Chemical changes in hydrothermal treated wood: FTIR analysis of combined hydrothermal and dry heat-treated wood

By B. Tjeerdsma, Holger Militz. Holz als Roh- und Werkstoff, 2005

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Wood specimens of Beech (Fagus silvatica L.) and Scots pine (Pinus sylvestris L.) modified by a hydrothermal treatment process were analysed by means of Fourier transform infra red spectroscopy (FTIR). The chemical transformation of the cell-wall material was studied and associated with improved wood qualities. For this purpose, FTIR spectroscopy was used as since this technique has been found appropriate to determine the intensity of specific bonds and functional groups within the polymeric structure. Cleavage of acetyl groups of the hemicellulose has been found to occur in the first treatment step under moist conditions and elevated temperature. This results in the formation of carbonic acids, mainly acetic acid. Most of the acetyl groups were found to be cleaved during the treatment of wood at high temperature, whereas only partial deacetylation was found to occur at moderate treatment temperature. The concentration of accessible hydroxyl groups was measured by acetylation and found reduced after treating at high temperature. Esterification reactions were found to occur under dry conditions at elevated temperature in the curing step, indicated by the increase of the specific ester carbonyl peak at 1740 cm−1 in the FTIR spectrum. The esters that were formed turned out to be mainly linked to the lignin complex, considering that the newly formed carbonyl groups were found present in heat-treated wood, yet were found to be absent in the isolated holocellulose. Esterification contributes to a decrease of hygroscopicity of wood and consequently improvements of its dimensional stability and durability. However, the role of esterification in the decrease of hygroscopicity in the hydrothermal treatment process examined is believed to be minor compared to the influence of cross-linking reactions known to occur during thermal treatment of wood.ZusammenfassungDas Holz hydrothermisch modifizierten Buchen- und Kiefernholzes wurde mit FTIR Spektroskopie untersucht. Die chemischen Veränderungen wurden mit dem Hintergrund veränderter Holzeigenschaften diskutiert. Abspaltungen von Acetylgruppen der Hemicellulosen finden vor allem bereits im ersten Prozessschritt unter feuchten Bedingungen und bei erhöhten Temperaturen statt. Dieses führt zur Bildung von Essigsäure und anderen Carbonsäuren. Bei niedrigeren Temperaturen werden weniger Carbonsäuren freigesetzt. Durch Acetylierung wurde der Gehalt an freien Hydroxylgruppen bestimmt. Durch die Hitzebehandlung reduziert sich der Gehalt freier Hydroyxlgruppen. Die Zunahme des Carbonylesterpeaks bei 1740 cm−1 im FTIR Spektrum lässt sich durch Veresterungsreaktionen im heißen aber trocknen Curingschritt erklären. Diese Ester sind vor allem an den Ligninkomplex gebunden und weniger an die Holocellulose. Durch Veresterungen wird ein hygroskopisches, dimensionsstabiles und dauerhaftes Material geschaffen. Die Veränderung der Materialeigenschaften beruht jedoch vor allem auch auf cross-linking Reaktionen die während des Prozesses ablaufen.

Subfields: Biomedical Engineering, Building and Construction, Organic Chemistry

View Paper: https://www.semanticscholar.org/paper/a26c74a0a4a53817ca87f696c263889be7844713

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Citations in the corpus

Chemical changes of heat treated pine and eucalypt wood monitored by FTIR (2013, background): “At the same time there is a carbohydrate dehydratation that reduces accessible OH groups (Weiland and Guyonnet 2003) and leading to the formation of furfural and hydroxymethylfurfural (Tjeerdsma and Militz 2005).”
PINE WOOD MODIFICATION BY HEAT TREATMENT IN AIR (2008, background): “…compounds, plays an important role but the degradation of the amorphous regions of cellulose and the cross-linking reactions also contribute to the decrease on equilibrium moisture content as reported by several authors (Bhuiyan and Hirai 2005;Tjeerdsma et al. 1998a; Tjeerdsma and Militz 2005).”
Influence of steam heating on the properties of pine (Pinus pinaster) and eucalypt (Eucalyptus globulus) wood (2007, background): “In the last few years research on the heat treatment of wood has been active regarding the understanding of the chemical changes in treated wood (Kotilainen et al. 2000; Zaman et al. 2000; Sivonen et al. 2002; Wikberg and Maunu 2004; Nuopponen et al 2004a, b; Bhuiyan and Hirai 2005; Tjeerdsma and Mi”
Thermal treatment of wood using vegetable oils: A review (2018, background): “The reduction in EMC can be caused by several heat-induced factors such as diminishing amount of the water affinity hydroxyl groups [72]; inaccessibility of hydroxyl groups to water molecules due to increment of cellulose crystallinity [73,74]; and further crosslinking caused by the polycondensation”
Extractive composition and summative chemical analysis of thermally treated eucalypt wood (2008, background): “The ether linkages of lignins are cleaved and new free phenolic hydroxyl groups and a- and b-carbonyl groups arise, which are responsible for crosslinking via formation of methylene bridges (Tjeerdsma et al. 1998; Nuopponen et al. 2004; Wikberg and Maunu 2004; Tjeerdsma and Militz 2005).”
Strength properties of thermally modified softwoods and its relation to polymeric structural wood constituents (2007, methodology): “Heat treatment, such as the two-stage treatment method used in this study, causes a modification of the main components and changes the chemical composition of wood as described in previous studies [6, 35, 46, 48] and by several other authors [4,10,13,16,37,39,41,43,44].”
A review of wood thermal pretreatments to improve wood composite properties (2013, neutral): “Dimensional stability, resistance against fungal degradation, water vapor sorption, and durability are improved in torrefied wood (Jämsä and Viitaniemi 2001; Kamdem et al. 2002; Tjeerdsma and Militz 2005; Hakkou et al. 2006; Borrega and Kärenlampi 2008; Ates et al. 2009; Ibach 2010; Pfriem et al. 20”
Relations between chemical changes and mechanical properties of thermally treated wood 10th EWLP, Stockholm, Sweden, August 25–28, 2008 (2009, result): “This is consistent with the results of Kotilainen et al. (2000) who found an increase of this absorption band for spruce and Scots pine, and with the results of Schwanninger et al. (2003) for beech, and of Tjeerdsma and Militz (2005) for beech and Scots pine.”
Optimisation of a two-stage heat treatment process: durability aspects (2006, methodology): “…to be transformed selectively into a hydrophobic network (Tjeerdsma et al. 1998b); and (e) a decrease of some wood components and especially hemicelluloses; lignin modifications and the formation of new ether linkages; reduction of hygroscopic wood properties (Weiland and Guyonnet 1997, 2003).”