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Exploring the Wood Adhesive Performance of Wheat Gluten
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Coating Technology.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increasing environmental concern has reawakened an interest in materials based on renewable resources as replacement for petroleum-based materials. The main objective of this thesis was to explore plant proteins, more specifically wheat gluten, as a binder in wood adhesives intended for typical solid wood applications such as furniture and flooring.

Alkaline and acidic dispersions of wheat gluten were used as wood adhesives to bond together beech wood substrates. Soy protein isolate was used as a reference. The tensile shear strengths of the substrates were measured for comparison of bond strength and resistance to cold water. AFM in colloidal probe mode was used to investigate nanoscale adhesion between cellulose and protein films. Wheat gluten was divided into the two protein classes; glutenins and gliadins, and their adhesive performance was compared with that of wheat gluten. Heat treatment and mild hydrolysis were investigated as means for improving bonding performance of wheat gluten. The treated wheat gluten samples were analysed by SE-HPLC and 13C-NMR to correlate molecular size distribution and structural changes with bonding performance.

Soy protein isolate is superior to wheat gluten, especially in regards to water resistance. However, the bond strength of wheat gluten is improved when starved bond lines are avoided. The AFM analysis reveals higher interfacial adhesion between soy protein isolate and cellulose than between wheat gluten and cellulose. These results partly explain some of the differences in bonding performance between the plant proteins. Soy protein isolate contains more polar amino acid residues than wheat gluten and possibly interacts more strongly with cellulose. Furthermore, the bond performances of wheat gluten and glutenin are similar, while that of gliadin is inferior to the others, especially regarding water resistance. The extent of penetration of the dispersions into the wood material has a large impact on the results. The bonding performance of gliadin is similar to the others when over-penetration of the dispersion into the wood material is avoided. Moreover, the bond strength of the wheat gluten samples heated at 90°C was in general improved compared to that of wheat gluten. A small improvement was also obtained for some of the hydrolyzed wheat gluten samples (degree of hydrolysis: 0-0.6 %). The improvements in bonding performance for the heat treated samples are due to polymerization, while the improvements for the hydrolyzed samples are due to denaturation. The 13C-NMR analysis of the treated samples confirms some degree of denaturation.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , 74 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:23
Keyword [en]
plant protein, wood adhesive, mechanical properties, wheat gluten, soy protein isolate, gliadin, glutenin, adhesion, hydrolysis, heat treatment, AFM
National Category
Polymer Technologies
Identifiers
URN: urn:nbn:se:kth:diva-94883ISBN: 978-91-7501-348-0 (print)OAI: oai:DiVA.org:kth-94883DiVA: diva2:526419
Public defence
2012-06-01, Sal K2, Teknikringen 28, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20120514Available from: 2012-05-14 Created: 2012-05-11 Last updated: 2012-05-14Bibliographically approved
List of papers
1. Comparing bond strength and water resistance of alkali-modified soy protein isolate and wheat gluten adhesives
Open this publication in new window or tab >>Comparing bond strength and water resistance of alkali-modified soy protein isolate and wheat gluten adhesives
2010 (English)In: International Journal of Adhesion and Adhesives, ISSN 0143-7496, E-ISSN 1879-0127, Vol. 30, no 2, 72-79 p.Article in journal (Refereed) Published
Abstract [en]

The tensile strength of beech substrates bonded with dispersions of alkali-denatured soy protein isolate (SPI) and wheat gluten (WG) was measured for comparison of bond strength and resistance to cold water. The proteins were denatured with 0.1M NaOH (pH 13). Dispersions with different protein concentration and viscosity were investigated. The adhesive properties were studied at different press temperatures (90, 110, and 130 degrees C) and press times (5,15, and 25 min). Two types of application methods were used in order to overcome the problem with different viscosity of the dispersions. In addition, SPI was denatured at two different pH levels (approximately 10 and 13) and with two different concentrations of salt (158 mu M and 0.1 M), in order to compensate for the different isoelectric points of the proteins. The adhesive properties of WG powder with different particle sizes were also compared. The tensile strengths of the wood Substrates were measured according to somewhat simplified versions of the European Standards EN 204 and EN 205. The bond lines were studied with light microscopy. The results indicate that the adhesive properties of SPI are superior, particularly with regard to water resistance. However, the water resistance of WG was to some extent improved when starved adhesive joints could be avoided. Similar tensile strength values were obtained for the dispersions of alkali-denatured SPI regardless of pH or salt concentration. No apparent difference in adhesive strength was observed for the WG dispersions from powder with different particle sizes.

Keyword
Adhesives for wood, Novel adhesives, Wood, Mechanical properties of, adhesives, Plant protein
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-19163 (URN)10.1016/j.ijadhadh.2009.09.002 (DOI)000274078200003 ()2-s2.0-71949084148 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Plant proteins as wood adhesives: Bonding performance at the macro- and nanoscale
Open this publication in new window or tab >>Plant proteins as wood adhesives: Bonding performance at the macro- and nanoscale
2013 (English)In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 44, 246-252 p.Article in journal (Refereed) Published
Abstract [en]

Soy protein isolate and wheat gluten were studied to evaluate their wood bonding performance. A multiscale approach was employed, combining tensile shear strength measurements, optical microscopy, and adhesion measurements at the nanoscale using atomic force microscopy. Tensile shear strength measurements were performed on beech wood substrates bonded with either dispersions of soy protein isolate or wheat gluten to investigate bond strength and water resistance. The results reveal a significant difference in bond strength between the plant proteins. Soy protein isolate is superior to wheat gluten, especially regarding water resistance, both under acidic and alkaline conditions. Cross sections of the wood substrates were examined by optical microscopy to study protein penetration and bond line thickness. The results indicate that a proper bond can be obtained using lower amount of soy protein isolate than wheat gluten. Atomic force microscopy in colloidal probe mode was used to investigate nanoscale adhesion between cellulose and solvent cast protein films. The results show that adhesion between the plant proteins and the wood component is important for the bonding performance. Further, it is shown that the results from atomic force microscopy and tensile shear strength measurements display the same trend demonstrating that the bonding properties translates well spanning regimes from the macro- to the nanoscale. The presented multiscale approach is shown to have great potential and may be used in the future to predict properties at different length scales in the design and formulation of new bioadhesives.

