Research Articles

Structural elements of the arylglycerol b-syringyl ether type are very frequent in hardwood lignins. A variety of crystalline dimeric lignin models representing different diastereomeric forms of structural elements in lignin of this type have been studied using X-ray crystallography. Bond distances and bond angles in the model compounds are in all probability nearly identical with those of the corresponding structural elements in lignins. Special attention was paid to the geometry of the b-O-syringyl linkage, since the reactivity of this linkage is of particular interest in connection with pulping reactions. The crystal structures of the model compounds suggest that two types of conformations are predominating; in both of them the aromatic rings are separated by ca. 4.5 Å (maximal distance 4.9-5 Å). Based on X-ray crystallographic data from four compounds a sequence of units (5 aromatic rings, 8 chiral C-atoms) attached to each other by b-syringyl ether linkages was constructed. The appearance of the resulting oligomer illustrates that stereoisomerism can be expected to influence the shape of the lignin molecules to a great extent.

Alkaline pre-extraction and hydrothermal hydrolysis were carried out with eucalyptus chips. Two methods were used to determine and calculate the extraction yield of five-carbon sugars. One is an indirect method, based on the difference of pentosan content between the chips before and after pre-extraction. The other method is to directly measure the content of five-carbon sugars in the extracting solution. The results indicated that there was a defined relationship between the two methods. For alkaline pre-extraction, a good logarithmic relationship was shown. There was a good linear relationship for hot water prehydrolysis. So the pentosan content of the extracted chips could be predicted from the results of the latter method, referring to the two relational expressions. In this study, a simple and rapid method of spectrophotometry was introduced, which will help in the evaluation of extraction yield of five-carbon sugars during biomass processing.

Gamma-proteobacterium JB, an alkali-tolerant soil isolate, produced laccase (8X103 nkat/L) in M162 medium. The optimization of process conditions (pH, incubation time, agitation, and CuSO4 concentration) for laccase production during submerged fermentation was carried out using response surface methodology (RSM) based on a central composite design (CCD). Maximum laccase production achieved was 7.4 X 104 nkat/L at pH 8.0, 210 rpm, 100 µM of CuSO4 after 60 h of incubation. This design of experiment methodology increased laccase production by 9.3 fold over the control. Experimental findings were in close agreement with the model predictions.

The residues of the wood cell wall compound middle lamella affect the composition of the relevant pulp fiber surface layers and influence the fibers’ bleachability. The objective of the present work was to separate the eucalyptus kraft and birch organosolv pulp fiber wall surface layers by hydromechanical peeling and to proceed with enzyme boosted bleaching of the separated fiber wall layers. The initial content of lignin and heteroaromatic compounds (“false” lignin) was determined by chemical methods and UV-spectra. The separated fiber wall surface layers representing the residues of the primary wall P and outer layer S1 of the secondary wall, as well as the main part of the secondary wall were exposed to the bleaching sequence peroxide-xylanase treatment-alkaline extraction-peroxide (P1-X-E-P2). brightness measurements revealed significant distinctions between the preparations. The final brightness of the main part of eucalyptus kraft pulp fibers reached 67%, while the brightness of the surface layers attained only 50% ISO. Similar results were obtained for birch organosolv pulp. It was concluded that the main reason for the described phenomena is the discordant chemical composition of the different fiber wall layers.

The structure of jute fibre has been modified using caustic soda up to a limit in order to improve its performance. The SEM micrographs of untreated jute fibres show a smooth surface, while alkalised jute fibres show rough and void regions between individual fibre cells. The study showed that the tensile strength and Young’s modulus of jute fibre bundles depends on the physical characteristics of its internal structure such as the cellulose content, changes in the crystalline region content expressed in terms of crystallinity index, and micro-fibril angle. Results also showed tensile properties optimised at 0.24% NaOH (w/w). Overall, alkalised fibres exhibit brittle fracture. The study demonstrated the dependence of tensile properties on the changes in fibre structure following alkalisation.

Different molecular weight fractions of lignosulfonates (LS), LS having different cations, and modified LS with different degree of sulfonation and intrinsic viscosity were prepared and used as dispersants for Dimethomorph water-dispersible granules (DWG). The suspending ratio of DWG was tested to evaluate the effectiveness of LS as a dispersant. Moreover, the stability of DWG suspensions was measured by a new instrument (Turbiscan LabExpert). The suspending ratios of DWG having different molecular weight fraction of LS increased with increasing molecular weight in a suitable range. The kind of cation associated with the LS didn’t have an obvious influence the effectiveness of LS as a dispersant. Furthermore, the higher degree of sulfonation of LS, of which the intrinsic viscosity was similar, the better was its effectiveness as a dispersant. When the intrinsic viscosity increased within a suitable range, the effectiveness of LS as a dispersant increased. Similar findings were achieved by evaluating the stability of DWG suspensions with all the LS as dispersants, and larger molecular weight could decrease the growth of particle size.

