Starch-Based Composite Films with Enhanced Hydrophobicity, Thermal Stability, and UV-Shielding Efficacy Induced by Lignin Nanoparticles

Thehighly efficient utilization of lignin is of great importance for the development of the biorefinery industry. Herein, a novel "core–shell" lignin nanoparticle (LNP) with a diameter of around 135 nm was prepared, after the lignin was isolated from the effluent of formic acid fractionation via dialysis. In an attempt to endow composite materials with vital functionalities, the LNP was added to the starch film and the starch/polyvinyl alcohol (PVA) or starch/polyethylene oxide (PEO) composite film. The results showed that the hydrophobicity performance of the synthesized films was enhanced significantly. Specifically, the dynamic water contact angle value of the starch/PVA composite film with 1% (wt) addition of LNPs could be maintained as high as 122° for 180 s; the starch/PEO composite film also achieved an excellent water contact angle above 120°. The addition of LNPs promoted the formation of some rough structures on the film surface, as shown by the scanning electron microscopy images, which could repel the water molecules efficiently and are closely related to the enhanced hydrophobicity of the starch film. What is more, the as-prepared LNP conferred strengthened thermal stability and ultraviolet blocking properties on the starch composite film. The structural combination of the polymer film with LNPs holds the promise for providing advanced functionalities to the composite material with wide applications.