ABSTRACT:Dissolution of cellulose into aqueous (aq) calcium thiocyanate solution was investigated with emphasis on solvent structure and interactions with cellulose. The aq calcium thiocyanate (Ca(SCNh) solution with concentration (CcaT) more than 48.5 wt% could dissolve any celluloses. Solvation measurement revealed that in wt%, the solvent system is formulated by Ca(NCS)2 • xH20 (x 4) + yH 2 0 (y 6), which exhibits mainly non-dissociated thiocyanate with high specific viscosity, as proved by electric conductivity, specific viscosity and IR or 13 C NMR measurements on solvent as a function of concentration of calcium thiocyanate. In this regard, the most stable 4 hydrate calcium thiocyanate is concluded from energy calculation as trans-trans configuration of Ca(-N = C = S) · 4H20. DSC and IR analyses suggested that dissolution of cellulose takes place by first attack of Ca(NCS)2 • xH2 0 (x 4) towards ring oxygen in cellulose. Ca(NCSh · xH2 0 (x 4) becomes 4-hydrates-like structure (sixcoordinate complex of Ca) and cellulose forms a 5-membered ring by coordinating two oxygen atoms (0(5) and 0(6)) in the glucopyranose unit, and then cellulose dissolves on heating. In this process, some ligand exchange might occur if the hydration number is more than 2. This coordination of cellulose is quite characteristic, compared with other solvents, such as cuprammonium hydroxide, which coordinate with 0(2) and 0(3) hydroxyl groups.
ABSTRACT:A new type of hydrogel, transparent cellulose hydrogel (TCG), is the aqueous dispersion of cellulose nanofibers (microfibrils) 10 nm in width and several hundreds nanometers in extended fiber length, and shows unique rheological properties leading to unique applications. The rheological properties of TCG, especially their dependences on temperature were investigated through the spin-spin relaxation time (T 2 ) analysis in 1 H NMR for water in the systems. Viscosity under low shear stress and T 2 of water (being very short for T 2 value) were proved to be constant in a wide range of temperature (ca. 30-80 C). These results may be explained by two considerations that network in TCG gradually grows with increasing temperature but collapses by adding weak shear stress and that TCG gel has large amount of bound water. It was also confirmed that the ionic strength such as pH and NaCl concentration sensitively influences on rheological parameters. With increasing ionic strength, the network formation and the successive aggregation of microfibrils occur and both should be interpreted in terms of the electrostatic interaction between negative charge on a cellulose surface and cationic aqueous layer around it (i.e., electric double layer). [DOI 10.1295/polymj.36.684] KEY WORDS Cellulose / Hydrogel / Nanofiber / Microfibril / Rheology / Spin-Spin Relaxation Time / Network / We have already found a preparation method of a new type of hydrogel, transparent cellulose hydrogel (TCG, Figure 1a), an aqueous dispersion of cellulose microfibrils (degree of polymerization: ca. 40) having low crystallinity with about 10-15 nm in diameter and several hundred nanometers in extended length ( Figure 1b) and reported the results for its characterization and properties. 1,2 This new nanomaterial was prepared by downsizing by chemical (hydrolysis reaction) 3 and mechanical (smashing by a ultra high pressure homogenizer) techniques. Resultant cellulose microfibrils in TCG are flexible fibrous particles, i.e., ''nanofibers'', having nano-size diameter (Figure 1b) and show strong attractive interaction based on hydrogen bonding between hydroxyl groups localized densely on their surfaces, leading to quite unique rheological properties. In view of the application, four major unique properties of TCG are pointed out 2 as follows: 1) Rheological properties such as very high viscosity under the low share stress, a large thixotropic character and low fluctuation of rheological parameters in the range of ambient temperature to the higher temperature region, 2) Formation of transparent coating film on substrate materials by drying, 3) Formation of cellulose microspheres having average particle size of less than 5 mm by spray drying, and 4) Stabilizing ability as an additive for aqueous suspension systems such as aqueous dispersion of inorganic particles (SiO 2 , TiO 2 , . . ., etc.) and O/W type emulsion (also as an emulsifier).Especially from an industrially applicable aspect, we discovered that TCG is a gel which can be sprayed by only ...
ABSTRACT:Attempt was made to clarify the structural change of wood pulp during the treatment of concentrated aqueous (aq) calcium thiocyanate (aq Ca(SCN)z) solution at room temperature. For this purpose, X-ray, DSC, and CPIMAS 13 C NMR were used to measure changes of crystalline structure and formation of cellulose-solvent complex. X-Ray data indicated that 55 wt% aq Ca(SCN)2 so ln. causes intracrystalline interplanar swelling of the wood pulp, forming cellulose--calcium thiocyanate addition compound. The interplanar spacing of (ITO), (110), and (200) planes increased for the former two planes and slightly decreased for the last one for treatment time td of 90 min. From DSC thermo grams of cellulose-55 wt% aq Ca(SCN)z soln. mixture, exothermic heat !'J.H for the formation of the addition compound was estimated to be ca. II kcal mol-1 , which was far iower than that for generation of cellulose sodium salt. The cellulose recovered from the system has quite different crystalline structure depending on treatment time and the reagents used for recovery. Up to td = 90 min, water recoverd the mixture of natural cellulose crystal (Cell
ABSTRACT:Attempt was made to investigate the solubility and the dissolved state of various cell uloses in aqueous (aq) calcium-and sodium-thiocyanate solution. Almost all cell uloses used in this study were soluble in 55 wt% aq calcium thiocyanate (Ca(SCN) 2) soln. at about 100°C, while 60wt% aq sodium thiocyanate (NaSCN) soln. dissolves only limited cellulose mainly regenerated from cellulose solution. The solubility of cellulose in 60wt% aq NaSCN was independent of the crystal form, crystallinity and the degree of polymerization of cellulose and this was explained only in terms of the degree of breakdown of intramolecular hydrogen bonds in the cellulose solid. Using 2-dimensional NMR six carbon peaks in 13 C NMR spectra of cellulose in two solvents were successfully assigned. The comparison of chemical shifts of cellulose in 55 wt% aq Ca(SCN)2 solution and 10% sodium hydroxide (NaOH) solution strongly suggested that calcium atoms as electron acceptors coordinate with oxygen atoms in glucose ring and primary alcohol at C(6) position, in the same manner of cellulose dipped in 55 wt% aq Ca(SCN)z solution at room temperature. In the 13 C NMR spectrum of cellulose-60% aq NaSCN solution system, C(3), C(2), and C(6) peaks were observed at lower magnetic field side, implying that sodium atoms interact with hydroxide groups at C(2), C(3), and C(6) positions of glucopyranose in cellulose molecules.
: The gelation conditions of cellulose/aqueous calcium thiocyanate solution system were determined by temperature jump method and the structure of the gel was analyzed by DSC and X-ray measurements. The time necessary to occurring gelation was shorter for the higher molecular weight sample, the solution with higher concentration, and at lower temperature. For the all solutions, cloud point was observed before occurring gelation, suggesting that the gelation was induced by liquid-liquid two phase separation. The heat to formation of 1 mol of network junctions in the gel and the mean molecular weight of the chain adjoining adjacent crosslinks were estimated from melting point determined by ball drop method and the heat of fusion by DSC. The X-ray diffraction curve indicated that the gel is almost amorphous.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.