Adsorption of chlorhexidine onto cellulosic fibers

Comparative investigations of adsorption properties of chlorhexidine (CHX) on two cellulose fibers, bleached cotton and viscose, were studied in order to obtain dry gauzes covered with known amount of this antiseptic. Adsorption isotherm results carried out at 293 and 323 K can be described by Langmuir isotherm model, nevertheless, at high concentration correlation is better to Freundlich isotherm. Electrokinetic potential evolution with CHX concentration, shows that initial negative zeta potential of cotton and viscose diminish its absolute value as the concentration of the treatment increases; both fibers present an isoelectric point at high concentration of CHX that is 0.3 mM for viscose and 0.8 mM for cotton. Electrostatic interactions between cationic groups of CHX and carboxylic acid groups of the fibers could explain adsorption at low concentration, but when it is higher than these values, possible hydrogen bonding between the amine groups of CHX and hydroxyl groups of cellulose could explain increasing adsorption when it is hindered by electrostatic repulsion as it is predicted by Freundlich model, that describes heterogeneous surface and multilayer adsorption. Adsorption kinetics isotherms reveal that the process is quick with t _1/2 values of 5.4 min for cotton and 2.8 min for viscose. Differences in adsorption behaviour between the two fibers could be attributed to structural differences as we have observed from estimation of CI index based on FTIR spectra. Values obtained 1.6 for viscose and 2.2 for cotton could explain that the amount of CHX adsorbed on viscose is higher than it is on cotton. Finally desorption experiments performed with 0.01 M of NaCl solution at room temperature and pH 6 reveals the possibility of therapeutical application of these fibers although further investigations must be done to optimize the process.     

Fibrillation Tendency of Cellulosic Fibers. Part 2: Effects of Temperature

The influences of temperature, concentration of swelling agents and fiber materials on the fibrillation tendency in various cellulosic fibers in aqueous solutions were investigated in terms of fibrillation stability and fibrillation sensitivities to alkali and heat. The fibrillation stability and the fibrillation sensitivity to swelling agents were evaluated with a critical point of fibrillation (CPF_conc.) that is the concentration of the swelling agents where fibrillation begins, and the ratio of initial increase in fibril number to increase in concentration of swelling agent (I_i). The fibrillation sensitivity to heat was estimated with the increase in I_i against temperature. The CPF_conc. of lyocell fiber was 16.7 mol/l water in ethanol/water mixture at 25 °C and decreased to 0 mol/l at 80 °C, indicating acceleration of the fibrillation at higher temperatures. The I_i of lyocell was enhanced from 3.50 to 7.57 count l/mol. The CPF_conc. increased in the order of viscose > cross-linked lyocell > modal > lyocell while the I_i decreased in the order of viscose < modal < cross-linked lyocell < lyocell at 40 °C. The I_i of lyocell fiber increased to the greatest extent with increase in temperature as compared with the other cellulosic fibers. Lyocell fiber has the lowest fibrillation stability and the highest fibrillation sensitivities to alkali and to heat resulting in the highest fibrillation tendency.     

Enzymatic removal of cellulose from cotton/polyester fabric blends

The production of light-weight polyester fabrics from a polyester/cotton blended fabric, by means of the enzymatic removal of the cellulosic part of the material, was investigated. The removal of cotton from the blended fabric yielded more than 80% of insoluble microfibrillar material by the combined action of high beating effects and cellulase hydrolysis.Other major features of this enzymatic process for converting cotton fibers into microfibrillar material are bath ratio, enzyme dosage and treatment time.     

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.     

Chitin/cellulose blend fibers prepared by wet and dry‐wet spinning

We describe the wet and dry‐wet spinning of multifilament cellulosic composite fibers, namely chitin/cellulose fibers. The direct solution process for the two biopolymers based on an ionic liquid as solvent represents an environmentally friendly and alternative technology to the industrially applied viscose and lyocell process. Both cellulose and chitin possess good solubility in 1‐ethyl‐3‐methylimidazolium propionate ([C₂C₁Im][OPr]) and were spun into multifilament composite fibers. Moreover, for the first time, pure chitin multifilament fibers were obtained by dry‐wet spinning. The effect of chitin addition on the filament properties was investigated and evaluated by microscopic, spectroscopic, and mechanical analyses.     

