A simple method for preparation of lignin/TiO2 nanocomposites by sulfonation degree regulation and their application in polyurethane films

The waterborne polyurethane (WPU) exposed to outdoor environment for a long time are more likely to reduce their mechanical performance and service life. This work describes a simple and effective method to obtain the homogeneous lignin/TiO2 nanocomposite as the anti-UV additive to improve the applicability of WPU. The SKLs/TiO2 were prepared by the gradient sulfonation kraft lignin (SKLs) and tetrabutyl titanate. The particle morphology and hybrid structure of SKLs/TiO2 are characterized by FT-IR, zeta potential analysis, XPS, TG and SEM. Interestingly, it was found that the change of π-π interactions and electrostatic repulsion between SKL molecules effected the forming of SKLs/TiO2 nanocomposite. The lignin content and morphology of SKLs/TiO2 nanocomposite could be controlled by regulating the sulfonate group content on lignin molecular. Furthermore, the SKLs/TiO2 nanocomposites was successfully applied on water polyurethane film as the additive, when SKLs/TiO2 content increased from 0 wt% to 5.0 wt%, the tensile strength increased 43%, the elongation at break increased from 240.0% to 352.0% and the UV transmittance reduced from 87% to 1.7% below 400 nm, which greatly improved the UV resistance and mechanical properties. The results of this study are of significant and practical importance to the high-value-added utilization of lignin.