Preparation And Characterization Of Hydrophobically Modified Polyacrylic Thickeners

Hydrophobically modified alkali-soluble latex thickeners were prepared by semi-batch emulsion polymerization using methacrylic acid, ethyl acrylate, diallyl phthalate as the main monomers, ammonium persulfate (APS) as initiator, OP-21, OP-9 and sodium dodecylbenzene sulfonate as emulsifiers, with a varying amount of behenyl polyoxyethylene ether methacrylate (BEM) as functional monomer. Polymerization was easily carried out and stable polymer latex was obtained.The effects of various factors on performance of the thickener were studied. The properties of the thickeners themselves were characterized. Viscosity, particle size and size distribution of the thickener latexes were determined. It was found that particle size increased with BEM content. Viscosity and light transmittance variations with pH were followed at different solids of the latexes. Light transmittance of thickener latexes sharply increased when pH varied from 6.5 to 7.5, and remained relatively constant with continuing pH increase; while for the viscosity, a significant increase was also observed, followed by a slow decline after a maximum. Compared with latex thickener without BEM, thickening performance and shear resistance of the associative latex thickeners were enhanced when BEM content was below 5.0 wt% relative to total monomers mass and at 0.5 wt% solid or higher. However, performance and shear resistance of the thickeners bearing more BEM (8.0% or higher) were deteuriorated, eventually because of their decreased solubility in water. A detailed discussion on the machanisms of BEM thickening was given. In addition, the critical association concentration of the hydrophobically modified alkali-soluble latex thickeners was examined. The effects of temperature and electrolyte on the dynamic viscosity were also investigated. Dynamic viscosity of thickener latexes decreased when temperature varied from 0℃to 40℃, the associative thickeners prepared with 2.5 wt% of BEM content performed best in electrolyte resistance among all samples.Styrene-butyl acrylate (St-BA) copolymer latex were prepared by semi-batch emulsion polymerization using APS as initiator, OP-40, OP-9 and Sodium dodecylbenzene sulfonate as emulsifiers, N-hydroxymethyl acrylamide and N, N'-methylene diacrylamide as functional monomers.Thickening performance of associative thickeners for P(St-BA) latex was investigated. The effect of thickeners amounts and pH on viscosity of the P(St-BA) latexes were studied. Results showed that the samples done with 2.5 wt% BEM manifested highest thickening effect among all samples. The thickened latexes with associative thickeners manifested good rheological properties. Thickeners modified with BEM possessed higher thickening performance with less functional monomer than those prepared with triphenylethyl phenoxy polyoxyethylene ether methacrylate.