•The anisotropy of cyclic compression experiments is performed under two main planes and different loading orientations.•The deformation process of microstructures for wood was investigated based on ...morphology observation.•A scalar damage variable is defined considering the degradation of the secant stiffness due to cracking.•The unified uniaxial constitutive models of wood under the cyclic compressive load are established.
A desirable objective is to develop a unified constitutive model for wood that can effectively capture its uniaxial cyclic compressive behaviors. To achieve this goal, quasi-static cyclic compression tests have been conducted to supplement the limited cyclic experimental data available. Observation of deformation within the cell structure led to the concluded that material failure resulted from the coalescence of shear or tensile microcracks and the rearrangement of cell structures in regions under compressive stress. Based on the experimental results, a secant stiffness degradation-based and an empirical-based unified constitutive model for wood were proposed. Comparison between the predicted and experimental results indicated that the two proposed models could accurately capture the nonlinear characteristics of wood.
Hydrolysis of lignocellulosic biomass is a crucial step for the production of sugars and biobased platform chemicals. Pretreatment experiments in a semi-continuous plant with diluted sulphuric acid ...as catalyst were carried out to measure the time-dependent formation of sugars (glucose, xylose, mannose), furfurals, and organic acids (acetic, formic, and levulinic acid) at different hydrolysis temperatures (180, 200, 220 °C) of one representative of each basic type of lignocellulose: hardwood, softwood, and grass. The addition of the acid catalyst is followed by a sharp increase in the sugar concentration. Xylose and mannose were mainly formed in the initial stages of the process, while glucose was released slowly. Increasing the reaction temperature had a positive effect on the formation of furfurals and organic acids, especially on hydroxymehtylfurfural (HMF) and levulinic acid, regardless of biomass type. In addition, large amounts of formic acid were released during the hydrolysis of miscanthus grass. Structural changes in the solid residue show a complete hydrolysis of hemicellulose at 180 °C and of cellulose at 200 °C after around 120 min reaction time. The results obtained in this study can be used for the optimisation of the hydrolysis conditions and reactor design to maximise the yields of desired products, which might be sugars or furfurals.
•Impregnated of wood with boron compounds could be used in thermoplastic composites manufacturing.•Samples with borax provided better mechanical properties compared to the samples with boric ...acid.•Boron compounds were still present without leaching out from wood flour surface in the matrix.•BbFRs increased LOI levels and amount of char residues during TGA analysis.•Burning rate of the composite with BbFRs at 40wt.% fiber loading was reduced by 50%.
The aim of this study was to investigate the effect of boron based fire retardants (BbFRs) and fiber loading on mechanical, fire and thermal performances of impregnated spruce wood flour (WF) filled high density polyethylene composites. For this purpose, WF was impregnated with solution of boric acid, borax and their mixture and dried before composite manufacturing. The effect of leaching on the limiting oxygen index (LOI) levels of samples with BbFRs was also investigated. Based on the test results, samples with borax provided better mechanical properties compared to the samples with boric acid, and showed 19% improvement on tensile modulus for 40% fiber loadings compared to control samples. In addition, BbFRs increased LOI levels and charring, and reduced the burning rate speed by 50%. Presence of boron after leaching was shown with SEM–EDX and LOI tests. It appears that especially borax could have potential to be utilized in wood plastic composites as fire retardants.
The aim of this study was to test caffeine – harmless to health and eco-friendly natural compound – as a potentially effective fungicide and insecticide for wood protection. Caffeine treatment of ...wood, using simple and cheap long-term dipping technology, was tested against the brown-rot fungus Rhodonia placenta and termite Reticulitermes flavipes. Fungi and insects can cause severe loss of functionality of wooden structures. The current search for of nature-friendly products is understandable in the context of the changing world environment. The experiment with caffeine-treated refractory Norway spruce (Picea abies) wood lasted for 16 weeks against the rot attack according to EN 113, and for 6 weeks against the termite attack according to EN 118. Mass losses of caffeine treated wood samples without ageing, caused by R. placenta and R. flavipes were small, only 1.4% or 0.5%, respectively. Results clearly suggested that caffeine is an alternative to commercial biocides, e.g., to the reference in wood well fixable Bochemit QB, containing boric acid and alkylbenzyldimethylammonium chloride. Caffeine was sensitive for leaching out from wood by water even in the presence of an additional hydrophobic protective layer. Based on the achieved results it is possible to recommend caffeine treatment as an environmentally friendly alternative for wood protection, but only in the interior or outdoor under roof area against termite attack and also against brown-rot fungi. Treatment with caffeine had no negative impact on the compression strength and colour of the spruce wood, while it improved surface wetting important for potentially follow-up coating or adhesive applications.
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•Eco-friendly caffeine treatment of spruce wood increased its resistance against termites.•Treatment is effective also against brown-rot fungi attack.•Simply, cheap long-term dipping technology was sufficient for caffeine wood protection.•Water-leachable caffeine was not fixed in the wood with tested hydrophobic layer.•This treatment is useful for preventive wood protection indoor or outdoor in roof area.
•Residual hemicellulose in cellulose sample favors nanofibrillation.•Non-derivatized holocellulose and cellulose samples produce good quality CNF.•Residual hemicelluloses improve stability of ...cellulose nanofibers.•Hemicelluloses, especially mannan, improve the mechanical properties of nanopaper.•Low lignin content does not compromise nanofibrillation of cellulose sample.
