Ca(2+) sorption on regenerated cellulose fibres

High calcium content in cellulose materials can cause considerable problems in pulp processing, textile chemical treatment and consumer use, e.g. dyeing operations or household laundry. The Ca(2+) binding capacity of cellulose also is of relevance in food and medical applications. Through their carboxyl group content regenerated cellulose fibres can act as weak anion exchangers, thus all types of regenerated cellulose fibres such as lyocell, viscose and modal fibres, show a distinct ability to bind Ca(2+) ions. The binding capacity is limited by the carboxyl group content, which was determined with 15mmol/kg for lyocell fibres and 20mmol/kg for viscose fibres, using the Methylene Blue sorption method. The presence of bound Ca(2+) also was demonstrated by complex formation with alizarin. The molar ratio between carboxylic group content and bound Ca(2+) ions was one Ca(2+) ion for a single carboxyl group. As a result of Ca(2+) sorption a positive net charge of the cellulose results and another anion has to be bound as counter ion for reasons of charge neutralisation. Results of potentiometric titrations indicate HCO(3)(-) to be present as counter ion in the Ca(2+) cellulose system. Thus under the experimental conditions studied, bound Ca(2+) is proposed to be present in the form COO(-)Ca(2+)HCO(3)(-).     

Surface activation of dyed fabric for cellulase treatment

Surface activation of fabric made from cellulose fibres, such as viscose, lyocell, modal fibres and cotton, can be achieved by printing of a concentrated NaOH-containing paste. From the concentration of reducing sugars formed in solution, an increase in intensity of the cellulase hydrolysis by a factor of six to eight was observed, which was mainly concentrated at the activated parts of the fabric surface. This method of local activation is of particular interest for modification of materials that have been dyed with special processes to attain an uneven distribution of dyestuff within the yarn cross-section, e.g., indigo ring-dyed denim yarn for jeans production. Fabrics made from regenerated cellulose fibres were used as model substrate to express the effects of surface activation on indigo-dyed material. Wash-down experiments on indigo-dyed denim demonstrated significant colour removal from the activated surface at low overall weight loss of 4-5%. The method is of relevance for a more eco-friendly processing of jeans in the garment industry.     

Biologically active fibers based on chitosan-coated lyocell fibers

The possibilities of obtaining biologically active cellulose–chitosan fibers were examined. An effective two-stage method was developed. The first stage involves the formation of dialdehyde cellulose by the potassium periodate oxidation of lyocell fibers, which is able to form Schiff’s base with chitosan. In the second stage, chitosan-coated lyocell fibers were prepared by subsequent treatment of oxidized lyocell fibers with a solution of chitosan in aqueous acetic acid. The impact of this two-stage protocol on the chemical and physical properties of lyocell fibers was evaluated by determining carbonyl group content, fineness and tensile strength of fibers, as well as chitosan content in the composite cellulose–chitosan fibers. Antibacterial activity of the chitosan-coated lyocell fibers against different pathogenens: Staphylococcus aureus and Escherichia coli, was confirmed in vitro experiments.     

Sorption of alkaline earth metal ions Ca2+ and Mg2+ on lyocell fibres

Ca²⁺ and Mg²⁺ content of cellulose fibres is of relevance for a wide range of applications e.g. textile processing, pulp/paper, food. Sorption of Ca²⁺ and Mg²⁺ ions were found on lyocell type regenerated cellulose fibres. Higher affinity was found for Ca²⁺ ions compared to Mg²⁺ ions. At pH 9, fibre saturation was observed at a calcium binding capacity of 18–20 mmol/kg. A carboxylic group content of 18 mmol COOH per kg fibre material was determined based on the Methylene Blue absorption. This indicates a 1:1 molar stoichiometry between the carboxylic groups present in the fibres and the bound Ca²⁺ ions. Thus it is proposed that the salt in fibre shows the general composition (Cell-O^? Ca²⁺ X^?), X^? being an anion bound in the salt to achieve charge neutrality.The sorption of Ca²⁺ also can be demonstrated by complex formation with 1,2-dihydroxy-9,10-anthraquinone (alizarin) which forms a red-violet Ca²⁺-complex. Colour fixation thus can be used as an indicator for the Ca²⁺-ions bound in the fibre.     

Monocomponent endoglucanase treatment increases the reactivity of softwood sulphite dissolving pulp

Softwood dissolving pulp was treated with a commercial monocomponent fungal endocellulase. The reactivity of the pulp for the production of rayon and cellulose derivatives as determined with the Fock method increased drastically with relatively low amounts of enzyme, and the yield loss and decrease of viscosity were moderate. The mechanism behind the increased reactivity is discussed.     

