Surface modification of cellulose fibers using dielectric barrier discharge

U teorijskom delu doktorske disertacije sistematizovani su najznačajniji literaturni podaci vezani za strukturu i reaktivnost celuloze i celuloznih vlakana. Posebna paţnja je posvećena mogućnostima modifikacije celuloznih vlakana sa akcentom na sve više zastupljeno korišćenje netermalne plazme u obradi celuloznih tekstilnih materijala. Dat je uporedni pregled karakteristika ureĎaja za dobijanje netermalne plazme kao i karakteristika same plazme dobijene u različitim konfiguracijama i tehničkim rešenjima. Posebna paţnja je posvećena dielektričnom barijernom praţnjenju (DBD), kao trenutno najperspektivnijoj tehnici dobijanja plazme na atmosferskom pritisku imajući u vidu potencijalnu primenu u obradi tekstilnih materijala. Proučeni su literaturni navodi i sistematizovani rezultati drugih istraţivačkih grupa dobijeni proučavanjem interakcije tekstilnih materijala sa DBD-em u različitim gasovima (vazduh, azot i kiseonik). U eksperimentalnom delu doktorske disertacije proučavan je uticaj DBD-a na strukturu, svojstva i reaktivnost prirodnih i regenerisanih celuloznih vlakana, odnosno pamuka i viskoze. Kao izvor plazme, korišćena su dva ureĎaja, prvi u kome se kao radni gas koristi vazduh, uz dodatak zeolita u radno polje praţnjenja radi kontrole vlaţnosti prilikom praţnjenja i u kome razmak izmeĎu elektroda iznosi 3 mm; drugi koji pruţa mogućnost obrade u različitim gasovima, od kojih su korišćeni vazduh, azot i kiseonik i gde je razmak izmeĎu elektroda podešen na 0,5 mm u cilju dobijanja homogenijeg praţnjenja. Nakon modifikovanja DBD-em ispitivane su morfološke promene (SEM, AFM), promene u strukturi uzorka (GPC-MALLS), promene u strukturi površine uzorka (ATR-FTIR, XPS), promene u sorpcionim svojstvima (brzina kvašenja, sadrţaj vlage, sposobnost zadrţavanja vode). Na odabranim uzorcima vršena je sorpcija srebra, bakra i cinka, u cilju dobijanja biološki aktivne celuloze. UtvrĎeno je da predtretman DBD-em poboljšava sorpciju pomenutih jona u uzorcima, shodno čemu je i antimikrobna aktivnost poboljšana. TakoĎe, uvoĎenjem jona Ag+, Cu2+ i Zn2+ sniţava se specifična zapreminska električna otpornost uzoraka, što je takoĎe eksperimentalno utvrĎeno. Starenje uzoraka nakon tretiranja plazmom dovodi do povećane sorpcije jona metala što moţe imati značajnu ulogu u industrijskoj primeni. Pored povećane sorpcije, utvrĎena je i selektivnost u antimikrobnoj aktivnosti prema odreĎenim patogenima u iii zavisnosti od vremena starenja nakon tretiranja plazmom koje prethodi sorpciji metala iz vodenih rastvora. Kao posledica delimičnog uklanjanja primarnog zida sa pamučnih vlakana tokom obrade plazmom u kiseoniku, došlo je do značajnog poboljšanja rastvorljivosti pamučnih vlakana u sistemu DMAc/LiCl. Istovremeno, modifikovan je postupak rastvaranja vlakana viskoze u pomenutom sistemu čime se pruţa mogućnost nesmetanog rastvaranja vlakana viskoze bez destrukcije celuloznih lanaca. Veoma značajnom se pokazala obrada celuloze u DBD-u sa azotom kao radnim gasom, pri čemu su dobijena multifunkcionalna svojstva ispitivanih celuloznih vlakana. Visokofunkcionalizovana površina vlakana utiče na redukovanje jona srebra te dolazi do in situ formiranja čestica nanometarskih dimenzija nakon sorpcije jona srebra na modifikovanim uzorcima. TakoĎe, uz obradu jonima bakra, na površini vlakana viskoze nakon obrade DBD plazmom u N2 i nakon sorpcije jona kalcijuma, dolazi do formiranja mikročestica bakra zvezdastog oblika. Mikročestice su nastale spajanjem mikropločica bakra i vezane za funkcionalizovanu površinu vlakana pokazale su odličnu stabilnost pri pranju. Celulozna vlakna, nakon obrade plazmom u N2, pokazuju smanjenu hidrofilnost i smanjenu moć sorpcije metalnih jona što je direktna posledica ablacije hidroksilnih grupa sa površine materijala pomoću plazme, bez narušavanja drugih značajnih sorpcionih svojstava (sposobnosti zadrţavanja vode, sadrţaja vlage). Uprkos smanjenoj sorpciji jona metala, antimikrobna aktivnost uzoraka obraĎenih u DBD plazmi u N2 ostaje skoro nepromenjena. Posebno je značajno što se kod uzoraka viskoze nakon tretiranja pomoću N2 DBD i jonima bakra javlja takozvani efekat „latice ruţe‖ (eng. pettal effect), gde se kapi vode zadrţavaju na površini materijala bez kvašenja. Predloţeni način obrade omogućava dobijanje hidrofobnog materijala korišćenjem netoksičnih hemikalija tokom jednostavnog postupka modifikovanja.In the theoretical part of