Vapor pressure determination by thermogravimetry

A method for measuring the vapor pressures of a wide range of materials using a conventional thermobalance and standard sample holders is described. The equipment is calibrated using pure reference materials of known vapor pressure and exploiting the relationship between volatilization rate and vapor pressure based on the Langmuir equation for free evaporation. Enthalpies of vaporization and sublimation can be determined, in some cases, the melting temperature and enthalpy of fusion can be obtained directly from thermogravimetry. Applications to the study of plasticizers and UV absorbers are described. Poor correlation of experimental results with predicted values obtained by molecular modeling is found. The application of modulated temperature thermogravimetry for the determination of enthalpies of sublimation and vaporization is also explored.