Influences of sodium hydroxide and oxalic acid treatments on physical, mechanical, thermal properties, and morphology of ramie fibers

The environmentally friendly properties of natural fibers cause their use as reinforcement in polymer matrices to continue to grow. However, its hydrophilic properties can significantly reduce interfacial interactions. Chemical treatment is one method used to reduce the hydrophilic nature of ramie fibers. This study aimed to investigate the effects on ramie fiber of three chemical treatments: oxalic acid at a concentration of 5 (wt.), sodium hydroxide at 3, 5, and 7 (wt.), and a combination of both treatments. Physical properties, moisture content, tensile strength, X-ray diffraction, Fourier transform infrared spectroscopy (FT-IR), thermal properties, contact angle, and morphology of ramie fibers before and after treatment were observed in this investigation. FT-IR test results showed a partial loss of amorphous content and more intense cellulose peaks in treated ramie fibers. The combination treatment of alkali and oxalic acid gave the best results, which initiated the dissolution of some of the lignin, hemicellulose, and extractive content. XRD results indicated the surface treatment also led to a 20.35 rise in the crystalline index. In addition, there was a significant increase in tensile strength of 136.10 in fibers soaked with chemicals. The morphology of the fibers with treatment showed defibrillation and loss of contaminants on the fiber surface, which was the cause of the smaller fiber diameter. Therefore, this optimum treatment is expected to improve the interfacial properties of natural fibers and polymer matrices so that they can enhance the properties of composites when applied in industries. © 2024 The Authors