Oxidized Cellulose Fibers Research Articles

Twin-screw extrusion for the production of nanocellulose-PVA gels with a high solid content

Twin-screw extrusion (TSE) is a recent strategy used to prepare nanocelluloses at high solid contents. However, various aspects of the mechanism of disintegration and the role of fiber pretreatment remain to be elucidated. Oxidized cellulose fibers with carboxyl contents between 300 and 700 μmol·g−1 were extruded in the presence of polyvinyl alcohol (PVA) at a 80/20 (w/w) ratio, to produce high-consistency nanocellulose gels at 15 wt% solid content, ready for use in multiple applications. The influence of the origin of the pulps and the oxidation treatment on the efficiency of fiber disintegration was evaluated by porosity measurement. The rheological properties of the nanocellulose-PVA gels and the mechanical properties and transparency of the resulting nanopapers were studied as well. Combining TSE and rotor-stator dispersion or short sonication homogenization contributed to enhancing the fibrillation during extrusion, providing a method to increase the fraction of nanocellulose in a much less energy-consuming manner.

Novel chitosan/gelatin/oxidized cellulose sponges as absorbable hemostatic agents

Chitosan/gelatin (CG) composite sponges containing oxidized cellulose fibers (OF) crosslinked with tannic acid were fabricated by freeze-drying as hemostatic agents. The cellulose fibers were oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO). Fourier transform infrared spectroscopy proved the formation of carboxyl groups on cellulose fibers. Addition of OF increased the swelling ratio of CG sponges. The amount of bleeding was measured after 10 s on hepatic trauma in a rat model. To assess the in vivo bio-absorbability of the samples, the sponges were implanted in the liver for 21 days and the volume of the repaired tissue was measured from histopathological analysis. The biocomposite sponge fabricated by addition of 30% OF suspension into CG solution showed the lowest amount of bleeding and the highest bio-absorbability after 21 days. The findings of this study indicate that the addition of OF into CG increased the clotting capability as well as the bio-absorbability of the biocomposite sponges.

One-step processing of plasticized starch/cellulose nanofibrils nanocomposites via twin-screw extrusion of starch and cellulose fibers

Nanocomposites based on thermoplasticized starch filled with cellulose nanofibrils (CNFs) were produced in a single step by twin-screw extrusion of corn starch granules, glycerol as a plasticizer, and oxidized cellulose fibers. The objective was to demonstrate the possibility to produce CNFs in situ during the processing of the nanocomposite when a hydrophilic polymer matrix was used. For comparison purpose, nanocomposites were also prepared by extrusion of a previously prepared CNF suspension, corn starch granules and glycerol. The nanocomposites were characterized in terms of mechanical properties, morphology, crystallinity, and transparency. The nanocomposites prepared via in situ fibrillation displayed a higher strength than those produced by incorporating readily prepared CNFs. In addition, the transparency degree up to a 15 wt% CNF content was similar for the two processing routes, confirming the effective breakdown of pretreated cellulose fibers into CNFs during the extrusion process.

Oxidized Cellulose Fibers for Reinforment in Poly(Lactic Acid) Based Composite

Oxidized Cellulose Fibers for Reinforment in Poly(Lactic Acid) Based Composite

Characterization and control of oxidized cellulose in ramie fibers during oxidative degumming

Oxidative degumming with hydrogen peroxide provides an efficient pathway and new alternative for natural fiber extraction. In this work, the oxidized cellulose introduced into ramie fibers during the oxidative degumming process was systematically characterized in terms of x-ray photoemission spectroscopy, nuclear magnetic resonance, Fourier transform infrared spectroscopy and scanning electron microscopy. The differences of chemical components, chemical shift, surface structure and surface morphology were analyzed and compared within oxidized cellulose fibers with different oxidation degrees. In addition, the relationship between oxidized cellulose contents and mechanical properties of degummed fibers were further discussed. The results show that the number of oxidized groups increases with increasing oxidation. In addition, the greater presence of oxidized cellulose contributes to a larger loss of tenacity, breaking elongation, flexibility and degree of polymerization in degummed fibers. This study could offer useful information in better understanding the reaction characteristics of oxidative degumming and better control of degummed fiber quality. The contents of oxidized cellulose in ramie fibers could be an effective indicating factor to demonstrate oxidative degumming efficiency and fiber properties.

TEMPO-mediated oxidation of cellulose in carbonate buffer solution

The reaction stability is a challenge in the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of cellulose. Carbonate buffer solution (Na2CO3/NaHCO3) was used to study pH effects on stability of the oxidation reaction in this work. The structure and morphology of cellulose fibers were characterized by XRD and SEM techniques, respectively. It was found that the carboxyl content of oxidized cellulose was changed with different composition ratio of buffer solutions. The highest carboxyl content was obtained at the molar ratio of 7:3. The NaClO addition, as well as reaction temperature, affected the process of the oxidation reaction. The carboxylate content of the oxidized cellulose was increased as the temperature and NaClO consumption increased. However, both temperature and NaClO consumption have negative effect on yield. SEM results showed that the morphology of oxidized cellulose fibers was significantly changed at high reaction temperature. XRD showed that the oxidized cellulose fibers maintained the crystal structure of cellulose I. However, the crystallinity was decreased from 56.4 to 40.8 % with increasing oxidation temperature from 25 to 40 °C.

