Volume 68, Issue 7

A comprehensive model for alkaline extraction (E) of chlorine dioxide delignified (D 0 ) softwood kraft pulp (KP) is presented. The dynamics of the process is modeled by taking into account both irreversible and reversible chemical reactions and gas-liquid and liquid-liquid mass transfer. Equations linking molecular-scale composition (amounts of monomeric lignin and carbohydrate structures) and general engineering parameters [κ number (KN), brightness, intrinsic viscosity, total organic carbon (TOC), chemical oxygen demand (COD), etc.] are presented. The model is capable of reproducing the development of KN and brightness from the molecular-level kinetics. Reactions responsible for the darkening of chlorine dioxide bleached (D 0 ) pulp in alkali, brightening of pulp due to the action of hydrogen peroxide and oxygen, and reduction in KN were identified. The model predicts the chemical composition of both fiber wall and filtrate. This feature enables studies concerning the interaction of the AE chemistry with upstream (D 0 washing) and downstream (D 1 stage) processes. Quantitative physicochemical modeling approach also points out shortcoming in the present knowledge.

Twelve monolignol (coniferyl alcohol, sinapyl alcohol and p -coumaryl alcohol) β-glycosides (β-glucosides, β-galactosides, β-xylosides and β-mannosides) were synthesised to obtain fundamental NMR data for the analysis of phenyl glycoside type lignin-carbohydrate complexes (LCCs). That is, the 1,2- trans glycosides (the β-glucosides, β-galactosides and β-xylosides) and the 1,2- cis glycosides (the β-mannosides) were synthesized by means of Koenig-Knorr glycosylation and β-selective Mitsunobu glycosylation strategies, respectively. In addition, dihydromonolignol and p -hydroxybenzaldehyde derivative β-glycosides were also prepared from the corresponding monolignol glycosides and their intermediates, respectively. The correlation observed for the C 1β -H 1β bonds of the sugar moieties in the HSQC spectra of the all β-glycosides varied and were in the range of δ C / δ H 96–104/4.7–5.4 ppm. Especially, it was found that the correlations derived from the C 1β -H 1β bonds of the guaiacyl and p -hydroxyphenyl β-mannosides were close to those derived from the C 1α -H 1α bonds of the 4- O -methyl-α-D-glucuronic acid moieties described in the literature.

Two new iridoids were isolated and identified to three known ones, namely, loganic acid ( 2 ), sweroside ( 3 ), and 7- O -tigloylsecologanol ( 4 ), from the stems of Viburnum erosum . Dried stems of V. erosum were extracted with 80% methanol (MeOH), and the concentrated extract was partitioned successively with ethyl acetate (EtOAc), n -butyl alcohol ( n -BuOH), and H 2 O. Five compounds were isolated after repeated silica gel (SiO 2 ), octadecyl SiO 2 (ODS), and Sephadex LH-20 column chromatography of the EtOAc fraction. The chemical structures of the compounds were determined based on spectroscopic data from 1 H- and 13 C-NMR, DEPT, and 2D-NMR (gCOSY, gHSQC, gHMBC) data. The new iridoids were identified as 3,7-dihydroxy-8-methyl-cyclopenta[ c ]pyran-4-carboxylic acid ( 1 ) and rel -(1 S ,5 R ,9 S )-9-ethenyl-1-( β -D-glucopyrinosyloxy)-5,9-dihydro-5-{2-[(2-methylbut-2-enoyl)oxy]ethyl}-1 H -pyran-4-carboxylic acid ( 5 ) and named viburnin and epi-7- O -tigloylsecologanolic acid, respectively. This is the first report of the isolation of these five iridoids from V. erosum .

The capability of Trichoderma gamsii to biologically control sapstain fungi has been investigated. Six ophiostomatoids, including Ophiostoma floccosum, O. piceae, O. piliferum, O. ips, Grosmannia koreana, and G. piceaperda , were inhibited by the extracts of T. gamsii . Of the various cultivation periods, 7 days of T. gamsii cultivation produced antifungal compounds most efficiently. The crude extracts of T. gamsii inhibited O. ips , G. koreana, and G. piceaperda by over 99%. The crude extracts of T. gamsii were isolated, and the compounds were purified by thin layer chromatography (TLC), open column chromatography, ultra-performance liquid chromatography combined with quadrupole time-of-flight mass spectrometry (UPLC-QToF-MS) and NMR spectroscopy. The active fractions were separated based on the degree of T. gamsii antifungal activity. The compound 6-pentyl-α-pyrone (6PAP) was evaluated as a biological control agent for sapstain fungi.

