Volume 72, Issue 2

Lignin-based carbon fibers (LCFs) from the renewable resource softwood kraft lignin were synthesized via oxidative thermostabilization of pure melt-spun lignin and carbonization at different temperatures from 1000°C to 1700°C. The resulting LCFs were characterized by tensile testing, scanning electron microscopy (SEM), X-ray diffraction (XRD) and confocal Raman spectroscopy. The microstructure is mainly amorphous carbon with some nanocrystalline domains. The strength and stiffness are inversely proportional to the carbonization temperature, while the LCFs carbonized at 1000°C exhibit a strength of 628 MPa and a stiffness of 37 GPa. Furthermore, the application potential of LCFs was evaluated as negative electrodes in a lithium-ion battery (LIB) by electrochemical cycling at different current rates in a half-cell setup. The capacity drops with the carbonization temperature and the LCFs carbonized at 1000°C have a capacity of 335 mAh g −1 . All LCFs showed good cycling stability. Because of the mechanical integrity and conductivity of the LCFs, there is no need to apply current collectors, conductive additives or binders. The advantage is an increased gravimetric energy density compared to graphite, which is the most common negative electrode material. LCFs show a promising multifunctional behavior, including good mechanical integrity, conductivity and an ability to intercalate lithium for LIBs.

Quantitative determination of cellulose content by means of diglyme [bis(2-methoxyethyl) ether] isolation is useful for rapid screening experiments. However, diglyme isolation from softwoods results in a certain amount of residual lignin in the cellulose. In this paper, the lignin content (L) in diglyme cellulose of three pine species ( Pinus halepensis Miller, Pinus sylvestris L. and Pinus pinaster Aiton) was analysed by ATR-FTIR spectroscopy and analytical pyrolysis (Py). Py allowed lignin quantification. The influence of wood milling on cellulose yield was also analyzed and it was shown that a particle size between 10 and 60 mesh did not noticeably influence the cellulose yield or L; however, ball-milling to powder did cause a cellulose loss of around 37%. The diglyme method is only reproducible if the experimental parameters are standardized and meticulously followed.

The lipophilic and hydrophilic extractives in the sapwood (sW) and heartwood (hW) of stems from Pinus halepensis Mill and Eucalyptus camaldulensis Dehnh trees grown in the north of Algeria were analyzed. The extraction of dried samples was carried out in an accelerated solvent extractor (ASE). The lipophilic substances were first extracted with n -hexane and then the hydrophilic ones with acetone/water. The extractives were analyzed by gas chromatography-flame ionization detection (GC-FID), GC-mass spectroscopy (MS) and high-performance size-exclusion chromatography (HPSEC). The largest amount of lipophilic extractives (≈13.4 mg g −1 ) was observed in the hW of P. halepensis , while the hW of E. camaldulensis contained the largest amount of hydrophilic extractives (≈116.3 mg g −1 ). Lipophilic extractives are mainly composed of oleoresins (resin acids, terpenes), fats (fatty acids, glycerides, steryl esters, sterols) and waxes (fatty alcohols). Hydrophilic extractives are composed of polyphenols (stilbenes, flavanols), sugars (monosaccharides) and sugar alcohols (cyclic polyols). The main identified lipophilic extractives are resin acids in pine and glycerides in eucalypt. The main identified hydrophilic extractives are cyclic polyols in pine and flavanols and monosaccharides in eucalypt. The total content of extractives is higher in hW than in sW.

The bark-water relation and the moisture transport in bark are essential for the living tree but also for the industrial utilization of bark. Thus the bark-water relation of beech ( Fagus sylvatica ) and spruce ( Picea abies ) have been studied in the present work. The sorption isotherms were determined at 35°C for both wood and bark and the water diffusivity was measured under steady state conditions (cup method) and under unsteady state conditions, i.e. via sorption test. The sorption isotherms were calculated based on the Hailwood-Horrobin (HH) model. It was observed that beech wood and bark have a similar hygroscopic behavior, whereas spruce bark is more hygroscopic than spruce wood in all the relative humidity (RH) ranges. The radial diffusivity was in the range 1.2·10 −11 –2.2·10 −11 m 2 s −1 for spruce and beech bark, respectively, when the driving force of the diffusion is the gradient of bound water.

The time domain nuclear magnetic resonance (TD-NMR) technique was applied to observe the water states, water migration and the T 2cutoff of sapwood (sW) and heartwood (hW) of Xinjiang poplar and Mongolian Scotch pine wood during drying. Three components in the T 2 spectrum could be observed for poplar and pine at room temperature, and a large, short time component and a small, long time component of free water was visible at the melting point of water. During drying, the long time T 2 component diminished rapidly above the fiber saturation point (FSP), and almost disappeared close to or below the FSP. The short time components of the T 2 distributions slightly enlarged with decreasing moisture content (MC) above the FSP but rapidly diminished and shifted to the left side below the FSP. The bound water content estimated based on the T 2cutoff is in agreement with previous findings. Free and bound water have been found to be in two primary states both in poplar and pine. The loss of free water was rapid and profound but the bound water slightly increased with decreasing MC above the FSP, and the free water evaporated completely close to the FSP, where the bound water began to disappear significantly.

