(488d) Effects of Lignin Structure on the Performance of Cellulose-Lignin Biodegradable Films

The development of high-performing biobased packaging material as a potential replacement for low-density polyethylene (LDPE) can combat the plastic pollution problem. The experimental and computational evaluation of protic (PIL) and aprotic ionic liquid (AIL)-cosolvent system for dissolution and blending of cellulose, a structural polymer, and lignin, a barrier matrix, to fabricate bioplastics are reported. Thereafter, extensive characterization and benchmarking with LDPE and Biobag, a commercial bioplastic, were conducted to ensure adequate strength, processability, appeal to users, protection of the packaged product from environmental factors (water vapor, UV-rays, and oxidants), thermal and biodegradation. These cellulose-lignin films demonstrated superior UV-blocking, faster biodegradation, and lower thermal degradation temperatures. They exhibit comparable surface roughness with LDPE. 100% cellulose had a comparable water vapor transmission rate (WVTR) with the Biobag. The plasticizing and barrier effects of hardwood, softwood, grasses, and technical lignin were evaluated to reduce brittleness and water vapor transmission rates. The percentage elongation at break (%E_b) varies with lignin source & structure following the trend: Grassy lignin increased %E_b, softwood lignin reduced %E_b while technical & hardwood lignin had a near neutral effect on %E_b. WVTR depends on lignin monomers' total polar surface area (tPSA), which drives the affinity for water vapor. Antioxidant properties of lignin monomer’s phenolic hydroxyl groups depend on an interplay of pKa and structural stabilization effects on the bond dissociation energy (BDE). These results show that cellulose & lignin, abundant biobased materials, 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.