Volume 69, Issue 8

The wood samples of Populus euphratica Oliv. (Salicaceae) are common archaeological plant remains in the hot and arid regions of western China. However, it is difficult to identify P. euphratica wood based on traditional wood anatomical methods alone. DNA barcoding might provide a higher security for species identification. In this study, aged wood specimens stored for approximately 30, 60, and 80 years and archaeological wood up to 3600 years old were in focus to explore the potential of DNA extraction and PCR amplification for different-sized fragments, ranging between 100 and 800 bp, taken from wood stored for different periods. The results indicated that DNA fragments of more than 100 bp could be successfully retrieved from a wood specimen stored for about 80 years based on a modified Qiagen kit protocol. However, it was impossible to obtain DNA segments from the 3600-year-old wood according to the current extraction protocol. Moreover, it was deduced that two-stage PCR amplification could play a significant role in the analysis of DNA retrieved from aged wood materials. With the aid of phylogenetic analysis, based on the short DNA barcode rbcL -2 of 202 bp in length, it was possible to differentiate P. euphratica from the other species of the Populus genus.

This paper reports on the formation of methanol (MeOH) during conventional oxygen delignification (OD) of four typical alkaline pulps, namely, southern pine kraft pulp (SP-KP), wheat straw soda pulp (WS-SP), and eucalyptus kraft pulp (E-KP) with κ numbers (KN) of 32.8 and 16.9 (E-KP 32.8 and E-KP 16.9 ). Based on the mass transfer effect of MeOH and a proposed demethoxylation reaction pathway of lignin, two kinds of kinetic models were proposed to predict MeOH formation. The results show that the two-stage pseudo kinetic model with a first-order rate equation is adequate, which was further modified to a first-order kinetic model by means of which MeOH formation during OD of the pulps can be effectively predicted. Finally, the single set of kinetic parameters for the WS-SP, E-KP 32.8 , and E-KP 16.9 pulps was calculated. The proposed kinetic model is considered as a valuable tool for the prediction and control of MeOH formation during OD of various alkaline pulps.

To upgrade the utilization of kraft lignin (KL) for high-performance lignin-based materials (e.g., carbon fiber), the purity, molecular mass distribution (MMD), and thermal properties need to be improved and adjusted to target values. Therefore, different methods, such as ultrasonic extraction (UE), solvent extraction, dialysis, and hot water treatment (HWT), were applied for the purification of KL. The chemical and thermal properties of purified lignin have been characterized by nuclear magnetic resonance, Fourier transform infrared, gel permeation chromatography, elemental analysis, differential scanning calorimetry, and thermogravimetric analysis. The lignin fractions obtained by UE with ethanol/acetone (E/A) mixture (9:1) revealed a very narrow MMD and were nearly free of inorganic compounds and carbohydrates. Further, the E/A-extracted lignin showed a lower glass transition temperature ( T g ) and a clearly detectable melting temperature ( T m ). Dialysis followed by HWT at 220°C is an efficient method for the removal of inorganics and carbohydrates; however, lignin was partly forming condensed structures during the treatment.

A modified alkaline nitrobenzene oxidation (NBO) method was developed to enable the analysis of the biphenyl structures of cedar wood lignin. The most essential point of the process is a modified work-up process in pyridine and a prolonged gas chromatography analysis of the silylated products. By applying this mean to cedar wood meal, a novel biphenyl product, dehydrovanillin-vanillic acid (1-carboxy-1′-formyl-4,4′-dihydroxy-3,3′-dimethoxy-5,5′-biphenyl), was detected together with known products, dehydrodivanillin and dehydrodivanillic acid. The highest total yield of biphenyl products was detected when NBO was carried out for 2–4 h at 170°C. The work-up procedure was slightly modified so that the biphenyl products can be quantified. The NBO conversion rates of biphenyl linkages of lignin were also examined with a biphenyl-type lignin model compound, and this gave rise to 75% biphenyl-type NBO degradation products. Under the same condition, the total yield of vanillin and vanillic acid (VA) from a non-condensed-type β-O-4 model compound was 89%. Because the latter did not exhibit any peak of the biphenyl products, it can be concluded that all the biphenyl products obtained by NBO (0.17 mmol g -1 ) were from the lignin of the native wood. It was calculated that at least 6.7 of 100 phenylpropanoid units of cedar lignin were involved in biphenyl structures even if the NBO conversion rate was not taken into consideration. The synthesis and analytical data of 11 lignin model compounds is described.

