Heat treatment of Pinus pinaster and Eucalyptus globulus woods, two important species in Portugal, was made in the absence of air by steaming, inside an autoclave, for 2 to 12h at 190 ºC to 210ºC. Mass losses increased with treatment time and temperature reaching 7.3% for pine and 14.5% for eucalypt wood. The wood behaviour with moisture was improved. The equilibrium moisture content decreased by 46% for pine and 61% for eucalypt, the dimensional stability increased (maximum anti-shrinking efficiency in the radial direction of 57% and 90% for pine and eucalypt respectively) and the surface wettability was lowered. In relation to mechanical properties, the modulus of elasticity was little affected (maximum decrease of 5% for pine and 15% for eucalypt) but the bending strength was reduced (by 40% at 8% mass loss for pine and 50% at 9% mass loss for eucalypt wood).The variation of properties was related to treatment intensity and mass loss but significant improvements could already be obtained for a 3-4% mass loss without impairing the mechanical resistance. The response of eucalypt was higher than that of pinewood. Heat treatment of eucalypt wood shows an interesting potential to improve the wood quality for solid timber products. IntroductionThe first studies on heat treatment to improve dimensional stability of wood have been carried out by Stamm et al. (1946) Heat treatment reduces the equilibrium moisture content of wood (Jämsä and Viitaniemi 2001; Nakano and Miyazaki 2003; Gosselink et al. 2004;Wang and Cooper 2005; Metsä-Kortelainen et al. 2005) and improves its dimensional stability (Kollmann and Schneider 1963; Viitaniemi et al. 1997; Epmeier et al., 2001; Yildiz 2002; Bekhta and Niemz 2003; González-Peña et al. 2004; Wang and Cooper 2005) and rot resistance (Kim et al. 1998; Kamdem et al. 2002; Hakkou et al. 2006), thereby allowing treated wood to be used in less favourable 3 conditions and to compete with tropical wood of higher cost. Heat treatment also darkens the wood (Mitsui et al. 2001; Bekhta and Niemz 2003) which is an advantage for light coloured woods which are usually less appealing to the consumer. The major disadvantage is the reduction of mechanical resistance (Kim et al. 1998, Kubojima et al. 2000 Bengtsson et al. 2002; Reiterer and Sinn 2002; Epmeier et al. 2004; Unsal and Ayrilmis 2005; Johansson and Morén 2006) that can be an impediment for some uses. Although wettability decreases (Pétrissans et al. 2003; Hakkou et al. 2005a Hakkou et al. .2005b) the gluing process can be adapted for treated wood (Militz 2002)..In the last few years research on the heat treatment of wood has been active namely 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 Nuopponen et al . 2004b Bhuiyan et al. 2005 Pinus pinaster and Eucalyptus globulus are two of the forest species with most planted area in Portugal. Pine wood is used for all kinds of carpe...

A hardwood, Eucalyptus globulus Labill., and a softwood Pinus pinaster Aiton., were heat treated at temperatures between 170 and 210ºC in an oven and in an autoclave. The samples were pre-extracted with dichloromethane, ethanol and water and ground prior to Fourier Transform Infrared (FTIR) spectroscopic analysis.The heat treatment caused significant changes in the chemical composition and structure of wood, in lignin and polysaccharides. Hemicelluloses were the first to degrade as proved by the initial decrease of the 1730 cm -1 peak due to the breaking of acetyl groups in xylan. Hardwood lignin changed more than softwood lignin, with a shift of maximum absorption from 1505 cm -1 to approximately 1512 cm -1 due to decrease of methoxyl groups, loss of syringyl units or breaking of aliphatic side-chains. The macromolecular structure becomes more condensed and there is a clear increase of non-conjugated (1740 cm -1 ) in relation to conjugated groups (1650 cm -1 ). However, the changes induced by the thermal treatment are difficult to monitor by FTIR spectroscopy due to the different chemical reactions occurring simultaneously.

