Chemical changes in irradiated polypropylene studied by X-ray photoabsorption and advanced EPR/ENDOR spectroscopies

Pulsed and Continuous-wave (CW) Electron Paramagnetic Resonance (EPR) in combination with X-ray absorption near edge structure (XANES) analysis is used to study the bulk and surface modification of isotactic polypropylene (i-PP) conducted by X-ray irradiation and O2, Ar and N2 plasma treatments. In all cases, a midchain peroxy radical is the major species detected by CW-EPR, with little delocalization onto the i-PP main chain, as revealed by X-band Mims electron nuclear double resonance and hyperfine sublevel correlation. Besides, surface functionalization of plasma treated i-PP is discussed on the light of XANES results with emphasis in the more complex case of N2 plasma modification. The article gives a comprehensive picture of the chemical changes that occur in irradiated i-PP, with implications in sterilization, surface activation, and adhesion enhancement procedures.