Properties and performance of kenaf fiber-sawdust polymeric sandwich bio-composites

Abstract

The increasing demand for environmentally friendly and sustainable structures have led the engineers and scientists to develop new bio-based composites. Natural fibers in composites present many advantages which include high strength and stiffness to low weight ratios, biodegradability, renewability, economic viability and so on. Currently, the use of mechanical fastening joints exists in the production of sandwich composite structures, but literature indicates that it has unavoidable drawbacks such as the structure failing prematurely with a load far below the maximum strength of component parts. As a result, an adhesively bonded joint is a better method of joining.This research investigates the properties and performance of a novel sandwich composites incorporating kenaf fiber-polyester matrix as skin material and sawdust-polyester matrix as core material, respectively. To this end, the kenaf fiber-polyester skin was fabricated in a unidirectional orientation with fiber volume fraction of 40 % from preliminary study, while the sawdust-polyester core was produced in a random arrangement with fiber volume fraction of 20%, also from preliminary study and this was produced by varying the thickness of the core. Both the Kenaf Fiber Reinforced Polyester (KFRP) skins and the Sawdust Reinforced Polyester (SDRP) core were tested interm of tension, flexure, compression, and shear. These tests were carried out to determine their constituent material properties. Consequently, three types of bio-composites sandwich were manufactured based on geometry, and was subjected to flexural load through three-point bending test to establish the flexural properties. Numerical investigation was carried out using ABAQUS FEA code to validate experimental results. Besides, it has been observed from literature that the use of natural fiber composites have been restricted to non-structural and semi-structural applications due to not having sufficient test data on fracture toughness at adhesive joint. Therefore, the adhesive bond behaviour of the KFRP adherend and the SDRP adherend sandwich composites was carried out through the Double Lap Shear (DLS) joint test to ascertain the bond shear strength and stresses at the joints. The DLS joints were fabricated with different bond lengths and bond widths using polyester adhesive as joint material and subjected to direct axial compression load. Numerical simulation was implemented to validate experimental results. The results of the KFRP tensile properties shows that stiffness and strength were found to be highest in the longitudinal direction and least in the transverse direction with percentage difference of 152.50 % for the modulus of elasticity and 175.24 % for tensile strength, respectively. Also observed is that there exist a considerably variability in the SDRP tensile, compressive and flexural strengths, nevertheless, their stiffnesses are comparably closed to each other. The results of the core shear stress and facing bending stress of the bio-composites sandwich revealed an increment of 13.90 % was recorded as the core thickness increased from 10 mm to 20 mm for core shear stress, while the facing bending stress saw an increment of 13.93 % as the core thickness increased from 10 mm to 20 mm. Excellent agreement was reached between the numerical simulations and the experiments in predicting the flexural properties. Furthermore, it was found that the lap length and bond width increases the load carrying capacity of the joints but decreases the bond shear strength. The numerical analysis results were in good accord with the experimental results, and the use of KFRP and SDRP in bonded assemblies have demonstrated promised with good potentials for use in structural applications.