Particle formation and growth in semibatch emulsion polymerisation reactors
An investigation of emulsion polymerisation of butyl acrylate in batch and semibatch reactors has been carried out. The important phenomena of particle formation and kinetics in semibatch emulsion reactors with neat monomer feed and monomer emulsion feed have been studied. An investigation of batch emulsion polymerisation of butyl acrylate was also undertaken in order to provide the supporting evidence to elucidate particle formation in the semibatch emulsion process. Different start-up procedures were studied to determine their effect on the particle formation and kinetics of the polymerisation reaction. The effects of monomer distribution, emulsifier distribution, initiator distribution, feed rate, temperature and pre-period time on the particle formation and steady-state rate of polymerisation were investigated. Experimental studies reveal that particle formation in semibatch emulsion polymerisation is influenced by partitioning of ingredients, such as emulsifier and monomer, between the charge and the feed rate and controlling the growth rate of particles at monomer-starved conditions. The latter is applied by adjusting the monomer or monomer emulsion feed rate at a desired level. Changes in start-up procedure were found to have a significant effect not only on the transients before a steady-state, but also on the ultimate steady-state rate of polymerisation reaction achieved and final number of particles obtained. All variables affecting primary and secondary particle formation, and especially emulsifier concentration, could equally influence the steady-state rate of polymerisation reaction. Evidence was obtained indicating that secondary nucleation can occur through homogenous nucleation. The particle size distribution (PSD) development in the course of reaction for the semibatch emulsion process was investigated. Partitioning of ingredients between the charge and the feed and monomer starved nucleation were founa to be the main two factors that control the PSD and number of particles formed.