Preparation method of self-assembled lignin / copper ion nanoparticle reinforced polyvinyl alcohol film

Abstract

The invention discloses a preparation method of self-assembled lignin / copper ion nanoparticles reinforced polyvinyl alcohol film. First, an alkaline solution of alkali lignin and an alkaline solution of Cu(NO3)2 are mixed and heated for reaction, and an LNP@Cu suspension is obtained after dialysis; then the LNP@Cu suspension and a PVA solution are heated and stirred and mixed evenly to obtain a film-forming solution, and the film-forming solution is cast and dried to obtain a modified PVA film material. The present application provides a simple bionic design strategy, adding LNP@Cu as granular nano-domains into the PVA film to improve the mechanical properties of the PVA plastic film. The polar groups on the surface of LNP@Cu can form abundant hydrogen bonds with the PVA matrix. The present application provides a simple, feasible, green and sustainable method for producing multifunctional environmentally friendly materials, and is beneficial to promoting the high-value utilization of lignin.

Description

Technical Field

[0001] The invention belongs to the field of polymer film material preparation, and in particular relates to a method for preparing a self-assembled lignin / copper ion nanoparticle reinforced polyvinyl alcohol film. Background Art

[0002] As environmental problems gradually worsen, the development and utilization of biodegradable plastics have attracted the attention of researchers. Biodegradable plastics based on starch, polylactic acid, cellulose, polyvinyl alcohol, etc. have been widely developed and reported, but their poor mechanical properties and water resistance limit their practical applications. Among them, polyvinyl alcohol is a biodegradable water-soluble polymer with good acid and alkali resistance, solvent resistance and film-forming properties, and is recognized as an emerging green and environmentally friendly material. However, the mechanical properties of polyvinyl alcohol film materials still need to be further improved to broaden their application range. In addition, since polyvinyl alcohol molecules contain a large number of alcohol hydroxyl groups, they are sensitive to moisture and have poor water resistance. At present, researchers have developed reinforcing agents such as SiO2, graphene, carbon nanotubes, and alkyl ketene dimers. However, most of these materials are non-biodegradable and very expensive, which is not conducive to industrial production. Therefore, it is urgent to develop a green, environmentally friendly and economical additive for the enhancement and modification of polyvinyl alcohol plastics.

[0003] Lignin is the most abundant natural polyphenol polymer in the world. It is widely available and inexpensive as a byproduct of papermaking and biorefining in industry. Studies have reported that adding lignin to the PVA system can increase its strength and water resistance and impart it with antioxidant and UV shielding properties. However, lignin itself contains functional groups such as hydroxyl and methoxy groups that can form strong hydrogen bonds and are prone to agglomeration, resulting in weak interfacial forces with the PVA matrix, which leads to limited improvement in the mechanical properties of the composite material. In order to break through this limitation, studies have found that the methoxy and hydroxyl groups in lignin can undergo self-catalytic redox reactions with metal ions to generate quinone or catechol structures. The reaction is simple and efficient, and the quinone and catechol groups on the surface of lignin nanoparticles can form hydrogen bonds with the hydroxyl groups in PVA to enhance interfacial interactions, thereby enhancing the mechanical properties of the PVA film. A variety of lignin-metal ion nanoparticles have been prepared, among which lignin-copper ion (LNP@Cu) exhibits excellent antibacterial properties and low cytotoxicity, and is a promising green enhancer that can be used to manufacture durable and multifunctional PVA films.

[0004] In nature, the mussel byssus epidermis has both high strength and high toughness, which is mainly due to the distribution of labile particles containing catechol-iron ion cross-links in the protein matrix. These particles can effectively inhibit crack extension by generating microcracks, thereby enhancing the mechanical properties. Summary of the invention

[0005] Purpose of the invention: Inspired by the epidermis of mussel byssus, this study adopted a simple bionic design strategy to add LNP@Cu as a granular nanodomain into the PVA film to improve the mechanical properties of the PVA plastic film. The polar groups on the surface of LNP@Cu can form abundant hydrogen bonds with the PVA matrix. This application provides a simple, green and sustainable method for producing multifunctional environmentally friendly materials, and is conducive to promoting the high-value utilization of lignin.

