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Development of sustainable bio-adhesives for engineered wood panels – A review
Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.ORCID iD: 0000-0002-5188-4817
Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology. (GoFP)ORCID iD: 0000-0002-6909-2025
Luleå university of technology.
Linnaeus University, Faculty of Technology, Department of Forestry and Wood Technology.ORCID iD: 0000-0001-6940-3850
2017 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, no 61, p. 38604-38630Article in journal (Refereed) Published
Abstract [en]

Changes in both formaldehyde legislations and voluntary requirements (e.g. Germany RAL) are currently the driving factors behind research on alternatives to amino-based adhesives; moreover, consumer interest in healthy and sustainable products is increasing in bio-based adhesives. Sources of formaldehyde emissions in wood-based panels as well as different emission test methods have been discussed, and the main focus of this review is on the research conducted on sustainable bio-based adhesive systems for wood panels. Lignin, tannin, protein, and starch have been evaluated as both raw materials and adhesive alternatives to existing amino-based thermosetting adhesives. Adhesion improving modifications of these bio-based raw materials as well as the available and experimental crosslinkers have also been taken into account.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017. Vol. 7, no 61, p. 38604-38630
National Category
Wood Science
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
URN: urn:nbn:se:lnu:diva-67192DOI: 10.1039/c7ra06598aISI: 000407442000059Scopus ID: 2-s2.0-85027223659OAI: oai:DiVA.org:lnu-67192DiVA, id: diva2:1130076
Available from: 2017-08-08 Created: 2017-08-08 Last updated: 2019-10-14Bibliographically approved
In thesis
1. Towards low-emitting and sustainable particleandfibreboards: Formaldehyde emission test methods and adhesives from biorefinery lignins
Open this publication in new window or tab >>Towards low-emitting and sustainable particleandfibreboards: Formaldehyde emission test methods and adhesives from biorefinery lignins
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

High volumes, fast production speed, and low material costs have been historically the driving factors of the particle- and fibreboard industries. However, in recent years the fossil-fuel dependency and health issues of the formaldehyde-containing adhesives used in the production have gained attention from both legislators and consumers. The latest example of legislation development is the change that the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety of Germany  (Bundesministerium für Umwelt, Naturschutz und Nukleare Sicherheit) made to their testing method, effectively lowering the formaldehyde emission levels of wood-based panels in Germany from the European emission level of 0.1 ppm (E1, EN 717-1) to 0.05 ppm. As the emission levels of requirements decrease, market opportunities arise for formaldehyde-free bio-based adhesive systems. The aim of this thesis was thus to evaluate the different formaldehyde test methods at low emission levels (<0.05 ppm), and to explore new adhesive alternatives to the formaldehyde and petroleum-based systems used today.

As formaldehyde emissions decrease, choosing the right measurement method becomes increasingly important. Repeatability and correlation between the main European and American formaldehyde measurement chambers, described in EN 717-1 and ASTM D 6007 standards respectively, were determined. In addition, an alternative fast factory method based on emissions was evaluated, and the effect of reducing the conditioning time before emission measurements was investigated. A literature research was conducted on different bio-based raw materials in order to review their potential, from both scientific and industrial viewpoints, as alternatives to the current petroleum-derived and formaldehyde-based adhesives. Lignin residues from biorefinery processes were chosen for further testing due to their increasing volumes and potential to suit various pathways for adhesive making. Three different biorefinery lignins were compared, and ammonium lignosulfonate was chosen for making adhesives for particleboards by using one petroleum-based and one bio-based crosslinker.

The main conclusion of the formaldehyde emission part of the thesis was that formaldehyde emissions can be measured both accurately and quickly at low levels using chamber methods, even at factory environment. There was a good correlation between the American D 6007 and European EN 717-1 chamber methods at emission levels <0.05 ppm for both particleboards (r2 = 0.9167) and fibreboards (r2 = 0.9443). Further understanding on the effect of edge-sealing of boards and analytical methods described in the standards was obtained. It was confirmed that a fast chamber method with 1 day conditioning and 15 minutes measuring time could be used for factory formaldehyde control for most board types.

The bio-based adhesives’ literature review revealed a large amount of studies on different sustainable adhesive systems, some of which seem promising. Both soy protein and tannin were found to be partially commercialized, with certain pre-requisites. Kraft-lignin was especially well researched, but was found to be difficult to use for other applications than partial replacement of phenol in phenol-formaldehyde (PF) adhesives due to poor water solubility and purity. Lignin residues from biorefinery processes were found to be a less studied, growing raw-material source with a lot of potential. Thus, supercritical water hydrolysis lignin (SCWH) and two biorefinery lignosulfonates were chemically and thermally characterized, and evaluated as raw materials for value-added applications, including adhesives. SCWH lignin was found to have more β-R linkages and lower amount of impurities than the lignosulfonates. High amount of phenolic hydroxyl groups indicated that SCWH would be well suited for phenol replacement in PF adhesives. The two lignosulfonates had more aliphatic hydroxyl groups, which can be interesting for other crosslinking reactions than PF. Ammonium lignosulfonate (ALS) was chosen for further evaluation as having slightly better properties than sodium lignosulfonate (SLS). ALS was combined with one bio-based crosslinker, furfuryl alcohol (FOH), and one synthetic crosslinker, 4,4’-diphenylmethane diisocyanate (pMDI), and tested as particleboard adhesive. Although in veneer tensile shear strength testing the crosslinkers worked equally well, pMDI provided significantly better results in particleboards. In addition, higher emissions than what can be expected from wood particles alone were detected from the particleboard samples crosslinked with FOH, even though FOH can be classified as non-formaldehyde added adhesive system. Further research is needed to elucidate how much the lignin contributes to the final adhesion strength when it is used together with pMDI.

This thesis has provided new insights on formaldehyde emissions and bio-based adhesives towards healthier and more sustainable particle- and fibreboards. It has been proven that formaldehyde emissions can be measured accurately at emission levels of wood, enabling comparisons of formaldehyde-free systems. Formaldehyde-free adhesives based on a biorefinery lignin type and pMDI showed promising results for particleboards. However, these results need to be improved by different modifications of the lignin in order to bring the adhesive system to the economical and performance level required by the particleboard industry.

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2019. p. 78
Series
Linnaeus University Dissertations ; 363/2019
Keywords
Wood board industry, chamber methods, dynamic microchamber (DMC), bio-based adhesives, lignosulfonates, supercritical water hydrolyzed lignin, crosslinkers, fibreboards, particleboards
National Category
Polymer Technologies Polymer Chemistry
Research subject
Technology (byts ev till Engineering), Forestry and Wood Technology
Identifiers
urn:nbn:se:lnu:diva-89560 (URN)978-91-88898-98-2 (ISBN)978-91-88898-97-5 (ISBN)
Public defence
2019-11-06, Homeros (F332), Hus F, Växjö, 13:00 (English)
Opponent
Supervisors
Funder
Knowledge Foundation, project titled “New environment-friendly board materials”
Available from: 2019-10-14 Created: 2019-10-14 Last updated: 2019-10-14Bibliographically approved

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Hemmilä, VenlaAdamopoulos, StergiosKumar, Anuj

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