Strong nanopaper

1. A nanopaper comprising clay and microfibrillated cellulose nanofibres wherein the MFC nanofibres and the layered clay are orientated substantially parallel to the paper surface, wherein the clay is a silicate with a layered or platelet structure, wherein the nanopaper further comprises a water soluble cross-linker that is chitosan.

2. The nanopaper according to claim 1 wherein the clay comprises particles in the nanometer range.

3. The nanopaper according to claim 1 wherein the length of the microfibrillated cellulose nanofibres is in the range of 5-20 μm.

4. The nanopaper according to claim 1 wherein the lateral dimension of the nanofibres is in the range of 10-30 nm.

5. The nanopaper according to claim 1 wherein the amount of microfibrillated cellulose is more than 10 wt % and less than 50 wt %.

6. The nanopaper according to claim 1 wherein the amount of clay is more than 10 wt % and not more than 90 wt %.

7. The nanopaper according to claim 1 wherein the cross-linker is positively charged when in an aqueous solution.

8. The nanopaper according to claim 1 wherein the amount of cross-linker is more than 5 wt % and not more than 50 wt % based on the total weight of the nanopaper.

9. The nanopaper according to claim 1 wherein the tensile stress of the nanopaper is at least 30 MPa for samples of 40 mm in length, 60-80 μm thick and 5 mm wide; using 100N load cell and at a frame rate of 5 fbs; and wherein the tests were conducted at a humidity of 50% and at 23° C.

10. The nanopaper according to claim 1 wherein the paper consists of the microfibrillated cellulose, clay and water soluble cross-linker.

11. A coating comprising the nanopaper of claim 1 .

12. The coating according to claim 11 wherein the nanopaper comprises multiple layers of clay and nanofibres.

13. A method for preparing the nanopaper according to claim 1 , the method comprising:

preparing a suspension of clay and microfibrillated cellulose nanofibres;

mixing said suspension;

filtrating said suspension;

obtaining or forming a film of said filtrated suspension; and

drying of said film.

14. The method according to claim 13 wherein the suspension contains up to 2 wt % of microfibrillated cellulose.

15. The method according to claim 13 wherein the microfibrillated cellulose is in the form of colloids in the suspension.

16. The method according to claim 13 wherein microfibrillated cellulose nanofibres are derived from pulp exposed to an enzymatic treatment in order to obtain a pretreated pulp.

17. The method according to claim 16 wherein the pretreated pulp is mechanically beaten.

18. The method according to claim 17 wherein the mechanically beaten pulp is exposed to homogenization.

19. The method according to claim 13 wherein a water soluable cross-linker that is chitosan is added.

20. The method according to claim 19 wherein the concentration of cross-linker is more than 5 wt % and not more than 50 wt % based on the total mass of components.

21. The method according to claim 13 wherein the suspension is flocculated.

22. A method of coating a surface with the nanopaper of claim 1 comprising:

forming a solution or a suspension comprising clay and microfibrillated cellulose nanofibres;

coating the surface with the solution or suspension to form the nanopaper of claim 1 .

23. The method of claim 22 wherein the coating is done by dipping, spraying or smearing.

24. The method of claim 22 wherein the coating step is repeated.

25. The method of claim 22 wherein the solution or suspension further comprises chitosan.

26. The nanopaper of claim 1 , wherein the nanopaer is used as paper, filter paper, fire or heat resistant material, reinforcement compound, wall paper, cardboard, paperboard, liquid packing board, packing material, food packaging, water vapor barrier, fat barrier, liquid barrier, gas barrier, coatings, speaker membranes, battery membranes or bullet proof material.

27. The method according to claim 13 wherein the suspension contains 0.5 to 2 wt % of microfibrillated cellulose.

28. The method according to claim 13 wherein the suspension contains 0.6 to 1.6 wt % of microfibrillated cellulose.