Lignin-based thermosetting film material and preparation method and application thereof

Abstract

The application discloses a lignin-based thermosetting film material and a preparation method and application thereof. The lignin and a crosslinking agent are dissolved in an organic solvent to perform a heating reaction by a thermosetting method to obtain a polymer solution, and then the polymer solution is cast and heated to be cured into an independent crosslinking film. The preparation method can prepare the lignin-based thermosetting film material, and the lignin-based thermosetting film material has good mechanical properties, wherein the tensile strength is 11.86 MPa, the elongation at break is 117.81%, and the toughness is 12.31 MJ / m 3 The lignin-based film prepared by the method is simple in preparation, environment-friendly, green and degradable, and can be applied to the fields of mulching films, packaging materials and photothermal materials.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of high-value utilization of lignin, and particularly relates to a lignin-based thermosetting film material and a preparation method and application thereof. BACKGROUND

[0002] Plastic film materials obtained from fossil resources have the characteristics of light weight, low price, corrosion resistance and the like, and have been widely used in various fields of modern society. However, fossil resources are non-renewable resources, and the environmental problems caused by their non-degradability are threatening human health and the ecological environment. Therefore, the development of bio-based film materials with low cost and wide application has attracted widespread attention.

[0003] Lignin is one of the three major components of lignocellulosic biomass and is the second most abundant renewable natural polymer. It has the characteristics of low cost, antioxidant, biodegradability and ultraviolet blocking activity, and is a good bio-based polymer material to replace petroleum-derived polymer materials. Therefore, it is of great significance to develop lignin-based film materials with excellent performance.

[0004] Thin film materials need to be long and regular chain molecular structure from the molecular level, and lignin usually leads to poor performance due to its complex structure and brittleness. At present, the strategies for preparing lignin-based film materials are to modify lignin or to composite lignin with other polymers. In recent years, researchers have prepared lignin-based thermoset materials through chemical crosslinking of lignin. Gioia et al. (Gioia C, Colonna M, Tagami A, et al. Lignin-based epoxy resins: unravelling the relationship between structure and material properties [J]. Biomacromolecules, 2020, 21(5).) prepared thermoset films from alkali lignin, which was first fractionated by sequential solvent extraction, then modified with epoxy chloropropane, and finally reacted with poly(oxirane) diamine crosslinking agent. Chumakov et al. (Chumakov AP, Brett C J, Schwartzkopf M, et al. Exploring the Effects of Different Cross-Linkers on Lignin-Based Thermoset Properties and Morphologies [J]. ACS Sustainable Chemistry & Engineering, 2021.) prepared thermoset films using isolated alkali lignin, which was then modified by reaction with allyl chloride, and then crosslinked using a multifunctional thiol crosslinking agent.

[0005] In the prior art, lignin is usually modified or compounded with other polymers before being used to prepare thin film materials, which may be accompanied by irreversible and uncontrolled chemical reactions, and the preparation process is complicated and difficult to operate. SUMMARY

[0006] To solve the shortcomings and deficiencies of the prior art, the primary purpose of the present application is to provide a preparation method of lignin-based thermoset film material.

[0007] Another purpose of the present application is to provide a lignin-based thermoset film material prepared by the above preparation method.

[0008] Still another purpose of the present application is to provide the application of the above lignin-based thermoset film material.

[0009] The purposes of the present application are achieved by the following technical solutions:

[0010] A method for preparing a lignin-based thermosetting film material, comprising the following steps:

[0011] The lignin is dissolved in an organic solvent and / or an organic solvent aqueous solution, a crosslinking agent is added, a heating reaction is performed, a polymer solution is obtained, the polymer solution is cast in a mold, and a heating curing is performed to obtain the lignin-based film material.

[0012] Preferably, the lignin is at least one of alkali lignin, enzymatic hydrolysis lignin, and lignin sulfonate; more preferably, at least one of alkali lignin, enzymatic hydrolysis lignin, and sodium lignin sulfonate; and most preferably, alkali lignin.

[0013] Preferably, the organic solvent is at least one of dimethyl sulfoxide (DMSO), N-methyl pyrrolidone (NMP), and N-vinyl pyrrolidone (NVP); the organic solvent aqueous solution is at least one of a gamma-valerolactone (γ-GVL) aqueous solution, a propylene carbonate (PC) aqueous solution, and an ethylene carbonate (EC) aqueous solution; and the mass concentration of the organic solvent in the organic solvent aqueous solution is 50-70 wt.%.

