Preparation And Coating Properties Of Polyacrylate/Nanosilica Composite Latexes

Waterborne polyacrylate latexes are applied in various fields,such as constructions,textiles,papermaking,petroleum and industrial anticorrosion,due to their advantages of adjustable molecular structure and performance,environmental benignancy and weather resistance.However,the polyacrylate coating also has disadvantages such as poor heat resistance,bad water resistance and low hardness,so its development in practical applications is limited.Compounding polyacrylates with rigid and wear-resistant inorganic nanoparticles to prepare organic-inorganic nanocomposite emulsion is an effective way to enhance the performance of polyacrylate coatings.However,the compatibility between inorganic nanoparticles and the polymer is always low due to their polarity differenence,and the dispersion of inorganic nanoparticles in the polymer matrix is uneven.Therefore,it is often necessary to perform chemical modification of inorganic particles before polymerization,which also means the preparation process of composite emulsions is complicated.In response to the above problems,in-situ Pickering emulsion polymerization and miniemulsion polymerization methods were applied to synthesize polyacrylate/nanosilica composite emulsion by adding a auxiliary monomer which can form a hydrogen bond interaction between nanosilica in the thesis.The polymerization kinetics,size distribution,morphology and the formation mechanism of composite particles,as well as the characteristics of composite latex films were studied.Firstly,MMA copolymer/nanosilica composite latexes were prepared by Pickering emulsion polymerization using methyl methacrylate(MMA)as the main monomer,1-vinylimidazole(1-VID)as the auxiliary monomer,silica as the Pickering emulsifier,and azobisisobutamidine hydrochloride(AIBA)as the initiator.Without any previous surface treatment,silica nanoparticles could be adsorbed onto the surface of latex particles and acted as an emulsifier in the polymerization with the help of auxiliary monomer and AIBA initiator.It was shown by transmission electron microscopy that the synthesized composite particles had an obvious "strawberry-like" structure.Influences of AIBA concentration and nanosilica usage on the monomer conversion,average size and size distribution of composite latexes were investigated.It was found that the rate of Pickering emulsion polymerization was increased as the concentration of AIBA increased.The size distribution of the composite particles became narrower with the increase of AIBA concentration,and gradually widened with the increase of amount of silica.Due to physics interactions between AIBA and silica,1-VID and silica,stable emulsions with high silica content(i.e.,21%?27%)could be successfully prepared.Secondly,silica sols with different particle sizes were prepared by the sol-gel method using ethyl orthosilicate as the precursor and ammonia water as the catalyst.MMA copolymer/nanosilica composite latexes were synthesized by in-situ miniemulsion polymerization using MMA as the main monomer,1-VID as the auxiliary monomer,sodium dodecyl sulfate(SDS)/hexadecane(HD)as the main emulsifier/emulsifier,and oil-soluble azobisisobutyronitrile(AIBN)as the initiator.Effects of temperature,AIBN concentration and the amount of silica on the polymerization kinetics were studied.The results showed that the miniemulsion polymerization rate was increased as the temperature and AIBN initiator concentration increased.The presence of silica had a certain retarding effect on the miniemulsion polymerization.Influences of silica particle size and usage,emulsifier concentration on the morphology of composite particles were also studied.When nanosilica with a size of 20 nm was added in the polymerization system,the size of the composite latex particles was mainly affected by the concentration of SDS emulsifier.However,when emulsifier Tween-80 was used in the early stage of polymerization and a small amount of SDS was added in the later stage,the silica acted as the Pickering emulsifier to ensure the stability of the composite latex.The sizes of the composite latex particles with different amounts of silica were ranged between 90?200 nm,and the average size of composite particles was increased and size distribution became wider ad the usage of silica increased.X-ray photoelectron spectroscopy(XPS)proved the presence of silica particles on the surface of MMA copolymer latex particles.Finally,polyacrylate/nanosilica composite latexes containing different amounts of nanosilica were prepared by miniemulsion polymerization using MMA and BA as monomers,1-VID as auxiliary monomers,SDS as the main emulsifier and HD as the co-emulsifier.The formation of composite particles was confirmed by transmission electron microscopy and the film forming process of composite emulsion was affected by temperature.The hydrophobicity and glass temperature of the composite films were increased with the increase of the silica content in the latex film.AFM analysis of the surface morphology found that the addition of silica increased the surface roughness and water resistance of the latex films.The tensile strength and storage modulus of latex films were increased when the silica content ranged from 3%?9%.