Preparation Of Binary Distribution High Solid Content Polyacrylate Emulsion

This work focused on the emulsion polymerization system of methyl methacrylate (MMA)/butyl acrylate (BA)/sodium dodecyl sulfate (SDS)/persulfate. Firstly, a series of seed latices with different solid contents, particle sizes (PS) and particle size distributions (PSD), the number of latex particle per unit volume of water (Np) was prepared by means of seed semi-continuous emulsion polymerization; and then high solid content (HSC) polyacrylate emulsions with bimodal particle size distribution were prepared by using the small and large seed lattices as the seeds. The effect of the surfactant coverage, the monomer feeding rate, BA content, the ratio of the number and the diameter of the large seed lattices to the small seed lattices on the solid content and the stability of the emulsion were systematically investigated. By determining the viscosity, particle size and its distribution of latex particles, the latex particle volume fraction and other performance indicators, the relationships between these performance indicators and the reaction parameters were established.On the base of the experimental results, the optimal process conditions to prepare the high solids content polyacrylate emulsion with bimodal particle size distribution was determined. The main results of this work are as follows:1. In order to prepare HSC polyacrylate emulsions with bimodal particle size distribution, there is a critical emulsifier coverage which need to overcome; and then the higher the surfactant coverage, the lower the viscosity of lattices. However, an extremely high surfactant coverage leads to the re-generation of latex particles by micellar nucleation, which influences the particle size and its distribution of latex particles.2. The monomer feeding rate is another important parameter. If the monomer feeding rate is too fast, the heat dissipation of the reaction system is difficult; moreover, the residual MMA and BA in aqueous phase will form new particles by flocculation nucleation and precipitation nucleation respectively, which reduces the surfactant coverage and decreases the stability of the emulsion system.3. BA content is another important parameter, because it influences the migration rate of MMA and the viscoelastic property of the latex particles. If the BA content is quite low, part of MMA will dissolved in the aqueous phase and then form new particles by flocculation nucleation; if the BA content is quite high, it will lead to the mutual cohesion between latex particles. The adhesive phenomenon seriously reduce the stability of the emulsion.4. The ratio of the number and the diameter of the large seed lattices to the small seed lattices constantly influence the particle size and its distribution of the latex particles in the polymerization process. A coordination of the particle size ratio and the number ratio can improve the space occupancy of latex particles and thereby increasing the solid content of the polymer emulsion.5. The latex particles in the HSC polyacrylate emulsion prepared by means of seeds in this work was bimodal particle size distribution. It was found that the optimal synthetic conditions were as follows:the surfactant coverage was between 101.8% and 113.5%, the monomer feeding rate was less than 2.07g/min, BA content was 20%, the ratio of the number of the large seed lattices to the small seed lattices was 2.14～2.37, the ratio of the diameter of the large seed lattices to the small seed lattices is 3.6～5.0, the solid content of polymer emulsion can achieve to 71.8% under these conditions.The results of this work provides important theoretical guidance to control the initiate secondary nucleation by one-step emulsion polymerization and how to effectively improve the space occupancy of latex particles, thereby prepare high solid content polymer emulsion with low viscosity.