Thermal behavior of cellulose fibers with enzymatic or Na<Subscript>2</Subscript>CO<Subscript>3</Subscript> treatment

Summary New regenerated cellulose fibers were developed during the last decades as environmentally friendly systems. In this work, three fibers: lyocell, modal and viscose were subjected to an enzymatic treatment. Likewise, different lyocell fibers were washed in a Na₂CO₃ solution under severe conditions. Analysis was performed by means of differential scanning calorimetry, thermogravimetry and scanning electron microscopy. In all samples, at low temperature, water desorption was detected. Furthermore, thermal analysis shows wide exothermic processes that began between 250 and 300°C corresponding to the main thermal degradation and it is associated to a depolymerization and decomposition of the regenerated cellulose. It is accompanied with mass more than 60% mass loss. Kinetic analysis was performed and activation energy values 152-202 kJ mol^-1 of the main degradation process are in agreement with literature values of cellulose samples.     

Visualisation of the fibrillar and pore morphology of cellulosic fibres applying transmission electron microscopy

Applying transmission electron microscopy (TEM) on ultra-thin cross-sections of fibres, the main characteristics of the internal morphology of cotton and the main man-made cellulosic fibres (modal, viscose and lyocell) could be visualised. To obtain an appropriate contrast for TEM, isoprene was polymerised into the swollen fibres after a stepwise solvent exchange from water to acetone. The included polymer is stainable with osmium tetraoxide. Significant differences in distribution of pore sizes and pore arrangements in the cellulosic fibres were seen. Cotton showed very small pores in the bulk of the fibre, but drying cracks and flat pores between the sheets of the secondary wall appear as larger pores. Lyocell contains only nanopores in the bulk of the fibre with a slight gradient in pore density, and a very porous skin layer. In viscose and modal, a very wide pore size distribution from nanometer to micrometer size can be seen.     

Isolation and Identification of Residual Chromophores in Cellulosic Materials

A general procedure was developed for the isolation of residual chromophores in or on cellulosic material, which were hitherto inaccessible to structure elucidation due to their extremely low content in the ppb concentration scale. It is applicable to cellulosic pulp, cellulosic fibers (viscose, Lyocell) and cellulose derivatives (acetate, carbonyl-labeled cellulose) as well. The chromophore identification comprises treatment of the cellulosic material with boron trifluoride – acetic acid complex (BF₃*2HOAc) containing sulfite, chromatographic separation of the resulting chromophore-containing mixture, and structure determination of the main constituents by NMR / MS and comparison to authentic samples. Both adsorbed and covalently bound aromatic and quinoid compounds are selectively released by the treatment. Covalent ester, ether and secondary alkyl links between chromophore and cellulose are broken. Two cellulosic example substrates have been analyzed for their chromophore content: Lyocell fibers and non-bleached viscose fibers, and up to eleven chromophores per sample have been identified.     

Crystallinity changes in lyocell and viscose-type fibres by caustic treatment

One of the most important treatments performed on cellulosic fibres to improve properties such as dimensional stability, tensile strength and lustre, is mercerisation. The aim of this work was to study the crystallinity, accessibility and unit cell structure changes occurring in three types of regenerated cellulose fibres (lyocell, modal and viscose) that were mercerised with caustic soda solutions of different concentrations. Differences were observed between the behaviour of the viscose type fibres (viscose and modal) and that of the lyocell fibres. For the viscose type fibres, the proportion of crystalline regions increased at low alkali concentrations, while for lyocell fibres a decrease in crystallinity was observed. In all three fibres there was a transformation from cellulose II to amorphous cellulose. While for lyocell the transformation was partial, the modal and in particular the viscose fibres showed a complete transformation, and the swelling agent caused the fibre to dissolve at high caustic concentrations.     

