Simona Strnad

Reactivity and electrokinetical properties of different types of regenerated cellulose fibres

Abstract Comparative investigations between new lyocell, conventional viscose and modal fibres were made in order to explain the reasons for the differences in the reactivity and electrokinetic properties of these fibres. Lyocell fibres are a new generation of regenerated cellulose fibres produced using environmentally friendly process, which account for the main differences in the fine structure of each fibre despite having the same chemical composition. Analyses of the structural characteristics of lyocell fibres and their comparison with viscose and modal fibres were performed. The molecular (density ρ, degree of polymerisation DP, molecular mass M) and the fine structure (crystallinity index CrI, molecular orientation fΔn, void volume Vp) of cellulose fibres were investigated. Differences in the molecular and fine structure between various types of regenerated cellulose fibres cause different reactivity, sorption and electrokinetic properties. Differences in the reactivity of investigated regenerated cellulose fibres were analysed using various methods for determining water adsorption (moisture sorption, water retention, swelling in water) and adsorption of different types of surfactants (spectroscopic determination of the surfactant adsorption). The accessibility of free adsorption places in the less ordered regions of cellulose fibres was investigated by determining of electrokinetic properties. The zeta potential (ζ) was determined using streaming potential measurements as a function of the pH and structure/concentration of surfactants in the liquid phase. The structure analyses show that the new lyocell fibres have a greater degree of crystallinity and molecular orientation, and the voids structure is similar to that of viscose fibres (T. Kreze, Dissertation, University of Maribor, 1999). The adsorption phenomena in the aqueous medium and the reactivity of fibres depend, with the exception of the portion and orientation of amorphous regions, predominantly on the void system i.e. diameter, volume and inner surface of voids. The voids of modal fibres are the smallest. The voids of lyocell fibres are similar than those of viscose fibres, and so are their swelling and adsorption properties in aqueous medium (T. Kreze, S. Strnad, K. Stana-Kleinschek, V. Ribitsch, Mater. Res. Innovations, 4(2/3) (2001) 107–114). There exists an excellent correlation between structure, adsorption and electrokinetic properties.

Characterization of amino groups for cotton fibers coated with chitosan

The adsorption of chitosan onto cellulose cotton fibers introduces antimicrobial properties, mainly created by the amount and location of amino groups. Therefore, it is important to be able to analyze both parameters, especially in a heterogeneous system, namely cotton fibers coated with chitosan. In this research, three different analytical techniques were applied to determine amino groups of cotton fibers coated with chitosan. The number of positively charged groups was determined indirectly by the spectrophotometric method using Acid Orange 7 dye, and the use of polyelectrolyte titration. In addition, the chemical surface composition regarding non-modified, as well as modified cotton fibers (coated with chitosan), was investigated using X-ray Photoelectron Spectroscopy (XPS). The results from a combination of these methods show that chitosan treatment introduces more than 14 mmol/kg of accessible amino groups onto the cotton fibers. The results were in good agreement with the results of XPS. The use of spectrophotometric and titration methods in combination with XPS appears to be a very useful tool for identifying the formation of amino groups in modified cotton fibers and their surfaces.

Improvement of the hemocompatibility of PET surfaces using different sulphated polysaccharides as coating materials.

In this study, sulphated polysaccharides were investigated in respect to their blood compatibility properties (hemocompatibility). Pure chitosan was treated with sulphating agents such as SO(3)/pyridine complex and chlorosulfonic acid (HClSO(3)) to obtain 3,6-O-sulfochitosan with low and high concentration of sulfur. These synthetically derived materials and the commercially available sulphated polysaccharides heparin and dextran sulfate, both with high concentrations of sulfur, were coated onto PET foils to act as surfaces with strong antithrombotic activity. This treatment should lead to better blood compatibility properties of PET materials for medical applications. To examine this, the optimized free hemoglobin method was applied to determine the antithrombotic activity of these surfaces. Glass as the standard thrombotic surface and a heparin-coated PET surface as a surface well-known for its strong antithrombotic activity were used as internal references. The experiments showed that dextran sulfate and sulphated chitosan with high concentrations of sulfur demonstrated the same antithrombotic activity as heparin over the whole period of measurement time. In addition, a relationship between the sulfur concentration in these sulphated polysaccharides and their blood compatibility properties can be demonstrated in this article.

Mild and Selective Oxidation of Cellulose Fibers in the Presence of N-Hydroxyphthalimide

The oxidation reaction of regenerated cellulose fibers mediated by N-hydroxyphthalimide (NHPI) and various cocatalysts at room temperature for different time intervals and various amounts of low concentration sodium hypochlorite solution has been investigated to produce oxidized cellulose (OC), a biocompatible and bioresorbable polymer. The results revealed that the nonpersistent phthalimide-N-oxyl (PINO) radical generated in situ from NHPI in both, metallic or metal-free systems, is a powerful agent in this kind of transformation. Moreover, the reaction converts highly selectively C(6) primary hydroxyl groups to carboxylic groups under mild reaction conditions and shorter reaction times than previously reported. The amounts of negatively charged groups in OC were determined by means of potentiometric titration. Further characterization of the products were accomplished by using Fourier transform infrared spectroscopy/attenuated total internal reflection spectroscopy (FT-IR/ATR), environmental scanning electron microscopy (ESEM), and X-ray and energy-dispersive X-ray (EDX) spectroscopy. Notably, water retention values of the oxidized fibers increased by 30% in comparison with the original nonoxidized sample, as a result of the introduction of hydrophilic carboxylate groups.

