One-stage thermo-hydro treatment (THT) of hardwoods: an analysis of form stability after five soaking-drying cycles

Vladimirs Biziks 1 , Bruno Andersons 2 , Errj Sansonetti 2 , Ingeborga Andersone 2 , Holger Militz 1 ,  and Juris Grinins 2
  • 1 Wood Biology and Wood Product, Burckhardt Institute, Georg-August University, Göttingen, Büsgenweg 4, 37077 Göttingen, Germany
  • 2 Latvian State Institute of Wood Chemistry, Dzerbenes str. 27, Riga LV-1006, Latvia
Vladimirs Biziks, Bruno Andersons, Errj Sansonetti, Ingeborga Andersone, Holger Militz and Juris Grinins

Abstract

A newly developed thermo-hydro treatment (THT) for use in a one-stage heat treatment process was examined by focusing on the form stability-related properties of European aspen (Populus tremula), birch silver (Betula pendula), and gray alder (Alnus incana). In particular, wood specimens were subjected to THT in a saturated steam atmosphere in a pilot-scale autoclave heated between 140 and 180°C for 1–3 h. Several parameters of untreated and treated samples after several soaking and drying cycles were compared, namely, the changes in the volumetric swelling, swelling in the radial and tangential directions, cell wall total water capacity, and anti-swelling efficiency (ASE). Due to repeated wetting in the cyclic water submersion-drying test, the original ASE of 73% decreased to 65% (180°C for 1 h), and the original ASE of 33% decreased to 5% (140°C for 1 h). Wood modified at 170°C presented good results that were not significantly lower than wood treated at higher temperatures while consuming less energy to deliver ASE improvement and was selected as optimum. To increase the ASE by 1%, the amount of energy consumed was decreased by 41%, 39%, and 17% compared with the treatment regimes of 160°C for 1 h, 160°C for 3 h, and 180°C for 1 h, respectively. The new THT regime led to improved long-term dimensional stability due to the cross-linking of cell wall polymers, which resulted in increased cell wall rigidity.

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Holzforschung is an international scholarly journal that publishes cutting-edge research on the biology, chemistry, physics and technology of wood and wood components. High quality papers about biotechnology and tree genetics are also welcome. Rated year after year as one of the top scientific journals in the category of Pulp and Paper (ISI Journal Citation Index), Holzforschung represents innovative, high quality basic and applied research.

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