Mechanical properties of acrylic based latex blend coatings

A complete characterization of the mechanical properties of acrylic based latex blend coatings comprising hard (T-g = 45 degrees C) and soft (T-g = -5 degrees C) phases is presented. Although clear and transparent in appearance, these blends remain phase separated through the entire range of compositions based on their hard phase content. Blends with less than 50% hard phase (soft blends) show a typical rubber-like behavior with large elongation to break and low stiffness, whereas those with more than 50% hard phase (hard blends) exhibit a progressively glassy behavior. The values of effective Young's moduli and Poisson's ratios lie within the bounds calculated from Hashin-Shtrikman models and exhibit a sigmoidal shaped profile as a function of composition, in close agreement with the solutions of Hill-Budiansky equations. These results, along with interpretations based on a percolation theory, indicate that a phase inversion to a continuous hard matrix from the soft one occurs around 30-40% hard phase content, a conclusion further supported by scanning electron micrographs of the fracture surfaces.