Mechanical shearing-mediated ultra-low acid hydrolysis for efficient preparation of microcrystalline cellulose and applications in PLA composites

Mechanical shearing-mediated acid hydrolysis with only 1.55% HCl achieved a 96.65% MCC yield. • The resulting MCC exhibited high crystallinity, good thermal stability, and uniform particle size. • As a reinforcing agent, MCC improved PLA crystallization, mechanical properties, water vapor barrier and food preservation. • Life cycle assessment confirmed lower environmental impacts of the proposed MCC process than commercial MCC production. Conventional microcrystalline cellulose (MCC) production generally relies on high-concentration acid hydrolysis, leading to low yield (<90%), substantial energy consumption and environmental pollution. Herein, this study presents a sustainable and efficient strategy for preparing MCC via ultra-low hydrochloric acid (HCl) hydrolysis mediated by mechanical shearing force to overcome these bottlenecks. This optimized process achieved an exceptional yield of 96.65% at an extremely low HCl concentration of merely 1.55% at 90 °C for 95 min, far below the acid dosages employed in current methods. The improved hydrolysis efficiency stemmed from the mechanical shearing force, which effectively disrupted the intermolecular hydrogen bonds of cellulose, thereby loosening its structure and facilitating H⁺ penetration to promote glycosidic bond cleavage. The as-prepared MCC featured a uniform particle size (79.62 μm), high crystallinity (85.86%), excellent thermal stability (T max = 380.2 °C) and good dispersion stability, surpassing the overall performance of commercial MCC. As a reinforcing agent, MCC significantly improved the properties of polylactic acid (PLA) via hydrogen bonding and heterogeneous nucleation. Specifically, the PLA composite incorporated with 3 wt% MCC exhibited a 56.25% increase in tensile strength, a 24.92% improvement in elongation at break, a 40.11% enhancement in crystallinity, a 52.47% reduction in water vapor permeability (WVP), and a remarkable food preservation effect compared with neat PLA. Furthermore, life cycle assessment (LCA) indicated significantly lower environmental impacts of the ultra-low acid hydrolysis process relative to commercial MCC production. This work provides a sustainable and industrially viable route for MCC production, with broad application potential in food packaging, biomedical and composite materials.