Formation, derivatization and applications of bacterial cellulose

Acetobacter xylinum produces highly crystalline cellulose extracellulary using glucose as a carbon source. The polymer formed is free of other biogenic compounds, separable in a simple way and characterized by its high water-absorption capacity. Stepwise solvent exchange from water to unpolar solvents leads to a drastic decrease of the water content of the bacterial cellulose without decrease of the highly swollen and activated state. Heterogeneous as well as homogeneous derivatizations, e.g. carboxymethylation, silylation and acetylation, were performed on the wet or dried biopolymer. Furthermore, different methods for formation of hollow fibres during biosynthesis were investigated. Such tubes may have applications as biocompatible material in medicine.     

Hydrolysis and transformation of cellulose with Aspergillus niger IBT-90 enzymes

Hydrolysis and transformation of Fibrenier cellulose (USA) with enzymes from Aspergillus niger IBT-90 was studied. The process was performed at 50°C and pH 4.8 for 24 h using an enzyme complex either as a properly diluted culture filtrate or as a mixture of isolated and purified enzymes from A.niger IBT-90. In the latter experiments, enzyme-substrate ratios expressed as units of activity per 1 g of cellulose were as follows: endoglucanase E₁ and E₂, 40; β-glucosidase, 40 and cellobio-hydrolase, 2. Cellulose concentration was 5%. It was proved that the crude celluloytic complex from A. niger IBT-90 exhibits higher efficiency in the decomposition of cellulose in comparison to the mixture of enzymes isolated from this complex, as was revealed in assays of reducing sugars and determinations of light transmission throughout cellulose fibres using a computer analysis of the microscopic image. Comparison of both the endoglucanases E₁ and E₂ showed that the first enzyme is more active against cellulose. It liberated more reducing sugars and caused more significant decomposition of fibres. The predominant effect of the endoglucanase E₂ was a smoothing of the fibre surface. The cellobiohydrolase split a cellulose fibre into many short fibres.     

Arundo donax—Source of musical reeds and industrial cellulose

Arundo donax has played an important role in the culture of the western world through its influence on the development of music. Reeds for woodwind musical instruments are still made from the culms, and no satisfactory substitutes have been developed. This grass has also been used as a source of cellulose for rayon and considered as a source of paper pulp.     

A technique to determine friction at the fingertips

This article proposes a technique to calculate the coefficient of friction for the fingertip- object interface. Twelve subjects (6 males and 6 females) participated in two experiments. During the first experiment (the imposed displacement method), a 3-D force sensor was moved horizontally while the subjects applied a specified normal force (4 N, 8 N, 12 N) on the surface of a sensor covered with different materials (sandpaper, cotton, rayon, polyester, and silk).The normal force and the tangential force (i.e., the force due to the sensor motion) were recorded. The coefficient of friction (mu(d)) was calculated as the ratio between the tangential force and the normal force. In the second experiment (the beginning slip method), a small instrumented object was gripped between the index finger and the thumb, held stationary in the air, and then allowed to drop. The weight (200 g, 500 g, and 1,000 g) and the surface (sandpaper, cotton, rayon, polyester, and silk) in contact with the digits varied across trials. The same sensor as in the first experiment was used to record the normal force (in a horizontal direction) and the tangential force (in the vertical direction). The slip force (i.e., the minimal normal force or grip force necessary to prevent slipping) was estimated as the force at the moment when the object just began to slip. The coefficient of friction was calculated as the ratio between the tangential force and the slip force. The results show that (1) the imposed displacement method is reliable; (2) except sandpaper, for all other materials the coefficient of friction did not depend on the normal force; (3) the skin-sandpaper coefficient of friction was the highest mu(d) =0.96+/-0.09 (for 4-N normal force) and the skin-rayon rayon coefficient of friction was the smallest mu(d) =0.36+/-0.10; (4) no significant difference between the coefficients of friction determined with the imposed displacement method and the beginning slip method was observed. We view the imposed displacement technique as having an advantage as compared with the beginning slip method, which is more cumbersome (e.g., dropped object should be protected from impacts) and prone to subjective errors owing to the uncertainty in determining the instance of the slip initiation (i.e., impeding sliding).     

