Water accessibility to hydroxyls confined in solid wood cell walls

Thybring, Emil Engelund; Piqueras, Sara; Tarmian, Asghar; Burgert, Ingo

doi:10.1007/s10570-020-03182-x

Cited by 29 publications

(34 citation statements)

References 47 publications

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“…If the degraded components are subsequently leached out, the cell wall will lose these bulking agents, resulting in a reduction in dry volume. • Removal of OH groups, which will reduce the hydrophilicity of the wood [155]. This will change the free energy of mixing between the wood polymer network and the penetrating water molecules, which is related to the interaction parameter of the Flory-Huggins theory [156].…”

Section: Dimensional Stabilitymentioning

confidence: 99%

Thermal modification of wood—a review: chemical changes and hygroscopicity

2021

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Thermal modification is a well-established commercial technology for improving the dimensional stability and durability of timber. Numerous reviews of thermally modified timber (TMT) are to be found in the scientific literature, but until now a review of the influence of cell wall moisture content during the modification process on the properties of TMT has been lacking. This paper reviews the current state of knowledge regarding the hygroscopic and dimensional behaviour of TMT modified under dry (cell wall at nearly zero moisture content) and wet (cell wall contains moisture) conditions. After an overview of the topic area, the review explores the literature on the thermal degradation of the polysaccharidic and lignin components of the cell wall, as well as the role of extractives. The properties of TMT modified under wet and dry conditions are compared including mass loss, hygroscopic behaviour and dimensional stability. The role of hydroxyl groups in determining the hygroscopicity is discussed, as well as the importance of considering the mobility of the cell wall polymers and crosslinking when interpreting sorption behaviour. TMT produced under wet processing conditions exhibits behaviour that changes when the wood is subjected to water leaching post-treatment, which includes further weight loss, changes in sorption behaviour and dimensional stability, but without any further change in accessible hydroxyl (OH) content. This raises serious questions regarding the role that OH groups play in sorption behaviour. Graphical abstract

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Section: Dimensional Stabilitymentioning

confidence: 99%

Thermal modification of wood—a review: chemical changes and hygroscopicity

2021

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“…The exchanged hydrogen can be quantified either gravimetrically by a dry mass increase of 1 g per mol exchanged hydrogen (Pönni et al 2014;Uimonen et al 2020), or spectroscopically by the shift of the OH stretching band to lower wavenumbers (Mann and Marrinan 1956;Hofstetter et al 2006;Salmén and Stevanic 2018). This provides an estimate for the number of accessible OH groups in lignocelluloses, which has been applied to study the relationship between sorption sites and absorbed water (Gibbons 1953;Rouselle and Nelson 1971;Guthrie and Heinzelman 1974;Popescu et al 2014;Altgen et al 2018;Salmén and Stevanic 2018;Thybring et al 2020). Correlations between the concentration of accessible OH groups and the amount of absorbed water have been found for cellulosic fibers (Gibbons 1953;Jeffries 1964;Rouselle and Nelson 1971;Guthrie and Heinzelman 1974) and for solid wood (Popescu et al 2014;Altgen et al 2018).…”

Section: Introductionmentioning

confidence: 99%

“…Several studies have shown that the amount of absorbed water can change independently from the OH accessibility (Stevens and Smith 1970;Rautkari et al 2013;Salmén and Stevanic 2018). There is evidence that additional factors have a strong impact on the amount of absorbed water without affecting the sorption site density, such as the degree of crosslinking in heat-treated wood (Altgen et al 2018;Willems et al 2020) or the spatial availability of wood cell walls in modified wood (Thybring et al 2020;Altgen et al 2020). Furthermore, Lindh et al (2016) showed that OH(3) groups in cellulose that are associated with the C(3) atom of the glucose units are unreactive to H-D exchange, but these OH groups may still form hydrogen bonds with water molecules.…”

