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Published on January 1, 2006

New Insights into the Freeze-Thaw Stability of Polymer Latexes

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Date Published January 1, 2006

This Report has been authored by:H.T. Davis at University of Minnesota #with# Xiaobo Gong at University of Minnesota #with# Joerg Leuninger at BASF AG #with# Cheng-Le Zhao at BASF AG #with# Rolf Dersch at BASF AG #with# Konrad Roschmann at BASF AG #with# L.E. Scriven at University of Minnesota

Freeze-Thaw (F/T) stability of polymer latexes and waterborne coatings formulations is of considerable industrial importance. Because of environmental concerns and legislative measures, there has been a driving force in recent years in the coatings industry to develop low-or-zero VOC (Volatile Organic Compounds) waterborne formulations. In a lower VOC formulation (<50 g/L), the amount of antifreeze such as glycols that can be added has to be substantially reduced and is most probably no longer sufficient to impart F/T stability. It is a challenging goal that the next-generation polymer latexes be improved in such a way that they are not only F/T-stable themselves but are also capable of providing F/T stability to the coatings formulations which are based on them. Partly because of the lack of adequate microscopic techniques, fundamental aspects of F/T stability have not been studied extensively and are not well understood. The objective of this work is to try to clarify and better understand the effects of the key factors affecting the F/T stability of polymer latexes. In addition to following viscosity changes during F/T cycles, we apply advanced cryogenic SEM technique coupled with a high pressure freezing apparatus, which allows us to visualize micro-structural changes and to study the effects of the freezing and thawing processes separately. Relationships between F/T stability and polymer and colloidal characteristics are analyzed. Cryogenic electron micrographs also provide information for understanding the cause of viscosity rise during the F/T processes in F/T unstable latex.