Molecular weight distribution and functional group profiles of TEMPO-oxidized lyocell fibers

The effects of TEMPO-mediated oxidation, performed with NaClO, a catalytic amount of NaBr, and 2,2′,6,6′-tetramethylpiperidine-1-oxy radical (TEMPO), were studied on lyocell fibers by means of GPC using multiple detection and group-selective fluorescence labeling according to the CCOA and FDAM methodology. The applied method determines functional group content as a sum parameter, as well as functional group profiles in relation to the molecular weight of the cellulose fibers. Both the CHO and COOH profiles, as well as molecular weight alterations, were analyzed. A significant decrease in the average molecular weight was obtained during the first hour of TEMPO-mediated oxidation, but prolonged oxidation time resulted in no strong additional chain scission. Significant amounts of COOH groups were introduced in the high molecular weight fractions by the oxidation with higher concentrations of NaClO (2.42–9.67 mmol NaClO/g fiber) after modification times of 1 h or longer.     

Lignin deficiency in transgenic flax resulted in plants with improved mechanical properties

Flax (Linum usitatissimum L.) is a very important source of natural fibres used by the textile industry. Flax fibres are called lignocellulosic, because they contain mainly cellulose (about 70%), with hemicellulose, pectin and lignin. Lignin is a three-dimensional polymer with a high molecular weight, and it gives rigidity and mechanical resistance to the fibre and plant. Its presence means the fibres have worse elastic properties than non-lignocellulosic fibres, e.g. cotton fibres, which contain no lignin. The main aim of this study was to produce low-lignin flax plants with fibres with modified elastic properties. An improvement in the mechanical properties was expected. The used strategy for CAD down-regulation was based on gene silencing RNAi technology. Manipulation of the CAD gene caused changes in enzyme activity, lignin content and in the composition of the cell wall in the transgenic plants. The detected reduction in the lignin level in the CAD-deficient plants resulted in improved mechanical properties. Young's modulus was up to 75% higher in the generated transgenic plants (CAD33) relative to the control plants. A significant increase in the lignin precursor contents and a reduction in the pectin and hemicellulose constituents was also detected. A decrease in pectin and hemicellulose, as well as a lower lignin content, might lead to improved extractability of the fibres. However, the resistance of the transgenic lines to Fusarium oxysporum was over two-fold lower than for the non-transformed plants. Since Fusarium species are used as retting organisms and had been isolated from retted flax, the increased sensitivity of the CAD-deficient plant to F. oxysporum infection might lead to improved flax retting.     

Mutagenic characteristics of river waters flowing through large metropolitan areas in North America

The hanging technique using blue rayon, which specifically adsorbs mutagens with multicyclic planar structures, has the advantages over most conventional methods of not having to bring large volumes of water back to the laboratory for extraction of organic materials. Therefore, for the same effort the hanging blue rayon technique allows for the analysis of more samples from remote sites, although it has a disadvantage of not allowing quantitative analysis. In this study, the blue rayon hanging technique was used to collect organic mutagens in river waters that flow through metropolitan areas in northeastern North America. Monitoring was performed at a total of 21 sites: the Providence River system (4 sites), the Charles River (2 sites), the Potomac River (6 sites), the St. Lawrence River (5 sites), the Hudson River (3 sites), and the East River (1 site). Mutagenicity was evaluated using the Salmonella assay with strains TA98, TA100, YG1024, YG1041, and YG1042 with and without metabolic activation. The results demonstrated that strains YG1041 and YG1024 were much more sensitive than TA98 with S9 mix. Fifteen samples out of 21 were positive in YG1041 with S9 mix. Six samples gave 5000-18,400 revertants/g blue rayon equivalent. YG1042 was also much more sensitive than TA100. Eight samples were positive in YG1042 with S9 mix. The highest activity was 10,200 revertants/g blue rayon equivalent. The overall results showed that rivers flowing through major cities in North America contain frameshift-type, aromatic amine-like mutagenic activity. However, the levels of mutagenic activity in these rivers were much lower than expected based on prior analyses and calculated population-to-discharge ratios. Further research, such as detailed chemical analyses and/or simultaneous comparisons of several different adsorbents (e.g. XAD and blue rayon), will be needed to clarify the observed differences between North American blue rayon values and published values for European and Asian river systems.     

