Sorption and surface energy properties of thermally modified spruce wood components

Susanna Källbom*, Michael Altgen, Holger Militz, Magnus Wålinder

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

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Abstract

The objective of this work is to study the water vapor sorption and surface energy properties of thermally modified wood (TMW) components, ie wood processing residuals in the form of sawdust. The thermal modification was performed on spruce wood components using a steam-pressurized laboratory-scale reactor at two different temperature (T) and relative humidity (RH) conditions, T ¼ 150°C and RH ¼ 100% (TMW150), and T ¼ 180°C and RH ¼ 46% (TMW180). A dynamic vapor sorption (DVS) technique was used to determine water vapor sorption isotherms of the samples for three adsorption-desorption cycles at varying RH between 0% and 95%. Inverse gas chromatography (IGC) was used to study the surface energy properties of the samples, including dispersive and polar characteristics. The DVS results showed that the EMC was reduced by 30-50% for the TMW samples compared with control samples of unmodified wood (UW) components. A lower reduction was, however, observed for the second and third adsorption cycles compared with that of the first cycle. Ratios between EMC of TMW and that of UW samples were lower for the TMW180 compared with the TMW150 samples, and an overall decrease in such EMC ratios was observed at higher RH for both TMW samples. The IGC results showed that the dispersive contribution to the surface energy was higher at lower surface coverages, ie representing the higher energy sites, for the TMW compared with the UW samples. In addition, an analysis of the acid-base properties indicated a higher KB than KA number, ie a higher basic than acidic contribution to the surface energy, for all the samples. A higher KB number was also observed for the TMW compared with the UW samples, suggested to relate to the presence of ether bonds from increased lignin and/or extractives content at the surface. The KB was lower for TMW180 compared with TMW150, as a result of higher modification temperature of the first, leading to cleavage of these ether bonds.

Original languageEnglish
Pages (from-to)346-357
Number of pages12
JournalWood and Fiber Science
Volume50
Issue number3
Publication statusPublished - 1 Jan 2018
MoE publication typeA1 Journal article-refereed

Keywords

  • Acid-base properties
  • Dynamic vapor sorption (DVS)
  • Inverse gas chromatography (IGC)
  • Norway spruce
  • Surface energy
  • Thermally modified wood

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