Effects of carboxyl-group counter-ions on biodegradation behaviors of TEMPO-oxidized cellulose fibers and nanofibril films

The biodegradation behaviors of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose fibers (TOCs) and TEMPO-oxidized cellulose nanofibril (TOCN) films containing various carboxyl-group counter-ions were studied. Na+, H+, Ca2+, NH4 +, Cu2+, K+, and Cs+ were introduced into the TOCs or TOCN films, by ion-exchange treatment, as the carboxyl-group counter-ions. TOCs suspended in distilled water were treated with a commercial crude cellulase, and the TOCN films were subjected to soil burial tests. The crude-cellulase-treated products obtained from the TOCs were separated into water/ethanol-insoluble and -soluble fractions, i.e., high- and low-molecular-weight fractions, respectively. The degradation behaviors of the TOCs were evaluated from the weight recovery ratios of the water/ethanol-insoluble fractions and their viscosity-average degrees of polymerization. The results showed that the degradation behaviors of the TOCs were greatly influenced by the counter ion, and the counter-ion order of degradability was Na+ ≈ NH4 + ≈ K+ ≈ Cs+ ≫ Ca2+ > H+ > Cu2+. These degradability differences were influenced by the swelling behavior of the corresponding TOCs in distilled water; the higher the swelling degree of the TOC, the higher the degradation efficiency of the TOC in the reaction with crude cellulase. Similar biodegradation behaviors were observed in soil burial tests for TOCN films containing various carboxyl-group counter-ions in soil burial test; again the counter ion greatly influenced the resultant biodegradability. The biodegradation behaviors of TOCs and TOCN films can therefore be controlled by selecting an appropriate carboxyl-group counter-ion.

Highly charged nanocrystalline cellulose and dicarboxylated cellulose from periodate and chlorite oxidized cellulose fibers

Softwood cellulose pulp was oxidized by a two-step oxidation process with sodium periodate followed by sodium chlorite at pH 5.0. The oxidized product was first separated into two fractions by centrifugation, and the supernatant was further separated in two fractions by addition of ethanol and centrifugation. Different levels of oxidation were performed on cellulose, and the mass ratio and carboxyl content of each fraction were determined. The first precipitate, which amount decreases with increasing oxidation level, consists of short fiber fragments (microfibrils) with length of 0.6–1.8 μm and width around 120 nm, which for sufficiently high oxidation levels, could readily be made into cellulose nanofibrils by stirring. The second precipitate (after alcohol addition) has a very high crystalline index of 91 % and contains rod-like particles with length of 120–200 nm and diameter around 13 nm, reminiscent of nanocrystalline cellulose. The supernatant contains water-soluble dicarboxylated cellulose, as proven by liquid C-13 NMR.

ANTIBACTERIAL FIBERS BASED ON CELLULOSE AND CHITOSAN

Cellulose and chitin are the most abundant polysaccharides in nature. Chitin is the natural amino polysaccharide and is estimated to be produced annually almost as much as cellulose. These resources are renewable and inexhaustible if rationally utilised. Unique properties of chitin and chitosan (chitin derivative obtained by the deacetylation of chitin), such as antibacterial activity, biocompatibility, non-toxicity and bioresorptivity make these materials very suitable and important biomaterials. During our studies, we examined the possibilities of obtaining composite, biologically active cellulose-chitosan fibres. Аn effective two-stage procedure for obtaining antibacterial fibers based on cellulose and chitosan was developed. The first stage involves the formation of dialdehyde cellulose by potassium periodate oxidation of cellulose fibers, which is able to form Schiff’s base with chitosan. In the second stage, chitosan coated cellulose fibers were prepared by subsequent treatment of oxidized cellulose fibers with a solution of chitosan in aqueous acetic acid. Maximum percentage of chitosan introduced into/onto the cellulose fibers was 0,51 % (w/w). Antibacterial activity of cellulose fibers coated with chitosan as the active component against bacteria Escherichia coli and Staphylococcus aureus, was confirmed by in vitro experiments .

