Influence of concentration of redox couple on freeze–thaw stability of styrene-acrylic copolymer latex

Abstract

Styrene-acrylic copolymer latexes were synthesized by emulsion polymerization process using sodium formaldehyde sulphoxylate (SFS) and tert-butyl hydroperoxide (TBHP) as redox initiators. Approximately 100% conversion was achieved successfully at 50°C. The redox polymerization was carried out at varied dosages of redox concentration; the lowest dosage of 0.3% was sufficient to achieve ~100% conversion. The molecular weight of the polymer was decreased with an increase in redox concentration as expected. The properties such as viscosity, specific conductivity, particle size, molecular weight, and Tg (by differential scanning calorimetric and dynamic mechanical analysis) of the redox polymers are reported. The other important property of the latexes is their freeze–thaw (F–T) stability. Even though ~100% conversion was achieved at 0.3% redox initiator couple, it failed in F–T stability test. Latexes prepared above 0.5% redox initiator couple successfully pass the five F–T cycles. The effect of sulfate from SFS, and tertiary butyl from TBHP species on the stability of the latexes is discussed. The F–T stability of the emulsions is very crucial in the coatings industry, and this article brings some insight into the effect of concentration of redox species on the stability of emulsions. Moreover, low-temperature processes are always appreciated in terms of safety and energy savings.