Abstract
In order to delay the undesirable discoloration of poly(vinyl chloride) (PVC) by heating, the synergetic effect of poly(vinyl alcohol) (PVA) as co-stabilizer with a mixture of zinc and calcium stearates was clarified. Usually, the abrupt discoloration was caused by the formation of a π-complex between the cool colour-producing metal chloride, i.e. the zinc chloride from the metal soap, and double bonds from the dehydrochlorination of the PVC chain. Firstly, the effect of using various PVA having different degrees of polymerization before melt blending with PVC was investigated. When the PVA and PVC were pre-mixed in the powder state, the compound obtained showed a lower stabilization effect on the discoloration of PVC. On the other hand, when a PVA aqueous solution was prepared and the PVC powder was added to the PVA solution, and dried, the resulting compound showed an excellent stabilization effect. Secondly, the dispersed PVA domain size in the PVC sheets was measured quantitatively by image processing analysis, using the optical micrographs of the sheets. As a result, it was found that there was a good relationship between the dispersibility of PVA and its stabilization effect. That is, the co-stabilizing effect of PVA increased with a decrease in the domain size. This fact was also confirmed by using different polyols as co-stabilizer.