Zdenka Peršin

Improvement of chitosan adsorption onto cellulosic fabrics by plasma treatment.

Oxygen plasma treatment was applied in order to improve the adsorption of chitosan onto viscose fabric. Modification of the surface and adsorption of chitosan was monitored by determination of XPS spectra, determination of contact angles from rates of water imbibition, and conductometric titration. The plasma treatment resulted in hydrophilization of the surfaces through oxidation. The hydrophilic surfaces were stable for at least 24 h. The treatment also yielded binding sites that resulted in over 20% increase of the amount of chitosan adsorbed over that adsorbed on nontreated fabric. Layers of chitosan adsorbed after plasma treatment were substantially more active as antimicrobial agents than those on nontreated surfaces.

Novel cellulose based materials for safe and efficient wound treatment.

The present study aims at achieving effects of improved hydrophilicity and microorganism inhibition, which are rarely simultaneously present in wound dressings. Viscose fibers in their non-woven form were modified using two different pathways. Effects of a two-step procedure, i.e. alkaline or oxygen plasma treatment followed by the attachment of silver chloride nanoparticles were compared to a one-step procedure, i.e. ammonium plasma treatment, which results in both desired material characteristics simultaneously. The surface properties of untreated and differently modified cellulose samples were analyzed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), in vitro silver release, and hydrophilicity measurements. The treatment effect on antimicrobial activity was determined by the AATCC 100-1999 standard test. In light of the introduced wound dressing preparation procedures and the desired wound dressing characteristics, the effectiveness of the used procedures was evaluated. Antimicrobial activity was proven against all Gram negative bacteria, while the Gram positive bacteria survive the as-prepared samples. Hydrophilicity was proven to be excellent using both preparation procedures. The mentioned results prove the potential of the used procedures and encourage future developments toward the clinical proof of concept.

Determining the Surface Free Energy of Cellulose Materials with the Powder Contact Angle Method

Different treatment processes such as alkaline washing, bleaching, and slack-mercer ization are used to improve the sorption characteristics of cellulose fibers. The differences between the sorption properties of cellulose fibers are measured with tensiometry, and their sorption velocities are measured with liquids of different polarities. From those measurements, contact angles are determined using the Washburn equation. The surface free energy of the cellulose fibers is determined from contact angle data obtained with the Owens-Wendt-Rabel-Kaeble approximation. Results show that among these treatments, slack-mercerization produces the lowest contact angle and the highest surface free fiber energy, and has therefore the largest influence on sorption ability. Viscose fibers (raw and treated) have the lowest contact angle and the highest surface free energy, and are the most hydrophilic compared to lyocell and modal fibers. This is explained by their crystalline structure and the accessibility of their surface groups to polar liquids.

X-ray study of pre-treated regenerated cellulose fibres

Abstract. Regenerated cellulose fibres have had an important role to play in the man-made fibre field. The very special characteristics of different types of regenerated cellulose fibres, e.g. mechanical properties, sorption characteristics, and aesthetics were conditioned by the differences in their fine structure due to fibre formation processes. Additionally, the finishing processes could influence the fibre structure. A study was done of the crystalline structures of a solvent-spun cellulose fibre type (Lenzing Lyocell), made according to the NMMO process, and two conventional cellulosic fibre types, made by the viscose process (Lenzing Viscose and Lenzing Modal). The fibres were pre-treated (bleached and slack mercerised) and structural changes were followed by wide angle and small angle x-ray scattering (WAXS and SAXS), respectively. The periodical structure, determined by long spacing, was nearly the same in all the different types of fibres. A slight increase was observed after the treatment of viscose and modal fibres, but an unpronounced fall of a long period accompanied the pre-treatment of lyocell fibres. Some changes in crystallinity and crystalline orientation occurred due to the treatment conditions. The structural changes were correlated to the iodinesorption and mechanical properties.

Comparison study of TEMPO and phthalimide-N-oxyl (PINO) radicals on oxidation efficiency toward cellulose

Regenerated cellulose fibers, type viscose, have been oxidized with sodium hypochlorite and catalytic amounts of sodium bromide by using two different protocols: first, involving the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and second, employing N-hydroxyphthalimide (NHPI). The reactions were carried out at room temperature and pH=10.5 for 2.5h. Viscose oxidized samples were analyzed and compared in terms of the negative charged groups content, as determined by potentiometric titration and methylene blue adsorption, morphologies and crystallinities changes, as well as changes in the degree of polymerization. The highest content of the carboxylic groups and the best preservation of the morphology and molecular weight of the original material have been found in the case of using NHPI/anthraquinone as oxidation mediators. TEMPO-mediated oxidation leads to the highest depolymerization and cause significant degradation of the cellulosic material.

