Key message
Increasing environmental pressures appearing over the last few years have led to important changes in the field of wood protection. In this context
,
new technologies
,
based either on ...thermal or chemical modifications
,
suggest increasing interest in prospect of programmed ban of biocide products
.
•
Context
The evolution of the regulations on the use of biocide products has led to important changes in the field of wood preservation, leading to an increasing interest for non-biocide treatments like thermal or chemical modifications to face to the programmed ban of biocide products.
•
Aims
The paper reviews the different non-biocide alternatives developed currently on an industrial scale, highlighting their main characteristics and applications.
•
Results
Different treatments have been developed on an industrial scale involving mainly thermal modifications and acetylation, furfurylation and DMDHEU constituting already available solutions.
•
Conclusion
Different non-biocide alternatives already exist and will become more important in the next decades due to the increasing legislative pressure driven by environmental considerations.
In this study, modification of European beech wood (
Fagus sylvatica
) through in situ esterification of sorbitol and citric acid (SorCA) was investigated at two curing temperatures, 140 and 160 °C. ...In order to determine the optimum condition for modification, an aqueous solution of SorCA at varying concentrations was evaluated (10, 20, 30, and 55% w/w). Physical, mechanical, chemical, and durability properties of the modified wood were examined. Results have disclosed that among different SorCA concentrations, treatment with SorCA at 30% w/w was considered as the optimum concentration independent of the curing temperature. Under these conditions, anti-swelling efficiency increased to approx. 55% and modulus of elasticity increased slightly with approx. 9% in comparison with untreated wood. Decay resistance against white-rot (
Trametes versicolor
), brown-rot (
Coniphora puteana
), and soft-rotting microfungi classified the SorCA-30%-modified wood as very durable. In addition, thermogravimetric study evidenced that SorCA 30%-modified wood has a lower thermal decomposition temperature in comparison with untreated wood/wood control by 20 °C difference, indicating that the SorCA-modified wood possibly has fire-retardant properties. However, due to the acidic properties of the SorCA solution, modulus of rupture (MOR) and mainly work to maximum load in bending decreased considerably.
Intraspecific macromolecule variation in stemwood, knotwood, and branchwood was studied using analytical pyrolysis with the intention of introducing a rapid working method to assess the variance in ...lignin content using analytical pyrolysis and highlight variability markers. The study was performed on Picea abies, Abies alba, and Pseudotsuga menziesii. Lignin determined via analytical pyrolysis–GC/MS (Py-lignin) can be used to identify variations in lignin content, compared to using classical Klason lignin values as a reference method for lignin determination, which requires a correction factor. Principal component analysis (PCA) was performed to identify biopolymer pyrolysis product markers for different species, tissues, or heights that could help highlight structural differences. Douglas fir was differentiated from spruce and silver fir in the levoglucosan amount. Guaiacol was more present in spruce wood, and creosol was more present in Douglas fir. Knotwood was structurally close to stemwood in spruce and silver fir, but there was a clear transition between stemwood and branchwood tissue in Douglas fir. Knotwood was differentiated by higher furan compounds. Branchwood was clearly separate from stemwood and knotwood and presented the same markers as compression wood in the form of phenylpropanoid lignins (H-lignin) as well as isoeugenol and vinyl guaiacol, the two most produced lignin pyrolysis products.
Fatty acids (FA) and their derivatives with long alkyl chain structures are good candidates for wood esterification to confer thermoplastic properties to wood. Nevertheless, they do not react easily ...with hydroxyl groups of wood. In this study, we investigated the reactivity of wood with various fatty acids of different chain lengths using trifluoroacetic anhydride (TFAA) as the impelling agent in various reaction conditions. Generally, the esterification of fatty acids without solvents resulted in higher Weight Percentage Gain (WPG) and ester content than the reaction in the presence of CH2Cl2. The esterification reaction could be performed effectively at room temperature, though an increased reaction temperature provoked degradation of the esterified wood. WPG of 67% was obtained for the C3 and 253% for the C16 alkyl chain analogs, respectively. Nevertheless, the ester content was fairly uniform, with values between 10.60 and 11.81 mmol ester/gram of wood for all chain lengths. A higher quantity of reagent led to higher ester content, which tended to stabilize after a ratio of 1:4 wood and TFAA/FA. The esterification reaction was performed rapidly, with an ester content between 7.65 and 9.94 mmol ester/gram of wood being achieved only after 15 min of reaction. Fourier transform infrared spectroscopy (FTIR) analysis was performed to confirm the drastic chemical changes of wood before and after esterification. Morphological observation by scanning electron microscope (SEM), softening measurement by thermomechanical analysis (TMA), and contact angle measurements demonstrated the possibility of esterified spruce wood being applied as a new bioplastic.
