Volume 72, Issue 4

A novel norneolignan glycoside ( 1 ), categorized as an unusual 7-noraryl-4′,7-epoxy-8,5′-neolignan glycoside, four new phenolic glycosides ( 2–5 ), and a known neolignan glycoside ( 6 ) have been isolated from the ethanolic extract of the stems of Viburnum fordiae Hance. Dried stems of V. fordiae were extracted with 95% ethanol, and the concentrated extract was portioned successively with petroleum ether, ethyl acetate and n -butanol. The n -butanol portion was subjected to the macroporous resin HPD-100, silica gel, octadecyl SiO 2 , MCI gel and Sephadex LH-20 columns to obtain six compounds. Their structures including absolute configurations were determined by spectroscopic data [ 1 H and 13 C nuclear magnetic resonance (NMR), total correlation spectroscopy (TOCSY), heteronuclear single quantum coherence (HSQC), heteronuclear multiple-bond correlation (HMBC) and optical rotatory dispersion (ORD)] and chemical methods.

The mechanism of lignin dehydrogenative polymerization (DHP), made by means of horseradish peroxidase (HRP), was studied in comparison with other plant peroxidases. Interestingly, HRP is efficient for guaiacyl type polymer formation (G-DHPs), but is not efficient in the case of syringyl type DHPs (S-DHPs). It was previously demonstrated that lignification-related Arabidopsis thaliana peroxidases, AtPrx2, AtPrx25 and AtPrx71, and cationic cell-wall-bound peroxidase (CWPO-C) from Populus alba are successful to oxidize syringyl- and guaiacyl-type monomers and larger lignin-like molecules. This is the reason why in the present study the DHP formation by means of these recombinant peroxidases was tested, and all these enzymes were successful for formation of both G-DHP and S-DHP in acceptable yields. CWPO-C led to S-DHP molecular size distribution similar to that of isolated lignins.

A simple and efficient method was developed for preparing medium density fiberboard (MDF) reinforced with chitosan via the traditional hot-press manufacturing process. The mechanical and dimensional properties of the MDF were investigated as a function of the chitosan amount. At the 4% level of added chitosan, the MDF reached the optimal performance and met completely the requirements of the Chinese national standard GB/T 11718-2009. Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD) characterizations revealed that wood fibers and chitosan might interact with each other through the formation of hydrogen and amide bonds during the hot-pressing process. The fracture surfaces of the MDFs are indicative for strong bonds at the interface, which explain the excellent MDF performance.

A novel process has been developed for manufacturing poplar wood scrimber boards (SBs), in the course of which thick veneers are produced first and then the oriented wood fiber mats (OWFMs) are fabricated in a pilot scale fluffing machine. A low molecular weight phenol-formaldehyde (PF) resin is applied for gluing and the cold-prepressing of the mats is followed by hot-curing between 120 and 130°C for 12 h. The mechanical properties and dimensional stability of the SB OWFM s were measured. The new process resulted in significantly better mechanical properties of SB OWFM s compared with those of raw wood and other poplar wood-based composites. All data including the dimensional stability of SB OWFM s increased with increasing density.

Beech wood has been treated by impregnation followed by heating at various temperatures with solutions containing citric acid (CA) or tartaric acid (TA) alone or in combination with glycerol (G), i.e. with G+CA and G+TA. The resulting modified woods were tested in terms of resistance to leaching, durability and dimensional stability. These properties are improved as a function of heating temperature, which leads to higher levels of poly-esterification involving grafting onto wood simultaneously with thermal degradation of wood. Dimensional stability of all treated wood was increased, but glycerol does not have a positive effect with this regard. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy contributed to understanding the effects of the different treatments. In situ polymerization of G+TA at 140°C increased the bending resistance, while G+CA polymerization does not compensate notably the mechanical weakness induced by thermal degradation of wood at higher temperatures. However, G+CA treatment is more efficient regarding leaching and decay resistance, than that with G+TA.

The effects of the penetration of polymeric diphenyl methane diisocyanate (pMDI) on the chemical structure as well as the static and dynamic mechanical properties of wood cell walls (CWs) were investigated by atomic force microscopy with infrared radiation (AFM-IR) and nanoindentation (NI). Results indicated that the possible penetration of some pMDI molecules into the CW affected the mechanical properties of wood CW significantly. The physical and chemical interactions between pMDI and CW may strengthen the connections between the cell-wall materials and thus improved the static elastic modulus and short-term creep resistance of the CW. The elastic modulus ( E r ) of CWs was increased from 16.5 to 17.7 GPa; the creep ratio of the CWs decreased by 15% after the penetration of pMDI. Dynamic NI properties indicated that the effective penetration of pMDI had a positive effect on the reduced storage modulus ( E r ′), whereas it negatively affected the loss modulus ( E r ″) and the damping coefficient (tan δ ) of wood CW in a large frequency scale.

