Dielectric study of viscose rayon and viscose hydrocelluloses. I.

Both dielectric and x-ray results on viscose rayon and its hydrolysis residues show a rapid increase in the lateral order arrangement of the fiber chains in the earlier stages of hydrolysis. On the other hand, a divergence between the two measurements is found in the later stages of acid action. This is explained in terms of the role played by the fractions of molecular low dimensions which are in sensitive to x-ray diffraction but contribute to the polarizability of the dielectrics.     

Infra-red study on the oxidation of cotton cellulose,viscose rayon and their hydrolysis residues

The i.r. absorption band at 5·8 μm, characteristic of the CO group resulting from the oxidation of cellulosic fibres, has been used to study the effect of acid hydrolysis on the accessible OH groups of cotton cellulose and viscose rayon. The results obtained in this investigation, and those previously found by measurement of the rate constant of oxidation, show that both the i.r. and the rate constant of oxidation may be used as quantitative measures of the accessible OH groups in the various cellulosic fibres. The effect of temperature on the rate constant of oxidation of some hydrolysis residues was studied. The activation energies of oxidation of the late cotton hydrocellulose and viscose hydrocellulose residues have been found to be 12·2 and 13·3 kcal. respectively.     

Effect of ferric chloride on acid hydrolysis of viscose rayon

A comparison between the fine structure of viscose hydrocelluloses prepared by acid hydrolysis of viscose fibers in the absence and presence of ferric chloride is given. The results indicate that ferric chloride has little effect on the change in x-ray crystallinity indices accompanying acid-hydrolysis of the fibers. On the other hand, specific volume results show that the inner fine structure of hydrocelluloses prepared by hydrolyzing the fibers with free acid differs from that for hydrocelluloses prepared with an HCl-FeCl₃ reagent.     

Physicochemical and thermal studies of viscose rayon borate fiber and its carbon fiber

Nonhalogen compounds have been studied for improvements in the flameproofing property and toxicity of flame retardants. Borate compounds have properties of multifunctional smoke suppressants, flame retardants, and afterglow suppressants. In this study, borate was coupled onto the surface of viscose rayon felt. Coupling and carbonization were confirmed by attenuated total reflectance Fourier transform infrared (ATR FTIR). The initial carbonization temperature was certified with ATR FTIR, elemental analysis of carbon, and thermogravimetric analysis. In the carbonization step, all chemical groups of the surface of the viscose rayon felt degraded to the various gases. Moreover, the weight percentage of the carbon element increased with increasing carbonization temperature. Initial rapid thermal degradation temperatures of viscose rayon prepared at various temperatures increased with the increasing reaction temperature. The activation energy was calculated with the Freeman and Carroll method. The activation energy of borate‐coupled viscose rayon decreased much more than before coupling. However, the activation energy increased with the increasing carbonization temperature in the carbonization step. Viscose rayon borates showed higher limiting oxygen index (LOI) values and volumetric resistance rate values than viscose rayon phosphates. In this article, the relationship between the activation energy and LOI is studied. The synthesized viscose rayon borate is found to be highly effective as a flame retardant and electrically resistant. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3875–3883, 2001     

Effect of acid hydrolysis on the apparent specific volume of viscose rayon

The apparent specific volumes of viscose rayon and its hydrolysis residues, prepared by the action of 0·2 and 1 N HCl at 100°, were measured dilatometrically in the range 5–50° using toluene as displacement medium. The variation of the specific volume at 20° with the progress of hydrolysis showed a characteristic minimum, dependent on the hydrolytic conditions. These results, with those previously obtained from i.r. studies showed that the crystallinity of the fibre increased till 2·5% dissolution, and then decreased. Also, it was found that the second order transition of viscose rayon is primarily a function of its accessibility rather than its DP.     

Effect of acid hydrolysis on accessibility of micropores and thermal transition of viscose rayon

The changes in micropores accessible to toluene but inaccessible to decalin taking place during acid hydrolysis of viscose rayon were followed by specific volume measurements. The results show that these changes at the different stages of hydrolysis are of different order and dependent on the hydrolytic conditions. Also, it was found that the decalin molecules, which are larger than toluene molecules, could not follow the gradual disappearance of the thermal transition of viscose rayon with the progress of hydrolysis.     

Improving the reactivity of kraft-based dissolving pulp for viscose rayon production by mechanical treatments

The capacity of dissolving pulp to react with carbon disulfide under the defined conditions, known as the “Fock reactivity,” is an important parameter in determining the processability, end-product quality, and environmental impact in downstream rayon production. This study was aimed at improving the reactivity of kraft-based dissolving pulp by mechanical treatments, such as grinding and PFI refining, which can induce additional accessible surfaces in the compact cellulose structure via fiber cutting and fibrillation, respectively. Results showed that the Fock reactivity of a kraft-based dissolving pulp was increased from 49.3 to 71.8 % by 6-min grinding treatment under the conditions studied. Such a treatment led to increases in the fines content and specific surface area while decreasing the fiber length, intrinsic viscosity, and the crystalline ratio of cellulose. PFI refining can also result in changes in the fiber morphology and cellulose structure; a 25,000 PFI revolution treatment led to an increase in the Fock reactivity from 49.3 to 58.3 % for the same dissolving pulp.     