Thermoplastic materials can be obtained through solvent free wood esterification with fatty acid using trifluoroacetic anhydride (TFAA) as promoter. This study aims to investigate the mechanism of ...wood thermoplasticization mechanism by understanding the role of each wood component in esterification. High accessibility for acylation was found in cellulose indicated by the highest weight percent gain (WPG), followed by lignin and hemicelluloses. However, significant chemical structural changes were recorded for each spruce wood components observed by Fourier-transform infrared spectroscopy (FTIR) and cross-polarization/magic angle spinning solid state nuclear magnetic resonance (CP/MAS 13C NMR), promoting thus the improvement of their thermal properties detected by (thermogravimetric analysis) TGA and (differential scanning calorimeter) DSC. Cellulose as a major component wood played an important role in wood plasticization, indicated by the low softening temperature before degradation recorded by (thermomechanical analysis) TMA. Hemicelluloses presenting lower WPG, showed the same effect as cellulose on thermoplasticization supported by the low softening temperature observed by TMA and (scanning electron microscope) SEM. Acylated lignin did not show thermoplastic properties, but resulted in important hydrophobic aspects of materials.
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•Thermoplastic and translucent films were obtained through solvent free esterification using several fatty acids and TFAA.•Varying fatty acids length in wood esterification resulted ...relatively uniform ester content of esterified wood.•Chemical, thermal and surface properties of esterified wood were evaluated and gave various results depending on the fatty acid chain length.
Transforming wood into thermoplastic material has long been a challenging research topic, nevertheless the application of this technology to the industrial level hampered because of the complex method available. Here, we demonstrate a promising method converting spruce sawdust into thermoplastic material by esterification with various fatty acids of different chain length (4–18 carbon). The esterification was carried out using trifluoroacetic anhydride (TFAA) as a promoter. Weight percentage gain (WPG) of 70% was obtained for the shortest fatty acid used in this study (C4) and increased with the length of fatty acid chain to 271.3% (C18) and ester content were uniformly achieved ranged between 9.10 and 11.27 mmol/gram of wood. Chemical analysis by FTIR and CP/MAS 13C NMR revealed hydroxyl group of esterified wood was replaced by the ester group and alkyl chain. XRD analysis showed decrystallization of cellulose in esterified spruce sawdust. Esterified wood exhibit higher thermal stability observed by TGA and DSC, and presented several softening temperatures observed by TMA. Thermoplastic, translucent, and flexible film were obtained after hot pressing. In contrast with previous research, our study revealed that thermoplastic wood sheet could be obtained by esterification without solvent and at room temperature after only 4 h of reaction.
Application of natural fibers always faces incompatibility problems due to hydrophilic nature of the fibers which resulted in poor interactions with thermoplastic polymer matrix. The objective of ...this research was to provide thermoplastic properties to the natural fibers by solvent free esterification using trifluoroacetic anhydride (TFAA) as impelling agent and fatty acids as acylating agent, without any plasticizers or thermoplastic polymer. We also want to make these fibers hydrophobic, potentially addressing incompatibility issues at the fiber matrix interface. The reactivity of esterification varied depending on the chemical composition of the fibers indicated by different values of weight percent gain (WPG). Cotton and flax fiber were chosen for further characterization due to their high content of cellulose which resulted in high ester content. Significant changes in chemical structure were detected using FTIR indicated by substitution of hydroxyl groups with alkyl side chains from fatty acids. This chemical change followed by thermal properties improvement observed by TGA. Thermoplasticity of fatty acids esterified fibers successfully achieved indicated by softening temperature at about 60 and 130°C observed by DSC and TMA, and disappearance of fibers aspect to homogenous and smooth surface of the film. Significant improvements of surface hydrophobicity were also observed by measuring contact angle of water drops to the surface of the film.
