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Vegetable oils reaction within wood studied by direct 13C excitation with 1H decoupling and magic-angle spinning NMR
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. (Polymer Technology)
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry.ORCID iD: 0000-0002-6524-1441
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.ORCID iD: 0000-0003-3201-5138
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(English)Manuscript (preprint) (Other academic)
National Category
Polymer Chemistry
URN: urn:nbn:se:kth:diva-33179OAI: diva2:413762
QS 20110429Available from: 2011-04-29 Created: 2011-04-29 Last updated: 2012-09-26Bibliographically approved
In thesis
1. Chemical Interactions between Fatty Acids and Wood Components during Oxidation Processes
Open this publication in new window or tab >>Chemical Interactions between Fatty Acids and Wood Components during Oxidation Processes
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fatty acids auto-oxidation on wood is proposed to follow a complex free radical interaction mechanism. The aim of this study was to analyze the effect of wood constituents on oxidation of fatty acids and thereby the entire drying process, and to characterize the fatty acids-wood interaction by using analytical instruments such as RT-IR and NMR.

The auto-oxidation process of polyunsaturated fatty acids was analyzed in combination with wood model compounds, softwood and hardwood. The results showed that the oxidative drying process of unsaturated fatty acids was indeed affected by wood constituents. Wood morphology is heterogeneous and porous. A problematic issue in fatty acid-wood system is its heterogeneity and complexity.

The most hydrophobic polymer of the main constituents of wood is lignin and it interacted with the oxidation process and lignin structures inhibited or retarded the reaction. However, wood carbohydrates such as lactose and sucrose increased the rate of fatty acids oxidation, thus carbohydrates may function as catalysts.

The fatty acids pattern affects not only the structure of the dried oil itself but also the surrounding wood materials. Not only the oil structures were affected but also the lignin was to some extent oxidized as a competing reaction with the oil oxidation. Further, a formation of chemical bonds between the oil and the lignin structures was not observed, i.e. the oils were not immobilized on lignin by covalent bond formation to any significant extent. The analysis on oils in wood using NMR and FTIR demonstrated that highly reactive linoleic acid interacted in wood significantly, while it was not immobilized to the same extent. Oleic acid on the other hand interacted more slowly but was immobilized in the wood structure.

A number of wood species (hardwood and softwood) were tested for how they affected the drying process, where Norway spruce dried the fastest and hazelwood the slowest. Generally it appeared to be a connection between high density and slow drying. It can thus be concluded that different wood components affect the oil drying process in different ways. According to the results, it can also be concluded that the structure of the oil and different wood species are crucial in the overall protective performance of the system.

Abstract [sv]

Fettsyrors oxidation på trä följer en komplicerad friradikal-interaktionsmekanism. Syftet med detta arbete var att öka kunskapen om detta samt att utveckla nya system baserade på vegetabiliska oljor för att erhålla nya förbättrade system för utvändigt skydd av trä med miljövänlig teknik. Oxidationsprocessen av fleromättade fettsyror analyserades i kombination med modellföreningar av trä, både lövträ och barrträ. Oxidationsreaktionen karakteriserades genom att använda olika analytiska instrument, t.ex. RT-IR och NMR.  Resultaten visade att oxidationsreaktionshastigheten påverkades av träkomponenterna. Lignin som är den mest hydrofoba delen av trä, inhiberar eller retarderar oxidationsreaktionen. Däremot träkolhydrater t.ex. laktos och sackaros (1 vikt%) ökade reaktionshastigheten av fettsyraoxidationen och fungerade som katalysator i torkningssystemet.

NMR-analyser visade att fettsyror kan samverka med träkomponenter under oxidationsprocessen. Studierna visar dock att ingen mätbar mängd olja kemisk reagerar ihop med lignin d.v.s. fettsyror reagerade inte på lignin genom kovalenta bindningar. NMR studier av olika oljor i trä visar vidare att mer reaktiva oljor (exempelvis linolja) reagerar snabbt men att merparten av dessa oxidationsreaktioner inte leder till att oljan immobilseras på en molekylär nivå. Mindre reaktiva oljor å andra sidan (exempelvis oljor med hög oljesyrahalt) torkar långsammare men på de ställen där de reagerar leder detta till större andel immobiliserad olja. Modellstudier mellan torkande oljor och olika ligninkomponenter visar att det sker en kemisk samverkan mellan ligninet och oljorna under oxidationsprocessen. En mycket viktig faktor är att inte enbart oljan oxideras utan att även en del ligninstrukturer kemisk förändras under denna process. Trä är ett heterogent material, samt oxidationen av fettsyror med träkomponenter medför ett komplext och heterogent system.

RT-IR analyserna visade att t.ex. gran ökar oxidationstiden men hasselträ har den mest antioxidativa effekten på oxidationen av fettsyror. Från denna studie kan slutsatsen dras att olika träkomponenter påverkar torkningsprocessen hos olja på olika sätt och olika träslag har olika effekter på torkningsprocessen, bland annat beroende på trädensitet och den kemiska sammansättningen av trästrukturen. Dessutom har struktursammansättningen av fettsyrans kolkedjor också avgörande betydelse för oxidationsmekanismen på träytan.


Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 63 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2012:41
National Category
Engineering and Technology
urn:nbn:se:kth:diva-102815 (URN)978-91-7501-470-8 (ISBN)
Public defence
2012-10-12, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Knut and Alice Wallenberg Foundation, 8405Formas, 243-2006-273

QC 20120926

Available from: 2012-09-26 Created: 2012-09-26 Last updated: 2012-09-26Bibliographically approved

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