Preparation Of Inorganic Nano-Particles/Emulsifier-Free Styrene-Acrylate Composite Emulsion

The technique of styrene-acrylate emulsion polymerization using reactive emulsifier which can participate in polymerization and can become parts of the formed film after reaction in place of traditional emulsifier can solve the disadvantages of traditional emulsion products such as the film water resistance and surface properties declining because of the dissociative emulsifier existing. It is possible that emulsions with more excellent function can be prepared on condition that inorganic nano-particles are compounded with emulsifier-free emulsions. This kind of composite can combine the perfect film water resistance of emulsifier-free emulsions and high rigid and strength of nano-particles.The styrene-acrylate emulsion polymerization using reactive emulsifier was studied first, in order to obtain harder film, the five-unit system of styrene, butyl acrylate, acrylic acid, acrylonitrile and methyl methacrylate was chosen according to the monomers characteristics and roles played in emulsion system. Furthermore, influences of the concentration of acrylic acid, acrylonitrile, reactive emulsifier, initiator, monomer proportion between styrene and methyl methacrylate, polymerization temperature on properties of emulsion were studied through orthogonal test and single factor test using reactive emulsifier. The better experimental components and conditions that were gotten finally were : St was 15.2%, MMA was 9.9%, AN was 3.7%, n-BA was 15.6%, AA was 2.3%, reactive emulsifier was 0.9%, initiator was 0.3%, chain transfer agent(DDMC) was 0.9%, NaHCO₃ was 0.2%, polymerization temperature was 85℃.On the basis, using the technique of pre-emulsification semi-continuous seeded polymeriz -ation system, modified inorganic nano-particles/styrene-acrylate composite emulsions obtained by in-situ emulsion polymerization had been prepared. The polymerization conditions were opt -imized through the inorganic nanoparticles choosing and orthogonal test. The results showed that the pre-emulsification mixture was 25.0% of its total weight, the nano-TiO₂ was 1.5% of the total monomers weight, the initiator using in seeded polymerization was 30% of its total weight, the seeded polymerization temperature was 85℃were the best experimental conditions. The thermal analysis results showed that the composite latex film presented higher thermal stability than the latex film unmodified by the nano-particles, and its physical properties were superior to nano-TiO₂ / emulsifier-included styrene-acrylate composite emulsion on the whole. The film of the nano-TiO₂/ emulsifier-free styrene-acrylate composite emulsion had a hardness up to 2H grade, and the water absorption was reduced by 29% which indicated that the film water resistance was improved. The structure and the morphology of the composite emulsion particles had been characterized. The TEM images showed that the emulsifier-free composite emulsion particles had core-shell structure. The light scattering experiments showed that the average particle size of nano-TiO₂/ emulsifier-free styrene-acryla -te composite emulsion was 79.8nm.Furthermore, the apparent kinetics and particles nucleation mechanism of nano-particles / emulsifier-free styrene-acrylate composite emulsion were studied. The results showed that in the stage of seeded polymerization, the modified nano-TiO₂ particles adsorbed emulsifier were the predominant particle nucleation, in the stage of shell-polymerization, the nucleation mechanism was "micellar nucleation". The apparent kinetics equation was R_p= k[I]^0.15[E]^0.83[M]^0.69, and the apparent active energy of the polymerization system was 104.3kJmol"1. Through the study of the effect of different dropping speed on the rate of polymerization, the coefficient of apparent kinetics K was used to discuss the polymerization condition. The results showed that with the increasing of mixture dropping speed, the condition of polymerization changed from starved to semi-starved semi-flowed state, and untill over-flowed state of the batch process finally. If the polymerization wanted to keep starved condition steadily, the time of feeding should be longer than 140min.In addition, the physical properties of coatings which were prepared by using nano-TiO₂ / emulsifier-free styrene-acrylate composite emulsions, emulsifier-free styrene- acrylate emulsio -ns and nano-TiO₂/ emulsifier-included styrene-acrylate composite emulsions, emulsifier-inclu -ded styrene-acrylate emulsions respectively were tested. The results showed that compoundin -g of nano-TiO₂ and reactive emulsifier could improve the coating film water resistance and the scrub resistance. The film water resistance of coating that was prepared by using nano-TiO₂ / emulsifier-free styrene-acrylate composite emulsions was over 126h, and its scrub number was over10000, which indicated that the coating property was improved obviously.This study results provide some theoretical and experimental basises for the polymerizati on and application of inorganic nano-particles / emulsifier-free styrene-acrylate composite emulsion.