Study On The Coagulation Of ACR Latex

Acrylate copolymer (ACR) is a new kind of modifier for PVC, which can improve the processibility or impact strength of PVC when ACR with different composition and structure is used. So, ACR has wide application foreground and good economic benefit. The present work investigated the coagulation mechanism and influencing factors of ACR latex based on the fundamental investigation of preparation technology of coagulated particles. The results would provide theoretical and practical instruction for the industrial coagulation of ACR latex and other latexes.Different latex had different coagulation effects. Latex was more difficult to coagulate with higher ^-potential. When the concentration of coagulant was higher than critical coagulation concentration (ccc), the coagulated ACR particles could naturally sedimentate. Bivalent metallic cations electrolyte and inorganic acid were most suitable for coagulation process among all the inorganic electrolytes.The formation of coagulated particles undergoes three stages: particle-formation stage, aggregate-growth stage and particle-broken stage. Dispersion of coagulant at particle-formation stage was the key aspect of coagulation process. Aggregated particles become more and more compact and the coagulated particles formed at the aggregate-growth stage. Particle size, coagulation efficiency and C.V. were increased with time at the early two stages. In the continue agitation, particle diameter will be descended because of particles broken into many smaller particles. Then, coagulation efficiency was leveled off and C.V increased. It is showed that the mechanism of batch coagulation and semicontinous coagulation are similar, excluding the different time of particle-formation and aggregate-growth stages, i.e., different coagulating speed of two stages.It was proved by experiments that particle diameter increased with exponential order when temperature was increased. The particle size of coagulated ACR particles could be adjusted by the variation of coagulating temperature. Tg of polymer on latex particle surface was very important for selecting suitable temperature. The latex particles in the coagulated particle would fused together and the particle surface would shrink and become smooth when temperature was higher than Tg.IfIVThe batch coagulation experiment showed that the particle size, coagulating speed and C.V. only increased when the ionic concentration of coagulant increased in specific range. The coagulated particle size and coagulation efficiency of core-shell ACR latex increased in range of 10%~15% solid content. If solid content >15%, system viscosity and C.V. would increase. As agitation speed increased, coagulation efficiency and speed increased, but particle diameter decreased.The semi-continuous experiment showed that particle size and coagulation speed increased with higher concentration of H2SO4 coagulant when the concentration of H+ in latex system maintained consistent. As [H+] in latex system increased by adding F^SC^, system viscosity and coagulation efficiency increased, but particle size increased firstly and decreased later. When copolymerization-latex solid content ranged from 16% to 20%, the operation character of latex, coagulation efficiency, amount of coagulant and particle size distribution (PSD) was good. The amount of used coagulant decreased and PSD widened as solid content increased. The particle size, coagulation efficiency and speed increased as agitation speed increased. But the influence of agitation speed was weaker than that of the concentration of coagulant.The packing density of coagulated particle powder was effectively improved in the semi-continuous coagulation process, by adding higher efficiency coagulant, coagulating at higher temperature and shorter agitation stabilization time, selecting proper curing temperature and time, and applying segmentation-dry method.Pilot-plant experiment showed that agitation played an important role in coagulation. The packing density of powder changed no more, and more b...