Toughening agent and preparation method thereof as well as toughened regenerated cellulose membrane and preparation method thereof

Abstract

The invention discloses a flexibilizer and a preparation method thereof, and a toughened regenerated cellulose membrane and a preparation method thereof. The preparation method comprises the following steps: mixing tannic acid powder and lipoic acid powder in an N-N dimethylacetamide (DMAC) solution under an alkaline condition, and carrying out a heating reaction to prepare the toughening agent. The flexibilizer with different toughening effects is prepared by controlling the proportion of all the components, and the method is simple to operate and mild in reaction condition. The obtained flexibilizer solution is blended with a cellulose solution, and the regenerated cellulose membrane is obtained through gelling, soaking, washing and drying. The prepared regenerated cellulose membrane has excellent mechanical properties, transparency and thermal stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of plastic production, and particularly relates to a bio-based plastic that is easy to process and has high strength and toughness, and a green preparation method thereof. Background Art

[0002] Non-renewable and non-degradable petroleum-based plastics have penetrated into the natural environment and human society. Plastics not only cause environmental pollution problems, but also have an impact on human health. (Bucci, Tulio, & Rochman, 2020) It is estimated that 10 to 40 million tons of microplastics are generated annually, and modeling predictions suggest that large-scale environmental pollution may occur within the next 70 to 100 years. (Thompson et al.) Research reports have detected plastic-related chemicals in multiple tissues and organs of the human body. (Seewoo et al., 2024) Due to concerns about the environment and health, sustainable bioplastics have received great attention.

[0003] Cellulose is one of the most abundant renewable resources on Earth and has great potential in the preparation of bio-based degradable plastics. (Agarwal, Ralph, Reiner, & Baez, 2018) However, cellulose-based plastics often exhibit the characteristics of high strength and low ductility. This is because the structure of natural cellulose itself is highly regular (Salem et al., 2023), and it is difficult to dissipate energy when subjected to external forces. Currently, chemical cross-linking and adding petroleum-based chemical toughening agents are common methods to improve the mechanical properties of cellulose membranes (Cazón, Velazquez, & Vázquez, 2020; Cortes Ruiz et al., 2024; Hou et al., 2024; Li, Zhu, Xu, Yu, & Fan, 2024; X. Li et al., 2024; Yang et al., 2024; X. Zhang, Fang, Cheng, Li, & Liu, 2024; C. Zhao, Gong, Lin, Zhang, & Wang, 2023). For example, Zhang and colleagues (Ye et al., 2019) chemically cross-linked cellulose with epichlorohydrin and then developed a new type of cellulose plastic through a pre-stretching assisted strategy, with an elongation at break exceeding 40% and a toughness as high as 41.1 MJ / m 3; Dai et al. (2024) blended polyvinyl alcohol and cellulose nanofibers to prepare a flexible film with a maximum stress of 64.8 MPa and an elongation at break of 61.4%. However, adding petroleum-based polymers usually reduces the degradation rate of cellulose plastics. (Abraham et al., 2012; Hu et al., 2021) There are also some studies that improve the overall toughness of materials by adding inorganic fillers or modified nanoparticles (Kong et al., 2024; W. Li et al., 2024; Qiao et al., 2020; Tang et al., 2023; Tian et al., 2024; T. Wang, Wang, Ji, Li, & Yang, 2024; Yue et al., 2022; Zou et al., 2023), but the elongation at break is still less than 10%. Therefore, there is a need for a toughening agent with green raw materials and a simple synthesis method to toughen regenerated cellulose films, and it is of great significance to obtain bioplastics with excellent mechanical properties. Summary of the Invention

[0004] The object of the present invention is to provide a preparation method of a toughening agent and a preparation method of a toughened regenerated cellulose film to solve the problems existing in the prior art. The present invention prepares toughening agents with different toughening effects by controlling the proportions of various components. This method has a simple operation method and mild reaction conditions. The present invention also blends the obtained toughening agent solution with a cellulose solution, and obtains a regenerated cellulose film through gelation, soaking, washing, and drying. The prepared regenerated cellulose film has excellent mechanical properties, transparency, and thermal stability.

[0005] To achieve the above object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a preparation method of a toughening agent, comprising the following preparation steps:

[0007] (1) Dissolve a certain amount of Tris base in a DMAC solution, and dissolve it at a certain temperature to obtain a first mixed solution;

[0008] (2) Add a certain amount of tannic acid powder to the obtained first mixed solution, and fully dissolve it to obtain a second mixed solution;

[0009] (3) Adjust the temperature of the second mixed solution to above 75°C (preferably 75°C - 90°C), add a certain amount of lipoic acid powder, fully react for a period of time, cool down, and centrifuge to obtain the supernatant, which is the toughening agent.

