Effect of surface treatment of Kenaf fiber with Zinc Oxide nanoparticles on the properties of unsaturated polyester/Kenaf fiber biocomposites

Increasing need for materials with special features have brought various new inventions, one of the most promising hope for new material with special features and functionalities is composites materials. Thus, this study reports the surface treatment of zinc nanoparticles into kenaf/polyester polymer composite (UP/KF-ZnONPs). UP/KF-ZnONPs composites were fabricated by using hand lay-up process. Initially, composites of unsaturated polyester/ kenaf (UP/KF) containing 1 layer up to 4 layers of kenaf fiber (equal to 10% up to 40% w/w% of KF) were prepared to study the effect of KF layers on UP composite. These composites were compared with a control system containing unsaturated polyester (UP) only. The properties of these composites were evaluated in term of mechanical properties (tensile strength, tensile modulus, flexural strength, flexural modulus and elongation at break), morphology (SEM), chemical structure (FTIR), thermal properties (TGA) and water uptake test. It was shown that the composite with 4 layers of KF showed the highest tensile strength as compared to that of other layers into the composites. The results of the mechanical tests suggest that kenaf fibers improved the mechanical properties of the composites. Moreover, the thermal stability of UP/KF composites was improved with increasing the layers of KF from 1 to 4 layers. SEM analysis showed that more fiber pull-outs are observed in higher loading of KF in composites from the 1 layer to 4 layers fiber composite. The water uptake test revealed the water uptake increased with increasing loading of KF layer and the period of immersion until it has been saturated almost after 3 weeks of the test period. In addition, these composites were exposed outdoor for consecutive six months with interval of 1 month. To study the effect of weathering conditions and the capability of the composites to withstand weather conditions. The mechanical properties (tensile strength, tensile modulus, flexural strength, flexural modulus and elongation at break) were observed. In addition, FTIR spectra analysis and TGA as well as SEM were conducted. Unfortunately, the mechanical properties of the composites started to decrease constantly after the first month of exposure to weathering conditions. From the mechanical properties result obtained it clearly seen that natural fiber and their composites are not able to withstand the environmental condition because they have poor wettability, incompatibility with polymeric matrices and high water uptake. Due to the high water uptake properties (which was confirmed by FTIR analysis), there are formation of voids in interfacial adhesion between fiber and matrix which can reduce the mechanical properties of composite such as flexural strength or flexural modulus this clearly supported by SEM results. To overcome this problem, the surface treatment of KF with ZnONPs was carried out. KF was treated with 5 different percentage of ZnONPs, i.e. 1%, 2%, 3%, 4%, and 5 wt%. The properties of UP/KF-ZnONPs composites were evaluated in term of mechanical properties (tensile strength, tensile modulus, flexural strength, flexural modulus and elongation at break), morphology (SEM), chemical structure (FTIR), thermal properties (TGA), contact angle measurement and water uptake test. UP/KF-ZnONPs composites with 2% of ZnONPs had the most stable mechanical properties with moderate elastic properties compared with that of the remaining ZnO NPs systems. The presence of ZnONPs in the composites was confirmed by FTIR analysis and the thermal stability was improved by ZnONPs surface treatment. The water repellant capability, which was confirmed by contact angle measurement that showed that KF became more hydrophobic after surface treatment with ZnONPs, is good enough to achieve the high performance of the composite to prevent the degradation of the composite.