Effect of Compounded Fiber Length Dispersion on the Mechanical Property, Rheology, and Crystallization of Glass Fiber Reinforced Polypropylene Composites Under Thermal‐Oxidative Aging

In this work, the long glass fiber (LGF) with compounded fiber length reinforced polypropylene (PP) composites were prepared by melt compounding and blending. The influence of thermal‐oxidative aging on the mechanical property, rheology, and crystallization behaviors of PP/LGF composites was investigated systematically. The effect of aging at 120°C for 50 days on the static mechanical properties is very slight, including a lower than 10% variation in tensile and bending strength. The fracture morphology displays that some fiber interfaces have undergone debonding, which is the reason for the decrease in dynamic mechanical properties. The samples with longer/shorter compounded fibers exhibit a smoother variation trend in damping and viscosity with aging time compared with the composites with only a single fiber length. Due to the post‐curing effect caused by crosslinking during aging, the crystallinity of PP in the composites shows an increasing trend after 50 days of aging compared with the unaged sample. The tensile, blending, and impact strengths of PP composites with compound fiber lengths of 3/12 mm aged at 120°C for 50 days are 90.6 MPa, 117.7 MPa, and 18.8 kJ/m 2 , respectively. In addition, under the same average fiber length, the 3/12 mm fiber‐reinforced PP composites show the best comprehensive mechanical properties through the preferential shearing effect.