Method For Preparing A Lignosulfonate Polymer

Abstract

A method is provided for preparing a water-insoluble lignosulfonate polymer from a first solution containing lignosulfonate precursors, which involves a) separating the lignosulfonate precursors from the first solution and providing a second solution with at least 5 wt % of lignosulfonate precursors obtained from the first solution, wherein the separating comprises filtering out components with a predefined particle diameter and separating low-molecular weight components including salts and low-molecular organic compounds, b) adding a radical-forming enzyme and gas to the second solution, wherein the gas comprises oxygen, and c) polymerizing the lignosulfonate precursors of the resultant solution of b).

Other related aspects are described and claimed.

Claims

1-14. (canceled)

15. A method for preparing a water-insoluble lignosulfonate polymer from a first solution containing lignosulfonate precursors comprising: a) separating the lignosulfonate precursors from the first solution and providing a second solution with at least 5 wt % of lignosulfonate precursors obtained from the first solution, wherein the separating comprises filtering out components with a predefined particle diameter and separating low-molecular weight components including salts and low-molecular organic compounds, b) adding a radical-forming enzyme and gas to the second solution, wherein the gas comprises oxygen, and c) polymerizing the lignosulfonate precursors of the resultant solution of b).

16. A method according to claim 15, wherein: the first solution comprises a raw liquor.

17. A method according to claim 15, wherein: the second solution comprises at least 10 wt % of lignosulfonate precursors obtained from the first solution.

18. A method according to claim 15, wherein: the filtering of a) is configured to filter out components with a particle diameter of less than 1 μm.

19. A method according to claim 15, wherein: the filtering of a) is configured to filter out components with a particle diameter of less than 100 nm.

20. A method according to claim 15, wherein: the low-molecular components comprise components having a molecular weight of less than 500 Da.

21. A method according to claim 15, wherein: the gas of b) further comprises an admixture of other gases.

22. A method according to claim 21, wherein: the admixture of other gases is not more than 10% by volume of the gas.

23. A method according to claim 21, wherein: the admixture of other gases is not more than 5% by volume of the gas.

24. A method according to claim 15, wherein: the lignosulfonate precursors of the first solution comprise lignosulfonate oligomers with a molecular weight of more than 500 Da.

25. A method according to claim 15, wherein: the lignosulfonate precursors of the first solution comprise lignosulfonate oligomers with a molecular weight of more than 5000 Da.

26. A method according to claim 15, wherein: the second solution is an aqueous solution.

27. A method according to claim 15, wherein: the radical-forming enzyme is selected from the group consisting of a laccase, a peroxidase, or a mixture thereof.

28. A method according to claim 15, wherein: the pH of the solution in b) is between 5 and 9.

29. A method according to claim 15, wherein: the pH of the solution in b) is between 6 and 8.

30. A method according to claim 15, wherein: at least one additive is added during or after the polymerization of c).

31. A method according to claim 30, wherein: said at least one additive is selected from the group consisting of elastomers, plasticizers, stabilizers and polymers.

32. A method according to claim 15, further comprising: foaming the resultant solution of b) during polymerization of c) to form a lignosulfonate polymer foam.

33. A method according to claim 15, further comprising: pouring the resultant solution of b) during polymerization of c) to form a lignosulfonate polymer material.

34. A method according to claim 33, wherein: the lignosulfonate polymer material comprises a lignosulfonate bioplastic.

35. A method according to claim 15, wherein: the radical-forming enzyme of b) has an activity between 10 nkat/mL and 500 nkat/mL.

36. A method according to claim 15, wherein: the radical-forming enzyme of b) has an activity between 50 nkat/mL and 200 nkat/mL.

37. A lignosulfonate polymer prepared by a method according to claim 15.

38. A lignosulfonate polymer according to claim 37, wherein: the lignosulfonate polymer is a solid at room temperature.

39. A lignosulfonate polymer according to claim 37, wherein: the lignosulfonate polymer has an average molecular weight between 200 kDa and 800 kDa.

40. A lignosulfonate polymer according to claim 37, wherein: the lignosulfonate polymer has an average molecular weight between 300 kDa and 500 kDa.

41. A water-retaining means for a growth substrate comprising a lignosulfonate polymer prepared by a method according to claim 15.

42. A growth substrate for plants comprising a lignosulfonate polymer prepared by a method according to claim 15.

43. A growth substrate according to claim 42, wherein: the lignosulfonate polymer is between 0.1 wt % and 5 wt % of the growth substrate.

44. A growth substrate according to claim 42, wherein: the lignosulfonate polymer is between 1 wt % and 3 wt % of the growth substrate.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0049] The Figures serve to further clarify the effects of the present invention.

[0050] FIG. 1 shows the course of viscosity as a function of the reaction time in a first method according to the invention;

[0051] FIG. 2 shows the course of the average molecular weight as a function of the reaction time in the first method according to the invention;

[0052] FIG. 3 shows the water absorption of a lignosulfonate polymer prepared and dried by the method according to the invention;

[0053] FIG. 4 shows the course of the relative humidity of growth substrates comprising a lignosulfonate polymer according to the invention;

[0054] FIG. 5 shows the tensile strength of lignosulfonate polymer materials according to the invention;

[0055] FIG. 6 shows the elongation at break of lignosulfonate polymer materials according to the invention.

DETAILED DESCRIPTION

EXAMPLE 1

Preparation of a Lignosulfonate Polymer

[0056] The first exemplary embodiment describes the preparation of a water-insoluble lignosulfonate polymer, in particular a hydrogel containing a lignosulfonate polymer, by a method according to the invention.

[0057] The starting substance for the method according to the invention according to the first exemplary embodiment is brown liquor, such as is usually produced as a waste product.