Control of Precision Grip Force in Lifting and Holding of Low-Mass Objects

Few studies have investigated the control of grip force when manipulating an object with an extremely small mass using a precision grip, although some related information has been provided by studies conducted in an unusual microgravity environment. Grip-load force coordination was examined while healthy adults (N = 17) held a moveable instrumented apparatus with its mass changed between 6 g and 200 g in 14 steps, with its grip surface set as either sandpaper or rayon. Additional measurements of grip-force-dependent finger-surface contact area and finger skin indentation, as well as a test of weight discrimination, were also performed. For each surface condition, the static grip force was modulated in parallel with load force while holding the object of a mass above 30 g. For objects with mass smaller than 30 g, on the other hand, the parallel relationship was changed, resulting in a progressive increase in grip-to-load force (GF/LF) ratio. The rayon had a higher GF/LF force ratio across all mass levels. The proportion of safety margin in the static grip force and normalized moment-to-moment variability of the static grip force were also elevated towards the lower end of the object mass for both surfaces. These findings indicate that the strategy of grip force control for holding objects with an extremely small mass differs from that with a mass above 30 g. The data for the contact area, skin indentation, and weight discrimination suggest that a decreased level of cutaneous feedback signals from the finger pads could have played some role in a cost function in efficient grip force control with low-mass objects. The elevated grip force variability associated with signal-dependent and internal noises, and anticipated inertial force on the held object due to acceleration of the arm and hand, could also have contributed to the cost function.     

Role of supramolecular cellulose structures in enzymatic hydrolysis of plant cell walls

The study of biomass deconstruction by enzymatic hydrolysis has hitherto not focussed on the importance of supramolecular structures of cellulose. In lignocellulose fibres, regions with a different organisation of the microfibrils are present. These regions are called dislocations or slip planes and they are known to be more susceptible to various forms of degradation such as acid hydrolysis. Traditionally the cellulose within these regions has been assumed to be amorphous, but in this study it is shown by use of polarized light microscopy that dislocations are birefringent. This indicates that they have a crystalline organisation. Dislocations may be entry points for endoglucanases. Using a fluorescent labelled endoglucanase combined with confocal fluorescence microscopy, it is shown that the enzyme selectively binds to dislocations during the initial phase of the hydrolysis. Using a commercial cellulase mixture on hydrothermally treated wheat straw, it was found that the fibres were cut into segments corresponding to the sections between the dislocations initially present, as has previously been observed for acid hydrolysis of softwood pulps. The results indicate that dislocations are important during the initial part of enzymatic hydrolysis of cellulose. The implications of this phenomenon have not yet been recognized or explored within cellulosic biofuels.     

Structure study of cellulose fibers wet-spun from environmentally friendly NaOH/urea aqueous solutions

In this study, structure changes of regenerated cellulose fibers wet-spun from a cotton linter pulp (degree of polymerization approximately 620) solution in an NaOH/urea solvent under different conditions were investigated by simultaneous synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS). WAXD results indicated that the increase in flow rate during spinning produced a better crystal orientation and a higher degree of crystallinity, whereas a 2-fold increase in draw ratio only affected the crystal orientation. When coagulated in a H2SO4/Na2SO4 aqueous solution at 15 degrees C, the regenerated fibers exhibited the highest crystallinity and a crystal orientation comparable to that of commercial rayon fibers by the viscose method. SAXS patterns exhibited a pair of meridional maxima in all regenerated cellulose fibers, indicating the existence of a lamellar structure. A fibrillar superstructure was observed only at higher flow rates (>20 m/min). The conformation of cellulose molecules in NaOH/urea aqueous solution was also investigated by static and dynamic light scattering. It was found that cellulose chains formed aggregates with a radius of gyration, Rg, of about 232 nm and an apparent hydrodynamic radius, Rh, of about 172 nm. The NaOH/urea solvent system is low-cost and environmentally friendly, which may offer an alternative route to replace more hazardous existing methods for the production of regenerated cellulose fibers.     

Sorption properties of TEMPO-oxidized natural and man-made cellulose fibers

Cotton and lyocell fibers were oxidized with sodium hypochlorite and catalytic amount of sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO), under various conditions. Water-insoluble fractions, collected after TEMPO-mediated oxidation, were analyzed and characterized in terms of weight loss, aldehyde and carboxyl contents, and sorption properties. Aldehyde and carboxyl groups were introduced into the oxidized cotton up to 0.321 and 0.795 mmol/g, and into the oxidized lyocell up to 0.634 and 0.7 mmol/g, respectively, where weight loss was generally lower than 12% for cotton and 27% for lyocell. Oxidized cotton and lyocell were shown to exhibit 1.55 and 2.28 times higher moisture sorption than the original fibers, respectively, and water retention values up to about 85% for cotton and 335% for lyocell, while iodine sorption values of oxidized fibers were lower up to 35% for cotton and up to 18% for lyocell than the original fibers.     

