PVA/(ligno)nanocellulose biocomposite films. Effect of residual lignin content on structural, mechanical, barrier and antioxidant properties.

Nanocelluloses with and without residual lignin were isolated from wheat straw. In addition, the effect of TEMPO-mediated oxidation on the production of lignin-containing nanocellulose was studied. The different nanocelluloses were used as reinforcing agent in Poly(vinyl alcohol) films. The morphology, crystallinity, surface microstructure, barrier properties, light transmittance, mechanical and antioxidant properties were evaluated. The translucency of films was reduced by the addition of nanocellulose, however, the ability to block UV-light increased from 10% for PVA to >50% using lignin-containing nanocellulose, and 30% for lignin-free samples. The mechanical properties increased considerably, however, for loads higher than 5% a negative trend was observed presumptively due to a clustering of nanocellulose components in PVA matrix. The barrier properties of the films were improved with the use of nanocellulose, especially at small amounts (1-3%). The antioxidant capacity of films was increased up to 10% using lignin-containing nanocellulose compared to 4.7% using PVA.