Tannic acid modified cellulose-based water-plastic polymer as well as preparation method and application thereof

Abstract

The invention discloses a tannic acid modification-based cellulose-based water-plastic polymer as well as a preparation method and application of the tannic acid modification-based cellulose-based water-plastic polymer. The structural general formula of the tannic acid modified cellulose-based water-plastic polymer is # imgabs0. The water-plastic polymer constructed on the basis of nanocellulose has high mechanical strength, efficient recoverability and remolding capacity, effectively solves the problem of environmental pollution caused by non-degradable wastes, and is simple to prepare, environment-friendly and easy for large-scale production.

Description

Technical Field

[0001] The present invention relates to a tannic acid-modified cellulose-based hydroplastic polymer, a preparation method thereof, and an application thereof, belonging to the field of polymer materials. Background Art

[0002] Plastics, with their excellent specific strength characteristics and outstanding processing and forming capabilities, have shown extensive application potential in multiple fields such as packaging materials, textile manufacturing, transportation, building structures, and electronic technology. The continuous concerns about resource shortages and environmental challenges of petroleum-based plastics have promoted the development of sustainable bioplastics derived from natural raw materials. Cellulose nanofibers, characterized by their abundant availability and excellent mechanical properties, have become candidates for sustainable bioplastics. However, the high crystallinity and strong hydrogen bond network of cellulose nanofibers seriously hinder their processing and utilization. Although chemical modification methods can effectively break down their stubborn structure and thus improve the processing flexibility of molecular chains, this process is often accompanied by an inevitable reduction in the degree of polymerization of cellulose and a degradation of mechanical properties caused by intense chemical reactions. In addition, during the preparation of cellulose-based bioplastics, processing and forming are another important factor leading to high production costs. Against this background, the water-assisted processing strategy of cellulose-based bioplastics has shown significant advantages, opening up a new path for exploring low-cost, low-energy-consuming, and sustainable processing methods. Although water-assisted processing improves the plasticity of molecular chains, it is still challenging to achieve large deformations and reorganizations of cellulose segments. In addition, for an in-depth exploration of the intrinsic hydroplastic mechanism, there is an urgent need to develop and design innovative hydroplastic materials to further promote the scientific and technological progress in this field. Summary of the Invention

[0003] In order to improve the processing flexibility of cellulose-based bioplastics and effectively solve the key problems such as the difficult forming of cellulose-based bioplastics and the insufficient mechanical properties of hydroplastic polymers in the prior art, the present invention proposes a tannic acid-modified cellulose-based hydroplastic polymer, a preparation method thereof, and an application thereof.

[0004] To solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0005] A tannic acid-modified cellulose-based hydroplastic polymer, the general structural formula thereof is:

[0006]

[0007] wherein, n is a positive integer, and 1 ≤ n ≤ 10; R is: -NH, -CH 2 any one of them.

[0008] The above-mentioned tannic acid-modified cellulose-based hydroplastic polymer exhibits excellent mechanical properties, with a tensile fracture stress reaching 90.3 MPa. At the same time, the material shows excellent plasticity under water-assisted forming conditions and can be easily processed into various complex two-dimensional and three-dimensional structures, which provides greater flexibility for material design and processing and greatly expands its application potential in the field of material design and processing. In addition, due to the dense dynamic imine bond network and highly ordered microstructure inside the material, its recycling performance is significantly improved, and it can be efficiently recycled and reused under mild conditions, providing strong support for the development of circular economy and highly conforming to the current concept of circular economy development. More notably, after the end of its service life, the material can be completely biodegradable in the natural environment within 120 days, effectively solving the environmental pollution problem of traditional plastics. This unique combination of properties, including high strength, excellent formability, high recycling efficiency, and complete biodegradability, not only ensures the high performance of the material but also minimizes its impact on the environment, making it an ideal material choice for green manufacturing.

[0009] The preparation method of the above-mentioned tannic acid-modified cellulose-based hydroplastic polymer includes the following steps: First, surface-functionalized nanocellulose fibers are prepared through a tannic acid grafting reaction, and then a tannic acid-modified cellulose-based hydroplastic polymer is constructed based on the dynamic imine bond cross-linking mechanism.

[0010] To balance reaction efficiency and product quality, the preparation method of the tannic acid-modified cellulose-based hydroplastic polymer includes the following steps:

[0011] 1) Tannic acid surface grafting: Nanocellulose fibers and tannic acid are used in tris(hydroxymethyl)aminomethane and an oxygen-rich environment to convert phenolic group-containing tannic acid molecules into oxidized tannic acid with an α-hydroxy-o-quinone structure, and then modified onto the surface of nanocellulose fibers through non-covalent bonding to obtain tannic acid-modified nanocellulose fibers;

[0012] 2) Construction of the dynamic cross-linking network: The tannic acid-modified nanocellulose fibers obtained in step 1 are cross-linked with polyamine through Schiff base reaction to form a dynamic imine bond network, and a tannic acid-modified cellulose-based hydroplastic polymer is prepared.

