Modified lignin as raw material for polyurethane adhesives
Lignin is the most abundant aromatic renewable resource in the world. In wood lignin acts as the glue-molecule for cellulose and it forms 15-30 % of the wood material. In the pulp and paper industry lignin is a by-product in the scale of 50 million tons every year worldwide. Biorefinery concepts add around 20 million tons to this figure. However, only 2 % of total lignin is used as renewable feedstock for example as aggregates or dispersants. The majority is incinerated in the pulp factories to power reactor systems. The aim of this work is to promote the material utilization of lignin and to achieve a new high-value building block for adhesive synthesis. Lignin is a three dimensional irregular macromolecule which consist of 4-hydroxyphenylpropanoid units with functional groups like hydroxil, methoxy, carbonyl and carboxyl. In order to get an optimized polyol precursor. Not till then it is possible to synthesize waterbourne polyurethane dispersions from this lignin polyol in a typical acetone process. These were characterized by DSC (diffraction scanning calorimetry), SEC (size exclusion chromatography), Zeta potential and light diffraction measurements. The adhesive properties are determined by tensile tests.