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Chemical Interactions between Fatty Acids and Wood Components during Oxidation Processes
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
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.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:41
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-102815ISBN: 978-91-7501-470-8 (print)OAI: oai:DiVA.org:kth-102815DiVA: diva2:556760
Public defence
2012-10-12, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation, 8405Formas, 243-2006-273
Note

QC 20120926

Available from: 2012-09-26 Created: 2012-09-26 Last updated: 2012-09-26Bibliographically approved
List of papers
1. Effect of model lignin structures on the oxidation of unsaturated fatty acids
Open this publication in new window or tab >>Effect of model lignin structures on the oxidation of unsaturated fatty acids
2010 (English)In: Polymers from Renewable Resources, ISSN 2041-2479, Vol. 1, no 2Article in journal (Refereed) Published
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-33164 (URN)2-s2.0-80054046757 (Scopus ID)
Note
QC 20110429Available from: 2011-04-29 Created: 2011-04-29 Last updated: 2012-09-26Bibliographically approved
2. Oxidation of methyl linoleate in the presence of lignin
Open this publication in new window or tab >>Oxidation of methyl linoleate in the presence of lignin
Show others...
2011 (English)In: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331X, Vol. 72, no 3, 325-333 p.Article in journal (Refereed) Published
Abstract [en]

The overall aim of this study is to develop new wood modifications using vegetable oils to obtain improved durability of wood materials in an environmentally friendly way. Nuclear magnetic resonance (NMR) and Fourier-transform infrared (FT-IR) spectroscopies were used to study oxidation and possible chemical coupling reactions between polyunsaturated fatty acids and model lignin compounds in order to better understand the interactions between oxidatively drying systems such as vegetable oils or alkyds with the lignin part in wood. This was done by studying mixtures of different model lignin compounds and methyl linoleate. The oxidation process was analyzed at 70 °C both in methyl linoleate alone and in combination with 20 wt% of lignin model compounds. The effects of those compounds on the oil polymerization processes were monitored by NMR (both 13C and 1H experiments) and the domain specific reactivity and patterning were then combined with FT-IR data. No covalent bonds having formed between the oil and the model compounds were detected by combination of several 13C/1H 2D NMR methods. From the spectra, the oxidation degrees of model compounds were calculated, and for some lignin model compounds alcohols were oxidized to carbonyls during the process. Those results were in excellent agreement with FT-IR data and oxidation mechanisms were proposed. The combination of both analytical techniques was necessary to have a better understanding of these systems: NMR demonstrated the absence of chemical bond and quantified oxidation degree of model lignin molecules while FT-IR focused on oil oxidation.

Keyword
Fourier Transform Infrared FT-IR, Methyl linoleate, Model lignin compounds, Nuclear Magnetic Resonance NMR, Oxidative drying, Unsaturated fatty acids, Wood modification
National Category
Engineering and Technology
Research subject
SRA - Production
Identifiers
urn:nbn:se:kth:diva-49743 (URN)10.1016/j.porgcoat.2011.05.004 (DOI)000297454800013 ()2-s2.0-80054012132 (Scopus ID)
Funder
XPRES - Initiative for excellence in production research
Note
QC 20111201Available from: 2011-11-29 Created: 2011-11-29 Last updated: 2017-12-08Bibliographically approved
3. Vegetable oils reaction within wood studied by direct 13C excitation with 1H decoupling and magic-angle spinning NMR
Open this publication in new window or tab >>Vegetable oils reaction within wood studied by direct 13C excitation with 1H decoupling and magic-angle spinning NMR
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-33179 (URN)
Note
QS 20110429Available from: 2011-04-29 Created: 2011-04-29 Last updated: 2012-09-26Bibliographically approved
4. Effect of wood carbohydrates on the oxidation of unsaturated fatty acids
Open this publication in new window or tab >>Effect of wood carbohydrates on the oxidation of unsaturated fatty acids
2013 (English)In: Progress in organic coatings, ISSN 0300-9440, E-ISSN 1873-331X, Vol. 76, no 7/8, 1068-1074 p.Article in journal (Refereed) Published
Abstract [en]

The aim of this study is to better understand the oxidation mechanism of the fatty acids applied on wood surfaces. In the present study, model hemicellulose compounds were used to measure the effect of polysaccharides on auto-oxidation of methyl linoleate utilizing infrared spectroscopy (RT-IR). The auto-oxidation process of methyl linoleate was measured in combination with 1 wt% reducing and non-reducing hemicellulose model compounds (HMC) at 70 degrees C. The effect of HMC on the methyl linoleate auto-oxidation process was also compared with the effects of glycerol and glyceraldehyde, using same analytical method and reaction conditions. The IR-spectra of methyl linoleate with 1 wt% carbohydrates before and after oxidation were analyzed and peak intensity variations during oxidation in the region of 3010 cm(-1), 990 cm(-1), and 970 cm(-1) were calculated during oxidation process. It was observed that lactose and sucrose accelerated the radical reactions; however, glycerol has an anti-oxidative effect on the fatty acids oxidation. An interaction mechanism for these findings is proposed and discussed.

National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-102821 (URN)10.1016/j.porgcoat.2013.03.002 (DOI)000319647300009 ()2-s2.0-84876959410 (Scopus ID)
Note

Updated from "Submitted" to "Published"  QC 20130710

Available from: 2012-09-26 Created: 2012-09-26 Last updated: 2017-12-07Bibliographically approved
5. Effect of wood structures on fatty acids oxidation
Open this publication in new window or tab >>Effect of wood structures on fatty acids oxidation
(English)Manuscript (preprint) (Other academic)
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-102823 (URN)
Note

QS 2012

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

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