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Hemicelluloses and other Polysaccharides for Wood Adhesive Applications
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology, Coating Technology.
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The growing environmental awareness has led to an increased interest in bio-based polymers as replacement for fossil-based materials. The purpose of the work described in this thesis was to investigate the possibility of using hemicelluloses and other polysaccharides as replacement for fossil-based polymers in wood adhesives. Together with cellulose and lignin, hemicellulose is the main constituent of wood. In the pulp industry, significant amounts of hemicelluloses are obtained as by-products and combusted for energy recovery, but there is a growing interest in the biorefinery concept where all side-streams are utilized. If valuable applications, such as adhesives, of hemicelluloses and other by-products are found, large amounts can be obtained from the pulp industry. Water dispersions of hemicelluloses and other polysaccharides have been prepared and evaluated as adhesives for bonding different wood substrates together. The dry bond strength, water resistance, and heat resistance were investigated by exposing the bonded wood specimens to different conditioning methods and thereafter measuring the tensile shear strengths. As a replacement, the bio-based wood adhesive must possess similar or even better properties than the fossil-based adhesives. A commercial poly(vinyl acetate) (PVAc) wood adhesive used for indoor applications has been used as a reference benchmark. Wood hemicelluloses themselves do not have sufficient bonding performance probably because their low molecular weight does not provide adequate strength and makes the adhesive too brittle. The addition of dispersing agents and crosslinkers to the hemicellulose dispersions can significantly improve the bonding performance, and hemicellulose in combination with poly(vinyl amine) showed promising results superior those of PVAc. A fully bio-based adhesive comprising of hemicellulose and chitosan, another bio-based polysaccharide, obtain surprisingly good bonding performance especially with regard to water resistance. Gums, polysaccharides with similar structures to those of hemicelluloses but with higher molecular weights, have also been studied and locust bean gum dispersions without any modification showed a very good bonding performance with high dry bond strength and water resistance on a par with those of PVAc and a heat resistance superior to that of PVAc. Chitosan has very good adhesive properties especially with regard to water resistance, but the high viscosity of the chitosan dispersion makes it difficult to apply. Chitosan-grafted-PVAc dispersions were therefore prepared and an adhesive very similar in appearance to PVAc was obtained with a good bonding performance as well as good applicability.

Place, publisher, year, edition, pages
Kungliga Tekniska högskolan, 2018. , p. 74
Series
TRITA-CBH-FOU ; 2018:22
National Category
Polymer Technologies
Research subject
Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-228298ISBN: 978-91-7729-790-1 (print)OAI: oai:DiVA.org:kth-228298DiVA, id: diva2:1208901
Public defence
2018-06-11, Kollegiesalen, Brinellvägen 8, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20180521

Available from: 2018-05-21 Created: 2018-05-21 Last updated: 2018-05-21Bibliographically approved
List of papers
1. Gum dispersions as environmentally friendly wood adhesives
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2014 (English)In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 52, p. 736-744Article in journal (Refereed) Published
Abstract [en]

Today, wood adhesives are mainly prepared from petroleum-based polymers. There is an ambition to decrease the utilization of petroleum-based raw materials and introduce bio-based polymers instead. However, the utilization of bio-based polymers is often limited due to insufficient properties in terms of water resistance or heat resistance. In this study bio-based dispersions have been prepared of locust bean gum, guar gum, xanthan gum and tamarind gum and evaluated as wood adhesives. Due to the high viscosity of the dispersions, a low dry solids content of 6. wt% was used. The film forming properties have been investigated and contact-angle measurement have been performed to obtain an indication of water resistance. Wood substrates have been bonded together and the bonding performance has been evaluated with different techniques. The gum dispersions have been compared with a commercial poly(vinyl acetate)-based wood adhesive and the results demonstrate that gums can be used as binders for wood adhesives. Locust bean gum dispersions show remarkable results - comparable to the commercial wood adhesive - even though the dry solids content is very low. The locust bean gum dispersion fulfills the D2 and WATT 91 requirements for wood adhesives according to the European Standard EN 204 and European Standard EN 14257.

Keywords
Biopolymer, Locust bean gum, Polysaccharide, Tensile shear strength, Water resistance, Wood adhesive
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-140834 (URN)10.1016/j.indcrop.2013.12.001 (DOI)000332189200098 ()2-s2.0-84890852493 (Scopus ID)
Note

QC 20140131

Available from: 2014-01-31 Created: 2014-01-31 Last updated: 2018-05-21Bibliographically approved
2. Xylan - A green binder for wood adhesives
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2015 (English)In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 67, p. 483-493Article in journal (Refereed) Published
Abstract [en]

Wood adhesives are mainly prepared from polymers derived from petroleum-based resources. With the increasing concern for the environment, it is necessary to find alternatives derived from bio-based resources that can replace petroleum-based polymers. To enable this transition it is important that the adhesive properties in terms of bond strength, water resistance and heat resistance are similar, and that the alternative can compete in terms of cost. Hemicelluloses are a byproduct from the pulp industry. From environmental and economic perspectives it is preferable to utilize all components from wood and decrease the amount of low-value byproducts. In this study, hemicelluloses are suggested to be used as binders in wood adhesives, why water dispersions of xylan have been prepared and evaluated. However, xylan itself cannot be used as a wood adhesive due to its limited bonding performance, especially regarding the water resistance. With the addition of dispersing agents, poly(vinyl alcohol) or poly(vinyl amine), and crosslinkers, such as glyoxal or hexa(methoxymethyl) melamine, the xylan dispersions demonstrate promising results. Wood veneers bonded with xylan dispersions and evaluated with ABES, Automated Bonding Evaluation System, demonstrate a good bond strength and surprisingly good water resistance. Several xylan dispersions fulfill the D1 and WATT 91 requirements for wood adhesives according to European Standards EN 204 and EN 14257, exhibiting good bond strength and heat resistance. Xylan dispersed in a poly(vinyl amine) solution also shows remarkable water resistance and reaches the threshold for the D2 criterion according to European Standard EN 204.

Keywords
Wood adhesive, Polysaccharide, Hemicellulose; Xylan, Tensile shear strength, Water resistance
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-171905 (URN)10.1016/j.eurpolymj.2015.02.021 (DOI)000357750900046 ()
Note

QC 20150812

Available from: 2015-08-12 Created: 2015-08-10 Last updated: 2018-05-21Bibliographically approved

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