[0014] More preferably, the organic solvent is at least one of dimethyl sulfoxide (DMSO) and N-methyl pyrrolidone (NMP); the organic solvent aqueous solution is a gamma-valerolactone (γ-GVL) aqueous solution; and the concentration of the organic solvent in the organic solvent aqueous solution is 60-70 wt.%.

[0015] Preferably, the crosslinking agent is a diglycidyl ether; more preferably, at least one of 1,4-butanediol diglycidyl ether (BDDE), polyethylene glycol diglycidyl ether (PEGDE), and bisphenol F diglycidyl ether (BFGDE), wherein the molecular weight of the polyethylene glycol diglycidyl ether is 400-1000; and most preferably, at least one of 1,4-butanediol diglycidyl ether (BDDE) and polyethylene glycol diglycidyl ether (PEGDE); and most preferably, polyethylene glycol diglycidyl ether (PEGDE) with a molecular weight of 500-1000.

[0016] Preferably, the mass fraction of the lignin in the organic solvent and / or the organic solvent aqueous solution is 10-40%; more preferably, 20-40%; and most preferably, 20-30%.

[0017] Preferably, the mass ratio of the lignin to the crosslinking agent is (1-4):1; and more preferably, (2-4):1.

[0018] Preferably, the heating reaction is performed at a temperature of 80-90°C for 2-3 hours.

[0019] Preferably, the heating curing procedure is: 75-85 DEG C for 0.5-1 h, then 95-105 DEG C for 0.5-1 h, and finally 115-125 DEG C for 4-10 h; more preferably, 75-85 DEG C for 0.5-1 h, then 95-105 DEG C for 0.5-1 h, and finally 115-125 DEG C for 6-10 h; and most preferably, 75-85 DEG C for 0.5-1 h, then 95-105 DEG C for 0.5-1 h, and finally 115-125 DEG C for 6-7 h.

[0020] The lignin-based thermosetting film material prepared by the preparation method.

[0021] The lignin-based thermosetting film material prepared by the preparation method.

[0022] More preferably, the lignin-based thermosetting film material is applied in ground cover, packaging material and photothermal material.

[0023] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0024] The preparation method of the present application does not need to modify the lignin raw material in advance, directly uses the industrial lignin, has a simple process, and the double epoxy structure of the crosslinking agent is opened by heating, and crosslinks with the phenolic hydroxyl group of the lignin to form a dense three-dimensional ether network structure in the curing process, so that the prepared lignin-based thermosetting film has excellent mechanical properties, wherein the tensile strength is as high as 23.52 MPa, the elongation at break is as high as 117.81%, and the toughness is as high as 12.31 MJ / m 3 ; and the most preferred gamma-valerolactone has low volatility in aqueous solution, stable chemical properties, and good biocompatibility, is a green and environmentally friendly organic solvent with high safety for human body. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Figure of the lignin-based thermosetting film material prepared in Example 1.

[0026] Figure 2 Figures a and b are SEM images of the cross section of the lignin-based thermosetting film material prepared in Examples 4 and 14, respectively.

[0027] Figure 3 Figures a and b are stress-strain performance graph and toughness graph of the lignin-based thermosetting film material prepared in Examples 1-6, respectively. DETAILED DESCRIPTION

[0028] The present application will be further described in detail below in combination with examples and drawings, but the embodiments of the present application are not limited thereto.

[0029] The unspecified conditions in the embodiments of the present application are carried out according to the conventional conditions or the conditions suggested by the manufacturers. The raw materials, reagents and the like used without specifying the manufacturers are all conventional products that can be commercially available.

[0030] Example 1

[0031] The alkali lignin was added to DMSO at a mass fraction of 20%, and after stirring and dissolving uniformly, the BDDE crosslinking agent was added, wherein the mass ratio of lignin to crosslinking agent was 2:1, and the solution was heated in an 80°C oil bath for 2h to obtain a polymer solution, which was then cast in a silica gel mold, and first kept at 80°C for 30min, then kept at 100°C for 30min, and finally kept at 120°C for 6h to prepare a lignin-based film material, which had a tensile strength of 10.34MPa, an elongation at break of 30.43%, and a toughness of 2.72MJ / m 3 .

