FTIR spectroscopy study of polyamide-6 irradiated by electron and proton beams

Polyamide-6 (PA-6) irradiated by a 500 kGy electron beam (EB) dose or by 500 and 1000 kGy proton beam (PB) doses was examined by FTIR spectroscopy, crosslinked portion determination, DSC and tensile properties measurements. When using the same dose (500 kGy), the decrease in both melting temperature and crystallinity is similar for both radiation types; however, the EB generates more gel than the PB. According to FTIR spectra, irradiation by PB leads to more extensive structural changes; this result is assigned to the larger proton dimension compared to the electron. The PB results in attacking original crystalline phase, generation of unsaturated structures in ethylene sequences, a splitting of macromolecules into fragments that contain amine groups and terminal methyl moieties unlike the EB where similar effects were not observable. Consequently, PB irradiation results in less pronounced growth of Young modulus and strength as well as higher elongation compared to EB. FTIR analysis of both PA-6 irradiated by the PB applying dose of 1000 kGy and gel isolated from it showed that beside amorphous phase, the gel fraction contains also mixed crystalline phase, however, a small amount of crystalline phase with fully planar conformation is also present. The results indicate that the gel crystalline phase in the gel contains also a new component that originates from shorter macromolecule fragments generated by the PB radiation.