Surface modification of natural fibers using bacteria: depositing bacterial cellulose onto natural fibers to create hierarchical fiber reinforced nanocomposites

Triggered biodegradable composites made entirely from renewable resources are urgently sought after to improve material recyclability or be able to divert materials from waste streams. Many biobased polymers and natural fibers usually display poor interfacial adhesion when combined in a composite material. Here we propose a way to modify the surfaces of natural fibers by utilizing bacteria ( Acetobacter xylinum) to deposit nanosized bacterial cellulose around natural fibers, which enhances their adhesion to renewable polymers. This paper describes the process of modifying large quantities of natural fibers with bacterial cellulose through their use as substrates for bacteria during fermentation. The modified fibers were characterized by scanning electron microscopy, single fiber tensile tests, X-ray photoelectron spectroscopy, and inverse gas chromatography to determine their surface and mechanical properties. The practical adhesion between the modified fibers and the renewable polymers cellulose acetate butyrate and poly(L-lactic acid) was quantified using the single fiber pullout test.     

Regenerated cellulose-silk fibroin blends fibers

Fibers made of cellulose and silk fibroin at different composition were wet spun from solutions by using N-methylmorpholine N-oxide hydrates (NMMO/H(2)O) as solvent and ethanol as coagulant. Different spinning conditions were used. The fibers were characterized by different techniques: FTIR-Raman, scanning electron microscopy, wide-angle x-ray diffraction, DSC analysis. The results evidence a phase separation in the whole blends compositions. The tensile characterization, however, illustrates that the properties of the blends fibers are higher respect to a linear behaviour between the pure polymers, confirming a good compatibility between cellulose and silk fibroin. The fibers containing 75% of cellulose show better mechanical properties than pure cellulose fibers: modulus of about 23 GPa and strength to break of 307 MPa.     

Cross-linking chitosan into UV-irradiated cellulose fibers for the preparation of antimicrobial-finished textiles

Chitosan cross-linked cellulose fibers were prepared using non-toxic procedures in order to confer antimicrobial properties to cellulose fibers. Citric acid was used as the cross-linker and NaH₂PO₄ as catalyst in previously UV-irradiated cellulose fibers. Further heat dried-cure process and washing with detergent, water and acetic acid (0.1 M) gave a maximum incorporation of chitosan of 27 mg per gram of functionalized textile. The thermogravimetric analysis of the material with the highest chitosan content showed an increased thermal stability compared to cellulose and chitosan. The UV-irradiation induced morphological changes, such as less entangled cellulose fibers, as observed by scanning electron microscopy, which was prompted to enhance the chitosan incorporation. The biomass and spore germination percentage of Penicillium chrysogenum and colony forming units per millilitre for Escherichia coli decreased significantly on the composed materials as compared to raw cellulose fiber and it was similar to that obtained with a commercial antimicrobial cellulose fiber.     

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.     

Structure, morphology and thermal characteristics of banana nano fibers obtained by steam explosion

In this work, cellulose nanofibers were extracted from banana fibers via a steam explosion technique. The chemical composition, morphology and thermal properties of the nanofibers were characterized to investigate their suitability for use in bio-based composite material applications. Chemical characterization of the banana fibers confirmed that the cellulose content was increased from 64% to 95% due to the application of alkali and acid treatments. Assessment of fiber chemical composition before and after chemical treatment showed evidence for the removal of non-cellulosic constituents such as hemicelluloses and lignin that occurred during steam explosion, bleaching and acid treatments. Surface morphological studies using SEM and AFM revealed that there was a reduction in fiber diameter during steam explosion followed by acid treatments. Percentage yield and aspect ratio of the nanofiber obtained by this technique is found to be very high in comparison with other conventional methods. TGA and DSC results showed that the developed nanofibers exhibit enhanced thermal properties over the untreated fibers.     