[0010] Preferably, in step (1), the mass of the Tris base is 0.5 g - 1.0 g; the volume of the DMAC is 5 - 10 ml; the dissolution temperature is 75 - 90 °C; the reaction pH of the first mixed solution is 7 - 12.

[0011] Preferably, in step (2), the mass of the tannic acid powder is 0.004 g - 0.03 g.

[0012] Preferably, in step (3), the reaction temperature is 75 °C - 85 °C; the mass of the lipoic acid powder is 0.05 g - 0.08 g; the reaction time is 10 min - 60 min.

[0013] The present invention also provides a toughening agent prepared by the above preparation method.

[0014] The present invention also provides a preparation method of a flexible composite film, comprising the following steps:

[0015] (1) Adding the prepared toughening agent to a certain amount of cellulose solution, and reacting at a certain temperature for a certain time to obtain a blend solution;

[0016] (2) Pouring the blend solution onto a polytetrafluoroethylene mold, taking it out after gelling for a period of time, immersing it in hydrochloric acid for exchange for a period of time, then taking it out and dialyzing and washing it in deionized water, and then drying it under a certain pressure and temperature to obtain a tough cellulose film.

[0017] Preferably, in step (1), the content of the toughening agent is 5 wt% - 25 wt%; the reaction temperature is 40 °C - 120 °C; the reaction time is 1 h - 6 h.

[0018] Preferably, in step (2), the gelling time is 6 h - 24 h; the concentration of the hydrochloric acid is 1 mol / l; the dialysis time in deionized water is 6 h; the drying temperature is 45 - 60 °C.

[0019] The present invention also provides a tough regenerated cellulose film obtained by the above preparation method of a toughened regenerated cellulose film.

[0020] The present invention prepares a toughening agent composed of tannic acid and lipoic acid through a Michael addition reaction. This toughening agent contains a large number of phenolic hydroxyl groups and dynamic disulfide bonds and is suitable for toughening cellulose films. The tensile strength of the cellulose film prepared by the present invention can be adjusted within the range of 70 - 130 MPa, and the elongation at break can be adjusted within the range of 30% - 120%. It has ultra-high toughness and transparency, as well as excellent thermal stability, and can be used in the packaging field as a bio-based plastic.

[0021] Compared with the prior art, the advantages of the present invention are as follows: Most of the high-efficiency toughening agent materials in the prior art are petroleum-based chemicals, and the synthesis process has harsh conditions and complex processes; the raw materials of the toughening agent of the present invention are all bio-based materials, and the synthesis method is simple, the conditions are mild, the toughening efficiency is high, and the toughness of the prepared toughened composite film is higher than that of most of the films prepared by bio-based toughening methods. Description of the Drawings

[0022] Figure 1 It is the infrared spectrogram of the toughening agent and lipoic acid.

[0023] Figure 2 It is the SEM image of the pure cellulose film and the cellulose film containing the toughening agent.

[0024] Figure 3 It is the stress-strain curve diagram of the pure cellulose film and the cellulose film containing the toughening agent.

[0025] Figure 4 It is the ultraviolet spectrogram of the pure cellulose and the cellulose film containing the toughening agent.

[0026] Figure 5 It is the optical diagram of the pure cellulose and the cellulose film containing the toughening agent. Detailed Embodiments

[0027] The present invention will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto. For process parameters not specifically noted, conventional techniques can be referred to.

[0028] Example 1 Preparation of the Toughening Agent

[0029] (1) Take 0.5 g of Tris base and add it to 5 ml of DMAC solution. Heat it to 75 °C and stir at 500 rpm for 10 min to obtain the first mixed solution;

[0030] (2) Take 0.004 g of tannic acid powder and add it to the first mixed solution. Stir at 75 °C and 500 rpm for 10 min to obtain the second mixed solution;

[0031] (3) Take 0.05 g of lipoic acid powder and add it to the second mixed solution. React at 75 °C and 500 rpm for 10 min. After centrifugation, take the supernatant to obtain the toughening agent.

[0032] As Figure 1 shown, compared with the infrared spectrum of lipoic acid, a peak of the S-Ar bond appears at 1016 cm -1 in the toughening agent, which indicates that a Michael addition reaction occurs between tannic acid and lipoic acid in this example, and the toughening agent is successfully prepared.

[0033] Example 2 Preparation of the Toughening Agent

[0034] (1) Add 1 g of Tris base to 10 ml of DMAC solution, heat up to 85 °C, stir at 500 rpm for 10 min to obtain the first mixed solution;

[0035] (2) Take 0.03 g of tannic acid powder, add it to the first mixed solution, stir at 85 °C and 500 rpm for 10 min to obtain the second mixed solution;

[0036] (3) Take 0.03 g of lipoic acid powder, add it to the second mixed solution. Adjust the temperature to 75 °C, react at 500 rpm for 30 min, centrifuge and take the supernatant to obtain the toughening agent.

