Effect of substituents on dielectric beta-relaxation in cellulose

The dielectric characteristics for some cellulose derivatives, namely chlorodeoxycellulose (Cell-Cl; degree of substitution of chlorine, DSCl = 0.87), bromodeoxycellulose (Cell-Br; DSBr = 0.92) and thiocyanatodeoxycellulose (Cell-SCN; DSSCN = 0.88), all substituted only at C-6, together with those of regenerated cellulose, have been investigated in the temperature range - 60 to 120 degrees C, and in the frequency range 0.2-100 kHz. Only one relaxation process, designated as beta, was identified within the frequency and temperature ranges studied. The activation energy of this relaxation increases in the order Cell-Cl < Cell-Br < Cell-SCN, suggesting that the bulkiness of the substituent was the determining factor of the activation energy. The characteristic dielectric parameters, namely polarization magnitude (Delta epsilon) and shape parameter (alpha or <(beta) over bar>), were obtained by the analysis of absorption bands and are discussed in relation to the substituent effect.