Study On Preparation And Properties Of High-solid-content Polyacrylate Latex

One of the major challenges in emulsion polymerization over the past two decades was how to increase the solid content of latex products. Multi-modal particle dispersed colloid is one of the efficient routes to produce HSC latexes. In order to verify relationship between secondary nucleation, colloidal stability and rheological properties during the preparation process, this thesis attempted to obtain bi-modal and tri-modal Poly (methyl methacrylate/n-butyl acrylate/acrylic acid)[P(MMA/BA/AA)] latex vie semi-continuous seeded emulsion polymerization. As a result, in situ nucleation and colloid growth in multi-dispersed system seemed more different from traditional preparation technology.Using large-sized and mono-dispersed seeded latex as medium plus a semi-continuous monomer-feeding technology was an effective method for preparing high solid content (HSC) latex. A series of key factors, such as surfactant, monomer composition, seeded particle size, reaction temperature, feeding rate and pH of latex products were studied during re-nucleation section. It was found that using anionic surfactant lauryl sodium sulfate (SDS) and nonionic surfactant as a compound system could help to improve the stability of colloids, and also reduced viscosity of products. The results showed that when m(SDS)/m(OS-15) was1.5/0.5, the seed particle size was487nm, the content of MMA and AA in monomer was about40wt%and3wt%respectively, reaction temperature was80℃, and feeding time was more than60min (feeding rate was1.67g/min), the colloidal system was able to provoke a compliant re-nucleation, and maintained an excellent growth of subsequent particles. Naturally, these process conditions would provide a desired PSD and obtain a HSC latex with low-viscosity and high-stability. The viscosity of corresponding latex was able to keep a lower value, below500mPa-s when shear rate was20s-1.In addition, tri-modal (composited) latex was succeed in producing with a large particle size was about600nm, medium-size about200nm and small-size about80nm o The preparation process contained two steps:(1) Preparing bimodal P(MMA/BA/AA) seeded emulsion with solid content at60wt%by semi-continuous seeded emulsion polymerization (large particle size was550nm and small was120nm);(2) Using the seeded emulsion as medium, SDS and OS-15as compound surfactant, sodium bicarbonate (SBC) as buffer and ammonia persulfate (APS) as initiator to prepare tri-modal latex by semi-continuous emulsion polymerization. And also make a comparison between films of two corresponding latexes.