This study was conducted to explain the tensile strength loss of wood due to the modification with 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) and glutaraldehyde (GA). Modified and control wood blocks were macerated to deliberate fibres, and handsheets were produced thereof. The nitrogen content of the fibres indicated that maceration removed the major proportions of DMDHEU. The stability of GA in wood during maceration was not assessed. Tensile strength determined at zero span (z-strength) and finite span (f-strength) was equal for the handsheets from DMDHEU-modified fibres and the control handsheets. The microscopic appearance of the tested finite-span paper strips from DMDHEU-modified fibres mainly indicated interfibre failure and did not differ from the fibre fracture mode of the control handsheets. In contrast, the z-strength of the handsheets from GA-modified fibres was lower than that of controls and decreased with increasing content of GA in the initial modified wood. The f-strength behaviour of the handsheets from GA-modified fibres was the opposite: it was higher than that of controls and increased with increasing GA content. The microscopic appearance of the rapture zones of the finite-span testing mainly indicated intrafibre failure for the GA-modified fibres. It was concluded that cross-linking is likely to be the major reason for tensile strength loss of GA- and DMDHEU-modified wood. In terms of DMDHEU-modified wood, the incrustation of the cell wall by the resin and the reduction in pliability could play an additional role.

Mechanical pulp fibers (MPFs) and chemical pulp fibers (CPFs) from moso bamboo have been characterized in terms of their length and width distributions, and their reinforcing effects in unsaturated polyester (UPE) composites have also been investigated. CPF-UPE composites had much higher tensile strength, flexural strength, and flexural modulus than MPF-UPE composites. CPF-UPE composites also absorbed less water than MPF-UPE composites. Treatments of the fibers with a combination of 1,6-diisocyanatohexane (DIH) and 2-hydroxyethyl acrylate (HEA) significantly increased the tensile strength, flexural strength, flexural modulus, and water resistance of the resulting composites. Fourier transform infrared and X-ray photoelectron spectroscopy analyses indicated that DIH-HEA was bound onto bamboo fibers (BFs) via carbamate linkages. The scanning electron microscopy images of the tensile-fractured surfaces of the composites revealed that the DIH-HEA treatments for BFs greatly improved the interfacial adhesion between the fibers and UPE resins.

The mechanical properties of cell wall layers of bamboo fibers (BFs) and the interphase between BFs and maleated polypropylene polymer (MAPP) were investigated by means of peakforce quantitative nanomechanics based on atomic force microscopy. This technique is well suited for simultaneous imaging of several important material indicators, such as elastic modulus, deformation at peak force, and adhesion force between probe tip and sample. Furthermore, quantitative local mechanical information could be extracted from the obtained images by means of profile analysis. In case of BFs, the elastic modulus of the secondary cell wall and the compound middle lamella was found to be 21.3±2.9 GPa and 14.4±3.6 GPa, respectively, which agrees well with data measured by the nanoindentation technique. Additionally, this technique was also applied for bamboo plastic composites, and data from the transitional zone (interphase) between BFs and the MAPP matrix, with a thickness of 102±18 nm, could be obtained.

The applicability of amino acid tricine has been investigated for the modification of solid wood. Oak, walnut, cherry, and birch wood lamella were impregnated with a tricine solution and subjected to a drying process. The interaction between tricine and wood components was analyzed by attenuated total reflectance-Fourier transform infrared and nuclear magnetic resonance spectroscopy, and the reactions only with hemicelluloses were detected. Xylosylamine structures were found among the reaction products of xylose and tricine, and solid oak wood also showed this type of reaction. The equilibrium moisture content of the modified wood decreased, and this finding was interpreted as an indication of a modification of the polysaccharides. The hardness and tensile strength of the tricine-modified lamellae increased significantly. The change of the physical properties is probably due to the low moisture content with increased hydrogen bonding between wood cell wall components. A crystalline layer of tricine on the cell walls was observed by means of electron microscopy.