[0013] The above reactions are carried out under mild conditions, ensuring the efficient preparation of the material.

[0014] This application uses renewable tannic acid to modify cellulose and then reacts with the green monomer diamine to prepare a hydroplastic polymer, which has good biodegradability and is incomparable with using petroleum-based materials such as acrylamide or acrylate as the polymer substrate.

[0015] In step 1), the preparation of the nanocellulose matrix is as follows: Using bleached softwood pulp cellulose as the raw material, its suspension is dispersed by a high-pressure homogenization device. Under the action of high-pressure shearing and collision, the cellulose is subjected to strong shearing force and impact force, effectively breaking and dispersing the cellulose bundles and gradually breaking them into nanoscale cellulose.

[0016] To optimize the yield, as one of the selected preparation schemes, in step 1), the preparation of the nanocellulose matrix includes the following steps:

[0017] a) Use a fiber disaggregator to perform efficient and fine dissociation pretreatment on bleached softwood pulp cellulose to obtain a cellulose suspension; at the same time, to ensure the uniformity of the suspension and avoid possible blockage problems during the subsequent high-pressure homogenization process, use a (500W power) ultrasonic processor to perform ultrasonic treatment on the cellulose suspension for 15 - 20 minutes, and use the ultrasonic cavitation effect to further disperse the fibers;

[0018] b) Circulate and homogenize the cellulose suspension obtained in step a) through a high-pressure homogenizer. After homogenization, perform a centrifugation operation (10000 rpm, 10 min) to remove incompletely dissociated fibers or impurities, adjust the concentration of the cellulose nanofiber suspension as needed, and store it at below 4°C for later use to maintain its stability and performance.

[0019] To improve the dissociation efficiency, in step a), during the dissociation pretreatment, the rotation speed of the fiber disaggregator needs to be controlled at 2000 - 3500 rpm, and the treatment time is controlled at 10 - 40 min to initially dissociate the cellulose fibers by high-speed shearing force to form micron-scale fibers; in step b), the operating pressure of the high-pressure homogenizer is set at 500 - 1500 bar, and the number of homogenization cycles is 10 - 20 times to ensure the obtained cellulose nanofibers have uniform sizes.

[0020] To ensure the reaction quality, as one of the preferred implementation schemes, in step 1), tannic acid-modified nanocellulose fibers are prepared by a one-pot aqueous method, including the following steps:

[0021] 1.1) Place a cellulose nanofiber suspension with a mass concentration of 1.2 - 1.3 wt% in a reactor, and then add a 1.0 M tris(hydroxymethyl)aminomethane buffer solution to adjust the pH value of the suspension to 8 - 8.5;

[0022] 1.2) Add tannic acid to the suspension obtained in step 1.1), and under the room temperature condition of an oxygen atmosphere, stir and react at a rotation speed of 300 - 500 rpm for 5 - 6 hours. The suspension turns light yellow, and a tannic acid-modified nanocellulose fiber suspension is obtained. Transfer the obtained tannic acid-modified nanocellulose fiber suspension to a sealed container and store it in a refrigerator at 4°C to maintain its stability for subsequent experiments.

[0023] The mass ratio of the above-mentioned nanocellulose fiber to tannic acid is (1 - 3.5):(0.1 - 1.5) to optimize the modification effect and maintain the structural integrity of the nanocellulose. It is further preferably 1:(0.15 - 0.5).

[0024] To improve the reaction efficiency, as one of the preferred implementation schemes, step 2) is to uniformly mix the tannic acid-modified nanocellulose fiber suspension with polyamine at room temperature, react for 12 - 18 hours, then perform degassing treatment, pour it into a mold, and transfer it to a forced-air oven (40°C, 3h) for drying and forming to obtain a tannic acid-modified cellulose-based hydroplastic polymer.

[0025] To optimize the reaction efficiency and take into account the product quality at the same time, the polyamine is at least one of 1,4-butanediamine, 1,5-diaminopentane, 1,6-hexanediamine, 1,8-octanediamine, 1,10-diaminodecane or polyethyleneimine. It is further preferably at least one of 1,8-octanediamine, 1,10-diaminodecane or polyethyleneimine; the mass ratio of the tannic acid-modified nanocellulose fiber to the polyamine is (1 - 10.5):(1 - 5.5) to ensure the high efficiency of the reaction and the stability of the product performance.

[0026] The above-mentioned tannic acid-modified cellulose-based hydroplastic polymer has excellent mechanical properties and plasticity, is environmentally friendly, self-healing, and can be used to replace plastics.

[0027] The above-mentioned tannic acid-modified cellulose-based hydroplastic polymer can be arbitrarily adjusted in shape under specific water-assisted conditions.

