Today most wood adhesives are made from fossil-based polymers and contain hazardous ingredients. e.g.Formaldehyde. With growing environmental concerns, there is a need to develop bio-based and harmless substitutes. The aim of this study is to investigate and upgrade hemicelluloses, a by-product from digestion, as the main component of wood adhesives. Wood adhesives were made from a variety of sources: xylan from beech wood, hemicellulosic liquids obtained by hydrolysing hardwood, and ultrafiltered softwood hemicellulose obtained from the process water of a thermomechanical pulp mill. Hemicelluloses themselves do not show sufficient binding performance, but excellent binding strength and water resistance were obtained in combination with poly (vinylamine). It has also been shown that chitosan can be used as a bio-based amino functional alternative to synthetic poly (vinylamine) with similar or superior properties. Hemicelluloses alone show insufficient water resistance, but hemicelluloses in combination with chitosan show exceptionally good binding performance, especially with regard to water resistance. Adhesives made from liquids rich in hardwood and softwood hemicelluloses, regardless of their structural differences, showed similar bond strength when combined with amino-functional polymers (polyvinylamine and chitosan). The current study is an example of how side streams from the pulp industry in combination with chitosan can be used to replace fossil materials in search of a more sustainable society.

Graphic summary: A fully bio-based wood adhesive that appreciates hemicellulose-rich side streams from the pulp industry

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