Dielectric studies on cellulose fibers

Abstract

A method for obtaining the intrinsic dielectric constant and loss factor of dry cellulose fiber along the fiber axis was developed, and the dielectric properties of viscose rayon, Bemberg (cuprammonium rayon), and cotton sliver were measured over the frequency range from 500 cycles/sec. to 3 Mcycles/sec. and the temperature range from −60 to + 20°C. by using the mutual inductance bridge. Only one dispersion could be observed in this temperature and frequency range. Cole‐Cole's circular are law could be satisfactorily applied to the data obtained, and the parameters of the are (ϵ0 – ϵ∞) and β for the three samples could be determined at each temperature. The value of (ϵ0 – ϵ∞), which is proportional to concentration of the dipoles contributing to the orientation, increased with rising temperature and reached a limiting value at about −20°C. The value of β relating to the width of the distribution of relaxation times also increased with rising temperature, showing a little rise in the degree of increase at temperatures above −20°C. On the other hand, the apparent activation energy for dipole orientation, as calculated from the temperature dependence of the dispersion frequency, reached a maximum around −20°C. All these facts suggest that some transition will take place in the neighborhood of −20°C. This temperature is not considered to be likely to be the glass transition temperature for dry cellulose, since −20°C. is too low for a primary transition in stiff molecules such as cellulose, and since the observed value of the apparent activation energy is too small to activate the segmental movement of the main chains. It might be possible to expect some secondary transition, probably of a thermodynamical nature, relating to the movement of local parts such as side chains, especially methylol groups on glucose residue, at about −20°C., though there is no other support for this expectation. Moreover, the effect of the fine structures on the dielectric properties is that the magnitude of (ϵ0 – ϵ∞) at each temperature decreases in the order, viscose rayon > Bemberg > cotton sliver, and this order parallels that of the accessibility of the three samples. This fact suggests that the dipoles in the amorphous region and on the surface of the crystallite provide the chief contribution to this dispersion.

Chemistry and water-repelling properties of phenyl-incorporating wood composites

“…As expected, the samples show an r max ′′ ε progression from KPF untr > KPF TEOS > KPF PTEOS > KPF PTMOS , which is in good agreement with the reduction of EMC (Seidman and Mason 1954;Ishida et al 1959;Norimoto 1976;Jinzhen and Guangjie 2002;Sugiyama and Norimoto 2006). Considering their higher EMC, a stronger decrease of r max ′′ ε could be expected in the KPF untr during drying.…”

Anisotropy of Dielectric Constant in Coniferous Wood

“…The intrinsic dielectric constants, which means the dielectric constant of substance itself, of cotton parallel to the fiber axis at i MHz and infra-red frequencies, which are estimated from the data shown by Ishida et al (1959), are 5.40 and 4.10 at 2O°C. Hermans (1949) computed the two principal refractive indices for crystalline native cellulose, i. e. 1.618 and 1.543, so that its intrinsic dielectric constants in the two principal directions at optical frequencies are 2.618 and 2.381.…”

Estimation of molecular structure in amorphous poly(4,4′‐dioxydiphenyl‐2,2′‐propane carbonate) by dielectric measurements and Monte Carlo calculations

“…-1 < j S 100/n,, where ns is given by eq. (3) and j is an integer. Thus, we have where p i 2 is the square dipole moment of the ith segment in the polymer chain.…”

“…The procedure and apparatus for dielectric measurements were similar to those described in a previous paper. 3 In order to obtain the effective dipole moment, we applied onsager's equation 4irN 3 Lo to the dielectric data in the rubbery state. Here, ps2 is the mean-square dipole moment per effective chain segment, nS% the number of monomer units in a segment, k is the Boltzmann constant, T is the absolute temperature, and N is the number of dipoles per unit volume.…”

“…The procedure and apparatus for dielectric measurements were similar to those described in a previous paper. 3 In order to obtain the effective dipole moment, we applied onsager's equation…”