With regard to the sustainability and biological origin of plastic components, regenerated cellulose fiber (RCF)-reinforced polymers are expected to replace other composites in the future. For use under severe conditions, for example, as a housing in the engine compartment, the resistance of the composites and the impact on the fiber and fiber-matrix adhesion must be investigated. Composites of bio-polyamide with a reinforcement of 20 wt.% RCF were compounded using a twin-screw extruder. The test specimens were manufactured with an injection molding machine and aged under conditions of high humidity at 90% r. H, a high temperature of 70 °C, and water storage using a water temperature of 23 °C for 504 h. Mechanical tests, single-fiber tensile tests (SFTT), single-fibre pull-out tests (SFPT), and optical characterization revealed significant changes in the properties of the composites. The results of the SFPT show that accelerated aging had a significant effect on the bio-polymer and an even stronger effect on the fiber, as the single-fiber tensile strength decreased by 27.5%. Supplementary notched impact strength tests revealed a correlation of the impact strength and the accelerated aging of the RCF-reinforced composites. In addition, it could be verified that the tensile strength also decreased at about 37% due to the aging effect on the RCF and a lowered fiber-matrix adhesion. The largest aging impact was on the Young’s modulus with a decrease of 45% due to the accelerated aging. In summary, the results show that the strengthening effect with 20 wt.% RCF was highly decreased subsequent to the accelerated aging due to hydrolysis and debonding because of the shrinkage and swelling of the matrix and fiber. These scientific findings are essential, as it is important to ensure that this bio-based material used in the automotive sector can withstand these stresses without severe degradation. This study provides information about the aging behavior of RCF-reinforced bio-based polyamide, which provides fundamental insights for future research.

Bio-based polyamides (PA) represent an emerging class of engineering biopolymers that combine high performance with renewable origins. In particular, PA5.10, derived from renewable monomers, offers an attractive alternative to petroleum-based matrices in sustainable composite applications. To advance the understanding of its environmental stability, this study explores the chemical resistance and degradation pathways of neat PA5.10 and regenerated cellulose fiber (RCF)-reinforced PA5.10 (20 wt%). Standardized specimens were prepared by twin-screw extrusion and injection molding and subsequently exposed to aqueous, acidic, alkaline, and organic environments for up to 168 h. Characterization included tensile testing, Fourier-transform infrared spectroscopy (FTIR), melt volume rate (MVR), moisture uptake, and scanning electron microscopy (SEM). Hydrolytic and chemical aging caused chain splitting processes, fiber swelling, and fiber-matrix debonding, as evidenced by viscosity reduction, altered FTIR spectra, and mechanical deterioration. The composites exhibited pronounced sensitivity in acidic and alkaline media, with moisture uptake further reducing tensile strength and modulus. These findings provide new insights into the chemical stability of bio-based polyamides and highlight key challenges for their long-term use in sustainable composite applications. Addressing these limitations through targeted material design will be essential to expand the application range of RCF-reinforced bio-based polyamides in automotive and engineering sectors.

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/m ² 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.