[0037] Preparation of toughening agent in Example 3

[0038] (1) Add 1 g of Tris base to 10 ml of DMAC solution, heat up to 90 °C, stir at 500 rpm for 10 min to obtain the first mixed solution;

[0039] (2) Take 0.017 g of tannic acid powder, add it to the first mixed solution, stir at 90 °C and 500 rpm for 10 min to obtain the second mixed solution;

[0040] (3) Take 0.08 g of lipoic acid powder, add it to the second mixed solution. Adjust the temperature to 75 °C, react at 500 rpm for 60 min, centrifuge and take the supernatant to obtain the toughening agent.

[0041] Preparation of toughened regenerated cellulose film in Example 4

[0042] (1) Add 15 wt% 0.06 g of the toughening agent to 40 ml of cellulose solution, react at 40 °C for 6 h to obtain the blended solution;

[0043] (2) Pour the blended solution onto a polytetrafluoroethylene mold, take it out after gelling for 6 h, immerse it in hydrochloric acid for exchange for a period of time, then take it out and dialyze in deionized water for 6 h, and then dry it at 15 MPa and 45 °C to obtain the toughened cellulose film.

[0044] Figure 2 The surface morphologies of the pure cellulose film (Figures A and B) and the toughened cellulose film (Figures C and D) at different scales are shown. It can be seen that the surfaces of both films are relatively smooth and uniform, but in comparison, the toughened cellulose film is rougher.

[0045] Preparation of toughened regenerated cellulose film in Example 5

[0046] (1) Add 5 wt% 0.02 g of the toughening agent to 40 ml of cellulose solution, react at 75 °C for 3 h to obtain the blended solution;

[0047] (2) Pour the blended solution onto a polytetrafluoroethylene mold, take it out after gelling for 12 h, immerse it in hydrochloric acid for ion exchange for a period of time, then take it out and dialyze it in deionized water for 6 h, and then dry it at 15 MPa and 50 °C to obtain a tough cellulose membrane.

[0048] Preparation of Toughened Regenerated Cellulose Membrane in Example 6

[0049] (1) Add 0.1 g of toughening agent with a content of 25 wt% to 40 ml of cellulose solution, and react at 120 °C for 3 h to obtain a blended solution;

[0050] (2) Pour the blended solution onto a polytetrafluoroethylene mold, take it out after gelling for 12 h, immerse it in hydrochloric acid for ion exchange for a period of time, then take it out and dialyze it in deionized water for 6 h, and then dry it at 15 MPa and 60 °C to obtain a tough cellulose membrane.

[0051] Figure 3 are the stress-strain curve graphs of the composite films prepared under the conditions of different temperatures, toughening agent addition amounts, and tannic acid ratios. It can be seen from Figure 3 that the above variables have a certain influence on the mechanical properties of the films, and toughened films with different mechanical properties can be prepared by controlling the changes of the variables.

[0052] Figure 4 are the ultraviolet transmittance spectrograms of different films. The transmittances of the composite films with different contents of toughening agents in the visible light wavelength region (400 - 800 nm) are all about 90%. Combining Figure 5 , it can be shown that the toughened composite film has high transparency. In addition, it can be seen from Figure 5 that the color of the film containing more toughening agent will gradually deepen, which is caused by the chromophore groups in tannic acid.

[0053] Comparative Example 1

[0054] Pour 40 ml of cellulose solution onto a polytetrafluoroethylene mold, take it out after gelling for 6 h, immerse it in hydrochloric acid for ion exchange for a period of time, then take it out and dialyze it in deionized water for 12 h, and then dry it at 15 MPa and 45 °C to obtain a tough cellulose membrane.

[0055] Comparative Example 2

[0056] Pour 40 ml of cellulose solution onto a polytetrafluoroethylene mold, take it out after gelling for 12 h, immerse it in hydrochloric acid for ion exchange for a period of time, then take it out and dialyze it in deionized water for 6 h, and then dry it at 15 MPa and 50 °C to obtain a tough cellulose membrane.

[0057] Comparative Example 3

[0058] Pour 40 ml of the cellulose solution onto a polytetrafluoroethylene mold, take it out after gelling for 12 h, immerse it in hydrochloric acid for ion exchange for a period of time, then take it out and dialyze it in deionized water for 6 h, and then dry it at 15 MPa and 60 °C to obtain a tough cellulose membrane.

[0059] Testing:

[0060] (1) Take appropriate amounts of the toughening agents in Examples 1, 2, and 3, dry them, and then perform infrared spectroscopy detection. Use the attenuated total reflection accessory of a Nicolet IS50 Fourier transform infrared spectrometer to analyze the chemical structure. Scan 32 times in the range of 4000 - 500 cm -1 at room temperature, with a resolution of 4 cm -1 to complete data acquisition. (2) Cut the films prepared in Examples 4, 5, 6 and Comparative Examples 1, 2, and 3 appropriately, stick them on conductive glue, and use a Quorum SC7620 sputtering coater to sputter gold for 45 seconds with a current of 10 mA. Subsequently, use a TESCAN MIRA LMS scanning electron microscope to capture the sample morphology. During the morphology imaging process, the acceleration voltage is 3 kV, and the detector is an SE2 secondary electron detector.

