Effect of thermal aging on the long‐term dynamic and stress relaxation behavior of glass‐fiber reinforced polypropylene composites

Abstract The increasing use of glass‐fiber reinforced polypropylene (GFPP) composites in a wide range of applications requiring long‐term service in challenging environments underscores the importance of its long‐term durability. This study aimed to investigate the effect of thermal aging on the long‐term dynamic durability and stress relaxation of GFPP composites. The time–temperature equivalence principle (TTSP) was used to assess the dynamic modulus at various temperatures and frequencies, as well as the relaxation modulus at different temperatures and relaxation times. To better understand long‐term durability behavior, the study also examined the impact of molecular structure on the durability of GFPP. Changes in chemical composition, crystallinity, melting point, and melt flow index of GFPP due to thermal aging were measured and analyzed using Fourier transform infrared spectroscopy, and differential scanning calorimetry, respectively. The results revealed that oxidation led to a decrease in the crystallinity and molecular weight of GFPP. The destruction of GFPP's molecular structure due to oxidation resulted in reduced long‐term durability. While TTSP can predict the long‐term durability of GFPP for decades or even centuries, its application in predicting the long‐term durability of GFPP is more suitable for nonaging conditions. Highlights Thermal aging reduces glass‐fiber reinforced polypropylene (GFPP's) long‐term durability. Time–temperature equivalence principle predicts GFPP durability under aging. GFPP's activation energy drops with thermal aging. Long‐term GFPP behavior aligns with Williams–Landel–Ferry model. Predictive models refine understanding of GFPP longevity.