Defence of doctoral thesis: Tijana Todorovic – Polysaccharide-based wood adhesives
KTH | WWSC
It is highly desirable to increase the use of renewable resources and reduce fossil-dependence due to sustainability concerns. As a consequence, it is expected that the use of the wood-based materials will increase in the future. Therefore, adhesives will have an important role since they allow for the use of lower-quality and recycled wood. At present, adhesives are mainly fossil-based and contain toxic components which can present a health risk. Extensive research is being conducted with the goal to replace fossil- with bio-based adhesives, and eliminate toxic components.
In this work, several polysaccharides have been investigated as wood adhesives, of which wood hemicelluloses are an interesting alternative. When applied between wood veneers, wood hemicelluloses alone do not exhibit sufficient strength, but combined with chitosan, they exhibit impressive strength and even sufficient water resistance. Since the molecular weight of hemicelluloses can affect the adhesive performance, locust bean gum has been used as a model in order to investigate this effect. An optimal molecular weight, 320-530 kDa in this case, is necessary for achieving the highest bond strength. These adhesives also show promising results in particleboards, and their internal bond strength fulfills the standard requirements for P2 boards (SS-EN 319), which are commonly used for furniture in dry conditions. High mat moisture contents are necessary for sufficient hydration of polysaccharides and internal bond strength; hence, a high mat moisture content (35-45 %), a pressing temperature of 150 °C, and pressing time of 15 min, yielded strong particleboards with no signs of steam blistering or delamination.
With the goal to partially replace fossil content in PVAc adhesives chitosan has been used in emulsion polymerization of VAc, as a surfactant and grafting site. Besides lowering the fossil content to 60 %, the water resistance was significantly improved.