Structures and physical properties of rigid polyurethane foams with water as the sole blowing agent.

Rigid polyurethane foams blown by varying water level were prepared in this study. The structures and physical properties of rigid polyurethane foams blown by water were measured with FT-IR, universal testing machine (Instron3365), scanning electron microscope (SEM) and differential scanning calorimeter (DSC). The results show that polyurea and polybiuret were the typical characteristics, and the cream time and gel time were shorter for the fully water blown rigid foam than that for the fully cyclopentane blown foams. The density of foam samples decreased from 45.0 kg/m³ to 27.4 kg/m³ with the increase of water level from 3 pph to 7 pph. Compressive strength exhibited the similar behavior with density. The average cell size of foam samples ranged from 241 μm to 356 μm with the increase of water level from 3 pph to 7 pph, respectively. At the same time, poorer dimensional stability was encountered with the increase of average cell size due to fast diffusion rate of CO₂ out of the foam. The results of thermal analysis show that the glass transition temperature ( T _g) shifted to a higher temperature with the increase of isocyanate level when more water was used as chemical blowing agent. [ABSTRACT FROM AUTHOR]