Immobilized enzyme cellulose hollow fibers: I. Immobilization of heparinase

The immobilization of heparinase to tresyl-chloride-activated cellulose hollow fibers for the removal of heparin from the bloodstream was examined. Whole blood can be circulated through cellulose hollow fibers without hemolysis and the tresyl chloride chemistry provides a strong linkage which limits the release of the enzyme from the support. The tresylation and immobilization methods were modified and optimized to improve the heparinase activity retained by cellulose. Pretreatment of the hollow fibers with 0.05/V sodium hydroxide increased the degree of tresylation and the immobilization yield by a factor of five. The use of triethylamine as the organic base in the tresyl chloride activation resulted in threefold greater activity retention by the support than when pyridine was used. Together, sodium hydroxide pretreatment and triethylamine enhanced the activity retained by cellulose to 26.2 +/- 7.0% of that bound to the support. The activity retention was also a function of the technique used for immobilization. The best results were achieved when the enzyme was applied to the activated fibers once every 12 to 24 h for a total of four times. The active enzyme loading on the fibers was 0.3 mg heparin degraded/h cm(2) when 4.5 mug protein/cm(2) was bound to the fibers.     

Immobilized enzyme cellulose hollow fibers: III. Physical properties and in vitro biocompatibility

The initial testing of the safety of a cellulose-heparinase hollow fiber device was assessed with respect to physical properties and in vitro biocompatibility. The material cleared urea and creatinine without passing albumin, even at high flow rates. The clearance of urea and creatinine by cellulose-heparinase was equal or slightly reduced in comparision to the cellulose device. The cellulose-neparinase device tolerance to now rates was also unchanged. In addition, scanning electron microscopy of the lumen established the uniformity of the material. The analysis of clearance rates and the scanning electron micrographs show there to be no damage to the cellulose membrane after tresyl chloride activation and heparinase immobilization. The investigation of biocompatibility in an in vitro test system with whole human blood indicated that there were no significant changes in the biocompatibility of cellulose with bound heparinase. There was no change in the level of red blood cells, white blood cells, or platelets over the course of in vitro whole blood perfusion through cellulose or cellulose-heparinase hollow fiber devices. Low levels of plasma hemoglobin and complement activation were observed with cellulose and cellulose-heparinase devices. Thus, the cellulose hollow fibers can be functionalized without any changes in in vitro performance.     

Solution blowing of submicron-scale cellulose fibers

Solution blowing is an innovative process for spinning micro-/nano-fibers from polymer solutions using high-velocity gas flow as fiber forming driving force. Submicron-scale cellulose fibers were successfully solution blown by two improvement measures. First, cellulose solution was directly blown to fibers of 260-1900nm in diameter by raising the air temperature along the spinning line which was proved to accelerate the evaporation of solvent and fiber forming. Second, coaxial solution blowing technique was established with cellulose solution and polyethylene oxide (PEO) solution used as core and shell liquids, respectively. The core-shell structures of the fibers were examined by SEM and TEM. Cellulose fibers with diameter between 160nm and 960nm were further obtained after removing PEO shell. X-ray diffraction studies showed that the two kinds of submicron-scale cellulose fibers are mostly amorphous.     

The structure of plant cell walls: v. On the binding of xyloglucan to cellulose fibers

Cell wall strength is decreased by both auxin treatment and low pH. In a recently proposed model of the plant cell wall, xyloglucan polymers are hydrogen-bonded to cellulose fibrils, forming the only noncovalent link in the network of polymers which cross-link the cellulose fibers. The decreased strength of the cell wall seen upon lowering the pH might be due to an effect of hydrogen ions on the rate of xyloglucan creep along cellulose fibers. This paper investigates binding of xyloglucan fragments to cellulose. At equilibrium, the per cent of nine- and seven-sugar xyloglucan fragments which are bound to cellulose is sensitive to both temperature and the concentration of nonaqueous solvents. However, neither the per cent of xyloglucan fragments bound to cellulose at equilibrium, nor the rate at which the xyloglucan fragments bind to cellulose, is sensitive to changes in hydrogen ion concentration. These results support the hypothesis that, within the cell wall, xyloglucan chains are connected to cellulose fibers by hydrogen bonds, but these results suggest that this interconnection between xyloglucan and cellulose is unlikely to be the point within the wall which regulates the rate of cell elongation.     

