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Journal of Mechanical Engineering Science and Technology (JMEST)

Abstract

A major development in materials science toward reinforcement materials in biopolymer composites has been caused by a worldwide trend toward sustainable manufacturing and the rise of the circular economy. However, their mechanical properties can often be affected by their hydrophilic properties, lack of surface compatibility, and their presence of molecular bonding, such as lignin and hemicellulose. Alkaline surface modification has been widely reported as an effective technique to increase structural stability and fibermatrix adhesion. This study evaluated the effects of alkalizing three types of local natural fibers—bamboo fiber (BF), pineapple leaf fiber (PALF), and sisal (SF)—with sodium hydroxide (NaOH) at varying concentrations (0, 3, and 6 wt.%) on their morphology, chemical structure, crystallinity, and tensile properties. SEM surface analysis showed improved fibrillation and removal of surface impurities. SEM surface analysis showed that the alkali treatment improved fiber fibrillation and eliminated surface contaminants, both of which increased the potential for interfacial bonding. The decreased amount of lignin and hemicellulose was confirmed by FTIR spectra, which were especially evident at higher NaOH concentrations. Meanwhile, XRD analysis showed that the alignment of cellulose chains increased the crystalline pattern index. Significant gains were observed in tensile testing, particularly in PALF, where a 6% NaOH treatment increased tensile strength to 1660 MPa. These results show that alkalinization changes the molecular structure of natural fibers and improves their mechanical integrity, which makes them more appropriate for composite applications. This contributed to the development of green composites with both structural and functional applications.

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