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Xuan paper is a classic Chinese handmade paper with long history and has been listed as a national intangible cultural heritage since 2009, which is mainly composed of wingceltis (Pteroceltis tatarinowii) phloem fibers and straw fibers. Due to the unique properties of wingceltis phloem fibers, Xuan paper is spotless, flexible, stable, and durable, and is widely used by calligraphers, painters, or museums for restoration. Uncovering the variation of phloem fiber properties throughout the traditional pulping process is essential for a comprehensive understanding of the special performance of Xuan paper. In this study, chemical, structural, and mechanical characterization was conducted on the raw bark (phloem fiber), treated phloem fiber, and pulp fiber at different steps of the traditional pulping process for making Xuan paper. The compositional and morphological analysis revealed the effective removal of the matrix polymers, while the phloem fiber almost retained the original fiber structure during the traditional process. Wide-angle X-ray scattering results indicated that the relative crystallinity of cellulose increased and crystals expanded after the lime cooking and exposure to sun and rain. Compared to the raw phloem fibers, the ultimate stress and tensile stiffness of pulp fibers decreased by 24.35% and 9.79%, respectively. However, the fracture strain and fracture toughness of pulp fibers showed a drastic promotion, which might be attributed to the energy dissipation caused by the cell wall structure, the breaking and reforming of hydrogen bonds, and the slipping and rearrangement of cellulose microfibrils. [ABSTRACT FROM AUTHOR]

Thermal modification is widely applied to improve moisture dynamics of wood, however often decreasing the mechanical strength. It is therefore required to enhance the mechanical strength of thermally modified timber (TMT), for example by impregnation with adhesives. Specimens, cut from Douglas-fir, were thermally modified (TM) either after phenol formaldehyde (PF) resin impregnation (IM-TM) or before (TM-IM). The microstructural and chemical properties were investigated with SEM and FTIR. Compressive stress, as one of the important mechanical properties, was measured using a universal testing machine, while strain distribution was recorded with digital image correlation (DIC). The results show that the compressive stress of TM specimens can be enhanced significantly by PF resin impregnation. Compressive stress differences between IM-TM and TM-IM specimens are small despite of the larger amount of resin in TM-IM specimens. Thermal modification decomposes part of the PF resin in the cell lumens and promotes chemical reaction between the PF resin and wood. PF resin improves the stiffness and ductility of the wood cell wall, resulting in smaller strain and homogenous distribution thereof. These factors lead to high compressive stress of IM-TM and TM-IM specimens. Although PF resin impregnation contributes to narrowing strain accumulation in earlywood of TM specimens, control specimens have the smallest strain ratio between earlywood and latewood. The findings of this study are helpful for optimizing the cost effective thermal-impregnation technology of producing TMT with improved compressive stress. [ABSTRACT FROM AUTHOR]

To investigate effects of furfurylation on interactions between moisture sorption and humidity conditioning of wood, Pinus spp. wood was impregnated with furfuryl alcohol solution. After oven drying, furfurylated wood and untreated wood were subjected to two environments where initial relative humidity (RH) was, respectively, about 60% and 80% at 25 °C. Dynamic mass and RH were continuously recorded with a self-assembled device. Furfural resin polymerized in cell walls, cell lumina and some pits, which caused mass gain and cell wall bulking. Furfurylation weakened humidity conditioning performance and hygroscopicity of wood, and the RH increased by over 20.7% while moisture content decreased by over 33.6% for furfurylated wood compared to untreated wood after conditioning at initially about 80% RH. Humidity conditioning process was generally divided into four stages according to changing rate, where RH exhibited sharp increase, slow increase, slight decrease and sub-equilibrium, respectively. Moisture content showed a negative linear relation with RH in the first three stages. This was a result of combined effects of the pressure from water vapor gradient and moisture content gradient, the temperature changes during sorption, the hindrance from capillary systems and attraction of other water molecules. The interaction rate between humidity conditioning and moisture sorption was decelerated for blocking of water passages, reduction in sorption sites and hydrophobicity increase due to furfurylation. Over 45.2% decrease in moisture change rate with RH was caused by furfurylation in the first stage. The study can help in understanding the effects of furfurylation on interactions between moisture sorption and humidity conditioning of wood and facilitate better application of modified wood in human settlement practically. [ABSTRACT FROM AUTHOR]