Characterisation of surface properties of chemical and plasma treated regenerated cellulose fabric

The aim of this research work was to study the surface properties and sorption characteristics of differently treated regenerated cellulose fabrics. Surface modifications of viscose, modal and lyocell samples caused by using standard chemical pre-treatment procedures were compared to an alternative activation procedure by applying low pressure oxygen plasma treatment. The elemental chemical composition of the modified fabric surfaces was investigated using X-ray photoelectron spectroscopy (XPS), while hydrophilic/hydrophobic properties were evaluated by determining the water contact angles, as well as thoroughly analysed using Owens–Wendt surface energy (SFE) and surface polarity investigations. Standard chemical and also plasma treatments changed the surface chemistry of cellulose. Bleaching and alkaline treatments increased the surface carboxylic acid content by approximately 4.8% while plasma treatment increased it by approximately 9.7%. As a consequence, higher hydrophilicity arises as proved by water contact angle decrease; i.e. 24% (61°) after standard chemical treatments and 70% (20°) after plasma treatment. Both chemical treatments increase the SFE and polar components, while the reduction of dispersive components was less pronounced. The oxygen activation treatment has the greatest influence on the SFEs of the samples as well as on polarity of the samples.

Modification of cellulose non-woven substrates for preparation of modern wound dressings

Different ways are presented of modifying cellulosic non-woven substrates, which can serve as potential wound dressings with satisfactory antimicrobial and hydrophilic properties. For safe attachment of silver particles without a measurable release from the used materials, a sol–gel derived process was used. Alkaline and oxygen plasma treatments were used to improve the hydrophilicity of the materials. Their efficiency was determined by measuring contact angles and water retention values. Scanning electron microscopy (SEM) was used for determination of sample morphology prior to and after treatment. The efficiency of silver attachment and activity was evaluated by in vitro release studies and antimicrobial tests. Atomic force microscopy (AFM) and SEM, combined with dynamic light scattering, were used for determination of silver particle size. Additionally, we evaluated the influence of treatment on technological parameters, important for application performance, i.e. mechanical properties and air permeability.

The study of plasma's modification effects in viscose used as an absorbent for wound-relevant fluids

Extreme non-equilibrium oxygen plasma was used for the deep functionalisation of viscose materials used for the healing of chronic wounds. Those thermal effects, which usually appear during plasma treatment due to the influence of charged particles, were avoided effectively by using electrode-less discharge at a very low power density of 25 W/l volume. A huge flux of neutrally reactive atoms at room temperature of 3x10(23)m(-2)s(-1), allowed for the effective diffusion of O-atoms into inter-fibril space and thus the activation of fibrils throughout the non-woven materials. Apart from the standard Wilhelmy balance and pedant drop method for determining the absorption dynamics on a macroscopic scale, optical polarisation microscopy was applied for studying the microscopic effects. The sorption characteristics were determined for saline solution, exudate, and blood and the results showed a dramatic improvement. Focusing on hydrophobic recovery prevention, the modified samples were stored for 10 days in air, nitrogen, and argon atmospheres. Some ageing effects occurred, whilst the absorption properties were independent of the storage atmosphere.

Estimation of the surface energy of chemically and oxygen plasma-treated regenerated cellulosic fabrics using various calculation models

The aim of this work was to evaluate and compare the surface energies (SFEs) of regenerated cellulose fabrics modified by washing, bleaching, conventional chemical treatment (slack-mercerization), and plasma treatment. Three commonly used methods of estimating apolar, polar, and acid/base contributions were applied: geometric mean (GM), using diiodomethane (MI) and water as probes; van Oss—Good—Chaudhury (vOGC), using MI, tetrahydrofuran (THF), and chloroform (CF); and Owens—Wendt—Rabel—Kaelble (OW), using water, MI, THF, CF, ethanol and ethylene glycol. All treatments gave rise to more hydrophilic materials, as indicated by a decrease in the water contact angle. The GM and OW methods both showed that the polar component of the SFE increased after bleaching or conventional chemical treatment and, in particular, after plasma treatment. The vOGC method showed much smaller effects and indicated decreasing polarity after plasma treatment. This was probably due to the use of acid and base probes that did not contain hydroxyl groups in the determination of vOGC parameters, that is, the effect of the treatments was to introduce acid functionalities that could interact strongly with hydroxyls (hydrogen bonding) but not with the Lewis base THF or Lewis acid CF.

Ammonia plasma treatment as a method promoting simultaneous hydrophilicity and antimicrobial activity of viscose wound dressings

Viscose non-woven was treated by NH3 plasma. Different exposure times were used in order to find the optimum conditions for simultaneously improved hydrophilicity and antimicrobial activity, as desired effects by wound dressings. Both chemical and morphological modifications were studied by X-ray photoelectron spectroscopy and atomic force microscopy, respectively, revealing functionalization with nitrogen groups as well as formation of rich morphology at sub-micrometer scale. The wetting rise curves increased from 0.04 g2 s–1 for non-treated material to 1 g2 s−1 after prolonged treatment. The water contact angle decreased almost linearly with treatment time from 90° for non-treated samples to about 40° for samples treated for 140 s and remained rather constant thereafter. The AATCC 100–1999 standard test revealed reduction on all used bacteria, more pronounced for Gram-negative, that is, E. coli and P. aeruginosa, then for Gram-positive, that is, a significant for S. aureus and a marginal for E. faecalis.