Effect of thermal stabilizers composed of zinc barbiturate and calcium stearate for rigid poly(vinyl chloride)

Zinc barbiturate [Zn(H 2 L) 2 ·2H 2 O, abbreviated as ZnL 2 ] was synthesized by a precipitation method in aqueous solution, and investigated as a co-stabilizer with calcium stearate (CaSt 2 ) for rigid poly(vinyl chloride) (PVC) by the discoloration test and the dehydrochlorination test at 180 °C. ZnL 2 exhibits high stabilizing effect with excellent initial colour of PVC films. In comparison with the synergistic effect of CaSt 2 /ZnSt 2 stabilizers, the CaSt 2 /ZnL 2 stabilizers in mass ratios ranging from 0.3/1.2 to 0.6/0.9 exhibit better synergistic effect. Moreover, PVC films stabilized by CaSt 2 /ZnL 2 show better initial colour with the addition of dibenzoyl methane as an auxiliary stabilizer . The mechanism of stabilizing action of ZnL 2 is also proposed. ZnL 2 may replace the labile chlorine atoms to interrupt the formation of conjugated double bonds in PVC chains, and act as the absorber of hydrogen chloride to restrain the self-catalytic dehydrochlorination.