[0032] Example 2-6

[0033] In Example 2, the organic solvent used was NMP, and the others were the same as in Example 1. Among them, the tensile strength was 15.05MPa, the elongation at break was 28.30%, and the toughness was 3.61MJ / m 3 .

[0034] In Example 3, the organic solvent used was NVP, and the others were the same as in Example 1. Among them, the tensile strength was 2.54MPa, the elongation at break was 33.7%, and the toughness was 0.65MJ / m 3 .

[0035] In Example 4, the organic solvent used was a γ-GVL aqueous solution, wherein the mass concentration of γ-GVL was 70wt.%, and the others were the same as in Example 1. Among them, the tensile strength was 23.52MPa, the elongation at break was 22.25%, and the toughness was 4.21MJ / m 3 .

[0036] In Example 5, the organic solvent used was a PC aqueous solution, wherein the mass concentration of PC was 50wt.%, and the others were the same as in Example 1. Among them, the tensile strength was 6.36MPa, the elongation at break was 7.64%, and the toughness was 0.29MJ / m 3 .

[0037] In Example 6, the organic solvent used was an EC aqueous solution, wherein the mass concentration of EC was 70wt.%, and the others were the same as in Example 1. Among them, the tensile strength was 9.97MPa, the elongation at break was 11.79%, and the toughness was 0.78MJ / m 3 .

[0038] Example 7

[0039] The enzymatic lignin was added to the γ-GVL aqueous solution (the mass concentration of γ-GVL was 70 wt.%) at a mass fraction of 20%, and after stirring and dissolving uniformly, the BDDE crosslinking agent was added, wherein the mass ratio of lignin to crosslinking agent was 2:1, and the polymer solution was obtained after heating reaction in an 80°C oil bath for 2h, and then the solution was cast in a silica gel mold, and the lignin-based film material was prepared by keeping the mold on a heating plate at 80°C for 30 min, then at 100°C for 30 min, and finally at 120°C for 6h, and the tensile strength, elongation at break, and toughness of the film material were 13.23 MPa, 17.08%, and 1.79 MJ / m 3 .

[0040] Example 8

[0041] The sodium lignosulfonate was added to the γ-GVL aqueous solution (the mass concentration of γ-GVL was 70 wt.%) at a mass fraction of 20%, and after stirring and dissolving uniformly, the BDDE crosslinking agent was added, wherein the mass ratio of lignin to crosslinking agent was 2:1, and the polymer solution was obtained after heating reaction in an 80°C oil bath for 2h, and then the solution was cast in a silica gel mold, and the lignin-based film material was prepared by keeping the mold on a heating plate at 80°C for 30 min, then at 100°C for 30 min, and finally at 120°C for 6h, and the tensile strength, elongation at break, and toughness of the film material were 3.37 MPa, 50.32%, and 1.13 MJ / m 3 .

[0042] Example 9

[0043] The alkali lignin was added to the γ-GVL aqueous solution (the mass concentration of γ-GVL was 70 wt.%) at a mass fraction of 10%, and after stirring and dissolving uniformly, the BDDE crosslinking agent was added, wherein the mass ratio of lignin to crosslinking agent was 1:1, and the polymer solution was obtained after heating reaction in an 80°C oil bath for 2h, and then the solution was cast in a silica gel mold, and the lignin-based film material was prepared by keeping the mold on a heating plate at 80°C for 30 min, then at 100°C for 30 min, and finally at 120°C for 4h, and the tensile strength, elongation at break, and toughness of the film material were 12.13 MPa, 9.48%, and 0.75 MJ / m 3 .

[0044] Example 10

[0045] The alkali lignin was added to the γ-GVL aqueous solution (the mass concentration of γ-GVL was 70 wt.%) at a mass fraction of 30%, and after stirring and dissolving uniformly, the BDDE crosslinking agent was added, wherein the mass ratio of lignin to crosslinking agent was 3:1, and the polymer solution was obtained after heating reaction in an 80°C oil bath for 2h, and then the solution was cast in a silica gel mold, and the lignin-based film material was prepared by keeping the mold on a heating plate at 80°C for 30 min, then at 100°C for 30 min, and finally at 120°C for 8h, and the tensile strength, elongation at break, and toughness of the film material were 21.80 MPa, 20.11%, and 3.32 MJ / m 3 .

