Preparation method of cellulose material with double-network structure and product thereof

Abstract

The invention provides a preparation method of a double-network structure reinforced cellulose material and a product thereof, and the preparation method comprises the following steps: adding lignin into an ionic liquid, heating and dissolving to prepare a lignin solution; adding cellulose fibers into the lignin solution, and heating and dissolving to prepare a lignin / cellulose solution; adding glutaraldehyde into the lignin / cellulose solution, heating and stirring to obtain a crosslinked lignin / cellulose mixed solution; and finally, gelatinizing and forming to prepare the high-strength cellulose ionic gel with the double-network structure. The ionic liquid adopted by the invention can dissolve lignin and cellulose fibers, so that polyhydroxy groups are exposed to serve as chemical crosslinking sites, and meanwhile, the ionic liquid can serve as a catalyst to promote aldolization of aldehyde groups of glutaraldehyde and hydroxyl groups of lignin and cellulose molecules to form stable chemical bonds; a cellulose molecular network and a lignin molecular network are constructed to prepare the cellulose material with a double-network structure, and the cellulose material has excellent strength performance.

Description

Technical Field

[0001] The present invention belongs to the fields of green natural polymer materials and flexible electronic technologies, and particularly relates to a preparation method and a product of a cellulose material with a double-network structure.

Background Art

[0002] Ionic gels are a class of quasi-solid new composite materials with a three-dimensional network, which use ionic liquids as the dispersed phase and inorganic substances, organic substances or inorganic-organic mixtures as the solid matrix. Among them, ionic gels prepared from petroleum-based polymers have been studied more, but petroleum-based polymers have disadvantages such as non-renewability and non-degradability. Cellulose, with advantages such as low cost, renewability, biodegradability, easy modification and processability, is a good substitute for petroleum-based polymers. The cellulose ionic gels prepared therefrom inherit the characteristics of cellulose and ionic liquids. However, the formation of most cellulose ionic gels mainly relies on weak physical interactions (mainly hydrogen bond interactions between cellulose molecules and between cellulose and ionic liquids), which limits the mechanical strength of cellulose ionic gels and further restricts their practical applications under high loading conditions.

[0003] Constructing a double-network structure, using a softer polymer network to absorb and disperse stress, and a harder cross-linked network to provide strength and elasticity, and precisely regulating the interaction between the two can significantly improve the mechanical properties of the gel. The methods for constructing a double-network structure often include physical cross-linking, chemical cross-linking, and physical-chemical double cross-linking. Among them, physical cross-linking forms a three-dimensional network structure by introducing dynamic non-covalent bonds (such as hydrogen bonds, van der Waals forces, ionic bonds, hydrophobic interactions, etc.) into the molecular chain. However, the effect of non-covalent bonds is not as good as that of covalent bonds, and its mechanical property enhancement mechanism is not high. Therefore, it becomes possible to introduce covalent bonds mainly by chemical cross-linking. Chemical cross-linking connects molecular chains through covalent bonds to construct a molecular cross-linked network, which can significantly improve the mechanical properties of gel materials. The high-density hydroxyl groups on the cellulose molecular chain provide an ideal platform for constructing covalent bonds. Stable covalent bond networks are formed between cellulose molecules to regulate the microstructure of ionic gels, thereby significantly improving the strength and toughness of cellulose ionic gels. The influencing factors include the concentration and cross-linking time of the cross-linking agent. Precisely adjusting the cross-linking density can control the mechanical properties of cellulose ionic gels. Among them, a high cross-linking density can achieve the mechanical properties of the gel (such as tensile strength and compressive strength). The reason is that a high cross-linking density reduces material deformation by enhancing intermolecular connections: cross-linking points make the polymer chains bind more tightly, inhibiting the sliding and breaking of molecular chains when stressed; and the uniformly distributed cross-linked structure can make stress transfer evenly inside the material, avoiding local overstress leading to rupture, thereby improving the overall mechanical properties of the gel material.

Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a preparation method and product of a cellulose material with a double-network structure. The method has simple steps, is easy to operate and control, and the prepared cellulose ion gel with a double-network structure has high mechanical strength and can be widely applied in fields such as flexible electronics and life health monitoring. At the same time, due to the biocompatibility and environmental friendliness of lignin and cellulose, the prepared high-strength cellulose material exhibits the characteristics of environmental protection.

