Understanding the effect of processing temperature and carbon nanotube addition on the viscoelastic response of polyurethane foams

We experimentally demonstrate a strategy to design the microstructure and hence viscoelastic behavior of polyurethane (PU) foams. PU foams are fabricated at two temperatures (room and −5°C) and reinforced with varying concentrations of oxidized carbon nanotubes (CNTs). Hierarchical pores, thicker cell walls, higher density, and low porosity are recorded in PU foams processed at −5°C. The addition of CNTs improves the cell wall stiffness and thermal stability of PU foams. Master curves constructed from dynamic mechanical analysis show that processing at −5°C and addition of 1.6 wt.% oxidized CNTs enhance the storage modulus of PU foams over a wide temperature and frequency range. Prony series analysis reveals that PU foams fabricated at −5°C have significantly lower relaxation time. Moreover, the elastic modulus of PU foams processed using optimized conditions shows stronger rate dependency in comparison to other types of PU foams fabricated in this work.