[0046] Example 11

[0047] The alkali lignin was added to the γ-GVL aqueous solution (the mass concentration of γ-GVL was 70 wt.%) at a mass fraction of 40%, and after stirring and dissolving uniformly, the BDDE crosslinking agent was added, wherein the mass ratio of lignin to crosslinking agent was 4:1, and the polymer solution was obtained after heating reaction in an 80°C oil bath for 2h, and then the solution was cast in a silica gel mold, and the lignin-based film material was prepared by keeping the mold on a heating plate at 80°C for 30 min, then at 100°C for 30 min, and finally at 120°C for 10h, and the tensile strength, elongation at break, and toughness of the film material were 17.25 MPa, 24.55%, and 3.57 MJ / m 3 .

[0048] Example 12

[0049] The alkali lignin was added to the γ-GVL aqueous solution (the mass concentration of γ-GVL was 70 wt.%) at a mass fraction of 20%, and after stirring and dissolving uniformly, the BDDE crosslinking agent was added, wherein the mass ratio of lignin to crosslinking agent was 2:1, and the polymer solution was obtained after heating reaction in an 80°C oil bath for 2h, and then the solution was cast in a silica gel mold, and the lignin-based film material was prepared by keeping the mold on a heating plate at 80°C for 30 min, then at 100°C for 30 min, and finally at 120°C for 7h, and the tensile strength, elongation at break, and toughness of the film material were 20.52 MPa, 23.0%, and 3.83 MJ / m 3 .

[0050] Example 13

[0051] The alkali lignin was added to the γ-GVL aqueous solution (the mass concentration of γ-GVL was 70 wt.%) at a mass fraction of 20%, and after stirring and dissolving uniformly, the BFDGE crosslinking agent was added, wherein the mass ratio of lignin to crosslinking agent was 2:1, and the polymer solution was obtained by heating under an 80°C oil bath for 2h, and then the polymer solution was cast into a silica gel mold, and the lignin-based film material was prepared by keeping at 80°C for 30min, then at 100°C for 30min, and finally at 120°C for 4h on a hot plate, and the tensile strength of the lignin-based film material was 23.11 MPa, the elongation at break was 18.81%, and the toughness was 2.52 MJ / m 3 .

[0052] Example 14

[0053] The alkali lignin was added to the γ-GVL aqueous solution (the mass concentration of γ-GVL was 70 wt.%) at a mass fraction of 20%, and after stirring and dissolving uniformly, the PEGDE crosslinking agent (molecular weight was 500) was added, wherein the mass ratio of lignin to crosslinking agent was 2:1, and the polymer solution was obtained by heating under an 80°C oil bath for 2h, and then the polymer solution was cast into a silica gel mold, and the lignin-based film material was prepared by keeping at 80°C for 30min, then at 100°C for 30min, and finally at 120°C for 7h on a hot plate, and the tensile strength of the lignin-based film material was 11.86 MPa, the elongation at break was 117.81%, and the toughness was 12.31 MJ / m 3 .

[0054] Performance test

[0055] (1) Lignin film morphology

[0056] The cross-section of the lignin-based thermosetting film material prepared in Examples 4 and 14 was tested by SEM, and the SEM images are shown in Figs. 4a and 4b, respectively. Figure 2

[0057] It can be seen from the test results that the lignin-based thermosetting film material is crosslinked and dense, and no holes are observed. Compared with the lignin-based thermosetting film material prepared by the BDDE crosslinking agent, the cross-section of the lignin-based thermosetting film material prepared by the PEGDE crosslinking agent is smoother and softer. This may be due to the influence of the length of the molecular chain of the crosslinking agent on the performance. The three-dimensional network formed by the crosslinking of the crosslinking agent with a short molecular chain is tight, so the material has better rigidity; the three-dimensional network formed by the crosslinking of the crosslinking agent with a long molecular chain is sparse, so the material has better flexibility. The BDDE crosslinking agent has a short molecular chain, and the tensile strength of the film material prepared by the BDDE crosslinking agent is good, which shows rigidity and toughness; while the PEGDE crosslinking agent has a long molecular chain, and the elongation at break of the film material prepared by the PEGDE crosslinking agent is good, which shows flexibility.

