Study of crystallization behavior of electron beam irradiated polypropylene and high-density polyethylene

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.