Mechanical properties of acrylic based latex blend coatings

A complete characterization of the mechanical properties of acrylic based l atex blend coatings comprising hard (T-g = 45 degrees C) and soft (T-g = -5 degrees C) phases is presented. Although clear and transparent in appearan ce, these blends remain phase separated through the entire range of composi tions based on their hard phase content. Blends with less than 50% hard pha se (soft blends) show a typical rubber-like behavior with large elongation to break and low stiffness, whereas those with more than 50% hard phase (ha rd 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 functio n of composition, in close agreement with the solutions of Hill-Budiansky e quations. These results, along with interpretations based on a percolation theory, indicate that a phase inversion to a continuous hard matrix from th e soft one occurs around 30-40% hard phase content, a conclusion further su pported by scanning electron micrographs of the fracture surfaces.