Radiation-induced transformation of polypropylene morphology and visco-elastic behaviour

Isotactic polypropylene (iPP), irradiated by a Co-60 gamma source, has been investigated. A correlation between the shear rate and the physical and ch emical crosslinking density of the macromolecular chains at irradiation is given. The electron microscopy analysis (EMA), thermal-mechanical analysis (TMA), dynamo-mechanical analysis (DMA) and wide angle X-ray scattering sho w that a secondary radiation-induced crystallization is initiated at D = 7. 32 Mrad and new microcrystalline regions are created. They are built up of the straight parts of the macromolecular chains and are inhomogeneously dis tributed on the surfaces of the strongly stressed interlamellar and intersp herolitic spaces. The new microcrystalline regions have different effects o n the large-scale and small-scale operated modes of the micro-Brownian mobi lity. This determines the abnormal dose behaviour of the storage modulus, G ', thermo-mechanical curves, S(T), and X-ray crystallinity.