Degradation of TEMPO-oxidized cellulose fibers and nanofibrils by crude cellulase

The biodegradation behavior of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose fibers (TOCs) suspended in water and TEMPO-oxidized cellulose nanofibrils (TOCNs) dispersed in water by a commercial crude cellulase was studied. Products crude cellulase-treated for 0–7 days were separated into water/ethanol-insoluble and -soluble fractions. Weight recovery ratios and viscosity-average degrees of polymerization of the water/ethanol-insoluble fractions clearly decreased with crude cellulase-treatment time, showing that both TOCs and TOCNs have biodegradability. Water/ethanol-soluble fractions were subjected to size-exclusion chromatography (SEC) with photodiode array (PDA) detection to obtain SEC elution patterns detected by reflective index and UV spectra of each SEC pattern elution slice. SEC–PDA and 13C-NMR analyses showed that glucuronosyl unit-containing molecules present on microfibril surfaces in TOCs and TOCNs were primarily cleaved by hydrolyzing enzymes present as contaminants in the crude cellulase to form glucuronic acid as one of the major water-soluble degradation compounds. After the glucuronosyl units in TOCs and TOCNs were degraded and removed from microfibril surfaces by the hydrolyzing enzymes, cellulose chains newly exposed on the microfibril surfaces were rapidly hydrolyzed by cellulases predominantly present in the crude cellulase to form cellobiose. Both TOCs and TOCNs having sodium carboxyl groups are thus biodegradable, but TOCN having free carboxyl groups had clearly low biodegradability by the crude cellulase. Thus, biodegradation behavior may be controllable by controlling the structure of carboxyl group counter ions in TOCs and TOCNs.

Physical immobilization of Rhizopus oryzae lipase onto cellulose substrate: Activity and stability studies

Rhizopus oryzae lipase (ROL) was immobilized by adsorption onto oxidized cellulose fibers and regenerated films. The maximum adsorption level increases with the raise in the amount of carboxylic groups on cellulose surface confirming that adsorption is being governed mainly by electrostatic interaction between the enzyme and the substrate. This hypothesis was further confirmed by ζ-potential measurements showing a decrease in the ζ-potential of the fibers after enzyme adsorption. XPS analysis showed an intensification of the N 1s peak attesting the presence of the enzyme on the surface. The effect of temperature, pH and solvent polarity on the immobilized enzyme activity and stability was investigated. The catalytic esterification of oleic acid with n-butanol has been carried on using hexane as an organic solvent. A high conversion yield was obtained (about 80%) at 37 °C with a molar ratio of oleic acid to butanol 1:1 and 150 IU immobilized lipase. The adsorption achieved two successive cycles with the same efficiency, and started to lose its activity during the third cycle.

Self-Aggregation of Cationic Surfactants onto Oxidized Cellulose Fibers and Coadsorption of Organic Compounds

In this work, the adsorption of cationic surfactant and organic solutes on oxidized cellulose fibers bearing different amounts of carboxylic moieties was investigated. The increase in the amount of -COOH groups on cellulose fibers by TEMPO oxidation induced a general rise in surfactant adsorption. For all tested conditions, that is, cellulose oxidation level and surfactant alkyl chain length (C12 and C16), adsorption isotherms displayed a typical three-region shape with inversion of the substrate zeta-potential which was interpreted as reflecting surfactant adsorption and aggregation (admicelles and hemimicelles) on cellulose fibers. The addition of organic solutes in surfactant/cellulose systems induced a decrease in surfactant cac on the cellulose surface thus favoring surfactant aggregation and the formation of mixed surfactant/solute assemblies. Adsorption isotherms of organic solutes on cellulose in surfactant/cellulose/solute systems showed that solute adsorption is strictly correlated to (i) the surfactant concentration, solute adsorption increases up to the surfactant cmc, where solute partitioning between the cellulose surface and free micelles causes a drop in adsorption, and to (ii) solute solubility and functional groups. The specific shape of solutes adsorption isotherms at a fixed surfactant concentration was interpreted using a Frumkin adsorption isotherm, thus suggesting that solute uptake on cellulose fibers is a coadsorption and not a partitioning process. Results presented in this study were compared with those obtained in a previous work investigating solute adsorption in anionic surfactant/cationized cellulose systems to better understand the role of surfactant/solute interactions in the coadsorption process.

Structural studies of electrospun cellulose nanofibers

Non-woven mats of submicron-sized cellulose fibers (250–750nm in diameter) have been obtained by electrospinning of cellulose solutions. Cellulose are directly dissolved in two solvent systems: (a) lithium chloride (LiCl)/N,N-dimethyl acetamide (DMAc) and (b) N-methylmorpholine oxide (NMMO)/water, and the effects of (i) solvent system, (ii) the degree of polymerization of cellulose, (iii) spinning conditions, and (iv) post-spinning treatment such as coagulation with water on the miscrostructure of electrospun fibers are investigated. The scanning electron microscope (SEM) images of electrospun cellulose fibers show that applying coagulation with water right after the collection of fibers is necessary to obtain submicron scale, dry and stable cellulose fibers for both solvent systems. X-ray diffraction studies reveal that cellulose fibers obtained from LiCl/DMAc are mostly amorphous, whereas the degree of crystallinity of cellulose fibers from NMMO/water can be controlled by various process conditions including spinning temperature, flow rate, and distance between the nozzle and collector. Finally, electrospun cellulose fibers are oxidized by HNO3/H3PO4 and NaNO2, and the degradation characteristics of oxidized cellulose fibers under physiological conditions are presented.