The thermal expansion of mannan I obtained from ivory nuts

We have investigated the thermal expansion of mannan I crystals obtained from the endosperm of ivory nuts using X-ray diffraction in the temperature range of from room temperature to 250 °C on heating. Seven major diffractions were observed, and all the d-spacings gradually increased with increasing temperature. However, discontinuities indicating a phase transition were observed at a temperature of 130 °C. The unit cell parameters showed an anisotropic thermal expansion between the intermolecular hydrogen bonded direction and the covalently bonded direction, where the a and b axes lengths increased, but the c-axis length decreased with increasing temperature. Although the reason for the contraction of the c-axis length on heating is not clear, the thermal behavior should be related to the crystal structure and hydrogen bonding system of mannan I.