This paper investigates the reinforcement of rigid polyurethane foams with carbon
nanotubes or graphite in order to improve their mechanical and thermal properties as
well as fire resistance. A small addition of carbon nanotubes (up to 0.05 wt.%) improves
the mechanical strength by about 20%, which was attributed to the strengthening effect
of nanotubes and the change in the foam structure, i.e. the smaller size of pores and
their narrower distribution. For higher nanotube content, the pore size does not change
but the overall porosity significantly increases which results in a decrease in the
mechanical strength. The thermal stability of nanocomposite foams and their
flammability increase as a result of the formation of a carbon layer forming at the
polymer surface. The addition of graphite greatly improves the fire resistance of
polyurethanes foams but significantly deteriorates the bending strength due to the poor
adhesion to the polyurethane matrix.