Impregnation of wood with paraffin wax emulsion (PWE) is a common eco-friendly approach for improving water repellency. In this study, loblolly pine ( Pinus taeda ) and Scots pine ( Pinus sylvesteris ) samples were impregnated with PWEs with different solid contents and particle sizes, and the influence of the impregnation parameters on wax penetration and distribution in treated wood was elucidated by time domain nuclear magnetic resonance (TD-NMR). A good linear correlation (R 2 =0.981) between wax content determined by TD-NMR and weight percent gain (WPG) of the impregnated wood was established. According to wax loading and distribution data, loblolly pine has a much better permeability than Scots pine. With decreasing solid content and particle size, the penetration of PWE increases in both species. The water contact angles (CA) on the surface at different depths of wood were also determined, and the CA results were consistent with the wax distribution found by the TD-NMR analysis.

Archaeological wood of 13 excavated oak piles from five historical bridge generations in Bavaria, dated from 1447 to 1787, was investigated by means of light microscopy (LM) and cellular UV-microspectrophotometry (UMSP) to study the ageing and natural resistance of the excavated wood. Furthermore, the mineral content of the ancient wood was determined to evaluate the impact of mineral inclusions on microbial resistance, tested using a mini block fungal test. The LM and UMSP analyses revealed well preserved cell wall structures and no significant modification of the lignin composition and distribution in predominant parts of the piles. Slight microbial decay caused by soft rot and erosion bacteria was only detectable at the outermost millimetres of individual piles. The fungal mini block tests yielded mass losses of ancient oak samples between 15% and 30%, independent of their analysed mineral content. The results provided evidence that the fungal resistance of the investigated ancient wood is mainly determined from the special soil with its high mineral content.

To preserve natural forests, forest plantations with fast-growing species are promoted. In the present work, the heartwood durabilities of Dyera costulata , Neolamarckia cadamba and Khaya ivorensis , from both plantations and natural forests, have been tested in comparison with rubberwood in laboratory and above-ground tests against the subterranean termite Coptotermes curvignathus . Both young trees from forest thinning and mature trees were tested. The results show that there is no significant difference in weight loss between planted trees and trees from a natural forest. The results were also compared with those of rubberwood.

The properties of oriented bamboo scrimber boards (OBSB) have been investigated at three density levels (0.8, 0.9, and 1.0 g cm 3 ), while the boards were made from moso bamboo ( Phyllostachys pubescens ) grown in Taiwan (T-OBSB) and China (C-OBSB). A non-destructive technique (NDT), ultrasonic-wave velocity ( V u ) measurements were applied and the dynamic modulus of elasticity (MOE dyn ) was calculated. Moreover, static modulus of elasticity (MOE), modulus of rupture (MOR), profile density distribution, internal bond strength (IB), springback (SB), and dimensional stability were determined based on traditional methods. Positive linear relationships between density and V u , MOE dyn , MOE and MOR were observed, no matter if the measurements were done parallel (//) or perpendicular (⊥) to the fiber direction of the OBSBs. Moreover, V u (//) , MOE dyn,u(//) , MOE (//) , and MOR (//) were higher than V u (⊥) , MOE dyn,u(⊥) , MOE (⊥) and MOR (⊥) . C-OBSB had slightly lower V u (//), V u (⊥) , MOE dyn,u(//) and DMOE u(⊥) values than T-OBSB. T-OBSB had higher MOE (//) , MOE (⊥) and MOR (//) than C-OBSB, but less MOR (⊥) . The profile density distribution of high-density T-OBSB showed singnificant data scattering. The profile density distribution of C-OBSB was homogeneous at all density levels. IB and SB data are directly proportional to density, but water absorption, thickness swelling and volumetric swelling are inversely proportional to density. T-OBSB has better bonding and strength properties, and dimensional stability than C-OBSB.

The chemical properties, dimensional stability, mechanical strength and termite resistance of urea formaldehyde (UF) bond rubberwood (RW) particleboard (PB) were assessed after a two-step oil heat treatment (OHT). The PB was immersed in palm oil before heating to 180, 200, and 220°C in a laboratory oven for 2 h. Anti-swelling efficiency (ASE) and water repellency efficiency (WRE) as well as bending (MOE, MOR) and internal bonding strength (IB) were determined. Resistance against a subterranean termite, Coptotermes curvignathus Holmgren, was tested. The degradation of hemicelluloses and cellulose, that are mainly responsible for wood wetting processes, was confirmed by Fourier transform infrared (FTIR) spectra. Formation of an elevated cross-linking density in lignin also contributed to the dimensional stability, where 93.6% ASE and 46.3% WRE were achieved in the samples treated at 220°C. Mechanical properties of treated samples were inferior to the control samples due to hemicelluloses degradation and breakage of the UF bonding network. A significant improvement in termite resistance has been found in the treated samples.