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 chemical 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 show 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 distributed on the surfaces of the strongly stressed interlamellar and interspherolitic spaces. The new microcrystalline regions have different effects on the large-scale and small-scale operated modes of the micro-Brownian mobility. This determines the abnormal dose behaviour of the storage modulus, G', thermo-mechanical curves, S(T), and X-ray crystallinity.