Composition and properties of wood and cellulose of tropical plants

A component, chemical and morphological composition of wood of the Howea fosteriana palm and the Cereus peruvians cactus and the wood stem of the Dracaena sanderiana was studied. The supramolecular structure and the physicochemical properties of cellulose samples which were extracted from the wood species were examined by wide-angle X-ray scattering, Fourier transform infrared spectroscopy, high-resolution ¹³CP/MAS nuclear magnetic resonance in a solid state, and scanning electron microscopy.     

Structural properties of cellulose and cellulase reaction mechanism

The effects of structural properties and their changes during cellulose hydrolysis on the enzymatic hydrolysis rate have been studied from the reaction mechanism point of view. Important findings are the following: (1) The crystallinity index (CrI) of partially crystalline cellulose increases as the hydrolysis reaction proceeds, and a significant slowing down of the reaction rate during the enzymatic hydrolysis is, in large part, attributable to this structural change of cellulose substrate. (2) The crystallinity of completely disordered cellulose, like phosphoric-acid-treated cellulose, does not change significantly, and a relatively high hydrolysis rate is maintained during hydrolysis. (3) The specific surface area (SSA) of partially crystalline cellulose decreases significantly during enzymatic hydrolysis while the change in SSA of regenerated cellulose is found to be negligible. (4) The value of degree of polymerization (DP) of highly ordered crystalline cellulose remains practically constant whereas the change in DP of disordered regenerated cellulose is found to be very significant. (5) Combination of these structural effects as well as cellulase adsorption, product inhibition, and cellulase deactivation all have important influence on the rate of cellulase reaction during cellulose hydrolysis. More experimental evidence for a two-phase model, which is based on degradation of cellulose by simultaneous actions of cellulase complex on the crystalline and amorphous phases, has been obtained. Based on experimental results from this study and other results accumulated, the mode of cellulase action and a possible reaction mechanism are proposed.     

Effect of microaerobic conditions on the degradation kinetics of cellulose

Limited oxygen supply to sludge digesters has shown to be an effective method to eliminate hydrogen sulfide from the biogas produced during anaerobic digestion but uneven results have been found in terms of the effect on the degradation of complex organic matter. In this study, the effect that the limited oxygen supply provoked on the “anaerobic” degradation of cellulose was evaluated in batch-tests. The microaerobic assays showed to reach a similar maximum production of methane than the anaerobic ones after 19 d and a similar hydrolytic activity (considering a first order rate constant); however, the microaerobic assays presented a shorter lag-phase time than the anaerobic test resulting in faster production of methane during the first steps of the degradation; specifically, the maximum methane production found in the anaerobic test in 19 d was found in the microaerobic test before the day 15.     

Investigation of electrorheological properties of biodegradable modified cellulose/corn oil suspensions

Considerable scientific and industrial interest is currently being focused on a class of materials known as electrorheological (ER) fluids, which display remarkable rheological behaviour, being able to convert rapidly and repeatedly from a liquid to solid when an electric field (E) is applied or removed. In this study, biodegradable cellulose was modified and converted to their carboxyl salts. Modified cellulose is characterised by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, energy dispersive spectroscopy (EDS), thermogravimetric analysis (TGA) and conductivity measurements. Suspensions of cellulose (C) and modified cellulose (MC) were prepared in insulated corn oil (CO). The effects of electric field strength, shear rate, shear stress, temperature, etc. of these suspensions onto ER activity were determined. Rheological measurements were carried out via a rotational rheometer with a high-voltage generator to investigate the effects of electric field strength and particle concentration on ER performance.The results show that the ER properties are enhanced by increasing the particle concentration and electric field strength. Also the cellulose-based ER fluids exhibit viscoelastic behaviour under an applied electric field due to the chain formation induced by electric polarization between particles.     

Effect of solvent exchange on the solid structure and dissolution behavior of cellulose

Effects of solvent exchange and milling on the solid structure of cellulose were investigated, using small- and wide-angle X-ray scattering and solid-state NMR. The solvent exchange facilitated the dissolution of cellulose in LiCl/DMAc with no change of the crystalline structure of cellulose. In contrast, the milling never facilitated the dissolution of cellulose, though the crystalline structure was almost destroyed. These facts show that the crystalline structure of cellulose hardly affects the dissolution in LiCl/DMAc. The fractal dimensions determined by the small-angle X-ray scattering measurements were increased by the solvent exchange, suggesting that the aggregation state of the cellulose microfibril is affected. It was also suggested by the NMR (1)H spin relaxation time measurements that the solvent exchange enhances the molecular mobility of cellulose and shortens the characteristic length along the microfibril, which allows easier access of the solvent molecule to cellulose.     

