Thermal expansion of polyurethane foam at low temperature

The mean linear thermal expansion coefficient of a newly developed polyurethane foam with a blowing agent of HFC245fa was measured from the liquid nitrogen temperature to room temperature by means of a relative comparison method in this paper. An automatic temperature measuring system, a vacuum system and an electrical heating system were adopted in the experiment. The relative comparison method has been analyzed, and according to the Kelvin model, a model describing thermal expansion of the foams was introduced. A very low thermal expansion with a slowly increasing trend versus temperature rising from 77 K to 230 K was shown in the result. In addition, it was indicated that the thermal expansion rate along a direction perpendicular to the pore rise is a bit higher than that along a parallel direction.