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• Thin samples exhibit a single hydrolytic mechanism throughout the material. • Thick samples show a surface and bulk hydrolytic mechanism. • Glass fibers enhance stability and protect composites from brittleness. • Sizing of glass fibers (GF) is affected by hydrolysis. • Cross-linking reactions occur for heavily degraded PA66 in the melt-state. In this work, we investigated the accelerated hydrolytic degradation behavior of unfilled polyamide 66 (PA66) and glass fiber (GF)-reinforced PA66 composites by use of thin injection molded samples. The primary goal of this study was to decrease the required evaluation time of GF-PA66 compounds for use in heating applications, targeting faster qualification of new or recycled materials and also addressing the critical factors of composite durability. According to the data, hydrolysis leads to a linear reduction in molar mass with time until reaching an equilibrium point of 10 kg/mol at 2500 h at 95 °C. The effect of thickness was significant: thin samples exhibited uniform bulk erosion, while thick samples experienced surface erosion with hydrolysis progressing inward to the core. Hydrolytic aging most significantly affected the PA66 matrix, while the glass fiber sizing was shown by X-ray Photoelectron Spectroscopy to be partially removed. The presence of glass fibers had a stabilizing role in the dimensional stability of the composites and limited embrittlement. Last, rheological analysis identified degradation mechanisms in the melt state, revealing that the primary process involved the recombination of fragmented chains and post-condensation reactions, leading to an increase in storage modulus. These findings highlight the need for additives to enhance interfacial adhesion between damaged GF and the polymer matrix, and reactive additives to suppress cross-linking and increase PA66 molar mass. These modifications are crucial for upgrading degraded materials for potential secondary applications, making recycling viable.
Gkaliou et al. (Sat,) studied this question.