Nanocomposites from natural cellulose fibers filled with kaolin in presence of sucrose

This work introduces, for the first time worldwide, an advanced nanocomposite involving two additives – a nanoadditive and a conventional additive – within a matrix of natural cellulose fibers. The first additive (the nanoadditive) is sucrose, which incorporates the nanoporous structure of the cell walls of cellulose fibers. The second additive (the conventional additive) is kaolin, the famous paper filler. Kaolin is enmeshed between the adjacent cellulose fibers. This advanced paper nanocomposite was prepared by simple techniques.

The present work shows, for the first time, that sucrose can overcome the ultimate fate of deterioration in strength of paper, due to addition of inorganic fillers such as kaolin. This deterioration was counteracted by incorporating cellulose fibers with sucrose, which leads to incorporation beating of the fibers, and thus increases the strength of the produced paper nanocomposites. In addition, sucrose was proven – for the first time – to act as retention aid for inorganic fillers such as kaolin. We called this phenomenon incorporation retention to differentiate it from the conventional types of retention of inorganic fillers.

Recent studies, by the authors and others, have shown that incorporating cellulose fibers, with sucrose, leads to paper nanocomposites of enhanced strength (breaking length). Also, sucrose is privileged by its small size (0.8 nm), substantial hydrogen bonding capacity, low cost, and abundance. Therefore, sucrose was chosen as a nanoadditive in this work. The present study shows that the nanoadditive sucrose may find its use as a new retention aid and strength promoter in papermaking.     

Changes in the structural properties and rate of hydrolysis of cotton fibers during extended enzymatic hydrolysis

An extended enzymatic hydrolysis of cotton fibers by crude cellulase from Trichoderma pseudokoningii S-38 is described with characterization of both the enzyme changes of activities and cellulose structure. The hydrolysis rates declined drastically during the early stage and then slowly and steadily throughout the whole hydrolysis process the same trend could be seen during the following re-hydrolysis process. Morphological and structural changes to the fibers, such as swelling, frequent surface erosion, and variation in the packing and orientation of microfibrils, were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Observation of X-ray diffraction and IR spectra suggests that the hydrolysis process results in a gradual increase in the relative intensity of the hydrogen bond network, and a gradual decrease in the apparent crystal size of cellulose. The I(alpha) crystal phase was hydrolyzed more easily than was the I(beta) crystal phase. Apart from the inactivation of CBHs activity, changes in the packing and arrangement of microfibrils and the structural heterogeneity of cellulose during hydrolysis could be responsible for the reduction in the rate of reaction, especially in its later stages. The results indicate that the enzymatic hydrolysis of cellulose occurs on the outer layer of the fiber surface and that, following this, the process continues in a sub-layer manner.     

Grafting of softwood kraft pulps fibers with fatty acids under cold plasma conditions

Cold plasma treatment is used to modify the cellulosic fibers for a variety of applications. The grafting of softwood unbleached (UBP) and bleached (BP) kraft pulp fibers has been performed under the action of cold plasma discharges, using different kinds of fatty acids. The grafted samples are characterized by FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), termogravimetry (TG-DTG) and X-ray diffraction (XRD). All these methods confirm the morphological and structural changes after plasma treatment which determines the modification in cellulosic fiber properties. The active centers created within the cellulose chains by plasma treatment were used to initiate grafting reactions with fatty acids. Such modification is useful to enhance the fibers properties such as softness and to change hydrophilic/hydrophobic balance.     