[0006] In order to solve the above technical problems, the present invention discloses a method for preparing a self-assembled lignin / copper ion nanoparticle reinforced polyvinyl alcohol film, which is characterized by comprising the following steps:

[0007] (1) mixing an alkaline solution of alkali lignin with an alkaline solution of Cu(NO3)2 and heating them to react, and obtaining a LNP@Cu suspension after dialysis;

[0008] (2) The LNP@Cu suspension and the PVA solution are heated and stirred to obtain a film-forming solution, and the film-forming solution is cast and dried to obtain a modified PVA film material.

[0009] The alkaline solution of alkali lignin is obtained by the following steps: dispersing alkali lignin in a sodium hydroxide solution with a pH of 10 to 11.5, ultrasonicating in a water bath, standing overnight, and taking the upper lignin solution as the alkaline solution of alkali lignin, wherein the concentration of lignin in the alkaline solution of alkali lignin is 10 to 20 mg / mL.

[0010] The Cu(NO3)2 alkaline solution is obtained by dissolving Cu(NO3)2 in a sodium hydroxide solution with a pH of 10 to 11.5, and the concentration of the Cu(NO3)2 alkaline solution is 1.88 to 3.75 mg / mL.

[0011] In step (1), the alkaline solution of the alkaline lignin is heated to 80-95°C, and then Cu(NO3)2 is added dropwise to the lignin solution. After the addition is completed, stirring is continued to maintain the temperature at 80-95°C for 2-3 hours. The LNP@Cu suspension obtained after the reaction is dialyzed in deionized water for 2-3 days, and the water is changed several times a day. The pH of the dialyzed LNP@Cu suspension is 7.04.

[0012] In step (2), the PVA solution is prepared by adding PVA to deionized water to swell the PVA to obtain a PVA suspension, and then the suspension is heated to 80-95° C. and stirred for 2-3 h to fully dissolve it. The stirring rate is 600-1000 rmprmp, and the PVA concentration is adjusted to 0.05-0.1 g / ml.

[0013] Preferably, the addition amount of LNP@Cu accounts for 1 to 10 wt % of the prepared modified PVA film material.

[0014] Beneficial effects: Compared with the prior art, this application has the following advantages:

[0015] (1) LNP@Cu is easy to prepare, and copper ions are evenly distributed in lignin nanoparticles, which can effectively increase the surface active functional groups of lignin nanoparticles;

[0016] (2) LNP@Cu has good compatibility with PVA, which significantly improves the strength and toughness of the PVA film, while also giving the film good UV shielding properties and water resistance. The resulting film can maintain a transparency of more than 90%. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the design strategy for PVA-LNP@Cu membrane;

[0018] Figure 2 Shown are the transmission electron microscopy images and Cu elemental scans of LNP@Cu in Example 1;

[0019] Figure 3 Shown are photos of modified PVA film materials prepared with different LNP@Cu addition amounts;

[0020] Figure 4 Shown are the mechanical properties of modified PVA film materials prepared with different LNP@Cu addition amounts. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] This application provides a simple biomimetic design strategy to add LNP@Cu as granular nanodomains into PVA film to improve the mechanical properties of PVA plastic film (e.g. Figure 1 As shown). The polar groups on the surface of LNP@Cu can form abundant hydrogen bonds with the PVA matrix. The study deeply analyzed the interaction between LNP@Cu and the PVA matrix, as well as the effect of LNP@Cu on the mechanical properties, ultraviolet (UV) shielding properties and water resistance of the film. The results of this study not only provide a simple, green and sustainable method for producing multifunctional environmentally friendly materials, but also help promote the high-value utilization of lignin.

[0023] Example 1

[0024] 1) 1.8 g of alkali lignin (Sigma Aldrich) was dispersed in 90 mL of sodium hydroxide solution with a pH of 11 and placed in a water bath ultrasound for 3 h to assist the dissolution of the lignin to obtain a lignin dispersion. The lignin dispersion was allowed to stand overnight to remove undissolved lignin, and the upper lignin solution was taken for the next reaction.

[0025] 2) Dissolve 337.5 mg of Cu(NO3)2 in 90 mL of sodium hydroxide solution with a pH of 11 to obtain a Cu(NO3)2 solution.

[0026] 3) The lignin solution was heated to 90°C at 800 rpm with stirring, and the Cu(NO3)2 solution prepared in step 2) was slowly added to the lignin solution while maintaining heating and stirring. After the addition was completed, stirring and heating were maintained to allow the reaction to continue for 2 hours to obtain a LNP@Cu suspension.

