The influence of the start up procedure of the emulsion copolymerization of styrene and butyl acrylate in a semi-batch reactor

The emulsion copolymerization of Styrene (Sty)-Butyl acrylate (BuA) was carried out in a semibatch reactor with sodium lauryl sulphate (SLS) as surfactant and potassium persulphate (KPS) as initiator. The effects related to the distribution of the monomer, the surfactant, and the initiator on the copolymer composition and the overall behaviour of the reactor were thoroughly studied. It was found that BUA rich initial charge increased the polymerization rate, reduced the particle sizes, and minimized the composition drift. The experimental data showed that the free unadsorbed surfactant in the reactor increased with increasing the fraction of the BuA monomer initially charged in the reactor. This led to an increase in the number of polymer particles and in return increased the polymerization rate. In addition, cross-linked copolymer was obtained when the BuA content was high indicating the possibility of gel effect which as well led to the apparent increase in the polymerization rate. The water-solubilities of the monomers did not affect the reaction kinetics or the copolymer composition. This was demonstrated experimentally and by means of mathematical modeling. Reducing the surfactant and the initiator concentrations showed the general behaviour of lower polymerization rates and larger particle sizes. The copolymer composition was not affected by the changes in the surfactant and the initiator concentrations in the reactor. Feeding part of the initiator or the surfactant during the semi batch stage while maintaining constant concentrations showed major effects on the sizes and the numbers of the polymer particles, and the polymerization rate. This is believed to be related to the change in the agitation intensity as a result of varying the volume of the initial charge. No effects were observed on the copolymer composition and the monomers mass fraction in the particles.