Preparation and evaluation of polymer-encapsulated UV filter nanocapsules with miniemulsion polymerization

Abstract

Ultraviolet (UV) filter nanocapsules were prepared by encapsulating organic UV filter octyl dimethyl para-aminobenzoic acid (OD-PABA) with miniemulsion polymerization using an amphiphilic random copolymer poly(styrene-co-methacrylic acid) (P(St-co-MAA)) as an emulsifier, methyl methacrylate (MMA) as the monomer and ethylene glycol dimethacrylate (EGDMA) as the crosslinker. TEM showed that the nanocapsules had irregularly spherical shape with an average diameter of 320 nm, and OD-PABA crystalline grains were encapsulated. The molar ratio of St to MAA in P(St-co-MAA) and the polymer emulsifier concentration, as well as the molar ratio of MMA to EGDMA in polymer coating significantly influenced the encapsulation efficiency and the leakage rate. At the optimum conditions, the encapsulation efficiency of OD-PABA reached to 33%. OD-PABA leakage in isopropyl myristate (IPM) could be ignored since the leakage rate maintained 1.3% during continuous stirring for 24 h. UV reflectance spectra showed that the UV filter nanocapsules had broad-spectrum UV blocking owing to the absorbance of OD-PABA combined with the scattering and reflection of the nanocapsules at submicron level. The sun protection factor (SPF) of the UV filter nanocapsules sunscreen improved by 300% compared with the free OD-PABA formulations. Moreover, OD-PABA encapsulated in the nanocapsules could reduce the cytotoxicity significantly through the evaluation of the sunscreen safety with MTT method.