Dielectric investigation of the effect of ferric chloride on viscose fibres

Measurements of the dielectric constant and the dielectric loss, at frequencies of 0.05-10 kHz over a temperature range of 10–60 °C, were carried out on viscose fibres, viscose with iron adsorbed and with iron removed. The results obtained show that: (i) a relaxation process is observed in the low-frequency region only in the case of the viscose-iron complex, and (ii) the variation of the dielectric constant with temperature showed a transition at about 30 °C with the untreated fibres, and the transition disappeared when the fibres were treated with ferric chloride. These results, together with changes in hydrogen bonding obtained from infrared spectra for these samples are discussed. Oxidation and adsorption of ferric ions can modify the dielectric properties of viscose fibres.     

Study on syntheses of phosphates and transition‐metal complexes on viscose rayon felt for flame retardancy

High‐performance materials for flameproofing, phosphates (polyphosphate and ammonium phosphate) were synthesized on viscose rayon felt. This surface reaction has the advantage of a nonblooming effect and an application in thermosetting plastics. Metal complexes have the effect of reducing the amount of smoke. Therefore, in the second step, transition‐metal complexes were synthesized on the viscose rayon ammonium phosphate felt. This article focuses on the surface modification of phosphates and metal complexes on viscose rayon. All reactions were confirmed by attenuated total reflectance Fourier transform infrared and time‐of‐flight secondary ion mass spectrometry. As the concentrations of phosphoric acid and urea increased, the peak intensities of ammonium ion groups and phosphate groups greatly increased. The thermal properties of the synthesized materials were studied with thermogravimetric analysis and oxygen index testing. On the basis of the experimental results, the synthesized flame‐retardancy materials showed excellent physicochemical and thermal effects and flame retardancy. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2815–2823, 2000     

Dielectric relaxation studies of dipolar aromatics in polyethylene. II. Oriented low-density polyethylene

Stretched polyethylene has been used for several years by organic spectroscopists as a means of orienting isolated aromatic molecules. Dielectric relaxation studies are reported which consider dipolar aromatic molecules dissolved in stretched polyethylene in order to learn more about the environment of these oriented molecules. The research builds on earlier studies of the dielectric relaxation behavior of dipolar aromatic molecules dissolved in unoriented low density polyethylene. Studies demonstrate that molecules in the amorphous phase are oriented at temperatures below the glass transition, both the β and γ relaxations being orientation dependent. It is shown through studies of oriented rods that large numbers of the orientable molecules are immobilized by the oriented polyethylene and cannot relax. An essential criterion for immobilization to occur is that molecules exhibit geometrical symmetry.     

Structure and thermal properties of bamboo viscose,Tencel and conventional viscose fiber

Comparative investigations of new regenerated cellulosic fibers, bamboo viscose fiber and Tencel, together with conventional viscose fibers have been carried out to explain the similarity and difference in their molecular and fine structure. The analyses jointly using SEM, XRD and IR reveal that all the three fibers belong to cellulose II. Tencel consists of longer molecules and has a greater degree of crystallinity, while bamboo viscose fiber has a lower degree of crystallinty. TG-DTG-DSC study shows three fibers resemble in thermal behavior with a two-step decomposition mode. The first step is associated to water desorption, suggesting that bamboo viscose fiber holds better water retention and release ability, the second a depolymerization and decomposition of regenerated cellulose, indicating that Tencel is more thermally stable in this process than bamboo and conventional viscose fiber.     

Dielectric spectra broadening as the signature of dipole-matrix interaction. II. Water in ionic solutions

In this, the second part of our series on the dielectric spectrum symmetrical broadening of water, we consider ionic aqueous solutions. If in Part I, dipole-dipole interaction was the dominant feature, now ion-dipole interplay is shown to be the critical element in the dipole-matrix interaction. We present the results of high-frequency dielectric measurements of different concentrations of NaCl/KCl aqueous solutions. We observed Cole-Cole broadening of the main relaxation peak of the solvent in the both electrolytes. The 3D trajectory approach (described in detail in Part I) is applied in order to highlight the differences between the dynamics and structure of solutions of salts on one hand and dipolar solutes on the other hand.     

Dielectric dispersion of polypeptide solutions. II. Helix-coil transition of poly(epsilon-carbobenzoxy-L-lysine) in m-cresol.

