eXPRESS Polymer Letters (Jan 2008)
Stabilizing effect of epoxidized sunflower oil as a secondary stabilizer for Ca/Hg stabilized PVC
Abstract
Unsaturated triglyceride oil sunflower was epoxidized and characterized by chemical and spectroscopic methods. Epoxidized sunflower oil (ESO) was used as an organic thermal co-stabilizer for rigid poly(vinyl chloride) (PVC) in the presence of tricalcium dicitrate (Ca3(C6H5O7)2) and mercury (II) acetate (Hg(CH3COO)2). The thermo-oxidative degradation of PVC was studied in the presence of these ternary stabilizer systems at 170, 180, 190 and 200°C in N2 atmosphere. The effects of metal carboxylate combination Ca/Hg in the absence and in the presence of epoxidized sunflower oil on static heat treatment of PVC have been studied. The formation of polyene sequences was investigated by UV-visible and FT-IR spectroscopy and by comparing viscosity data obtained in the presence and in the absence of the additives. It was found that the additives retard the rate of degradation and reduce the extent of polymer chain scission associated with the thermal degradation of poly(vinyl chloride). Synergistic effects were found when stabilizer was blended in 50:50 weight ratios with either. It was found that ESO exerted a stabilizing effect on the degradation of PVC. The activation energy for degraded PVC in absence of stabilizers was 38.6 kJ•mol–1 and in the presence of Ca/Hg and Ca/Hg/ESO were 53.3 and 64.7 kJ•mol–1 respectively. In order of compare the efficiency of the epoxidized sunflower oil with these metal soap stabilizers, thermal stabilities were evaluated on the basis of evolved hydrogen chloride determined by conductometry technique and degree of discoloration are discussed.
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