Licentiate seminar: Tijana Todorovic – Hemicellulose-based wood adhesives
Supervisor: Professor Eva Malmström, KTH, and Linda Fogelström, KTH
Opponents: Francisco Vilaplana, KTH and Magdalena Sterley, RISE
The defense will be held online via Zoom.
The increasing sustainability concern encourages the society to use sustainable resources. In the wood industry the main component is from a renewable resource, but others are not. One of the fossil-based components is the adhesive. The wood adhesive industry is, besides the sustainability issue, facing environmental and health issues since most adhesives contain formaldehyde. Many biobased polymers show promising results as wood adhesives, and could therefore be used in the wood industry.
Wood hemicelluloses that originate from the pulp industry as a sidestream could be used in the adhesive production, but their bonding performances need to be improved. When used alone, wood hemicelluloses do not have sufficient bond strength. On the other hand, locust bean gum which has similar structure to hemicelluloses but substantially higher molecular weight gives a significantly higher bond strength. The investigation of the molecular-weight effect on bonding properties shows that solely low molecular weight hemicelluloses do not show sufficiently high strength to be used as wood adhesives. Hemicellulose-like compounds with very high molecular weight, over 1,000 kDa, show higher strength, but their dispersions are very viscous, which limits the applicability and the penetration of the adhesive into the wood. A proper balance between adhesive properties, such as molecular weight, dry content and viscosity, and the application method, leads to an improved bond strength.
When wood hemicelluloses are used together with high molecular weight amino-functional polymers, the bond strength is further increased. Additionally, the water resistance is significantly improved. The hypothesis is that these improvements are the results of synergetic effects of high molecular weight, electrostatic interactions and hydrogen bonding between the amino-functional polymer and the hemicelluloses in the adhesives, and between the adhesive and wood.