Towards better UV-blocking and antioxidant performance of varnish via additives based on lignin and its colloids

Organosolv lignin (OL) extracted from pine wood was self-assembled into uniform nanocolloidal spheres (OLCS) in acetone/water and blended with varnish for better UV-blocking and antioxidant performance. The UV transmittance of the varnish with 1% OL was lower than that of a commercial varnish containing synthetic UVA and UVB blocker. Samples coated with OL-based varnish and UV irradiated for 100 h showed 84 and 69% less color change, respectively, compared to that of pure and commercial varnishes. Due to the higher surface area and better compatibility, the varnish blended with 1% OLCS showed better UV-blocking and photostability than those based on 1% OL additive. The color change of varnish was not perceptible. The lignin-based additives significantly enhanced the hardness and adhesion performance of the varnish and had little influence on the esthetic appearance of the samples. The hardness and modulus of elasticity of varnish increased by 61 and 36%, respectively, in the presence of 1% OLCS. The possible enhancement mechanism was explained by molecular interaction forces.