Dielectric analysis of cellulose and its vinylic copolymers

Abstract

SYNOPSISThe real and imaginary parts of the complex dielectric permittivity, d and t", for some vinylic copolymers of cellulose [prepared with vinyl acetate (VA) and methyl acrylate (MA) and Ce (IV) ions as initiator] and for cellulose were measured over a frequency band of 0.1-10' kHz and a temperature range from -40 to 100OC. In vinylic copolymers of cellulose, we observed one dielectric relaxation attributed to the a-relaxation of the vinylic side chain grafted on cellulose. In cellulose dielectric spectra, this relaxation did not appear, but we detected one relaxation that may correspond to the p-relaxation. For these vinylic copolymers of cellulose, the t" against t' plot gives a skewed arc that closely resembles that of the Davidson-Cole model, with a broader distribution for high frequencies that shows the overlap of several relaxations in the process considered. Some differences observed between the vinylic copolymers of cellulose may be due to the composition and the length of the vinylic side chains and to the frequency of grafting on the cellulose.

Electrical conductivity and dielectric properties of nanofibrillated cellulose thin films from bagasse

“…Studying the dielectric constant and dielectric loss as a function of temperature and frequency is one of the most suitable methods of studying cellulose structure to explore its use in electrical applications . Cellulose in the form of paper sheets or regenerated cellulose (cellophane) has been used as a dielectric materials for electrical insulation; its electrical properties have been extensively studied .…”

Biodegradation studies of cellulose and its vinylic graft copolymers by thermal analysis and mechanical spectroscopy

“…As it can be seen in Table III, copolymers CD1 and CB1 show lower T m values of the α‐peak than those of copolymer CD2, confirming the molecular origin of this relaxation. On the other hand, for the same PMA percentage in the grafted chains, the maximum temperature of the α‐peak increases with the crystallinity index of the cellulosic substrate (crystallinity index: Cel.D = 0.48 and Cel.B = 0.58) 4. This suggest again that the cellulose main chain hinders the motion of the vinylic grafted chains.…”

“…A , B , and T ∞ are three parameters that result from the application of a least‐squares fit to an experimental ln f m versus 1/ T m values set. Dielectric results obtained from other works4–6 for the dielectric α‐relaxation have been considered to carry out the determination of these parameters.…”

“… Arrhenius map for the undegraded copolymers of cellulose showing: the α‐, α′‐, and β‐relaxations for sample CD1 (▵) and the α‐ and β‐relaxations for samples CD2 (□), and CB1 (○). Dielectric results obtained from other works4–6 for the dielectric α‐relaxation have been considered as CD1 (▵), CD2 (□), and CB1 (○). …”

Composites Made from Lignocellulosics and Thermoset Polymers

“…In the second step, chain scissions occur and also water molecules are lost due to the intramolecular condensation of hydroxyls. Finally, in the third step, pyrolitic degradation of the wood components occur [6,7] . According to the above scheme, there are esentially no qualitative variations between the degradation processes of the different wood species [8] .…”