Section: Introductionmentioning

confidence: 99%

Humidity-dependence of the hydroxyl accessibility in Norway spruce wood

Altgen

Rautkari

2020

Cellulose

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This study aimed at a better understanding of the wood-water interaction, in particular the role of the hydroxyl accessibility during the humidity-dependent change in moisture content. Thin sections (80 µm) of never-dried Norway spruce sapwood that contained early- and latewood were used for the experiments. Sorption isotherm measurements confirmed the humidity-dependent moisture content changes and the effect of the first drying of the wood sections. Changes in hydroxyl accessibility were then determined by deuteration of the sections using deuterium oxide, followed by their re-protonation in water (H2O) vapor at different relative humidity: 15, 55 or 95%. The deuteration and re-protonation of the wood sections were quantified by dry mass changes as well as by changes in the OH and OD stretching vibrations in the Fourier transform infrared spectra. The results showed that the deuterated sections could be almost completely re-protonated in H2O vapor, nearly irrespective of the applied relative humidity. Therefore, changes in hydroxyl accessibility were not the driving force for the humidity-dependent changes in moisture content. However, a slow re-protonation rate at low relative humidity had to be considered. Nonetheless, a small quantity of OD groups persisted the re-protonation in H2O vapor and liquid H2O, which was not related to the drying of the wood. Graphic abstract

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“…By determining the difference in dry mass of the sample before and after conditioning, one can calculate the moles of accessible hydroxyl groups in the sample from the difference in the molar mass of hydrogen and deuterium. For untreated, acetylated and furfurylated wood, a 10-hour D 2 O conditioning period is sufficient for the samples to reach equilibrium [32,35,36,38,62]. However, preliminary trials with SCA-modified wood showed sample mass had not stabilised after 10 h of D 2 O conditioning.…”

Section: Preliminary Sorption Experimentsmentioning

confidence: 99%

“…Thermal modification reduces water uptake by degrading hydrophilic hemicellulose [30] and crosslinking wood polymers, preventing them from expanding to accommodate water molecules [31]. Bulking cell wall modifications, like acetylation, reduce cell wall moisture content by replacing hydroxyl groups with less hydrophilic acetyl groups [32][33][34] and filling the cell wall with physically larger chemical groups [35,36]. Impregnation chemical modifications, like furfurylation, polymerise chemicals within the cell wall where they block space available for water molecules [37,38].…”

Section: Introductionmentioning

confidence: 99%

Leachability and Decay Resistance of Wood Polyesterified with Sorbitol and Citric Acid

Beck

2020

Forests

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Research Highlights: Polyesterification of wood with sorbitol and citric acid (SCA) increases decay resistance against brown-rot and white-rot fungi without reducing cell wall moisture content but the SCA polymer is susceptible to hydrolysis. Background and Objectives: SCA polyesterification is a low-cost, bio-based chemical wood modification system with potential for commercialisation. Materials and Methods: This study investigates moisture-related properties and decay resistance in SCA-modified wood. Scots pine sapwood was polyesterified at 140 °C with various SCA solution concentrations ranging from 14–56% w/w. Dimensional stability was assessed and leachates were analysed with high-performance liquid chromatography (HPLC). Chemical changes were characterized with attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and spectra were quantitatively compared with peak ratios. Low-field nuclear magnetic resonance (LFNMR) relaxometry was used to assess water saturated samples and decay resistance was determined with a modified EN113 test. Results: Anti-swelling efficiency (ASE) ranged from 23–43% and decreased at higher weight percentage gains (WPG). Reduced ASE at higher WPG resulted from increased water saturated volumes for higher treatment levels. HPLC analysis of leachates showed detectable citric acid levels even after an EN84 leaching procedure. ATR-FTIR analysis indicated increased ester content in the SCA-modified samples and decreased hydroxyl content compared to controls. Cell wall water assessed by non-freezing moisture content determined with LFNMR was found to increase because of the modification. SCA-modified samples resisted brown-rot and white-rot decay, with a potential decay threshold of 50% WPG. Sterile reference samples incubated without fungi revealed substantial mass loss due to leaching of the samples in a high humidity environment. The susceptibility of the SCA polymer to hydrolysis was confirmed by analysing the sorption behaviour of the pure polymer in a dynamic vapour sorption apparatus. Conclusions: SCA wood modification is an effective means for imparting decay resistance but, using the curing parameters in the current study, prolonged low-level leaching due to hydrolysis of the SCA polymer remains a problem.

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Water accessibility to hydroxyls confined in solid wood cell walls

Cited by 29 publications

References 47 publications

Thermal modification of wood—a review: chemical changes and hygroscopicity

Thermal modification of wood—a review: chemical changes and hygroscopicity

Humidity-dependence of the hydroxyl accessibility in Norway spruce wood

Leachability and Decay Resistance of Wood Polyesterified with Sorbitol and Citric Acid

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