Water whitening of polymer films: Mechanistic studies and comparisons between water and solvent borne films

[Display omitted] •All polymer films water whiten, given the right conditions of time and temperature.•Water immersion temperature and wet Tg of the polymer are critical parameters.•Whitening degree depends upon polymer polarity and diffusivity of water in polymer.•Water borne films whiten rapidly due to the percolating paths of defects in film.•Mechanism of water whitening in solvent and water borne films is the same. Water whitening of polymer films derived from solution, bulk and emulsion polymerization processes was studied by the use of UV–vis-NIR spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), as well as visual observations. In addition to quantifying the wavelength dependent light scattering of the films over time, the different physical forms of water present in blushed films were quantified by DSC. SEM was used to observe sections of the films and characterize the scattering domains responsible for the whitening phenomenon. We studied the same polymers with and without the surfactants and salts used in emulsion polymerization, and compared the blushing of water borne and solvent borne films. We have found that all of the wide variety of (co)polymers we used water whiten under the right conditions of time and temperature. Residual surfactants and salts in latex derived films make the blushing process more rapid and more extensive than for the same polymer without them, but they are not the principal cause for water whitening. Neither is the particulate nature of the starting point for latex films, as the same whitening process occurs in solvent borne films of the same polymer. Both absorbance measurements and SEM images show that there is water domain size growth within the polymeric matrix over time. The size and number of the water domains are responsible for the water whitening effect and both can be restricted by the stiffness of the polymeric matrix. Mechanistic modeling of the time dependence of whitening has led to the prediction that the extent of whitening of non-latex based polymer films is directly proportional to the inherent water solubility in the polymer as well as the diffusivity of water within the polymer at the temperature of testing.