Lignin-based waterproof coating
A method of forming a coating on a substrate is provided comprising forming a lignin solution by at least partially dissolving lignin in a solvent, coating the lignin solution onto the substrate and exposing the lignin coated substrate to a treatment selected from the group consisting of a heat treatment and an acid treatment. The coating provides for improved waterproofing and/or strengthening of the substrate.
1. A method of forming a coating on an external surface of a formed substrate including the steps of:
(a) forming a lignin solution by at least partially dissolving a lignin in an alkaline solution, wherein the lignin is not a lignosulfonate lignin and wherein the lignin solution consists essentially of lignin, glycerol and plasticiser as the only non-solvent components;
(b) coating the lignin solution onto the external surface of the formed substrate; and
(c) exposing the lignin coated substrate to a treatment selected from the group consisting of a heat treatment and an acid treatment,
to thereby form a coating on the external surface of the formed substrate.
2. The method of claim 1 wherein the substrate is selected from the group consisting of lignocellulosic substrates, lignocellulosic derived substrates, cellulosic substrates and cellulosic derived substrates.
3. The method of claim 1 wherein the alkaline solution is an aqueous alkaline solution.
4. The method of claim 1 wherein the lignin solution consists essentially of lignin as an active waterproofing and/or strengthening agent.
5. The method of claim 1 wherein the % by weight amount of the glycerol in the lignin solution is between 1 to 30%.
6. The method of claim 1 wherein the plasticiser is present in the lignin solution in a % by weight amount of between 0.1% to 10%.
7. The method of claim 1 wherein the pH of the lignin solution at coating is between about 7.0 to 9.5.
8. The method of claim 1 , wherein the acid treatment comprises contacting the lignin coating with an acid having a pH below 4.0.
9. The method of claim 1 , wherein the alkaline solution is an ammonia solution.
10. A method of forming a coating which remains on substantially only an external surface of a formed substrate including the steps of:
(a) forming a lignin solution by at least partially dissolving a lignin in alkaline solution, wherein the lignin is not a lignosulfonate lignin and wherein the lignin solution consists essentially of lignin, glycerol and a plasticiser as the only non-solvent components;
(b) coating the lignin solution onto the external surface of the formed substrate; and
(c) exposing the lignin coated substrate to a treatment selected from the group consisting of a heat treatment at a temperature of between 120° C. to 240° C. and an acid treatment,
to thereby form a coating which remains on substantially only an external surface of the formed substrate.
11. The method of claim 10 , wherein the substrate is selected from the group consisting of lignocellulosic substrates, lignocellulosic derived substrates, cellulosic substrates and cellulosic derived substrates.
12. The method of claim 10 , wherein the alkaline solution is an aqueous alkaline solution.
13. The method of claim 10 , wherein the lignin solution consists essentially of lignin as an active waterproofing and/or strengthening agent.
14. The method of claim 10 , wherein the % by weight amount of the glycerol in the lignin solution is between 1 to 30%.
15. The method of claim 10 , wherein the plasticiser is present in the lignin solution in a % by weight amount of between 0.1% to 10%.
16. The method of claim 10 , wherein the pH of the lignin solution at coating is between about 7.0 to 9.5.
17. The method of claim 10 , wherein the acid treatment comprises contacting the lignin coating with an acid having a pH below 4.0.
18. The method of claim 10 , wherein the alkaline solution is an ammonia solution.
19. A method of forming a coating which remains on substantially only an external surface of a formed substrate including the steps of:
(a) forming a lignin solution, wherein the lignin is the major active waterproofing and/or strengthening agent, and is present in the solution at greater than 50% by weight of active waterproofing and/or strength enhancing elements, by at least partially dissolving a lignin in an alkaline solution and wherein the lignin is not a lignosulfonate and the lignin solution consists essentially of lignin, glycerol, and a plasticiser as the only non-solvent components;
(b) coating the lignin solution onto the external surface of the formed substrate; and
(c) exposing the lignin coated substrate to a treatment selected from the group consisting of a heat treatment at a temperature of between 120° C. to 240° C. and an acid treatment,
to thereby form a coating which remains on substantially only external surface of the formed substrate.