Volume 76, Issue 9

Wood characteristics of trees grown in agroforestry systems are little studied, even if growth conditions are different from conventional stands. This work aimed to determine the impact of the agroforestry system on the heartwood formation process of hybrid walnut ( Juglans regia × nigra ) trees, especially the resulting extractive contents. Ethanol and water extractions were successively performed on wood samples taken across the diameter of the trunk of agroforestry (AF) and forest (FC) walnut trees to get the radial distribution of the extractive contents. All the samples were analyzed by NIR-spectroscopy and NIR-hyperspectral imaging. Statistical discriminant models were developed to classify the samples from both different forestry systems, according to their chemical composition. The results indicated no significant differences between the values of extractive contents of AF and FC walnut woods, whatever the radial position. At the intra-tree scale, the quantity of extractives does not increase significantly with the radial position. However, partial least squares-discriminant analysis (PLS-DA) regression models, developed with NIRS measurements, showed that significant chemical differences exist between AF and FC trees, especially for extractives composition and lignin content. This allowed to classify wood specimens from both forestry systems. These results were confirmed by hyperspectral camera analyses.

Eucalyptus globulus Labill is an important raw material for pulpwood for which low lignin content and high S/G ratios are important parameters. This work shows a highly significant positive and strong correlation between S/G ratio and acid-soluble lignin (ASL) content among E. globulus trees. Although significant, the negative correlation between the S/G ratio and Klason lignin is weak, and there is no correlation with total lignin content. The Klason residue has a lower S/G ratio than that of the original wood. This suggests that the contribution of the S units to the solubilisation of lignin in acidic conditions is not limited to the S units but also to the G units. This effect becomes more pronounced as the percentage of S units increases.

The accelerated creep behavior during water desorption of wood was modeled on the Kohlausch–Williams–Watts (KWW) function and free volume concept. Assuming that the water desorption rate dmc/dln t $\text{dmc/dln\,t}$ is involved in the creation of a new free volume, the net creep compliance during desorption J du ( t ) was obtained as  ln J du ( t ) = β c ln t − β c ( ln τ c 0 + k f   dmc / d ln t ) + ln J c ∞ $\mathrm{ln} {J}_{\text{du}}\left(t\right)={\beta }_{\text{c}} \mathrm{ln} t-{\beta }_{\text{c}}\left(\mathrm{ln} {\tau }_{\text{c}0}+{k}_{\text{f}}\,\text{dmc}/\text{d}\mathrm{ln} t\right)+\mathrm{ln} {J}_{\text{c}\infty }$ where β c , τ c0 and J c∞ are the stretching parameter, characteristic time of the relaxation, and long-time asymptote compliance at a constant moisture content (mc) equal to the initial mc of the accelerated creep, respectively, and k f is the coefficient of the water desorption rate. These parameters were determined by simulation using experimental data and literature results and were found to be reasonable. The simulation results agreed well with the experimental ones. This verifies the validity of the model and its derived equations.

Strength loss caused by fungal degradation is an important factor to be considered during tree-stability assessment. Detailed information on the relationship between static mechanical properties in relation to the heterogeneity of density and dynamic mechanical parameters of wood degraded by the soft-rot fungus Kretzschmaria deusta can improve the understanding of its decay process and the interpretation of results obtained from stress-wave-based non-destructive methods used for tree-stability assessment. This research presents density profiles of artificially inoculated samples with K. deusta and static mechanical properties of green beech wood in relation to physical parameters (density, moisture content, vibroacoustic parameters). A statistically relevant difference ( p  < 0.01) in the variability of density distribution between degraded and intact samples was proved. Relevant correlations were proved among modulus of rupture ( M O R $MOR$ ), mass loss and variability longitudinal density distribution. A strong linear relationship between M O R $MOR$ and static modulus of elasticity ( M O E $MOE$ ) of degraded and intact specimens was presented. A strong relationship was also proved between M O R $MOR$ and dynamic parameters (dynamic modulus of elasticity ( M O E D $MOED$ ) and stress-wave velocity in longitudinal direction ( c l ${c}_{l}$ )). M O E D $MOED$ showed a stronger correlation to M O R $MOR$ than c l ${c}_{l}$ proving the importance of density in assessing strength loss through non-destructive methods.

