Effect of hard segments on the thermal and mechanical properties of water blown semi-rigid polyurethane foams

Abstract

Water blown semi-rigid polyurethane foams with different ethylene glycol (EG) content were prepared. EG is used as chain extender to vary hard segments content of semi-rigid polyurethane foams. The effect of EG on foam molding process, hard segment structure and the relationship between structure and thermal, mechanical properties of foams has been investigated. Results indicate that the addition of EG contributes to preparing flawless foams, and reduces the apparent density of foams due to the increase in cell size. Fourier transform infrared analysis (FTIR) displays the existence of hydrogen bonds among polyurea segments, which is influenced by reactant activity. Dynamic mechanical analysis (DMA) manifests different phase mixing and soft domains Tg of foams with different EG content. Soft domains Tg is dependent on the purity of soft domains controlled by urethane hard segments and dissolved urea groups. Thermo gravimetric analysis (TGA) illustrates that thermal stability of foams is associated with hard segments content in foams. Mechanical tests demonstrate that improvements of mechanical properties of foams can be achieved by modifying foam formulation to increase microphase separation of polyurea segments.