Volume 69, Issue 1

The aim of the study was to investigate the possibility to use spruce xylan more efficiently by possible relocation of dissolved xylan with certain characteristics from the first part of the kraft cooking to the later part, when precipitation occur. The characteristics of re-located xylan was controlled by replacing half the black liquor (BL) at a late stage of a kraft cook, with the same amount of black liquor containing spruce xylan with known molecular weight and content of uronic acid (UA). Pulp with addition of xylan with high amount of UA groups responded strongly on beating, resulting in improved tensile strength. It is proposed that the best effect of xylan on tensile strength occurs when the xylan penetrates some distance into the subsurface of the fiber wall. Both low molecular weight (M w )and a high degree of substitution decreases the tendency of xylan to aggregate, which enables the dissolved xylan to penetrate some distance into the exposed fiber surface. Upon beating, this xylan will be exposed thus facilitating improved fiber-fiber joint formation, which leads to increased tensile strength.

There is still a challenging question about how lignosulfonates (LS), such as non-sulfonated lignins, aggregate and disaggregate in solution. In the literature, the reported critical aggregation concentration (CAC) of LS varies by orders of magnitude. In the present work, the aggregation of a purified sodium LS (NaLS) from a softwood has been studied by size exclusion chromatography and capillary viscometry. It was found that intermolecular aggregates form at relatively high concentrations. Disaggregation is an extremely slow process for spray dried samples and proceeds for several weeks. The process can be speeded up by increasing the pH and/or temperature. The very slow disaggregation may explain the strongly varying (and sometimes very low) CAC values reported in the literature. An interaction energy of about 8 kJ mol -1 monomer was calculated.

Sodium lignosulfonate (NaLS) was dissolved in saline solutions, and the dissolving process was examined by a combination of static and dynamic light scattering. When NaLS was dissolved in 1.2 mol l -1 NaCl solution for 24 h and filtered through a 0.45 μm syringe filter, only a fast relaxation mode was observed, which was attributed to the co-diffusion of NaLS molecular ions and counterions. When the concentration of NaCl was below 1.2 mol l -1 or the dissolving time was <24 h, an additional slow relaxation mode (SRM) appeared due to hindered motions of electrostatically interacting chains. Without filtering or filtering followed by rising temperature to 38°C, SRM appeared due to aggregation, which occurred at a position similar to that caused by electrostatic interaction. For poly(sodium styrenesulfonate) (NaPSS) and modified bamboo lignin derivate with open polyelectrolyte structures, 0.1 mol l -1 NaCl was enough to inhibit the electrostatic interaction. For NaLS with a closed polyelectrolyte structure, the SRM could not be removed until the concentration of NaCl reached 1.2 mol l -1 . Above observations give insights for the first time into the relationship between the SRM caused by electrostatically interacting chains and the diffusion mode due to NaLS aggregation, and the influence of the closed polyelectrolyte structure on the SRM.

Carboxymethylated lignin (CML) is well suited as a dispersant or natural adsorbent applied in ceramics, gypsum paste, graphite suspension, and water treatment. In this paper, the effects of COOH content in CML on its behavior in water and the dispersion stability of aqueous graphite suspension has been investigated by means of viscosimetry, surface tension measurement, fluorescence spectrometry, dynamic light scattering (DLS), Turbiscan Lab Expert (TLE) stability analysis, and ζ potential measurement. Viscosimetry clearly revealed the polyelectrolyte effect in diluted aqueous solution of CML. With a higher COOH content of CML, the surface tension of water is reduced. Moreover, the aggregation behavior of CML was strengthened with increasing COOH content, leading to a more compact molecular structure of the aggregates. Based on the results, an aggregation model was proposed to illustrate the variations in the solution behavior of CML with different COOH contents at various concentrations. The dispersion stability of aqueous graphite suspension was improved by adding CML with high COOH content.

Pinus radiata D. Don wood chips were submitted to a hydrothermal (HT) process, which is a pretreatment with pressurized water at P-factors of 20 (E1) and 1200 (E2), leading to 27% and 56% of hemicellulose removal, respectively. The residual wood chips were pulped by the chemithermomechanical (CTMP) and kraft processes. The pulp yield in the HT/CTMP process was in the range of 56–75%. The cellulose yields were not affected by the HT pretreatment, whereas the solubilization of hemicelluloses and lignin was intensified. The HT process provided energy savings in the refining of CTMP pulps, and the E1/CTMP pulp had a similar tensile and increased tear strength as the control wood. For kraft pulping, the HT wood chips demanded more active alkali (AA) to achieve a κ number (KN) of 30, and consequently, a decrease in pulp yield was observed (47.2% yield in the control and 44.4% and 37.8% in the E1 and E2 pulps, respectively). The fiber length decreased in the E1 and E2 kraft pulps compared with their control samples. In the E1 pulps, the tensile, tear, and burst indexes decreased by 10%, 25%, and 30%, respectively. Considering the low hemicellulose content and pulp viscosity in the range of 800–900 ml g -1 , the mild HT process of P. radiata would be better suited for preparing cellulose-rich materials instead of paper-grade pulps under the biorefinery concept.

