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High Leach-Resistant Fire-Retardant Modified Pine Wood (Pinus sylvestris L.) by In Situ Phosphorylation and Carbamylation
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.ORCID iD: 0000-0003-0852-5066
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 Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.ORCID iD: 0000-0002-5474-1512
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.ORCID iD: 0000-0003-4720-5380
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2023 (English)In: ACS Omega, E-ISSN 2470-1343, Vol. 8, no 12, p. 11381-11396Article in journal (Refereed) Published
Abstract [en]

The exterior application of fire-retardant (FR) timber necessitates it to have high durability because of the possibility to be exposed to rainfall. In this study, water-leaching resistance of FR wood has been imparted by grafting phosphate and carbamate groups of the water-soluble FR additives ammonium dihydrogen phosphate (ADP)/urea onto the hydroxyl groups of wood polymers via vacuum-pressure impregnation, followed by drying/heating in hot air. A darker and more reddish wood surface was observed after the modification. Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, solid-state 13C cross-polarization magic-angle-spinning nuclear magnetic resonance (13C CP-MAS NMR), and direct-excitation 31P MAS NMR suggested the formation of C–O–P covalent bonds and urethane chemical bridges. Scanning electron microscopy/energy-dispersive X-ray spectrometry suggested the diffusion of ADP/urea into the cell wall. The gas evolution analyzed by thermogravimetric analysis coupled with quadrupole mass spectrometry revealed a potential grafting reaction mechanism starting with the thermal decomposition of urea. Thermal behavior showed that the FR-modified wood lowered the main decomposition temperature and promoted the formation of char residues at elevated temperatures. The FR activity was preserved even after an extensive water-leaching test, confirmed by the limiting oxygen index (LOI) and cone calorimetry. The reduction of fire hazards was achieved through the increase of the LOI to above 80%, reduction of 30% of the peak heat release rate (pHRR2), reduction of smoke production, and a longer ignition time. The modulus of elasticity of FR-modified wood increased by 40% without significantly decreasing the modulus of rupture.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2023. Vol. 8, no 12, p. 11381-11396
National Category
Wood Science Physical Chemistry
Research subject
Wood Science and Engineering; Structural Engineering; Chemistry of Interfaces
Identifiers
URN: urn:nbn:se:ltu:diva-95881DOI: 10.1021/acsomega.3c00146ISI: 000960080200001PubMedID: 37008136Scopus ID: 2-s2.0-85150425157OAI: oai:DiVA.org:ltu-95881DiVA, id: diva2:1743575
Funder
Swedish Research Council Formas, 2021-00818
Note

Validerad;2023;Nivå 2;2023-04-21 (joosat);

Funder: OP RDE (Grant no.CZ.02.1.01/0.0/0.0/16_019/0000803); CT WOOD, Luleå University of Technology

Licens fulltext: CC BY License

Available from: 2023-03-15 Created: 2023-03-15 Last updated: 2023-09-22Bibliographically approved
In thesis
1. Innovative Water-Resistant Fire-Retardant Wood incorporating Ammonium Phosphate-based salts for Exterior Use Conditions
Open this publication in new window or tab >>Innovative Water-Resistant Fire-Retardant Wood incorporating Ammonium Phosphate-based salts for Exterior Use Conditions
2023 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wood is a naturally based material and plays an important role as a renewable resource when aiming for a sustainable society. Nevertheless, its inherently combustible property needs to be enhanced to comply with modern construction methods and regulations. Ammonium phosphate-based additives are often used to effectively increase the fire-retardancy (FR) of wooden products when needed. However, their water-solubility make them unsuitable for exterior use unless such properties are overcome. This PhD thesis focuses on the development of methodologies to alleviate consequences from water-leaching of wood treated with ammonium phosphate-based additives, enabling further development of new types of fire protected wood construction material for exterior uses. As such, two methodologies were explored in this thesis: 1) a composite-type fixation, involving the introduction of a hydrophobic polymer matrix for entrapping the FR additives, 2) a reactive-type fixation, which is to fix the FR additives by creating covalent bonding with the wood polymeric constituents.

In order to determine the influence of composite-type fixation systems, melamine-formaldehyde (MF) prepolymer, furfuryl alcohol (FA), and kraft lignin, respectively, were studied for immobilising ammonium phosphate-based FR-additives in wood by pressure impregnating Scots pine (Pinus sylvestris L.) sapwood with a solution of the prepolymer and fire-retardant additives (FRs), followed by drying and heating steps. Through the analysis of the treated wood materials, involving scanning electron microscopy energy dispersive spectroscopy (SEM-EDX) and thermal gravimetric analysis (TGA), the formation of a stable polymeric network structure entrapping the additives inside the wood with alleviating FRs’ water-leachability was proposed. In particular, MF-resin was able to encapsulate guanyl-urea phosphate (GUP) in the lumen of the wood. Further details on the distribution and structural features of FR additives and matrices within the wood structure are described in the thesis. 

Furthermore, the ability of FRs comprising ammonium dihydrogen phosphate (ADP) and urea to be fixed within the wood structure without the addition of polymeric materials was also investigated. This approach was accomplished by impregnating an aqueous solution containing the aforementioned additives, followed by drying and further heat treatment at 150°C. By analysis of the treated wood material by solid-state nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), and FTIR, the formation of a reactive-type fixation of FR to the wood structure was realised. By this way, phosphate and carbamylate groups from treated ADP/urea were found to have reacted with hydroxyl groups of the wood polymers. 

The fire performance of FR-treated wood materials was studied with a series of modern techniques, namely, limited oxygen index (LOI), microscale combustion calorimeter (MCC), and cone calorimeter tests. LOI and MCC were used as a simple test of fire stability of FR-treated and subsequently water exposed wood. By applying the cone calorimeter test, the predicted reaction-to-fire classification of FR-MF, FR-FA, and phosphorylated/carbamylated wood was established and, actually, reached the highest possible classification, class B. This classification was held even after the accelerated ageing test according to the European standard EN 84. In summary, this further suggested that these methodologies, which enhanced the water-leaching resistance of ammonium phosphate-based salts, have the potential to give a fire-retardant wood suitable for exterior uses.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2023
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Textile, Rubber and Polymeric Materials
Research subject
Wood Science and Engineering
Identifiers
urn:nbn:se:ltu:diva-101276 (URN)978-91-8048-381-0 (ISBN)978-91-8048-382-7 (ISBN)
Public defence
2023-12-05, A193, Forskargatan 1, 931 77 Skellefteå, Skellefteå, 10:00 (English)
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Supervisors
Available from: 2023-09-22 Created: 2023-09-22 Last updated: 2023-11-14Bibliographically approved

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Lin, Chia-FengKarlsson, OlovDas, OisikMensah, Rhoda AfriyieJones, DennisAntzutkin, Oleg N.Försth, MichaelSandberg, Dick

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