Structure–Property Optimization of Ramie-Derived Micro- and Nanocellulose: Correlation Between Crystallinity and Thermal Stability

This study explores the thermal-structural optimization of cellulose derived from ramie (Boehmeria nivea) fibers through a sulfate-free, environmentally friendly approach. Cellulose nanocrystals (CNC) and microcrystalline cellulose (MCC) were successfully isolated from α-cellulose using a combination of controlled HCl hydrolysis and mild ultrasonic treatment. FTIR analysis confirmed the preservation of the native structure of cellulose I, while XRD results calculated by the rigorous Segal method showed a significant increase in the crystallinity index (CrI), peaking at 79.4% for the MCC-R105. A clear correlation was established between crystallinity, crystallite size, and thermal stability; higher crystallinity and larger crystallites in MCC-R105 resulted in superior thermal resistance, with a maximum degradation temperature (Tmax) of 379°C. Although subsequent ultrasonication to produce CNC led to slight lattice fragmentation and a reduction in crystallite size to 24.2 nm, the resulting nanoparticles maintained high thermal stability (Tmax 358°C). SEM and PSA observations confirmed the formation of fragmented, rod-like CNC with a homogeneous size distribution. These findings demonstrate that the HCl-ultrasonic route is a technically viable strategy for producing high-purity, sulfate-free cellulose with tunable properties. The optimized MCC and CNC fractions hold great potential as sustainable building blocks for advanced bio-nanocomposites and green textile applications.