Supramolecular structure and properties of high strength regenerated cellulose films

Water-swollen cellulose films prepared from LiOH/urea solution were uniaxially drawn to investigate the effect of orientation on their supramolecular structure and properties. Their structures and properties were investigated with X-ray diffraction, atomic force microscopy and tensile testing. The results revealed that the drawing process led to substantial reorientation of the cellulose molecular chains, resulting in a significant improvement of their mechanical properties and water-resistance. With an increase of the drawn ratios from 1 to 1.22, the tensile strength of the films at dry and wet states increased from 89 to 213 MPa and 2.9 to 33.9 MPa, respectively. Furthermore, the drawn cellulose films also exhibited good biocompatibility with the capability of supporting cell adhesion and proliferation.     

Computer simulation of cellulose solvation in polar solvents

The solvation of cellulose molecules in water and N-methylmorpholine N-oxide has been investigated by the molecular-dynamics method. An analysis of simulation results yields the conformational characteristics of cellulose molecules in these solvents: the mean-square distance between polymer chain ends and the radial distribution function of monomer units. The radial distribution functions of oxygen atoms of solvents relative to protons of carbohydrate molecules are estimated. This step makes it possible to draw conclusions about the number and character of hydrogen bonds and the local structure of solvate shells.     

Nanoindentation of regenerated cellulose fibres

Nanoindentation was performed on cross sections of regenerated cellulose fibres with different structure and properties. Same as in single-fibre tensile tests, the elastic modulus of lyocell was higher than the elastic modulus of viscose. However, in spite of its tensile strength being twice as high as viscose, the hardness of lyocell was 15% lower than viscose. The overall degree of orientation of cellulose chains being higher in lyocell than in viscose, it is proposed that reduced lateral bonding in lyocell is the reason for the low hardness measured by nanoindentation compared to viscose.     

Nonalkali swelling solutions for regenerated cellulose

Swelling of regenerated cellulose in nonalkali aqueous solutions containing lithium chloride and urea (LiCl/urea/water) was examined. The effect of solution concentration on fiber properties was studied using microscopy, weight gain (swelling), and mechanical strength tests. The regenerated cellulose samples included lyocell fibers, viscose fibers, and fibers spun from alkali. The change in the mechanical properties of treated fibers was smaller than that of fibers treated with alkali to the same level of swelling. The degree of swelling in these solutions was related to the propensity for the formation of Li–cellulose coordination complexes, and these were enhanced by reductions in both urea and water content.     

The surface charge of regenerated cellulose fibres

In this paper the influence of charged species on the sheet strength of viscose fibres was investigated. Four samples of chemical modified viscose fibres, as well as a reference fibre were studied. The swelling of these viscose fibres and the breaking length of hand sheets have been determined. Comparing the results, the influence of both, swelling and surface charge on the bonding force, is evident. The allocation of the charges, induced by cationic starch and Carboxmethylcellulose, has been analyzed by Titration, attenuated total reflection spectroscopy (ATR) and X-ray photoelectron spectroscopy (XPS). Titration was used to make a first estimation of the charge distribution within the fibre. Using ATR and XPS, more detailed information about the surface charge has been achieved. All measurement methods showed a significant amount of charge on the fibre surface.     

The microcrystalline structure of regenerated cellulose fibers as studied in negatively stained ultrathin sections

Summary The microcrystalline structure of viscose rayon and Fortisan, a highly oriented regenerated cellulose fiber, is studied with a new modification of negative staining, by the electron microscope. With this method, the microcrystalline structure of the viscose rayon can be directly observed.The ultrastructure is found to consist of closely packed oblong particles of uniform size in homogeneous distribution, except for the presence of voids and dense skin structures. The particles can be isolated and be demonstrated by metal shadowing as well as by negative staining in the section. The diameter of the particles is 32–40 Å in viscose and somewhat in Fortisan. These dimensions correspond to those calculated from small-angle X-ray scattering for the size of the microcrystallites.In length sections of Fortisan, the particles are seen to be aligned in longitudinal direction, forming long strings of 300–400 Å length.The particles are concluded to be the cellulose microcrystallites as studied by X-ray methods and the particle strings correspond to the molecular strings suggested byKratky.

---

Zusammenfassung Die mikrokristalline Struktur von Viskosefasern und Fortisan einer hochorientierten regenierten Zellulosefaser wird elektronenmikroskopisch mit einer neuen Modifikation von negative staining (Färbemethode) untersucht. Mit dieser Methode wird die kristalline Struktur der Faser unmittelbarer Beobachtung zugänglich.Die Ultrastruktur stimmt überein mit dichtgepackten länglichen Partikeln gleicher Größe in homogener Verteilung, mit Ausnahme des Auftretens von Hohlräumen und von dichten gepackten Hautstrukturen. Die Partikel lassen sich isolieren und können sowohl durch Metallbedampfung wie durch negatives staining hinsichtlich ihres Querschnitts untersucht werden. Der Durchmesser ist 32–40 Å in Viskose und etwas größer in Fortisan. Diese Dimensionen entsprechen denen, die sich für die Größe der Mikrokristallite aus Kleinwinkelstreuung ergeben.In den Längsschnitten von Fortisan findet man die Partikel in longitutinaler Richtung aufgereiht, sie bilden lange Stränge von 300–400 Å. Es ist anzunehmen, daß diese Partikel die vonKratky in Zellulose vermuteten Stränge aus Mikrokristalliten sind.

