Effect of shear condition on the thermal stabilization of ethylene-propylene-carbon monoxide terpolymer

The thermal decomposition behavior of the terpolymer of ethylene, propylene, and carbon monoxide (EPCO), stabilized by calcium hydroxyapatite (CHA) as an acid scavenger and 2,2′-oxamidobis-[ethyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] (OHP) as a radical scavenger, was investigated in terms of shear, temperature and stabilizer composition. The optimum composition of two stabilizers was affected by shear condition as well as thermal history. The thermal stability at the static state evaluated by DSC indicated that the simultaneous use of CHA and OHP produced a synergistic effect and the optimum composition of CHA/OHP ranged from 4/1 to 8/1 by wt at the total content of 0.5 wt%. However, dynamic rheological analysis revealed that shearing changed the optimum composition of the stabilizers to 7/1 by wt but had little effect on the total stabilizer content. In addition, the synergistic effect was not observed at the particular composition of 1/4 by wt. The increase of melt viscosity of EPCO with time ascertained that the thermal decomposition of EPCO accompanied crosslinking through the intermolecular aldol condensation reaction.