Dielectric dispersion measurements were made on dilute solutions of poly(epsilon-carbobenzoxy-L-lysine) in m-cresol; this system underwent a very sharp thermal helix-coil transition of inverse type around 30 degrees. Mean-square dipole moments "mu-2" and mean rotational relaxation times t were obtained as functions of molecular weight and helical fraction fN. It was found that "mu-2"-one-half varied almost linearly with fN-one-half over a substantial portion of the transition. The relaxation times corrected for solvent viscosity and temperature changed only slightly with fN except in the region of small fN, while, at fixed fN, they displayed molecular weight dependence characteristic of rod-like molecules. These results can be explained if the transition is assumed to proceed almost in all-or-none fashion. This assumption is consistent with the previous finding from statistical thermodynamic analyses that the transition of the system PCBL-m-cresol is highly cooperative, with standard deviation of population one-half being 0.0025 to 0.0027, where standard deviation of population is the cooperativity parameter. Application of Nagai's theory of "mu-2" for interrupted helices yielded the result that standard deviation of population-one-half was in the range 0.001 to 0.005 and the monomeric dipole moment in the helical conformation was 5.4 to 6.2 D.     

Dynamics of glass-forming liquids. XII. Dielectric study of primary and secondary relaxations in ethylcyclohexane

The dynamics of ethylcyclohexane are investigated by high resolution dielectric spectroscopy aiming to characterize the relevant relaxational features of this simple system in its fluid, supercooled liquid, and glassy states. The dielectric signature of structural relaxation is a primary loss peak with amplitude Deltaepsilon=0.01, and a secondary loss process is found in the glassy state. This beta relaxation is compared with a "slow" process revealed by ultrasonics and with previously found gamma and chi processes in similar materials containing the cyclohexyl group. The results suggest that this secondary process is an intramolecular mode rather than a Johari-Goldstein process, consistent with its persistence in the liquid state at slow relaxation times which exceed those of the alpha process. The dielectric activity of such a slow process requires that the dipole magnitude changes with the intramolecular transition, whereas a change in dipole direction only would be masked by the faster structural relaxation.     

Molecular chain conformation and crystallite structure of cellulose. I. Fine structure of rayon fibers

A most reasonable folded-chain model for the fine structure of rayons (cellulose II) has been developed through experimental work on a theoretical basis. All the materials uniformly gave a levelling-off DP of about 40, equivalent to a length around 200 Å, for cellulose molecule segments at the early stage of heterogeneous acid hydrolysis when the first minor fraction is scarcely dissolved. Measurements by small-angle and wide-angle x-ray scattering put the crystallite length from various rayon fibers at about 200 Å, without exception. A family of GPC chromatograms, furthermore, on the hydrolyzed cellulose exhibited a single peak considered to represent monodispersed materials. These data suggest that clearly divided sections exist within the microfibril along its axis in a regular manner at an interval of about 200 Å. This cannot be explained in terms of the fringed micelle model. On the other hand, the possibility that cellulose II may have a folded-chain conformation has been demonstrated. A single cellulose molecule is essentially folded back and forth in the (101) plane to form a sheetlike structure. Such a structure is the basic unit that can fit perfectly into the unit cell of cellulose II. The cellulose molecule can achieve a fairly sharp U-turn in the (101) plane, with only one glucose unit of in the half-boat conformation. A crystallite consists of a number of sheets held together by secondary forces in the (101) plane. Accordingly, crystallographically, the crystallites are closely packed at the surface of each fold at its longitudinal edges to make up the cellulose microfibril. According to our model, the oxygen atom of the glucosidic link in the fold, where acid hydrolysis would have to take place, protrudes partially from the surface of the crystallite; a pair of atoms at the folds are then facing each other and are therefore, accessible for hydrolysis. This would explain chain scission of cellulose II at these sites in hydrolysis. This folded-chain model is supported further by other experimental evidence.     

Relaxation properties of some segmented polyurethane-CaCO3 composites. A Dielectric study

Dielectric relaxation in three segmented polyurethane-CaCO₃ composites was investigated between ?70°C and +150°C in the 300 Hz to 100 kHz frequency range. Two of the polymers contained a polyacetal-polyether soft segment, whereas the soft component of the third polymer was polypropylene oxide. The hard segments consisted of 4,4′-diphenyl methane diisocyanate in two cases and toluene-2,4-diisocyanate in the third case. In parallel studies two calorimetric relaxations, designated α and α′, were observed for each sample and were determined to be glass transitions of the soft and hard segments, respectively. In general, the transition temperatures decrease with increasing filler content. High frequency, low temperature permittivities increase while low frequency, high temperature AC conductivities generally decrease with increasing filler content. The shift in the transition temperatures can be explained using the adsorption theory of filler-polymer interactions and the densities of the samples. The interfacial polarization mechanism becomes important only above the α′ transition temperature and below 1 kHz.     

Dielectric study of hot-pressed nanocomposite polymer electrolytes

Ion-conducting nanocomposite polymer electrolyte films based on poly(ethylene oxide)-NaPO₃ 3: 1 with up to 15 wt % of SiO₂ have been prepared using recently developed hot-press technique instead of conventional solution cast method. With 7 wt % of SiO₂, the film conductivity has been enhanced by an order of magnitude. The materials have been characterized by Fourier transform infrared spectrometry and thermogravimetric analysis. For the composition with the highest conductivity, the temperature dependences of ionic mobility, mobile ions concentration, ionic transference number, and ionic drift velocity have been determined. Dielectric constant and dielectric loss have been measured. The conductivity enhancement has been discussed on the basis of existing theories of dielectrics.