This paper investigated the impact of the amounts of lignin and hemicelluloses on cellulose nanofibers (CNFs). Birch and spruce wood were used to prepare holocellulose and cellulose samples by classical methods. To better assess the effect of the chemical composition on the CNF performance and simplify the process for CNF preparation, no surface derivatization method was applied for CNF preparation. Increased amounts of hemicelluloses, especially mannans, improved the defibration process, the stability of the CNFs and the mechanical properties, whereas the residual lignin content had no significant effect on these factors. On the other hand, high lignin content turned spruce nanopapers yellowish and, together with hemicelluloses, reduced the strain-at-break values. Finally, when no surface derivatization was applied to holocellulose and cellulose samples before defibration, the controlled preservation of residual lignin and hemicelluloses on the CNFs indicate to be crucial for the process. This simplified method of CNF preparation presents great potential for forest-based industries as a way to use forestry waste (e.g., branches, stumps and sawdust) to produce CNFs and, consequently, diversify the product range and reach new markets.
Chemical composition and morphological properties of Norway spruce wood and bark were evaluated. The extractives, cellulose, hemicelluloses, and lignin contents were determined by wet chemistry ...methods. The dimensional characteristics of the fibers (length and width) were measured by Fiber Tester. The results of the chemical analysis of wood and bark show the differences between the trunk and top part, as well as in the different heights of the trunk and in the cross section of the trunk. The biggest changes were noticed between bark trunk and bark top. The bark top contains 10% more of extractives and 9.5% less of lignin. Fiber length and width depends on the part of the tree, while the average of these properties are larger depending on height. Both wood and bark from the trunk contains a higher content of fines (fibers <0.3 mm) and less content of longer fibers (>0.5 mm) compared to the top. During storage, it reached a decrease of extractives mainly in bark. Wood from the trunk retained very good durability in terms of chemical composition during the storage. In view of the morphological characteristics, it occurred to decrease both average fibers length and width in wood and bark.
Production of biochar from corn cob and corn stalk has gained great interest for efficient waste management with benefits of improving soil properties, increasing crop productivity, and contributing ...to carbon sequestration. This study investigated slow pyrolysis of corn cob and corn stalk at 600 °C to characterize yields and properties of products, with focus on solid biochar. Spruce wood, a rather well studied woody biomass, was also included for comparison purposes. It was observed that yields of biochar and condensates from corn cob, corn stalk, and spruce wood were comparable. However, gas release profiles and yields from the three biomasses were quite different, which is mainly related to the different chemical compositions (i.e., hemicellulose, cellulose, lignin, and inorganic species) of the studied raw feedstocks. The produced biochars were analyzed for proximate analysis, CHNS-elemental analysis, specific surface area and specific pore volume for pores in the nm-range, inorganic composition, solid functional groups, and aromaticity. The corn cob and corn stalk biochar presented significantly higher concentration of inorganic elements, especially P and K, favoring soil application. The SEM analysis results showed that the spruce wood biochar has different microstructure than corn cob and corn stalk biochars. Condensates and light gases, as by-products from biochar production, contained over 50% of the energy and 40% of the total carbon of the initial biomass. Utilization of the condensates and light gases as valuable resources is therefore critical for improving environmental and energy benefits of the biochar production process.
•The SEM images clearly showed that how the fungal hyphae spread in the cell lumens.•FT-IR analysis elucidated polysaccharide degradation with increasing time.•FT-Raman analysis powerfully revealed ...changes in the lignin.•The extensive degradation changes the carbohydrate/lignin ratio.
Spruce sapwood was subjected to brown rot fungi (Coniophora puteana) for up to 80days to study the degradation of the cell wall. The chemical composition of spruce sapwood that was modified by brown-rot fungi causing mass losses up to 60.99% was examined using Fourier transform infrared (FT-IR) and FT-Raman spectroscopy. During the first stage of brown rot, no changes were observed using light microscopy but electron microscopy clearly showed how the cell lumens were occupied by fungal hyphae. FT-IR and FT-Raman results revealed that carbohydrate peaks simultaneously diminished or disappeared with mass loss as decay proceeded. However, as the decay proceeded and the wood polysaccharides depolymerized, the intensity of peaks corresponding to lignin increased. However, the lignin content maintains relatively constant.
•Industrial manufacture of 3-layered, beech-spruce hybrid CLT.•Rolling shear properties were tested with compression shear and bending tests.•Rolling shear modulus and strength exceed classic ...softwood CLT by 7 and 3 times.•Sufficiently accurate calculation as a rigid composite ignoring shear-lag.•Greatly enhanced load capacity and deflection behavior as compared to softwood CLTs.
A hybrid, three-layered, softwood-hardwood cross-laminated timber build-up with outer layers of European spruce (Picea abies) and a center cross-layer of European beech (Fagus sylvatica) has been investigated with regard to out-of-plane bending. The determination of the rolling shear properties of the beech cross-layer performed by different test and measurement methods comprising bending and compression shear tests was of primary interest. The shear capacity of the composite is significantly influenced by the spruce longitudinal shear strength at the beech-spruce interface. The characteristic values of rolling shear modulus and strength of the beech cross-layer from the bending tests were Gr,mean=350N/mm2 and fv,r,05=2.6N/mm2, respectively. Direct strain gauge measurements and compression shear tests resulted in 10–20% higher values. The high rolling shear properties render the shear lag implications of the softwood CLTs to a negligible quantity. The hybrid build-up can be designed as a rigid composite with small error versus a more exact analysis. The novel investigations reveal the great potential of mixed softwood-hardwood CLT build-ups for structural elements in the building sector.
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