Extraction of cellulose and preparation of nanocellulose from sisal fibers

In this work a study on the feasibility of extracting cellulose from sisal fiber, by means of two different procedures was carried out. These processes included usual chemical procedures such as acid hydrolysis, chlorination, alkaline extraction, and bleaching. The final products were characterized by means of Thermogravimetric Analysis (TGA), Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and Scanning Electronic Microscopy (SEM). The extraction procedures that were used led to purified cellulose. Advantages and disadvantages of both procedures were also analyzed. Finally, nanocellulose was produced by the acid hydrolysis of obtained cellulose and characterized by Atomic Force Microscopy (AFM).     

Oriented cellulose films and fibers from a mesophase system

Cellulose mesophases were obtained by preparing concentrated solutions of cellulose (20–55%) in a mixture of N-methyl-morpholine N-oxide (MMNO) and water. The anisotropy depends on four interconnected parameters: the temperature of the solution which, in general, must be lower than 90°C; the concentration of cellulose which must exceed 20%; a water content such that the mole ratio water/anhydrous MMNO is smaller than unity; and the degree of polymerization of the dissolved cellulose. The anisotropic cellulose solutions can readily be oriented during extrusion or casting thus giving fibers or films which upon regeneration exhibit high orientation.     

Recovery of wool from flax fibers using nitric acid

The principal possibility of preparing wool from cottonized flax fibers using nitric acid both in the course of cooking and in the bleaching step was studied. The influence of the nitric acid concentration and cooking time on the extent of flax delignification was examined.     

Thermogravimetric measurement of amorphous cellulose content in flax fibre and flax pulp

Usually the raw material for flax pulp production is a blend which contains fibres and shives. In order to better understanding the structure of these materials and the effects of flax pulping, X-ray diffraction and thermogravimetry analysis under air atmosphere have been used. There was a significant effect of the fibre size on the composition, crystallinity, and thermal behaviour of the flax pulps. On the other hand, data obtained from thermogravimetric analysis have been modelled on the basis of two cellulose types characterized by different crystallinity levels, using kinetics equations based on the nucleation concept. As a result of these simulations, composition of the samples, pulp crystallinity and the proportion of amorphous cellulose are calculated.     

Isolation and characterization of cellulose nanofibers from four plant cellulose fibers using a chemical-ultrasonic process

Cellulose nanofibers (CNFs) were isolated from four kinds of plant cellulose fibers by a chemical-ultrasonic treatment. The chemical composition, morphology, crystalline behavior, and thermal properties of the nanofibers and their intermediate products were characterized and compared. The CNFs extracted from wood, bamboo, and wheat straw fibers had uniform diameters of 10–40 nm, whereas the flax fibers were not uniformly nanofibrillated because of their initially high cellulose content. The chemical composition of each kind of nanofibers was mainly cellulose because hemicelluloses and lignin were significantly removed during chemical process. The crystallinity of the nanofibers increased as the chemical treatments were applied. The degradation temperature of each kind of nanofiber reached beyond 330 °C. Based on the properties of the CNFs, we expect that they will be suitable for use in green nanocomposites, filtration media and optically transparent films.     

Preparation of mixed cellulose ethers by the reaction of short flax fibers and cotton linter with monochloroacetamide

The conditions of preparation of mixed cellulose ethers containing carboxy and amino groups by the reaction of samples of short flax fiber and cotton linter with monochloroacetamide were examined. The influence of the amino groups of the mixed cellulose ethers on the rheological properties of their aqueous solutions was elucidated.     

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.     

Biochemical and physicochemical treatment of flax fibers

Conditions were found for separating concomitant substances from cellulose in short flax fibers by treatment with surfactant and enzyme solutions. The chemical composition of the treated fibers was analyzed, and their structural organization was studied by IR Fourier spectroscopy.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 10, 2004, pp. 1743–1746.Original Russian Text Copyright © 2004 by Shamolina, Bochek, Zabivalova, Vlasova, Volchek, Sinitsin.     

Electrospinning of ultrafine cellulose acetate fibers: Studies of a new solvent system and deacetylation of ultrafine cellulose acetate fibers

Electrospinning of cellulose acetate (CA) in a new solvent system and the deacetylation of the resulting ultrafine CA fibers were investigated. Ultrafine CA fibers (∼2.3 μm) were successfully prepared via electrospinning of CA in a mixed solvent of acetone/water at water contents of 10–15 wt %, and more ultrafine CA fibers (0.46 μm) were produced under basic pH conditions. Ultrafine cellulose fibers were regenerated from the homogeneous deacetylation of ultrafine CA fibers in KOH/ethanol. It was very rapid and completed within 20 min. The crystal structure, thermal properties, and morphology of ultrafine CA fibers were changed according to the degree of deacetylation, finally to those of pure cellulose, but the nonwoven fibrous mat structure was maintained. The activation energy for the deacetylation of ultrafine CA fibers was 10.3 kcal/mol. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 5–11, 2004     

Synthesis of cyanoethyl ethers of cellulose from flax fiber production waste

Conditions of preparation of cellulose cyanoethyl ethers with different degrees of substitution, based flax fiber production waste were examined. The chemical structure of the resulting cellulose ethers and variation of the structure of the cellulose materials during cyanoethylation were examined by IR-Fourier spectroscopy and X-ray diffraction analysis. The degree of substitution of cellulose ethers was examined in relation to cyanoethylation conditions and chemical composition of the initial cellulose materials.     

Sorption properties of plasma-modified flax fibers

Effect of plasma modification on the sorption properties of short flax fibers for Zn(II) ions was studied.     

