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Dimensional stabilisation of Scots pine (Pinus sylvestris L.) sapwood by reaction with maleic anhydride and sodium hypophosphite
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0003-4335-8419
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0002-7711-9267
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Department of Wood Processing and Biomaterials, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Kamýcká 129, Suchdol, 165 21, Praha 6, Czech Republic.ORCID iD: 0000-0002-5565-6651
Department of Forestry, Wood Sciences and Design, Laboratory of Wood Science and Technology, University of Thessaly, 43100, Karditsa, Greece.
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2021 (English)In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 79, no 3, p. 589-596Article in journal (Refereed) Published
Abstract [en]

Wood has the ability to absorb and desorb moisture, which can affect its dimensional size when in use. Limiting this can provide products with greater shape stability and less stresses on external coatings. One method that has been investigated for achieving this has been through chemical modification. In this work, the dimensional stabilisation imparted to Scots pine sapwood by chemical modification with maleic anhydride (MA) combined with sodium hypophosphite (SHP) was investigated. The influence of concentration of MA, treatment temperature and treatment period on weight percent gain (WPG) and bulking coefficient (BC) during treatment with MA and SHP of wood was studied. Furthermore, dimensional stability was determined by the water soak/oven dry method (wet-dry cycle) through five cycles in order to determine the hydrolytic stability of the ester bond and any potential cross-linking reactions. Wood blocks (20 × 20 × 10 mm) modified with MA combined with SHP exhibited lower weight loss following water soaking than unmodified blocks or MA-treated blocks. Wood blocks modified with MA and SHP showed the best anti-swelling efficiency and minimum wet-volume (water-saturated). However, as the concentration of SHP increased, dimensional stability was diminished without any increase in weight percentage gain after water soaking. When combined with FTIR results, it appeared that the modification with MA and SHP seemed to form cross-linking between wood constituents, though high concentration of SHP did not seem to result in additional cross-linking.

Place, publisher, year, edition, pages
Springer, 2021. Vol. 79, no 3, p. 589-596
National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-82413DOI: 10.1007/s00107-020-01650-6ISI: 000604492600006Scopus ID: 2-s2.0-85098672079OAI: oai:DiVA.org:ltu-82413DiVA, id: diva2:1518052
Funder
Vinnova, 2017-02697Swedish Research Council Formas, 2017-00419
Note

Validerad;2021;Nivå 2;2021-05-17 (johcin);

Finansiär: OP RDE (CZ.02.1.01/0.0/0.0/16_019/0000803)

Available from: 2021-01-15 Created: 2021-01-15 Last updated: 2025-03-26Bibliographically approved
In thesis
1. Wood Modification with Maleic Anhydride and Sodium Hypophosphite
Open this publication in new window or tab >>Wood Modification with Maleic Anhydride and Sodium Hypophosphite
2025 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wood has been a crucial material for construction throughout history. However, due to poor natural durability of wood, it is difficult to use outdoors without any additional treatment. Conventionally, wood has been fully or partially impregnated with preservatives. However, some substances are harmful to mankind and environment, hence, regulated strictly. Therefore, methods for achieving sustainable protection of wood have been required and one method that has been investigated for achieving this has been through chemical modification. 

This doctoral thesis aims to develop a new modification system for solid wood in use class 3. The objective was to develop a wood modification system based on maleic anhydride (MA) and sodium hypophosphite (SHP) that enables exterior use without leaching by weathering. To meet this requirement, the modification should involve formation of stable cross-linking, altering the interaction between moisture and wood, consequently enhancing dimensional stability and biological resistance. 

To test the possibility of using MA and SHP, Scots pine sapwood (Pinus sylvestris L.) was treated with various ratio of chemical reagents, curing temperatures and durations. The treated wood was subjected to repetitive wet-dry cycle to assess its dimensional stability and leachability of chemical reagents. The result indicated formation of a stable cross-linking between wood constituents. 

To further investigate the formation of cross-link, solid-state 13C cross-polarization magic-angle-spinning (CP-MAS) nuclear magnetic resonance (NMR), 31P MAS NMR and X-ray photoelectron spectroscopy (XPS) were employed. The findings indicated that the cross-linking was likely to involve phosphonate (C-P-O) bonds. These results provided a deeper fundamental understanding of the reaction mechanisms between wood, MA and SHP, providing further scope for improved treatment systems in the future.

The impact of the modification on wood-water interactions was analyzed using low-field nuclear magnetic resonance (LFNMR) to study water in the wood at a saturated state. Additionally, the hydrophilicity of cell walls was studied via infrared spectroscopy after deuteration using liquid D2O. The results indicated that the modification reduced the affinity of the wood cell wall to water without altering the number of accessible hydroxyl groups.  

Finally, the modified wood was evaluated for fungal decay resistance, mechanical strength test (bending), and thermal stability. The modification significantly reduced mass loss caused by wood-decaying fungi by limiting the moisture uptake in wood and altering the chemical structure of wood. On the other hand, the modification did not improve resistance to fungal growth on the wood surface, suggesting that nutrient accessibility on surface was not influenced by the modification. A bending test showed that while the modulus of elasticity (MOE) was not affected, modulus of rupture (MOR) decreased to half that of untreated wood. Thermal resistance was improved due to the presence of phosphonate, which can promote the formation of a protective char layer and radical moieties. 

This study demonstrated the potential of modifying wood with MA and SHP to enhance durability, dimensional stability, and fire resistance. The modification formed stable cross-link within the wood components, reducing water interaction and improving resistance to biological degradation. However, the reduction in MOR limits its suitability for load-bearing applications. Despite this, the results suggest that the modified wood could be a viable alternative for non-load bearing exterior applications.

Future research should focus on optimising the modification process by reducing temperature, duration, and solvent use while maintaining performance. Investigating catalysts for the reaction may help address these challenges. Additionally, long-term field testing under real environmental conditions is needed to evaluate the durability and stability of the modified wood. Environmental impact assessments and life cycle analysis will also be crucial for ensuring commercial feasibility and sustainability.

Place, publisher, year, edition, pages
Luleå University of Technology, 2025
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Wood Science
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-112139 (URN)978-91-8048-803-7 (ISBN)978-91-8048-804-4 (ISBN)
Public defence
2025-05-27, A193, Luleå University of Technology, Skellefteå, 09:00 (English)
Opponent
Supervisors
Available from: 2025-03-26 Created: 2025-03-26 Last updated: 2025-05-06Bibliographically approved

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Kim, InjeongKarlsson, OlovJones, DennisSandberg, Dick

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