[0028] The method for shaping or recycling and reusing the above-mentioned tannic acid-modified cellulose-based hydroplastic polymer is as follows: soak it in water at room temperature for 3 - 5 minutes, then shape it into the desired shape (shape editing can be carried out using a mold, etc.), and dry it at a temperature of 25 - 35°C (20 - 30 minutes). The shape is solidified, and the above steps can be repeated.

[0029] The above-mentioned tannic acid-modified cellulose-based hydroplastic polymer can be completely recycled and reused by hot pressing or depolymerization methods;

[0030] The hot pressing method is as follows: Grind the water-plastic polymer material activated in water for 20 - 30 minutes into fragments, and hot press for 0.1 - 1 h under the conditions of a temperature of 70 - 95°C and a pressure of 1 - 8 MPa;

[0031] The depolymerization method is as follows: Stir the water-plastic polymer fragments in a 5 wt% aqueous acetic acid solution at room temperature for 1.5 - 5 h, then remove acetic acid by vacuum distillation, supplement polyamine, mix at a temperature of 20 - 30°C, stir and react for 8 - 12 hours, perform degassing treatment, re-pour into a mold, and dry and form; wherein, the supplementary amount of polyamine is 5 - 50 wt% of the mass of the water-plastic polymer.

[0032] Unless otherwise specified, all percentages in this application are mass percentages.

[0033] For technologies not mentioned in the present invention, refer to the prior art.

[0034] The beneficial effects of the present invention are as follows:

[0035] 1. Solvent-free green process: The present invention adopts a production process without organic solvents, which can be efficiently completed under normal pressure, simplifies the production process, reduces the operation difficulty, and provides technical support for large-scale industrial production.

[0036] 2. Both high performance and sustainability: The water-plastic polymer constructed based on nanocellulose in the present invention has both high mechanical strength, high recycling efficiency and reshaping ability, and effectively solves the environmental pollution problem of non-degradable waste.

[0037] 3. Flexible forming: The water-plastic polymer constructed based on nanocellulose in the present invention can achieve diverse wet forming through a dynamic imine bond network activated by water molecules, realizing forming flexibility and diversity.

[0038] 4. Fast natural degradation: The all-bio-based material can be completely degraded within 120 days under natural conditions, avoiding environmental accumulation and fully embodying the concept of green environmental protection.

[0039] 5. High humidity resistance: The water-plastic polymer constructed based on nanocellulose in the present invention has excellent mechanical strength stability and shape stability in a wide humidity range, still has excellent mechanical properties and shape retention ability in a high humidity environment. After being placed in an 80% RH environment for 30 days, its tensile strength is still as high as 74.3 MPa, significantly superior to various commercial non-degradable plastics. The tensile strength of the material is still as high as 70.4 MPa after ultrasonic treatment underwater, showing excellent shape stability and mechanical property retention ability.

[0040] 6. Aging resistance: The water-plastic polymer constructed based on nanocellulose in the present invention shows significant anti-photoaging performance.

[0041] 7. Strong self-healing ability: The water-plastic polymer based on nanocellulose in this invention exhibits remarkable self-healing characteristics. When left standing for 1 hour at 25°C and 80% RH, the cracks on the material surface completely disappear, and the strength recovery rate can reach over 96%. Description of the Drawings

[0042] Figure 1 Transmission electron microscope image of the nanocellulose fibers prepared in Example 1.

[0043] Figure 2 Fourier transform infrared spectrum of the tannic acid-modified nanocellulose fibers in Example 1.

[0044] Figure 3 Ultraviolet-visible absorption spectrum of the tannic acid-modified nanocellulose fibers in Example 1.

[0045] Figure 4 Process flow chart for the preparation of the tannic acid-modified cellulose-based water-plastic polymer in Example 1.

[0046] Figure 5 Fourier transform infrared spectrum of the tannic acid-modified cellulose-based water-plastic polymer in Example 1.

[0047] Figure 6 Solid-state nuclear magnetic resonance carbon spectrum of the tannic acid-modified cellulose-based water-plastic polymer in Example 1.

[0048] Figure 7 Surface scanning electron microscope image and energy-dispersive X-ray spectrometer spectrum of the tannic acid-modified cellulose-based water-plastic polymer in Example 1.

[0049] Figure 8 Water-assisted molding flow chart of the tannic acid-modified cellulose-based water-plastic polymer in Example 1.

[0050] Figure 9 Tensile stress-strain curves of the tannic acid-modified cellulose-based water-plastic polymer in Example 1 under different humidity conditions.

[0051] Figure 10 Comparison chart of the tensile strength between the tannic acid-modified cellulose-based water-plastic polymer in Example 1 and widely used commercial plastics.

[0052] Figure 11 Comparison chart of the physical images and mechanical properties of the tannic acid-modified cellulose-based water-plastic polymer in Example 1 before and after underwater ultrasonic treatment.

