Dynamic-mechanical analysis of the photo-degradation of long glass fibre reinforced polypropylene: Mechanical properties' changes

Polypropylene matrix composites, with different degrees of reinforcement with long glass fibres, are employed in different fields of the industry, such as aeronautics or automotive. Samples of the material were exposed to artificial accelerated photo-ageing in UV chamber (Heraeus Xenotest 150S). Their high content of glass fibres causes a surface degradation that can seriously affect mechanical properties. Therefore, dynamic mechanical and tensile tests were carried out in order to compare the changes of the properties with exposure time. These modifications are accompanied with microscopic changes in the crystallinity as can be seen in the thermal analysis experiments.     

Radiation aging and chemi-crystallization processes in polyoxymethylene

The radiochemical degradation of a polyoxymethylene homopolymer (POM) was used to study the effects of molar mass changes in the crystalline structure. The dose rate was 20 kGy h⁻¹ with doses of up to 30 kGy used. Both WAXS and SAXS were used to analyse the structures. Results showed that, under irradiation, the polymer undergoes random chain scission. The radiochemical yield was found to be G = 1.6 chain scission events per 100 eV. It was found that no crosslinking occurs and that only one chain scission mechanism, leading to the formation of formate groups, operates. Proof for the existence of chemi-crystallization is evidenced by (i) an increase in the crystallinity ratio as well as (ii) a decrease in the amorphous layer thickness. Simple models, derived from Rault’s theory, are used to predict both (i) and (ii) from molar mass values.