The effect of suspending agents on the suspension polymerization of vinyl chloride
The suspension polymerisation of vinyl chloride is the main industrial process used for the manufacture of PVC. The aim of this project was to study the suspension polymerisation of vinyl chloride monomer to form PVC. The work concentrated on the effects that the choice of suspension stabilisers (PVA's), pH and other environmental factors had on the properties of both the initial droplet suspension and the polymerising system throughout the course of the reaction. Experiments were carried out using a pressurised 11 stainless steel jacketed reactor connected to an external optical cell. Progress of the polymerisation was monitored optically by taking samples into the cell at regular intervals and examining them with a microscope which had an attached camera. Properties that were studied included the drop size and drop size distribution of the initial droplet suspension, the stabiliser take-up during the reaction and the particle size distribution, porosity and physical appearance of the polymer particles. The work showed that the choice of suspension stabiliser not only effected the drop size and drop size distribution of the initial suspension but also effected the properties and particle size of the final polymer product which was produced. The pH of the system was also discovered to effect both drop stability and the course of the polymerisation. Lowering the pH (pH 10) had a drastic effect. At high pH, the droplet suspension that was formed was highly unstable and the polymer product that was formed consisted of very large, coarse grains. Other environmental factors (reactor heat up rate, oxygen concentration, the location of secondary PVA (aqueous or organic phase), delaying the addition of the primary PVA and simultaneous charging of both phases to the reactor) were also discovered to effect the properties of both the droplet suspension and the polymer product although the suspension was found to be more resilient to changes in the operating conditions than the polymer.