[0061] (3) Test the films prepared in Examples 4, 5, 6 and Comparative Examples 1, 2, and 3 on a universal material testing machine: Cut the specimens into a width of 15 mm and a length of 200 mm, randomly select multiple points to measure their thickness and take the average. Set the clamp spacing to 100 mm and the test rate to 50 mm / min to break the specimens, and record the tensile strength (MPa) and elongation at break (%) generated when the specimens break. Measure 3 times for each group.

[0062] The tensile strength can be calculated according to the specimen thickness, width, and maximum force (2.1):

[0063]

[0064] In the formula:

[0065] σ —— Tensile strength of the specimen, MPa;

[0066] F —— Maximum force when the specimen breaks, N;

[0067] S —— Initial stress area of the specimen, mm 2 ;

[0068] d, b —— Thickness and width of the specimen, mm.

[0069] The elongation at break can be calculated according to the initial length and instantaneous fracture length of the specimen (2.2):

[0070]

[0071] In the formula:

[0072] ε——elongation at break or strain of the specimen, %;

[0073] L1, L0——initial length and instantaneous fracture length of the specimen, mm.

[0074] (4) Cut the films prepared in Examples 4, 5, and 6 and Comparative Examples 1, 2, and 3 into pieces of 1×4 cm in size respectively, and place them in a UV-2600i ultraviolet-visible spectrophotometer to measure the light transmittance from 200 to 800 nm.

[0075] It should be understood that the detailed description of the technical solution of the present invention by means of the optimized embodiments above is illustrative rather than restrictive. It cannot be determined that the specific implementation manners of the present invention are limited to this. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, modifying the technical solutions recorded in each embodiment, or equivalently replacing some of the technical features, should all be regarded as belonging to the patent protection scope determined by the claims submitted for the present invention.

[0076] The above embodiments of the present invention are only examples for clearly explaining the present invention, rather than limitations on the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. It is not necessary and impossible to enumerate all the implementation manners here. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the claims of the present invention.

Claims

1. A preparation method of a toughening agent, characterized in that, It includes the following preparation steps: (1) Dissolve Tris base in a DMAC solution and dissolve it at a certain temperature to obtain a first mixed solution; (2) Add tannic acid powder to the obtained first mixed solution and fully dissolve it to obtain a second mixed solution; (3) Adjust the temperature of the second mixed solution to 75°C - 90°C, add lipoic acid powder, fully react, and cool down Cool down, centrifuge, and take the supernatant to obtain the toughening agent.

2. The preparation method of a toughening agent according to claim 1, characterized in that In step (1), the mass of the Tris base is 0.5 g - 1.0 g; the volume of the DMAC is 5 - 10 ml.

3. The preparation method of a toughening agent according to claim 1, characterized in that, In step (1), the dissolution temperature is 75 - 90°C; the reaction pH of the first mixed solution is 7 - 12.

4. The preparation method of a toughening agent according to claim 1, characterized in that, In step (2), the mass of the tannic acid powder is 0.004 g - 0.03 g.

5. The preparation method of a toughening agent according to claim 1, characterized in that, In step (3), the reaction temperature is 75°C - 85°C; the mass of the lipoic acid powder is 0.05 g - 0.08 g; the reaction time is 10 min - 60 min.

6. The toughening agent prepared by the preparation method according to any one of claims 1 to 5.

7. A method for preparing a tough regenerated cellulose film, characterized in that, It includes the following steps: (1) Add the toughening agent according to claim 5 to a cellulose solution, react to obtain a blended solution; (2) Pour the blended solution obtained in step (1) onto a mold, take it out after gelling, immerse it in hydrochloric acid for exchange, then take it out and put it into deionized water for dialysis washing and drying to obtain a tough cellulose membrane.

8. The preparation method of a tough regenerated cellulose film according to claim 7, characterized in that, In step (1), the content of the toughening agent is 5 wt% - 25 wt%; the reaction temperature is 40°C - 120°C; the reaction time is 1 h - 6 h.

9. The preparation method of a tough regenerated cellulose film according to claim 7, characterized in that, In step (2), the gelling time is 6 h - 24 h; the hydrochloric acid concentration is 0.5 - 1 mol / l; the deionized water dialysis time is 2 h - 12 h; the drying temperature is 45 - 60°C.

10. The tough regenerated cellulose membrane prepared by the preparation method of the tough regenerated cellulose membrane according to any one of claims 7 to 9.

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