MeV energy electron beam induced damage in isotactic polypropylene

A few thin films of isotactic polypropylene were irradiated with 6 MeV energy electrons, in the fluence range from 5 × 1014 to 2 × 1015 electrons/cm2. The structural, optical and mechanical properties were characterized by techniques such as FTIR, UV–vis, XRD, SEM, hardness and contact angle measurements. The FTIR spectra indicate that C–H and C–C bonds are scissioned and an isotactic arrangement of chains is partially destroyed. Moreover, the new carbonyl groups (C=O) are observed, which signifies oxidation. The UV–vis spectra shows a red shift in the absorption edge from pristine value of 240 to 380 nm, which corresponds to decrease in the optical band gap from 5.17 to 3.27 eV. This is because of the formation of conjugated double bonds as well as carbonization. The crystalline properties were analysed using XRD and it shows no profound change. This result may attribute that the radiation-induced changes have probably occurred to a large extent in amorphous regions. However, surface morphology by SEM and contact angle measurements showed considerable surface roughening, which indicates an uneven evolution of gases from the surface. Interestingly, the surface hardness of the films was found to increase with fluence and it may be due to crosslinking and carbonization on the surface. Overall, in conclusion this study shows considerable modifications in the physicochemical properties of isotactic polypropylene irradiated by 6 MeV energy pulsed electrons.