Reaction kinetics of styrene emulsion polymerization stabilized by mixed surfactants of SDS and NP-40

The effects of the mixed surfactants of anionic sodium dodecyl sulfate (SDS ) and nonionic nonylphenol polyethoxylate with an average of 40 units of et hylene oxide per molecule (NP-40) on the reaction kinetics of the styrene e mulsion polymerization were investigated. The polymerization rate is faster for the reaction system stabilized by the mixed surfactants with the wt% N P-40 in the surfactant mixture W(NP-40) = 50 or 90% as compared to the syst em stabilized only by SDS or NP-40 ( W(NP-40) = 0 or 100%). In addition, th e effectiveness of NP-40 to stabilize the latex particles is greatly reduce d as the reaction temperature (T) is increased. However, incorporation of a small amount of SDS into the reaction system makes it insensitive to T. A reaction scheme was proposed to qualitatively explain the kinetic data and the particle size and particle size distribution data for the runs with Var ious levels of W(NP-40) at 60 degrees C. During the very early stage of pol ymerization, limited bridging flocculation plays an important role in the n ucleation of latex particles for the runs with W(NP-40) = 100 and 90%. On t he other hand, the nucleated particles are relatively stable for the run wi th W(NP-40)= 0%. The run with W(NP-40) = 50 % shows an intermediate particl e nucleation behavior.