Comparison of Dielectric Loss Spectra of Paper Materials in the Temperature and Moisture Content Domains, 1999 International Paper Physics Conference Proceedings

C.J. Garvey, I. H. Parker, G.P. Simon

Dielectric relaxation spectroscopy has been selected as a method for studying the molecular motions of the polymer constituents of paper as a function of temperature and moisture content. The x-ray diffraction patterns of Whatman number 4 filter paper and eucalypt kraft bleached and eucalypt NSSC unbleached handsheets reveal heterogeneous systems of differing degrees of crystallinity and crystallite size. It was found that thermal degradation of the samples limits the temperature range for the experiment to below 220 o C. The glass transition is observed for the dry pure highly crystalline cellulosic filter paper but not for the other samples at a temperature ca. 180 o C. A series of secondary relaxations, the position of which is insensitive to frequency, are found in the temperature range -50 o to 100 o C. The filter paper has a fine structure to the loss peaks which is lost in the other samples and broadened in the NSSC handsheet. This implies that both chemistry and the polymer morphology of paper affects the position of the glass transition temperature and secondary relaxations. Using a novel electrode system, loss spectra have been collected for a range of frequencies as a function of filter paper moisture content/relative humidity. Two relaxation peaks appear in the loss data as a function of moisture content both of which show a frequency dependence, agreeing qualitatively with existing theories of the action of a plasticiser on a polymer ie., they depress the glass transition temperature.