Incorporation of lignin in polyurethane products
Composition comprising lignin dispersed in a polyisocyanate wherein the (d90) mean particle size of the dispersed lignin is less than 5 μm, preferably less than 2 μm, more preferably less than 1 μm and use of said composition in various polyurethane applications, in particular structural wood adhesives.
1. A composition comprising lignin dispersed in a polyisocyanate characterised in that the (d90) mean particle size of the dispersed lignin is less than 5 μm.
2. The composition according to claim 1 , wherein at least 50% of the dispersed lignin particles have a particle size of at least 500 nm.
3. The composition according to claim 1 , wherein the lignin is free of ash content, sulphur content, and/or ion content.
4. The composition according to claim 3 , wherein the ash content of the lignin is below 1 wt %.
5. The composition according to claim 3 , wherein the suphur content of the lignin is below 1 wt %.
6. The composition according to claim 3 , wherein the content of each of sodium, potassium, calcium and magnesium in the lignin is below 0.03 wt %.
7. The composition according to claim 1 , wherein the lignin is an organosolv lignin or a Kraft lignin.
8. The composition according to claim 1 , wherein the lignin has a moisture content of less than 10 wt %.
9. The composition according to claim 1 , wherein the polyisocyanate is an aromatic polyisocyanate.
10. The composition according to claim 1 , wherein the amount of lignin is between 1 and 25 wt %.
11. A process for producing a composition as defined in claim 1 using a three roll mill.
12. An isocyanate-terminated prepolymer, wherein the prepolymer is the reaction product of a stoichiometric excess of a polyisocyanate with a composition comprising lignin dispersed in an isocyanate-reactive compound wherein the (d90) mean particle size of the dispersed lignin is less than 5 μm.