Thermal and Hydrothermal Aging Effects on the Mechanical Performance of Unidirectional Glass Fiber-Reinforced Thermoplastic Composite Tapes

Unidirectional fiber-reinforced thermoplastic composite (FRTC) tapes combine continuous-fiber load carrying with the toughness and processability of thermoplastics. However, their durability under thermal and aqueous exposure remains a concern. This study evaluated the aging response of glass fiber-reinforced polypropylene (GF-PP) and polyethylene (GF-PE) tapes subjected to dry thermal aging and distilled-water (DW) immersion at 95 °C for up to 4 weeks. Longitudinal tensile properties (ASTM D3039) and water uptake (ASTM D5229M) were measured. The GF-PP tape exhibited a higher saturation water absorption (0.530%) and apparent diffusion coefficient (20.4×10-14 m2/s) than the GF-PE tape (0.206% and 9.63×10-14m2/s, respectively). After 4 weeks of dry thermal aging, GF-PP and GF-PE retained 91.5% and 81.2% of their tensile strength, compared with 68.7% and 51.0% after hydrothermal aging. Although GF-PE absorbed less water than GF-PP, it exhibited greater mechanical degradation, indicating that water uptake alone does not govern tensile durability. The results suggest that dry thermal aging primarily promotes fiber-matrix weakening and reduces stress-transfer efficiency, whereas hydrothermal aging accelerates matrix plasticization, interfacial deterioration, debonding, and progressive damage accumulation. These findings demonstrate that the durability of FRTC tapes depends on the combined effects of temperature, moisture transport, matrix type, and fiber-matrix load-transfer efficiency.