doctoral dissertation, the most significant literature data concerning cellulose structure and properties have been systematically reviewed. Special attention has been given to the possibilities of cellulose fibers modification with an emphasis on more and more popular use of non-thermal plasma for cellulosic textile materials treatment. Comparative overview of various devices and characteristics of non thermal plasmas, obtained in different device configuration and technical characteristics, is given. Having in mind potential industrial application, special attention is devoted to the most perspective technique for obtaining atmospheric pressure plasma, so called dielectric barrier discharge (DBD). Literature data and results from other research groups regarding interaction of textile materials with DBD obtained in various gasses (air, nitrogen and oxygen) were studied systematically. The influence of DBD treatment on the structure, properties and reactivity of natural and regenerated cellulose fibers, i.e. cotton and viscose, was studied in the experimental part of doctoral dissertation. Two types of devices were used as plasma source; first device was operating in atmospheric air, with addition of zeolite granules in the field of discharge for the humidity control during the discharge and in which electrode gap was 3 mm; second device offers possibility of using different gasses for treatment, of which air, nitrogen and oxygen were used and electrode gap was 0.5 mm for obtaining more homogenous discharge. After DBD treatment, morphological changes (SEM, AFM), changes in the samples structure (GPC-MALLS), surface changes (ATR-FTIR, XPS), changes in sorption properties (wettability, moisture sorption, water retention value) have been investigated. On the chosen samples, a sorption of silver, copper and zinc has been performed in order to obtain biologically active cellulose. It was found that DBD pretreatment significantly improves sorption of aforementioned ions, and consequently, the antimicrobial activity is also improved. Also, addition of Ag+, Cu2+ and Zn2+ ions to the cellulose leads to a decrease of volume resistivity of samples which was also measured. The ageing of samples after plasma treatment leads to improved sorption of metal ions and this can have serious impact in industrial application. Beside improved sorption of ions, selectivity of antimicrobial activity against specific pathogens has been determined and found to be v dependent on days of ageing after the plasma treatment which precedes sorption of metals form aqueous solution. As a consequence of partial removal of primary wall in cotton fibers during plasma treatment in oxygen, significant improvement of solubility was achieved in DMAc/LiCl solvent. At the same time, the standard procedure of viscose dissolution in the above mentioned solvent has been modified which provided easier dissolution of viscose fibers without destruction of cellulose chains. Cellulose treatment in nitrogen DBD proved to be a very significant for obtaining multifunctional properties of cellulose fibers. Highly functionalized surface of fibers induces reduction of silver ions on modified samples and in situ formation of silver particles of nanometer size. Also, treatment with copper ions, after N2 DBD plasma treatment and calcium sorption, leads to the formation of star-shaped microparticles of copper on the viscose fibers surface. Microparticles were formed by assembling of trigonal microplates of copper and bonded to the functionalized surface of fibers exhibited excellent stability toward washing. Cellulose fibers, after nitrogen plasma treatment, show reduced hydrophilicity and reduced ability to bind metal ions from solution which is direct consequence of etching and ablation of hydroxyl groups from the surface of fibers using plasma, without significant deterioration of other sorption properties (water retention value, moisture sorption). However, antimicrobial activity of samples treated in N2 DBD plasma, despite decreased metal ions sorption, remains almost unchanged, with a much lower consumption of ions. Especially significant result is the appearance of so called ―petal effect‖ after N2 DBD treatment of viscose with subsequent sorption of copper, when during wetting of modified viscose, a drop of water sticks to the surface. Proposed procedure enables obtaining hydrophobic material using non-toxic chemicals during simple process of modification

