PEG Surface Modification of Microcrystalline Cellulose@Nanotitanium Dioxide Core–Shell Composite to Improve Sunscreen Performance

Polyethylene glycol (PEG) is commonly used to prevent particle aggregation of nanotitanium dioxide (nano-TiO₂) through steric hindrance. The particle aggregation of microcrystalline cellulose@nano-TiO₂ core-shell sunscreen composite (MCC@nano-TiO₂) makes the powder difficult to grind and also boosts the probability of nano-TiO₂ peeling off during grinding. It is essential to inhibit agglomeration by surface treatment to avoid adverse effects in cosmetic applications. First, the structural and UV protection capability of the composite was investigated before and after the complete coverage of MCC by nano-TiO₂. Then, different amounts of PEG were added in the later stages of composite preparation to fix PEG onto the particle surfaces. Systematic examinations were then conducted to investigate the effects of PEG modification on structure and properties. Results reveal that at an MCC:nano-TiO₂ mass ratio of 60:40, a 6% PEG modification significantly enhances the dispersibility and UV protection by altering the nano-TiO₂ shell structure. Notably, PEG is exposed on the particle surface, which markedly increases UV reflection and scattering, thereby extending the UVA protection range. The critical absorption wavelength (λ_c) was 376 nm. PEG modification also minimizes agglomeration and potential release of nano-TiO₂ particles. This study lays a foundation for the industrialization of MCC@nano-TiO₂ and provides new ideas for the surface modification of core-shell nano-TiO₂ materials.