Process for binding lignocellulosic materials using polyisocyanate compositions
A process for binding lignocellulosic material comprising the steps of a) bringing lignocellulosic material into contact with a methylene bridged polyphenyl polyisocyanate composition and b) subsequently allowing said material to bind wherein said polyisocyanate composition has a surface tension below or equal to 46 mN/m.
1. A process for binding lignocellulosic material comprising:
a) bringing the lignocellulosic material into contact with a methylene bridged polyphenyl polyisocyanate composition having a surface tension below or equal to 46 mN/m and wherein the polar contribution of the surface tension is at least 6 mN/m; and
b) subsequently allowing said material to bind.
2. The process according to claim 1 , wherein said polyisocyanate composition comprises methylene bridged polyphenyl polyisocyanate modified by adding monol or diols, branched polyols, amines, wetting agents and/or surfactants.
3. The process according to claim 1 , wherein monoalkyl ethers of polyethylene glycols are added to the methylene bridged polyphenyl polyisocyanate in an amount of at least 10 pbw.
4. The process according to claim 1 , wherein the lignocellulosic material is primarily wood based and fibrous in nature.
5. The process according to claim 4 , wherein the wood fibers are single wood fibers and/or bundles of such fibers.
6. The process according to claim 5 , wherein the fibers have lengths of 7 mm or below and width/thickness of 0.005 to 0.2 mm and the fiber bundles are less than 2 cm long and less than 1 mm wide/thick.
7. The process according to claim 1 , wherein the polyisocyanate composition is applied in such an amount as to give a weight ratio of polyisocyanate to lignocellulosic material in the range 0.1:99.9 to 20:80.
8. The process according to claim 1 , wherein step b) involves pressing the lignocellulosic material at 120° C. to 300° C. and 2 to 6 MPa specific pressure.
9. The process according to claim 1 , wherein the surface tension is below 40 mN/m and the polar contribution of the surface tension is less than or equal to 10 mN/m.
10. The process according to claim 1 , wherein the surface tension is below 30 mN/m and the polar contribution of the surface tension is less than or equal to 20 mN/m.
11. The process according to claim 1 , wherein the polyisocyanate composition comprises methylene bridged polyphenyl polyisocyanate modified by pre-reacting the methylene bridged polyphenyl polyisocyanate with a monol or a polyol.
12. The process according to claim 11 , wherein the monol or the polyol has an ethylene oxide content of more than about 20 wt. %.
13. The process according to claim 5 , wherein the wood fibers have been pre-treated to remove extractives from the surfaces of the wood fibers.
14. The process according to claim 1 , wherein the lignocellulosic material is brought into contact with the methylene bridged polyphenyl polyisocyanate composition by at least one of mixing, spraying or spreading the methylene bridged polyphenyl polyisocyanate composition with or onto the lignocellulosic material.
15. The process according to claim 1 , wherein the lignocellulosic material has been premixed with at least one of grinded foam waste, a mineral filler, glass fibers, mica, rubber, plastic fibers or a fabric.
16. The process according to claim 1 , wherein the methylene bridged polyphenyl polyisocyanate composition further comprises at least one of a wax, a colorant, a fungicide or an insecticide.