Ultrasound-Induced Structural Modification of Cellulose in Poplar Wood: Effects on Crystallinity and Enzymatic Hydrolysis Efficiency

The crystalline structure of cellulose plays a crucial role in its reactivity, which is particularly important in biomass processing involving enzymatic hydrolysis. This study investigates the effect of low-frequency ultrasound (40 kHz) on the efficiency of enzymatic hydrolysis of cellulose in poplar wood and its structure, with a focus on its crystallinity and susceptibility to enzymatic hydrolysis. Two experimental pathways were explored: ultrasound-assisted hydrolysis of raw wood and isolated cellulose. Structural modifications were assessed using Fourier-transform infrared spectroscopy to determine the Lateral Order Index (LOI) and Total Crystallinity Index (TCI), providing insight into the reorganisation of cellulose microstructure. To evaluate hydrolysis efficiency, glucose yields were quantified by high-performance liquid chromatography. The application of ultrasound to raw wood resulted in minimal improvement in sugar release, whereas pretreatment of extracted cellulose led to a modest acceleration of enzymatic hydrolysis. The results show that ultrasound-assisted hydrolysis of raw wood did not significantly increase glucose yield, reaching only 9.9 ± 0.3% and 10.1 ± 0.8% for two poplar hybrids. Only slight increases in TCI and no significant changes in LOI were observed after 4 h of ultrasonic exposure. It indicates limited disruption of the crystalline structure under the tested conditions.