A STUDY OF TEXTURES OF POLYETHYLENE POLYMERIZED BY γ-RAY IRRADIATION IN GAS PHASE

Textures of polyethylene polymerized by γ-ray irradiation in gas phase were studied by electron microscopy, thermal analysis, X-ray analysis including the effects of annealing and the fuming nitric acid treatment.Electron microscopy revealed that the as-polymerized polyethylene consisted of irregular aggregation of ill-defined lamellae. Fibrillar network was occasionaly observed but these are considered as resulted by some mechanical action during or after the polymerization.DTA thermograms and the peak temperature also suggest that the crystals formed are unstable showing rather low peak temperature (120.4°C_??_125.2°C) and that the lower the polymerization temperature, the more unstable. The effect of the fuming nitric acid treatment (for instance, weight loss) is bigger for the product of polymerization at lower temperature. As the branch content was higher for the product at higher temperature, on the other hand, the X-ray crystallinity and the peak temperature were lower for the product at higher temperature.The residue of the fuming nitric acid treatment showed, however, higher crystallinities than the original samples and the crstallinity and melting temperature of the etched crystals of the higher temperature product became higher than that of the lower temperature product. Moreover annealing of the 30°C product give rise to much bigger increased crystallinity (as revealed by the weight loss due to the etching) than that of 90°C product. The size of the individual lamellar crystals as revealed by a X-ray method seems bigger for high temperature product. All the above results imply that the as-polymerized products are composed of irregular lamellar which are rather unstable against the heat and the attack of the chemical agent and that such features are more pronounced for the lower temperature product. The effects of the branching (i. e. the increase in the branch content with polymerization temperature) of the poymerization temperature are opposed by those of the crystallization (polymerization) temperature.