Study Of The Encapsulation Of Ultraviolet Absorption Sunscreen By Miniemulsion Polymerization

In order to obtain a higher Sun protection factor?SPF?,a large amount of organic ultraviolet?UV?absorbents are required in the sunscreen cosmetics.However,organic UV absorbent could easily penetrate into the skin and cause photosensitivity reactions of skin,so the amount of it in cosmetics is limited.The organic UV absorbent encapsulated by the polymers can not only isolate itself from the skin,but also scatter or reflect UV light.Especially,the organic UV absorbent is encapsulated with miniemulsion polymerization,in which submicron particles with strong UV shielding could be prepared.In this thesis,the miniemulsion polymerization method was used to prepare polymer-encapsulated organic ultraviolet absorbent nanocapsules.The safety and sunscreen properties of the nanocapsules were explored,which provided a potential possibility for its application in cosmetics.The main contents are summarized as follows:2-Ethylhexyl salicylate?EHS?is a common oil-soluble UVB organic ultraviolet absorbent that easily penetrates into the skin and can cause phototoxic reactions.In view of the side effects of EHS on the skin,it was encapsulated by miniemulsion polymerization.Styrene?St?was chosen as the encapsulating material owing to the similar benzene ring structure to EHS,and the crosslinking agent ethylene glycol dimethacrylate?EGDMA?was added to prevent EHS leakage.Sodium dodecyl sulfate?SDS?combined with tween 80 was used as the emulsifier in miniemulsion to synthesize a polymer-encapsulated EHS sunscreen.The effects of the molar ratio of St to EGDMA,the mass ratio of EHS to encapsulating materials,and the molar ratio of SDS to tween 80 on the encapsulation and loading efficiency were investigated by single factor experiments.The cell viability of polymer-encapsulated EHS in human skin fibroblasts?HSF?cells,the leakage in the common solvent in cosmetics and the sun protection performance were evaluated.The results showed that the optimal molar ratios of St to EGDMA,the mass ratio of EHS to encapsulating material and the molar ratio of SDS to tween 80 was 1:1,1:1,1:1.5,respectively.Under the optimal conditions,the encapsulation efficiency of EHS reached to65%and the loading efficiency was 39%.The leakage rate of EHS from the polymer sunscreen in isopropyl myristate?IPM?for 24 h was only 1.3%.HSF cell viability of the polymer-encapsulated EHS was much higher than that of free EHS.Therefore,the safety of the polymer-encapsulated EHS was significantly improved.In addition,compared with free EHS,the SPF value of the polymer-encapsulated EHS which loaded the the equivalent of free EHS was increased by 47%.In the above work,though the emulsification performance was improved with the emulsifier of non-ionic surfactant tween 80 combined with SDS,tween 80 reduced the electrostatic repulsive force on the surface of the miniemulsion droplets.Therefore,the miniemulsion droplets were prone to coalescing each other during the polymerization process,and the spherical nanocapsules were hardly formed,which limited the enhancement of SPF value of the polymer-encapsulated EHS.In order to obtain well dispersed nanoparticles,superparamagnetic oleic acid?OA?modified Fe₃O₄ nanoparticles?OA-Fe₃O₄ NPs?were added to the oil phase for the first time to facilitate the nucleation.The oil phase EGDMA was emulsified by SDS whose hydrophilic lipophilic balance value was more suitable to EGDMA.The effects of the molar ratio of methyl methacrylate?MMA?to EGDMA,the mass ratio of EHS to encapsulating materials,and the mass of OA-Fe₃O₄on the EHS encapsulation and loading efficiency were investigated by single factor experiments.Moreover,the HSF cell viability of EHS nanocapsules,the EHS leakage in the common solvent in cosmetics and sun protection performance were evaluated.It was found that the optimal conditions were EGDMA as encapsulating material,m?EHS?:m?EGDMA?as 1:1 and the mass of OA-Fe₃O₄ of 0.005 g.Under the optimal conditions,the encapsulation and loading efficiency was 37%and 29%,respectively.Due to adding OA-Fe₃O₄ NPs in the oil phase,the nanocapsules were spherical with an average particle size of 116 nm.The leakage rate of EHS nanocapsules in IPM for 24 h was only0.8%.HSF cell viability was significantly improved in the EHS nanocapsules,compared with in the equivalent of free EHS.And SPF value was increased by 150%.To make further improvement in emulsifying ability,an amphiphilic random copolymer polystyrene-co-methacrylic acid?P?St-co-MAA??was used as the emulsifier instead of SDS.The encapsulating material was consisted of MMA and EGDMA.The core material is 4-dimethyl amino benzoate of ethyl-2-hexyl?OD-PABA?,an oil-soluble UVB ultraviolet absorbent with high UV protection,but a direct contact of OD-PABA with the skin could cause side effects such as photoallergy and contact dermatitis.Single factor experiments were conducted to optimize the molar ratio of lipophilic monomer to hydrophilic monomer in P?St-co-MAA?,the concentration of P?St-co-MAA?,and the molar ratio of monomer to crosslinking agents on the effects of the encapsulation and loading efficiency of OD-PABA.The HSF cell viability,leakage in the common solvent of cosmetics and sunscreen performance of OD-PABA nanocapsules were evaluated.It was found that the optimal conditions of n?St?:n?MAA?in P?St-co-MAA?,the concentration of P?St-co-MAA?and n?MMA?:n?EGDMA?was 6:4,1.0%and 1:8,respectively.Under the optimal conditions,the average particle size of OD-PABA nanocapsules was 318 nm,and the encapsulation and loading efficiency of OD-PABA nanocapsules were 33%and 17%,respectively.The leakage rate of the nanocapsules in IPM for 24 h was 1.3%.Compared free OD-PABA with OD-PABA nanocapsules loading the equivalent of free OD-PABA,the HSF cell viability of OD-PABA nanocapsules was significantly improved,and the SPF value was increased by 300%.The sun protection ability of OD-PABA nanocapsules is ascribed to the UV absorption of encapsulated OD-PABA,the UV absorption of P?St-co-MAA?self-assembly aggregating on the surface of the nanocapsules,and the scattering and reflection of UV light by submicron nanocapsules.