Volume 71, Issue 4

A part of kraft lignin (KL) can be used as a value-added product without detracting the chemical recovery and the energy balance of the kraft mill. The focus of this study is the production of light-weight carbon fibres (CFs) from KL obtained by the LignoBoost process. For this purpose, crude KL and various cellulose products from kraft pulping of hardwood (HW) and softwood (SW) were dissolved in 1-ethyl-3-methylimidazolium acetate ([EMIm][OAc]) and submitted to dry-jet wet-spun to obtain precursor fibres containing 70% KL and 30% cellulose, which were thermally stabilised and further converted by thermal treatments into CF. The initial and final products were characterised with respect to, e.g. mole mass distribution, thermal properties, tensile strength and tensile modulus determination. The optimised precursor fibres are smooth and flexible with similar mechanical properties as commercial textile fibres. The best CFs made had a tensile strength of 780 MPa and a tensile modulus of 68 GPa and are thus stronger and stiffer than those produced by melt-spinning of SW-based lignins alone. The new CFs based on dry-jet wet-spun precursors still have a high potential for further improvements.

Japanese beech ( Fagus crenata ) was decomposed by a semi-flow process in hot-compressed water (HCW) at 150~230°C/10 MPa for 25 min. Mainly hemicelluloses and partly the lignin moiety of the wood was affected and liquefied in water. A part of the liquefied products can be precipitated after 12 h standing at ambient conditions. The precipitates are composed of around 90% of lignin, which was quantified and characterized by various chemical and spectroscopic methods in comparison of milled wood lignin (MWL), which is considered to be a representative compound for the native lignin in wood. The yield of the precipitated lignin (L precip ) is higher than that of MWL and its syringyl content is also higher as demonstrated by alkaline nitrobenzene oxidation (NBO) giving rise to higher syringaldehyde/vanillin (SA/VA) ratios. Its OH phen group content was also high. The interpretation is that L precip is mainly from the secondary wall, and accordingly, the presented semi-flow HCW treatment offers the possibility for an efficient lignin isolation.

The torrefaction is a thermal pre-treatment to improve biomass quality for biofuel applications. In this study, the effects of a mild torrefaction (T) on eight eucalypt species ( Eucalyptus botryoides, E. globulus, E. grandis, E. maculata, E. propinqua, E. rudis, E. saligna and E. viminalis ) have been compared. Namely, the mass loss (ML), the equilibrium moisture content (EMC), density and chemical composition were determined and FTIR spectra were recorded of the initial and torrefied woods (TWs). The average ML was 11% and the heat-treated woods had an overall 10% density decrement. All the TW had 50% lower EMC compared to untreated wood samples (W). Elemental composition showed that carbon content increased from 48% to 53% and the oxygen/carbon ratio decreased from 0.80 to 0.65. The chemical changes induced by T included an increment of extractives, a 20% higher lignin content and a 16% lower holocellulose content in relation to W. The hemicelluloses modification is manifested by a decrease of xylose, galactose, and acetyl groups in TWs. The fourier transform infrared (FTIR) spectra of the different wood species were very similar, and reflected in a uniform manner the chemical changes upon T. Because of the similar reaction of the eucalypt species, they can also be used in form of mixed eucalypt feedstock as biofuel.

The aim of the present study was to investigate the extractives of Gmelina arborea stem from the sapwood (sW) to heartwood (hW) including the transition zone (tZ) between them by means of quantitative GC-MS, while the spatial distribution of four typical compounds was analysed by TOF-SIMS. The focus was on gmelinol, paulownin, 7′- O -ethyl arboreol, and β-sitosterol, which were isolated and purified from hW. The four compounds revealed a characteristic distribution pattern corresponding to their key role in biosynthesis and depending on their susceptibility to secondary reactions in the hW.

The origin of sorption hysteresis in the wood-water system is still under debate. In nanoporous-fluid systems, in general, hysteresis is explained as the manifestation of metastable states in a single pore-fluid system and that is further complicated by the pore connectivity. Cell walls are considered as micro-mesoporous materials and capillary condensation in the entire hygroscopic region is proposed as an alternative sorption mechanism. In the present work, the woods of Douglas-fir, aspen and western red cedar were in focus and the pore connectivity has been investigated by observing five experimentally generated hysteresis patterns comprised by up to 4 th scanning curves at 25 and 40°C. Special attention was given to the congruency property from one pattern as it is known from the literature that deviation from this property can reveal the extent of pore connectivity. Consistent patterns were found for the species-temperature combinations. Further, the high extent of congruency property indicated the dominance of independent cell wall pores.