The formation of free radicals in pine and kwila woods and cellulose and kraft lignin was studied to understand better the impact of radiation on wood degradation. Wood specimens were irradiated with sources emitting in the UV, Vis, and IR regions and then analyzed by electron spin resonance (ESR) spectroscopy and the increment of free radicals generated was measured. In addition, samples were irradiated by color filtered light. Lignin was found to be more susceptible to radiation than cellulose. Kwila wood is more photostable than pine, probably due to the photoprotective extractive contents in the former. As expected, lower energy wavelengths generated fewer free radicals. However, fluorescent lighting generated as many free radicals as UV irradiation indicating that high-energy visible radiation is equally harmful to wood surfaces. Light-colored filters absorbing the latter wavelength region reduced the photodegrading damage. Accordingly, transparent stains containing colored pigments which imitate the filter effect should provide better protection of wood surfaces against sunlight.

Aluminum hydroxide [Al(OH) 3 ] film on wood substrate has been synthesized by means of the hydrothermal (HT) method for improvement of wood’s mechanical properties and resistance to combustion. The HT temperature was set to 100°C and 120°C, and the reaction time varied from 4 h to 10 h. X-ray diffraction (XRD) and X-ray photoelectron spectrometry (XPS) results show that the thin film grown on wood surface was amorphous Al(OH) 3 and the relative crystallinity of treated woods slightly improved. SEM observation revealed that the Al(OH) 3 film is composed of regular micro/nano-sized spheres, whose production and size increase with the reaction time, and some AlO(OH) structures emerged at 120°C with reaction times longer than 6 h. The storage modulus of the wood treated at 100°C and 120°C for 8 h can be improved by 30%, while the viscoelastic properties are also influenced by the HT treatment and Al(OH) 3 coating. The limiting oxygen index of raw wood rose from 24.7% to 27.9% after the treatment, which can be interpreted as a moderate improvement of the fire resistance.

The lignin distribution in poles of waterlogged archaeological Picea abies (L.) Karst, which was decayed by erosion bacteria (EB) under anoxic conditions for approximately 400 years, was topochemically identified by transmission electron microscopy (TEM) and high resolution UV-microspectrophotometry (UMSP). Lignin rich cell wall compartments such as cell corner (CC), compound middle lamella (CML), torus, initial pit border and mild compression wood (CW) appeared morphologically well preserved together with S1 and S3 layers and epithelial and ray parenchyma cells. Residual material (RM) from degraded S2 showed a varied lignin distribution as evidenced by the different local UV-absorbance intensities. However, evaluation of UV-absorbance line spectra of RM revealed no change in conjugation of the aromatic ring system. Presence of RM with both very low and very high lignin absorbances showed evidence for disassembly of lignin during degradation combined with aggregation of lignin fragments and physical movement of these fractions. In contrast to TEM analysis, locally decreasing lignin content was found by UMSP in CML regions.

In the focus was the question whether metal alkoxide coupling agents – titanium, silane, and zirconium – form covalent bonds to wood and how they improve coating adhesion. In a previous work, a downshift of the lignin infrared (IR) band ∼1600 cm -1 was shown to be consistent with the formation of ether linkages between lignin and titanium coupling agent. In the present work, changes were found in the attenuated total reflectance-Fourier transform IR (ATR-FTIR) spectra of lignin and wood mixed with silane, and titanium coupling agents, and to a lesser extent for a zirconium coupling agent. This was seen as evidence for covalent bonds between lignin phenolics and the coupling agents. No spectral changes were observed when the coupling agents were mixed with the wood constituents cellulose and hemicellulose. For verification of the results, a modified EN 311 wet adhesion pull strength test was performed with softwood panels painted with a solvent-borne alkyd/acrylic coating. The results revealed an improved adhesion for all tested coupling agents compared to the untreated reference. The spectroscopic and pull test results underline that the presence of the lignin moiety in wood is of central importance for improved wood coating adhesion.

The affinity of particleboard (PB) to water is one of the main limitations for using PB in moisture-rich environments. PB dimensional stability and durability can be improved by reducing the available hydroxyl groups in wood through hemicellulose removal, for example, by hot water extraction (HWE), which increases wood resistance to moisture uptake. The resulting liquid fraction from HWE is rich in hemicelluloses and can be used for chemicals and fuels, and the solid fraction is less hydrophilic. The objective of this study was to investigate the effects of HWE of softwood chips (conducted at 160°C and 90 min) and hardwood chips (160°C and 120 min) on the properties of PB panels. HWE increased compressibility and reduced springback by 34% and 44% for pine and maple chips, respectively, which positively impacted the PB properties. Water absorption of pine PB panels was lowered by 35% and that of maple PB panels by 30%, while reduction of thickness swelling was lowered by 39% for pine PB and 56% for maple PB after 24 h of immersion in water. The mechanical properties were not significantly affected.

