Effect of Acid Concentration on Structural, Thermal, and Morphological Properties of Cellulose Nanocrystals from Sugarcane Bagasse and Their Reinforcement in Poly(Furfuryl) Alcohol Composites

This study investigates the impact of sulphuric acid concentration (40% vs. 60%) on the extraction of cellulose nanocrystals (CNCs) from alkali-treated sugarcane bagasse (SCB) and their reinforcement in poly(furfuryl) alcohol (PFA) composites. Probing into the physicochemical changes through scanning electron microscopy (SEM) displayed drastic morphological changes, alkali removal of noncellulosic components followed by sulphuric acid hydrolysis further refined cellulose to nanoscale morphologies. The X-ray diffraction (XRD) study showed that after alkali treatment, the crystallinity was significantly higher (65%), and the crystallinity index of CNCs prepared from 40% H₂SO₄ was greater than the CNCs prepared from 60% H₂SO₄ (61%). Fourier transform infrared spectral and thermogravimetric analysis (TGA) suggested that improving the polymeric performance by the incorporation of a CNC resulted in a decrease in the thermal stability of the modified polyelectrolyte, which was largely attributed to higher sulphate esterification achieved at higher acid concentrations. It is possible to use CNCs to achieve higher mechanical performance while also indicating that optimizing thermal properties and mechanical performance of high-performance materials will require an improved understanding of the microstructural parameters governing the polymer–filler interface. This work demonstrates that acid concentration critically balances CNC crystallinity and thermal performance, offering insights for optimizing sustainable nanocomposites.