Silica/montmorillonite nanoparticles (silica/MMT-NPs) were synthesized by sol–gel method for stabilizing paraffin oil Pickering emulsion (oil-in-water) which was used for wood treatment. The self-condensation during silica/MMT-NPs preparation resulted in intercalation rather than delamination for MMT, leading to increased droplet size of Pickering. The droplet size increased with the increasing concentration of silica/MMT-NPs owing to the aggregation of nanoparticles. After Pickering treatment, a rough surface could form via silica/MMT-NPs deposition in cell lumens, which was covered by paraffin to attain hydrophobicity. Moreover, paraffin penetration and pore-filling of hybrids in cell walls were beneficial for decreasing water absorption, and nanoparticles improved the thermal stability. These findings indicated a synergistically effect provided for improving properties of treated woods via one-step method. [ABSTRACT FROM AUTHOR]

Thermal treatment (TMT) impacts the mechanical strength of wood. Investigating the compressive strength (CS) of thermally treated wood with variable growth ring orientation is helpful to better understand the effect of TMT on mechanical performance of wood. Specimens, cut from spruce wood, were classified according to two growth ring orientations, namely 10 degree (fc10) and 40 degree (fc40), these two situations commonly exist in practice. Six replicates from each type were thermally treated with saturated steam at two different temperatures (180 °C and 210 °C), respectively. Dimensional changes, chemical composition, and microstructure of the specimens were monitored before and after TMT using FTIR spectroscopy and optical microscopy. Compressive stress of specimens was determined and, simultaneously, strain distribution was recorded using digital image correlation. The results show that TMT caused mass loss and shrinkage in tangential and radial directions. Changes in chemical composition were mainly due to hemicellulose degradation. For both treated and untreated samples, the CS perpendicular to the grain and deformation of fc10 samples were higher and smaller than that of fc40 samples, respectively. TMT results in brittle wood tissue, which hampered strain transfer along growth rings and changed failure modes of samples. Mechanical strength of fc40 samples was sensitive to be impacted by TMT. Prior to TMT, failure modes of fc10 and fc40 specimens were shear deformation and growth ring buckling, respectively. After TM, failure modes of all specimens changed to shear failure parallel to growth ring boundaries. These structural changes mainly occurred in earlywood. The output of this work contributes to the effective application and scientific evaluation of mechanical performance of TMT wood by considering growth ring orientations. [ABSTRACT FROM AUTHOR]

Laminated veneer lumber (LVL) is an important engineered wood product. Internal structural changes have a substantial influence on the mechanical performance of LVL. To investigate the relationship between the internal structural changes and the compressive strength, poplar LVL layering is manufactured by taking into account the veneer lathe checks, namely lathe checks both facing inwards (TLLT), lathe checks both oriented outwards (LTTL) and lathe checks in one layer facing outwards (LTLT). Macroscopic compressive strength of the samples is measured using a universal testing machine. Microscopic internal structural changes are periodically recorded with X-ray CT when the samples are compressed using a load cell. The results show that the compressive strength of LTLT is significantly higher than that of LTTL and TLLT types of LVL. During the compression test, density increase in the samples is non-homogenous. There is a minor increase in density of the glue line, while this is larger in regions with a low density. Density increase is mainly induced by collapse of large vessels. However, the presence of phenol formaldehyde resin can enhance the resistance of vessels against collapse. Structural changes, i.e., vessels collapse and collapse propagation, are likely to occur in locally heterogeneous regions. Propagation of collapsed vessels is more frequently observed in regions where large vessels are contiguous. [ABSTRACT FROM AUTHOR]

Both medium density fiberboard (MDF) and oriented strand board (OSB) are increasingly used in construction, yet when exposed, water sorption can cause internal structural changes, as such decreasing mechanical strength and increasing decay risk. It is, therefore, essential to understand the interaction between structural changes and water sorption of MDF and OSB. Detailed water sorption behavior and related structural changes in two types of MDF and two types of OSB were periodically monitored using a gantry-based X-ray CT scanner. Water sorption causes local swelling in MDF, resulting in reduced swelling or even shrinkage in neighboring regions. Then again, local shrinkage can increase water resistance and possibly decrease water content locally. Obviously, local swelling results in structural changes. Such structural changes predominantly seem to appear in the transition area between high and low porosity regions. Structural changes, such as glue bonding detachment and cracking, could facilitate water intake in both MDF and OSB. For the studied T-MDF and OSB-A, the relative position of wood fibers/strands and the volume of the voids hardly changed during water sorption, which probably contributes to the decrease in water sorption along newly formed cracks and voids induced by structural changes. [ABSTRACT FROM AUTHOR]