Effect of Chemical Treatments and PVA Coating of Fiber on the Properties of Kenaf Fiber Reinforced Epoxy Composites

Md. Abdul Kader, Mahmudul Islam Hridoy, Md. Tanvir Khan Somrat, Md. Abdul Wares, Syed Mamun R Rasid, Muhammad Toufiq Imrose Khaledi

Abstract

In this study, kenaf fiber-based bio-composites were manufactured using a combination of hand lay-up and compression molding techniques to develop sustainable engineering materials. The fibers were treated with NaOH, acetic anhydride and PVA coating. The effects of these treatments on the surface morphology of fibers were investigated using scanning electron microscopy (SEM). A series of mechanical tests and water resistance capacity were performed to explore the influences of fiber treatments on the properties of composites. The results revealed that the NaOH treated fibers improve moisture resistance, strength and ductility. Acetic anhydride treated fibers enhance moisture resistance, flexibility, and impact strength. PVA coating increases flexibility and impact strength while reducing moisture resistance and other mechanical properties. The combination of all the studied treatments enhances flexibility and impact strength by sacrificing stiffness and moisture resistance. These findings highlight the potential of chemical treatments in optimizing the properties of bio-composite for advanced applications.

Conclusion

In this study, the effects of different chemical treatments (NaOH, acetic anhydride and PVA coating) of kenaf fiber on the mechanical and moisture resistance properties of kenaf fiber-based bio-composites were explored. The bio-composites were manufactured using a combination of hand lay-up and compression molding technique. The surface morphology of the composites was analyzed using Scanning Electron Microscopy (SEM). A series of experimental tests including tensile test, impact test, hardness test, and water absorption test were conducted to evaluate the properties of manufactured bio-composites. The following specific conclusions can be drawn from the thorough investigation of this study: 1. NaOH treatment enhances the mechanical properties of the composite (tensile strength by 6%, elongation by 64% and impact strength by 17%). This is achieved by improving the fiber-matrix adhesion and dispersion of fiber within the matrix. However, this treatment reduces stiffness by 26% and hardness by 17% due to increased flexibility of the composite. Additionally, NaOH treatment significantly improves moisture resistance by 32.7% through the removal of the water-absorbing component (hemicellulose) from the fiber. 2. The acetic anhydride treatment improves the moisture resistance by 46% by replacing the hydrophilic hydroxyl group with the hydrophobic acetyl group in the fiber. This treatment increased fiber flexibility, resulting in an 118% improvement in elongation. The weak fiber-matrix bonding resulted from this treatment, combined with increased flexibility, contributed to a 59% enhancement in impact strength. However, this treatment leads to the formation of micro-cracks and excessive delignification in the fiber, which caused a reduction in tensile strength by 33%, stiffness by 64%, and hardness by 61%. 3. The PVA coating improves the elongation by 152% and impact strength by 43.8% due to inherent flexibility of PVA. However, the hydrophilic nature of PVA leads to decrease in strength by 23%, stiffness by 67% and moisture resistance by 11%. Additionally, the enhanced flexibility due to the PVA coating resulted in a 28% reduction in hardness. 4. The combined effect of NaOH, acetic anhydride, and PVA treatments of fibers results in a balanced set of mechanical properties of the composites. While the tensile strength and hardness remain unchanged, enhanced flexibility leads to a 102% increase in elongation and a 25% improvement in impact strength. However, this increased flexibility comes with a 56% reduction in stiffness. The combined treatment also decreases moisture resistance by 32%, primarily due to the hydrophilic nature of PVA.

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