1H Spin–Spin Relaxation Time of Water and Rheological Properties of Cellulose Nanofiber Dispersion, Transparent Cellulose Hydrogel (TCG)

Abstract

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 ...

Flocculated flow of microfibrillated cellulose water suspensions: an imaging approach for characterisation of rheological behaviour

“…A small amount of added NaCl is expected to increase the G' to some extent (Lowys et al 2001), due to a moderate electrostatic screening effect allowing the fibrils to come into slightly closer contact and increasing the interfibrillar friction. On the other hand, higher NaCl concentrations result in the energy barrier collapse and aggregation of the fibrils (Ono et al 2004), as seen in Fig. 13.…”

“…New applications, besides using MFC in suspension form, have been proposed in composites utilizing the transparency of the most defibrillated MFC grades (Ono et al 2001;Ono et al 2004;Saito et al 2006) and the low thermal expansion of fibrils in e.g. optoelectronics (Yano et al 2005).…”

“…in flocs, has received only limited attention Ono et al 2004;Hill 2008;Lasseuguette et al 2008). Studies performed with both macroscopic fibre suspensions (Björkman 2000;Karema et al 2001;Chen et al 2002;Björkman 2005;Salmela and Kataja 2005;Hubbe 2007) and micro scale colloidal suspensions (Hubbe and Rojas 2008;Mewis and Wagner 2009a), however, show the great significance of flocculation and the need to analyse its contribution to suspension characteristics.…”

Flocculation of microfibrillated cellulose in shear flow

“…In addition to these, flocculation can be affected by non-DLVO interactions like steric and electrosteric interactions caused by polymers and polyelectrolytes in the system (Hubbe and Rojas 2008). All these forces and thus the floc structure can be changed for example by salt addition (Ono et al 2004;Saarikoski et al 2012), polyelectrolyte addition (Wågberg and Nordqvist 1999;Hubbe 2007;Karppinen et al 2011) or by changing the pH (Beghello 1998). The suspension structure and the related rheological properties are important for the processing of MFC, e.g., pumping or storage, and in some applications, e.g., use as a stabilizer in dispersions or rheology modifier in paints and coatings.…”

Surface functionalization of nanofibrillated cellulose using click-chemistry approach in aqueous media

“…In the case of unmodified and azide functionalized NFC, the addition of acid slightly increases the viscosity and moduli of the suspensions. A small increase in ionic strength by the dissociation of the weak acid leads to a moderate screening of the electrostatic repulsions between fibrils (Agoda- Tandjawa et al 2010, Ono et al 2004, which would allow for increased interfibrillar friction and thus an increase in the stiffness of the system. On the other hand, the addition of acetic acid to the suspension of 1,2,3-triazole-4-methanamine functionalized NFC, results in lower viscosity and a dramatic drop in moduli.…”