The effect of alkalization on the mechanical and water absorption properties of nonwoven kenaf fiber/unsaturated polyester composites produced by resin‐transfer molding

In the present study, mechanical and water absorption properties of the nonwoven kenaf fiber (KF)/unsaturated‐polyester composites manufactured by resin transfer molding were investigated. Nonwoven KF mats with an aerial density of 1350 g/m² were treated with a 6% NaOH solution for 3 h. The influence of the fiber treatment on the properties of the composites was investigated with Fourier transform‐infra red (FTIR), X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscope (AFM), and dynamic contact angle technique (DCAT). Mechanical properties measurements were conducted via determination of flexure and fracture toughness. A general trend was observed whereby alkalized KF composites gave superior mechanical properties compared to as‐received KF composites. The XRD and DCAT results indicated an enhancement of the crystallinity index and surface energy of the alkali‐treated KF. SEM and AFM of the treated KF showed the removal of impurities and a reduction of roughness on the KF surface with alkalization. Water immersion induced a drastic loss of the mechanical properties of the composites albeit better retention of properties was observed in the case of alkalized KF composites. The fracture surfaces were inspected by SEM which confirmed the quality of the interface. POLYM. COMPOS., 37:3516–3526, 2016. © 2015 Society of Plastics Engineers