EFFECT OF γ-RAY IRRADIATION ON POLYVINYL CHLORIDE FIBERS (I)

Abstract

To examine the effects of γ-ray irradiation on the physical properties of polyvinyl chloride (PVC) fibers, their densities, breaking strengths, breaking elongations, viscosities and thermal shrinkages were measured for samples, subjected in vacuum to the γ-ray radiation from cobalt 60 source at room temperature. The radiation doses were ranged from 0 to 3×107r.The breaking strength decreases with increasing dosage, but the detectable irradiation effects are found neither in densities nor in breaking elongations.The degrees of polymerization estimated from viscosity measurements decreased with irradiation at lower dosages, while they showed a tendency to rise at higher dosages again.The irradiation effects on the thermal shrinkage (percent shrinkage versus temperature curve) markedly become visible only at the higher temperature range. Both the unirradiated and the low irradiated specimens are ultimately broken due to the flow of the molecular chains accelerated with rising temperature, after showing the maximum contraction at about their melting temperature (180_??_190°C).The higher the radiation dosage, the more the flow of the molecular chains becomes remarkable from lower temperature, corresponding to the chain scission due to irradiation, while for the drastically irradiated specimens in our experiments, the flow stops at about 260°C and at the same time the shrinkage of the fibers begins to appear again.These characteristic behaviours may be explained by the facts that the radiation-induced radicals, which are relatively stable at room temperature, become reactive at higher temperature range and take part in the cross-linking reaction effectively.