Momordica Angustisepala as Reinforcement in Polymer Composites
Ikechukwu Emmanuel Okonkwo
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The use of natural fibers as reinforcements for polymers has been receiving great attention in recent times. This is because natural fibers are cheap, abundant and environmentally friendly. Momordica Angustisepala is one of such fibers, and this research explored its potentials for use as reinforcement in polypropylene. The effects of pretreatment were also examined to determine its efficacy in improving fiber-polymer adhesion which has been noted as a persistent problem in similar composites. Fiber treatments were performed using sodium hydroxide, potassium hydroxide, silane, dicumyl peroxide, maleic anhydride, and sodium hypochlorite. The raw and treated fibers were studied to determine the tensile properties as well as the density and water absorption. Selection of the best fiber treatment was made using Minitab’s Central Composite Design, (CCD). Composites were produced with the fibers and polypropylene, using compression moulding. Tests were performed to determine the mechanical properties of the composites, the density and the water absorption. The morphology of the fibers and composites were also studied using scanning electron microscopy (SEM). The moisture content of the fiber at room temperature was determined to be 7.2% and its water absorption was 95%. Various chemical treatments decreased the water absorption of the fiber bundles to 80% - 40% range and decreased bulk density in most cases from 1.11g/cm3 to 1.1g/cm3 – 0.6g/cm3 range. Fiber treatment with 5% NaOH for 1 hour was selected for composite production since it offered fibers with best tensile strength and modulus as well as moderate water absorption and density. Results of composite tests showed a decrease in most mechanical properties, except Young’s modulus which was increased by 2.0%. Tensile strength decreased by 24%, but the tensile strength and Young’s modulus of the treated-fiber composite were higher for than that of the raw-fiber composite. Flexural strength and modulus decreased by 7.0% and 18.7% respectively. Impact strength was reduced by 65.9%. The composites have higher density and water absorption than the original polymer. However, the density of the composite was decreased by 4.7% when treated fibers were used instead of raw fibers, and water absorption was similarly decreased by 2.3%. From SEM images, better adhesion was observed in the fiber-matrix interphase of the treated-fiber composite. Therefore, pretreatment was effective in improving the tensile properties of treated-fiber composites when compared to raw-fiber composites. Similarly, chemical treatments also helped to cushion the effects of fiber-addition on the density and moisture resistance of the composites. However, reinforcement was only achieved in the stiffness of the composite since other mechanical properties of the polymer were higher than that of the composite. Future researches may determine the effects of using higher weight fractions of fiber, or using other processing methods, for producing the composite.