Polymerization
Polyvinyl Chloride (PVC) is one of the most widely used synthetic polymers in the resins market. The product is highly resistant to other chemical products and can be easily mixed with many additives.
There are several processes for producing PVC, one of which is suspension polymerization. In this process, vinyl chloride monomer is dispersed in water by vigorous agitation. Polymerization is started by means of water soluble reactives. The addition of suspension stabilizing agents lowers coalescence of the forming PVC particles, protecting them by means of a thin film. Hydrophobic and hydrophilic properties of the suspending agent (or its solubility in monomer or water) are key factors in the final resin properties.
Hydroxypropyl Methyl Cellulose (ARBOCEL® CE) is one of the most commonly used suspension agents.
Hydroxypropyl Methyl Cellulose (HPMC) helps to control particle size, allows its uniform distribution and influences porosity, according to the end uses of the resin. One of the characteristics of the resin is related to its ability to quickly absorb a large number of additives, like plasticizers, impact modifiers and stabilizers.
Resins made by this method have a particle size of 50 to 300 μm. The grain has a smooth surface and is irregular in shape. It has a porous interior, with primary particles of 1 - 3 μm size. The exterior is covered by a skin or membrane of 0.5 -1.0 μm thickness and consists mostly of PVC. This peculiar and complex morphology is due to the insolubility of PVC in its own monomer.
Ultra low viscous ARBOCEL® CE is the most suitable product for PVC manufacturing processes. Methoxy and hydroxypropyl substitution levels and the aqueous viscosity determine the performance characteristics as a PVC suspending agent, and although the operating conditions have some influence on the morphology of the grain, the suspension agent used has the greatest effect.