Microwave-associated ZnCl2 pretreatment followed by enzymatic hydrolysis for high-efficiency production of nanocellulose from Eucalyptus dissolving pulp

Herein, we developed a novel microwave-associated ZnCl2 pretreatment followed by enzymatic hydrolysis for high-efficiency and environmentally friendly production of nanocellulose. With a short pretreatment time (60 s), nanocellulose was yielded with a high overall yield of 87.99 % from Eucalyptus Dissolving Pulp (EDP). Characterization analysis revealed that microwave-associated ZnCl2 pretreatment can efficiently swollen the structure of EDP, and after enzymatic hydrolysis, the nanocellulose in spherical shape was formed with abundant functional groups, low crystalline index, and poor thermal stability. By Energy Dispersive X-Ray Spectroscopy (EDS) and inductively coupled plasma mass spectrometry (ICP-MS) analysis, approximately 20 wt% of zinc distributed on the surface and in the interior of cellulose, that may lead to the low Zeta potential of the nanocellulose and the formation of nanospheres. Furthermore, through optimization of the pretreatment process, it was feasible to increase the solid concentration of EDP to 3 wt% while concurrently reducing the ZnCl2 concentration to 0.1 mol (ZnCl2 & sdot;9H2O). Under this condition, ultrafine cellulose nanocrystals (CNC) and cellulose nanofiber (CNF)/CNC blend were produced with an outstanding yield of 93.3 %. Moreover, the recyclability of ZnCl2 post-pretreatment was demonstrated, as ZnCl2 could be efficiently reused for subsequent pretreatment cycles. Notably, even after five cycles of recycling, the nanocellulose yield remained consistently above 90 %. Overall, this study highlights the viability and sustainability of microwave-assisted ZnCl2 pretreatment for efficient nanocellulose production, offering a sustainable and cost-effective route for industrial-scale applications.