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Synthesis and performance of novel renewable polyurethane adhesives from chemically modified lignin

: Heinrich, L.

Hinterwaldner, Stephan (HerausgeberIn):
in-adhesives 2019. Symposium on Innovations in Adhesives and their Applications : Munich, Germany, February 25-26, 2019
Kirchseeon/Germany: MKVS GbR, 2019
Symposium on Innovations in Adhesives and their Applications <2019, Munich>
Fraunhofer WKI ()

Adhesives based on renewable materials have recently been attracting attention due to the looming petroleum shortness and because of the new product design possibilities bio-based materials offer. Lignin, a byproduct recovered in large amounts from pulp and paper mills, is one of the most promising bio-based materials for adhesive applications due to its densely connected molecular structure rich in hydroxyl functional groups, shown below. While lignin has already successfully been used to replace phenol in phenolformaldehyde adhesives for particle boards [1] , plywood [2] and laminated veneer lumber [3], its application in formaldehyde free adhesives cured through non-condensation mechanisms remains underexplored. The reason for this lies on one hand in the difficulty of processing lignin, which is a non-melting solid with low solubility in common solvents, and on the other hand in its heterogeneity and multi functionality, which make it difficult to produce a chemically exactly defined material from it. In this work, chemical modifications of lignin with different renewable and non-renewable building blocks, such as succinic acid, 1,2-propanediol, fatty acids and polyethylene glycol were used to yield polymeric materials suitable for different noncondensation adhesive applications. Ligninpolymers with melting points up to 99°C were obtained, while viscosities could be varied between 8 mPas (at 100 s-1, 25°C) and 18 000 mPas (at 100 s-1, 100 °C). The lignin derivatives were integrated in different types of adhesive formulations, including emulsion polymerisation isocyanates (EPI), 2-component polyurethanes (2K-PU) and polyurethane dispersions. Both the dry and the wet shear strength of the thus obtained adhesives were tested and results will be presented. The evaluation showed that lignin derivatives have great potential to replace and complement petroleum-based binders in adhesive portfolios.