Encapsulating TiO2 in Lignin-Based Colloidal Spheres for High Sunscreen Performance and Weak Photocatalytic Activity

TiO2 is widely used in cosmetic products but its poor dispersibility and photocatalytic degradation hazard still affect its performance. In this work, quaternized alkali lignin (QAL) is applied to encapsulate TiO2 by self-assembly and endows TiO2 with excellent sunscreen performance and safety. Results show that the nano TiO2 particles were well trapped in lignin colloidal spheres (LCS) via hydrogen bonding. The LCS encapsulated TiO2 (LCS@TiO2) had a water contact angle as high as 89 degrees in comparison to only 22 degrees in the TiO2 disk control sample. Thus, compatibility with the hydrophobic cream was improved. The photocatalytic activity of TiO2 could be effectively eliminated after modification. The dark color of QAL was significantly whitened by trapped TiO2. When the ratio (w/w) of LCS to TiO2 was 0.5, the LCS@TiO2 presented the best synergistic effect; the sun protection factor (SPF) value of the cream containing 25 wt % LCS@TiO2 reached 84.82.