THERMAL DEGRADATION OF POLY(VINYL CHLORIDE)/POLYSTYRENE BLENDS IN THE PRESENCE OF DERIVATIVES OF Hura crepitans SEED OIl.

Abstract

Poly(vinyl chloride) (PVC) is a versatile polymer that has found applications in various sphere of our daily life. However, it is intrinsically unstable at elevated temperatures usually employed in processing it into useful articles. The thermal stability of poly(vinyl chloride) (PVC) has been reported to improve in a blend with polystyrene (PS) and compatibility of the polymers was a factor which influenced the stabilization process. There has been no report of thermal stability of PVC/PS blends in the presence metal soap of seed oil. In this study, the thermal degradation of poly(vinyl chloride)/polystyrene (PVC/PS) blends in the absence and presence of metal soaps of Hura crepitans seed oil (HCSO) has been investigated in air and under nitrogen atmosphere. Metal soaps of Hura crepitans seed oil; Al, Ba, Ca, Mg and Zn were prepared by precipitation method involving metathesis in alcohol. Kinetics of thermal degradation of PVC and the blends were carried out titrimetrically in the temperature range 170-190 oC under nitrogen atmosphere. The interaction of the additives with PVC was studied with FTIR spectrophotometer while the melt properties of PVC and the blends were determined using differential scanning calorimeter. The thermal stability study of the polymer and the blends was carried with thermogravimetric analyzer under nitrogen and air atmospheres. In the absence of metal soaps, the kinetics of thermal degradation of PVC in PVC/PS blends, 95/5, and 90/10 ratios, measured titrimetrically under nitrogen atmosphere in the temperature range 170- 190 oC, was determined by the rates of dehydrochlorination of the polymer. The rates of dehydrochlorination were of the order, 10-2 %min-1 and showed stabilization of PVC by PS in the blends. Specifically, at 190 oC, the rates of dehydrochlorination of PVC under nitrogen atmosphere were reduced by 23.7 and 11.2% for the 95/5 and 90/10 blends respectively with calculated activation energy of 50.7kJ mol-1for the process. In the presence of HCSO soaps of Al, Ba, Ca, Mg and Zn, there were marked reductions in stabilization of PVC by PS and were associated with increased polarity of the blends. Miscibility of the blends was enhanced by the soaps, as was evident from FTIR and DSC analyses, showing from the latter, single Tgs of 98.2 and 96.2 oC for 95/5 and 90/10 blends respectively. The enhanced stability of PVC in the blends by PS and reduced stability of the polymer in the presence of metal soaps were confirmed by thermogravimetry. PS enhanced thermal stability of PVC in PVC/PS blends while the presence of metal soaps of Hura crepitans seed oil in PVC/PS blends is antithetical to thermal stability of PVC.