A lignin micro-nanosphere / PVA composite film material and its preparation method and application

Abstract

The invention discloses a lignin micro-nanosphere / PVA composite film material and a preparation method and application thereof. The material comprises the following steps: dissolving purified lignin in tetrahydrofuran (THF) with a lignin concentration of 3-7 mg / mL, dripping water into the material, stirring continuously during the dripping process, and having a volume ratio of THF to water of 1:1-8 to obtain a mixed solution; dialyzing the mixed solution to obtain a lignin micro-nanosphere suspension; adjusting the concentration of the dialyzed lignin micro-nanosphere suspension to 1-5 mg / mL, adding solid polyvinyl alcohol and glycerol into the material with a mass fraction of 1%-5% of the polyvinyl alcohol and a mass fraction of 1%-5% of the glycerol, and uniformly mixing the mixture to obtain a mixed solution; and forming a film from the mixed solution.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-nano lignin composite materials, and in particular relates to a lignin micro-nano ball / PVA composite film material and a preparation method and application thereof. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Microplastics refer to plastic particles with a diameter of less than 5mm. They generally fall into two categories: primary microplastics, which are plastic particles discharged into the aquatic environment through rivers and sewage treatment plants, such as those in cosmetics. Secondary microplastics are formed when larger plastic waste fragments and reduces in size through physical, chemical, and biological processes. Compared to "white pollution" plastics, microplastics pose a greater threat to the environment and organisms. Therefore, the research and development and production of green, biodegradable packaging materials are urgently needed.

[0004] Lignin is an aromatic polymer and the only naturally renewable aromatic compound that is abundant. Lignin and its derivatives have potential commercial value due to their UV resistance, antibacterial, antioxidant, biodegradable, and non-toxic properties. Polyvinyl alcohol (PVA) is a biodegradable polymer that is water-soluble and film-forming, while industrial alkali lignin is soluble in organic solvents but insoluble in water. Therefore, due to their different water solubilities, the preparation of composite film materials by mixing alkali lignin with PVA solutions requires hydrophilic modification of the lignin. Quaternization is commonly used to obtain water-soluble lignin, but this method is complex and costly, making it unsuitable for commercial applications. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a lignin micro-nanosphere / PVA composite film material and its preparation method and application.

[0006] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a lignin micro-nanosphere / PVA composite film material, comprising the following steps:

[0008] The purified lignin was dissolved in tetrahydrofuran (THF) at a concentration of 3 to 7 mg / mL, and water was added dropwise thereto with continuous stirring during the addition process. The volume ratio of tetrahydrofuran to water was 1:1 to 8 to obtain a mixed solution.

[0009] The mixed solution is dialyzed to obtain a lignin micro-nanosphere suspension;

[0010] Adjusting the concentration of the lignin micro-nanosphere suspension obtained by dialysis to 1-5 mg / mL, then adding solid polyvinyl alcohol and glycerol thereto, with the mass fraction of polyvinyl alcohol being 1%-5% and the mass fraction of glycerol being 1%-5%, and mixing them uniformly to obtain a mixed solution;

[0011] The mixed solution is then formed into a film.

[0012] Lignin is insoluble in water. Water is added dropwise with continuous stirring. In this state, the lignin dissolved in tetrahydrofuran is precipitated and microspheroidized.

[0013] The purpose of dialysis is to remove organic solvents and impurities. The purpose of adding solid polyvinyl alcohol is to maintain the concentration of the lignin micro-nanosphere suspension; the purpose of adding glycerol is to better form a film.

[0014] In some embodiments, the method for purifying lignin is as follows: dissolving crude lignin in a mixed solution of 1,4-dioxane and water to obtain a mixed solution, wherein the mass ratio of 1,4-dioxane to water is 6 to 10:1; the water is an acidic aqueous solution;

[0015] The mixed solution is placed in an oil bath at 80-90°C, extracted and impurities removed, and then acid precipitated to obtain pure lignin.

[0016] The crude lignin is dissolved in a mixture of 1,4-dioxane and water to purify the lignin and remove impurities from the crude lignin. The water is an acidic aqueous solution, in which the acid catalyzes the degradation of sugars.

[0017] Preferably, the pH value of the acidic aqueous solution is 1.5 to 2.5.