Tree growth stress (GS) consists of an elastic component and a viscoelastic locked-in component. The elastic component is released instantaneously by cutting wood, whereas the locked-in component remains. The latter can be released by hot water treatment, which is known as hygrothermal recovery (HTR). In this paper the mechanism behind HTR is described and interpreted in terms of the microfibril angle (MFA) in the cell wall as follows: during cell-wall maturation, axial tensile stress is generated in the cellulose microfibrils (CMF), whereas isotropic compressive stress is generated in the matrix of lignin-hemicellulose (MT). Some amount of microscopic stresses remains following the removal of the wood from the living stem. Hygrothermal (HT) treatment induces recovery of remaining compressive stress in the MT, which causes its expansion. Axial tensile stress in the CMF are released by HT softening of the MT. This causes the CMF to contract along its length and to expand laterally. The combined effect of the expansions of the MT and contraction of the CMF causes the wood to deform anisotropically. This is the HTR of wood. The degree of anisotropy is determined by the MFA on the basis of reinforced-matrix theory.

The potential for extraction of copper from wood treated with micronised, nano or soluble forms of copper has been evaluated in view of chemical remediation. In focus were EDTA, oxalic acid, bioxalate, and d -gluconic acid for extraction of Cu from treated wood. Bioxalate extractions for 24 h resulted in Cu removal over 95% for all tested materials, and the effectiveness of oxalic acid extraction was very similar to that of nano-CuO-treated wood. Bioxalate was more effective than oxalic acid in removing Cu from ACQ-D, MCQ, MCA, CA-C and Cu-ethanolamine treated wood. d -gluconic acid extractions resulted in the lowest Cu removal for nano-CuO even though d -gluconic acid was effective for all other materials. As the pH of d -gluconic acid decreased, Cu removal was improved except for nano-CuO. There is no distinctive difference in Cu removal from wood treated with ACQ-D, MCQ, CA-C, MCA and Cu-ethanolamine.

There are gaps in our knowledge regarding temporal changes in wood stability and mechanical properties in the context of wood durability. Energetic analyses have been performed in this study based on experimental results on the bending fatigue of wood under multiple loading conditions. New findings regarding the fatigue limit and fatigue life ( N f ) are presented. The strain energy (SE) obtained from stress-strain envelopes until wood reaches its N f is a value specific to wood species and static strength regardless of the loading conditions. This value is about 50% higher than the SE in static tests. The relationship between mean energy loss (EL) and stress level (SL) to the point of fatigue failure is bilinear, and the mean EL is closely related to N f . Moreover, the SL – when mean EL approaches a specific value (∼1.10 kJ m -3 per cycle) as N f approaches infinity – is considered to be the fatigue limit; the latter is estimated to be about 20–30% of static strength.

Silver fir and Norway spruce wood have been thermally modified (TMW) for 3–4 h at 160°C, 180°C, 200°C, and 220°C by means of the thermovacuum process (Termovuoto), and the ultrastructural and chemical changes in the compound middle lamella (CML), including the middle lamella cell corner (ML cc ) regions (CML cc ), were investigated. Severe anatomical and histochemical changes were prominent above treatment temperatures of 200°C; thus, woods treated at 220°C for 4 h were in focus. Immunocytochemical studies showed that noncellulosic polysaccharides, such as pectin, xyloglucan, xylan, and mannan, were significantly degraded in CML cc regions of TMWs. After treatment, the CML cc regions were composed almost entirely of modified lignin with increased amounts of acidic groups. With cytochemical staining for lignin, many electron dense particulates were detected in the CML cc regions of TMWs, indicating early degradation/alteration by the Termovuoto treatment.

Young Araucaria heterophylla (Salisb.) Franco seedlings have been grown tilted to obtain compression wood (CW), opposite wood (OW), and normal wood (NW). Mechanical and anatomical properties of these wood tissues have been assessed. CW had characteristics associated with low severity. OW and NW did not differ significantly in their properties and were found to have a considerably lower microfibril angle and higher modulus of elasticity than those of juvenile corewood of Pinus radiata D. Don.

Douglas fir ( Pseudotsuga menziesii ) lumber was tested in terms of off-axis modulus of elasticity (MOE off-axis ) and off-axis logarithmic decrement ( λ off-axis ) by longitudinal and flexural vibration (VT long and VT flex ) methods. Similar to the results obtained in a previous study, these results indicate that the values of MOE off-axis are dependent on the length-to-width ratio of specimens when the value of off-axis angle ( θ ) is approximately 15°. Although the λ off-axis values are also dependent on the length-to-width ratio, the dependence is not pronounced over a specific range of θ . To measure the λ off-axis value accurately, as well as the MOE off-axis value, the specimen should be sufficiently slender.