Quantification of Water-Sensitivity of Latex Films by Optical Transmission Measurements
|Date Published||January 1, 2005|
Polymer films prepared from coalescing latex polymers often have the disadvantage of being water-sensitive. Two main reasons for the water-sensitivity are: 1) the necessity of using water soluble additives such as water-soluble initiators and surfactants in the polymerization process, and 2) various water soluble co-monomers that are difficult to incorporate randomly into the polymer backbone. In this presentation, we shall discuss mechanisms of film-formation from latex polymers and describe the measurement of drying and water-sensitivity of latex films by optical transmission (ratio of voltages that is acquired into a CVS/Excel computer file). In such measurements, we draw down a thin film of latex to give a low initial optical transmission and monitor the increase of optical transmission with time as the film dries. Such film can then be subjected to various conditioning protocols before its water-sensitivity is evaluated by the same instrument. In this case we place a layer of water (or a solution of a chemical) on the film and monitor the decrease of the optical transmission as the film ‘blushes’ and becomes hazy or even white. We present various examples of drying of latex films from functionalized styrene-butadiene latexes, styrene-acrylic latexes, acrylic latexes, and natural rubber.