The in-plane shear strengths (IPSS) of copy paper, filter paper, and sack paper were obtained from an asymmetric four-point bending (AFPB) test. Rectangular tabs of medium-density fibreboard (MDF) were bonded to the paper specimen. The length of the clearance between the tabs was varied, and the influence of the clearance on the IPSS value was investigated. The IPSS obtained from the AFPB test was compared with that obtained from a 35° off-axis tension (OAT) test, which was proposed in a previous study. The IPSS values obtained from the AFPB tests on the copy paper and sack paper were significantly lower than those obtained from the 35° OAT tests because of the localised buckling caused by the negative principal stress. In contrast, the IPSS values obtained from the AFPB and OAT tests on the filter paper were in agreement when the clearance length was >5 mm because the buckling effect was excluded.

The load transfer between wood particles and the matrix was analyzed by observation of the strain patterns in thin films of high density polyethylene (HDPE) with embedded wood particles subjected to tensile loading. Optical measurement techniques based on the digital image correlation (DIC) principle were employed for quantitative measurement of strain distributions on the surfaces of the specimens. Interpretation of these measurements in terms of load transfer between the particle and the matrix below the surface proved challenging and required a structured approach. In this paper, quantitative descriptors were selected as synthesized metrics to support the quantitative interpretation of the measured strains. X-ray computed tomography (XCT) scans were used to assess the effect of the position of the particles in the film specimens on the strains patterns observed on the surface.

Steam explosion (SE) is a promising hydrothermal pretreatment technology for future biorefineries. In this study, the three steps of the steam explosion process, (1) the steam treatment (2) the explosion, and (3) the impact step were separately considered and their effects on structural changes of wood were studied. The SE experiments were performed on single wood pieces in different experimental set-ups at 7 and 14 bar pressure with 5 and 10 min treatment times. Mercury porosimetry and environmental scanning electron microscopy analyses were conducted to characterise both internal and external changes in the wood. It was found that the explosion step is not responsible for the disintegration of the wood material into small pieces; instead, the disintegration occurs due to impact of softened wood chips. However, the porosity profiles of the tracheids change during the explosion step. Altogether, all three steps of the SE process contribute in a synergistic way to an increase in pore size and total intrusion volume.

The wood moisture sorption (WMS) isotherm is generally considered to contain information on the water-cell wall interaction and the abundance of water sorption sites (SSs) in wood. The Hailwood-Horrobin (HH) model – as an example of the multilayer surface sorption models – is discussed for its suitability to analyze experimental WMS isotherms, to elaborate the fundamental sorption parameters. Based on multiple independent experimental and theoretical arguments, it was concluded that the basics of the surface multilayer-sorption models do not apply to wood. This is clearly illustrated by applying the analysis to the temperature-dependence of WMS isotherms, to the comparison of adsorption vs. desorption isotherms and to the quantification of SSs in wood. A sorption site occupancy (SSO) model is presented as an alternative for the HH model. It provides a comprehensive, thermodynamically consistent and quantitative basis for the analysis of WMS isotherms. The predicted SS densities are realistic and can be used to quantify sorption hysteresis and cell wall relaxation.

In this study, changes in the hygroscopic properties of two main wood species for violin making, Norway spruce and sycamore, after treatment with Physisporinus vitreus and Xylaria longipes were investigated. Swelling and moisture sorption capacity of wood at the growth ring scale were visually and quantitatively assessed by thermal neutron radiography analysis. It was demonstrated that the fungal treatment improved the dimensional stability of both Norway spruce and sycamore, but also increased their moisture adsorption capacity. Dynamic vapor sorption tests and measurements of the changes in dimensions of the specimens in the laboratory were in good agreement with the results of neutron radiography analysis. The main difference between the moisture sorption of the untreated controls and treated wood was observed at high relative humidity, e.g., above 75%. The contradictory behavior of the increased hygroscopicity and reduced swelling was explained by selective degradation of the chemical components and condensation of the moisture content gained in the capillary voids that developed in the cell walls during fungal decay.

European beech ( Fagus sylvatica L.) and Norway spruce [ Picea abies (L.) Karst.] have been thermally modified in a combined air-steam atmosphere between 70°C and 150°C and pressures up to 4 bar, and the changes of dimensions and moisture contents (MC) of the samples were studied in-situ by means of neutron imaging (NI). This non-invasive testing method offers unique opportunities. NI is highly sensitive for hydrogen and thus well suited for monitoring the MC changes, although some metals (e.g., Al), indispensable for sample environments under high temperature and pressure, are practically transparent to neutrons. The results show that the modification induced changes of MC and dimensions both in radial and tangential direction can well be determined by NI. Dimensional changes from water saturation to oven-dry state, the sorption isotherms, and the differential swelling were observed. Additionally, the sorption behaviour at 20°C was investigated after thermal modification and colour measurements were carried out before and after the thermal treatment.

