Optimization of Mild Alkali Treatment and Effect of Cultivar on the Structural, Morphological, and Thermal Properties of Rice Straw Particles as Potential Biocomposite Reinforcements

Abstract

Abstract Rice straw is a widely available lignocellulosic residue and a promising feedstock for use in reinforced polymer composites. However, its utilization is limited by high ash and silica contents that obstruct its processing and interfacial adhesion with polymer matrices. Besides, the interactive effects of mild alkali treatment parameters and cultivar-intrinsic features of straw particles remain not fully examined. In this study, rice straw culm particles of Japonica Koshihikari and Indica IRRI104 cultivars were mild alkali-treated (1–3 wt% NaOH, 30 °C). Optimal conditions of 1.50 wt% NaOH for 10.97 h (Japonica Koshihikari ) and 11.58 h (Indica IRRI104 ) were realized using central composite design of response surface optimization. Solid yields of 50.85% and 55.32% with reductions in ash of 83% and 80% and silica of 78% and 73% were achieved per cultivar, respectively. Structural and chemical analyses confirmed reduction in hemicellulose, lignin, and silica–ash contents among mild alkali-treated straw particles. Furthermore, cultivar-dependent morphological and thermal properties improvements were presented. The onset and maximum decomposition were shifted to higher temperatures for optimal treated particles. Overall, these results demonstrated how optimized mild alkali treatment can tailor rice straw particles’ structural, morphological, and thermal properties, enhancing their valorization potential and integration in composites. Graphical Abstract