Abstract
The effects of maleic anhydride, stearic acid and water absorption on the physical and flexural properties of injection moulded short hemp fiber-reinforced thermoplastic composites were investigated, in order to understand the suitability of these materials for outdoor applications. The water absorption, diffusion mechanisms and kinetics of composites were evaluated by immersing the specimens in distilled water at 23 °C. Flexural fracture surface morphologies were investigated in order to compare the results of flexural tests with qualitative morphological observations. The process of water absorption was found to follow the Fickian mode of diffusion. Flexural properties ( and ) were affected by the water absorption. The addition of maleic anhydride and stearic acid enhanced the resistance to water absorption of composites and resulted in a slight increase of flexural properties of composites based on a high-density polyethylene (HDPE) matrix. The reduction in flexural properties induced by the degradation of matrix-fiber interfacial bonding due to water absorbed was confirmed by scanning electron microscopy analysis.
Highlights
Natural fiber-reinforced polymer composites, produced by combining lignocellulosic fibers with phenolic resin, were first introduced in 1908
The Thermal Gravimetric (TGA) curve shows that the onset of PP degradation occurs at around 221 ◦C, while the Differential Scanning Calorimetry (DSC) curve for high-density polyethylene (HDPE) exhibits an endothermic melting peak at 130 ◦C and the TGA curve show that the degradation begins at around 219 ◦C
Enhanced (Tables 11 and 12) Ef of 4.03 and 2.46 GPa, and σf m of 59.31 and 41.64 MPa were obtained for PP5 (CA) and HDPE7 (CA + SA) composites composed of 40 wt% hemp fiber, respectively
Summary
Natural fiber-reinforced polymer composites, produced by combining lignocellulosic fibers with phenolic resin, were first introduced in 1908. Glass fibers accounts for 90% of the total market volume for fiber-reinforced plastics (short and long fibers, roving, woven, fabrics and mats), whereas natural fibers account for only 2–2.5% and are currently being used in construction (decking), automotive (door trim panels, engine and transmission covers) and packaging applications [3]. Despite the better properties of hemp fibers, such as lower density (1.2–1.6 g/cm3) compared to that of glass fiber (2.4 g/cm3), high specific mechanical properties as well as relatively low cost, renewability and biodegradability, their inherent hydrophilic character, low resistance to micro-organisms, low thermal stability and flammability, restricts their use in many structural as well as outdoor applications, hindering its market growth [5,6,7,8]. Hemp fibers are used to reinforce thermoplastics with the aim of increasing their strength [10]
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