Investigation of the synergistic effects of UV radiation and elevated temperatures on regenerated cellulose fiber-reinforced bio-polyamide 5.10 composites

Abstract This study examines the thermo- and photo-oxidative degradation of bio-based polyamide 5.10, both neat and reinforced with 20 wt% regenerated cellulose fibers (RCF). The materials were additionally modified with two UV stabilizers: a hindered amine light stabilizer (HALS) and a UV absorber. Samples were stored for 168 h at 23 °C, 50 °C, 70 °C, and 90 °C under 50% rH, with and without 1000 W/m2 UV exposure. Pronounced degradation was observed in the neat and non-stabilized batches, including molecular chain splitting, embrittlement, surface polarity reduction, and yellowing. In contrast, HALS-containing formulations exhibited superior stabilization, retaining thermal, mechanical, and optical properties. RCF-reinforced PA5.10 showed moisture-induced plasticization at moderate conditions and embrittlement at higher temperatures. SEM analysis revealed increased fiber ruptures in UV-aged neat composites, whereas HALS-stabilized specimens maintained predominant fiber pull-out behavior. Melt volume rate testing confirmed molecular weight reduction due to oxidative degradation and a linear polynomial regression was used to demonstrate the characteristic degradation mechanisms. Overall, HALS provided effective protection against both thermal and photo-chemical aging across all storage conditions. These findings demonstrate the potential of HALS-stabilized, RCF-reinforced PA5.10 composites as sustainable alternatives to petro-chemical polyamides for applications demanding long-term resistance to combined thermo- and photo-oxidative stress.