Alkali lignin (AL), an anionic polymer, is a byproduct of the paper industry. AL was first modified by quaternization to synthesize quaternized alkali lignin (QAL). The aim of the present study is to reveal the effects of sodium dodecyl benzenesulfonate (SDBS) on the microstructure of QAL. The interaction between SDBS and QAL is studied by means of zeta potential, fluorescence spectrophotometer, and static contact angle measurement. The results indicated that there is an electrostatic interaction and a hydrophobic interaction between QAL and SDBS. The SDBS/QAL complex can self-assemble into lignin-based colloidal spheres (LCSs) in an ethanol/water mixture, which have remarkable avermectin (AVM) encapsulation efficiency and antiphotolysis performance. The cumulative release amount of AVM encapsulated by LCS (LCS@AVM) after 72 h was 77%, and the release was still going on. The release behaviors of LCS@AVM can be controlled by adjusting the ratio (w/w) of LCS to AVM. More than 85% of AVM could be preserved even after 96 h of UV irradiation. LCS showed controlled release and UV-blocking performance for AVM.

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° in comparison to only 22° 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.

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