Method for preparing high-strength and high-toughness polyvinyl alcohol composite film by recycling waste polyimide

Abstract

The invention discloses a method for preparing a high-strength and high-toughness polyvinyl alcohol composite film by recycling waste polyimide, which comprises the following steps: mixing a waste polyimide material with organic diamine to perform ammonolysis reaction, recycling the organic diamine through reduced pressure distillation after the reaction is finished, uniformly mixing the organic diamine with a degradation product pure water, and filtering to obtain filtrate as a hydrogen bond cross-linking agent; and mixing and molding with a polyvinyl alcohol solution. According to the invention, the recycling of polyimide is realized, the method is green and environment-friendly, and accords with the concept of sustainable development, and the obtained polyvinyl alcohol composite film has high strength, high toughness, good transparency and good ultraviolet shielding performance.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a method for upgrading and recycling waste polyimide to prepare a high-strength and high-toughness polyvinyl alcohol composite film. Background Art

[0002] Polyvinyl alcohol (PVA), as a commercially inexpensive polymer, has been widely used in the fields of packaging, electronics / electrics, optical devices, and optical fibers due to its excellent biodegradability, extraordinary mechanical properties, and high transparency. Due to the existence of a large number of hydrogen bonds within and between molecular chains, PVA usually exhibits higher strength and lower toughness. Therefore, improving the toughness of PVA materials, especially in the biomedical field, has become a popular research area.

[0003] Due to the mutual exclusion of the strengthening and toughening mechanisms, materials with high strength and stiffness usually exhibit low deformation and toughness. Therefore, simultaneously achieving the strengthening and toughening of polymer materials remains a major challenge in this field. Adding plasticizers usually enhances the toughness of PVA films. However, this also leads to a decrease in the Young's modulus and tensile strength of PVA films. To solve this problem, researchers have developed new composite materials to improve the comprehensive properties of materials. In the prior art, Song et al. selected a series of pyrimidine-derived polyamine molecules and melamine as crosslinking agents to improve the strength, stiffness, and toughness of PVA, while enhancing the thermal properties [Song, P. et al. Macromolecules. 48, 3957–3964 (2015)]. Liu et al. designed small-molecule polyamines with unique structures, and by combining these small-molecule polyamines with PVA, high toughness, high ductility, and high strength of the composite film can be achieved [Liu, L. et al. Adv. Mater. 33, 2105829 (2021)]. However, the synthesis process of additives usually requires high energy consumption, and most of the raw materials of these additives are non-renewable, which leads to a large amount of energy waste and overexploitation of resources, thus having a negative impact on the environment.

[0004] To alleviate this problem, more and more research has started to focus on the direction of material recycling and greening. The present invention recycles and upgrades waste polyimide (PI) materials into hydrogen bond crosslinking agents, and develops PVA composite films with both high toughness and high strength. This method can not only reduce the energy consumption brought by traditional synthetic additives, but also reduce the environmental burden by recycling waste. Summary of the Invention

[0005] The purpose of the present invention is to convert waste polyimide into high-value-added materials through chemical recycling technology.

[0006] Another object of the present invention is to provide a method for upgrading and recycling waste polyimide to prepare a high-strength and high-toughness polyvinyl alcohol composite film.

[0007] To achieve the above object, the technical solution of the present invention is as follows:

[0008] A method for recycling waste polyimide to prepare a high-strength and high-toughness polyvinyl alcohol composite film, which comprises the following steps:

[0009] (1) Mix waste polyimide with an organic diamine, stir at 80-120 °C for 2-6 hours until complete degradation, and separate the excess organic diamine and degradation products by vacuum distillation; during the degradation process, the C─N bond of polyimide is broken by the organic diamine to form an amide product and monomeric diamine; after mixing the degradation product with pure water and dispersing it evenly, the monomeric diamine (solid product) and amide product (filtrate) are separated by filtration, and the filtrate is stored refrigerated and can be directly used as a hydrogen bond crosslinking agent;

[0010] (2) Dissolve polyvinyl alcohol particles in water to prepare a polyvinyl alcohol solution;

[0011] (3) Add the hydrogen bond crosslinking agent obtained in step (1) to the polyvinyl alcohol solution, heat and stir for 6-18 h, cool to room temperature, and then form and dry to obtain a high-strength and high-toughness polyvinyl alcohol composite film.

