Volume 72, Issue 11

Adsorption of xylan on pulp is a potential method to improve its properties, especially refinability for high quality printing and writing (P&W) paper grades. In this study, elephant grass [ Pennisetum purpureum (Schumach.)] xylan was used for this purpose. The xylan was extracted using cold caustic extraction (CCE) from P. purpureum brown pulp, produced by the Soda-AQ process (kappa 20). Xylan resorption was accomplished during the oxygen delignification phase of eucalypt [ Eucalyptus globulus (Labill.)] pulp to avoid problems induced by the colour of the lignin-contaminated deposited xylan. Immunolabelling and enzymatic peeling methodologies were compared for the analysis of the spatial distribution of xylan in the fibre wall. The labelling appeared unevenly as faint and brighter patches on fibre surfaces. Increased labelling of xylan was detected on the samples with precipitated P. purpureum xylan. The enzymatic peeling method using a total hydrolysis enzyme mixture yielded a composition gradient as a function of time, showing clear xylose (Xyl) enrichment in the very beginning of the reaction, reflecting hydrolysis of fibre surfaces. Pure xylanase and endoglucanase hydrolyses yielded different product patterns and kinetics compared to total hydrolysis, but interpretation of those results in terms of xylan localisation was not straightforward.

The efficiency of the growth and properties of zinc oxide (ZnO) nanoparticles (ZnO-NPs) on pulp fibers was investigated. ZnO-NPs were grown on pulp fiber surface via an in situ chemosynthesis method at different concentrations. The modified pulp fibers were characterized by different analytical tools including field-emission scanning electron microscopy (FE-SEM), Fourier-transform infrared (FTIR) spectroscopy, X-ray power diffraction (XRD) and thermogravimetric (TG) analysis. Ultraviolet (UV) absorption and antibacterial properties of the paper made from treated and untreated pulp fibers were analyzed. The results revealed that the rod-like ZnO-NPs were successfully grown onto the fiber surfaces without aggregation. As the precursor concentration increased from 0.01 to 0.07 mol l −1 , the ZnO loading on the fibers increased from 4.2 to 23.4%, respectively. Compared to the untreated fibers, paper made from ZnO-treated fibers had a better UV absorption ability and antimicrobial effect against Escherichia coli and Staphylococcus aureus . However, the ZnO-treated pulp fiber reduced the zero span tensile index of the paper.

Lignin nanoparticles (LNPs) from renewable lignocelluloses can be a valuable building block for a variety of applications and could contribute to the economic development in rural agricultural communities. Current technologies for producing LNPs are not cost effective and use toxic solvents. In this study, LNPs were produced by fractionating poplar wood at ≤80°C with a recyclable hydrotrope p -toluenesulfonic acid ( p -TsOH) in an aqueous system. The dissolved lignin was separated as LNPs simply by diluting the spent liquor (SL) to the minimal hydrotrope concentration (HC min ) of 11.5%. The p -TsOH, a solid acid, can be easily recycled by re-concentrating the diluted SL after lignin separation. The LNP size, morphology, and surface charge were controlled by the dilution ratio, speed, pH, and ionic strength of the LNP sol. The LNPs were analyzed by dynamic light scattering (DLS) and found to be fairly stable in terms of mean particle size and surface charge over a period of 2 weeks. Fractionation conditions also affected LNP properties.

Effects of lignin on dynamic sorption and hygroexpansion were investigated. Poplar wood ( Populus cathay ) [20×20×4 mm 3 (radial×tangential×longitudinal)] was delignified at three levels and subjected to dynamic humidity changes, where the relative humidity (RH) changed sinusoidally between 45% and 75% at 25°C during 1, 6 and 24 h. Moisture contents (MC) and dimensional responses were recorded automatically. Scanning electron microscopy (SEM) results show that lignin was partly removed. MC and dimensions also varied sinusoidally with RH. At higher delignification levels, amplitudes, moisture sorption coefficients and humidity expansion coefficients became higher, but the phase lag displayed an opposite trend. The effects were due to the removal of the relatively hydrophobic lignin layers, in the course of which more hydroxyl groups of cellulose and hemicelluloses were accessible to humidity. A linear positive relation was found between the delignification rate and MC, and dimensional changes in the tangential direction. Lignin had a significant effect on sorption and hygroexpansion and this effect was greater for static sorption. Delignification reduced the hysteresis due to matrix stiffness decrement of wood, especially in the RH range of 55–65%.

Lignin has been submitted to electrochemical oxidation in the presence of nickel (Ni), cobalt (Co) and Ni-Co bimetallic electrocatalysts, which were prepared by a simple electrochemical deposition process. The composition and morphology of the catalyst were studied by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA). The effects of the three electrocatalysts on the electrochemical oxidation of lignin were observed by cyclic voltammetry and chronoamperometry. The degradation products were quantitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The rate of electrochemical oxidation of lignin is higher with Ni-Co bimetallic electrocatalyst with higher Co contents and the main products obtained were vanillin, apocynin and 3-methylbenzaldehyde.

