Hyperspectral imaging and chemometrics to investigate the chemical wood modification

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School of Chemical Engineering | Doctoral thesis (article-based) | Defence date: 2023-06-30
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Authors

Date

2023

Department

Biotuotteiden ja biotekniikan laitos
Department of Bioproducts and Biosystems

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Mcode

Degree programme

Language

en

Pages

88 + app. 68

Series

Aalto University publication series DOCTORAL THESES, 94/2023

Abstract

Wood possesses an anisotropic hierarchical structure that causes a heterogeneous distribution of chemical reagents in modified wood at different spatial scales. Due to the heterogeneity in chemical distribution, localised regions of wood may remain susceptible to moisture uptake, dimensional instability, and fungal decay. The identification of regions with insufficient chemical uptake is necessary to develop efficient treatment processes, but standard gravimetric methods are insensitive to the location of chemical reagents within the wood. The primary objective of this thesis was to analyse the suitability of spectroscopic-based imaging methods to reveal the distribution of chemical reagents in modified wood at different length scales. The studies focused on the chemical modification of wood with acetic anhydride, paraformaldehyde, and thermosetting resins. The added chemical reagents are known to either react with cell wall polymers to create covalent bonds or to polymerize macromolecules within the cell wall space. To analyze the chemical changes caused by the modification agents on different spatial scales, the studies combined two chemical imaging techniques that differ in their lateral resolution to identify the process-dependent heterogeneity in modified wood. Near-infrared (NIR) hyperspectral imaging identified and quantified the distribution of chemical reagents and the corresponding moisture content at a macroscopic scale of a few millimeters. Chemometric analysis not only revealed the sample-to-sample variations in chemical uptake and the associated moisture content but also highlighted the localised variations, most notably earlywood and latewood differences. Confocal Raman imaging validated the differences between earlywood and latewood on the cellular level and visualised chemical differences between cell wall regions. Following this, the moisture uptake and the consequent swelling of the modified samples were determined by the dynamic measurements of mass and dimensions within the hygroscopic range. The results indicated the effectiveness of chemical modifications in reducing the moisture content of untreated wood. Overall, the results in this thesis demonstrated the ability of chemical imaging techniques to localise chemical reagents in small woodblocks and larger board sections. The findings provide a step forward in understanding the chemical changes caused by wood modification in different hierarchical structures in wood on different length scales. In the future, the methods may be used to characterise other treatments and processes that affect the wood composition.

Description

Supervising professor

Rautkari, Lauri, Assoc. Prof., Aalto University, Department of Bioproducts and Biosystems, Finland

Thesis advisor

Altgen, Michael, Norwegian Institute of Bioeconomy Research, Norway
Mäkelä, Mikko, Prof., VTT Technical Research Centre of Finland, Finland
Belt, Tiina, Natural Resources Institute Finland, Finland

Keywords

near-Infrared hyperspectral imaging, confocal Raman imaging, wood modification, chemometrics, moisture content

Other note

Parts

  • [Publication 1]: Muhammad, Awais; Altgen, Michael; Mäkelä, Mikko; Altgen, Daniela; Rautkari, Lauri. 2020. Hyperspectral near-infrared image assessment of surface acetylated solid wood. ACS Applied Bio Materials, 3(8), 5223-5232.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202010165896
    DOI: 10.1021/acsabm.0c00626 View at publisher
  • [Publication 2]: Muhammad, Awais; Altgen, Michael; Mäkelä, Mikko; Belt, Tiina; Rautkari, Lauri. 2022. Quantitative prediction of moisture content distribution in acetylated wood using near-infrared hyperspectral imaging. Journal of Materials Science, 57, 3416-3429.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202202161913
    DOI: 10.1007/s10853-021-06812-2 View at publisher
  • [Publication 3]: Muhammad, Awais; Altgen, Michael; Belt, Tiina; Teräväinen, Venla; Mäkelä, Mikko; Altgen, Daniela; Nopens, Martin; Rautkari, Lauri. 2022. Woodwater relations affected by anhydride and formaldehyde modification of wood. ACS Omega, 7 (46), 42199-42207.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202212146870
    DOI: 10.1021/acsomega.2c04974 View at publisher
  • [Publication 4]: Altgen, Michael; Muhammad, Awais; Altgen, Daniela; Klüppel, André; Mäkelä, Mikko; Rautkari, Lauri. 2020. Distribution and curing reactions of melamine formaldehyde resin in cells of impregnation-modified wood. Scientific Reports, 10, 3366.
    DOI: 10.1038/s41598-020-60418-3 View at publisher
  • [Publication 5]: Altgen, Michael; Muhammad, Awais; Altgen, Daniela; Klüppel, André; Koch, Gerald; Mäkelä, Mikko; Olbrich, Andrea; Rautkari, Lauri. 2023. Chemical imaging to reveal the resin distribution in impregnation-treated wood at different spatial scales. Materials & Design, 225, 111481.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202301021033
    DOI: 10.1016/j.matdes.2022.111481 View at publisher

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https://urn.fi/URN:ISBN:978-952-64-1319-8

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[diss] Kemian tekniikan korkeakoulu / CHEM