Measuring and understanding blocking resistance in films cast from polymer latexes

Abstract

Good blocking resistance is a pre-requisite for the practical use of films cast from aqueous polymer dispersions in coating applications. However, most blocking resistance measurements are highly subjective and therefore differentiating between samples is a challenge and does not always represent performance in real situations. In this work, we report a method for the quantitative measurement of blocking resistance of films cast from emulsion polymers using a universal testing machine. A number of representative polymer latexes are prepared and the blocking resistance is measured using the technique. It is demonstrated that effects of time, temperature and pressure on blocking resistance can largely be understood from the rheological master curves of the films as determined by small amplitude oscillatory shear experiments. It is shown that samples with higher Young's modulus and higher terminal relaxation times result in improved blocking resistance.