[0053] Figure 12 Comparison chart of the physical images and mechanical properties of the tannic acid-modified cellulose-based water-plastic polymer in Example 1 before and after ultraviolet aging test.

[0054] Figure 13 Self-healing performance of the tannic acid-modified cellulose-based hydroplastic polymer in Example 1.

[0055] Figure 14 Recycling diagram of the tannic acid-modified cellulose-based hydroplastic polymer in Example 1;

[0056] Figure 15 Physical images for monitoring the degradation process of the tannic acid-modified cellulose-based hydroplastic polymer in Example 1.

[0057] Figure 16 Schematic diagram of the surface grafting of tannic acid in the present invention. Detailed implementation manners

[0058] To better understand the present invention, the content of the present invention will be further clarified below in conjunction with examples. However, the content of the present invention is not limited to the following examples only.

[0059] In each example where the temperature is not specifically stated, the operations are all carried out at room temperature (20 - 25 °C).

[0060] Example 1

[0061] Preparation of nanofibrillated cellulose:

[0062] 15 g of bleached softwood pulp cellulose (UPM Kaukas pulp mill, Finncon softwood pulp, the sources in the following examples are the same) was pretreated using a fiber disrupter, and mechanically disrupted continuously at a speed of 3000 rpm for 30 minutes. Through the high-speed shearing effect, the cellulose was preliminarily disrupted to the micron scale, and a cellulose suspension with a concentration of 1.5 wt% was prepared. To ensure the uniform dispersion of the suspension and prevent clogging problems during the high-pressure homogenization process, the suspension was ultrasonically treated for 20 minutes using a 500 W ultrasonic processor, and the ultrasonic cavitation effect was used to further disperse the fibers. Subsequently, the pretreated suspension was placed in a high-pressure homogenizer and homogenized 15 times at a pressure of 1000 bar to achieve the nano-scale dissociation of cellulose. After homogenization, a high-speed centrifuge was used to centrifuge at 10000 rpm for 10 minutes to separate and remove the incompletely dissociated fibers and impurities. Then, the concentration of the cellulose nanofiber suspension was adjusted to 1.25 wt%, and it was stored in a low-temperature environment at 4 °C to ensure its structural stability and performance retention. The morphology of the prepared cellulose nanofibers was characterized by transmission electron microscopy ( Figure 1 ). The image clearly shows that the cellulose nanofibers exhibit a typical nanofibril structure, with a smooth surface and uniform distribution, and an average diameter of about 10 nm. This result confirms that the high-pressure homogenization treatment successfully dissociates cellulose to the nano-scale, laying a structural foundation for subsequent functional modification and application.

[0063] Preparation of tannic acid-modified nanocellulose fibers:

[0064] Take 200 g of a cellulose nanofiber suspension with a concentration of 1.25 wt% and place it in a three-necked flask. Dropwise add 1.0 M tris(hydroxymethyl)aminomethane buffer solution to precisely adjust the pH value of the system to 8.5. Subsequently, under the condition of continuously introducing oxygen (flow rate 25 mL / min), add 0.75 g of tannic acid, and carry out magnetic stirring at a rotation speed of 500 rpm in a 25 °C constant temperature water bath. After the reaction lasts for 6 hours, the suspension gradually turns light yellow. Transfer the prepared suspension of tannic acid-modified nanocellulose fibers with a concentration of 1.6 wt% to a sealed container and store it in a 4 °C refrigerator to maintain its stability for subsequent experiments. The infrared spectrum analysis of the tannic acid-modified cellulose nanofibers shows that a significant C=O characteristic peak appears at 1712 cm-1 ( Figure 2 ), and this result confirms that tannic acid has been successfully grafted onto the surface of the nanocellulose. In addition, as Figure 3 shown, in the ultraviolet spectrum of the tannic acid-modified nanocellulose fibers, the characteristic absorption peak of tannic acid blue-shifts from 275 nm to 260 nm, indicating that the interaction between tannic acid and cellulose nanofibers is mainly driven by hydrogen bonds, van der Waals forces, and CH-π interactions. These spectral characteristics provide strong evidence for the effective binding between tannic acid and cellulose nanofibers.

