The Mechanical Properties of Pine Needle Fiber‐Reinforced Polymer Composites Under Different Environments

ABSTRACT This study investigated the mechanical and tribological properties of NaOH‐treated pine needle fiber‐reinforced epoxy composites (PNFREC) under various environmental conditions, including exposure to water, kerosene, and petrol. Pine needles from Himalayan forests were treated with a 10% NaOH solution to enhance their hydrophobicity and fiber‐matrix adhesion. Composites were fabricated using a hand lay‐up method with 30 wt. % bidirectional pine needle fiber mats and an epoxy matrix (LY‐556 resin and HY‐951 hardener). Water absorption tests revealed an average uptake of 3.22% ± 3.47% after 168 h, which is significantly lower than that of untreated composites. Mechanical testing under ambient conditions showed a 28.6% increase in tensile strength (45 MPa), a 27.3% improvement in flexural strength (70 MPa), a 66.7% enhancement in impact strength (25 kJ/m 2 ), and a 9.3% increase in Shore hardness (82 Shore D) compared to neat epoxy. Water exposure caused the most significant degradation, with a 15.6% reduction in tensile strength, a 17.1% decrease in flexural strength, a 20% drop in impact strength, and a 7.3% decline in Shore hardness, owing to interfacial weakening and matrix plasticization. Kerosene and petrol exposure led to minor reductions in mechanical properties due to limited matrix swelling and interfacial degradation. Tribological analysis revealed a 28.6% reduction in the specific wear rate (2.5 × 10 −5 mm 3 /N·m) under ambient conditions, which was attributed to the protective effect of the pine needle fibers. Water exposure increased the wear rate by 60% (4.0 × 10 −5 mm 3 /N·m) due to abrasive wear, whereas kerosene and petrol reduced the wear rate by 28% and 12%, respectively, through lubrication. Scanning electron microscopy (SEM) analysis correlated the mechanical and tribological performance with the microstructural features, revealing fiber‐matrix debonding, matrix cracking, and wear mechanisms. The results highlight the potential of PNFREC for sustainable structural applications, particularly in hydrocarbon environments, while addressing the challenges of moisture‐induced degradation.