Study of cellulosic fibres morphological features and their modifications using hemicelluloses

The microfibrilar structure and the morphology of the fibre are some of the most important characteristics that determine fibre performance during yarn making. This article is focused on understanding of morphological features of manmade cellulosic fibre and exploring an alternate way to alter fibre morphology. It is observed that though the chemical nature of different types of cellulose fibres viz. viscose, modal and lyocell is same; different processing routes lead to different cross-section and morphologies of fibres which leads to their characteristic properties and spinning behavior. A novel way is attempted to alter the fibre morphology of viscose fibre by changing the fibre regeneration kinetics and molecular weight distribution through addition of low molecular weight and branched structured hemicelluloses in spinning dope. Addition of hemicelluloses in the spinning dope prior to spinning and regeneration of viscose fibres is found to alter the morphology of the fibres without affecting tensile properties of the fibres.     

Splitting tendency of cellulosic fibers. Part 3: splitting tendency of viscose and modal fibers

The splitting tendency of viscose and modal fibers in aqueous alkali solutions of LiOH, NaOH, KOH and TMAH was investigated. The viscose fibers splitted up to 5–7 fibrils, whereas modal fibers splitted up to 2–4 fibrils depending on alkali type and concentration. The fibrillar structure of lyocell enables it to split more (15–20 fibrils) than viscose and modal fibers. Splitting occurs where internal stress of fiber is high due to different alkali or void distribution inside fiber. The splitting test couldn’t be achieved for viscose and modal fibers between 1 and 5 M concentration of NaOH and TMAH solutions due to breakage of fibers during test. Above 5 M concentration, no split can be observed due to even distribution of alkali inside fiber. Paper presented at the 7th World Textile Conference, AUTEX 2007, Tampere, Finland, 26–28 June 2007. Christian-Doppler Laboratory of Textile and Fiber Chemistry of Cellulosics is a Member of European Polysaccharide Network of Excellence (EPNOE), www.epnoe.org     

Water Accessibilities of Man-made Cellulosic Fibers – Effects of Fiber Characteristics

The dynamic vapor water sorption and desorption experiments were performed on cellulosic fibers with different characteristics. The hysteresis between moisture sorption and desorption cycle at 10% relative humidity (RH) was independent on the total moisture regain and approximately 45% for all materials except for viscose fibers. Brunauer–Emmett–Teller surface volume (V_m) for moisture sorption and retention capacity of liquid water (WRV) were also measured. The V_m and WRV increase in proportion to the total amount of moisture sorption (M_inf(total)) in all specimen except in poplar fiber. The coefficients of parallel exponential kinetics (PEK) were estimated by the curve-fitting of experimental data of the moisture regain, and the influences of the fiber characteristics on the PEK coefficients, the moisture regain, the hysteresis, V_m and WRV are discussed. The total equilibrium moisture content in the viscose fibers was higher but the moisture uptake and release rate was slower than the lyocell and poplar fibers. The cationization and the modification of shape of cross section accelerated the total equilibrium moisture content in the viscose fiber. A drying process at low temperature enhanced both the equilibrium moisture content and the moisture uptake and release rate in lyocell fibers while a spin finish retarded them. The total equilibrium moisture content was heightened by the crosslinking of the fiber, however, no obvious effect of the crosslinking on the moisture uptake and release rate was found. Effects of the type of the specimen and linear density on the moisture accessibilities are also discussed.     

