Band 73, Heft 3

The orthotropic viscoelastic creep (VEC) at a constant moisture content (MC) and mechano-sorptive creep (MSC) during the adsorption process were examined for Chinese fir ( Cunninghamia lanceolata ) under tension at 20, 40, 60 and 80% relative humidity (RH) (30°C). Free swelling was performed on matched specimens based on the strain partition assumption to better understand the characteristics of the mechano-sorptive (MS) phenomenon. Expansion, elastic and time-dependent creep behaviors of radial (R) and tangential (T) specimens were affected by the MC to a higher degree than those of the longitudinal (L) specimen. A higher proportion of elastic strain in total strain was found in the L specimen as compared with transverse specimens, regardless of VEC and MSC. The RH level had a greater effect on relaxation behavior in the L specimen for MSC. According to the three tests, expansion mainly dominated the creep strain during adsorption, especially for the L specimen. The MS strain exerted more influence on transverse specimens and had less contribution to the L specimen. Moreover, under all RH isohume (RHI) conditions, the unstable state contributed to MS strain diminishing as MC approached equilibrium moisture content (EMC). A shorter adsorption time to a new equilibrium state was achieved at the expense of intensifying the unstable state of the wood cell wall.

To clarify the viscoelasticity of earlywood (EW) and latewood (LW) within different growth rings of Chinese fir, the following data were determined: absolute dry density, percentage of tracheid cell wall, microfibril angle (MFA), modulus of elasticity (MOE), storage modulus (E′) and loss modulus (E″) within the 3 rd and 6 th growth rings (in heartwood, hW) and the 14 th and 18 th growth rings (in sapwood, sW). The E′ and E″ data were obtained by dynamic mechanical analysis (DMA) between −120°C and 120°C, at a heating rate of 1°C min −1 at the frequencies of 1, 2, 5 and 10 Hz under a dynamic load amplitude of 10 μm. All measured data were different between EW and LW. In the same growth ring, LW had a greater MOE and larger E′ than those of EW due to the higher density of LW. The MOE and E′ increased for both EW and LW with increasing tree age. The variation of MFA in different growth rings of EW influenced the MOE and E′. Both density and the MFA affected the MOE and E′ in LW. The profiles of E″ plots vs. DMA temperature reveal two maxima around −12°C (β mechanical relaxation process, βMRP) and 12°C (αMRP). The LW-MRP maxima are higher than those of EW, but in both cases increased with tree age. No frequency dependence was seen for the αMRP, whereas the loss peak temperature (LPT) of the βMRP increased with increasing frequency of DMA. Almost no difference in αLPT was observed between the four EW growth rings, and their βLPTs were similar. The LW-αLPT was almost the same in the four growth rings, but the hW-βLPT was higher than that of sW. In addition, the apparent activation energy (ΔH) of the hW-βMRP was greater than that of sW in both EW and LW, and the EW data>LW data in individual growth rings. These differences can be explained tentatively that hW and EW contain more extractives than sW and LW, and the deposited of extractives limit the motion of molecular segments within the cell walls.

Off-axis compression tests (OACT) were conducted on solid wood from six tree species, and the relationship between the off-axis compressive strength (OACStr) and the off-axis angle was predicted under the conventional Hill-type quadratic failure conditions, off-axis special failure conditions, and under a condition proposed in this study, which contains terms of interaction between the normal and shear stresses. The latter was an effective approach for accurately predicting the OACStr, although the physical meaning of the interaction terms is not yet clear. Under the off-axis specialized conditions, the approach was simple and accurate for predicting the OACStr, which includes the 45° off-axis angle.

Naturally occurring knots reduce the mechanical strength of wood. Veneers from sugi ( Cryptomeria japonica ) served as research material to study the effect of knots and holes. Veneer samples were first subjected to a three-point bending test to obtain measured modulus of elasticity (MOE) values. Then, near-infrared (NIR) hyperspectral imaging (HSI) was used to construct a prediction model and map the predicted MOE values. This is the first attempt for MOE prediction from the entire veneer surface based on NIR-HSI technology, while the mathematical part relies on chemometrics and cross-validation partial least squares regression (CV-PLSR). Maps of MOE prediction values could distinguish between latewood (LW) and earlywood (EW), as well as between a sound knot and a dead knot.

The objective of this work was to analyze the natural occurrence of slip planes (SPs) in Eucalyptus grandis wood fibers in terms of their characterization, distribution in the stem and associations with other wood characteristics. A 28-year-old E. grandis was studied, whose stems were sampled in the base-top direction. The longitudinal compressive stress regions (LCompSR, in the inner part of the stem) and longitudinal tensile stress region (LTensSR, in the outer parts of the stem) were separately considered. The following parameters were measured: microfibril angle (MFA), slip plane angle (SPA), number of SPs per millimeter (SP mm −1 ), slip plane index (SPI) and the relative abundance of SP in the fiber. The SPAs differ only slightly between LCompSR (76°) and LTensSR (77°). The base of the stem, which supports a larger mass, contains the most SPs and the number of SPs decreases from the base to the top. In the LCompSR, the SPI reduction was from 21 to 8%, and in the LTensSR, from 18 to 7%.

