The results were similar to Pandian et al. While the results of flexural strength of the immersion in acidic solution exhibited the largest reduction, are indicated for first, second, and third are 12.1%, 18.9%, and 29.0%, respectively. Followed by the flexural strength for the immersion in distilled water, the results were indicated for the first, second, and third weeks by 3.7%, 6.4%, and 16.2%, respectively. 5.11 shows the reduction of the flexural strength after the immersion in the sea water, distilled water, and acidic solutions. The results of flexural strength for the immersion in sea water, which indicated the lowest reduction, were decreased from first, second, and third weeks by 1.2%, 4.1%, and 10.3%, respectively. The phenomenon was supported by Yan and Chouw (2015), the degradation of water on cellulose and hemicellulose (the stiffness part of the natural fiber) reduces the stiffness of the natural fiber composites which further degrades the fiber and matrix interfacial bonding. Poor adhesion between fiber and matrix is caused by degradation of water during the immersion. While, the results of tensile moduli of the immersion in acidic solution exhibited the largest reduction, which are indicated for first, second, and third are 15.4%, 31.9%, and 38.1%, respectively. Followed by the immersion in distilled water, which indicated for first, second, and third are 7.2%, 11.1%, and 12.6%, respectively. The reduction of tensile moduli of the immersion in sea water is less, which indicated for first, second, and third are 1.9%, 3.3%, and 4.2%, respectively. The reduction of the moduli of the pultruded kenaf composites is clear after immersed for 3 weeks. 5.10 shows the effect of the immersion in sea water, distilled water, and acidic solution on the tensile modulus of pultruded kenaf composites. Hence, the increment time of the pultruded kenaf composites immersed in the solution increased the degradation of the composites.įig. (2015), the factors that increase the diffusion of water in the composites are the number of voids, interfacial bonding strength, and properties of the reinforced material. The possible reason is that the distilled water would lead further dispersion of water to the kenaf fiber and matrix interface, which thusly encourages to quicken the fiber and matrix debonding. The specimen immersed in sea water had the smallest reduction. The decrement in tensile strength of pultruded kenaf composites immersion in acidic solutions for 3 weeks is 43.1% from 148.5 to 84.5 MPa. The decrement in tensile strength of pultruded kenaf composites immersion in distilled water for 3 weeks is 12.6% from 148.5 to 142.2 MPa. 5.9 shows the effect of the immersion in sea water, distilled water and acidic solutions on the tensile properties of pultruded kenaf composites. The decrement in tensile strength of pultruded kenaf composites immersion in sea water for 3 weeks is 4.2% from 148.5 to 129.8 MPa. The morphological analysis from the micrographs of the composites were observed at a magnification of 50 and 100 µm using Hitachi S-3400N variable pressure SEM equipment with accelerating voltage of 15 kV carried out at Chemical Laboratory, Department of Chemical Engineering, Faculty of Engineering, University Putra Malaysia Selangor, Malaysia. In the observation of failure structure of the kenaf pultruded composites with the immersion effect in various solutions, the specimens were cut into 5 mm (height of rod). The sample size 10 mm diameter was tested with 21.6 J hammer sized. Energy losses caused by bearing friction and air resistance were disregarded due to their small contribution to the energy balance ( Hufenbach et al., 2008). The samples were cut at 160 mm with the span length 140 mm. Impact test was performed according to Hufenbach et al. The sample length was 120 mm and span length was 100 mm. Three point bending tests were performed according to ASTM D4475-96 standard (2003) at room temperature using a 5 kN Instron 4201 universal testing machine with the crosshead speed of 1.3 mm/min. The sample length was 250 mm and the crosshead movement speed was 5 mm/min. The tests were carried out at room temperature following the testing method for tensile pultruded glass fiber reinforced plastic rod (ASTM D 3916-02 (2002)). The tensile test was carried out using 100 kN Instron 3382 universal testing machine. The kenaf pultruded composite with a diameter of 10 mm were produced using the Pultrex pultrusion machine with maximum pulling capacity of 6 tons. Vinyl ester resin (Swancor 901) was purchased from Formalchem Sdn Bhd. Sahari, in Natural Fibre Reinforced Vinyl Ester and Vinyl Polymer Composites, 2018 5.4 The effect of immersion in various solutions on mechanical properties of pultruded kenaf reinforced vinyl ester composites 5.4.1 Pultruded kenaf composites preparation