Syneresis and rheology mechanisms of a latex-HEUR associative thickener system

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• 作者：Franceska A. Santos ; Tyler J. Bell…
• 关键词：Syneresis ; Rheology ; Associative thickener ; Shear ; thickening ; Bridging flocculation ; Latex ; thickener interactions
• 刊名：Journal of Coatings Technology and Research
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：14
• 期：1
• 页码：57-67
• 全文大小：
• 刊物类别：Chemistry and Materials Science
• 刊物主题：Tribology, Corrosion and Coatings; Surfaces and Interfaces, Thin Films; Polymer Sciences; Industrial Chemistry/Chemical Engineering; Materials Science, general;
• 出版者：Springer US
• ISSN：1935-3804
• 卷排序：14

文摘

This study focuses on the phase behavior, rheology, and interactions of polymer latex particles and a hydrophobically modified ethoxylated urethane (HEUR) associative thickener in water. At constant 0.25 latex particle volume fraction, increasing HEUR caused stable, followed by phase separated (syneresis), and stable mixtures as HEUR concentration increased from 0% to 2.0% (by weight) in the latex-thickener aqueous mixture. The mixtures that underwent syneresis were flocculated. The relationship between the flocculation behavior and the composition of the latex-HEUR mixtures is consistent with previous work reported by other investigators. However, detailed rheological data on systems like these that have undergone syneresis have not been reported. This paper presents detailed viscosity vs shear rate data and correlates viscosity trends with the both flocculation and syneresis behavior. The stable latex-HEUR mixtures at low HEUR levels show Newtonian or shear-thinning viscosity with well-defined low-shear Newtonian plateaus. As HEUR level is increased to levels at which syneresis is observed, erratic rheological profiles with shear thinning as well as thickening are observed. This type of shear thickening has been attributed to bridging flocculation by other investigators. When HEUR level is further increased to levels at which no syneresis is observed, low-shear Newtonian plateaus re-appeared, albeit at higher viscosities. Detailed analysis of syneresis and shear-thickening behavior of a latex-HEUR mixture containing 0.5% (by weight) HEUR showed two shear-thickening regions, one between 0.1 and 0.5 s−1 shear rate range and another between 30 and 100 s−1 shear rate range. Molecular weight distribution (MWD) of the HEUR thickener indicates that the two shear-thickening regions are related to the bi-modal nature of the thickener’s MWD.