Abstract
The dimensional stabilisation of wood using thermosetting resins relies on the resin uptake into the cell walls. This study tested if a conditioning step after the impregnation and before the final heat-curing enhances the cell wall uptake to improve dimensional stabilisation without increasing the chemical consumption. Small blocks of Scots pine sapwood were vacuum-impregnated with an aqueous melamine formaldehyde solution and conditioned at 33, 70, or 95 % RH for up to 1 week before drying and curing the blocks at 103 °C. However, the conditioning step decreased the cell wall bulking and the moisture exclusion effect compared to the immediate heat curing of the impregnated samples. Analyses of the resin-treated samples by scanning electron microscopy, IR spectroscopy and confocal Raman microspectroscopy provided evidence of wood hydrolysis and polycondensation of the resin within the cell lumen during the conditioning step. Hydrolysis and removal of wood constituents may have counterbalanced the cell wall bulking of the resin. Polycondensation of the resin in the lumen increased its molecule size, which could have hindered the cell wall diffusion of the resin.
Funding source: Research Council of Finland
Award Identifier / Grant number: 341701
Acknowledgments
This work made use of the Aalto University Nanomicroscopy Center (AaltoNMC) premises.
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Research ethics: Not applicable.
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Author contributions: T.S. and M.A. designed the experiments and conducted the water sorption and confocal Raman microspectroscopy measurements. T.S. performed the wood treatments and recorded the infrared spectra. M. Aw. applied PCA to the confocal Raman data. D.A. performed the SEM analyses. M.A. analysed the results together with T.S. and wrote the manuscript, which was reviewed by all authors.
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Competing interests: The authors state no conflicts of interest.
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Research funding: This work received funding from the Research Council of Finland (grant no. 341701).
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Data availability: The raw data can be obtained on request from the corresponding author.
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Supplementary Material
This article contains supplementary material (https://doi.org/10.1515/hf-2023-0084).
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