Title: Towards low-emitting and sustainable particle- and fibreboards – formaldehyde emission test methods and adhesives from biorefinery lignins
Subject: Forestry industry production systems
Faculty: Faculty of technology
Date: Wednesday 6 November 2019 at 1.00 pm
Place: Room Homeros (F332), building F, Växjö
External reviewer: Professor Luísa Maria Hora de Carvalho, Escola Superior de Tecnologia e Gestão de Viseu, Portugal
Examining committee: Professor Eva Malmström Jonsson, KTH, Sweden
Dr Graham Ormondroyd, Bangor University, Wales
Associate professor Johannes Konnerth, University of Natural Resources and Life Sciences, Vienna (BOKU), Austria
Chairperson: Professor Johan Bergh, Department of forestry and wood technology, Linnaeus University
Supervisor: Professor Stergios Adamopoulos, Department of forestry and wood technology, Linnaeus University
Examiner: Associate professor Åsa Rydell Blom, Department of forestry and wood technology, Linnaeus University
Spikning: Wednesday 16 October 2019 at 1.00 pm at the University library in Växjö
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 environmental and health issues of formaldehyde-containing adhesives used in the production have gained attention from both legislators and consumers.
Aim of this thesis was to evaluate 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. A good correlation was found between the main European and American formaldehyde measurement chambers, described in EN 717-1 and ASTM D 6007 standards respectively, 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 wood panels and analytical methods described in the standards was obtained. It was confirmed that a fast chamber method with 1 day conditioning and 15 min measuring time could be used for factory formaldehyde control for most particleboard types.
A literature review on bio-based adhesives revealed that the growing amounts of lignin residues from biorefineries could be a promising raw material source for adhesives. Thus, supercritical water hydrolysis lignin (SCWH) and two biorefinery lignosulfonates were evaluated as raw materials for value-added applications, including adhesives. SCWH was found more suitable for phenol-formaldehyde applications, while the higher amount of aliphatic hydroxyl groups of lignosulfonates made them interesting for other crosslinking reactions. Ammonium lignosulfonate was chosen for further evaluation and combined with one bio-based crosslinker, furfuryl alcohol, and one synthetic crosslinker, 4,4’-diphenylmethane diisocyanate (pMDI), and tested as particleboard adhesive. Although in veneer tensile shear strength testing the crosslinkers performed equally well, pMDI provided significantly better results in particleboards.
This thesis has provided new insights on formaldehyde emissions and bio-based adhesives towards healthier and more sustainable particle- and fibreboards. Formaldehyde emissions can be measured accurately at low emission levels, enabling comparisons of formaldehyde-free systems. Formaldehyde-free adhesives based on a biorefinery lignin type and pMDI showed promising results for particleboards. However, these adhesive systems need to be improved to bring them to the economical and performance level required by the particleboard industry.