EVALUATION OF RELATIVE-HUMIDITY EFFECTS ON FABRIC-SUPPORTED PAINTINGSBY DYNAMIC-MECHANICAL AND DIELECTRIC ANALYSIS

Measurements have been made of the glass transition temperature and th e viscoelastic parameters of prepared paint samples and complex sample s from paintings at increasing values of relative humidity in the rang e 54-94%. The complex modulus data obtained from dynamic mechanical me asurements were fitted to the Williams Landel Ferry equation. The real part of the complex modulus was found to fit the equation, and time t emperature superposition was used to make predictions on the long term effects on the storage modulus of samples exposed to these conditions . The lack of fit of the loss data, however, made it necessary to cons ider an alternative model which takes into account several relaxation processes. Dielectric measurements on these samples showed that the re sulting complex permittivity data could be fitted using a cooperative model given by the Dissado-Hill function. Values of the parameters cal culated by this function are given for the corresponding values of rel ative humidity.