Enhanced Pickering Emulsification of Nano Titanium Dioxide via Sodium Lignosulfonate for Sunscreen Formulations

A high-energy ball milling strategy was developed to optimize nano titanium dioxide (nano-TiO2) through sodium lignosulfonate (SL)-mediated electrostatic surface modification. At 20 wt % nano-TiO2 and 5 wt % SL, the colloidal system achieved optimal stability with a sun protection factor (SPF) elevation from 15 to 17. Subsequent emulsion formulation with various aqueous phase to oil phase mass ratios (κ) yielded a Pickering emulsion at different pH values, demonstrating exceptional interfacial stabilization via nano-TiO2 and SL electrostatic assembly. The optimized TSL-4 emulsion (κ = 1:1, pH = 4) exhibited remarkable storage stability (keeping over 25 SPF value after 6 weeks of accelerated test) and thermal resilience (maintaining above 91% SPF retention through 10 freeze–thaw cycles.). Biological evaluations of TSL-4 (κ = 1:1) emulsion demonstrated no phototoxicity (irradiated vs nonirradiated viability difference < 2%), low cytotoxicity (90% HaCaT cell viability), and minimal cutaneous permeation (no nanoparticle accumulation in subcutaneous layers). The biomass-compound-modified nano-TiO2 system establishes a multifunctional sunscreen platform that synergistically integrates UV attenuation, colloidal stability, and biosafety.