[0065] Synthesis of tannic acid-modified cellulose-based hydroplastic polymers: As Figure 4 shown, take 200 g of a tannic acid-modified nanocellulose fiber suspension with a concentration of 1.6 wt% and continuously react it with 0.35 g of 1,10-diaminodecane at 25 °C for 18 hours. After the reaction is completed, place the mixed system in a vacuum degassing device and degas it for 10 minutes under the condition of -0.1 MPa to eliminate the bubbles in the system. Subsequently, pour the degassed prepolymer into a polytetrafluoroethylene mold and transfer it to a forced-air drying oven for programmed temperature drying (maintain at 40 °C for 3 hours), and finally obtain a tannic acid-modified cellulose-based hydroplastic polymer with a regular three-dimensional network structure. As Figure 5 shown, the infrared spectrum analysis of the tannic acid-modified cellulose-based hydroplastic polymer shows that a characteristic peak of imine bond (C=N) appears at 1645 cm-1, while the C=O characteristic peak attributed to the o-benzoquinone structure of tannic acid disappears at 1712 cm-1, and this result strongly confirms that an imine bond has been successfully formed between the o-benzoquinone and the amino group on 1,10-diaminodecane. In addition, the solid-state nuclear magnetic carbon spectrum of the tannic acid-modified cellulose-based hydroplastic polymer ( Figure 6) This is also confirmed. Compared with cellulose nanofibers modified with tannic acid, the cellulose-based hydroplastic polymer modified with tannic acid shows a characteristic peak of imine bonds at 162 ppm and a characteristic peak of the aliphatic carbon chain of 1,10-diaminodecane at 35 ppm, indicating the formation of a dense imine bond network in the all-bio-based hydroplastic polymer. As Figure 7 shown, the scanning electron microscope image shows that the cellulose-based hydroplastic polymer modified with tannic acid has a dense surface structure. This is because the cellulose nanofibers modified with tannic acid and 1,10-diaminodecane are densely crosslinked through imine bonds, forming a stable structural network, thus presenting a pore-free plate-like morphology. At the same time, energy-dispersive X-ray spectroscopy analysis shows that the elements C, O, and N are evenly distributed in the material, further confirming the successful crosslinking of tannic acid and 1,10-diaminodecane and their uniform dispersion in the material. These results together reveal the chemical structure and microscopic morphological characteristics of the cellulose-based hydroplastic polymer modified with tannic acid.

[0066] Effect evaluation:

[0067] The cellulose-based hydroplastic polymer modified with tannic acid exhibits excellent water-assisted shape programmability and can achieve precise transformation from two-dimensional to three-dimensional structures (as Figure 8 shown). The water-assisted molding process includes the following three key steps: (1) Water activation stage: At room temperature, immerse the material in deionized water for 5 minutes to fully activate the dynamic imine bond network inside the material; (2) Shape editing stage: Use a custom mold to mechanically mold the water-activated material to prepare a spiral structure with complex geometric features; (3) Dehydration and shaping stage: Place the molded sample in an environment of 30 °C and 30-40% RH for 30 minutes to dehydrate and shape it, and the dynamic imine bond network is re-cured to fix the shape. The above process can be repeated. The shape programmability of the material is mainly attributed to the water-responsive dynamic imine bonds formed between the materials, which can reversibly break and recombine in the water environment, thus realizing the controllable molding of the material. Figure 9The stress-strain curves of the tannic acid-modified cellulose-based hydroplastic polymer material under different relative humidity conditions (30 - 90% RH) are shown (the freshly prepared tannic acid-modified cellulose-based hydroplastic polymer (not hydroformed) was placed in a temperature and humidity-controlled chamber where the humidity could be adjusted, and after adjusting to the corresponding humidity and standing for 48 hours, the tensile properties were tested), reflecting the change in the mechanical properties of the material with environmental humidity. Although the relative humidity changed from 30% to 90%, the overall change in the stress-strain curve of the material was relatively small, indicating its excellent mechanical strength stability in a wide humidity range. Especially in the low strain region (<5%), the difference in the initial modulus under each humidity condition was small, further demonstrating the stiffness stability of the material in a wide humidity range. In the medium strain region (5% - 15%), the fluctuation of the yield point stress of the material with humidity change under different humidity conditions was small. Even under the high humidity condition of 90% RH, the yield strength remained at a relatively high level, indicating that the material could still maintain good anti-deformation ability in a high humidity environment, further demonstrating the excellent mechanical property retention ability of the material in a high humidity environment. Additionally, as Figure 10 shown, the tannic acid-modified cellulose-based hydroplastic polymer developed in this study exhibited excellent mechanical property stability. After the hydroplastic polymer was placed in an 80% RH environment for 30 days, its tensile strength was still as high as 74.3 MPa (tensile strength at 30% RH: 90.3 MPa), which was significantly better than that of many commercial non-degradable plastics: polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), acrylonitrile-butadiene-styrene polymer (ABS), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and polycarbonate (PC), etc. At the same time, the mechanical properties of this polymer were also significantly better than those of many degradable plastics: poly(butylene adipate-co-terephthalate) (PBAT), polyhydroxyalkanoates (PHA), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(butylene succinate) (PBS), polycaprolactone (PCL), polylactic acid (PLA), etc. This finding highlights the excellent potential of the tannic acid-modified cellulose-based hydroplastic polymer in terms of mechanical properties, and more prominently, its great potential in replacing traditional petroleum-based plastics, providing new ideas and theoretical basis for the development of high-performance sustainable materials.

