Synthesis And Properties Of The SiO₂/Polyacrylate Composite Emulsion

At present, the development of high-performance water-based coatings become themainstream of coatings industry. It’s an inevitable trend that solvent-based coatings wouldbe replaced by high-performance water-based environment-friendly coatings. Polyacrylateemulsions which have been widely used in water-based coatings possess good filmformation properties and excellent film properties including transparence, flexibility andweather-resistance. However, they have drawbacks such as low hardness and poorwater/solvent resistance. In this paper, polyacrylate emulsions were modified by inorganicSiO₂sol and organic silicone respectively to prepare organic-inorganic composite emulsions,and the stability of the composite emulsions and the performance of their films were alsostudied. The results will provide scientific theories and practical experience for the designand synthesis of high performance composite emulsions and water-based coatings.In this paper, firstly alkaline silica sol was modified in the presence of cosolvent ofalcohol. The effect of the different types and dosages of silane coupling agent and cosolvent,the pH value, the reaction temperature and time on the modified silica sol were studied. Andthe semitransparent modified silica sol which can keep stable for4⁵months was prepared.Then the SiO₂sol/polyacrylate composite emulsion was synthesized using the modifiedsilica sol and acrylate monomer by semi-continuous in situ polymerization method. Thetypes and dosage of monomers, emulsifier, initiator, dropping speed of the monomers andthe dosage of the SiO₂sol and so on were studied, and stable composite emulsion withaverage particle size of145nm, high silicon content of20%, and excellent Ca²⁺, centrifugaland freeze-thaw stability was obtained.Secondly, based on the optimized technique formula and synthesis process of the SiO₂sol/polyacrylate composite emulsion, organic silicone was successfully introduced andprepared organic silicone modified SiO₂sol/polyacrylate composite emulsion. The optimumcondition of the polymerization process was as follows: organic silicone of B contentsaccounted3wt%of the total monomers mass and added in reaction system with the last1/5of the shell monomers at the end of the emulsion polymerization, the reaction temperature was at80℃, the agitation rate was300rpm. The stable organic silicone modified SiO₂sol/polyacrylate composite emulsion was obtained with average particle size at225.6nm,conversion rate of92.1%and solid contend of35%. The result of TEM analysis showed thatinorganic SiO₂particles were cladding in or adsorbing on the latex particles and nodissociative SiO₂particles in the latex.Finally, we focused on the mechanical properties, water resistance, glossiness, solventresistance of the composite emulsion’s latex films. The results indicated that thepolyacrylate emulsion composited with SiO₂can increase film hardness significantly, andcomposite emulsion modified by organic silicone can improve film properties of waterresistance, solvent resistance and glossiness enormously.