Properties of natural cellulose fibers from hop stems

This paper reports the development of natural cellulose fibers from hop stems with properties similar to that of hemp. Hop stems are currently considered as byproducts and have limited applications. Since hop belongs to the genus cannabis that also includes hemp, it should be possible to obtain natural cellulose fibers from the stems of hop plants with properties similar to that of hemp. A simple alkaline extraction was used to obtain fibers from the bark of hop stems. Fibers obtained have high cellulose content, low% crystallinity but show good orientation of the cellulose crystals to the fiber axis. The strength and modulus of the fibers are lower but elongation is higher than that of hemp. Based on the properties of the fibers, we expect that the hop stem fibers will be suitable for use in textiles and composites similar to the common cellulose fibers currently in use.     

Vaccination of biological cellulose fibers with glucose: a gateway to novel nanocomposites

This work introduces, for the first time worldwide, the means to preserve and protect the natural nanoporous structure of the never-dried plant cell wall, against the irreversible collapse, which occurs due to drying. Simultaneously, these means, used for the above-mentioned aim, provide a gateway to novel nanocomposite materials, which retain the super reactive and super absorbent properties of the never-dried biological cellulose fibers. The present work showed, for the first time worldwide, that glucose can be vaccinated into the cell wall micropores or nanostructure of the never-dried biological cellulose fibers, by simple new techniques, to create a reactive novel nanocomposite material possessing surprising super absorbent properties. Inoculation of the never dried biological cellulose fibers, with glucose, prevented the collapse of the cell wall nanostructure, which normally occurs due to drying. The nanocomposite, produced after drying of the glucose inoculated biological cellulose, retained the super absorbent properties of the never dried biological cellulose fibers. It was found that glucose under certain circumstances grafts to the never dried biological cellulose fibers to form a novel natural nanocomposite material. About 3-8% (w/w) glucose remained grafted in the novel nanocomposite.     

Electron microscopic study of the methylcellulose-mediated detachment of cellulolytic rumen bacteria from cellulose fibers

The presence of methylcellulose prevents the attachment of cellulolytic rumen bacteria to cellulose fibers. The addition of methylcellulose to pure cultures of these organisms in which the cells are already adherent to cellulose causes their detachment from this insoluble substrate and the inhibition of their growth. Methylcellulose is not used as a carbon source by these organisms and has no effect on their growth when glucose and cellobiose are the carbon sources. Attached cells of Bacteroides succinogenes orient themselves in the plane of the individual cellulose fibers and their methylcellulose-induced detachment, which is complete (almost 100%), leaves grooves where the cellulose has been digested. Attached cells of Ruminococcus albus colonize the cellulose in a looser and less regular pattern and their almost complete methylcellulose-induced detachment leaves less regular pits in the cellulose surface. On the other hand, attached cells of Ruminococcus flavefaciens colonize the cellulose surface in a random orientation by means of a discernible exopolysaccharide network, and their less complete methylcellulose-induced detachment leaves no residual impressions on the cellulose surface. These data support the suggestion that bacterial attachment is necessary for the digestion of highly ordered crystalline cellulose, and that cellulolytic species differ in the nature of their attachment to this insoluble substrate and in the nature of their enzymatic attack. Methylcellulose is an effective agent for detaching major rumen cellulolytic bacteria from their cellulosic substrate.     

Natural cellulose fibers from soybean straw

This paper reports the development of natural cellulose technical fibers from soybean straw with properties similar to the natural cellulose fibers in current use. About 220 million tons of soybean straw available in the world every year could complement the byproducts of other major food crops as inexpensive, abundant and annually renewable sources for natural cellulose fibers. Using the agricultural byproducts as sources for fibers could help to address the concerns on the future price and availability of both the natural and synthetic fibers in current use and also help to add value to the food crops. A simple alkaline extraction was used to obtain technical fibers from soybean straw and the composition, structure and properties of the fibers was studied. Technical fibers obtained from soybean straw have high cellulose content (85%) but low% crystallinity (47%). The technical fibers have breaking tenacity (2.7 g/den) and breaking elongation (3.9%) higher than those of fibers obtained from wheat straw and sorghum stalk and leaves but lower than that of cotton. Overall, the structure and properties of the technical fibers obtained from soybean straw indicates that the fibers could be suitable for use in textile, composite and other industrial applications.     