[0068] As Figure 11As shown, after 30 minutes of underwater ultrasonic treatment (frequency 40 kHz, power 500 W), the tannic acid-modified cellulose-based hydroplastic polymer exhibits excellent shape stability and mechanical property retention. Quantitative analysis shows that the hydroplastic polymer material does not undergo significant mass loss or volume change under intense ultrasonic cavitation, and there is no depolymerization phenomenon. This excellent stability is mainly attributed to the three-dimensional dynamic cross-linked network structure formed between tannic acid and cellulose molecules. This network can effectively dissipate the mechanical impact energy and shear stress generated by the ultrasonic cavitation effect through reversible imine bonds and hydrogen bond interactions. Mechanical property tests further confirm that the tensile strength of the material remains as high as 70.4 MPa after underwater ultrasonic treatment. These results indicate that the tannic acid-modified cellulose-based hydroplastic polymer has excellent anti-mechanical impact performance and environmental stability. As Figure 12 As shown, after 100 hours of irradiation with 365 nm ultraviolet light (50 W), the tannic acid-modified cellulose-based hydroplastic polymer shows significant anti-photoaging performance. Morphological analysis shows that there are no obvious color changes, cracks or powdering on the material surface, and good structural integrity is maintained. Mechanical property tests show that the stress-strain curves before and after irradiation are highly coincident, and the tensile strength retention rate reaches 90.3%. This excellent anti-ultraviolet performance is mainly attributed to the catechol structure in tannic acid molecules, which can absorb ultraviolet photons and convert them into heat energy, effectively protecting the cellulose matrix from photodegradation. The structural stability and mechanical property retention ability of the material indicate its important potential in outdoor application fields.

[0069] As Figure 13 As shown, the tannic acid-modified cellulose-based hydroplastic polymer in the present invention exhibits significant self-healing characteristics. Through in-situ observation of its self-healing process by optical microscopy, it is found that when a mechanical scratch with a length of 310 μm and a width of 10 μm is generated on the material surface and left standing at 25 °C and 80% RH for 1 hour, the cracks on the material surface completely disappear. This self-healing behavior is mainly attributed to the reversible recombination mechanism of the dynamic imine bond network inside the material. Under suitable temperature and humidity conditions, the breakage-recombination equilibrium of imine bonds shifts towards the recombination direction, thus achieving interface repair. Mechanical property tests show that the tensile strength recovery rate of the repaired material reaches 94.7%, confirming its excellent mechanical property recovery ability.

[0070] As Figure 14As shown in the figure, the tannic acid-modified cellulose-based hydroplastic polymer material can be reused by physical methods (hot pressing - shaping) and chemical methods (depolymerization - recycling). The physical method is to grind the hydroplastic polymer material activated in water for 30 minutes into fragments, and then reshape it by hot pressing (3 MPa, 90 °C, 1 h). The mechanical strength is basically unchanged compared with the initial state (change < 5%). The chemical method is to stir the hydroplastic polymer material in a 5 wt% acetic acid aqueous solution at room temperature for 2 h, then remove acetic acid by vacuum distillation (absolute pressure 40 mmHg), add 1,10-diaminodecane with a mass dosage of 25 wt% of the mass of the hydroplastic polymer material, mix at room temperature, stir and react for 12 h, carry out degassing treatment for 10 minutes under the condition of -0.1 MPa, then re-pour it into a mold and dry at 40 °C for 1 h to form. The mechanical strength is basically unchanged compared with the initial state (change < 5%). This shows that the tannic acid-modified cellulose-based hydroplastic polymer material has excellent recycling potential. In addition, a soil degradation experiment was carried out to explore the biodegradability of the tannic acid-modified cellulose-based hydroplastic polymer ( Figure 15 ). Disc samples of the tannic acid-modified cellulose-based hydroplastic polymer with a diameter of 20 mm were buried in natural soil (burial depth 5 cm), and its microscopic degradation morphology evolution was observed by regular sampling. The results showed that as the burial time extended, the surface of the material gradually changed from the initial smooth and dense structure to a porous and rough morphology, accompanied by obvious crack propagation and fragmentation. After 120 days of burial, the sample was almost completely degraded into debris, and the degradation rate could reach more than 95%. This series of morphological characteristic changes indicate that the tannic acid-modified cellulose-based hydroplastic polymer material exhibits excellent biodegradation performance in the natural soil environment. The research results confirm that this hydroplastic polymer material has good environmental compatibility, and its degradation products can be completely absorbed by the natural environment without causing secondary pollution, providing an important reference for the development of environmentally friendly polymer materials.

