Measuring the thickness swelling and set-recovery of densified and thermally modified Scots pine solid wood

The purpose of this study was to analyse the fundamental phenomena related to the swelling behaviour of densified and thermally modified wood under changing moisture content, as well as to investigate the differences in recovery behaviour between four different methods: (i) soaking–drying cycles, (ii) soaking–drying cycles in hot water, (iii) water-soaking with continuous data logging to measure dynamic changes in thickness and (iv) humid–dry cycles at different relative humidity (RH). Methods were applied to untreated, thermally modified, densified (D) and densified + thermally modified (DTM) Scots pine sap wood samples. Soaking methods were found to produce significantly higher set-recovery results than RH cycling, with higher temperature accelerating the relaxation during soaking. Repeated cycles increased the swelling of the densified samples. The RH thresholds for set-recovery were found to be between 65 and 75 % for the D samples and between 75 and 84 % in the case of DTM samples.

[1]  Parviz Navi,et al.  Combined Densification and Thermo-Hydro-Mechanical Processing of Wood , 2004 .

[2]  L. Salmén.  Viscoelastic properties ofin situ lignin under water-saturated conditions , 1984 .

[3]  P. Navi,et al.  Effects of Thermo-Hydro-Mechanical Treatment on the Structure and Properties of Wood , 2000 .

[4]  U. Bexell,et al.  Effects of semi-isostatic densification on anatomy and cell-shape recovery on soaking , 2006 .

[5]  Frederick A. Kamke,et al.  Density profile relation to hardness of viscoelastic thermal compressed (VTC) wood composite , 2011, Wood Science and Technology.

[6]  M. Gong,et al.  An Optimal Thermo-Hydro-Mechanical Densification (THM) Process for Densifying Balsam Fir Wood , 2013 .

[7]  Jozef Keckes,et al.  Cell-wall recovery after irreversible deformation of wood , 2003, Nature materials.

[8]  Ahmed Koubaa,et al.  DENSIFICATION OF WOOD VENEERS COMBINED WITH OIL-HEAT TREATMENT. PART I: DIMENSIONAL STABILITY , 2011 .

[9]  M. Hughes,et al.  Reducing the set-recovery of surface densified solid Scots pine wood by hydrothermal post-treatment , 2012, European Journal of Wood and Wood Products.

[10]  M. Hughes,et al.  The effect of process parameters on the hardness of surface densified Scots pine solid wood , 2012, European Journal of Wood and Wood Products.

[11]  M. Norimoto,et al.  Stress Relaxation of Sugi (Cryptomeria japonica D.Don) Wood in Radial Compression under High Temperature Steam , 1999 .

[12]  C. R. Welzbacher,et al.  Thermo-mechanical densification combined with thermal modification of Norway spruce (Picea abies Karst) in industrial scale – Dimensional stability and durability aspects , 2008, Holz als Roh- und Werkstoff.

[13]  R. Rowell,et al.  Swelling of wood , 1934, Wood Science and Technology.

[14]  Niels Morsing,et al.  Densification of Wood.: The influence of hygrothermal treatment on compression of beech perpendicular to gain , 1998 .

[15]  M. Gong,et al.  Interactive effect of surface densification and post-heat-treatment on aspen wood , 2010 .

[16]  W. Hillis,et al.  The Softening Temperatures of Wood , 1978 .

[17]  F. Kamke,et al.  Density profile and morphology of viscoelastic thermal compressed wood , 2009, Wood Science and Technology.

[18]  Lauri Rautkari,et al.  Surface modification of wood using friction , 2009, Wood Science and Technology.

[19]  T. Morooka,et al.  Radial compression of sugi wood (Cryptomeria japonica D. Don) , 1998, Holz als Roh- und Werkstoff.

[20]  Lauri Rautkari,et al.  Properties and set-recovery of surface densified Norway spruce and European beech , 2010, Wood Science and Technology.

[21]  L. Salmén,et al.  The effect of lignin composition on the viscoelastic properties of wood. , 1997 .

[22]  Ahmed Koubaa,et al.  Densification of wood veneers by compression combined with heat and steam , 2011, European Journal of Wood and Wood Products.

[23]  Masafumi Inoue,et al.  Steam or Heat Fixation of Compressed Wood , 2007 .

[24]  Andreja Kutnar,et al.  Densification of wood , 2007 .

[25]  P. U. A. Grossman,et al.  Requirements for a model that exhibits mechano-sorptive behaviour , 1976, Wood Science and Technology.

[26]  L. G. Esteban,et al.  Reduction of wood hygroscopicity and associated dimensional response by repeated humidity cycles , 2005, physics/0503174.

[27]  M. Boonstra,et al.  Semi-isostatic densification of heat-treated radiata pine , 2007, Wood Science and Technology.

[28]  M. Hughes,et al.  Hardness and density profile of surface densified and thermally modified Scots pine in relation to degree of densification , 2013, Journal of Materials Science.

[29]  Lauri Rautkari,et al.  The water vapour sorption properties of thermally modified and densified wood , 2012, Journal of Materials Science.

[30]  Kiho Jung,et al.  Mechanical and moisture-dependent swelling properties of compressed Japanese cedar , 2011 .