Adult Height in Patients with Advanced CKD Requiring Renal Replacement Therapy during Childhood.

BACKGROUND AND OBJECTIVES: Growth and final height are of major concern in children with ESRD. This study sought to describe the distribution of adult height of patients who started renal replacement therapy (RRT) during childhood and to identify determinants of final height in a large cohort of RRT children. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: A total of 1612 patients from 20 European countries who started RRT before 19 years of age and reached final height between 1990 and 2011 were included. Linear regression analyses were performed to calculate adjusted mean final height SD score (SDS) and to investigate its potential determinants. RESULTS: The median final height SDS was -1.65 (median of 168 cm in boys and 155 cm in girls). Fifty-five percent of patients attained an adult height within the normal range. Adjusted for age at start of RRT and primary renal diseases, final height increased significantly over time from -2.06 SDS in children who reached adulthood in 1990-1995 to -1.33 SDS among those reaching adulthood in 2006-2011. Older age at start of RRT, more recent period of start of RRT, cumulative percentage time on a functioning graft, and greater height SDS at initiation of RRT were independently associated with a higher final height SDS. Patients with congenital anomalies of the kidney and urinary tract and metabolic disorders had a lower final height than those with other primary renal diseases. CONCLUSIONS: Although final height remains suboptimal in children with ESRD, it has consistently improved over time

Influence of the nonselective oxidation conditions onto functional groups content in cellulose fibers

In this paper, the influence of oxidation with hydrogen peroxide onto functional groups content in natural cellulose fibers was studied. Changes in fibers obtained at various modification conditions were evaluated by determination of carbonyl and carboxyl group content in samples before and after modification. Oxidation with H2O2 leads to a significant increase in carbonyl group content already at shorter times and milder treatment conditions. Small change in carboxyl group content occurs at higher pH values (pH 11) and 6 vol % solution concentration. Taking into account nonselective nature of hydrogen peroxide as an oxidizing agent, the optimization of process in accordance with ultimate application of modified cellulose material can be performed by careful selection of oxidation conditions

Multipurpose nonwoven viscose/polypropylene fabrics: Effect of fabric characteristics on sorption and dielectric properties

In this work, sorption and dielectric properties of viscose/polypropylene multipurpose nonwoven fabrics were examined. The analysis of sorption behavior showed that the changes of the water absorptive capacity, the height of capillary rise and water retention value are in a function of viscose fiber content, total porosity, the pore size and used web bonding process. It is observed that dielectric properties at frequencies from 30 Hz to 140 kHz, for samples exposed to different relative air humidity and wet samples, are dependent on viscose fiber content, web bonding process, frequency of electric field and bulk free water content. The effective dielectric permeability of wet samples rapidly decreases with an increase in frequency up to 3 kHz while spectra of the AC specific electrical conductivity showed a plateau above 13 kHz. It is also observed that the dielectric properties of wet samples increase by several orders of magnitude compared to dry samples

Influence of hemicelluloses and lignin content on structure and sorption properties of flax fibers (Linum usitatissimum L.)