[0012] In a preferred embodiment of the present invention, the structural formula of the waste polyimide is:

[0013]

[0014] In a preferred embodiment of the present invention, the organic diamine is at least one of ethylenediamine, 1,3-propanediamine, and 1,4-butanediamine.

[0015] In a preferred embodiment of the present invention, in step (1), the waste polyimide and the organic diamine are mixed in a mass ratio of 1:2-20.

[0016] In a preferred embodiment of the present invention, in step (1), after filtration, a solid product and the filtrate are obtained, wherein the solid product is 4,4'-diaminodiphenyl ether, the filtrate contains an amide product, and the amide product contains an amide bond and an amino group.

[0017] In a preferred embodiment of the present invention, in step (2), the degree of polymerization of the polyvinyl alcohol particles is 1000-5000, the degree of alcoholysis is 98-100%, for example, the model is PVA 124. The polyvinyl alcohol particles can be dissolved in water by stirring at 85-95 °C for 1-5 h until completely dissolved.

[0018] In a preferred embodiment of the present invention, in step (2), the concentration of the polyvinyl alcohol solution is 5-12 wt%.

[0019] In a preferred embodiment of the present invention, in step (3), the addition amount of the hydrogen bond crosslinking agent is 1-10 wt% of the polyvinyl alcohol.

[0020] In a preferred embodiment of the present invention, in step (3), the heating and stirring temperature is 90-100 °C. By heating and stirring for a long time, it is ensured that the PVA and the hydrogen bond crosslinking agent are fully mixed; after molding through a mold, it is dried at room temperature for 20-30 h, and then dried at 50-70 °C for 12-24 h.

[0021] A high-strength and high-toughness polyvinyl alcohol composite film is prepared by the method for preparing a high-strength and high-toughness polyvinyl alcohol composite film by recycling the above-mentioned waste polyimide.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The hydrogen bond crosslinking agent obtained in the present invention is derived from the ammonolysis of waste polyimide, the reaction is mild, green and environmentally friendly, and conforms to the concept of sustainable development.

[0024] 2. The hydrogen bond crosslinking agent in the present invention is composed of a polymer containing a large number of amide bonds and amino groups, and is easy to form strong hydrogen bonds with polyvinyl alcohol.

[0025] 3. The preparation method of the polyvinyl alcohol film prepared in the present invention has a small addition amount of the hydrogen bond crosslinking agent and a simple preparation method.

[0026] 4. The polyvinyl alcohol composite film prepared in the present invention has high transparency and a high ultraviolet light barrier rate, and has both optical properties and weather resistance.

[0027] 5. The polyvinyl alcohol composite film prepared in the present invention has both high strength and high toughness, expanding the application range.

[0028] Other features and beneficial effects of the present invention will be described in the subsequent description, and part of them will be obvious from the description, or will be understood by implementing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the polyimide ammonolysis mechanism of the embodiment of the present invention.

[0030] Figure 2 It is a schematic diagram of the structure of the amide product (RDPI) of the embodiment of the present invention.

[0031] Figure 3 It is the FTIR spectrum of the polyimide and the ammonolysis mixture of Example 1.

[0032] Figure 4 1H NMR spectrum (a) and 13C NMR (b) spectrum of the ammonolysis mixture of Example 1

[0033] Figure 5 Transmittance test results of the polyvinyl alcohol films prepared in Comparative Example 1 and Examples 1-5 of the present invention

[0034] Figure 6 FT-IR diagrams of the polyvinyl alcohol films prepared in Comparative Example 1 and Examples 1-5 of the present invention

[0035] Figure 7 Tensile stress-strain curves of the polyvinyl alcohol films prepared in Comparative Example 1 and Examples 1-5 of the present invention

[0036] Figure 8 Toughness test results of the polyvinyl alcohol films prepared in Comparative Example 1 and Examples 1-5 of the present invention Detailed implementation mode

[0037] The present invention will be further explained below in conjunction with the accompanying drawings and specific examples

[0038] The structural formula of the polyimide in the following examples is

[0039]

[0040] Example 1

[0041] Preparation of hydrogen bond crosslinking agent

[0042] Add 5 g of polyimide (PI-1) to 15 mL of ethylenediamine and stir at 90 °C for 2 h. After the polyimide is fully degraded, the degradation solution (ammonolysis mixture) is distilled under reduced pressure to recover ethylenediamine and the degradation product. The recovered ethylenediamine can be reused again