[0018] More preferably, hydrochloric acid is used to adjust the pH value of the acidic aqueous solution. Using hydrochloric acid to adjust the pH value can purify dioxane and catalyze the degradation of sugars.

[0019] In some embodiments, the dialysis bag used in the dialysis is a 1000 Da dialysis bag, which is used to intercept lignin within a certain molecular weight range.

[0020] Preferably, the dialysis temperature is 45-55° C., the dialysis time is 10-15 h, and the water is changed every 3-5 h.

[0021] In some embodiments, the method for adjusting the concentration of the lignin micro-nanosphere suspension obtained by dialysis is rotary evaporation or adding water.

[0022] In some embodiments, the method of forming a membrane from the mixed solution is a casting method.

[0023] In a second aspect, the present invention provides a lignin micro-nanosphere / PVA composite film material prepared by the preparation method.

[0024] In a third aspect, the present invention provides an application of the lignin micro-nanosphere / PVA composite film material in the preparation of sunscreen film, express packaging, medical packaging, fruit and vegetable packaging, or meat packaging.

[0025] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0026] (1) The present invention provides a method for preparing a lignin micro / nanosphere / PVA composite film material having a simple preparation process, low cost, and excellent UV shielding performance. The present invention uses a self-assembly method to adjust the ratio of THF and water to prepare lignin micro / nanospheres of different sizes, and dissolves solid PVA in the lignin micro / nanosphere suspension. The preparation process is time-saving and labor-saving, and at the same time solves the shortcomings of lignin's poor dispersibility in water and the difficulty in controlling the size of lignin micro / nano particles, thereby preparing a uniform lignin micro / nanosphere / PVA composite film material.

[0027] (2) The method provided by the present invention can prepare a uniform lignin micro-nanosphere / PVA composite film with good UV shielding properties. Its anti-UV effect is much higher than that of pure PVA composite film materials, and the UV transmittance is less than 5%. This high-strength, high-UV shielding transparent lignin micro-nanosphere / PVA composite film material can be used in sunscreen films, express delivery, medicine, fruit, vegetable and meat packaging and other fields. By adjusting the ratio of THF and water, the particle size distribution and size of the lignin micro-nanospheres can be controlled, and the UV resistance of the lignin micro-nanosphere / PVA composite film material can be regulated. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0029] Figure 1 The micromorphology of micro-nano lignin balls prepared at different ratios of THF and H2O;

[0030] Figure 2 Comparison of the apparent properties of lignin micro / nanosphere / PVA composite films of different sizes;

[0031] Figure 3 UV light blocking properties of lignin micro / nanosphere / PVA composite films of different sizes, where A represents (LMNP1 / PVA film), B represents (LMNP2 / PVA film), C represents (LMNP3 / PVA film), and D represents (LMNP4 / PVA film). DETAILED DESCRIPTION

[0032] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0033] The present invention will be further described below with reference to the embodiments.

[0034] Example 1

[0035] A small amount of purified alkali lignin was fully dissolved in chromatographically pure tetrahydrofuran to prepare a lignin-tetrahydrofuran solution with an initial concentration of 5 mg / mL.

[0036] Deionized water was then added dropwise to the lignin-THF solution at a rate of 2 mL / min using a peristaltic pump, with a volume ratio of deionized water to THF of 1:1. This process was carried out at 25°C and with a magnetic stirring rate of 500 rpm.

[0037] The solution after dropwise addition was transferred into a 1000Da dialysis bag and dialyzed in deionized water at 50°C, with the water changed every 4 hours for 12 hours to obtain a lignin micro-nanosphere suspension (LMNP1).

[0038] Suspensions of lignin micro / nanospheres of varying sizes were adjusted to concentrations of 1, 2, and 5% by rotary evaporation or by adding water. Solid polyvinyl alcohol and 2% glycerol were then added to the suspensions to create a PVA-LMNP mixed solution, where the solid polyvinyl alcohol accounted for 5% of the solution by weight. The mixture was stirred at 500 rpm in a 100°C water bath for 6 hours. After uniform mixing, the mixture was dried in a 50°C vacuum drying oven containing phosphorus pentoxide for 12 hours. After drying, the LMNP1-PVA composite film was obtained.

[0039] Example 2

[0040] A small amount of purified alkali lignin was fully dissolved in chromatographically pure tetrahydrofuran to prepare a lignin-tetrahydrofuran solution with an initial concentration of 5 mg / mL.

