Volume 71, Issue 6

For producing wood products without fractures based on thermo-hygro-mechanical (THM) treatments, it is essential to understand how steaming and compression change the wood softening and cell wall components. In this paper, the effects of compression combined with steam treatment (CS) on the viscoelasticity of the in-situ lignin of Chinese fir has been investigated through dynamic mechanical analysis (DMA) under fully saturated conditions. Several variations were studied, such as the softening temperature (T g ) and apparent activation energy (ΔH a ) of the softening process in response to CS treatment conditions (such as steam temperature and compression ratio) under separate consideration of earlywood (EW) and latewood (LW). No difference between EW and LW with respect to the viscoelasticity was noted. T g and ΔH a of the lignin softening were nearly unaffected by the compression ratio, but were highly influenced by the steam temperature. The T g decreased significantly with CS treatments at or above 160 o C, but showed no appreciable change, compared to the native wood, at the lower steaming temperature of 140 o C. ΔH a increased at higher steam temperatures, while ΔH a showed a decreasing tendency with decreasing T g . This indicates that lignin undergoes a simultaneous depolymerization as well as a condensation during CS treatment.

The chemical characteristics of wheat straw lignin pretreated under dilute acid conditions were compared. After pretreatment, the lignin content of the solid residue increased as temperature increased (from 160°C to 190°C) and with the amount of acid added (0%, 0.25%, or 1% H 2 SO 4 ). Pretreatment at 190°C with increasing concentrations of acid catalyst led to a decrease in glucan content, whereas the glucan content remained almost constant at 160°C pretreatment regardless of the acid concentration. The xylan content decreased in proportion with increased acid concentration and pretreatment temperature. The residual lignins were characterized by solution-state, two-dimensional (2D) nuclear magnetic resonance (NMR) spectroscopy and size-exclusion chromatography (SEC). Results showed that more ether bonds were cleaved with increased pretreatment temperature and lower pH, whereas the levels of carbon-carbon bonded structures (e.g. phenylcoumaran and resinol units) were hardly affected. With a pretreatment of 160°C and 1% H 2 SO 4 , the majority of the β-O-4 bonds were cleaved. In addition, lignin depolymerization was more evident than repolymerization at higher pretreatment temperatures and lower pH. Documenting lignin structural changes as a function of pretreatment parameters provides a tool for biorefineries to gain flexibility in processing parameters with full control over the final properties of the products.

To elucidate the effect of soil conditions on the in planta distribution of inorganic elements, an aluminium (Al)-tolerant plant, Hydrangea macrophylla , was cultivated with the addition of Al ion to soils. Freeze-dried stems from the plants were analysed by time-of-flight secondary ion mass spectrometry (dry-TOF-SIMS). Freeze-fixed stems of the plants were analysed by cryo-TOF-SIMS. The inorganic metal content was quantified by inductively coupled plasma atomic absorption spectrometry (ICP-AES). The dry- and cryo-TOF-SIMS mapping analyses showed that in the native sample, inorganic elements are mainly localised in the cortex and pith. Al-treatment [i.e. Al 2 (SO 4 ) 3 administration to the soil] altered the distribution and content of inorganic metals. The actual amount of inorganic elements quantified by ICP-AES showed that Al-treatment on the soil increased the amounts of Na, Mg, Al and Ca and decreased that of K in the stem. The secondary ion counts of inorganic elements in freeze-dried and -fixed samples, determined by dry-/cryo-TOF-SIMS measurements, showed similar variations as that observed with ICP-AES measurements. These results are interpreted as that Al-treatment altered the distribution and amount of inorganic elements in the stems of Al-tolerant H. macrophylla plants.

Earlywood (EW) and latewood (LW) have different hygromechanical behaviors, if subjected to relative humidity (RH) variations. To understand this effect better, the adsorption mechanisms of EW and LW of Douglas fir were studied by 2D 1 H NMR relaxometry under conditions of equilibrium moisture content (EMC) at 20°C. Two bound water components were detected with relaxation times T 1 and T 2 indicating that they are located in distinct environments but these are similar in EW and LW. Sorption isotherms were calculated and analyzed based on the sorption model of Dent. A difference of sorption energy between the two water components is in agreement with their mobility difference observed on T 1 −T 2 correlation spectra. Moreover, for the two bound water components, EW and LW exhibit different sorption isotherms at high RH. This may be attributed to a difference of adsorption capacity. Based on the macrofibril models provided by the literature, the following hypothesis is proposed: bound water components are located in lamellar and lenticular areas, both leading to possible deformations.

The combined effects of initial microfibril angle (MFA) and moisture content (MC) on the longitudinal tensile properties of Masson pine ( Pinus massoniana Lamb.) wood foils has been investigated. Synchrotron X-ray diffraction (XRD syn ) combined with a custom-built microtensile device was applied for in situ monitoring of the MFA alterations in the foils under different initial MFAs and MCs conditions. The results demonstrate that the tensile properties are highly negatively correlated to both MFA and MC. Furthermore, the tensile modulus is more sensitive to MC change than tensile strength. At a higher MFA, the sensitivity of the two mechanical indicators to MC alteration is enhanced.

