Alteration of polyurea hard domain morphology by diethanol amine (DEOA) in molded flexible polyurethane foams

Abstract

In this study, the morphology of polyurea hard domains in flexible polyurethane molded foams was investigated to evaluate the influence of diethanol amine (DEOA), a commercially utilized cross-linking agent. Tapping Mode AFM was utilized to reveal that DEOA dramatically alters the morphology of the solid state. Without DEOA, the solid state phase separation leads to the formation of lamellae-like polyurea domains ca. 50–100 nm long by 5 nm wide, and these lamellae frequently aggregate to form larger precipitates ca. 30–50 nm in diameter. These larger aggregations appear to be evenly distributed in the material. However, when DEOA is added to the formulation, the hard domains become smaller and more geometrically isotropic, ca. 5 nm in diameter. Furthermore, in the DEOA containing material, the hard domains do not appear to form the larger 50 nm aggregates but instead remain distributed at ca. 10 nm apart. The addition of DEOA thus reduced the observed level of hard domain interconnectivity, an effect which is suggested to explain in part the corresponding reduction in modulus (i.e. stiffness) that is commonly observed when DEOA is added to such foam formulations. The morphological alterations observed using AFM were also found to correlate well with the DEOA induced changes in the small angle X-ray scattering profiles of these samples.