The Preisach model, the mathematical form of the independent domain model, has been used to describe water sorption hysteresis in wood for over 20 years, however, its geometric interpretation has not been fully explored. In this work, it is demonstrated that the geometric interpretation can be used to explain the five experimental hysteresis patterns identified in the first paper of this series. Additionally, a modification to the aforementioned model is suggested that involves a numerical implementation, which avoids the use of unknown parameters. Our approach was evaluated at 25 and 40°C by comparing the predicted 1 st to 4 th order scanning curves with experimental data for Douglas-fir, western red cedar and Aspen. The low prediction errors and well-maintained wiping-out property support the suitability of our approach. Compared to other models found in literature, the presented model has the advantage of high accuracy and easy implementation due to its nonparametric nature.

Treatment with polyethylene glycol (PEG) is the preferred method for the conservation of waterlogged archaeological wooden objects. However, PEG impregnation leads to softening and increased hygroscopicity of the material. The present study compiles experimental results concerning the full elastic properties of PEG impregnated archaeological wood from the Vasa ship in relation to its basic density, PEG content (PEGC) and moisture content (MC). The results show a correlation between a more porous microstructure and high PEGC, and consequently, higher MC. The PEG and moisture contribute to the mass of the wooden object as well as to the softening of the material, which are undesired properties in a larger load-carrying wooden structure. A compromise between the improved dimensional stability and degradation of mechanical properties should therefore be considered in the conservation of wooden objects treated with PEG.

A facile and effective method for the surface hydrophobization of medium-density fiberboards (MDFs) via the silver (Ag) mirror reaction has been investigated. The pristine MDF surface was treated with silver nitrate (AgNO 3 ) and subsequently with glucose to reduce Ag ions into Ag particles, which led to dual-size surface roughness. The roughness and morphology of the Ag-coated MDF surface were characterized by scanning electron microscopy (SEM), and the elemental composition and the crystal structure of the surface were determined via energy-dispersive X-ray spectroscopy (EDXS) and X-ray diffraction (XRD) analyses. The wettability of the MDF surface was measured by contact angle (CA) measurements. The results indicated that pure Ag particles were successfully deposited onto the MDF surface without any impurities. The Ag surface coating was water repellent as indicated by a CA of 136°, which slightly decreased with time. The hydrophobicity was derived from the air trapped in the surface cavities and the dual-size roughness.

Wood density and microfibril angle (MFA) are strongly correlated with wood stiffness, swelling/shrinkage, and its anisotropy. Understanding the spatial distribution of these data is critical for solid timber applications. In this study, near-infrared (NIR) hyperspectral imaging has been calibrated for evaluation of wood density and MFA in an effective manner. Briefly, five wood samples collected from both normal wood (NW) and compression wood (CW) moieties of two different Cryptomeria japonica trees were analyzed. Partial least squares (PLS) regression analysis was performed to determine the relationship between X-ray densitometry data obtained by SilviScan and NIR spectra, and cross-validation (leave-one-out) approach served for prediction performances. The validation coefficient of determination (r 2 ) between the predicted densities by the NIR technique and the X-ray data was 0.83 with a root mean squared error of cross-validation (RMSECV) of 105.2 kg m −3 . Regarding MFA, the r 2 was 0.77 and RMSECV 5.36°. Wood density was successfully maped as well as the MFA at a high spatial resolution. As a result, the detection of annual growth ring features and evaluation of aspects of heterogeneous wood quality has been facilitated. The mapping results were visually checked by looking at the difference between earlywood (EW) and latewood (LW) for density and by means of the Mäule color reaction indicating high lignin contents in CW in terms of MFA validation as CWs have high MFA values.

Thermal diffusivity (ThD) of Phyllostachys edulis (Moso bamboo) has been determined in three directions of the cylindrical coordinate system of the culm. A flash tube and an infrared camera system was utilised for this purpose. The results, calculated by the MATLAB programme, serve as a database for numerical simulation studies concerning the heat and moisture transfer behaviour of Moso bamboo. The porosity and complexity of cellular structure and interconnectivity are the essential parametres influencing the ThD of Moso bamboo.

The effects of brown-rot decay on the mechanical and chemical properties of poplar ( Populus cathayana Rehd.) wood were investigated, while the correlation of several properties to the decay degree and to each other were quantified. During the decay process, the losses in impact bending strength (IBS) and modulus of rupture (MOR) increased logarithmically with the degree of decay, whereas the losses in modulus of elasticity (MOE) and compressive strength parallel to grain (CS ∥ ) increased slowly with linear trends. The ranking of the four mechanical parameters for the response speed to decay and the degree of the influence of decay were IBS>MOR>MOE>CS ∥ . Hemicelluloses were preferably decomposed by the brown-rot fungus. The prominent degradation of cellulose began from a weight loss ( W L ) of 18.7%, where the relative crystallinity decreased. In summary, the degradation of hemicelluloses caused a fast and significant decrease in IBS while the subsequent removal of paracrystalline cellulose resulted in MOR loss. The variation of MOE was in correlation with the cellulose content. A decrease in CS ∥ was due to the slow deterioration of crystalline cellulose.