Enhanced cellulase production through random mutagenesis of Talaromyces pinophilus OPC4-1 and fermentation optimization

Reducing cellulase cost remains a major challenge for lignocellulose to fuel and chemical industries. In this study, mutants of a novel wild-type cellulolytic fungal strain Talaromyces pinophilus OPC4-1 were developed by consecutive UV irradiation, N-methyl-N`-nitro-N-nitrosoguanidine (NTG) and ethylmethane sulfonate (EMS) treatment. A potential mutant EMM was obtained and displayed enhanced cellulase production. Using Solka Floc cellulose as the substrate, through fed-batch fermentation, mutant strain T. pinophilus EMM generated crude enzymes with an FPase activity of 27.0 IU/mL and yield of 900 IU/g substrate. When corncob powder was used, strain EMM produced crude enzymes with an FPase activity of 7.3 IU/mL and yield of 243.3 IU/g substrate. In addition, EMM crude enzymes contained 29.2 and 16.3 IU/mL β-glucosidase on Solka Floc cellulose and corncob power, respectively. The crude enzymes consequently displayed strong biomass hydrolysis performance. For corncob hydrolysis, without supplement of any commercial enzymes, glucose yields of 591.7 and 548.6 mg/g biomass were obtained using enzymes produced from Solka Floc cellulose and corncob powder, respectively. It was 553.9 mg/g biomass using the commercial enzyme mixture of Celluclast 1.5 L and Novozyme 188. Strain T. pinophilus EMM was therefore a potential fungus for on-site enzyme production in biorefinery processes.     

Fibrillation tendency of cellulosic fibers—Part 4. Effects of alkali pretreatment of various cellulosic fibers

The effects of alkali type and the concentration in the alkali treatments on the weight loss in six cellulosic fibers and their influences on the fibrillation tendency were investigated. The fibril number of the cellulosic fibers pretreated with alkalis (FN_pre) increased with increasing the alkali concentrations as well as the weight loss of the fiber except in the lyocell fiber treated in NaOH and KOH solutions. The FN_pre in lyocell was reduced as the fibers were treated in 5 mol/l NaOH and KOH solutions. This result and the fact that the fibers were split in organic alkali such as tetramethylammonium hydroxide even at the low weight loss suggested that not only the loss of cellulose component but also reorganization of microfibril structure, inhomogeneous swelling of the fibers and other influences control the fibrillation tendency of cellulosic fibers.     

Analysis of retted and non retted flax fibres by chemical and enzymatic means

Flax fibres (Linum usitatissimum L.) were subjected to chemical and enzymatic analysis in order to determine the compositional changes brought about by the retting process and also to determine the accessibility of the fibre polymers to enzymatic treatment. Chemical analysis involved subjecting both retted and non retted fibres to a series of sequential chemical extractions with 1% ammonium oxalate, 0.05 M KOH, 1 M KOH and 4 M KOH. Retting was shown to cause minimal weight loss from the fibres but caused significant changes to the pectic polymers present. Retted fibres were shown to have significantly lower amounts of rhamnogalacturonan as well as arabinan and xylan. In addition the average molecular mass of the pectic extracts was considerably lowered. Enzyme treatment of the 1 M KOH extracts with two different enzymes demonstrated that the non retted extract contained a relatively high molecular weight xylan not found in the retted extract. Treatment of the 1 M KOH extracts and the fibres with Endoglucanase V from Trichoderma viride demonstrated that while this enzyme solubilised cellulose as well as xylan and xyloglucan oligomers from the extract, it had limited access to these polymers on the fibre. MALDI-TOF MS analysis of the material solubilised from the extract suggested that the xylan was randomly substituted with 4-O-methyl glucuronic acid moieties. The xyloglucan was shown to be of the XXXG type and was substituted with galactose and fucose units. The enzyme treatments of the fibres demonstrated that the xylan and xyloglucan polymers in the fibres were not accessible to the enzyme but that material which was entrapped by the cellulose could be released by the hydrolysis of this cellulose.     

Tensional stress generation in gelatinous fibres: a review and possible mechanism based on cell-wall structure and composition

Gelatinous fibres are specialized fibres, distinguished by the presence of an inner, gelatinous cell-wall layer. In recent years, they have attracted increasing interest since their walls have a desirable chemical composition (low lignin, low pentosan, and high cellulose contents) for applications such as saccharification and biofuel production, and they have interesting mechanical properties, being capable of generating high tensional stress. However, the unique character of gelatinous layer has not yet been widely recognized. The first part of this review presents a model of gelatinous-fibre organization and stresses the unique character of the gelatinous layer as a separate type of cell-wall layer, different from either primary or secondary wall layers. The second part discusses major current models of tensional stress generation by these fibres and presents a novel unifying model based on recent advances in knowledge of gelatinous wall structure. Understanding this mechanism could potentially lead to novel biomimetic developments in material sciences.