Josef Schurz

Problems and results of zeta-potential measurements on fibers

A survey is given on both theoretical background and methodical details of zeta-potential measurements on fibers. Electro-osmosis and streaming potential/streaming current measurements can be used in order to obtain correct zeta-potentials. Both measuring principles yield the same values for zeta-potential if the errors due to resistance measurements are avoided. This agreement as well as the independence of zeta-potential of applied voltage (in the case of electro-osmosis) and hydrostatic pressure (in the case of streaming potential/streaming current) point out that the Stern-potential at the boundary immobile/diffuse layer can be determined. Electrophoresis and measurement of other electrokinetic phenomena give values related to but not identical with the zeta-potential. Applications of electrokinetic measurements for investigating fiber problems in production, processing and finishing are reviewed. Parameters determining the zeta-potential of fibers are discussed.

Properties and structure of solvent-spun and viscose-type fibres in the swollen state

The conditioned and wet tensile strength resp. modulus of solvent-spun and viscose-type cellulose fibres was correlated with their crystallite and amorphous orientation factor. It was found that the extrapolation of these tensile properties to the maximum degree of orientation results in identical values of the tensile strength resp. modulus in the conditioned and water swollen state. Proportional to a decreasing orientation factor the loss of strength and modulus by swelling increases. Additionally, a positive correlation was found between the wet tensile strength resp. modulus and the intensity of the interference of the equatorial small-angle x-ray scattering measured in the swollen state. This interference is caused by the elementary fibrils. The intensity of this interference is a measure for the fibrillar character of the swollen fibre structure. The fibrillability of the fibres suspended in water correlates positively with the crystallite orientation factor.

Rheology of polymer solutions of the network type

The treatment of network solutions shall be presented in two steps. First, the phenomenological behavior will be discussed together with relevant rheological fundamentals. Then the implications of structure rheology will be outlined and the methods explained which allow a characterization of network solutions by means of rheological measurements. Finally, some experimental results will be shown to substantiate these discussions

Rheology of synovial fluids and substitute polymers

Synovial fluids are highly viscous and viscoelastic solutions responsible for lubrication and damping in joints. Based on work with both healthy and arthrotically deteriorated human knee joint syno...

An X-ray diffraction study of the crystalline to amorphous phase change in cellulose during high-energy dry ball milling

In methods used widely for determining crystallinity of cellulose substrates by X-ray wide angle diffraction the scattering characteristics of truly amorphous cellulose is needed. So far, such scattering curves have not been available. It was the aim of this study to arrive at an experimentally determined scattering curve of amorphous cellulose. For this purpose, two cellulose samples (a pine wood pulp and a microcrystalline powder) were ball milled in a high-energy equipment in order to destroy the crystalline structure. The structural changes in the cellulose samples and the kinetics of amorphization were followed by taking X-ray diffractograms. After 30min of milling, no more change in the structure could be observed and the diffraction curve of amorphous cellulose with two diffuse maxima at spacings of 0.427nm (strong) and 0.247nm (weak) was obtained. The amorphization was found to follow a first order kinetics, the rate constant of k=(0.0033±0.0004)s -1 holding for both samples. However, while the amorphization of the microcrystalline cellulose started immediately, with the wood pulp sample an induction period of about 300 seconds was observed, which is probably due to residual morphological structures present in this sample.

Investigation of the solution structure of hyaluronic acid by light scattering, SAXS, and viscosity measurements

SummaryHyaluronic acid in water exhibits a non-monotonous scattering function, which is explained in terms of multimerization leading to gel-like supermolecular particles. This tendency is highest in water, lower in buffer, and lowest in isotonic NaCl-solution + NaN3. Viscosity measurements show that with increasing concentration a network solution is formed. SAXS-measurements show that nonaggregated Hyaluronic acid is present either in form of double strands, or as supercoils with helical portions.ZusammenfassungHyaluronsäure zeigt in Wasser eine nicht-monotone Streufunktion, die als Ausdruck einer Multimerisation gedeutet wird, welche zu gelartigen übermolekularen Teilchen führt. Diese Tendenz ist in Wasser am stärksten, schwächer in Puffern, und am schwächsten in isotoner NaCl-Lösung + NaN3. Viskositätsmessungen zeigen, daß bei höheren Konzentrationen eine Netzwerk-Lösung gebildet wird. Röntgenkleinwinkel-Messungen ergeben, daß die nicht aggregierte Hyaluronsäure entweder in Form von Doppelsträngen oder als Superknäuel mit helikalen Anteilen vorliegt.

On the Elongation Mechanism of Regenerated Cellulose Fibres

The elongation at break äs well äs the tensile modulus of solvent spun cellulose fibres, both measured in the conditioned state, correlate with the amorphous orientation factor. The relevant regression curves are similar to that of the relation between the elongation at break resp. the tensile modulus and the crystallite orientation factor; the latter preceding the amorphous orientation factor with increasing total orientation. Hence it is concluded, that the elongation mechanism of regenerated cellulose fibre does not consist only of orientation of crystallites, but that additionally a straightening and orientation of the less ordered molecular segments in the interstices between the crystallites has to be assumed.

Photochemical degradation of hyaluronic acid by singlet oxygen

Changes of the rheological properties of hyaluronic acid (sodium-magnesium salt) solutions after exposure to UV radiation indicate a vigorous decrease in their viscosity, but its still strong shear rate dependence. Whereas the presence of the singlet oxygen sensitizer (anthracene-1-sulphonic acid) brings about a loss of shear dependence; the studied solutions show newtonian behavior.

Oil-water emulsions: Particle size distributions from elastic light scattering data

Abstract Particle size distributions are important quality criteria for pharmaceutical emulsions. Fat emulsions for intravenous administration should have a typical particle size of a few hundred nanometers and not overshoot an upper size limit of 2 μm. Particles with a higher diameter, suspected to cause adverse reactions (emboli), can be found in a phase contrast microscope. Our method uses elastic light scattering, i.e., the angular dependent scattering intensity to size particles in the range of 100 nm up to several micrometers. The advantage of this method compared with quasi-elastic light scattering is the higher resolution due to a higher information content of the experiment (much lower condition numbers of the matrix). It takes into account the actual relative refractive index and uses the Lorenz-Mie theory as a basis of the inversion procedure. This yields accurate number and intensity distributions, defined as the relative number of particles and the relative scattering intensity in the interval R and R + dR . Since the scattering intensity is roughly proportional to the sixth power of the radius, larger particles can be found in the intensity distribution even if their number is in the ppm range. We can therefore supply the producer with two important and well-defined kinds of information: (a) the number distribution, which provides the parameters of the particles like mean, standard deviation, and skewness; (b) the intensity distribution, which is a very sensitive control for undesired large particles.

The length of the crystalline domains in fibres of regenerated cellulose: determination of the crystallite length of cellulose II by means of wide-angle X-ray diffraction and transmission electron microscopy

The length of the cristalline domains of 15 different, weakly hydrolyzed fibres of regenerated cellulose was calculated according to 3 formulas from the integral breadths of the meridional vvide-angle x-ray reflection lines and compared with the statistical evaluations of electron micrographs ofthe desintegrated fibres. A satisfying conformity of both methods was obtained by use of the equation for the x-ray diffraction of microparacrystals for those fibres, whose orientation factor was higher than 0,6. This condition is explained by the ribbonlike shape of the elementary fibrils.