Effect of selected non-ionic surfactants on the flow behavior of aqueous veegum suspensions

The aim of this work was to investigate the influence of some non-ionic surfactants, Tween 80 and Brij 98, on the viscosity and flow behavior of a commercial montmorillonite clay, Veegum Granules. The effect of different concentrations of the surfactants on the shear stress-shear rate rheograms of hydrated concentrated clay suspensions was determined by shear viscometry. The addition of either surfactant increased the plastic viscosity and the yield stress of the suspensions. Furthermore both surfactants altered the thixotropy of the suspensions to an extent that depended on both the surfactant concentration and the time of equilibration of the surfactant and Veegum. Brij 98 had a greater and more rapid effect. It is proposed that the surfactant polar head-groups anchor at the tetrahedral sheet surface, leaving the alkyl chains extending away from the edges and faces. Consequently, the alkyl chains undergo hydrophobic interactions that facilitate the association between the platelets and increase the physical structure within the suspension. Stereochemical differences between the polar groups may lead to differences in the way the surfactants associate with the tetrahedral sheet and hence their ultimate effect on the rheological behavior. There is a significant interaction between these surfactants and montmorillonite clays, and the rheological changes that occur could have a major impact on any pharmaceutical formulation that uses these ingredients. Published: March 30, 2007     

Influence of cultivation conditions on mechanical and morphological properties of bacterial cellulose tubes

Bacterial cellulose (BC) was deposited in tubular form by fermenting Acetobacter xylinum on top of silicone tubes as an oxygenated support and by blowing different concentrations of oxygen, that is, 21% (air), 35%, 50%, and 100%. Mechanical properties such as burst pressure and tensile properties were evaluated for all tubes. The burst pressure of the tubes increased with an increase in oxygen ratio and reached a top value of 880 mmHg at 100% oxygen. The Young's modulus was approximately 5 MPa for all tubes, irrespective of the oxygen ratio. The elongation to break decreased from 30% to 10-20% when the oxygen ratio was increased. The morphology of the tubes was characterized by Scanning Electron Microscopy (SEM). All tubes had an even inner side and a more porous outer side. The cross section indicated that the tubes are composed of layers and that the amount of layers and the yield of cellulose increased with an increase in oxygen ratio. We propose that an internal vessel wall with high density is required for the tube to sustain a certain pressure. An increase in wall thickness by an increase in oxygen ratio might explain the increasing burst pressure with increasing oxygen ratio. The fermentation method used renders it possible to produce branched tubes, tubes with unlimited length and inner diameters. Endothelial cells (ECs) were grown onto the lumen of the tubes. The cells formed a confluent layer after 7 days. The tubes potential as a vascular graft is currently under investigation in a large animal model at the Centre of Vascular Engineering, Sahlgrenska University     

Effect of steam treatment on the properties of wood cell walls

Steam treatment is a hygrothermal method of potential industrial significance for improving the dimensional stability and durability of wood materials. The steaming results in different chemical and micromechanical changes in the nanostructured biocomposite that comprise a wood cell wall. In this study, spruce wood ( Picea abies Karst.) that had been subjected to high-temperature steaming up to 180 °C was examined, using imaging Fourier Transform Infrared (FT-IR) microscopy and nanoindentation to track changes in the chemical structure and the micromechanical properties of the secondary cell wall. Similar changes in the chemical components, due to the steam treatment, were found in earlywood and latewood. A progressive degradation of the carbonyl groups in the glucuronic acid unit of xylan and a loss of mannose units in the glucomannan backbone, that is, a degradation of glucomannan, together with a loss of the C═O group linked to the aromatic skeleton in lignin, was found. The development of the hygroscopic and micromechanical properties that occurred with an elevation in the steam temperature correlated well with this pattern of degradation in the constituents in the biocomposite matrix in the cell wall (hemicellulose and lignin).     