Structure of cellulose and microcrystalline cellulose from various wood species, cotton and flax studied by X-ray scattering

The structure of microcrystalline cellulose (MCC) made by mild acid hydrolysis from cotton linter, flax fibres and sulphite or kraft cooked wood pulp was studied and compared with the structure of the starting materials. Crystallinities and the length and the width of the cellulose crystallites were determined by wide-angle X-ray scattering and the packing and the cross-sectional shape of the microfibrils were determined by small-angle X-ray scattering. The morphological differences were studied by scanning electron microscopy. A model for the changes in microfibrillar structure between native materials, pulp and MCC samples was proposed. The results indicated that from softwood or hardwood pulp, flax cellulose and cotton linter MCC with very similar nanostructures were obtained with small changes in reaction conditions. The crystallinity of MCC samples was 54–65%. The width and the length of the cellulose crystallites increased when MCC was made. For example, between cotton and cotton MCC the width increased from 7.1 nm to 8.8 nm and the length increased from 17.7 nm to 30.4 nm. However, the longest crystallites were found in native spruce wood (35–36 nm).     

Solvent and enzyme induced recrystallization of mechanically degraded hemp cellulose

The structural degradation of cellulose fibre from hemp (Cannabis Sativa L.) by a ball-milling process and the recrystallization behavior of the product were studied. A linear increase in the Brunauer–Emmett–Teller specific surface area was observed; indicating the fibre bundles were being crushed and disrupted to single fibres, which was confirmed by SEM. An increase in the milling duration gradually destroyed the crystalline structure of the cellulose fibres, observed by a reduction of the 002 plane intensity in wide angle X-ray scattering measurements. The crystalline order index calculated from the area ratio of the 002 to the 021, 10 and 002 planes was decreased from 65 to 36 after milling for 330 min. Subsequently the lower thermal stability of ball-milled fibre was observed from a decrease in the temperature at the maximum mass loss rate using thermogravimetry. An increase in solvent polarity, solvent-fibre ratio, agitation speed and drying rate resulted in the rearrangement of ball-milled cellulose crystalline structure to a greater order. Moreover, an increase in the BET specific surface area and the amorphous fraction improved the scouring efficiency of the ball-milled cellulose using the pectate lyase enzyme (EC. 4.2.2.2).     

Variation of the reactivity of flax fiber cellulose in the course of flax ripening

Carboxymethyl cellulose ethers were prepared from flax fibers of various degrees of ripeness. The influence exerted by the degree of ripeness of flax fibers on their reactivity in carboxymethylation was examined. The rheological properties of aqueous solutions of the synthesized carboxymethyl cellulose were studied.     

Formation of cellulose microspheres and nanocrystals from mildly carboxylated fibers

Cellulose - The ultrastructure of mildly carboxylated swollen tracheids from which cellulose microspheres and cellulose nanocrystals (CNC) were formed was investigated. A mild etherification of...     

Hydrodynamically induced formation of cellulose fibers. I. Observations on the formation of cellulose fibers from stirred solutions

Like synthetic polymers, a natural polymer such as cellulose may crystallize in fibrous form from stirred solutions. In the present work, it is demonstrated that cellulose fibers can be formed by precipitation from dimethyl sulfoxide/paraformaldehyde solutions by two methods that involve different mechanisms of fiber formation, viz., (A) precipitation of cellulose by addition of nonsolvent to the stirred cellulose solution, and (B) precipitation of cellulose by coagulation of droplets of cellulose solution in a stirred precipitant. Both processes yield fibers with properties depending on the stirring speed and the coagulant strength. The molecular orientation and tensile strength of the fibers produced by method A was low, but increased with the stirring speed, while some fibers formed by method B reached extremely high orientation, depending on the thickness of the fibers. The two mechanisms of fiber formation are discussed on the basis of the experimental observations.     

Isolation of cellulose fibers from kenaf using electron beam

Cellulose fibers were isolated from a kenaf bast fiber using a electron beam irradiation (EBI) treatment. The methods of isolation were based on a hot water treatment after EBI and two-step bleaching processes. FT-IR spectroscopy demonstrated that the content of lignin and hemicellulose in the bleached cellulose fibers treated with various EBI doses decreased with increasing doses of EBI. Specifically, the lignin in the bleached cellulose fibers treated at 300 kGy, was almost completely removed. Moreover, XRD analyses showed that the bleached cellulose fibers treated at 300 kGy presented the highest crystallinity of all the samples treated with EBI. Finally, the morphology of the bleached fiber was characterized by SEM imagery, and the studies showed that the separated degree of bleached cellulose fibers treated with various EBI doses increased with an increase of EBI dose, and the bleached cellulose fibers obtained by EBI treatment at 300 kGy was separated more uniformly than the bleached cellulose fiber obtained by alkali cooking with non-irradiated kenaf fiber.     

Kinetics of water sorption in flax and PET fibers

Composite materials are usually reinforced by synthetic fibers as carbon, glass etc…. Because of their good mechanical properties and low density, natural fibers are being considered more preferentially as reinforcement. The application of natural fibers as reinforcements in composite materials requires a strong adhesion between the fiber and the matrix. The poor resistance towards water absorption is one of the drawbacks of natural fibers which makes it more important to understand the dynamic properties of penetration of water molecules through these heterogeneous materials. Water vapour sorption kinetics in natural flax fibers have been performed at 25 °C by using an electronic microbalance (IGA, Hiden). By using the Fickian model for a complete cylinder water diffusion coefficients have been determined and calculated at short times (first half-sorption) and long times (second half-sorption) of kinetic curve and for different water activities. The values obtained for D₁ and D₂ are rather similar on the all range of water activity. Generally, water diffusivity increases and then decreases with water activity. The increase of diffusivity at low water activities may be explained on the basis of the dual mode sorption (Langmuir and Henry sorption’s combination) whereas the decrease for the higher activities can be attributed to the immobilization of sorbed water molecules due to the water clustering.