Birch Cellulose Research Articles

Synthesis and Sulfation with Sulfamic Acid of Aerogels Based on Birch-Wood and Cotton Celluloses

Firstly, the structure and properties of cellulose aerogels produced from birch-wood and cottoncellulose and of, and products of their sulfation with a non-toxic sulfamic acid-urea complex in an environmentally safe solvent – a mixture of polyethylene glycol and sodium hydroxide are compared. Aerogels based on birch and cotton celluloses have similar values of apparent density (0,071–0,078 г/см3) and porosity (near 95 %). The products of sulfating of cellulose aerogels, in contrast to the originalbirch and cotton celluloses, are completely soluble in water. Their yield and degree of substitution are higher when using birch cellulose aerogel. By drying the dissolved products of sulfating of cellulose aerogels, smooth and transparent films were produced. The structure and morphology of the obtained aerogels and films were established by metods of scanning electron microscopy and atomic force microscopy. Birch cellulose aerogel (BCA) has a reticular microfibrillated porous structure, and cotton cellulose aerogel (CCA) has a spongy structure in which more cavities and cracks are observed than in the case of CCA. The surface of the film of sulfated BCA is formed by particles with a length 100–200 nm and width of 50–70 nm, and the films of sulfated CCA is formed by spherical particles with a diameter of 70–100 nm. The developed methods for obtaining sulfated cellulose films can be used in medicine to oreate anticoagulant coatings

Thermal characteristics of birch and its cellulose and hemicelluloses isolated by alkaline solution

AbstractCellulose and hemicelluloses were isolated from birch wood using a dilute alkaline solution and then consolidated into pellets as model compounds of cellulose and hemicelluloses in the wood cell wall. The purity of isolated cellulose and hemicelluloses was examined by Fourier-transform infrared spectroscopy and thermogravimetric analysis. The density, thermal diffusivity, heat capacity, and thermal conductivity were experimentally determined for consolidated birch powder, cellulose, and hemicelluloses in over-dry condition. The thermal degradation kinetic parameters of these materials were successfully calculated using a conversion rate step of 0.01, and the relationship with conversion rate was established. The results show that cellulose and hemicelluloses consolidated under 25 MPa had densities of 1362 kg/m3and 1464 kg/m3, respectively. The cell wall of birch powder in the oven-dry state was not collapsed under 25 MPa. The thermal diffusivity of consolidated birch powder, cellulose, and hemicelluloses linearly decreased with temperature, with values of 0.08, 0.15, and 0.20 mm2/s at room temperature, respectively. The specific heat capacity (1104, 1209, and 1305 J/(kg·K) at 22 °C, respectively) and thermal conductivity (0.09, 0.24, and 0.38 W/(m·K) at 22 °C, respectively) linearly increased with temperature, except for those for hemicelluloses which exhibited a nonlinear relationship with temperature above 120 °C, and their linear experimental prediction equations were given. Birch cellulose was more thermally stable than hemicelluloses. The thermal degradation kinetic parameters including activation energy and pre-exponential factor of birch powder, cellulose, and hemicelluloses varied with the conversion rate and calculation methods, with average activation energy in a conversion rate range of 0.02–0.15 of 123.2, 159.0, and 147.2 kJ/mol, respectively (using the Flynn–Wall–Ozawa method), for average natural logarithm pre-exponential factors of 25.0, 33.1, and 28.7 min−1, respectively. Linear and quadratic equations were fitted to describe the relationship between the kinetic parameters and conversion rates. These results give comprehensive thermal properties of the densified cellulose and hemicelluloses isolated from a specific wood.

Enhancement of the nanofibrillation of birch cellulose pretreated with natural deep eutectic solvent

In this study, we demonstrate a new bio-derived and non-toxic deep eutectic solvent composed of betaine hydrochloride (Bh) and glycerol (Gl) as a pretreatment medium for birch cellulose (Betula pendula) to prepare cellulose nanofibers (CNFs) using microfluidization. The co-solvent could readily penetrate into cellulose to swell the fibrillar structure and weaken the interaction within the hydrogen bond network. Moreover, the cationization of glycerol and cellulose by betaine hydrochloride further enhances the swelling process. All of these effects promote the nanofibrillation of cellulose and reduce the energy demand in CNF production. A high CNF mass yield of up to 72.5 % was obtained through co-solvent pretreatment using a Bh-to-Gl mole ratio of 1:2 at 150 °C for 1 h. The mole amount of betaine hydrochloride was noted to affect the nanofibrillation process and stability of the CNF suspension. The obtained CNFs possessed a cationic charge of 0.05–0.06 mmol/g, a diameter of 17–20 nm, and a degree of crystallinity of 67.7–74.4 %. The CNFs displayed good thermal stability comparable to that of the pristine cellulose. Thus, this study provides a green and efficient swelling strategy for producing CNFs with a low cationic charge density.