[0071] Example 2

[0072] Preparation of nanocellulose fibers: 15 grams of bleached softwood pulp cellulose was mechanically dissociated at 2500 rpm for 40 minutes to prepare a 1.5 wt% microscale cellulose suspension. After ultrasonic treatment at 500 W for 20 minutes, the suspension was homogenized under high pressure at 1200 bar for 20 times to achieve nanoscale dissociation. Centrifugation (10000 rpm, 10 minutes) was used to remove undissociated fibers, and the concentration was adjusted to 1.25 wt% and stored at 4 °C.

[0073] Preparation of tannic acid-modified nanocellulose fibers: The pH of 200 g of a 1.25 wt% nanocellulose suspension was adjusted to 8 with 1.0 M tris(hydroxymethyl)aminomethane buffer solution. 0.45 g of tannic acid was added, and the mixture was stirred at 25 °C in an oxygen atmosphere (25 mL / min) for 6 hours (stirring speed: 500 rpm) to obtain a light yellow suspension. The concentration was adjusted to 1.5 wt% and stored at 4 °C.

[0074] Synthesis of tannic acid-modified cellulose-based hydroplastic polymers: 200 g of the tannic acid-modified nanocellulose suspension was reacted with 0.65 g of polyethyleneimine (Mw = 600) at 25 °C for 18 hours. After degassing (degassing treatment for 10 minutes under -0.1 MPa), it was cast and dried at 40 °C for 3 hours to obtain a hydroplastic polymer with a three-dimensional network structure.

[0075] The above-prepared hydroplastic polymer material exhibits excellent comprehensive properties: its tensile strength reaches 90.6 ± 1.5 MPa, showing excellent mechanical properties; at the same time, the material has significant hydroplastic forming ability and can achieve precise plastic forming of complex shapes under room temperature immersion conditions. The plastic forming process can be repeated, and the specific conditions and process are the same as in Example 1. In addition, the material exhibits excellent self-healing performance. Under the conditions of 25 °C and 80% relative humidity, it can almost completely repair a surface scratch with a length of 350 μm and a width of 20 μm in only 1 hour, and the repair efficiency is over 95%. The hydroplastic polymer material also exhibits good recycling and reprocessing ability (the method is the same as in Example 1), and the mechanical strength of the recycled and reprocessed hydroplastic polymer material is basically unchanged from the initial state. The degradation performance test shows that the degradation rate of the material exceeds 95% after being buried in the natural soil environment for 120 days, showing good biodegradability and environmental compatibility.

[0076] Example 3

[0077] 15 g of bleached softwood pulp cellulose was mechanically dissociated at 3500 rpm for 25 minutes to prepare a microscale cellulose suspension with a concentration of 1.5 wt%. Subsequently, the suspension was ultrasonically treated with a 500 W ultrasonic processor for 20 minutes to further disperse the fibers. Then, the suspension was subjected to 15 high-pressure homogenization cycles at 1500 bar to achieve nanoscale dissociation of cellulose. After homogenization, the suspension was centrifuged at 10000 rpm for 10 minutes to remove incompletely dissociated fibers and impurities. Finally, the concentration was adjusted to 1.25 wt% and stored at 4 °C for later use.

[0078] Adjust the pH of 200 mL of a nanofibrillated cellulose suspension with a concentration of 1.25 wt% to 8.2 using 1.0 M tris(hydroxymethyl)aminomethane buffer solution, and then add 0.6 g of tannic acid. Under the condition of a constant temperature water bath at 25 °C, continuously introduce oxygen (flow rate: 25 mL / min) at a stirring speed of 500 rpm and react for 6 hours to obtain a light yellow homogeneous suspension. Store it in a refrigerator at 4 °C in the dark for later use.

[0079] Synthesis of tannic acid-modified cellulose-based hydroplastic polymer: React 200 g of a tannic acid-modified nanofibrillated cellulose suspension with 0.65 g of 1,8-octanediamine at 25 °C for 18 hours. After defoaming (defoaming treatment for 10 minutes under the condition of -0.1 MPa), pour it into a mold and dry it at 40 °C for 3 hours to obtain a hydroplastic polymer with a three-dimensional network structure.

[0080] The obtained hydroplastic polymer material has a tensile strength of 89.3 MPa, showing excellent mechanical properties; it has excellent hydroplastic forming ability, and can achieve precise plastic forming of complex shapes under the condition of immersion in water at room temperature. The plastic forming process can be repeated. The specific conditions and process are the same as those in Example 1. The material can repair a surface scratch of 350 μm × 20 μm within 1 hour at 25 °C and 80% relative humidity, and the repair efficiency is over 96%. The hydroplastic polymer material exhibits good recyclability (the method is the same as that in Example 1), and its mechanical strength is still basically equivalent to that of the original material (retention rate > 95%) after recycling and reprocessing. In addition, the degradation rate of the material exceeds 95% after being buried in natural soil for 120 days, showing good biodegradability and environmental compatibility.