Correlation between structure characteristics and adsorption properties of regenerated cellulose fibers

Abstract.We correlate fine structure with the adsorption behavior of new (lyocell) and conventional (viscose, modal) regenerated cellulose fibers. We have studied the molecular structure, the fine structure and, most important of all, the amorphous regions and voids in the system. Differences in adsorption properties of all three-fiber types were determined by using several methods for quantification of water, dye and iodine adsorption. The structural analysis shows that higher molecular weight, a higher degree of crystallinity and a higher molecular orientation are found in lyocell fibers [1]. Our results obtained by several independent methods demonstrate clearly that the adsorption properties of cellulose fibers depend, with the exception of the portion and orientation of amorphous regions, predominantly on the void system (diameter, volume and inner surface of voids) [2].

Influence of aqueous medium on mechanical properties of conventional and new environmentally friendly regenerated cellulose fibers

Abstract Comparative investigations between the new lyocell fibers and the regular viscose and modal types were made in order to explain the reasons for the differences in the mechanical properties of the fibers. The purpose was a systematic analysis of structure characteristics and of influence of aqueous medium on the mechanical properties. The properties determined in the wet state reflect the effect of the aqueous medium on the changes in the supermolecular structure during wet treatments [1, 2]. The new lyocell fibers consist of longer molecules and have a higher degree of crystallinity. Smaller but longer crystallites are oriented in the fiber axis direction and the voids structure is similar to that of viscose fibers [3]. Good mechanical properties are conditioned by the structure of the lyocell fibers, above all by high values of the orientation factor and crystallinity index. Sorption properties place lyocell fibers between the viscose and modal fibers. The water influence on the mechanical properties of lyocell fibers is considerably smaller compared to the viscose and modal fibers.

The significance of surface charge and structure on the accessibility of cellulose fibres

The electrokinetic properties of macroscopic solids can describe both the surface modifications as well as the interaction abilities during processing. Normally the zeta potential (ξ) is measured and can be used to develop, optimise and control the manufacturing process. The zeta potential of natural and regenerated cellulose fibres changes noticeably during the pre-treatment and finishing process and it is important for the quality of the final product (whiteness, colour, hydrophilicity). The pre-treatment of cellulose fibres improves the accessibility of dissociables groups. Further improvement of hydrophilicity (mercerisation) causes a pronounced increase in the surface charge density and a reduction in the degree of crystallinity and structural modifications. The progress of the chemical as well as the enzymatic treatment correlates with ξ. These data correlate very well with the results obtained using tensiometry, water retention, and water vapour and iodine adsorption. The changes in crystallinity index and the accessibility for low molecular components are well described by the latter methods.

Influence of Chemical Modification on Sorption and Mechanical Properties of Cotton Fibers Treated with Chitosan

In the case of conventional application of textiles, efficient and permanent fixation of chitosan is of major importance. Cotton fibers were differently pre-treated (alkali treatment, bleaching, demineralization) and then oxidized using differing procedures containing KIO4 solutions in order to discover which preparation procedure for cotton fibers is, from the viewpoint of mechanical and sorption properties, the most convenient for later treatments with chitosan. The results showed that all the oxidation procedures, even under very mild conditions, have a significant influence on the worsening of mechanical properties. The treatment of oxidized cotton with chitosan had no influence on breaking force and elongation, but increased Youngs initial modulus of fibers. Chitosan adsorption also increased the moisture absorption of the fibers. Contact angles with water, however, depend on the average molecular weight of the chitosan used. Chitosan with lower molecular weight increased the hydrophilicity of the treated fibers, but chitosan with higher molecular weight, decreased it.

Viscoelastic properties of fibrinogen adsorbed onto poly(ethylene terephthalate) surfaces by QCM-D

In presented study a new approach using QCM-D for biocompatibility determination was introduced. The adsorption of fibrinogen on PET and modified PET surfaces was monitored in situ using QCM-D. Protein layer thicknesses were estimated on the basis of a Voight based viscoelastic model. The hydrophilicities and morphologies of the surfaces were investigated using a goniometer and AFM. The results showed that PET surfaces coated with sulphated polysaccharides are more hydrophilic and more fibrinogen-repulsive than non-modified PET surfaces. QCM-D equipped with QTools modelling software is well-applicable to the characterisation of surface properties and can be optimised for biocompatibility determination.

One-shot carboxylation of microcrystalline cellulose in the presence of nitroxyl radicals and sodium periodate

Correction for ‘One-shot carboxylation of microcrystalline cellulose in the presence of nitroxyl radicals and sodium periodate’ by Sergiu Coseri et al., RSC Adv., 2015, 5, 85889–85897.