Properties of rigid polyurethane foams with blowing agents and catalysts

Rigid polyurethane foams (PUFs) were prepared from polymeric 4.4-diphenylmethane diisocyanate (PMDI) and polyether polyol with amine catalyst. Water was used as the chemical blowing agent and, cyclopentane and hydrofluorocarbon (HFC) were used as the physical blowing agents. The kinetic rate of forming the PUF increased with the catalyst and water content. The cell size of the PUF sample decreased with increasing amount of the blowing and gelling catalysts. In the case of the PUF sample blown by water only, the amount of the blowing catalyst had no significant influence on the density and the compressive strength of the PUF sample. In the case of the PUF sample prepared with using HFC or cyclopentane as the blowing agent, however, as the amount of the blowing catalyst increased, the density and the compressive strength of the PUF sample increased. The PUF sample blown by the physical blowing agent had smaller cell size than the PUF sample blown by the chemical blowing agent, if compared at same density. The PUF sample blown by mixed blowing agent (cyclopentane/water = 7/3, mole ratio) had lower thermal conductivity than the PUF samples blown by cyclopentane or water only, at the equal mole content of the blowing agents. This result suggests that the low thermal conductivity of the PUF sample blown by mixed blowing agent is due to the increase in the structural stability of the PUF foams.