Flexural properties of mica filled polyurethane foams

Abstract

Integral skin foams consist of a cellular core and a near solid skin of the same material surrounding the core. A study of the effect of mica on the flexural properties of free rise and integral skin polyurethane foams is presented. Addition of a small amount of mica (5% v/v) is found to significantly increase the flexural modulus of free rise foams; however, the modulus remains nearly constant with further increase in mica concentration when compared at equal densities. The flexural strength of free rise foams is found to decrease with an increase in mica concentration. Similar trends with mica concentration are obtained for the integral skin foams of a fixed overall density. In this case, the properties of the foams are also dependent on structural parameters such as the skin and core thicknesses and the corresponding densities which are measured. A three region model for the integral skin foam structure (core and two skins) is developed to obtain the flexural modulus and strength for foams with dissimilar upper and lower skins in terms of the thickness and the properties of the regions. Empirical equations, based on the experimental data for free rise foams with different mica loadings, relating the flexural modulus and flexural strength to the density, are used to calculate the properties of each region in the model. The predicted values obtained from the model are found to be in reasonable agreement with experimentally measured values of flexural modulus and flexural strength. The mode of failure (tensile rupture as opposed to wrinkling) is also correctly predicted by the model.