[0027] 4) The LNP@Cu suspension prepared in step 3 was dialyzed in deionized water for two days, with the water changed three times a day, and the dialyzed LNP@Cu suspension was collected and tested to have a pH of 7.04. Figure 2 This is the transmission electron microscope image of LNP@Cu. It can be seen from the image that lignin forms a sphere with a diameter of about 500nm. At the same time, the Cu element scanning results show that the Cu element is evenly distributed on the surface of the lignin nanoparticles, which helps the lignin to undergo a self-catalytic redox reaction with Cu ions to assemble into nanoparticles.

[0028] 5) 2 g of PVA was added to 30 mL of deionized water for swelling for 2 h, and the swollen PVA suspension was heated to 90° C. and stirred for 2 h to fully dissolve it, with a stirring rate of 800 rpm. While stirring and heating, LNP@Cu suspension was added to the PVA solution to make the LNP@Cu content 1 wt% of the final prepared PVA film material. The system temperature was maintained at 90° C. and stirring was continued for 1 h to fully mix the system to obtain a casting solution.

[0029] 6) Pour the casting liquid into a square plastic mold with a side length of 10 cm, place it in a vacuum oven, maintain vacuum and heat to 40°C to fully dry it to obtain a modified PVA film material. In order to test the film performance, the thickness of the film in the embodiment of the present application is set to be about 0.10 mm, which can be adjusted as needed in actual production. The film material prepared in this embodiment is named PVA / LNP@Cu-1%.

[0030] The mechanical properties, water resistance, UV shielding properties and transparency of the prepared PVA / LNP@Cu-1% film were tested, and the test results are listed in Table 1.

[0031] Example 2

[0032] 1) The preparation method of LNP@Cu suspension is the same as that of Example 1.

[0033] 2) 2 g of PVA was added to 30 mL of deionized water and swelled for 2 h, then heated to 90 ° C and stirred for 2 h to fully dissolve, and the stirring rate was maintained at 800 rpm. While stirring and heating, LNP@Cu suspension was added to the PVA solution to make the LNP@Cu content 2 wt% of PVA. The system temperature was maintained at 90 ° C and stirred for 1 h to fully mix the system to obtain a casting solution.

[0034] 3) The casting solution was poured into a square plastic mold with a side length of 10 cm, and the mold was placed in a vacuum oven. The mold was kept in vacuum and heated to 40° C. to fully dry the mold to obtain a modified PVA film material, which was named PVA / LNP@Cu-2%.

[0035] The mechanical properties, water resistance, UV shielding properties and transparency of the prepared PVA / LNP@Cu-2% film were tested, and the test results are listed in Table 1.

[0036] Example 3

[0037] 1) The preparation method of LNP@Cu suspension is the same as that of Example 1.

[0038] 2) 2 g of PVA was added to 30 mL of deionized water and swelled for 2 h, then heated to 90 ° C and stirred for 2 h to fully dissolve, and the stirring rate was maintained at 800 rpm. While stirring and heating, LNP@Cu suspension was added to the PVA solution to make the LNP@Cu content 2 wt% of PVA. The system temperature was maintained at 90 ° C and stirred for 1 h to fully mix the system to obtain a casting solution.

[0039] 3) The casting solution was poured into a square plastic mold with a side length of 10 cm, and the mold was placed in a vacuum oven. The mold was kept in vacuum and heated to 40° C. to fully dry the mold to obtain a modified PVA film material, which was named PVA / LNP@Cu-5%.

[0040] The mechanical properties, water resistance, UV shielding properties and transparency of the prepared PVA / LNP@Cu-5% film were tested, and the test results are listed in Table 1.

[0041] Example 4

[0042] 1) The preparation method of LNP@Cu suspension is the same as that of Example 1.

[0043] 2) 2 g of PVA was added to 30 mL of deionized water and swelled for 2 h, then heated to 90 ° C and stirred for 2 h to fully dissolve, and the stirring rate was maintained at 800 rpm. While stirring and heating, LNP@Cu suspension was added to the PVA solution to make the LNP@Cu content 2 wt% of PVA. The system temperature was maintained at 90 ° C and stirred for 1 h to fully mix the system to obtain a casting solution.

[0044] 3) The casting solution was poured into a square plastic mold with a side length of 10 cm, and the mold was placed in a vacuum oven. The mold was kept in vacuum and heated to 40° C. to fully dry the mold to obtain a modified PVA film material, which was named PVA / LNP@Cu-10%.