[0005] The present invention is implemented as follows:

[0006] A preparation method of a cellulose ion gel with a double-network structure, characterized in that it includes the following steps:

[0007] (1) Add lignin to an ionic liquid of 1-allyl-3-methylimidazolium chloride ([AMIM]Cl) type, and heat and dissolve at 90 ± 5 °C to prepare a lignin solution;

[0008] (2) Add cellulose fibers to the lignin solution, and heat and dissolve at 85 ± 5 °C to prepare a lignin / cellulose solution;

[0009] (3) Add glutaraldehyde to the lignin / cellulose solution, and heat and stir at 85 ± 5 °C to obtain a cross-linked lignin / cellulose mixed solution;

[0010] (4) Gelatinize and mold the lignin / cellulose mixed solution to prepare a high-strength cellulose ion gel with a double-network structure.

[0011] Further, in step (1), the molecular weight of lignin is 2000 - 102000 g / mol.

[0012] Further, in step (1), the dosage of lignin relative to the ionic liquid is 0.06 wt.% - 4.8 wt.%.

[0013] Further, in step (1), the ionic liquid is one of 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium acetate.

[0014] Further, in step (2), the dosage of cellulose fibers relative to the ionic liquid is 1 wt.% - 8 wt.%.

[0015] Further, in step (3), the dosage of glutaraldehyde relative to cellulose fibers is 0.1 wt.% - 0.6 wt.%.

[0016] Further, in step (3), the cross-linking time of glutaraldehyde is 0.5 h - 4 h.

[0017] Furthermore, a cellulose ion gel with a double network structure is prepared based on the preparation method of the cellulose ion gel with a double network structure described above.

[0018] In the present invention, natural polymer material cellulose fiber widely distributed in nature is selected as the matrix of the ion gel. By introducing ionic liquid, lignin and glutaraldehyde crosslinking agent, without adding extra catalyst, while the ionic liquid dissolves lignin and cellulose, it further catalyzes the crosslinking reaction between the hydroxyl reaction sites of cellulose and lignin and the aldehyde groups of the glutaraldehyde crosslinking agent, forming a lignin molecular network and a cellulose molecular network, and constructing a cellulose ion gel with a double network structure by a simple preparation method. It has the following advantages:

[0019] (1) The present invention uses cellulose fiber with low cost, biocompatibility, biodegradability and rich resources as the solid matrix, which is of great significance for promoting the high-value application of cellulose.

[0020] (2) The present invention uses lignin, the second most abundant plant polymer after cellulose, doped in the cellulose ion gel system, which can make full use of lignin.

[0021] (3) Through a simple chemical crosslinking process between lignin and cellulose, a stable double network structure is prepared, effectively improving the mechanical strength of the cellulose ion gel; the preparation method has simple steps, is easy to control, and does not add extra catalyst.

Specific Embodiments

[0022] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. Those not specified in the embodiments are carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified in the manufacturer are all conventional products that can be obtained through commercial purchase.

[0023] Example 1:

[0024] (1) 3 wt.% lignin with a molecular weight of 95,000 g / mol was added to an ionic liquid of 1-allyl-3-methylimidazolium chloride ([AMIM]Cl) and dissolved at 90 °C to obtain a lignin solution. 6 wt.% cellulose fibers were added to the lignin solution and dissolved at 85 °C to prepare a lignin / cellulose solution; 0.3 wt.% glutaraldehyde crosslinking agent was added to the lignin / cellulose solution and crosslinked for 1 h, and stirred at 85 °C to obtain a lignin / cellulose mixed solution, and finally it was gelled to prepare a cellulose ion gel with a double network structure. The tensile strength of this cellulose ion gel with a double network structure is 16.35 MPa, and the toughness is 12.5 MJ / m 3 , and the compressive strength is 12.4 MPa.

[0025] Control Example 1:

[0026] (1) 6 wt.% cellulose fibers were added to the ionic liquid and dissolved to obtain a cellulose solution. The mixed solution was gelled to prepare a cellulose ion gel. The tensile strength of this cellulose ion gel is 0.86 MPa, and the toughness is 0.15 MJ / m 3 , and the compressive strength is 4.21 MPa.

