Chitosan composite films with high-content technical alkali lignin

Technical alkali lignin (TAL) has been widely studied as the regulator in forming materials. When composited with non-thermoplastic polymers, its content was generally below 10 wt%, which is utterly inadequate in dealing with a difficult situation for the large-scale production of TAL. Here, we adjusted the solvent to form a series of high-strength chitosan-based composite films with high-content TAL. In detail, the water/N-methylpyrrolidone binary solvent mixtures were used. When the content of TAL reached 15 wt%, the resultant film showed a tensile strength of 26.29 MPa with elongation at break of 11.37 % that were 2.04 and 1.15 folds to that of pure chitosan film (CS), respectively. Even though a higher content of TAL (i.e., 23.4 wt%) was used, the composite film (CS/TAL 6:4) presented an enhanced tensile strength of 16.13 MPa, which was 25 % higher than the CS film. The as-prepared films also showed a surface protrusion of about 20 microm, contributing to their surface hydrophobicity and the consequent anti-swelling properties. Its thermo-stability and UV-blocking performance were also able to keep up with the reported works. At the same time, the composite film can also act as a coating for the anticorrosion efficiency of metal (i.e., Cu sheet here) with a 99.98 % efficiency in 0.1 mol/L KOH solution. The present work has shown a superior lignin film in both mechanical properties and content, which provided a novel route to the large-scale usage of TAL. Moreover, these results showed the potential of binary aqueous solvents in forming TAL-containing materials. This system can also be generalized to other polysaccharides/TAL composites.