High-performance biobased packaging: Ionic liquid-assisted cellulose-lignin bioplastics as sustainable alternatives to LDPE

The development of high-performing biobased packaging material as a potential replacement for low-density polyethylene (LDPE) can combat the plastic pollution problem. Here, bioplastics harnessing the strength of cellulose and the barrier properties of lignin are fabricated through solution blending using ethanolammonium nitrate, a protic ionic liquid (PIL), or aprotic 1-ethyl-3-methylimidazolium acetate, with γ-valerolactone (GVL) as a cosolvent. The resulting bioplastics were characterized to ensure adequate strength, smooth surface morphology, water vapor barrier, UV-rays blocking, antioxidant activity, thermal stability, and biodegradation. The cellulose-lignin films demonstrated superior UV-blocking, faster biodegradation, lower thermal degradation temperatures, and comparable surface roughness compared to LDPE. 100% cellulose film (100CF) had a comparable water vapor transmission rate (WVTR) to the Biobag. To prevent the structural heterogeneity of lignin from affecting bioplastics quality, we developed predictive structure–property relationships (SPRs) that connect the molecular structure of lignin from hardwood, softwood, grasses, and technical lignin to processing conditions and macroscopic performance metrics. Mechanistically, the total polar surface area (tPSA) of lignin drives the bioplastic film's affinity for water vapor; the bond dissociation energy (BDE) of the phenolic hydroxyl controls the antioxidant properties; and the energy gap of lignin's chromophores determines the extent of UV-blocking. Overall, Miscanthus lignin increased the percentage elongation of cellulose film from less than 5% to 30% and reduced WVTR from 511.64 ± 4.35 g/m 2 /day to 283.50 ± 3.79 g/m 2 /day. Hence, cellulose & lignin can be processed with environmentally friendly methods to yield bioplastic with improved protective capacity for packaged products while demonstrating comparable mechanical capacity & smoothness as LDPE.