The purpose of this study was to gain an in-depth understanding of the fatigue behavior of Japanese cypress as a result of compression. Repeated compression loading tests were conducted on small clear wood specimens in the form of a pulsating triangular wave of frequency 1.0 Hz, and 864000 repeated loading cycles were performed. The change in stiffness and the maximum strain (STR max ) with repeated loadings were investigated, based on the stress-strain relationship obtained from the test. Stiffness hardly changed under conditions of low stress levels (SLs), even under repeated loading. STR max increased exponentially as the number of loading cycles increased. Furthermore, the fatigue limit was predicted by analyzing the change of STR max with repeated loading. According to the analysis, the fatigue limit was revealed to be approximately 60% of the SL (standardizing the stress when the strain is 0.05 under static load).

A dynamic elastoplastic compression model of Norway spruce for virtual computer optimization of mechanical pulping processes was developed. The empirical wood behaviour was fitted to a Voigt-Kelvin material model, which is based on quasi static compression and high strain rate compression tests (QSCT and HSRT, respectively) of wood at room temperature and at high temperature (80–100°C). The effect of wood fatigue was also included in the model. Wood compression stress-strain curves have an initial linear elastic region, a plateau region and a densification region. The latter was not reached in the HSRT. Earlywood (EW) and latewood (LW) contributions were considered separately. In the radial direction, the wood structure is layered and can well be modelled by serially loaded layers. The EW model was a two part linear model and the LW was modelled by a linear model, both with a strain rate dependent term. The model corresponds well to the measured values and this is the first compression model for EW and LW that is based on experiments under conditions close to those used in mechanical pulping.

Poplar wood was modified by a combination of thermo-mechanical densification (TMD) and heat treatment (HT) process at five temperatures ranging from 170 to 210°C. A new two-step conditioning method (CM) is suggested, in the course of which the modified wood is submitted to 50°C/99% RH→25°C/65% RH, where RH means relative humidity in the climate chamber. The traditional one-step CM (25°C/65% RH) served as reference. The effects of conditioning history on hardness were observed and analyzed along with the change of dimensional stability. The hardness of the modified wood was lower in the case of the proposed CM due to more set-recovery release, but the extent of that decreased with the HT temperature. For a good hardness, HT 200°C should be selected with the proposed CM, which is different from the optimization output of 180°C obtained from the traditional CM. In conclusion, a specific assessment method for the performance characterization of this type of modified wood would be beneficial for the combined TMD and HT processes.

Poor acoustics is a common problem in many small closed rooms such as offices or dining rooms. Sound absorbing panels used as wall or ceiling coverings can be a remedy. In the present paper, the sound absorption properties of a composite made of two plywood skins bonded to an inner honeycomb core of plywood cells, designed by the authors in a previous study, were improved by drilling the surfaces. The holes communicate with the void cells of the core, activating the Helmholtz resonance effect. The acoustic behavior of small specimens and final-size samples are described, which were also tested in a reverberation chamber and in a real dining room. The developed lightweight composite plywood achieved α max 0.90 values (maximal sound absorption coefficients) around 400 Hz, i.e. in the low frequency range, resulting in being well suited for various acoustic improvements.

Brown rot (BR) fungi are highly destructive wood decaying organisms that utilise free radicals in the initial stages of decay. Although many wood extractives have been shown to have antioxidant (AO) activity, their ability to protect wood from radical-based degradation has received little attention. The present paper reports on the ability of Scots pine heartwood (hW) and knotwood (knW) extractives to inhibit radical-based degradation, with a focus on the Fenton reaction. AO assays showed that extract solutions and pure pinosylvins had good radical scavenging activity and weak to moderate ferrous iron binding and ferric iron reducing activities. AO assays were repeated with wood powders and showed that extractives were also active in wood: hW and knW had significantly higher activities than their extracted counterparts or sapwood. However, when wood powders were subjected to degradation by Fenton reagent, only knW showed reduced mass loss. Based on the activity profiles of knW and hW, it appears that the radical scavenging activity of pine extractives is more important than their interaction with iron. The results suggest that the AO activity of extractives may play a role in inhibiting BR, but its importance relative to the other biological activities of extractives is unknown.

The cryptic lifestyle of drywood termites makes it difficult to study their foraging behaviour and to detect infestations in hidden regions. In the present research, computer tomography (CT) scanning images were collected over a 1-year observation period of drywood termite Incisitermes minor (Hagen) in order to understand its foraging behaviour and, perhaps, to be able to detect the infestation as early as possible. Sitka spruce and Japanese cypress woods were the test objects. As CT scanning results show, foragers caused distinguished tunnelling patterns based on the physical properties of wood during gallery construction. The foragers primarily excavate along the earlywood in radial direction towards the outer surface of the wood to establish the primary and satellite chambers, followed by mainly superficial (0.3–3.0 cm under the surface) longitudinal expansion with occasional lateral deviations. The development of tunnelling is affected by the physical constraints of knots with their high density, high extractive and lignin contents, reaction wood (compression wood) and wood damage caused by wind.