[0043] Add distilled water to the degradation product and ultrasonically disperse it. 4,4'-Diaminodiphenyl ether precipitate is insoluble in water, filter, and collect the precipitate and filtrate. The obtained precipitate is washed and dried under vacuum to obtain the recovered 4,4'-diaminodiphenyl ether; the collected filtrate (amide product RDPI) is directly used as a hydrogen bond crosslinking agent

[0044] Prepare an 8 wt% polyvinyl alcohol solution: Dissolve 2 g of polyvinyl alcohol particles (model: PVA 124 type) in 23 ml of deionized water and stir at 90 °C for 2 h

[0045] Preparation of Polyvinyl Alcohol Composite Film: 0.02 g of hydrogen bond crosslinking agent was added to 25 g of 8 wt% polyvinyl alcohol solution, and the mixture was heated to 90 °C and stirred for 12 h to ensure sufficient mixing of PVA and each hydrogen bond crosslinking agent. After cooling to room temperature, the solution was gently poured into a self-made glass mold, dried at room temperature for 24 h, and then dried in a vacuum oven at 60 °C for 24 h to obtain a polyvinyl alcohol composite film (PVA-1) with a hydrogen bond crosslinking agent content of 1%.

[0046] Example 2

[0047] Preparation of Hydrogen Bond Crosslinking Agent: The same as in Example 1.

[0048] Preparation of 8 wt% Polyvinyl Alcohol Solution: 2 g of polyvinyl alcohol particles (model: PVA 124 type) were dissolved in 23 ml of deionized water and stirred at 90 °C for 2 h to obtain it.

[0049] Preparation of Polyvinyl Alcohol Composite Film: 0.06 g of hydrogen bond crosslinking agent was added to 25 g of 8 wt% polyvinyl alcohol solution, and the mixture was heated to 90 °C and stirred for 12 h to ensure sufficient mixing of PVA and each hydrogen bond crosslinking agent. After cooling to room temperature, the solution was gently poured into a self-made glass mold, dried at room temperature for 24 h, and then dried in a vacuum oven at 60 °C for 24 h to obtain a polyvinyl alcohol composite film (PVA-3) with a hydrogen bond crosslinking agent content of 3%.

[0050] Example 3

[0051] Preparation of Hydrogen Bond Crosslinking Agent: The same as in Example 1.

[0052] Preparation of 8 wt% Polyvinyl Alcohol Solution: 2 g of polyvinyl alcohol particles (model: PVA 124 type) were dissolved in 23 ml of deionized water and stirred at 90 °C for 2 h to obtain it.

[0053] Preparation of Polyvinyl Alcohol Composite Film: 0.11 g of hydrogen bond crosslinking agent was added to 25 g of 8 wt% polyvinyl alcohol solution, and the mixture was heated to 90 °C and stirred for 12 h to ensure sufficient mixing of PVA and each hydrogen bond crosslinking agent. After cooling to room temperature, the solution was gently poured into a self-made glass mold, dried at room temperature for 24 h, and then dried in a vacuum oven at 60 °C for 24 h to obtain a polyvinyl alcohol composite film (PVA-5) with a hydrogen bond crosslinking agent content of 5%.

[0054] Example 4

[0055] Preparation of Hydrogen Bond Crosslinking Agent: The same as in Example 1.

[0056] Preparation of 8 wt% Polyvinyl Alcohol Solution: 2 g of polyvinyl alcohol particles (model: PVA 124 type) were dissolved in 23 ml of deionized water and stirred at 90 °C for 2 h to obtain it.

[0057] Preparation of polyvinyl alcohol composite film: Add 0.15 g of hydrogen bond crosslinking agent to 25 g of 8 wt% polyvinyl alcohol solution, heat to 90 °C and stir for 12 h to ensure sufficient mixing of PVA and each hydrogen bond crosslinking agent. After cooling to room temperature, gently pour the solution into a self-made glass mold, dry at room temperature for 24 h, and dry in a vacuum oven at 60 °C for 24 h to obtain a polyvinyl alcohol composite film (PVA-7) with a hydrogen bond crosslinking agent content of 7%.

[0058] Example 5

[0059] Preparation of hydrogen bond crosslinking agent: The same as Example 1.

[0060] Preparation of 8 wt% polyvinyl alcohol solution: Dissolve 2 g of polyvinyl alcohol particles (model: PVA 124 type) in 23 ml of deionized water, stir at 90 °C for 2 h to obtain it.

