Mechanical properties of waterborne coatings

Waterborne colloidal polymer coatings are widely used in architectural and agricultural applications where they are subject to challenging environments, such as extremes of temperatures and relative humidities (RH). A new research investigates the effects of adding two common co-formulants, poly(acrylic acid) (PAA) and xanthan gum (XG), to waterborne polymer composite coatings in these environments. The mechanical properties of the resulting coatings are of particular interest. Hardness, creep and tack properties of thick (~400 μm) formulated model coatings were characterized using a micro-indentation technique operating in a single cycle within a bespoke environmental chamber. Measurements were made at three temperatures (16, 20 and 30 °C), which span the glass transition temperature (T_g) of the acrylic copolymer binder, and over three RH values of 10%, 43%, and 90%.

Range of environments

In formulated coatings, both the tack and creep deformation increase as the relative humidity increases, and this trend is observed at each temperature. The observed softening of the coatings at high RH can be attributed to water sorption in the components. The presence of glassy PAA has the effect of raising the hardness. The addition of hydrophilic XG surprisingly reduces tack adhesion while also raising the viscosity of the coating. According to the researchers, these findings will inform the formulation of waterborne colloidal coatings to function in a range of environments.

The study has been published in Progress in Organic Coatings, Volume 163, February 2022.