Calorimetry of two disperse dyes using thermogravimetry

A method for studying the volatilisation rate of materials using a conventional thermobalance and standard sample holders is described. This was used to study two dyes; CI Disperse Yellow 54 and CI Disperse Red 60. Using pure reference materials, a relationship between volatilisation rate and vapour pressure based on the Langmuir equation for free evaporation was used to calibrate the system. Thus, the vapour pressures of the dyes could be determined. Heats of sublimation and vaporisation were calculated from a plot of the logarithm of the vapour pressure against reciprocal absolute temperature. Extrapolation of the vapour pressure vs. temperature curve outside the experimentally measured region for Red 60 was made using the melting point and heat of fusion found by DSC. Good agreement was found with literature data. In favourable cases, the melting temperature and heat of fusion can be obtained directly from thermogravimetry. (C) 1998 Elsevier Science B.V.