DIRECT SIGNAL ANALYSIS APPLIED TO THE DETERMINATION OF THE RELAXATIONPARAMETERS FROM TSDC SPECTRA OF POLYMERS

A new method to evaluate the thermally stimulated depolarization curre nt curves based on the direct signal analysis is first applied here to the fitting of computer-generated curves to test its validity and acc uracy. The method consists in finding the N elementary curves that bes t fit the experimental spectrum. The adjustment of the tau(0) values a ssociated with each energy bin is also included in the fitting. The re sults are presented for a monoenergetic peak and a peak generated with a Gaussian broadened energy distribution both with a single tau(0). G ood agreement is also found when a random noise of width sigma(0) less than or equal to 0.01 J(max) is added to the data to simulate experim ental errors. Experimental complex curves corresponding to the gamma a nd beta overlapping relaxations in DGEBA-EDA epoxy resin system are se parated into their fine structure components. The complex band corresp onding to water dipoles physisorbed in different sites of the micropor osity of bituminous coal is analyzed and different processes are ident ified. The results are compared to those performed on cleaned peaks. F inally, the TSDC peak corresponding to the glass transition temperatur e in bisphenol-A polycarbonate is analyzed and could only be fitted by using a Vogel-Fulcher expression for the temperature dependence of th e relaxation times. (C) 1994 John Wiley & Sons, Inc.