The fibrillation of a bleached kraft eucalyptus pulp was investigated by means of a laboratory-scale disk grinder for the production of cellulose nanofibrils (CNF), while the parameters disk rotating speed, solid loading, and fibrillation duration were varied. The cumulative energy consumption was monitored during fibrillation. The degree of polymerization (DP) and water retention value (WRV) of the resultant cellulose fibrils were determined as measures of the degree of fibrillation, which was also visualized by scanning electron microscopy, field emission-scanning electron microscopy, and transmission electron microscopy imaging. A higher rotating speed than 1500 rpm did not improve the fibrillation judged by DP and WRV measurements. Solid loading has an insignificant effect on fibrillation in a wide range. The energy consumption ( E ) was determined as a function of the DP and WRV. The optimal grinding conditions were between 1200 and 1500 rpm at 2.0%–2.2% solid loading.

Fibers of aspen chemi-thermomechanical pulp (CTMP), spruce CTMP, bleached kraft pulp (BKP), and kraft pulp were treated by low-temperature plasma (air) aiming at the detection of the relationship between chemical components on the surface and the properties of sheets. The effects of plasma treatment were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy. The results show that the strength properties of sheets, especially the wet-tensile strength, were significantly improved, while optical properties were scarcely affected. Aspen and spruce CTMPs with abundant lignin and extractives were sensitive to plasma treatment in that the O/C ratio increased and lignin or extractive contents decreased. However, the crystallinity of BKP evidently decreased after plasma treatment owing to carbohydrate enrichment on the surface. Compared to the partial removal of noncarbohydrates through a laccase/mediator system, plasma treatment did not remove them in large amounts but created more carboxyl and hydroxyl groups, which improved the strength properties of paper sheets.

ZnO nanorod array coatings were successfully synthesized on wood surfaces using a conventional hydrothermal (CHT) and a microwave-assisted hydrothermal (MWHT) method. The reaction time of the MWHT method at high temperature was only 1/12th that of the CHT method. The MWHT-ZnO nanorods exhibited better crystallinity than those produced by the CHT method. The ZnO nanorod had a wurtzite crystal structure oriented along the c -axis. The MWHT nanorods with their higher (002)/(101) ratio were more conducive and improved the orientation degree of the ZnO nanorods. Field emission scanning electron microscopy (FE-SEM) images showed that the MWHT-ZnO nanorods had smaller diameters and narrower size distributions than those produced by the CHT method. However, both methods formed well-aligned array coatings that covered the wood surfaces, and the two coatings had similar UV protecting effects and inhibited discoloration.

Tensile tests of miniature spruce wood specimens have been performed to investigate the damage evolution in wood at the microscopic scale. For this purpose, the samples were stepwise tensile loaded in the longitudinal (L) and radial (R) directions and the damage evolution was monitored in real-time by acoustic emission (AE) and synchrotron radiation micro-computed tomography (SRμCT). This combination is of outstanding benefit as SRμCT monitoring provides an insight on the crack evolution and the final fracture at microscopic scale, whereas AE permits the detection of the associated accumulation and interaction of single damage events on all length scales with high time resolution. A significant drawback of the AE testing of wood has been overcome by means of calibrating the AE amplitudes with the underlying crack length development. Thus, a setup-dependent and wood species-dependent calibration value was estimated, which associates 1 μm 2 crack area generating of 0.0038 mV in the detected AE amplitude. Furthermore, for both L and R specimens, AE signals were classified into two clusters by using a frequency-based approach of unsupervised pattern recognition. The shares of AE signals of both clusters correlate with the ratio of the relative crack area of the interwall and transwall cracks gained from the fractographic analysis of SRμCT scans.

The fire performance of several types of wood-aluminum composites (WAC) was analyzed by the small vertical furnace test. The time needed to reach the temperature of 139°C/181°C ( T 139°C/181°C ) and the linear char rate of 300°C ( L 300°C ) were obtained by evaluating the fire performance of WAC. The T 139°C/181°C values ranged from 23.6 to 44.8 min. The presence and position of the aluminum alloy sheet remarkably affected the fire performance of WAC. In addition to an initial delay of 19 min, the L 300°C also increased when the aluminum alloy sheet was located on the surface. However, the times for 300°C only increased slightly when the aluminum alloy sheet was in the middle. The initial delay observed for the aluminum alloy sheet on the surface was reduced by more than 50% when the wood veneer was located on the surface of the aluminum alloy sheet. The mechanical properties of WAC were also investigated. It was concluded that the uniformity and strength of different composites was improved after the lamination of the aluminum alloy sheet. In addition, the modulus of elasticity of WAC quadrupled, and the bonding strength between the aluminum alloy sheet and the oriented strand board (OSB) was greater than that of the OSB.