Localization of oxidation in polypropylene

Accelerated weathering of unbleached and bleached Kraft wood fibre reinforced polypropylene composites

“…The degree of crystallinity of virgin PP is 38.8%. Therefore, a large fraction of the material is in the noncrystalline state, which allows a degree of permeability of oxygen to allow the photo-oxidation process to take place [14,15,38]. Since the glass transition temperature of PP (À10 C) [39] is below the exposure temperature (50 C), the freed segments in the amorphous region would have sufficient mobility to rearrange into a crystalline phase, which would explain the crystallinity index increasing from 38.8% for virgin PP to 40.9% after weathering for 1000 h [40].…”

Improved thermal oxidation stability of polypropylene films in the presence of β-nucleating agent

“…When PP exposure to a high temperature or an irradiation environment, the tertiary hydrogen atoms present in PP chains are susceptible to attack by oxygen [9]. Oxidative degradation of PP may occur during melt processing, storage and in-service, which would result in a remarkable deterioration in the mechanical properties and surface appearance of materials.…”

Review on the thermo-oxidative degradation of polymers during processing and in service

“…He showed that treatment of at 50 and 70 0 C oxidized PP films with SO 2 resulted in dark visible spots. Heterogeneity on a microscopic scale was shown by Billingham [49,50], UVmicroscopic pictures of oxidized PP (2 hours at 100 and 120 0 C) treated with DNPH (di-nitro-phenyl-hydrazine) revealed micron size oxidized spots. Similar results were obtained for an extruded PP pellet [49,51].…”

“…The origin of this heterogeneity is still under debate. Knight et al [50] attributed the heterogeneity of the oxidation of PP to local concentrations of polymerization catalyst residues. The fact that catalyst residues such as Ti can play an important role in the oxidation of PP has been described in several other publications [53][54][55][56][57].…”