Claims

1. A tannic acid-modified cellulose-based water-plastic polymer, characterized in that: Its general structural formula is: Wherein, n is a positive integer, and 1≤n≤10; R is any one of: -NH, -CH2.

2. A method for preparing the tannic acid-modified cellulose-based water-plastic polymer according to claim 1, characterized in that: The following steps are involved: Surface-functionalized nanocellulose fibers were first prepared by tannic acid grafting reaction, and then tannic acid-modified cellulose-based hydroplastic polymers were constructed based on the dynamic imine bond cross-linking mechanism.

3. The preparation method according to claim 2, characterized in that: The steps include: 1) Tannic acid surface grafting: The nanocellulose fibers are treated with tannic acid in a tris(hydroxymethyl)aminomethane and oxygen-rich environment to convert the phenolic tannic acid molecules into oxidized tannic acid with an α-hydroxy-o-quinone structure, thereby obtaining tannic acid-modified nanocellulose fibers; 2) Dynamic cross-linking network construction: The tannic acid-modified nanocellulose fibers obtained in step 1) are cross-linked with polyamines through a Schiff base reaction to form a dynamic imine bond network, thereby obtaining a tannic acid-modified cellulose-based water-plastic polymer.

4. The preparation method according to claim 3, characterized in that: In step 1), the preparation of the nanocellulose matrix comprises the following steps: a) pre-dissociating bleached conifer pulp cellulose using a fiber dissociator to obtain a cellulose suspension, and then ultrasonically treating the suspension for 15 to 20 minutes; b) The cellulose suspension obtained in step a) is subjected to a circulating homogenization treatment by a high-pressure homogenizer. After the homogenization is completed, the suspension is centrifuged, and the concentration of the cellulose nanofiber suspension is adjusted as required, and the suspension is stored at a temperature below 4° C. for later use.

5. The preparation method according to claim 4, characterized in that: In step a), during the dissociation pretreatment, the speed of the fiber disintegrator needs to be regulated at 2000-3500 rpm, and the treatment time is controlled at 10-40 min; in step b), the operating pressure of the high-pressure homogenizer is set at 500-1500 bar, and the number of homogenization cycles is 10-20 times.

6. The preparation method according to any one of claims 3 to 5, characterized in that: In step 1), tannic acid-modified nanocellulose fibers are prepared by a one-pot aqueous method, comprising the following steps: 1.1) placing a cellulose nanofiber suspension having a mass concentration of 1.2-1.3 wt% in a reactor, and then adding 1.0 M tris(hydroxymethyl)aminomethane buffer solution to adjust the pH value of the suspension to 8-8.5; 1.2) Add tannic acid to the suspension obtained in step 1.1), and stir the mixture at 300-500 rpm for 5-6 hours under room temperature in an oxygen atmosphere until the suspension turns light yellow to obtain a tannic acid-modified nanocellulose fiber suspension; the mass ratio of the nanocellulose fiber to the tannic acid is (1-3.5):(0.1-1.5).

7. The preparation method according to any one of claims 3 to 5, characterized in that: Step 2) is to mix the tannic acid modified nanocellulose fiber suspension and polyamine evenly at room temperature, react for 12 to 18 hours, then degas, pour into a mold, dry and shape, and obtain a tannic acid modified cellulose-based water plastic polymer.

8. The preparation method according to claim 7, characterized in that: The polyamine is at least one of 1,4-butanediamine, 1,5-diaminopentane, 1,6-hexanediamine, 1,8-octanediamine, 1,10-diaminodecane or polyethyleneimine; the mass ratio of the tannic acid-modified nanocellulose fibers to the polyamine is (1-10.5): (1-5.5).

9. An application of the tannic acid modified cellulose-based water-plastic polymer according to claim 1, characterized in that: Used to replace plastic.

10. The use according to claim 9, characterized in that: The method for shaping or recycling the cellulose-based water-plastic polymer modified by tannic acid is as follows: soaking in water for 3 to 5 minutes at room temperature, then shaping into a desired shape, and drying and curing at a temperature of 25 to 35° C., and the above steps can be repeated repeatedly; The cellulose-based water-plastic polymer modified by tannic acid is recovered and reused by a hot pressing method or a depolymerization method; The hot pressing method is as follows: the water-plastic polymer material activated in water for 20 to 30 minutes is ground into pieces, and hot pressed for 0.1 to 1 hour at a temperature of 70 to 95° C. and a pressure of 1 to 8 MPa; The depolymerization method is as follows: stirring the water-plastic polymer fragments in a 5wt% acetic acid aqueous solution at room temperature for 1.5 to 5 hours, removing the acetic acid by reduced pressure distillation, adding polyamine, mixing at a temperature of 20 to 30°C, stirring and reacting for 8 to 12 hours, degassing, re-pouring into a mold, and drying and forming; wherein the amount of the added polyamine is 5 to 50wt% of the mass of the water-plastic polymer.

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