The application of dielectric analysis and thermally stimulated current analysis to polymer coating solutions, films and coated substrates

Dielectric analysis was capable of distinguishing differences in the film formation mechanism of hydroxypropyl methylcellulose solutions and the various commercial ethyl cellulose colloidal dispersions. Although secondary transitions were observed with free films, the glass transition temperature was not detected due to electrode polarization.;Experimental parameters were developed for thermally stimulated current analysis which allowed the detection of primary and secondary transitions, interactions and incompatibilities of plasticized cellulosic free films. Teflon tape was used as an insulating material which prevented the injection of charges into the sample.;The method was also capable of detecting different transitions in uncoated and coated pellets. Curing the coated pellets resulted in lower depolarization current peaks at about the same temperature due to an increase in film density and decrease in dipolar activity. The effect of different curing temperatures on the film was also characterized. Distinct differences were observed in tablets of excipients with different amorphous contents. The glass transition of coated tablets could be observed for some systems but the detection was limited by the surface area to volume ratio.;Thermal windowing experiments differentiated individual modes of relaxation from global transitions. A single transition found in the Surelease free film was the result of the plasticizer present, bound water and the glass transition of the free film. Differences were observed in uncured and cured coated pellet film structure when the relaxation map data was converted to dielectric loss data indicating a film of greater density and lower dipolar activity.;The use of entropy and enthalpy of relaxation and compensation search methods for analyzing the relaxation maps did not correlate well with the thermally stimulated current or dielectric trans formation data. This was due to the complexity of the systems evaluated.