Heat treatment of Pinus pinaster and Eucalyptus globulus wood was made by hot air in an oven during 2 to 24 h at 170-200 ºC and by steam in an autoclave during 2 to 12 h at 190-210 ºC. The colour parameters L*, a* and b* were determined by the CIELAB method on radial, tangential and transverse sections for untreated and treated wood, and their variation with the treatment (ΔL*, Δa* and Δb*) were calculated in percent.In the untreated woods, for eucalypt wood lightness (L*) varied between 54.1-63.8% with a* between 7. 4-8.5 and b* 15.7-19.9, and for pine wood L* varied between 67.3-76.1%, a* between 6.9 -7.6 and b* 16.3 -24.1. With the heat treatment wood became darker, more for oven treatment (ΔL* about 50% for 4% mass loss), and at the same treatment conditions more for eucalypt wood. In general the contribution of the red colour (a*) and yellow (b*) decreased with the heat treatment. The transverse section darkened less in the two species and for both treatments, with small differences between radial and tangential sections. Lightness decrease was related to chemical changes, with good correlations with glucose (R 2 = 0.96), hemicelluloses (R 2 = 0.92) and lignin (R 2 = 0.86).As regards colour, the heat treatments showed an interesting potential to improve the wood quality for solid timber products from pine and eucalypt.3 IntroductionThe use of heat treatments to modify the properties of wood is not new and Tiemann (1920) already reported that high temperature drying decreased the wood equilibrium moisture content and swelling as well as Stamm and Hansen (1937) with wood heated in several gases. The first studies directed towards improvement of wood dimensional stability were carried out by Stamm et al. (1946) and further continued by Kollmann and Schneider (1963), Kollmann and. Fengel (1965), Fengel (1966, D'Jakonov and Konepleva (1967), Nikolov and Encev (1967), Burmester (1973), Rusche (1973 a, b), Giebeler. (1983, Hillis (1984), Bourgois and Guyonnet (1988), Bourgois et al. (1989) and Dirol and Guyonnet (1993).The development and commercialization of heat treatments to increase wood durability and dimensional stability was stimulated only recently by environmental concerns but there are already several commercial applications in some European countries and North America.The heat treatments reduce the equilibrium moisture content of wood and improve its dimensional stability and durability but may reduce the mechanical resistance, mainly of bending (Kollmann and Schneider 1963; Viitanen et al. 1994;Viitaniemi et al. 1997; Kim et al. 1998; Kubojima et al. 2000;Epmeier et al. 2001; Jämsä and Viitaniemi 2001; Rapp and Sailer 2001; Kamdem et al. 2002; Yildiz 2002;Bengtsson et al. 2002;Bekhta and Niemz 2003; Gosselink et al. 2004; Metsä-Kortelainen et al. 2006; Wang and Cooper 2005; Hakkou et al. 2006;Esteves et al. 2007).The heat treatment of wood changes its chemical composition by degrading both cell wall compounds and extractives. The thermal degradation starts by deacetylation of hemicellulos...

The structure of lignin and suberin, and ferulic acid (FA) content in cork from Quercus suber L. were studied. Extractive-free cork (Cork), suberin, desuberized cork (Cork sap ), and milled-cork lignins (MCL) from Cork and Cork sap were isolated. Suberin composition was determined by GC-MS/FID, whereas the polymers structure in Cork, Corksap, and MCL was studied by Py-TMAH and 2D-HSQC-NMR. Suberin contained 94.4% of aliphatics and 3.2% of phenolics, with 90% of ω-hydroxyacids and α,ω-diacids. FA represented 2.7% of the suberin monomers, overwhelmingly esterified to the cork matrix. Py-TMAH revealed significant FA amounts in all samples, with about 3% and 6% in cork and cork lignins, respectively. Py-TMAH and 2D-HSQC-NMR demonstrated that cork lignin is a G-lignin ( > 96% G units), with a structure dominated by β-O-4′ alkyl-aryl ether linkages (80% and 77% of all linkages in MCL and MCL sap , respectively), followed by phenylcoumarans (18% and 20% in MCL and MCL sap , respectively), and smaller amounts of resinols (ca. 2%) and dibenzodioxocins (1%). HSQC also revealed that cork lignin is heavily acylated (ca. 50%) exclusively at the side-chain γ-position. Ferulates possibly have an important function in the chemical assembly of cork cell walls with a cross-linking role between suberin, lignin and carbohydrates.

A "milled cork lignin" (MCL) and a lignin-carbohydrate complex (LCC) have been isolated from Quercus suber with respective yields of l .5 % and 0.32 %. Cork and the isolates were characterized by FTIR spectroscopy, elemental analysis, OMe determination, analytical pyroiysis (Py/GC/FID) and acid hydrolysis followed by determination of the monomeric sugars released. Cork contains a lignin-like material in 40% yield. MCL was enriched in this material up to 54%. The non-aromatic part contained suberinic acids and polysaccharides. Both FTIR spectroscopy and pyroiysis revealed the preponderance of guaiacyl-type aromatic rings. Pyroiysis released phenols of which 91 % were guaiacyl-type. The yield of phenol, o-cresol, dimethylphenol, p-hydroxy benzaidehyde was around 10% and that of syringyl-type phenols only l %. Acetic acid, äs one of the thermal degradation products of suberinic acids, was detected in high yields both in cork and in MCL. The ratio of hexosans/pentosans in cork was 1/0.76, in MCL 1/2.6, and in LCC 1/3.4. The problem related to the differentiation between lignin and the aromatic part of suberin is discussed.

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