Ultrasound eco-extraction of cactus-derived cellulose for reinforcement of biodegradable bio-plastics by cellulose nanocrystals integration

Cellulose was extracted from cactus (Opuntia ficus-indica) cladodes using an ultrasound-assisted technique with water or 80% ethanol. The highest yield was achieved with 80% ethanol extraction, reaching 72.45 ± 0.57%. The extracted cellulose was characterized using various techniques. FTIR and XRD spectra were typical of natural cellulose, displaying characteristic cellulose peaks. TGA analysis revealed three stages of thermal degradation. Similarly, DMA analysis described the extracted samples’ glass transition temperatures and provided insight into melting temperatures of the cellulose. Dynamic Vapor Sorption (DVS) characterization indicated that cellulose extracted using ultrasound in 80% ethanol contains more hygroscopic constituents, which favor the adsorption of water molecules. Fragmented cellulose was analyzed by LC-MS, revealing peaks corresponding to mono-, di-, and trisaccharide residues across the samples. Microstructural analysis was conducted using SEM, AFM, and TEM techniques. Observations confirmed the presence of cellulose, characterized by elongated and stepped fibrous cells approximately 0.08 μm in size. This research also aimed to extract cellulose nanocrystals (NCC), with a yield estimated at 44.06 ± 3.02%. Infrared analysis highlighted the characteristic functional groups of crystalline cellulose. The extracted nanocrystals were utilized to reinforce starch-based films. The surfaces of starch-based films reinforced with 1% and 2% cellulose nanocrystals exhibited a rough texture with heterogeneities corresponding to cellulose nanocrystal-rich areas. The chemical properties of the reinforced agro-materials were investigated, revealing enhanced hydrogen bonding between starch and cellulose nanocrystals. Furthermore, the reinforced films demonstrated significant improvements in mechanical properties.