In this work, alkali and oxidative treatments were employed to obtain flax fibers with different content of hemicelluloses and lignin, in order to study the influence of chemical composition on structure and sorption properties of flax fibers. The flax fibers were characterized using FTIR spectroscopy and FESEM microscopy, and by determination of chemical composition, carboxyl group content, electrokinetic and sorption properties. Adsorption of silver ions was used to evaluate flax fiber sorption properties, but also to obtain antimicrobial fibers whose antimicrobial activity was tested against Gram-negative bacteria Escherichia coli, Gram-positive bacteria Staphylococcus aureus and fungi Candida albicans. The progressive removal of hemicelluloses or lignin influenced the sorption properties through the increased liberation of elementary fibers and accessibility of functional surface groups of flax fibers. Removal of hemicelluloses led to increase of iodine sorption without significant change in functional groups content and electrokinetic properties. On the other hand, lignin removal led to an increase of functional groups content, namely carboxyl groups, which in turn influenced better moisture and silver ions sorption. Flax fibers with incorporated silver exhibit fair antimicrobial activity against Gram (-) E. coli, Gram (+) S. aureus and fungi C. albicans

TENDENCY OF TEXTILE MATERIALS TO GENERATE STATIC ELECTRICITY: METHODS FOR CHARACTERISATION AND CONTROL

U radu je ukazano na značaj poznavanja elektrofizičkih svojstava tekstilnih materijala. Dat je pregled metoda za određivanje električne otpornosti tekstilnih materijala, sa akcentom na metode razvijene na Katedri za tekstilno inženjerstvo Tehnološko-metalurškog fakulteta Univerziteta u Beogradu. Istaknut je značaj određivanja električne otpornosti vlakana i pređa u smislu pružanja informacija o sklonosti tekstilnih materijala ka generisanju statičkog naelektrisanja u procesu proizvodnje, a tkanina, pletenina i netkanih tekstilnih materijala sa aspekta karakterisanja gotovih tekstilnih proizvoda u pogledu stvaranja statičkog naelektrisanja i njegovog uticaja na upotrebna svojstva gotovih proizvoda. U radu je dat i prikaz metoda za kontrolu i sniženje statičkog naelektrisanja na tekstilnom materijalu.In this work, the importance of knowing the electrophysical properties of textile materials was pointed out. A review of the methods for determining the electrical resistance of textile materials is given, with emphasis on methods developed at the Department of Textile Engineering of the Faculty of Technology and Metallurgy, University of Belgrade. Determining the electrical resistance of fibers and yarns plays a role in providing information on the tendency of textile materials to generate static electricity in the production process. Determining the electrical resistance of woven, knitted and nonwoven fabrics allows us to predict whether these textile products would generate static electricity, and the impact it would have on the usability of finished products. This work also presents a review of methods for controlling and decreasing static electricity in textile materials

Obtaining Medical Textiles Based on Viscose and Chitosan/Zinc Nanoparticles with Improved Antibacterial Properties by Using a Dielectric Barrier Discharge

This study aimed to obtain functional viscose textiles based on chitosan coatings with improved antibacterial properties and washing durability. For that reason, before functionalization with chitosan/zinc nanoparticles (NCH+Zn), the viscose fabric was modified by nonthermal gas plasma of dielectric barrier discharge (DBD) to introduce into its structure functional groups suitable for attachment of NCH+Zn. NCH+Zn were characterized by measurements of hydrodynamic diameter and zeta potential and AFM. DBD-plasma-modified and NCH+Zn-functionalized fabrics were characterized by zeta potential measurements, ATR-FTIR spectroscopy, the calcium acetate method (determination of content of carboxyl and aldehyde groups), SEM, breaking-strength measurements, elemental analysis, and ICP-OES. Their antibacterial activity was determined under dynamic contact conditions. In addition to SEM, the NCH+Zn distributions on viscose fabrics were also indirectly characterized by measuring their absorbent capacities before and after functionalization with NCH+Zn. Washing durability was monitored through changes in the zeta potential, chitosan and zinc content, and antibacterial activity after 1, 3, and 5 washing cycles. The obtained results showed that DBD plasma modification contributed to the simultaneous improvement of NCH+Zn sorption and antibacterial properties of the viscose fabric functionalized with NCH+Zn, and its washing durability, making it suitable for the production of high-value-added medical textiles