Quantification of a tightly adsorbed monolayer of xylan on cellulose surface

The successive extraction and re-adsorption of a linear β-(1 → 4) xylan extracted from microfibrillated birch pulp was investigated using solid-state CP/MAS 13C NMR spectroscopy, specific surface area measurements, and atomistic molecular dynamics (MD) simulations. The NMR spectra confirmed that when in contact with cellulose after re-adsorption, the xylan molecules altered their conformation from the classical left-handed threefold structure found in the bulk to a different one, presumably a cellulose-like twofold system for quantities up to the equivalent amount of extracted xylan. Combining these observations with specific surface area measurements and the surface occupied by a xylosyl residue, it was possible to show that the re-adsorbed xylan in the modified conformation occurred only within the first adsorbed layer in direct interaction with the cellulose surface. It is only when an excess xylan was added and after full cellulose surface coverage, that the subsequent deposited layers took the classical threefold organization. Following the variation of xylan conformation in terms of sequential xylan addition allowed quantifying the surface of cellulose accessible for a tight adsorption of xylan, not only for microfibrillated birch cellulose, but for other samples as well. The MD simulations confirmed that xylan in threefold conformation had a weaker affinity for the cellulose surface than its twofold counterpart, thus supporting the hypothesis of the twofold conformation for xylan at the cellulose surface. The MD simulations also showed that in contact with cellulose, the adsorbed xylan was mainly organized as an extended molecular chain aligned parallel to the cellulose chain direction.

Cellulose Nanofibrils from Nonderivatizing Urea-Based Deep Eutectic Solvent Pretreatments.

Deep eutectic solvents (DESs) are a fairly new class of green solvents applied in various fields. This study investigates urea-based DES systems as novel pretreatments for cellulose nanofibril production. In the experiments, deep eutectic systems having urea and ammonium thiocyanate or guanidine hydrochloride as a second component were formed at 100 °C and then applied to disintegrate wood-derived cellulose fibers. The DES-pretreated fibers were nanofibrillated into three different levels of mechanical treatments with a microfluidizer, and their properties were analyzed. Moreover, nanofibril films were fabricated by solvent casting method. Both DES systems were able to loosen and swell the cellulose fiber structure as indicated by the increase in the lateral dimension of the fibers. Nonpretreated birch cellulose fibers had difficulties in mechanical nanofibrillation as clogging of the chamber occurred often. However, cellulose nanofibrils with widths ranging from 13.0 to 19.3 nm were successfully fabricated from DES-pretreated fibers with both systems. Translucent nanofibril films generated from DES-pretreated cellulose nanofibrils had good thermal stability and mechanical properties, with tensile strengths of approximately 135-189 MPa and elastic modulus of 6.4-7.7 GPa. Consequently, both urea-based DESs showed a high potential as environmentally friendly solvents in the manufacture of cellulose nanofibrils.

Saccharification of Cellulose by Recombinant Rhodococcus opacus PD630 Strains

The noncellulolytic actinomycete Rhodococcus opacus strain PD630 is the model oleaginous prokaryote with regard to the accumulation and biosynthesis of lipids, which serve as carbon and energy storage compounds and can account for as much as 87% of the dry mass of the cell in this strain. In order to establish cellulose degradation in R. opacus PD630, we engineered strains that episomally expressed six different cellulase genes from Cellulomonas fimi ATCC 484 (cenABC, cex, cbhA) and Thermobifida fusca DSM43792 (cel6A), thereby enabling R. opacus PD630 to degrade cellulosic substrates to cellobiose. Of all the enzymes tested, five exhibited a cellulase activity toward carboxymethyl cellulose (CMC) and/or microcrystalline cellulose (MCC) as high as 0.313 ± 0.01 U · ml(-1), but recombinant strains also hydrolyzed cotton, birch cellulose, copy paper, and wheat straw. Cocultivations of recombinant strains expressing different cellulase genes with MCC as the substrate were carried out to identify an appropriate set of cellulases for efficient hydrolysis of cellulose by R. opacus. Based on these experiments, the multicellulase gene expression plasmid pCellulose was constructed, which enabled R. opacus PD630 to hydrolyze as much as 9.3% ± 0.6% (wt/vol) of the cellulose provided. For the direct production of lipids from birch cellulose, a two-step cocultivation experiment was carried out. In the first step, 20% (wt/vol) of the substrate was hydrolyzed by recombinant strains expressing the whole set of cellulase genes. The second step was performed by a recombinant cellobiose-utilizing strain of R. opacus PD630, which accumulated 15.1% (wt/wt) fatty acids from the cellobiose formed in the first step.

