Synthesis And Performance Of Casein-based Hollow Nano Composite Emulsion

Natural polymer coating materials have attracted considerable interests along with the pursuit of environmental protection.As a kind of coating materials,casein with high temperature resistance,strong adhesion and other advantages,is the earliest and most widely used one of natural polymers in industries,especially in leather,paper-making,packaging and other fields.However,the pristine casein film is hard,brittleness and prone to mildew,which limit its application.In order to address the issues,researchers usually introduce other polymer components into casein by physical or chemical modification.Unfortunately,the modification always has an negative effect on their hygienic performance?air and water vapor permeability?although flexibility can be improved.In addition,the interface action of casein system during modification process is not obvious because of its complex structure.And researches on the relative polymerization mechanism lack of systematicness.Therefore,based on the polyacrylate modified casein system,this study put forward to design and to introduce hollow structure and inorganic nano components to obtain functional ambient film-forming emulsion.Further,anti-mould agent was loaded into the cavity thus obtaining a slow-released casein-based composite carrier.It has important scientific and practical significance to reveal the interfacial mechanism and explore the relationship between polymerization mechanism and controlled morphology in the process of modification.This work focused on:?1?Polyacrylate modified casein hollow microspheres were prepared from casein,methacrylic acid and acrylate monomers by emulsion polymerization and alkali swelling method.Effects of monomer ratio in shell components,swelling condition,methacrylic acid usage on structure of the latex particles and the opacity of coatings were investigated.The results of TEM,SAXS,AFM and DLS showed that nano scale hollow microspheres were successfully obtained,and their particle size was about 90 nm.Also,the as-prepared microsphere coatings can be formed at room temperature.FT-IR results confirmed that carboxyl groups migrated during the polymerization.SEM data demonstrated that there were many visible hollow holes on the surface and cross-section of the coatings.The obtained coatings showed excellent opacity.Application results showed that hygienic properties of the as-prepared hollow microspheres were significantly improved compared with that of core-shell microspheres.?2?In-situ blending and in-situ polymerization were separately used to introduce nano-SiO₂ thus prepare polyacrylate modified casein/SiO₂ hollow composite emulsion.Specifically,on one hand,nano-SiO₂ powders were introduced into polyacrylate modified casein system by in-situ blending.Effects of nano SiO₂ type,nano SiO₂ usage and coupling agent usage on emulsion stability,film opacity and mechanical properties of the hollow composite microspheres were investigated.The results showed that hollow composite emulsion coatings with good sanitary performance could be obtained when 1%of hydrophilic nano SiO₂ and 1.5%of coupling agent were added before swelling.And on the other hand,in-situ generated nano SiO₂ particles were introduced into the caprolactam-modified casein to synthesize hybrid Pickering stabilizer?CPL-CA/SiO₂ NPs?.Under action of the stabilizer,hollow composite emulsion was obtained by emulsion polymerization and alkali swelling routes.Emulsifying stability of the hybrid Pickering stabilizer was systematically investigated.Effects of precursor usage and coupling agent usage on performance of emulsion and and its coating were discussed.When the usage of precursor was 8%and coupling agent usage was 12%.The obtained hollow composite emulsion coatings had the expected mechanical properties and opacity performance.The results of TEM and AFM showed that the hybrid hollow microspheres produced by two methods had an average particle size of 160 nm.And nano SiO₂ were distributed on the outermost layer,which was helpful to improve the structural stability of the hollow composite microspheres.?3?Using the cavity of polyacrylate modified casein/SiO₂ hollow composite microspheres and the variable structure of hollow composite microspheres under swelling conditions,casein-based composite carrier was obtained by selecting appropriate process of loading anti-mould agent.The effects of anti-mould agent types,loading method,anti-mould agent usage,loading duration and loading temperature on particle size and their properties were investigated.Microstructure,size and loading efficiency of the as-prepared carrier were studied by TEM,SAXS,TGA and UV-Vis.The casein-based composite carrier could encapsulated 70%of the anti-mould agents when temperature was 90?and the anti-mould agent usage was 10%adding after swelling for 1 h.Results showed that casein-based composite carrier had good anti-mildew effects.TEM,SAXS and DLS data showed that the anti-mould agent was located inside the cavity or on the surface of the carrier.Compared with casein-based hollow composite microspheres without anti-mould agent,the particle size was obviously increased to about 200 nm after loading anti-mould agent.Application results revealed that hygienic performance of the casein-based composite carrier decreased significantly while mechanical properties decreased slightly,which further illustrated that the anti-mould agent were loaded into the cavity of casein-based composite carrier,thus blocked the channel of gas molecules or water vapor molecules.?4?Polyacrylate modified casein hollow microspheres and polyacrylate modified casein/SiO₂ hollow composite microspheres were fabricated via emulsion polymerization stabilized by CPL-CA and CPL-CA/SiO₂ NPs,respectively.The related interface mechanism was established.As for CPL-CA stabilizer,effect of concentration and pH on emulsion stability in oil-water interface was investigated.By controlling KH570/TEOS ratio,surface activity of CPL-CA/SiO₂ NPs was adjustable.The results showed that CPL-CA/SiO₂ NPs with excellent emulsifying stability can be used as solid particles for Pickering emulsion.It was found that wettability of particles and stabilization of hybrid Pickering stabilizer on interfaces would affect the emulsion polymerization mechanism.Optical microscopy results showed that CPL-CA/SiO₂ NPs had better emulsifying stability than that of CPL-CA.It was proved that SiO₂particles have a synergistic effect with CPL-CA on emulsifying stability.Structure evolution from a droplet to a latex particle was observed by optical microscopy.It was found that CPL-CA/SiO₂ NPs could be regard as solid particles in Pickering emulsion.As a special hybrid Pickering stabilizer,CPL-CA/SiO₂ NPs could be applied in Pickering emulsion polymerization.Also,this mechanism differed from the conventional Pickering mechanism.