[0027] Control Example 2:

[0028] (1) 6 wt.% cellulose fibers were added to the ionic liquid and dissolved to obtain a cellulose solution, and 0.3 wt.% glutaraldehyde crosslinking agent was added and crosslinked for 1 h, and stirred to obtain a crosslinked glutaraldehyde / cellulose solution. The mixed solution was gelled to prepare a cellulose ion gel with a single network structure. The tensile strength of this cellulose ion gel is 4.48 MPa, and the toughness is 2.51 MJ / m 3 , and the compressive strength is 5.46 MPa.

[0029] Control Example 3:

[0030] (1) 3 wt.% lignin with a molecular weight of 95,000 g / mol was added to the ionic liquid and dissolved to obtain a lignin solution. 6 wt.% cellulose fibers were added to the lignin solution and dissolved to prepare a lignin / cellulose solution. The mixed solution was gelled to prepare a cellulose ion gel. The tensile strength of this cellulose ion gel is 4.15 MPa, and the toughness is 2.13 MJ / m 3 , and the compressive strength is 5.59 MPa.

[0031] Example 2:

[0032] (1) 3 wt.% lignin with a molecular weight of 4300 g / mol was added to the ionic liquid 1-ethyl-3-methylimidazolium acetate and dissolved at 90 °C to obtain a lignin solution. 6 wt.% cellulose fibers were added to the lignin solution and dissolved at 85 °C to prepare a lignin / cellulose solution. 0.15 wt.% glutaraldehyde crosslinking agent was added to the lignin / cellulose solution and crosslinked for 1 h, and stirred at 85 °C to obtain a crosslinked lignin / cellulose mixed solution. The mixed solution was gelled to prepare a cellulose ion gel. The tensile strength of this cellulose ion gel is 5.43 MPa, the toughness is 3.73 MJ / m3, and the compressive strength is 6.59 MPa.

[0033] Example 3:

[0034] (1) 0.6 wt.% lignin with a molecular weight of 15000 g / mol was added to the ionic liquid 1-butyl-3-methylimidazolium chloride and dissolved at 85 °C to obtain a lignin solution. 6 wt.% cellulose fibers were added to the lignin solution and dissolved at 90 °C to prepare a lignin / cellulose solution. 0.3 wt.% glutaraldehyde crosslinking agent was added to the lignin / cellulose solution and crosslinked for 1 h, and stirred at 80 °C to obtain a crosslinked lignin / cellulose mixed solution. The mixed solution was gelled to prepare a cellulose ion gel with a double network structure. The tensile strength of this cellulose ion gel with a double network structure is 10.35 MPa, and the toughness is 7.9 MJ / m 3 , and the compressive strength is 8.53 MPa.

[0035] Example 4:

[0036] (1) 1.5 wt.% lignin with a molecular weight of 75000 g / mol was added to the ionic liquid 1-butyl-3-methylimidazolium chloride and dissolved at 95 °C to obtain a lignin solution. 6 wt.% cellulose fibers were added to the lignin solution and dissolved at 80 °C to prepare a lignin / cellulose solution. 0.45 wt.% glutaraldehyde crosslinking agent was added to the lignin / cellulose solution and crosslinked for 1 h, and stirred at 85 °C to obtain a crosslinked lignin / cellulose mixed solution. The mixed solution was gelled to prepare a cellulose ion gel with a double network structure. The tensile strength of this cellulose ion gel with a double network structure is 13.24 MPa, and the toughness is 10.1 MJ / m 3 , and the compressive strength is 10.42 MPa.

[0037] Example 5:

[0038] (1) Add 4.8 wt.% lignin with a molecular weight of 10000 g / mol to the ionic liquid 1-butyl-3-methylimidazolium chloride, and dissolve it at 90 °C to obtain a lignin solution. Add 6 wt.% cellulose fibers to the lignin solution, and dissolve it at 85 °C to prepare a lignin / cellulose solution. Add 0.6 wt.% glutaraldehyde crosslinking agent to the lignin / cellulose solution and crosslink for 1 h, and stir at 90 °C to obtain a crosslinked lignin / cellulose mixed solution. Gel the mixed solution to prepare a cellulose ion gel with a double-network structure. The tensile strength of this cellulose ion gel with a double-network structure is 15.49 MPa, and the toughness is 11.8 MJ / m 3 , and the compressive strength is 10.88 MPa.