The presence of blue-stain fungi considerably decreases the value of Pinus radiata timber, which is commercially important in Galicia (NW Spain). For this study, seven young pine trees growing in four different plantations were felled, and 20 discs were sampled from different heights in the stems. Parts of the discs were discoloured as a result of fungal infection. The discs were cut into small specimens. Defect-free specimens (controls) were selected for determining density and dimensional stability both in the volume and in the axial direction. Physical properties of fully blue-stained specimens and the controls were compared for each disc based on one-factor analysis of variance. As the factor was blue-stain, the other sources of variation were suppressed, such as tree source, height in the stem, ring width, cambial age and presence of heartwood or sapwood. Most of the physical properties analysed on some sample discs differed significantly between discoloured and unstained wood. The variables most affected by blue stain were basic density and volumetric shrinkage: blue-stained wood was 1.1% lighter and volumetric shrinkage was 5% higher in blue-stained wood than in the controls.

Waterlogged archaeological Norway spruce [ Picea abies (L.) Karst] poles were studied by means of confocal Raman imaging (CRI) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) analysis to determine lignin and polysaccharide composition and distribution in the cell wall. The waterlogged archaeological wood (WAW) was submerged under anoxic conditions for approximately 400 years and solely decayed by erosion bacteria (EB). CRI showed that decayed tracheids contain a residual material (RM) with heterogeneous lignin distribution; within the same tracheid RM often contained regions with intensities lower than sound S2 layers up to intensity values as high as the compound middle lamella (CML). CRI revealed strong depletion of carbohydrates in RM which indicated that EB are able to utilise the carbohydrate fraction of the cell wall effectively. Raman bands assigned to lignin did not show any difference between RM and sound S2. This is a hint that EB do not modify the lignin structure. Sound WAW free from EB decay showed evidence of loss of acetyl groups in glucomannan, loss of un-conjugated ester linkages in the lignin-carbohydrate complexes between xylan and lignin, and minor oxidation of the lignin polymer compared to recent reference material. This is evidence for abiotic decay in the course of waterlogging.

The aim of this research was to investigate the influence of different antioxidant systems containing vitamin E (VE) and antioxidant 168 (AO) on the photodegradation of wood flour/polypropylene (WF/PP) composites, as well as to provide insight into the processes taking place in these systems during weathering. Five groups of composites were treated in a QUV accelerated weathering tester for a total of 960 h. The surface color and the flexural properties of the weathered samples were tested. Additionally, the weathered surface was characterized by SEM, ATR-FTIR, and XPS. The results were: (1) composites with VE and AO showed less loss of flexural strength and modulus, as well as less color fading and fewer cracks on weathered surfaces than surfaces without antioxidants; (2) AO reacted with hydroperoxide and quinones and showed a synergistic effect with VE to further improve the anti-weathering ability of the composites; (3) 0.2% VE and 1.0% AO was the optimal formulation, yielding the best anti-weathering properties among all.

The present work is aiming at the elucidation of the tensile behaviour and fracture performance of moso bamboo ( Phyllostachys pubescens Mazei ex H. de Lebaie) by means of digital speckle correlation method (DSCM) and microscopic techniques. Results indicated that fibres play a major role in longitudinal tension and impeding crack radial propagation. Hybrid I-II failure mode was observed, i.e., crack opening (in tensile stress) and shear sliding (in shear stress). According to microscopic fracture characteristics, fibres extraction and stretching, filament formation in parenchyma with fibres bridging, interface debonding and the helix fracture of fibres happened in tension, which created more interfaces and dissipated more energy. The graded composite structure of bamboo provides intrinsic and extrinsic toughening mechanisms which contribute to improved toughness and physical properties.

The presence of fibrillar structures (FS) in the cell corner middle lamella (CCML) regions was demonstrated in several species of plants. The FS in the CCML of bass wood, oak wood, and bamboo became clearly visible after removal of lignin by wood decay fungi. The occurrence of FS in the CCML was also confirmed by examining early stages of cell wall formation in silver poplar, Japanese red pine, Arabidopsis and alfalfa. The fibrillar texture became increasingly less defined with the onset of lignification as the interfibrillar spaces were masked by lignin polymers and the fibrillar network became embedded within the lignin matrix. The FS stained positively with PATAg and ruthenium red, which is interpreted to be an indicator of the presence of structural polysaccharides (non-cellulosics and pectins). Our work demonstrated that fibrillar network is a characteristic feature of CCML of plant cell walls that is clearly visible prior to lignification of this cell wall region, but becomes invisible after the deposition of lignin.