Influence of alkali treatment on mechanical and morphological properties of ananas comosus and saccharum officinarum fibers

The mechanical and morphological characteristics of Ananas comosus (pineapple leaf fiber, PLF) and Saccharum officinarum (sugarcane bagasse fiber, SBF), both obtained from post-harvest agricultural waste, were investigated in order to ascertain the optimal alkali treatment conditions for high-performance bio-composite reinforcement. Tensile testing, SEM-EDS, FTIR, and XRD studies were used to assess untreated and NaOH-treated fibers (4.9%–6.2%) using ASTM C1557-20 single-fiber testing techniques. Alkali treatment enhanced surface roughness, decreased fiber diameter, and eliminated surface contaminants. Diameter reduction is very concentration-dependent, with the most noticeable effects at 6% for PLF and 5.0%–5.4% for SBF, according to Dunn’s post hoc analysis. For PLF and SBF, the ideal tensile strength was attained at 5.7% and 5.8% NaOH, respectively. Improved crystallinity and the elimination of non-cellulosic components were verified by structural and chemical analyses. This study’s novel contribution is the identification of a narrow window of optimal NaOH concentration using fine 0.1% increments, which captures subtle morphological and mechanical transitions not previously reported. It also establishes a direct correlation between controlled surface modification and tensile performance for both fibers. These results show that carefully controlled alkali treatment can greatly enhance PLF’s and SBF’s reinforcing potential, offering a refined processing approach for upcoming bio-composite applications. This work contributes to SDG 12 (Responsible Consumption and Production) through the valorisation of agricultural waste fibres, SDG 9 (Industry, Innovation and Infrastructure) by enabling mechanically reliable bio-reinforcements, and SDG 13 (Climate Action) by supporting renewable alternatives to synthetic fibres.