| Styrene-acrylate emulsions were synthesized by seed semmi-continuous emulsion polymerization with styrene(St) and butyl acrylate(BA) as main monomers. The effects of emulsifiers, methacrylic acid(MAA) content, morphology structure of latex particles and glass transition temperature(Tg) of copolymer on the freeze-thaw(F/T) stability of latex werestudied. The results showed that, with the same monomers, emulsions with soft core /hard shell were more stable than those with hard core /soft shell or homogeneous structure in the F/T processes. The F/T cycle times of emulsion, which had good Polymerization Stability, reached 10 times when the MAA content was 3wt%, the mass ratio of AG-124 to NKP-2 was 1 to 1 and the total emulsifier content was 2wt%.Fourier transform infrared spectroscopy(FT-IR), differential scanning calorimeter(DSC), transmission electron microscopy(TEM), Malvern laser scatter and viscometer were used to determine the F/T stabilization mechanism of emulsions. FT-IR analyses confirmed the copolymerization of polymerizable emulsifier, NKP-2 and main monomers. TEM and DSC analyses showed that structures of emulsion particles matched the designed morphology structure. Malvern laser scatter and viscometer results indicated that particle size and viscosity of emulsion, which was stable in the F/T cycles, were little changed. Theoretical analysis suggested that the F/T stability of emulsion was determined by the balance of four forces and the F/T process consists of four stages.Then the effect of methyacrylamide(MAM) content and hydroxypropyl methacrylate(HPMA) content on the properties of emulsion were studied to overcome the disadvantage of coatings with high pigment volume concentration(PVC). Also the effects of reaction temperature, ammonium persulfate(APS) content, dropping time of subsequent monomer and post polymerization process on monomer conversion ratio of emulsions were studied. The results showed that the introduction of MAM and HPMA improved the calcium ion stability and adhesion of emulsion, respectively. The emulsion with post polymerization process of t-BHP and FF6 M had reversely maximal monomer conversion rate(99.2%) when the reaction temperature was 80℃, the APS content was 0.5wt% and dropping time of subsequent monomer was about 4 hours.Finally, a high PVC and low VOC interior wall coatings without the addition of antifreeze was prepared with the self-made styrene-acrylate emulsion. The effects of types and content of additives on the properties of coatings were studied. The results showed thatthe addition of coalescent apparently improved the film forming property and wet-abrasion property of coatings. It was also found that the introduction of nonionic wetting agent with low HLB and combination of different types of thickeners were conducive to F/T stability of coatings. Coatings test results indicated that the interior wall coatings prepared showed high comprehensive properties, excellent F/T stability and perfect environmental performance. |
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