A quartz crystal microbalance with dissipation monitoring (QCM-D) was used to study the adsorption of the layer formed by silica nanoparticles (SNP) and cellulose nanofibrils (NFC) together with cationic polyacrylamide (C-PAM) on cellulose surface, accompanied by use of atomic force microscope (AFM) to study the interactions between cellulose surfaces. The purpose was to understand the multilayer build-up compared to complex structure adsorption. The layer thickness and consequently also the repulsion between surfaces increased with each addition step during layer formation in the SNP-C-PAM systems, whereas the second addition of C-PAM decreased the repulsion in the case of NFC-C-PAM multilayer formation. An exceptionally high repulsion between surfaces was observed when nanofibrillar cellulose was added. This together with the extremely high dissipation values recorded with QCM-D indicated that nanofibrillar cellulose formed a loose and thick layer containing a lot of water. The multilayer systems formed fully and uniformly covered the surfaces. Silica nanoparticles were able to penetrate inside the loose C-PAM structure due to their small size. In contrast, NFC formed individual layers between C-PAM layers. The complex of C-PAM and SNP formed only a partly covered surface, leading to long-ranged pull-off force. This might explain the good flocculation properties reported for polyelectrolyte-nanoparticle systems.

Kenaf (Hibiscus cannabinus) nanofibers were isolated from unbleached and bleached pulp by a combination of chemical and mechanical treatments. The chemical methods were based on NaOH-AQ (anthraquinone) and three-stage bleaching (DEpD) processes, whereas the mechanical techniques involved refining, cryo-crushing, and high-pressure homogenization. The size and morphology of the obtained fibers were characterized by environmental scanning electron microscopy (ESEM) and transmission electron microscopy (TEM), and the studies showed that the isolated nanofibers from unbleached and bleached pulp had diameters between 10-90 nm, while their length was in the micrometer range. Fourier transform infrared (FTIR) spectroscopy demonstrated that the content of lignin and hemicellulose decreased in the pulping process and that lignin was almost completely removed during bleaching. Moreover, thermogravimetric analysis (TGA) indicated that both pulp types as well as the nanofibers displayed a superior thermal stability as compared to the raw kenaf. Finally, X-ray analyses showed that the chemo-mechanical treatments altered the crystallinity of the pulp and the nanofibers: the bleached pulp had a higher crystallinity than its unbleached counterpart, and the bleached nanofibers presented the highest crystallinity of all the investigated materials.

The aim of this investigation was to find out how properties of a flocculation agent and flocculation kinetics affect the morphology of fibre flocs and how dewatering of a fibre suspension may be attributed to floc morphology. Fibre flocculation, analysed in terms of floc size, mass fractal dimension, floc strength, and the kinetic constant of flocculation, was measured with a digital image analysis system using cationic polyacrylamides as flocculants and NaCl as a coagulant. The results suggest that the kinetics of fibre flocculation is not a key factor determining floc properties but follows from the high bonding ability of the flocculation agent, which also lies behind the high floc density and size, i.e., the factors that lead to fast flocculation and improved floc properties are partly the same. In addition to interfibre bonding strength, the structure of the bonding layer of polymeric flocculants was found to be a significant factor describing floc morphology. Dewaterability of the fibre suspension was improved by increased floc density, which promotes fast water flow through the large voids around the dense flocs, while large, irregular flocs induced loose floc packing, which further improved dewatering by creating larger voids. Increased floc strength seemed to reduce the sealing of fluid passageways, particularly on the surface of the wire, where fibre squeezing could blind the filter fabric.

A quat-silicone micro-emulsion (particle size <40 nm), an amino-silicone macro-emulsion (110 nm), and an alkyl modified silicone macro-emulsion (740 nm) were used to modify Scots pine (Pinus sylvestris L.) sapwood. Treated and uncoated boards were exposed to natural weathering for one year along with water treated controls according to EN 927-3. The treatment with silicone emulsions did not enhance the color stability, which was assessed at three months intervals using a spectrophotometer and classified according to the CIE-Lab system. Treatment with amino-silicone emulsions gave a more yellowish appearance of the wood surface before weathering than the other silicones and the control. Boards treated with quat- and amino-silicone were less overgrown by staining fungi and displayed reduced surface roughness than those treated with alkyl-modified silicone and the control samples.