Knotwood of softwood species is rich in secondary metabolites, especially lignans. These metabolites can be extracted with organic solvents, and are known to be valuable sources of natural bioactive ...molecules. Here, we examine the intraspecific variability of the yield and compositions of ethanol extracts from knotwood along the stems of three economically significant softwoods
,
and
in view of further valorisation. Extractive yields from all three species were higher from knots at the base of the living crown than at the top. Lignans and terpenes were abundant in
and
extracts, and lignans were present in the highest concentrations at the crown base. Secoisolariciresinol and hydroxymatairesinol were the most abundant lignans in
and
, respectively.
extract composition was more diverse than those of the other species, containing taxifolin, small amounts of the lignan nortrachelogenin, and smaller amounts of secoisolariciresinol. A cyclitol, D-pinitol, was found in high concentrations in extracts from knots at the very top of the crown, particularly in
and
. Lignans, taxifolin and D-pinitol are reported to have anti-tumour properties, and valuable food-supplement markets exist for these compounds suggesting possibilities of further valorisation.
The lignan 7′-hydroxymatairesinol (1), extracted from the knotwoods of fir (Abies alba), spruce (Picea abies), and Douglas fir (Pseudotsuga menziesii), exhibited unexpected reactivity when ...esterification reactions were attempted on the hydroxy group at position C-7′. To circumvent the rapid intramolecular cyclization procedure, leading quantitatively to the lignan conidendrin (7), a simple strategy for 7′-esterification of 1 under mild conditions (three steps, up to 80% overall yield) was developed. Compared to hydroxymatairesinol (1) (log K′w = 1.49), the derivatives (2–5) had increased lipophilicity with log K′w > 3.1, as determined by a UHPLC method. Compounds 1–5 exhibited potent antioxidant properties in the same range as the standards ascorbic acid and α-tocopherol (IC50 = 20–25 μM) and higher than that of BHT using a DPPH radical-scavenging assay.
Purpose The surface characteristics of thermally and chemically modified wood, such as surface roughness, surface free energy (SFE) and wettability, are important properties that influence further ...manufacturing processes such as gluing and coating. The aim of this paper was to determine the influence of the surface roughness of thermally and chemically modified teak wood on their SFE, wettability and bonding quality for water-based acrylic and solvent-based alkyd varnishes. In addition, durability against subterranean termites in the field of these modified teak woods was also investigated to give a valuable information for their further application. Design/methodology/approach The woods tested in this study were fast-growing teak woods that were prepared in untreated and treated with furfuryl alcohol (FA), glycerol maleic anhydride (GMA) and thermal. SFE values were calculated using the Rabel method. The wettability values were measured based on the contact angle between varnish liquids and wood surfaces using the sessile drop method, and the Shi and Gardner model model was used to evaluate the wettability of the varnishes on the wood surface. The bonding quality of the varnishes was measured using a cross-cut test based on ASTM 3359-17 standard. In addition, durability against subterranean termites in the field of these modified teak woods was also investigated according to ASTM D 1758-06. Findings The results showed that furfurylated and GMA-thermal 220°C improved the durability of teak wood against termites. The furfurylated teak wood had the roughest surface with an arithmetic average roughness (Ra) value of 15.65 µm before aging and 27.11 µm after aging. The GMA-thermal 220°C treated teak wood was the smoothest surface with Ra value of 6.44 µm before aging and 13.75 µm after aging. Untreated teak wood had the highest SFE value of 46.90 and 57.37 mJ/m 2 before and after aging, respectively. The K values of untreated and treated teak wood increased owing to the aging treatment. The K values for the water-based acrylic varnish were lower than that of the solvent-based alkyd varnish. The untreated teak wood with the highest SFE produced the highest bonding quality (grades 4–5) for both acrylic and alkyd varnishes. The solvent-based alkyd varnish was more wettable and generated better bonding quality than the water-based acrylic varnish. Originality/value The originality of this research work is that it provides evaluation values of the durability and SFE. The SFE value can be used to quantitatively determine the wettability of paint liquids on the surface of wood and its varnish bonding quality.
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