Lignin was isolated through mild acidolysis from local wood sources such as beech wood and chestnut wood sawdust, a high-volume side product of wood industries. The lignin fractions were characterized by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), Fourier-transform infrared (FTIR), ultraviolet-visible (UV-Vis) and two-dimensional heteronuclear single-quantum correlation nuclear magnetic resonance (2D HSQC NMR) spectroscopies and size exclusion chromatography (SEC). The Klason lignin (KL) content and polysaccharide composition were determined using traditional methods. Lignin nanoparticles (LNPs) were prepared via a non-solvent method involving dialysis and characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and FTIR and UV-VIS spectroscopies. Semi-porous as well as hollow nanoparticles endowed with a spherical shape were observed. The large majority of the LNPs exhibited an average particle diameter of 90–120 nm. Dynamic light scattering (DLS) analysis showed that both distribution and frequency of dimensional classes of LNPs are clearly affected by the lignin solvent system, i.e. solvent selection governs the size distribution of LNPs.

A solvent-assisted and pyrogallol (PG)-protected headspace gas chromatography (HS-GC) method was developed to determine the pinene (α- and β-pinene) content in the kraft pulping black liquor (BL). Ethanol (EtOH) addition eliminated pinene’s micelles in BL by complete dissolution in the EtOH/BL medium. PG was applied to protect pinene from oxidation during the sample storage and measurement. The results showed that, with a 25% (v/v) of EtOH content and a 0.1 g of PG in 5-ml of sample solution, a rapid and stable pinene HS extraction can be obtained in 20 min at 80°C. The method has high precision with relative standard deviations within 4.2%. The sensitivity [limits of quantification (LOQ) are ~140 μg l −1 ] was high, and a good accuracy (recovery=96.0–104%) was typical for the pinene detection. The presented method is simple, rapid, accurate and is suitable for pinene quantification in biorefinery related processes and it leads to the preparation of high-value chemicals.

The treatment of wood surfaces with gas discharges is one of the methods to achieve better surface adhesion properties. Good penetration, spreading and wettability of the applied liquid adhesives and coatings is a crucial factor for their adequate mechanical properties. Plasmas are the result of electrical discharge and can be created in different ways. The plasma treatment (PT) is frequently executed prior to material bonding or coating via the so-called dielectric barrier discharges (DBD) at atmospheric pressure. This literature review summarizes the essential aspects of DBD PTs aiming at a better wettability and surface adhesion. After introduction of the principle of DBD, the individual effects of internal and external parameters of the process will be discussed, which influence the final properties of treated materials.

European oak wood (W) was thermo-mechanically modified (TM) via densifying at 100 and 150°C and the surface properties of the TMW were investigated. The contact angle (CA) of the wood with the reference liquids water and diiodomethane was determined using the sessile drop method. The surface free energy of the TMW on tangential sections within the first 60 s after applying a drop was analyzed. The roughness parameters Ra and Rz parallel (‖) and perpendicular (⊥) to the grain were investigated. The wettability analysis showed that densified wood had a higher CA and lower work of adhesion and surface free energy than non-densified wood. An X-ray photoelectron spectroscopy [XPS or electron spectroscopy for chemical analysis (ESCA)] analysis showed that the oxygen to carbon atoms ratio (O/C ratio) of densified wood surface was lower than that of non-densified wood. The carbon C1-C2 atoms ratio (C1/C2 ratio) increased with increasing TM temperature. The results were interpreted as being that extractives migrate to the surface and amorphous and glassy polymers, i.e. lignin and hemicelluloses, in wood are rearranged. Increasing densification temperature makes TMW surfaces more hydrophobic.

In Siberian larch, shear strength (SS) is lower in sapwood (sW) than in mature heartwood (hW) despite the similarity of their cell structures. In sW, SS was not correlated with other properties, not even with density. The aim of the present study was to find the parameters affecting the SS in sW. The diameters of earlywood (EW) and latewood (LW) tracheid lumens [radial diameter (RD)], as well as their double wall thicknesses (2CWTs), were measured from different wood types. The 2CWT beside the resin canals was measured and rays were counted. The wall:lumen ratio of tracheids was calculated. None of the measured and calculated characteristics significantly correlated with SS in hW, while a high 2CWT and wall:lumen ratio of EW increased the SS and a large RD decreased the SS in sW. Tracheids of sW were larger and their walls were thicker than those of mature hW. The EW of sW sheared through tracheids, but practically never through rays, while in the EW of mature hW, both rays and tracheids could be sheared. It is suggested that change in viscoelastic properties, occurring in cell walls during the transformation from sW to hW, improves wood shear properties.