[0045] The mechanical properties, water resistance, UV shielding properties and transparency of the prepared PVA / LNP@Cu-10% film were tested, and the test results are listed in Table 1.

[0046] Comparative Example

[0047] 2 g of PVA was swelled in 30 mL of deionized water for 2 h. The swollen PVA suspension was heated to 90 ° C and stirred for 2 h to fully dissolve it at a stirring rate of 800 rpm. The fully dissolved PVA solution was poured into a square plastic mold with a side length of 10 cm, and placed in a vacuum oven at 40 ° C to dry to obtain pure PVA film material with a thickness of about 0.10 mm.

[0048] Table 1 Comparison of mechanical properties, water resistance, UV shielding properties and transparency properties of the prepared modified PVA film materials

[0049]

[0050]

[0051] Figure 3 Shown are photos of modified PVA film materials prepared with different LNP@Cu addition amounts; Figure 4Shown are the mechanical properties of modified PVA film materials prepared with different LNP@Cu addition amounts. Analysis of the above four embodiments and comparative examples shows that after adding LNP@Cu, the mechanical properties of the film are significantly improved. When the addition amount of LNP@Cu is 5wt%, the strength and toughness of the film are the largest, which are 2.27 times and 4.04 times that of the unmodified PVA film, respectively. As the LNP@Cu content increases, the surface water contact angle of the film gradually increases from 59.1° of the pure PVA film to 90.0°, and the hydrophobicity of the surface film increases. In addition, the addition of LNP@Cu increases the UV shielding performance of the film. When the addition amount of LNP@Cu gradually increases to 10wt%, the film shields 84.8% of ultraviolet rays and can maintain a transparency close to 90%. The present invention adopts alkaline lignin and copper nitrate to prepare activated lignin nanoparticles LNP@Cu through autocatalytic redox reaction, and uses it to improve the performance of PVA film through bionic design strategy, so as to significantly improve the mechanical properties, water resistance and ultraviolet shielding properties of the film and maintain a transparency close to 90%. The method requires simple equipment, mild reaction conditions and high industrial feasibility, and can realize the development of green and environmentally friendly multifunctional PVA film materials. At the same time, it also has important economic and social significance for promoting the high-value utilization of lignin.

Claims

1. A method for preparing a self-assembled lignin / copper ion nanoparticle reinforced polyvinyl alcohol film, characterized in that: The steps include: The alkaline solution of alkali lignin and the alkaline solution of Cu(NO3)2 are mixed and heated to react, and a LNP@Cu suspension is obtained after dialysis; the alkaline solution of alkali lignin is obtained by the following steps: dispersing alkali lignin in a sodium hydroxide solution with a pH of 10-11.5, ultrasonicating in a water bath, standing overnight, and taking the upper lignin solution as the alkaline solution of alkali lignin, wherein the concentration of lignin in the alkaline solution of alkali lignin is 10-20 mg / mL; the alkaline solution of Cu(NO3)2 is obtained by dissolving Cu(NO3)2 in a sodium hydroxide solution with a pH of 10-11.5, and the concentration of the alkaline solution of Cu(NO3)2 is 1.88-3.75 mg / mL; the alkaline solution of the alkaline lignin was heated to 80-95°C, and then Cu(NO3)2 was added dropwise to the lignin solution. After the addition, stirring was continued to maintain 80-95°C for 2 hours. The LNP@Cu suspension obtained after the reaction was dialyzed in deionized water for 2-3 days, and the water was changed several times a day; The LNP@Cu suspension and the PVA solution are heated and stirred to be evenly mixed to obtain a film-forming solution, and the film-forming solution is cast and dried to obtain a modified PVA film material, wherein the addition amount of LNP@Cu accounts for 1 to 10 wt% of the prepared modified PVA film material.

2. The preparation method according to claim 1, characterized in that: In step (2), the PVA solution is prepared by adding PVA to deionized water to swell the PVA to obtain a PVA suspension, and then the suspension is heated to 80-95°C and stirred for 2-3 h to fully dissolve it. The stirring rate is 600-1000 rmp, and the PVA concentration is adjusted to 0.05-0.1 g / ml.

3. The polyvinyl alcohol film prepared by the preparation method according to any one of claims 1 to 2.

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