Measurement of thermal expansions of closed-cell polyurethane rigid foams at cryogenic temperatures with an extensometer technique

Abstract

The database of thermal expansion behavior of closed-cell polyurethane rigid foam at very low temperatures is required for designing and manufacturing thermal insulation components of various cryogenic systems. In the present work, thermal expansion behaviors of closed-cell polyurethane rigid foams with different densities were investigated in the 20 K-270 K temperature range by means of a high-resolution extensometer technique, which has been verified through comparison with standard values of an AISI 304 stainless steel rod. The comparison result demonstrates that the maximum deviation from the standard coefficient of thermal expansion of the AISI 304 in cryogenic temperatures is less than 6.6%. Testing results indicate that the cryogenic thermal expansions of closed-cell polyurethane rigid foams depend reversely on density. Moreover, the thermal expansion behavior of closed-celled polyurethane rigid foams exhibits difference from that of bulky amorphous isotropic polymers, which have been attributed to several factors such as enclosed air and cellular structure.