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.     

Modification of cellulosic fibers by UV-irradiation. Part II: After treatments effects

This work presents the comparative study on the dyeing behavior of cellulose fibers in alkaline solutions and under the influence of UV radiation. The cellulosic fabrics were pretreated followed by conventional mercerization technique or treatment with UV irradiation. For different time duration the reorganization of cellulose fibers by swelling treatments in alkaline solutions results in numerous structural modifications, causing changes of their accessibility and/or reactivity. The results revealed that the swelling of the cellulosic fibers depends on type of pre-treatment, dose of the radiation and the concentration of alkaline solution used. SEM analysis confirmed that UV irradiation of the cellulosic fibers leads to a higher swelling in comparison with any concentration of NaOH treatment. In comparison of both the treatments, the mercerized cellulosic fibers have shown better tear and tensile strength as compared to the untreated and UV irradiated one. There is adverse effect of UV radiation on the mechanical properties of UV radiation. Moreover, no loss in weight was observed after exposing the cellulose fabrics surface to UV radiation.     

Image analysis of modified cellulose fibers from sugarcane bagasse by zirconium oxychloride

Surface modification of natural fibers has been made using different methods. In this paper, cellulose fibers from sugarcane bagasse were bleached and modified by zirconium oxychloride in situ. The chemically modified cellulose fibers were compared to those of bleached ones. Cellulose fibers were modified with ZrO₂·nH₂O nanoparticles through the use of zirconium oxychloride in acidic medium in the presence of cellulose fibers using urea as the precipitating agent. The spatial distribution characterization of hydrous zirconium oxide on cellulose fibers was carried out by combining both processing and image analyses obtained by SEM and statistical methodologies. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TG) were also used to characterize the nanocomposite. Results indicated that ZrO₂·nH₂O nanoparticles of about 30-80 nm diameter deposited on cellulose fibers were heterogeneously dispersed.     

Easy alignment and effective nucleation activity of ramie fibers in injection-molded poly(lactic acid) biocomposites

The poly(lactic acid) (PLA)/ramie fiber biocomposites were fabricated, which exhibited considerable reinforcement effect comparable to the glass fiber at the same loading. The attempts were made to understand the flow-induced morphology of ramie fibers and PLA crystals in the injection-molded PLA/ramie fiber biocomposites, thus revealing its relationship to biocomposite mechanical properties. The polarized optical microscopy (POM) and two-dimensional wide-angle X-ray diffraction (2D-WAXD) were for the first time used to determine the distribution of nature fibers, which interestingly showed the ramie fibers aligned well along the flow direction over the whole thickness of injection-molded parts, instead of skin-core structure. This easy alignment of ramie fibers during the common processing was ascribed to the intrinsically high flexibility of ramie fibers and strong interfacial interaction between PLA chains and cellulose molecules of ramie fibers. Both 2D-WAXD and differential scanning calorimeter (DSC) measurements suggested that the PLA matrix in its ramie biocomposites had rather high orientation degree and crystallinity, which was attributed to effective heterogeneous nucleation induced by ramie fibers and local shearing field in the vicinity of fiber surface. Remarkable improvement of mechanical and thermo-mechanical properties was achieved for PLA/ramie fiber biocomposites, without sacrifice of toughness and ductility. Addition of 30wt% ramie fibers increased the tensile strength and modulus of PLA/ramie fiber biocomposites from 65.6 and 1468 MPa for pure PLA to 91.3 and 2977 MPa, respectively. These superior mechanical properties were ascribed to easy alignment of ramie fibers, high crystallinity of PLA, and favorable interfacial adhesion as revealed by scanning electron microscopy (SEM) observation and theoretical analysis based on dynamic mechanical analysis (DMA) data.