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

Abstract

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.

Spherical lignin particles: a review on their sustainability and applications

“…Gutiérrez-Hernández et al suggested that LNPs could be matched to the skin tone of the person using the sunscreen formulation. 114 Lignin has been combined with photoactive metal oxide nanoparticles to quench photocatalytic activity of titanium dioxide NPs [115][116][117] and to broaden the UV-blocking spectrum of zinc oxide NPs in sunscreen formulations. 114 The excellent ability of LNPs to stabilize emulsions is an additional advantage of their use in sunscreens.…”

Preparation and characterization of lignin-TiO2 UV-shielding composite material by induced synthesis with nanofibrillated cellulose

“…Morsella et al (2016) prepared lignin/TiO2 composites via UV irradiation in THF (tetrahydrofuran) solution, and they found that lignin can effectively reduce the photocatalytic activity of TiO2. However, large amounts of organic solvents, such as tetrahydrofuran and glutaraldehyde, were used, but these are toxic and not suitable for skincare products (Li et al 2019). The study of UVshielding of lignin showed that lignin exhibited antioxidant properties and acted as a free radical scavenger due to the presence of the phenolic hydroxyl groups; the phenolic hydroxyl groups also act as a proton donor and can stabilize the resulting radicals via substituents and delocalization (Sun et al 2014).…”

Nano-Structured Lignin as Green Antioxidant and UV Shielding Ingredient for Sunscreen Applications

“…Finally, the cavity of LNPs can be exploited for the physical encapsulation of both OCFs and PCFs to yield functionalized LNPs with UV shielding properties higher than the parent compounds. One example of this strategy is represented by the encapsulation of TiO 2 inside lignin-based colloidal nanoparticles to afford a stable UV filter deprived of undesired side-chain catalytic effect in the generation of radical species [ 143 ].…”