Fast-growing wood usually exhibits dimensional instability and inferior mechanical strength, which severely obstructs its wide application. To improve the dimensional stability and mechanical strength, biomass-derived furfuryl alcohol combined with polyethylene glycol (PEG) was vacuum-impregnated into wood hierarchical structures, causing cell wall bulking and porosity reduction. Furfural resin and PEG distributed in cell lumina, cell walls and middle lamella regions indicated by analyses of scanning electron microscope and fourier transform infrared spectroscopy. Wood porosity was generally reduced and the specific surface area decreased by over 65% analyzed by the nitrogen absorption. Consequently, wood hydrophobicity and dimensional stability were highly improved, and the water absorption and volumetric change decreased by over 55% and 78%. The flexural strength and modulus elasticity were improved by over 49% and 46%. Furfural resin helped the fixation of PEG in wood and significantly reduced PEG leaching. PEG with flexible linear molecular structure formed interpenetrating polymer network in wood hierarchical structures with furfural resin and reduced self-crosslinking of furfural resin. Accordingly, the impact toughness of compound modified wood increased by 39% compared with solely furfurylated wood. This study provided efficient and sustainable concepts to facilitate better industrialized application of wood furfurylation and improve service value of fast-growing wood.

This study examined the influence of lignin dehydrogenation polymer (DHP) deposition on the morphology and properties (e.g., tensile property, thickness, and water content) of cellulose microfibril-based gels. Cellulose microfibrils were isolated from wood powder and a stable hydrogel with a layered structure after treatment with 8% (w/v) NaOH were produced. Gels were artificially lignified of by repeated immersion in an ethanol solution containing lignification agents (coniferyl alcohol, horseradish peroxidase, and H 2 O 2 ) and evaporating the ethanol under vacuum. The use of ethanol allowed DHPs to penetrate the gel, and the deposition of DHPs was achieved by evaporating ethanol under reduced pressure. With increase in the number of lignification cycles to 10, the thickness and water content of the microfibril gels decreased and the ratio of DHP to cellulose, elastic modulus, and tensile strength increased. These results indicate that the elastic modulus of the gels improved not only because of the decrease in water content, but also because of the constrained motion of the microfibril network due to of DHP deposition. The reported artificially lignified cell wall model will help improve the understanding of how lignification contributes to the mechanical strength of plant cell walls.

This study demonstrates that bio-based products of lignin depolymerisation can potentially replace common antioxidants and UV absorbers in the plastics and cosmetics industries. The kraft lignin Indulin AT was used to obtain low-MW lignin and monomers & oligomers rich in phenolic hydroxyl groups. Both thermo-oxidative stability and antioxidant activity significantly improved upon lignin depolymerisation. The results from oxidation induction time differential scanning calorimetry (OIT-DSC) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) measurements show that the lignin based depolymerisation products are comparable with commercial antioxidants like pentaerythritol-tetrakis-(3-(3,5-di- tert -butyl-4-hydroxyphenyl)-propionate) (Irganox 1010). UV/vis spectroscopy was investigated to confirm absorption of the depolymerisation products in the UVA and UVB range (280–400 nm).

Cellulose-based handmade paper records a substantial amount of historical data and promotes human civilization. Due to the complexity of its structure and external factors, the deterioration of paper in the restoration of ancient books cannot be completely stopped. Nonetheless, the lack of microstructure analysis of handmade paper limits the understanding of its aging mechanism and storage life-span. Herein, CP/MAS 13 C NMR method was used to estimate the cellulose types, crystallinity, average lateral fibril dimension (LFD), and the average lateral fibril aggregate dimension (LFAD), relying on integrated spectral fitting from C1, C4, and C6 regions, respectively. Consequently, cellulose I β crystals were predominant in all handmade paper samples. Based on the results of C4 and C6 regions by peak separation method, bast paper ( Kaihua paper and Yingchun paper) demonstrated a higher crystallinity than bamboo paper ( Yuanshu paper). Additional analysis of the C4 data revealed that bast papers exhibit larger cellulose microfibrils, and their LFDs and LFADs were greater than bamboo papers. Moreover, external stress of Wiley milling reduced the LFAD from the original 9 elementary fibrils to 4 elementary fibrils with unchanged LFDs.

This work presents the evaluation of the porosity by image analysis, the quantitative analysis of the cell morphology from images obtained by scanning electron microscopy (SEM) and the oxygen transmission rate (OTR) of natural corks of different visual quality grades. Due to the natural variability of cork stoppers, statistically significant differences could not be established in the porosity of the corks according to their commercial quality. However, the determination of the surface porosity coefficient by image analysis in the tangential and axial sections of the corks allowed us to distinguish between high, medium and low quality classes. The cells in the tangential section were shaped between circular and hexagonal, with very regular perimeters regardless of the cork quality. While the cells of the radial and axial sections showed a square and rectangular shape, with more irregular perimeters, mainly in the lowest quality corks and in the axial section. Corks commercially classified as “flower”, “second” and “third” had the lowest OTR values and presented a similar statistical distribution in their cell perimeters in the axial section. While the corks with higher OTR values (superior and fourth qualities) corresponded with those with greater cell perimeters and greater dispersion in their distribution.