Effect of Fiber Loading on the Mechanical Properties of Kenaf and Fiberfrax Fiber-reinforced Phenol-Formaldehyde Composites

Abstract

In this study, mechanical properties such as tensile characteristics, flexural characteristics, impact strengths, and hardness of kenaf/phenol-formaldehyde (PF), fiberfrax/PF, and kenaf/fiberfrax hybrid PF composites have been investigated as a function of fiber loading. Composite samples were prepared by mixing the fibers and resin in a mixing chamber for 5 min. The composite sheets were prepared by pressing fiber-resin material in a steel mold at 120°C for 30 min at 10 MPa pressure. The test samples were cut from the composite sheets. At least five specimens were tested and mean value was taken for each composite according to ASTM standards. The reinforcing effects of kenaf and fiberfrax fibers were evaluated at various fiber loadings, that is, 19, 28, 36, 43, 52, and 62 vol. %. The hybrid effect of kenaf and fiberfrax fiber on the tensile, flexural, impact strengths, and hardness was also investigated for various ratios of kenaf/fiberfrax fiber loadings ranging between 1 : 0 and 0 : 1. Total fiber loading of the hybrid composites was 43 vol.%. The tensile, flexural strength, and hardness of the composites increased with increasing fiber loading up to 43 vol.% and decreased above this value for kenaf/PF composites. Impact strength of kenaf/PF composite showed a trend of increase with increasing fiber loading. The tensile and flexural strength of fiberfrax/PF composites increased by incorporation of fiberfrax fiber up to 36 vol. % and decreased beyond this value. However, the maximum impact strength and hardness were obtained for 52 vol. % fiberfrax fiber loading. The tensile, flexural, and impact strength values of fiberfrax/PF composites were found to be lower compared to kenaf/PF composites. With addition of fiberfrax fiber, the tensile, flexural, and impact strengths of the kenaf/fiberfrax hybrid PF composites decreased linearly and the hardness of the composite increased. The maximum hardness value was obtained for 0.25 : 0.75 kenaf/fiberfrax ratio.