[0061] Preparation of polyvinyl alcohol composite film: Add 0.22 g of hydrogen bond crosslinking agent to 25 g of 8 wt% polyvinyl alcohol solution, heat to 90 °C and stir for 12 h to ensure sufficient mixing of PVA and each hydrogen bond crosslinking agent. After cooling to room temperature, gently pour the solution into a self-made glass mold, dry at room temperature for 24 h, and dry in a vacuum oven at 60 °C for 24 h to obtain a polyvinyl alcohol composite film (PVA-10) with a hydrogen bond crosslinking agent content of 10%.

[0062] Comparative Example 1

[0063] Preparation of pure polyvinyl alcohol film: Dissolve 2 g of polyvinyl alcohol particles (model: PVA124 type) in 23 ml of deionized water, heat to 90 °C and stir for 12 h. After cooling to room temperature, gently pour the solution into a self-made glass mold, dry at room temperature for 24 h, and dry in a vacuum oven at 60 °C for 24 h to obtain a pure polyvinyl alcohol film (PVA).

[0064] As Figure 1 and Figure 2 shown, in the process of PI degradation to ammonolysis, when organic diamine reacts with PI, two amino groups can react with different parts of the PI molecular chain respectively to form multiple amide bonds. Therefore, there will be the following three situations in the amide product RDPI: One is that only one amino group in the organic diamine participates in the reaction, causing the imide to break, thus generating tetra-armed amine; the second is that the two amino groups of the organic diamine react with different molecular chains of PI respectively, thus forming a crosslinked structure and forming a polymer. The third is that the two amino groups of the organic diamine form intramolecular crosslinking on the same PI molecular chain, thus generating a cyclic structure or a polymer. Refer to Figure 3 FTIR spectrum of polyimide and ammonolysis mixture. It can be seen from the figure that the characteristic peaks of PI (1775 and 1710 cm -1) disappeared significantly. Meanwhile, the carbonyl stretch was observed at approximately 1615 cm -1 , the benzene ring skeletal vibration was at approximately 1496 cm -1 , and the C-O-C stretch vibration was at approximately 1212 cm -1 , indicating that PI was completely degraded into amide products. Refer to Figure 4 for the nuclear magnetic resonance 1 1H NMR spectrum (a) and 13 13C NMR (b) spectrum of the ammonolysis mixture. As can be seen from the figure, only a small amount of amide products were observed, which was due to the formation of amide oligomers caused by the two amino capping groups in the organic diamine.

[0065] The method of Examples 1 to 5 and Comparative Example 1 was used to prepare films with a thickness of approximately 90 μm for performance testing. Among them, an electronic universal testing machine was used for the mechanical property test, and the instrument model was CMT6503. The specific test parameters were: inlet force 0.5 N, tensile rate 5 mm / min. The test film sample size was 45×10 mm (length×width), and each sample was measured three times to reduce errors.

[0066] From Figure 5 the transmittance test results, it can be seen that the prepared PVA composite films all showed high transparency, and the transmittance in the visible light region also exceeded 87%. At the same time, by adding a hydrogen bond crosslinking agent to the PVA film, compared with ordinary PVA films, the ultraviolet protection performance of the PVA composite films obtained in Examples 1 to 5 was significantly improved (the light transmittance at a wavelength of 300 nm was basically 0%). In particular, with the increase of the hydrogen bond crosslinking agent, the ultraviolet protection ability of the PVA composite film gradually increased. This is because the amide bond and benzene ring in the hydrogen bond crosslinking agent itself have the ability to absorb ultraviolet light. When they are added to PVA, they can directly absorb part of the ultraviolet light, thereby reducing the ultraviolet transmittance. In addition, the hydrogen bond network formed between the hydrogen bond crosslinking agent and PVA can promote the synergistic absorption effect between the two, significantly improving the ultraviolet absorption ability of the entire composite film, which expands its ultraviolet protection function and application in related demand fields.

[0067] As Figure 6 shown in the FT-IR diagram, the stretching vibration peak of the hydroxyl group of the polyvinyl alcohol films prepared in Examples 1-5 was redshifted, indicating that strong hydrogen bond interactions were generated between PVA and the hydrogen bond crosslinking agent through various combinations of H and N or O atoms. The formation of hydrogen bonds can change the orientation and arrangement of PVA molecular chains, making them more compact and orderly. -

[0068] As Figure 7As can be seen from the tensile stress-strain curve, the PVA composite film prepared in Example 1 exhibits a yield strength as high as 206 MPa (an increase of 57.85% compared to pure PVA) and a fracture strain of 355% (an increase of 1379% compared to pure PVA).