Studying the effects of reaction conditions on components of dairy manure and cellulose accumulation using dilute acid treatment

The objectives of this study were to statistically study the effects of reaction conditions of temperature, acid concentration, and reaction time on manure components of cellulose, hemicellulose, lignin, and nitrogen during dilute acid treatment of dairy manure; and to further optimize the accumulation of cellulose for later enzymatic conversion to glucose. A 2(3) full factorial design was adopted to investigate the effects of the reaction conditions on each individual component and later followed by a 3-factor central composite design which was used to obtain the optimal conditions for cellulose accumulation. The results indicated that acid was the most important factor for changes of all the components. The results also showed that two other individual factors, reaction time and temperature, as well as the interactions among all three factors had significant influences on the changes. In addition, the optimal conditions for cellulose accumulation were 2.8h reaction time, 140 degrees C reaction temperature, and 1.0% acid concentration. Under these conditions cellulose content reached 31.0% while hemicellulose, lignin and nitrogen content were 3.2%, 20.8% and 2.4%, respectively.     

Physical properties of methylcelluloses in relation with the conditions for cellulose modification

A high molecular weight glycoprotein antigen was isolated by size exclusion chromatography on Sepharose 4B from an extract of the yeast Saccharomyces cerevisiae. The glycoprotein antigen Sc 500 was shown to be identical to the antigen termed gp200 previously isolated (Heelan et al., 1991). The MW of Se 500 was determined to be about 500 kDa by size exclusion chromatography on Superose 6 and 460 kDa ± 20k Da by size-exclusion chromatography/multi-angle laser light scattering (SEC/MALLS). Sc 500 contained 90% mannose and traces of N-acetylglucosamine. The amino acid composition revealed that serine and threonine were the most abundant amino acids of the protein part. By alkaline borohydride treatment some, but not all bonds between protein and carbohydrate were broken. This indicates that the main type of linkage between protein and carbohydrate is O-glycosidic and that a minor type is of N-glycosidic nature. Methylation analysis revealed that the mannose residues were connected by 1 → 2 and 1 → 3 linkages with 1 → 2, 1→ 6 linked branch points.

Purified Sc 500 was subjected to a series of chemical and enzymatic modifications followed by studies of antibody binding activity. Treatments with both periodate and alkaline sodium borohydride reduced the human serum IgA, IgG and monoclonal IgM antibody binding activity of Sc 500 whereas trypsin and pronase did not affect its ability to bind these antibodies. The mannosidase Man1 → 2,3,6Man reduced the IgM binding to Sc 500 while the other enzymes included in this experiment (Man1→2 Man, Manβ1 →4GlcNAc and PNGase F) had no effect on the antibody binding.     

Adsorption of cellulase on cellulose: Effect of physicochemical properties of cellulose on adsorption and rate of hydrolysis

In the cellulase-cellulose reaction system, the adsorption of cellulase on the solid cellulose substrate was found to be one of the important parameters that govern the enzymatic hydrolysis rate of cellulose. The adsorption of cellulase usually parallels the rate of hydrolysis of cellulose. The affinity for cellulase varies depending on the structural properties of cellulose. Adsorption parameters such as the half-saturation constant, the maximum adsorption constant, and the distribution coefficient for both the cellulase and cellulsoe have been experimentally determined for several substrates. These adsorption parameters vary with the source of cellulose and the pretreatment methods and are correlated with the crystallinity and the specific surface area of cellulose substrates. The changing pattern of adsorption profile of cellulase during the hydrolysis reaction has also been elucidated. For practical utilization of cellulosic materials, the cellulose structural properties and their effects on cellulase adsorption, and the rate of hydrolysis must be taken into consideration.     

Effect of acetylation on the material properties of glucuronoxylan from aspen wood

The effect of the degree of acetylation of glucuronoxylan on solubility, water content and thermal properties was investigated. Aspen glucuronoxylan, isolated by alkali extraction from wood chips, was acetylated to various degrees of substitution through reaction with acetic anhydride in formamide and pyridine by varying the reaction time. The degree of acetylation was determined by ¹H NMR spectroscopy. The molecular weight was decreased only to a small extent during the reaction, as seen by size exclusion chromatography. It was found that acetylation strongly affects the solubility properties as well as the equilibrium water content of the glucuronoxylans upon exposure to humidity. Samples with a high degree of acetylation are soluble only in aprotic solvents, whereas non-acetylated glucuronoxylan is partially soluble in hot water. In the same surrounding relative humidity, acetylated samples have lower water content than non-acetylated samples. Acetylation prevents thermal degradation, as shown by thermogravimetric analysis under nitrogen. Acetylation to a degree of substitution of 1.2 also results in a glass transition temperature, which we studied using differential scanning calorimetry, making it possible to thermoprocess acetylated glucuronoxylan.     