[0041] Deionized water was then added dropwise to the lignin-THF solution at a rate of 2 mL / min using a peristaltic pump, with a volume ratio of 1:2. This process was carried out at 25°C and a magnetic stirring rate of 500 rpm.

[0042] The solution after dropwise addition was transferred to a 1000 Da dialysis bag (Klamar Co., Ltd., Shang Hai, China) and dialyzed in deionized water at 50°C, changing the water every 4 hours for 12 hours to obtain LMNP2.

[0043] The concentrations of lignin micro-nanosphere suspensions of different sizes were adjusted to 1, 2, and 5% by rotary evaporation and water addition, and solid polyvinyl alcohol and 2% glycerol were added to the lignin micro-nanosphere suspensions to prepare a PVA-LMNP mixed solution, in which solid polyvinyl alcohol accounted for 5% of the solution mass.

[0044] During mixing, the mixture was stirred at 500 rpm in a 100° C. water bath for 6 h. After stirring evenly, the mixture was placed in a 50° C. vacuum drying oven filled with phosphorus pentoxide and dried for 12 h. After drying, the LMNP2-PVA composite film was obtained.

[0045] Example 3

[0046] A small amount of purified alkali lignin was fully dissolved in chromatographically pure tetrahydrofuran to prepare a lignin-tetrahydrofuran solution with an initial concentration of 5 mg / mL.

[0047] Deionized water was then added dropwise to the lignin-THF solution at a rate of 2 mL / min using a peristaltic pump, with a volume ratio of deionized water to THF of 1:4. This process was carried out at 25°C and with a magnetic stirring rate of 500 rpm.

[0048] The solution after dropwise addition was transferred to a 1000 Da dialysis bag (Klamar Co., Ltd., Shang Hai, China) and dialyzed in deionized water at 50°C, with the water changed every 4 hours for 12 hours to obtain LMNP3.

[0049] Suspensions of lignin micro / nanospheres of varying sizes were adjusted to concentrations of 1, 2, and 5% by rotary evaporation and water addition. Solid polyvinyl alcohol and 2% glycerol were then added to the suspensions to create a PVA-LMNP mixed solution, with the solid polyvinyl alcohol comprising 5% of the solution by weight. The mixture was stirred at 500 rpm in a 100°C water bath for 6 hours. After uniform mixing, the mixture was dried in a 50°C vacuum drying oven containing phosphorus pentoxide for 12 hours. After drying, the LMNP3-PVA composite film was obtained.

[0050] Example 4

[0051] A small amount of purified alkali lignin was fully dissolved in chromatographically pure tetrahydrofuran to prepare a lignin-tetrahydrofuran solution with an initial concentration of 5 mg / mL.

[0052] Deionized water was then added to the lignin-THF solution dropwise at a rate of 2 mL / min using a peristaltic pump, with a volume ratio of deionized water to THF of 1:8. This process was carried out at 25°C and with a magnetic stirring rate of 500 rpm.

[0053] The solution after dropwise addition was transferred to a 1000 Da dialysis bag (Klamar Co., Ltd., Shang Hai, China) and dialyzed in deionized water at 50°C, with the water changed every 4 hours. The dialysis was continued for 12 hours to obtain LMNP4.

[0054] The concentrations of lignin micro-nanosphere suspensions of different sizes were adjusted to 1, 2, and 5% by rotary evaporation and water addition, and solid polyvinyl alcohol and 2% glycerol were added to the lignin micro-nanosphere suspensions to prepare a PVA-LMNP mixed solution, in which solid polyvinyl alcohol accounted for 5% of the solution mass.

[0055] During mixing, the mixture was stirred at 500 rpm in a 100° C. water bath for 6 h. After stirring evenly, the mixture was placed in a 50° C. vacuum drying oven filled with phosphorus pentoxide and dried for 12 h. After drying, the LMNP4-PVA composite film was obtained.

[0056] Table 1 shows the average particle size and particle size distribution of lignin micro-nanospheres prepared at different ratios of tetrahydrofuran and water in Examples 1-4 of the present invention;

[0057] Table 1 Average particle size and particle size distribution of lignin micro-nanospheres

[0058] Sample name Average particle size (μm) Particle size range (μm) <![CDATA[LMNP1]]> 1.36 0.2-5.0 <![CDATA[LMNP2]]> 0.82 0.1-2.0 <![CDATA[LMNP3]]> 0.80 0.4-1.8 <![CDATA[LMNP4]]> 0.55 0.3-0.7

[0059] The microscopic morphology of the lignin micro-nanospheres of different sizes prepared in Examples 1-4 was characterized. Figure 1 As shown by Figure 1 It can be seen that with the increase of the ratio of tetrahydrofuran to water, the particle size of lignin microspheres tends to decrease.