Sulfur-free dissolving pulps and their application for viscose and lyocell

In this study, the concept of multifunctional alkaline pulping has been approved to produce high-purity and high-yield dissolving pulps. The selective removal of hemicelluloses was achieved by either water autohydrolysis (PH) or alkaline extraction (E) both applied as pre-treatments prior to cooking. Alternatively, hemicelluloses were isolated after oxygen delignification in a process step denoted as cold caustic extraction (CCE). Eucalyptus globulus wood chips were used as the raw material for kraft and soda-AQ pulping. In all process modifications sulfur was successfully replaced by anthraquinone. By these modifications purified dissolving pulps were subjected to TCF bleaching and comprehensive viscose and lyocell application tests. All pulps met the specifications for dissolving pulps. Further more, CCE-pulps showed a significantly higher yield after final bleaching. Morphological changes such as ultrastructure of the preserved outer cell wall layers, specific surface area and lateral fibril aggregate dimension correlated with the reduced reactivity towards regular viscose processing. The residual xylan after alkali purification depicted a lower content of functional groups and a higher molecular weight and was obviously entrapped in the cellulose fibril aggregates which render the hemicelluloses more resistant to steeping in the standard viscose process. Simultaneously, the supramolecular structure of the cellulose is partly converted from cellulose I to cellulose II by the alkaline purification step which did not influence the pulps reactivity significantly. Nevertheless, these differences in pulp parameters did not affect the lyocell process due to the outstanding solubility of the pulps in NMMO. Laboratory spinning revealed good fiber strength for both, regular viscose and lyocell fibers. The high molecular weight xylan of the CCE-treated pulps even took part in fiber forming.     

Introducing carboxyl and aldehyde groups to softwood-derived cellulosic fibers by laccase/TEMPO-catalyzed oxidation

For more cost-effective and/or value-added utilization of cellulosic fibers in pulp and paper industry, fiber engineering is an important concept. Essentially, fibers can be engineered via various mechanical, chemical, and biological processes. In the current study, the combined use of laccase and TEMPO was applied to introduce carboxyl and aldehyde groups to softwood-derived cellulosic fibers (bleached softwood kraft pulp). The process conditions in preparation of the engineered fibers were optimized. Under the conditions studied, the maximum increases in carboxyl and aldehyde contents were 360 % and 225 %, respectively. The effectiveness of the laccase/TEMPO system could be well explained by the reaction cycles in catalytic oxidation pathways. The findings of the current work may provide useful insights into the enzymatic modification of cellulosic fibers for papermaking applications.     

Effects of fiber physical and chemical characteristics on the interaction between endoglucanase and eucalypt fibers

Roles played by fiber physical and chemical characteristics in enzymatic hydrolysis of cellulosic materials were investigated by analyzing the interaction between an endoglucanase complex and eucalypt kraft fibers. PFI refining was employed to create the difference of fiber size distribution and morphology. Oxygen delignification and bleaching were employed to prepare fibers with different lignin and pentosan contents. The enzyme accessibility was monitored by adsorption at 4 °C and during hydrolysis at 40 °C. Molecular weight changes and reducing sugar released were monitored for digestibility of the samples. Greater maximum adsorption capacities of the enzymes were shown for the pulps with shorter and wider fibers and more fine fractions after refining. Highest amount of enzyme was adsorbed onto fibers with the least lignin contents at 4 °C. Fewer desorbed from fibers with higher lignin contents during hydrolysis at 40 °C. For unrefined fibers, less molecular weight reductions were observed for fibers with higher lignin contents. However, extensive fibrillation by refining negated the effects of lignin on the action of endoglucanase, similar molecular weight reductions were observed for fibers with three different lignin contents. Refining could be able to expose more reaction sites on the fiber surface, hence the impacts of lignin and pentosan diminished during hydrolysis for refined fibers.     

Xylan enriched viscose fibers

In this study, a new xylan enriched viscose fiber was developed. A high molecular weight xylan with a degree of polymerization of 150–200 was added during a late stage of the viscose production process. The xylan deriving from a cold caustic extraction (CCE) of an eucalypt paper pulp was introduced to the process after xanthation and thus neither objected to any degradation conditions during alkalization nor to the xanthation step. About 90 % of the added xylan was transferred to the final fiber. A xylan content of up to 7.5 % was achieved. Fiber properties like strength showed a comparable level to the reference fibers while the water retention value was clearly raised due to the higher content of hemicelluloses. The hemicellulose distribution over the fiber cross section was investigated by enzymatic peeling. Even though a segregation of the different polysaccharides was observed, the goal of a good blending of CCE-xylan into cellulosic fibers with new interesting features was achieved.     