Keyword
Adhesion, Atomic force microscopy, Mechanical properties, Soy protein isolate, Wheat gluten, Wood adhesives
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-94947 (URN)10.1016/j.indcrop.2012.11.021 (DOI)000315659400036 ()2-s2.0-84870865028 (Scopus ID)
Note

QS 20120514. Updated from manuscript to article in journal.

Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2017-12-07Bibliographically approved
3. Wheat Gluten Fractions as Wood Adhesives-Glutenins Versus Gliadins
Open this publication in new window or tab >>Wheat Gluten Fractions as Wood Adhesives-Glutenins Versus Gliadins
Show others...
2012 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 123, no 3, 1530-1538 p.Article in journal (Refereed) Published
Abstract [en]

Plant proteins, such as wheat gluten, constitute attractive raw materials for sustainable wood adhesives. In this study, alkaline water dispersions of the protein classes of wheat gluten, glutenin, and gliadin were used as adhesives to bond together wood substrates of beech. The aim of the study is to measure the tensile shear strength of the wood substrates to compare the adhesive performance of glutenin and gliadin and to investigate the influence of application method and penetration of the dispersions into the wood material. A sodium hydroxide solution (0.1M) was used as dispersing and denaturing agent. Dispersions with different protein concentrations and viscosities were used, employing wheat gluten dispersions as references. Two different application methods, a press temperature of 110 degrees C and a press time of 15 min, were employed. The tensile shear strength and water resistance of the wood substrates were compared, using a slightly modified version of the European Standard EN 204. The bond lines of the substrates were examined by optical microscopy to study the penetration and bond-line thickness. The results reveal that the adhesive properties of gliadin are inferior to that of both glutenin and wheat gluten, especially in terms of water resistance. However, the tensile shear strength and the water resistance of gliadin are significantly improved when over-penetration of the protein into the wood material is avoided, rendering the adhesive performance of gliadin equal to that of glutenin and wheat gluten.

Keyword
adhesives, mechanical properties, proteins, renewable resources, biopolymers
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-51267 (URN)10.1002/app.34312 (DOI)000296862700027 ()2-s2.0-80255126228 (Scopus ID)
Note
QC 20111212Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2017-12-08Bibliographically approved
4. Adhesive properties of wheat gluten after enzymatic hydrolysis or heat treatment - A comparative study
Open this publication in new window or tab >>Adhesive properties of wheat gluten after enzymatic hydrolysis or heat treatment - A comparative study
2012 (English)In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 38, no 1, 139-145 p.Article in journal (Refereed) Published
Abstract [en]

Wheat gluten, among other plant proteins, constitutes an attractive raw material for sustainable alternatives to today's petroleum-based wood adhesives. Nevertheless, the bonding performance, and especially the water resistance, of these plant proteins need to be improved to turn them into competitors equal in merit to today's petroleum-based products. The aim of this study was to investigate if mild hydrolysis or heat treatment of wheat gluten will improve its adhesive properties. Wheat gluten was hydrolyzed with the enzyme Alcalase (degree of hydrolysis 0.3-5.5%), or heat treated at different temperatures (50, 70, and 90 degrees C) and varying time intervals (15 min to 24 h). Alkaline water dispersions of these modified wheat gluten samples were used as adhesives to bond together wood substrates of beech at a press temperature of 110 degrees C and a press time of 15 min. The tensile shear strengths of the substrates were measured for comparison of bond strength and resistance to cold water. The substrates were evaluated according to a slightly modified version of the European Standard EN 204. Lower levels of hydrolysis (0.3-0.6%) and most of the heat treatments at 90 degrees C resulted in improved bond strength and water resistance. Nevertheless, the adhesive properties, especially the water resistance, need to be further improved to fulfill today's requirements for wood adhesives.

Keyword
Wood adhesives, Wheat gluten, Enzymatic hydrolysis, Heat treatment, Plant protein, Mechanical properties
National Category
Agricultural Sciences Biological Sciences
Identifiers
urn:nbn:se:kth:diva-94037 (URN)10.1016/j.indcrop.2012.01.021 (DOI)000302433400021 ()2-s2.0-84857023182 (Scopus ID)
Note
QC 20120507Available from: 2012-05-07 Created: 2012-05-07 Last updated: 2017-12-07Bibliographically approved
5. Characterization of Enzymatically Hydrolyzed or Heat Treated Wheat Gluten by SE-HPLC and 13C-NMR: Correlation with Wood Bonding Performance
Open this publication in new window or tab >>Characterization of Enzymatically Hydrolyzed or Heat Treated Wheat Gluten by SE-HPLC and 13C-NMR: Correlation with Wood Bonding Performance
(English)Manuscript (preprint) (Other academic)
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-94949 (URN)
Note
QS 2012Available from: 2012-05-11 Created: 2012-05-11 Last updated: 2012-05-14Bibliographically approved

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