Effect of cellulose reinforcement on the properties of organic acid modified starch microparticles/plasticized starch bio-composite films

The present paper describes the preparation and characterization of polysaccharides-based bio-composite films obtained by the incorporation of 10, 20 and 30wt% birch cellulose (BC) within a glycerol plasticized matrix constituted by the corn starch (S) and chemical modified starch microparticles (MS). The obtained materials (coded as MS/S, respectively MS/S/BC) were further characterized. FTIR spectroscopy and X-ray diffraction were used to evidence structural and crystallinity changes in starch based films. Morphological, thermal, mechanical, and water resistance properties were also investigated. Addition of cellulose alongside modified starch microparticles determined a slightly improvement of the starch-based films water resistance. Some reduction of water uptake for any given time was observed mainly for samples containing 30% BC. Some compatibility occurred between MS and BC fillers, as evidenced by mechanical properties. Tensile strength increased from 5.9 to 15.1MPa when BC content varied from 0 to 30%, while elongation at break decreased significantly.

Synthesis of highly cationic water-soluble cellulose derivative and its potential as novel biopolymeric flocculation agent

A water-soluble cationic cellulose derivative was synthesized by cationizing dialdehyde cellulose (DAC) produced by periodate oxidation of birch cellulose pulp by means of a reaction between aldehyde groups and cationic Girard's reagent T ((2-hydrazinyl-2-oxoethyl)-trimethylazanium chloride, GT) to produce cationic dialdehyde cellulose (CDAC). The effect of the aldehyde content of the DAC on its reactivity was evaluated and CDAC with a maximum of 4.27mmol/g of cationic groups was synthesized from highly oxidized cellulose. Water-soluble CDACs were obtained from DACs having an aldehyde group content of 11.77mmol/g or higher when the cationic group content exceeded about 3mmol/g. Promising preliminary results were obtained regarding the use of water-soluble CDAC as a new biopolymeric flocculation agent for calcium carbonate suspension.

Health and environmental safety aspects of friction grinding and spray drying of microfibrillated cellulose

Microfibrillated cellulose (MFC), also referred to as nanocellulose, is one of the most promising innovations for forest sector. MFC is produced by fibrillating the fibres under high compression and shear forces. In this study we evaluated the worker exposures to particles in air during grinding and spray drying of birch cellulose. Processing of MFC with either a friction grinder or a spray dryer did not cause significant exposure to particles during normal operation. Grinding generated small amount of particles, which were mostly removed by fume hood. Spray dryer leaked particles when duct valve was closed, but when correctly operated the exposure to particles was low or nonexistent. To assess the health effects of the produced MFC, mouse macrophages and human monocyte derived macrophages were exposed to MFC and the viability and cytokine profile of the cells were studied thereafter. No evidence of inflammatory effects or cytotoxicity on mouse and human macrophages was observed after 6 and 24 h exposure to the materials studied. The results of toxicity studies suggest that the friction ground MFC is not cytotoxic and does not cause any effects on inflammatory system in macrophages. In addition, environmental safety of MFC was studied with ecotoxicity test. Acute environmental toxicity assessed with kinetic luminescent bacteria test showed high NOEC values (>100 mg/l) for studied MFC. However, MFC disturbed Daphnia magna mobility mechanically when the test was performed according to the standard procedure.

Periodate oxidation of cellulose at elevated temperatures using metal salts as cellulose activators

The birch cellulose is effectively oxidized to the dialdehyde cellulose (DAC) at elevated temperatures by sodium periodate. Even though periodate decomposes at 55 °C and above with time, higher temperatures can be used if the oxidation time is sufficiently short and it has now been shown that temperatures up to 85 °C can be used during the oxidation. Lithium chloride can be used to further improve the oxidation efficiency. Other metal salts, such as calcium chloride can be used as well. These conditions provides possibility to use a lower amount of periodate to obtain high aldehyde contents in DAC.