The influence of e-beam irradiation on polypropylene (PP) and high-density polyethylene (HDPE) was investigated with the focus on crystallization. High temperature (200°C) creep test has revealed that HDPE gradually increases crosslinking density in the range 30-120 kGy while PP undergoes chain scission which was quantitatively evaluated by GPC. Mechanical properties were measured in the range -150 to 200°C by dynamic mechanical analysis (DMA). Small presence of C=C and C=O bonds was found in the irradiated PP by Fourier transform infrared spectroscopy (FTIR). Crystallization kinetics measured by differential scanning calorimetry (DSC) and hot-stage optical microscopy results were influenced by irradiation tremendously for HDPE and to a smaller extent for PP. Irradiation has caused a decrease in both, the number of nucleation centers and the growth rate of individual spherulites. Crystallization was analyzed in detail with the help of Hoffman-Lauritzen, Avrami and Arrhenius equations. Interestingly, increasing β-crystal formation with increasing irradiation level was discovered for PP by X-ray diffraction (XRD). Generation of defects in crystalline structure due to irradiation is discussed.

DSC; WAXD; SAXS; optical microscopy; FTIR; DMA