Southern pine ( Pinus spp.) sapwood samples were impregnated with silica sols with known zeta potential and particle size distribution at various pH values (3, 5, 7, 9, 11 and 13) to produce wood-silica composites (W Si Cs). The morphological and chemical properties of the composites were evaluated by scanning electron microscopy-energy dispersive X-ray (SEM-EDXA) and Fourier transform infrared (FTIR) spectroscopy. The overall performance of the composites was characterized by X-ray diffraction (XRD) and thermogravimetric (TG) analysis, and dynamic wettability tests, and their dimensional stability and surface hardness were also investigated as well. The pH value of the sols had a remarkable effect on the distribution of zeta potential and colloidal particle size, and on their penetration and distribution in the wood. The composites produced at pH 5 and pH 11 show relatively better impregnability and overall properties. In the first case the compatibility with the wood pH (ca. 5) is relevant, and at these pH values are the sol’s particle sizes low. Sols with pH around 13 resulted in inferior properties, such as increased water absorption, high thermal degradation and poor dimensional stability. This could be ascribed to wood degradation under high alkaline conditions. The results were discussed in view of the colloidal particle redistribution and the interaction between silica sol and wood.

Microfibril angle (MFA) is a major structural variable that describes the fine structure of the cell wall in wood. In this study, the relationships between the MFA of the S2 layer and the Poisson’s ratios and Young’s moduli (modulus of elasticity, MOE) of five wood species (agathis, larch, Japanese cedar, Japanese cypress and ginkgo) were determined by analyzing both their normal and compression woods. It was found that both the longitudinal MOE (MOE L ) and MOE of the cell-wall substance (MOE W ) decreased with increasing MFA, while the peaks values of Poisson’s ratio ( ν LT ) were obtained at MFAs of ≈25°. In particular, at MFAs lower than 25°, the ν LT increased with increasing MFA, and the opposite relationship was observed at MFA values exceeding 25°. This trend is in good agreement with the estimates obtained based on the theory of orthotropic elasticity with the underlying assumption that the orthotropic elasticity of materials is MFA-dependent. Hence, the MFA parameter incorporated into the orthotropic elasticity theory is useful for determination of the Poisson’s ratio.

Bamboo fiber (BF)-reinforced polypropylene (PP) composites (BPCs) have been investigated and it was shown by differential scanning calorimetry (DSC) that BF is a nucleation agent and accelerates the crystallization rate of the PP matrix. Numerical analyses according to Avrami, Avrami-Ozawa, and Friedman described well the nucleation mechanism, the crystallization rate and the activation energy for the non-isothermal crystallization behavior of BPCs, respectively. The Avrami approach indicated that BF as a reinforcement significantly changed the crystal growth mechanism of PP matrix during the cooling process. Based on the Avrami-Ozawa method, a lower cooling rate can achieve a certain relative crystallinity degree within a time period. According to the Friedman method, the activation energies of BPCs were lower than that of neat PP below a relative crystallinity of 35%, when the BF content was more than 60%.

Alseodaphne is a genus of timber trees (ca. 40 spp.) belonging to the Persea group of the Lauraceae. It is widely distributed in tropical Asia, but is often confused with Dehaasia and Nothaphoebe , and the systematics of the genus is unclear. Here, the complete chloroplast genome sequences of A. semecarpifolia will be reported, the type species of Alseodaphne , and two China-endemic species, A. gracilis and A. huanglianshanensis . The three plastomes were 153 051 bp, 153 099 bp and 153 070 bp, respectively. Comparative genomic analyses indicate that the three Alseodaphne plastomes have similar genome size and those are very different with previously published plastomes of Lauraceae in length. The length difference is directly caused by inverted repeats expansion/contraction. Four highly variable loci including psbD-trnM , ndhF - rpl32 , rpl32 - trnL and ycf1 among the three Alseodaphne species were identified as useful plastid candidate barcodes for Alseodaphne and Lauraceae species. Phylogenetic analyses based on 12 complete plastomes of Lauraceae species confirm a monophyletic Persea group comprising species of Alseodaphne , Phoebe , Persea and Machilus .