[0069] As Figure 8 shown in the toughness test results of the prepared PVA composite film, the toughness can reach 673 MJ / m 3 .

[0070] By using the hydrogen bond crosslinking agent in the examples, the formation of hydrogen bonds can change the orientation and arrangement of PVA molecular chains, making them more compact and orderly, thereby improving the tensile strength and modulus of the film. At the same time, the reversible breakage and reconstruction of hydrogen bonds enable the film to better disperse stress when subjected to external forces, avoiding stress concentration, and thus improving the toughness of the film. Thus, a PVA composite film with both high strength and high toughness is obtained, which will have a greater application space. For example, it can be used as a drug sustained-release carrier and tissue engineering scaffold in the biomedical field, making up for the limitations in medical device applications caused by the good biocompatibility and degradability of ordinary PVA but insufficient mechanical properties.

[0071] The above examples are only used to further illustrate a method for upgrading and recycling waste polyimide to prepare a high-strength and high-toughness polyvinyl alcohol composite film of the present invention. However, the present invention is not limited to the examples. Any simple modification, equivalent change, and modification made to the above examples based on the technical essence of the present invention all fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for recycling waste polyimide to prepare a high-strength and high-toughness polyvinyl alcohol composite film, characterized in that, It includes the following steps: (1) Mix the waste polyimide with an organic diamine, stir at 80 - 120 °C for 2 - 6 hours until complete degradation, and separate the excessive organic diamine and degradation products by vacuum distillation; mix the degradation products with pure water and make them disperse evenly, after filtration, the filtrate is used as a hydrogen bond crosslinking agent; (2) Dissolve polyvinyl alcohol particles in water to prepare a polyvinyl alcohol solution; (3) Add the hydrogen bond crosslinking agent obtained in step (1) to the polyvinyl alcohol solution, heat and stir for 6 - 18 h, after cooling to room temperature, form and dry to obtain a high-strength and high-toughness polyvinyl alcohol composite film.

2. The method for preparing a high-strength and high-toughness polyvinyl alcohol composite film by recycling waste polyimide according to claim 1, wherein The structural formula of the waste polyimide is:

3. The method for recycling waste polyimide to prepare a high-strength and high-toughness polyvinyl alcohol composite film according to claim 1, characterized in that: The organic diamine is at least one of ethylenediamine, 1,3-propanediamine, and 1,4-butanediamine.

4. The method for recycling waste polyimide to prepare a high-strength and high-toughness polyvinyl alcohol composite film according to claim 1, characterized in that: In step (1), the waste polyimide and the organic diamine are mixed in a mass ratio of 1:2 - 20.

5. The method for preparing a high-strength and high-toughness polyvinyl alcohol composite film by recycling waste polyimide according to claim 1, wherein: In step (1), after filtration, a solid product and the filtrate are obtained, where the solid product is 4,4'-diaminodiphenyl ether, and the filtrate contains an amide product, and the amide product contains an amide bond and an amino group.

6. The method for recycling waste polyimide to prepare a high-strength and high-toughness polyvinyl alcohol composite film according to claim 1, characterized in that: In step (2), the degree of polymerization of the polyvinyl alcohol particles is 1000 - 5000, and the degree of alcoholysis is 98 - 100%.

7. The method for recycling waste polyimide to prepare a high-strength and high-toughness polyvinyl alcohol composite film according to claim 1, characterized in that: In step (2), the concentration of the polyvinyl alcohol solution is 5 - 12 wt%.

8. The method for preparing a high-strength and high-toughness polyvinyl alcohol composite film by recycling waste polyimide according to claim 1, wherein: In step (3), the addition amount of the hydrogen bond crosslinking agent is 1 - 10 wt% of the polyvinyl alcohol.

9. The method for recycling waste polyimide to prepare a high-strength and high-toughness polyvinyl alcohol composite film according to claim 1, characterized in that: In step (3), the heating and stirring temperature is 90 - 100 °C; after forming through a mold, it is dried at room temperature for 20 - 30 h, and then dried at 50 - 70 °C for 12 - 24 h.

10. A high-strength and high-toughness polyvinyl alcohol composite film, characterized in that: It is prepared by the method for preparing a high-strength and high-toughness polyvinyl alcohol composite film by recycling the waste polyimide according to any one of claims 1 - 9.

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