[0058] In the first step of the method according to the invention, the brown liquor is filtered to remove solids, such as fibres or particles. A filter with a mesh size of about 5μm is used.

[0059] Subsequently, an ultrafiltration step is carried out to remove salts, low-molecular lignin and other impurities from the brown liquor that could have a negative influence on the polymerization or on the quality of the polymerisate. Ultrafiltration steps are carried out with membranes of different retention properties, namely 20 kDa, 5 nm and 10 nm. Thus, a sufficiently pure lignosulfonate precursor solution is obtained. In addition, a concentration of the lignosulfonate precursors in the aqueous solution is carried out. In the exemplary embodiment described herein, the concentration of the lignosulfonate precursors is about 11 wt % after all filtration steps. The average molecular weight of the lignosulfonate precursors in the prepared solution is about 26 kDa.

[0060] 2 L of the solution prepared as above are adjusted to a pH of about 7.0 by adding 1 M NaOH solution. Laccase from Myceliophthora thermophila is added until a final enzyme activity of about 160 nkat/mL is obtained. The reaction temperature in this exemplary embodiment is about 40° C. Preferably, the reaction temperature may be between 20° C. and 70° C.

[0061] While stirring with a propeller stirrer (600 rpm), pure oxygen is injected into the solution through a sinter frit. The rate of oxygen addition is about 200 mL/min. Every 30 minutes a sample is taken from the reaction mixture, from which the viscosity and the average molecular weight are determined. The course of the viscosity as a function of the reaction time is shown in FIG. 1. The course of the average molecular weight as a function of the reaction time is shown in FIG. 2.

[0062] FIG. 1 and FIG. 2 clearly show that both the viscosity of the solution and the molecular weight of the lignosulfonate polymers increase with the reaction time. This is an indicator for the successful polymerization of the lignosulfonate precursors.

[0063] After a reaction time of 250 min, the stirring and the addition of oxygen are stopped. If the mixture is allowed to rest, a gel-like solid is formed, which comprises lignosulfonate polymer and water. This gel-like solid is also called a hydrogel.

[0064] The hydrogel obtained is divided into pieces of about 20 g and dried at 80° C. for 12 hours in a drying oven. The weight reduction during drying is about 90 wt %, which suggests that about 90 wt % of the hydrogel is water. After complete drying, water is again added to the polymer, which causes the polymer to swell rapidly and to absorb water. No parts of the polymer can be observed to dissolve in water, so the lignosulfonate polymer obtained is insoluble in water.

[0065] The water absorption capacity of the dried polymer is tested by swelling the polymer pieces prepared as above. The course of the water absorption is shown in FIG. 3, where it can be seen that the water absorption amount substantially reaches a plateau after a swelling time of 20 min, which is about 600% of the original mass of the dry polymer.

EXAMPLE 2

Lignosulfonate Polymer as Water Reservoir

[0066] In this example, the lignosulfonate polymer obtained in the first exemplary embodiment is used as a water reservoir in a growth substrate for plants. The reswollen polymer of Example 1 is mixed with a sand-soil mixture in a content of about 5, 10 and 20 wt %. In addition, a sand-soil mixture without addition of polymer is prepared as a control.

[0067] 200 g of each of the growth substrates prepared in this way are placed in separate pots, with three pots of each substrate (sample and control) prepared. The substrates are soaked with water for 20 hours. After this time, excess water is poured off and three bean seeds are sown in each pot.

[0068] From this point on, no more watering is done, all pots are left at the same humidity, temperature and light level. After about 10 days, germination starts and a germination rate of about 94% (17 out of 18 seeds) is observed. In addition to observing the growth of the seedlings, the relative humidity of the growth substrate is measured at regular intervals. The course of the relative humidity of the substrate (average value of three pots with the same substrate) over time is shown in FIG. 3. While the relative humidity of the control substrate is already close to 0% after 11 days, it takes longer for the growth substrates containing hydrogel to dry out. For the growth substrate containing 20 wt % hydrogel, the relative humidity is still about 10% after 50 days.

[0069] The observation shown in FIG. 3 is consistent with the condition of the seedlings: While a clear wilting of the plants in the control substrates already starts after 15 days, the plants in the substrates containing hydrogel do not show any visible signs of water deficiency over the entire test period of 50 days.

EXAMPLE 3

Preparation of Lignosulfonate Polymer Materials

[0070] For this exemplary embodiment, the lignosulfonate polymerization is carried out according to the method according to the invention described in the first exemplary embodiment. Prior to completion of the polymerization, varying weight contents of sorbitol or glycerol are added to the reaction mixture as plasticizer and the mixture is homogenised. Mixtures containing 25 wt %, 28 wt %, 33 wt %, 40 wt % and 50 wt % of sorbitol/glycerol are prepared.

[0071] After stopping the addition of oxygen and the stirring, the viscous reaction mixture is poured into plastic Petri dishes to a pouring height of about 1 mm, 2 mm and 4 mm. The cast layers of material are allowed to dry at 80° C. for about 30 min. The mechanical properties of the material according to the invention are tested on the basis of the layers thus obtained.

[0072] After drying, the layers or films have thicknesses of about 0.10 mm to 0.40 mm.

[0073] Tests are carried out on the materials to determine their mechanical strength.

[0074] FIG. 5 shows the tensile strength of the materials obtained, FIG. 6 shows the elongation at break.

[0075] It can be seen that a lower tensile strength is obtained with a higher content of plasticizer. With sorbitol, the tensile strength is higher than with the same content of glycerol.

[0076] Substantially the opposite of what has been said about the tensile strength is true for the elongation at break, which is shown in FIG. 6. Samples with a higher content of plasticizer show greater elongation. Samples with glycerol show greater elongation than samples with the same content of sorbitol.