Thermal dehydrochlorination and stabilization of poly(vinyl chloride) in solution: Part III—Zn-Ca stearates as stabilizers

Abstract

The thermal degradation of poly(vinyl chloride) (PVC) in trichlorobenzene (TCB) solution at 187°C has been studied in the presence of various mixtures of zinc and calcium stearates, using coulometric titration of chloride ions, HCl evolution measurements and spectroscopic analysis (FTIR and UV) of the degraded polymer at various times. The substitution reaction, initially suggested by Frye and Horst 1,2 is clearly demonstrated, although the very small amount of stearate groups involved with respect to the number of vinyl chloride units makes it difficult and requires the use of high performance equipment and careful recording conditions. Many of the known features of the stabilization of PVC with mixed metal soaps are also observed. In addition, a transient complex between the metal stearates is observed which cannot be separated from the polymer because it shows the same solubility behavior. Evidence for secondary reactions between metal chlorides and stearic acid is given. Finally, the rates of the processes are very dependent on the amounts of structural defects in the initial polymer.