Reliable wood identification and proof of the provenance of trees is the first step for combating illegal logging. DNA barcoding belongs to the promising tools in this regard, for which reliable methods and reference libraries are needed. Machine learning approaches (MLAs) are tailored to the necessities of DNA barcoding, which are based on mathematical multivaried analysis. In the present study, eight Dalbergia timber species were investigated in terms of their DNA sequences focusing on four barcodes (ITS2, mat K, trn H- psb A and trn L) by means of the MLAs BLOG and WEKA for wood species identification. The data material downloaded from NCBI (288 sequences) and taken from a previous study of the authors (153 DNA sequences) was taken as dataset for calibration. The MLAs’ effectivity was verified through identification of non-vouchered wood specimens. The results indicate that the SMO classifier as part of the WEKA approach performed the best (98%~100%) for discriminating the eight Dalbergia timber species. Moreover, the two-locus combination ITS2+ trn H- psb A showed the highest success rate. Furthermore, the non-vouchered wood specimens were successfully identified by means of ITS2+ trn H- psb A with the SMO classifier. The MLAs are successful in combi- nation with DNA barcode reference libraries for the identification of endangered Dalbergia timber species.

Chemical analysis of the bark from four Hyrcanian forest species, Pterocarya fraxinifolia , Alnus subcordata , Gleditsia caspica and Parrotia persica were performed, and their total phenol contents, and antioxidant and chelating activities were evaluated. The greatest total phenol content (TPhC), 54.3% in dry extract, was detected in P. fraxinifolia bark and the lowest one in G. caspica bark with 4.5%. The 50% inhibitory concentrations (IC 50 ) in the radical-scavenging assay against DPPH radicals in bark acetone extracts of P. fraxinifolia , A. subcordata , G. caspica and P. persica were 0.17, 0.21, 13.35, 0.19 mg ml −1 , respectively. In the metal-chelating activity system, G. caspica extract demonstrated significant activity. Pterocarya fraxinifolia , A. subcordata and P. persica bark acetone extracts revealed a high potential for inhibition of DPPH radicals due to high amounts of phenolics. Superior health benefits can be expected from the compounds syringol, 4-vinylguaiacol, tyrosol, chavicol, resorcinol, hydroquinone, vanillin, rheosmin and acetophenone. Gleditsia caspica was found to have significant chelating activity due to isoeugenol.

Cooperage woods are rich in volatile compounds responsible for pleasant aromas described as coconut, vanilla, spice, caramel, toasty, etc. In the present work, the hot water extraction under 103 bar pressure of natural flavoring compounds from cooperage wood residues is described. It was possible to obtain aqueous extracts rich in diverse volatile compounds from the following wood species: oak ( Quercus alba and Quercus petraea ), chestnut ( Castanea sativa ), cherry ( Prunus avium ), false acacia ( Robinia pseudoacacia ) and lenga ( Nothofagus pumilio ), while the concentration of the components is similar to that obtained with organic solvents. The gas chromatography-mass spectrometry (GC-MS) analysis of aqueous extracts shows a wide spectrum of natural flavoring compounds, the composition of which are species dependent. The extracts exhibit antioxidant properties. Water extraction under subcritical conditions offers the possibility of a sustainable recovery of natural flavorings and antioxidant compounds from cooperage woods, which are well suited for application in the food industry.

Soy and corn gluten proteins are common ingredients in adhesives and resins together with kraft lignin and condensed tannin. The relative contribution of these additives to volatile organic compound (VOC) emissions in the course of processing hardwood veneer products was evaluated. Press emissions were captured and separated into condensate and gaseous fractions. High-performance liquid chromatography (HPLC) was employed to characterize aldehydes in condensate and gaseous fractions, while GCMS served for identification and quantitative determination of the compounds in the gas phase. Aldehydes dominate the press emissions with both proteinaceous binders producing significantly higher formaldehyde (FA), acetaldehyde (AcA) and hexaldehyde (hexA) emissions compared to pressed veneer without additives. Other aldehydes, including valeraldehyde and propionaldehyde were also captured, but in relatively lower amounts. In contrast, lignin as a binder led to lower FA content in press emissions, whereas tannin significantly reduced contributions of FA, AcA and other aldehydes. VOC emissions from plywood panels during chamber testing were similar to compounds evolved on hot-pressing.

A new type of plastic-film-reinforced pliable decorative sliced veneer (PF-RP-DSV) for wood product surface finishing was developed. The plastic film served as both the reinforcing and adhesive material. Consequently, the veneer did not need adhesives during preparation and wood surface finishing. However, the interface bonding strength between the two composite was low and the curling deformation was serious because of the large difference in polarity and thermal expansion coefficient of the two materials. In this paper, low-density polyethylene (LDPE) plastic film (PF) and a decorative sliced veneer (DSV) from Brachystegia laurentii were treated with plasma to improve interfacial adhesion and reduce curling deformation. The plasma-modified (PM) PF and DSV increased the bonding strength of the resulting composites and generated an evenly distributed quasi glue layer between the two materials. The PM-PF had more influence on the interface bonding strength than the PM-DSV. This effect can be attributed to the great decrease in crystallinity and increment of oxygen-containing functional group in the PM-PF. The veneer from B. laurentii can achieve good gluing performance and small curling deformation at a hot pressing temperature of 120°C, pressing time of 150s and pressing at 0.6 MPa.