Morphology, mechanical properties, and thermal stability of polyurethane-epoxide resin interpenetrating polymer network rigid foams

A series of rigid interpenetrating network foams (IPNFs) based on a rosin-b ased polyurethane (PU) and a crosslinked epoxide resin (ER) were prepared b y a simultaneous polymerization technique. The morphology, mechanical prope rties, thermal stability, and changes in the chemical structure during the thermal degradation process of the rigid IPNFs were investigated by scannin g electron microscopy (SEM), compressive testing, thermogravimetric analysi s (TGA), and Fourier-transform infrared spectroscopy (FTIR). The SEM microg raphs showed that the cell structure of the rigid IPNFs became less homogen eous with increasing ER content. The brittleness of the cell walls increase d as the ER content and the cure time of the rigid IPNFs increased. The com pressive strength of the rigid PU/ER IPNFs increased to a maximum value and then decreased with further increase in the ER content. Similar behavior w as observed for the elastic modulus. This behavior was related to the nonho mogeneous cells and more brittle cell walls for the rigid IPNFs with high E R content. The TGA data showed that the thermal stability of the rigid PU f oam increased with the addition of increasing levels of ER, due to the bett er thermal stability of the ER compared to that of the PU. With the excepti on of the ER alone, a two-stage weight-loss process was observed for all th ese rigid IPNFs and for the PU foam alone. The FTIR analysis suggested that the first stage of weight loss was due to the degradation of the polyol-de rived blocks of the PU, and the second weight loss stage was governed by bo th the degradation of the ER component and that of the isocyanate-derived b locks of the PU. (C) 2000 John Wiley & Sons, Inc.