From agricultural waste to active films: Enhanced crystallinity of spent mushroom substrate-derived cellulose via deep eutectic solvent-based microwave-assisted pretreatment and its application in reinforcing CMC-based composite films

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This study demonstrates the successful valorization of spent mushroom substrate (SMS), an abundant agricultural waste, into crystalline cellulose for advanced food packaging applications. A deep eutectic solvent (DES)-based microwave-assisted pretreatment was developed to extract and enhance cellulose crystallinity from SMS. Using optimized conditions—choline chloride and zinc acetate DES at 1:1 M ratio, 1:30 w/v cellulose-to-DES ratio, 640 W microwave power, and 2.5-min hydrolysis—the process yielded pretreated cellulose (PC) with 51.66 % crystallinity index and 95.82 % recovery yield. The PC was then incorporated into carboxymethyl cellulose (CMC)-based composite films along with zinc oxide nanoparticles (ZnONPs) and mushroom powder (MP). The resulting composite films exhibited superior mechanical properties, with CMC/PC/ZnONPs films achieving a tensile strength of 17.18 MPa and toughness of 4.72 MJ/m 3 . Integration of ZnONPs and MP enhanced UV-blocking capabilities while maintaining film transparency. The films demonstrated thermal stability with melting temperatures ranging from 257.5 °C to 281.83 °C. Notably, PC-containing films showed improved antioxidant activity, with IC 50 values of 4.59–8.57 mg/mL for 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) and 134.88–1389.15 mg/mL for 2,2-diphenyl-1-picrylhydrazyl (DPPH) assays. The composite films also exhibited strong antimicrobial properties against common foodborne pathogens ( Staphylococcus aureus , Escherichia coli , and Bacillus subtilis ), with inhibition zones exceeding 15 mm. This research establishes a sustainable approach to waste valorization while advancing the development of multifunctional, eco-friendly food packaging materials. • Sustainable approach valorizes spent mushroom substrate into eco-friendly materials. • Enhanced cellulose crystallinity via green microwave-assisted DES pretreatment. • CMC films reinforced with high-crystallinity cellulose, ZnONPs, and mushroom powder. • Composite films showed improved mechanical, optical, and thermal properties. • Films exhibited notable UV-blocking, antimicrobial, and antioxidant activities.