---

---

Research supported by the National Science Foundation and by I.T.T.-Rayonier Inc.     

Modelling the crystalline deformation of native and regenerated cellulose

The molecular mechanics modelling of the deformation of a number of proposed structures for the crystalline regions of cellulose I- , I- and II are reported. The structures used are from coordinates that have recently been reported, which have made particular reference to the ability to locate the positions of hydrogen bonds. By comparison to previously reported structures of cellulose, where the emphasis on this has also been made, and in a diagnostic way, it is shown that it is possible to make some conclusions as to their validity. The effect of removing the intramolecular hydrogen bonding is also reported. All structures, with one exception, are shown to be sensitive to this operation. Two approaches to the molecular mechanics modelling are reported, wherein the structures are minimised under restraint, by altering the c-spacing, within the COMPASS^TM forcefield to obtain a simple chain stiffness value or alternatively by performing a full elastic constants determination for the unit cell.     

Preparation of the water-soluble chitosan-coated oxidized regenerated cellulose gauze

A water-soluble chitosan-coated oxidized regenerated cellulose (ORC) gauze was prepared by the oxidation of a viscose gauze with NO₂/CCl₄ and subsequent treatment with a solution of chitosan in aqueous acetic acid and finally neutralization with NaOH/C₂H₅OH solution. A series of C6 ORC samples with different –COOH content were prepared and coated by chitosans (CTS) with different molecular weight (Mw) of 2,000, 50,000, 100,000 (denoted as CTS1, CTS2, CTS3). FT-IR and TG suggested the formation of the amide bond between the carboxyl group of ORC and the amino group of CTS. Kjeldahl nitrogen analysis of ORC gauze treated with CTS (CTS-ORC) showed that the percentage of chitosan with the lowest Mw of 2,000 introduced on ORC surface was highest and increased with oxidation time, while chitosans with medium and high Mw showed that the maximum percentage of chitosan introduced on ORC surface occurred at the oxidation time of 8 h. The neutralized chitosan-coated ORC gauze could still maintain its original morphological form and was water-soluble, and could form a transparent gel quickly for 5 s in water. The prepared water-soluble gauze could be anticipated to possess the improved hemostatic and antibacterial properties.     

Carboxyl groups in pre-treated regenerated cellulose fibres

The influence of peroxide bleaching and slack-mercerization on the amount of acidic groups in regenerated fibres (viscose, modal and lyocell) were studied. Conductometric titration was used to determine the total content of acidic carboxylic groups. Polyelectrolyte titration was used for surface and total charge determination, and to obtain information about the charge distribution and accessibilities of charged groups. Changes in fibre crystallinity to pre-treatment processes were characterized using iodine sorption (Schwertassek method) and correlated to treatments and the amount of carboxylic groups. For all three types of fibres the amount of accessible carboxyl groups was lowered by an increase in the degree of crystallinity. Bleaching with hydrogen peroxide causes some oxidative cellulose damage and, therefore, a larger amount of carboxyl groups (presumably formed at the end of cellulose chains). Slack-mercerization did not significantly change the total amount of acidic groups in the fibres, but their accessibility to cationic polyelectrolytes, in particular to polymers with high molecular weight was substantially lowered. Lidija Fras Zemljič, Zdenka Peršin, and Karin Stana Kleinschek are the members of the European Polysaccharide Network of Excellence (EPNOE).     

Computer simulation of the structure of the electrochemical double layer

We analyze and compare the structure of the electrochemical double layer obtained from molecular dynamics simulations of concentrated aqueous NaCl and CsF solutions near a model electrode. The electrode is modeled as a corrugated external potential in conjunction with the image charge model. Calculations are performed for uncharged electrodes and for electrodes carrying positive or negative surface charges.     

Orientation of cellulose crystallites in regenerated cellulose fibres under tensile and bending loads

The degree of orientation in regenerated cellulose fibres with a diameter of 36μm was determined using position-resolved synchrotron X-ray microbeam diffraction. The fibres were characterized in unstrained condition, under tensile strain, and in bending. A homogeneous distribution of the degree of crystalline orientation (Herman’s orientation factor f _c = 0.85) across the fibre thickness was found in the unstrained fibre. The degree of orientation of cellulose crystallites increased in a linear manner with increasing tensile strain applied to the fibre. Also in bending, a linear relationship between applied strain and the degree of crystalline orientation was found, where f _c increased in tension and decreased in compression. This linear relationship was found to be valid for both the tensile and the compressive zone of the bent fibre.     

