Influence of Alkaline Treatment and Fiber Morphology on the Mechanical, Physical, and Thermal Properties of Polypropylene and Polylactic Acid Biocomposites Reinforced with Kenaf, Bagasse, and Hemp Fibers

This study investigates the effect of slight surface treatment of Kenaf (KBF), Bagasse, and Hemp fibers on the mechanical, morphological, physical, and thermal properties of biodegradable composites. The composites were prepared by extrusion using 25 wt% fibers to reinforce 75 wt% polypropylene (PP) and plasticized poly(lactic acid) (PLA), with softwood fibers as a control. Fi-bers were treated with 5% sodium hydroxide (NaOH) for one hour. Mechanical properties (ten-sile, young’s modulus, and impact), physical properties (fiber mapping, density, brightness), and thermal properties (heat deflection temperature (HDT), melting temperature, melt flow ratio (MFR), and melt flow index (MFI)) were evaluated using standard procedures. The biocomposites morphology was studied by scanning electronic microscopy (SEM). Results showed improved tensile and impact strength for PP composites with treated Bagasse (6.6% and 22%) and Hemp (7% and 44.7%), while Kenaf showed minimal change, indicating its high intrinsic strength. Fiber addition increased the HDT of PP from 55°C to 119°C for untreated KBF, 100°C for softwood, 86°C for Bagasse, and 79°C for Hemp. Treated fibers reinforced PP composites achieved higher HDT, with Kenaf (124°C) performing best, followed by Bagasse (93°C). PLA composites showed slight increases in HDT with fiber reinforcement. Differential Scanning Calorimetry (DSC) revealed a slight melting temperature decrease for PP and a slight increase for PLA. Overall, Kenaf and Bagasse yielded superior mechanical and thermal performance, comparable to softwood, while Hemp demonstrated moderate results. The differences among the fiber’s performance were at-tributed to variations in fiber mapping and the intrinsic properties of the polymer matrices.