Mechanical behavior of cellulose microfibrils in tension wood, in relation with maturation stress generation

A change in cellulose lattice spacing can be detected during the release of wood maturation stress by synchrotron x-ray diffraction experiment. The lattice strain was found to be the same order of magnitude as the macroscopic strain. The fiber repeat distance, 1.033 nm evaluated for tension wood after the release of maturation stress was equal to the conventional wood values, whereas the value before stress release was larger, corresponding to a fiber repeat of 1.035 nm, nearly equal to that of cotton and ramie. Interestingly, the fiber repeat varied from 1.033 nm for wood to 1.040 nm for algal cellulose, with an increasing order of lateral size of cellulose microfibrils so far reported. These lines of experiments demonstrate that, before the stress release, the cellulose was in a state of tension, which is, to our knowledge, the first experimental evidence supporting the assumption that tension is induced in cellulose microfibrils.     

An electrochemical sensor based on cellulose nanocrystal for the enantioselective discrimination of chiral amino acids

A novel electrochemical sensor based on 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanocrystals (TOCNCs) and l-cystines (l-Cys) modified Au electrode (TOCNC/l-Cys/Au) has been fabricated for detection and discrimination of the enantiomers of phenylalanine (Phe), leucine (Leu), and valine (Val). The three amino acids are in connection with metabolism diseases. The TOCNC/l-Cys/Au electrode exhibited obvious peak current difference for the amino acid enantiomers by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The TOCNCs on the electrode surface expressed different interactions with d- and l-amino acids, so the electrochemical recognitions of the three amino acid enantiomers were achieved. TOCNCs were characterized by Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM). The modified electrodes were characterized by SEM and electrochemical techniques. According to DPV, peak currents of the two enantiomers decreased linearly with their concentrations. Furthermore, satisfactory results were obtained when this electrode was applied to measure the d- and l-Phe mixture. The experimental results show that TOCNCs are suitable material for chiral sensor. The contrast of serum sample of healthy people and patients with type 2 diabetes also was proposed, and significant difference was exhibited on the modified electrode. This work is significant for the screening, diagnosis, and treatment of multiple metabolic diseases.     

Representativeness of wood biomechanical properties measured after storage in different conditions

Obtaining representative values of green wood properties is essential for studies investigating the biomechanical aspects of tree development and ecology. Here, we compare the biomechanical properties of wood stored in various conditions between their collection in the field and their measurement. The study was performed on a large sample of wood specimens from different tropical species and different location in the trees, representing a wide diversity in wood structures. Elastic and viscoelastic properties are measured on green wood, and measured again after storage in different conditions: immersion in cold water during various durations, storage in an ethanol solution with or without washing in water, and air drying with or without rehydration. The systematic and random errors induced by these storage methods are quantified. Storage in cold water is the best way to preserve wood native properties. Soaking in ethanol is a fair alternative regarding elastic properties, but induces a significant change in viscoelastic properties. Air drying causes important, and partly irreversible, changes in mechanical properties. However, regarding elastic properties, this change is a systematic bias so that the air-dried elastic modulus provides a good basis for comparative studies of green wood stiffness.     

Effect of microwave irradiation on the physical properties and morphological structures of cotton cellulose

Microwave heating has been proved to be more rapid, uniform and efficient, and easily penetrate to particle inside. To investigate the effect of microwave irradiation on the physical property and morphological structure of cotton cellulose, cellulose fabric was treated with microwave irradiation at different conditions. The physical properties of the treated cellulose fabric were investigated. The morphological structures and thermal stabilities of the untreated and treated cellulose were investigated with differential scanning calorimetry (DSC) and X-ray diffraction. The results show that the physical properties of the treated cellulose fabrics were improved and the recoverability had not significant change. The thermal stability of the treated cellulose was changed. The crystallinity and preferred orientation of the treated cotton cellulose increased.