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 ...

An intimate relation between structure and mechanical properties of regenerated cellulose (Rayon, Benberg, etc.) has been investigated by measuring the humidity and temperature dependencies of infrared spectra, X-ray diffraction, and dynamic viscoelastic properties. At first the dynamic viscoelastic property and the infrared spectra were measured simultaneously during the increasing relative humidity at a constant rate (2% relative humidity/min) at room temperature. The Young's modulus was found to decrease remarkably around 40% relative humidity, where the content of the absorbed water increased largely as evaluated by the infrared spectral data. The water was considered to play a role as a plasticizer. Second, the temperature dependence of dynamic viscoelastic property was measured for the regenerated cellulose in a wide temperature region under the atmospheric environment. When the sample was heated from −150 °C, the anomalous phenomena could be observed in the temperature region of ca. −40 °C to room temperature:  the Young's modulus was diverged, and the intensity and peak position of the X-ray reflections were shifted and the infrared absorbance of the water molecule increased. When the liquid paraffin was pasted on the surface of the cellulose sample, such anomalous phenomena were not observed. The temperature region of these anomalous changes was found to correspond to the region where the absorbed water molecules changed the aggregation state drastically from solid ice to liquid water. In other words, the change in the aggregation state of the absorbed water is considered to affect the mechanical behavior of the regeneated cellulose quite seriously.

ABSTRACT:Morphological formation of the regenerated cellulose membranes from its cuprammonium hydroxide solution was investigated in connection with the change in the complex form between cellulose and cuprammonium hydroxide and material transportation during coagulation process using various aqueous coagulants (H +, Na +, K +, NH4 +, Ca 2 +, Mg 2 + with various counter ions). Scanning electron microscopically observation revealed that the morphological distribution estimated by pore size distribution in the thickness direction of the membranes are categorized into four types (two gradient types, homogeneously dense type and skin/void type) depending on pH and cation species (not anion species) of the coagulants, which are in turn the determinant of water permeability of the membrane. The each type of morphology was proved well correlated to the change in circular dichroism (CD) spectra taken for the coagulated gels as a function of coagulation time, which was also correlated to the transportation of ammonia and cupric ion from the original cellulose solution into the coagulants. Thus, the controlling of the morphology of the membranes from cellulose/cuprammonium hydroxide solution could be possible by simply selecting the cationic species of coagulants in general and the membrane with gradient pore distribution and having a relatively higher water permeability is obtainable by acid or ammonium salts as coagulant.