EFFECTS OF LONG-CHAIN ALKYL PEROXYDICARBONATES ON THE PROPERTIES OF PVC PRODUCED BY SUSPENSION POLYMERIZATION

Commercially available diethyl, dicetyl, and dimyristyl peroxydicarbonate initiators are investigated in a commercial PVC suspension polymerization recipe. Diethyl peroxydicarbonate, which is formed in situ by the reaction of hydrogen peroxide, lime, and ethylchloroformate, produced PVC with less "fish-eyes", whereas it has the disadvantage of being toxic and gives inconsistent polymerization times, therefore the reactor efficiency decreases. Dicetyl and dimyristyl peroxydicarbonates are solid, less toxic materials easy to handle, therefore, when these initiators are used, consistency between batches is obtained. However, PVC with coarse particles sizes containing considerable amounts of "fish-eyes" is obtained, which eventually causes processing problems. It is found that particle coarsening occurs as a result of water soluble impurities of initiators, and "fish-eyes" occur as a result of morphological changes. When dicetyl and dimyristyl type initiators are used, the number of non-porous PVC particles increases. This structure heterogeneity causes formation of ungellified spots, so-called "fish-eyes", during processing. It is found that the non-porous particles are formed due to accumulation of an excessive amount of initiator in a single vinyl chloride monomer droplet. When the distribution of these solid initiators is homogenized by adding them in solution, the formation of non-porous particles is inhibited. However, the coarsening effect still remains, which could be eliminated by extraction of initiator solutions with water just before they are fed to the reactor. Extraction also decreases the amount of crust formation.