Over the past several decades, the market share for waterborne coatings has increased at the expense of solventborne formulations. There were several drivers for this shift, but one of the primary motivations was a conversion to a more environmentally friendly medium in formulations. These waterborne formulations were still typically supplemented with other co-solvents to address some of the issues associated with utilizing water-based dispersions. For example, glycols were included to depress the freezing point of the water to protect the formulation in the event of exposure to freezing conditions, and to slow the evaporation of water during film formation in an effort to provide more robustness in the final application. Volatile coalescents were also used to temporarily depress the glass transition temperature of the higher-molecular-weight polymers in the latex to allow for adequate film formation at lower temperatures while still ultimately yielding a hard, resistant final film.
However, there is now an on-going push from government agencies and consumers to further mitigate health and environmental impact concerns by reducing the associated VOC content of waterborne formulations. This implies a significant reduction or elimination of glycols and volatile coalescents from formulations. Although the desire would be to provide low-VOC coatings with equivalent to superior performance as compared to higher-VOC predecessors, satisfactory alternatives to the co-solvents that delivered the key properties alluded to above have proven elusive to date. To better comprehend some of these inherent challenges, it is instructive to consider the underlying fundamental mechanisms.