Effect of zinc stearate and/or epoxidized soybean oil on gelation and thermal stability of PVC-DOP plastigels

Abstract

The effects of zinc stearate (ZnSt2) and/or epoxidized soybean oil (ESO) on mechanical properties and on thermal stability of plastigels obtained from polyvinylchloride (PVC) and dioctylphthalate (DOP) plastisols were studied using calorimetric, spectroscopic, and tensile-testing techniques. Plastigels having 2.5 or 5.0 part ZnSt2 and/or 5 part ESO and 60 part DOP per 100 part PVC (phr) were gelled by heating at 140°C. The tensile strength of plastigels with no additive and having 5 phr ZnSt2, ESO, and both ZnSt2 and ESO were 0.79, 0.46, 0.98, and 0.58 kN/cm2, respectively. The decrease of tensile strength of plastigels with ZnSt2 could be explained by the existence of ZnSt2 in the solid phase in plastigels, as shown by differential scanning calorimetry (DSC). ESO helped better fusion of the plastisols without any additive and with ZnSt2. Higher tensile strengths of ESO containing plates indicated more complete gelation of the plastisols. The thermal stability of plastigels in terms of color and their yellowness index (YI) were higher for ZnSt2 containing plastigels. Conjugated polyene concentrations were calculated from UV spectra of the films heated at 140°C. The reaction rate constant of the dehydrochlorination of PVC changed with the additives. Faster dehydrochlorination than control gels occurred in gels having ZnSt2 at long heating times due to the autoaccelerating effect of ZnCl2 formed by reaction of eliminated hydrogen chloride and ZnSt2. Organic acid formation reaction between ZnSt2 and HCl formed by dehydrochlorination is investigated from the IR band at 1540 cm−1 and 3400 cm−1 during heating of the plastigel films. A synergistic effect of ESO and ZnSt2 was observed when the mechanical strength and heat stability were considered together. Although ESO increased tensile strength, ZnSt2 increased thermal stability of the plastigels at early times when they were present simultaneously in plastisols. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2488–2498, 1999