, the polymerisation occurs in the presence of VCM only and no water is involved. The polymer precipitates from the VCM and after removal of residual VCM the polymer is passed directly to the finished product handling. Consequently its isolation is perhaps much simpler than that of the other two main process types.