Changes in the Inter- and Intra- Fibrillar Structure of Lyocell (TENCEL®) Fibers after KOH Treatment

Lyocell fibers were treated with KOH up to 8 M which was demonstrated to distribute homogeneously at the outer zones of fiber cross section compared to NaOH which accesses more deeply but less homogenously. Both NaOH and KOH solutions can be used to lower significantly the fibrillation of lyocell fibers. However, due to intrafibrillar swelling together with deep penetration ability of alkali seen for NaOH treatments results in great fiber tensile strength loss which is not observed for KOH treatments due to its inability to penetrate the fiber completely. The porous structure of fibers was studied by inverse size exclusion chromatography (ISEC) to identify mean pore diameter, total pore area and accessible pore volume (APV). Mean pore diameter of fibers decreased after KOH treatments which did not change after NaOH treatments. Wide angle X-ray diffraction analyses (WAXD) were applied to identify the crystallinity index and crystallite size. In general, fiber properties such as water retention value, carboxyl content using methylene blue sorption method, depth of color measured after dyeing with C.I. Direct Red 81 and weight loss were distinctly different in the ranges up to 2 M, 2-5 M and 5 to 8 M KOH. KOH treatment suggests new possibilities for the pretreatment of lyocell fibers to lower fibrillation while slightly lowering elongation at break without a distinct loss in tensile strength and with less decrease in carboxyl content and weight loss without changing dyeing properties of fibers compared to NaOH treatment.     

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.     

Covalent attachment of lysozyme to cotton/cellulose materials: protein verses solid support activation

Covalent attachment of enzymes to cellulosic materials like cotton is of interest where either release or loss of enzyme activity over time needs to be avoided. The covalent attachment of an enzyme to a cellulosic substrate requires either activation of a protein side chain or an organic functional group on the cellulosic substrate. Use of a water soluble carbodiimide to create an amide linkage as the covalent attachment between the enzyme and substrate represents an aqueous-based alternative which may be preferred for textile processes. Here we describe an amide bond-mediated lysozyme immobilization applied to cotton where either the carboxylate side chains of the protein or pendant carboxylates in a citrate, cross-linked cotton support are activated as the O-acyl-isourea intermediate, and the reactive amino nucleophiles are derived from amino-silanized cotton and the protein’s amino side chains, respectively. A comparison is made of the two activation approaches to covalently link lysozyme to two different cotton fabrics using the water soluble carbodiimide 1-cyclohexyl-3-(2-morpholinoethyl)-carbodiimide-metho-p-toluene sulfonate. A comparison of the resulting enzyme activities of lysozyme on two different cotton supports showed that linking lysozyme to citrate crosslinked cotton gave higher activity than on aminosilanized cotton. The lysozyme-cellulose conjugate formed on the citrate crosslinked nonwoven cotton fabric gave the highest yield and antimicrobial activity.     

Effect of alkali and ultraviolet aging on physical,thermal, and mechanical properties of fibers for potential use as reinforcing elements in glass/silicate composites

This work reports the effect of an alkaline environment and ultraviolet (UV) radiation on the physical, thermal, and tensile properties of different fibers selected as potential reinforcing elements to enhance the impact properties of brittle glass/silicate composites. The fibers, which included regenerated cellulosic (viscose and rayon), synthetic (ultrahigh molecular weight polyethylene, polypropylene, polyamide, acrylic), glass, ceramic, and steel, were aged in different alkaline solutions with pH ranging from 11.1 to 13.6 at 70°C for different periods of time and exposed to UV radiation for 330 h. The physical and thermal properties of aged fibers were studied using tensile testing, scanning electron microscopy, and simultaneous differential and thermogravimetric analysis. Results showed that the regenerated cellulosic fibers, acrylic, E‐glass, and A‐glass fibers could not withstand the highly alkaline environment. Overall, ultrahigh molecular weight polyethylene, UV‐stable polypropylene, polyamide 6.6, AR‐glass, ceramic (alumino borosilicate), and steel fibers performed very well under all conditions, indicating that they have the potential to be used as reinforcing elements in glass/silicate composites. Copyright © 2011 John Wiley & Sons, Ltd.