[0039] Example 6:

[0040] (1) Add 3 wt.% lignin with a molecular weight of 2000 g / mol to the ionic liquid 1-allyl-3-methylimidazolium chloride, and dissolve it at 90 °C to obtain a lignin solution. Add 6 wt.% cellulose fibers to the lignin solution, and dissolve it at 85 °C to prepare a lignin / cellulose solution. Add 0.3 wt.% glutaraldehyde crosslinking agent to the lignin / cellulose solution and crosslink for 2 h, and stir at 85 °C to obtain a crosslinked lignin / cellulose mixed solution. Gel the mixed solution to prepare a cellulose ion gel with a double-network structure. The tensile strength of this cellulose ion gel with a double-network structure is 5.45 MPa, and the toughness is 4.2 MJ / m 3 , and the compressive strength is 6.87 MPa.

[0041] Example 7:

[0042] (1) Add 3 wt.% lignin with a molecular weight of 10200 g / mol to the ionic liquid 1-allyl-3-methylimidazolium chloride, and dissolve it at 95 °C to obtain a lignin solution. Add 4 wt.% cellulose fibers to the lignin solution, and dissolve it at 90 °C to prepare a lignin / cellulose solution. Add 0.15 wt.% glutaraldehyde crosslinking agent to the lignin / cellulose solution and crosslink for 1 h, and stir at 90 °C to obtain a crosslinked lignin / cellulose mixed solution. Gel the mixed solution to prepare a cellulose ion gel with a double-network structure. The tensile strength of this cellulose ion gel with a double-network structure is 12.35 MPa, and the toughness is 9.4 MJ / m 3 , and the compressive strength is 9.42 MPa.

[0043] In summary, the present invention mixes lignin, cellulose fiber, ionic liquid and glutaraldehyde crosslinking agent. The ionic liquid can dissolve lignin and cellulose fiber, exposing multiple hydroxyl groups as chemical crosslinking sites. At the same time, the ionic liquid can act as a catalyst to promote the acetal reaction between the aldehyde group of glutaraldehyde and the hydroxyl groups of lignin and cellulose molecules, forming stable chemical bonds, constructing a cellulose molecular network and a lignin molecular network, preparing a cellulose material with a double-network structure, and presenting excellent strength performance.

[0044] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments we described are illustrative rather than used to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered by the scope protected by the claims of the present invention.

Claims

1. A preparation method of a cellulose ion gel with a double-network structure, characterized in that: It includes the following steps: (1) Add lignin to 1-allyl-3-methylimidazolium chloride ionic liquid, and heat and dissolve it at 90±5 °C to prepare a lignin solution; (2) Add cellulose fibers to the lignin solution, and heat and dissolve it at 85±5 °C to prepare a lignin / cellulose solution; (3) Add glutaraldehyde to the lignin / cellulose solution, and heat and stir it at 85±5 °C to obtain a cross-linked lignin / cellulose mixed solution; (4) Gel the lignin / cellulose mixed solution and mold it to prepare a high-strength cellulose ionic gel with a double-network structure.

2. The method according to claim 1, characterized in that: In step (1), the molecular weight of lignin is 2000-102000 g / mol.

3. The method according to claim 1, characterized in that: In step (1), the dosage of lignin relative to the ionic liquid is 0.06 wt.% - 4.8 wt.%.

4. The method according to claim 1, wherein: The ionic liquid in step (1) is one of 1-allyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, and 1-ethyl-3-methylimidazolium acetate.

5. The method according to claim 1, wherein: In step (2), the dosage of cellulose fibers relative to the ionic liquid is 1 wt.% - 8 wt.%.

6. The method according to claim 1, characterized in that: In step (3), the dosage of glutaraldehyde relative to cellulose fibers is 0.1 wt.% - 0.6 wt.%.

7. The method according to claim 1, wherein: In step (3), the cross-linking time of glutaraldehyde is 0.5 h - 4 h.

8. A cellulose ion gel with a double-network structure, characterized in that: The cellulose ionic gel with a double-network structure is prepared by the preparation method of a cellulose ionic gel with a double-network structure described in claims 1-7.