Durability of alkali and heat‐treated kenaf fiber/unsaturated polyester composite fabricated by resin transfer molding under natural weathering exposure

Nonwoven kenaf fiber (KF) mat‐reinforced unsaturated polyester resin composites were exposed to a natural weathering environment for 12 months. The composites were prepared using vacuum‐assisted resin transfer molding (RTM). Prior to molding, the KF mat was treated by immersing it in 6% NaOH solution for 3 hrs and by heating it at 140°C for 10 hrs, respectively. The influences of weathering exposure on the composites with respect to the different treatments were investigated using flexural properties, fracture toughness, Fourier transform infrared, thermal stability, color and scanning electron microscopy analyses. Natural weathering reduced the flexural and fracture toughness due to damage to composite structures, the formation of microcracks on the sample surface, discoloration, and chemical content alteration. A relatively better durability in terms of flexural properties was exhibited by alkali‐treated KF composites, although poor durability in fracture toughness was observed due to the improved fiber–matrix adhesion.