[0058] (2) Lignin film mechanical properties ​

[0059] The lignin-based thermosetting film materials prepared in Examples 1-6 were subjected to mechanical property tests, and the stress-strain diagrams and toughness diagrams obtained are shown in Figs. 1-6, respectively. Figure 3 a, b in the middle.

[0060] It can be seen from the test results that the mechanical properties of the lignin-based thermosetting film materials prepared by using different solvents to dissolve lignin are different, and the mechanical properties of the lignin-based thermosetting film material prepared by using the γ-GVL aqueous solution to dissolve lignin are the best, with a tensile strength of 23.52 MPa, an elongation at break of 22.25%, and a toughness of 4.21 MJ / m 3 This may be because the γ-GVL aqueous solution is beneficial to the breaking of strong hydrogen bonds in lignin and the combination of aromatic nuclei and aliphatic chain regions, so that lignin can better crosslink with the crosslinking agent to form a three-dimensional network structure, which prevents the movement of polymer chains, makes the material more solid, and increases the strength of the mechanical properties of the material.

[0061] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application.

Claims

1. A method for the preparation of a lignin-based thermoset film material, characterized by, The method comprises the following steps: dissolving lignin in an organic solvent and / or an aqueous organic solvent solution, adding a crosslinking agent, heating and reacting to obtain a polymer solution, casting in a mold, and heating and curing to obtain a lignin-based film material; the organic solvent is at least one of dimethyl sulfoxide, N-methyl pyrrolidone and N-vinyl pyrrolidone; the aqueous organic solvent solution is at least one of a gamma-valerolactone aqueous solution, a propylene carbonate aqueous solution and a vinyl carbonate aqueous solution; the concentration of the organic solvent in the aqueous organic solvent solution is 50-70 wt.%; the crosslinking agent is a diglycidyl ether.

2. The process for the preparation of lignin-based thermoset film material according to claim 1, characterized in that, the mass fraction of the lignin in the organic solvent and / or the aqueous organic solvent solution is 10-40%.

3. The method according to claim 1 or 2, c h a r a c t e r i z e d in that, the organic solvent is at least one of dimethyl sulfoxide and N-methyl pyrrolidone; the aqueous organic solvent solution is a gamma-valerolactone aqueous solution; the concentration of the organic solvent in the aqueous organic solvent solution is 60-70 wt.%; the mass fraction of the lignin in the organic solvent and / or the aqueous organic solvent solution is 20-40%.

4. The method according to claim 1 or 2, c h a r a c t e r i z e d in that, the mass ratio of the lignin to the crosslinking agent is (1-4):

1.

5. The method for preparing a lignin-based thermosetting thin film material according to claim 4, characterized in that, the crosslinking agent is at least one of 1,4-butanediol diglycidyl ether, polyethylene glycol diglycidyl ether and bisphenol F diglycidyl ether, wherein the molecular weight of the polyethylene glycol diglycidyl ether is 400-1000; or the crosslinking agent is at least one of 1,4-butanediol diglycidyl ether and polyethylene glycol diglycidyl ether; the mass ratio of the lignin to the crosslinking agent is (2-4):

1.

6. The method for preparing a lignin-based thermosetting thin film material according to claim 1 or 2, characterized in that, the lignin is at least one of alkali lignin, enzymatic hydrolysis lignin and lignin sulfonate.

7. The method for preparing a lignin-based thermosetting thin film material according to claim 1 or 2, characterized in that, the heating and reacting is performed at a temperature of 80-90℃ for 2-3h; the heating and curing is performed in the following procedure: first, 75-85℃ for 0.5-1h, then 95-105℃ for 0.5-1h, and finally 115-125℃ for 4-10h.

8. The method for preparing a lignin-based thermosetting thin film material according to claim 7, characterized in that, the heating and curing is performed in the following procedure: first, 75-85℃ for 0.5-1h, then 95-105℃ for 0.5-1h, and finally 115-125℃ for 6-10h.

9. A lignin-based thermosetting film material prepared by the method of any one of claims 1-8.

10. The use of the lignin-based thermosetting film material of claim 9 in mulch film, packaging material and photothermal material.

Images