Interfacial structure and properties of polyurethane/poly(methylacrylate-co-styrene) coating to regenerated cellulose film

A semiinterpenetrating polymer network (IPN) containing 72 wt % polyurethane (PU) and 6 wt % poly(methylacrylate-co-styrene) [P(MA-St)] was coated onto surfaces of regenerated cellulose (RC) film, which was prepared by coagulating a cellulose cuoxam from bagasse pulp. The interfacial structures, bonding manner, and the strength of the coated film were studied by infrared (IR),¹³C nuclear magnetic resonance (NMR), differential thermal analysis (DTA), transmission electron microscopy (TEM), and electron probe microscopy analysis (EPMA). It was shown that the RC film coated with PU/P(MA-St) has strong interfacial interactions, where covalent and hydrogen bonds are formed across the interface between cellulose and the PU/P(MA-St) coating. The interfacial structure of the coated film is regarded as a shared PU network crosslinked simultaneously with P(MA-St) and cellulose film. The tensile strength, water resistivity, and optical transmission of the coated films were considerably higher than that of the uncoated films. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2495–2501, 1997     

Preparation of porous regenerated cellulose microstructures via emulsion-coagulation technique

Cellulose - Cellulose-based materials, such as cellulose microspheres, have attracted enormous attention because of their widespread applications in water and protein purifications, chromatographic...     

Kinetic study on TEMPO-mediated selective oxidation of regenerated cellulose

The kinetics of the TEMPO-mediated oxidation of regenerated celluloses has been studied. It is revealed that the oxidation reaction of the regenerated celluloses by the 2,2,6,6-tetramethyl-piperidine-1-oxyl radical (TEMPO)–NaBr–NaOCl system can be approximately described by first-order kinetics with respect to substrate. In the concentration range used the rate constant k is directly proportional to the concentration of TEMPO, while it is proportional to the concentration of NaBr in a relatively lower range and tends to level off at higher concentration. The effect of temperature on the rate constant can be well described by the Arrhenius equation, the apparent activation energy measured is about 66.2 kJ/mol. The effect of the pH of the reaction solution, the crystallinity and morphology of the substrates on the oxidation rate is also discussed.     

Swelling and dissolution mechanisms of regenerated Lyocell cellulose fibers

The swelling and dissolution mechanisms of dry, never-dried and re-wetted Lyocell fibers were investigated using mixtures of N-methylmorpholine N-oxide and water with various contents of water (from monohydrate to 24% w/w). A radial dissolution starting from the outer layers was observed. Dissolution kinetics was dependent on the water content, the drying state and the spinning conditions. A buckling of the core of dry fibers was observed during swelling. This phenomenon was attributed to the deformation of the unswollen core to accommodate the contraction of the swollen parts of the fiber. In purely swelling conditions with no dissolution, a huge swelling of a very thin skin layer was observed in the first stage, followed then by a progressive swelling of the inside of the fiber. We postulate that this mechanism arose from the fact that this skin is much less crystalline than the core.     

Interaction of water with the regenerated cellulose membrane studied by DSC

One to three endothermal peaks atributted to melting of bulk and interfacial water were observed by DSC in the regenerated cellulose — water system. The profiles of thermal effects depend on water content, time of conditioning, film pretreatment and the conditions applied during the preceding freezing-thawing cycles. The occurrence might be deduced of melting-crystallisation processes. A large amount of non-freezable strongly bounded water was also detected. Although cellulose absorbs water quickly after immersion, the structural changes consisting on ordering of polymer fraction occur during further conditioning due to increase in strength of water binding. Using the membranes in the separation module at 90°C causes weakening of these bonds. Differences between interaction of particular cellulose films with water can be detected during the first, the second and the third heating. This revised version was published online in July 2006 with corrections to the Cover Date.     

Computer simulation of two-step atomization in graphite furnaces for analytical atomic spectrometry

The processes of sample fractionation by two-step atomization with the intermediate condensation of the analyte on a cold surface in graphite furnaces were theoretically studied. The transfer equation was solved for the atoms, molecules, and condensed particles of the sample from a flow of argon directed along this surface. The spatial distributions of vapor and the condensate formed were calculated depending on the composition and flow rate. It was found that a cold surface section with a length of 6 mm is sufficient for the complete trapping of atomic analyte vapor from an argon layer having a velocity of about 1 m/sec and a thickness of 5 mm. In this case, the molecules and clusters condensation coefficients smaller than unity were deposited insignificantly; that is, they were fractionally separated. The results of the shadow spectral visualization of the process of sample fractionation on a cold probe surface of in commercial HGA and THGA atomizers were interpreted. The advantages of analytical signals upon the evaporation of a sample condensate from the probe in these atomizers and inductively coupled plasma were demonstrated.     

Computer simulation and diffraction studies of the structure of liquid benzene

The review offers critical analysis of the results of the diffraction studies and computer simulation of the structure of liquid benzene. It is shown that until recently, structural studies were mainly investigations of the nearest surroundings of molecules, but did not ultimately provide reliable data. Modern approaches to studies of liquids at higher levels are considered, and a structural model of liquid benzene is suggested.