Abstract
The influence of electron-beam irradiation on polypropylene (PP) and high-density polyethylene (HDPE) was investigated with a focus on crystallization. A high-temperature (200°C) creep test revealed that the HDPE gradually increased cross-linking density in the range 30–120 kGy, while the PP underwent a chain scission which was quantitatively evaluated by gel permeation chromatography. The mechanical properties were measured in the range -150 to 200°C by a dynamic mechanical analysis. A small presence of C=C and C=O bonds was found in the irradiated PP by a Fourier transform infrared spectroscopy. Crystallization kinetics measured by differential scanning calorimetry and hot-stage optical microscopy results were influenced tremendously by irradiation for HDPE and to a lesser extent for PP. Irradiation caused a decrease in both the number of nucleation centres and the growth rate of individual spherulites. Crystallization was analysed in detail with the help of Hoffman–Lauritzen, Avrami and Arrhenius equations. Interestingly an increasing β-crystal formation with an increasing irradiation level was discovered for PP by X-ray diffraction. A generation of defects in the crystalline structure owing to irradiation was discussed.
Highlights
Polypropylene (PP) and polyethylene (PE) are the most widely used polymer materials in pure form and modified in various ways royalsocietypublishing.org/journal/rsos R
The high-temperature (200°C) creep test confirmed that e-beam radiation causes cross-linking in high-density polyethylene (HDPE) and chain scission in PP
Fourier transform infrared (FTIR) has pointed out the presence of C=C and C=O bonds in PP after irradiation
Summary
Polypropylene (PP) and polyethylene (PE) are the most widely used polymer materials in pure form and modified in various ways royalsocietypublishing.org/journal/rsos R. The main reactions during the irradiation process are chain scission, chain branching and cross-linking. All these reactions coexist and it is important to have detailed knowledge of the influence of the radiation level on the property change [4]. In order to predict the behaviour of carbonchain polymers exposed to ionizing radiation, an empirical rule can be used According to this rule, polymers containing a hydrogen atom at each carbon atom predominantly undergo cross-linking, whereas in the polymers containing a quaternary carbon atom, that is the unit -CH2-CR1R2CH2-, where R1 and R2 are groups other than H, the chain scission predominates [5]. A disproportionation or recombination reactions of two polymer radicals occur which leads to increased molecular weight
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