[0060] The apparent properties of the lignin micro-nanosphere / PVA composite film materials prepared in Examples 1-4 were characterized. Figure 2 As shown, Figure 2 In the table, 1:1, 1:2, 1:3, and 1:4 refer to the volume ratios of deionized water and tetrahydrofuran in Examples 1-4, respectively; 1%, 2%, and 5% refer to the concentrations of the lignin micro-nanosphere suspension, respectively. Figure 2 It can be seen that the lignin micro-nanosphere / PVA composite film material has good transparency, but with the increase of the concentration of the lignin micro-nanosphere suspension, the composite film gradually changes from colorless and transparent to brown and transparent.

[0061] Figure 3 This is a test chart of the UV light blocking performance of the lignin micro-nanosphere / PVA composite film prepared in Examples 1-4. Figure 3It can be seen that the UV spectrophotometry method shows that the UV blocking ability of the lignin micro-nanosphere / PVA composite film is significantly better than that of the PVA film. Under optimal conditions, the UV transmittance is less than 5%.

[0062] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a lignin micro-nanosphere / PVA composite film material, characterized by: The steps include: The purified lignin was dissolved in tetrahydrofuran at a concentration of 3 to 7 mg / mL, and water was added dropwise thereto with continuous stirring during the addition process. The volume ratio of tetrahydrofuran to water was 1:1 to 8 to obtain a mixed solution. The mixed solution is dialyzed to obtain a lignin micro-nanosphere suspension; Adjusting the concentration of the lignin micro-nanosphere suspension obtained by dialysis to 1-5 mg / mL, then adding solid polyvinyl alcohol and glycerol thereto, with the mass fraction of polyvinyl alcohol being 1%-5% and the mass fraction of glycerol being 1%-5%, and mixing them uniformly to obtain a mixed solution; The mixed liquid is made into a film; The prepared lignin micro-nanosphere / PVA composite film material has an ultraviolet transmittance of less than 5% and good transparency. As the concentration of the lignin micro-nanosphere suspension increases, the composite film gradually changes from colorless and transparent to brown and transparent. The lignin purification method comprises: dissolving crude lignin in a mixed solution of 1,4-dioxane and water to obtain a mixed solution, wherein the mass ratio of 1,4-dioxane to water is 6 to 10:1; the water is an acidic aqueous solution; the acid in the solution plays a role in catalyzing the degradation of sugars; The mixed solution is placed in an oil bath at 80-90°C, extracted and impurities removed, and then acid precipitated to obtain pure lignin.

2. The method for preparing the lignin micro-nanosphere / PVA composite film material according to claim 1, characterized in that: The pH value of the acidic aqueous solution is 1.5 to 2.

5.

3. The method for preparing the lignin micro-nanosphere / PVA composite film material according to claim 2, characterized in that: The pH value of the acidic aqueous solution is adjusted using hydrochloric acid.

4. The method for preparing the lignin micro-nanosphere / PVA composite film material according to claim 1, characterized in that: The dialysis bag used in the dialysis was a 1000Da dialysis bag.

5. The method for preparing the lignin micro-nanosphere / PVA composite film material according to claim 4, characterized in that: The dialysis temperature is 45-55℃, the dialysis time is 10-15h, and the water is changed every 3-5h.

6. The method for preparing the lignin micro-nanosphere / PVA composite film material according to claim 1, characterized in that: The method for adjusting the concentration of the lignin micro-nanosphere suspension obtained by dialysis is rotary evaporation or adding water.

7. The method for preparing the lignin micro-nanosphere / PVA composite film material according to claim 1, characterized in that: The method of forming a film from the mixed liquid is the casting method.

8. A lignin micro-nanosphere / PVA composite film material, characterized by: Prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the lignin micro-nanosphere / PVA composite film material according to claim 8 in the preparation of sunscreen film, express packaging, medical packaging, fruit and vegetable packaging or meat packaging.

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