A tannic acid-modified cellulose-based hydroplastic polymer, its preparation method and its application

Abstract

This invention discloses a tannic acid-modified cellulose-based hydroplastic polymer, its preparation method, and its applications. The general structural formula of the tannic acid-modified cellulose-based hydroplastic polymer is as follows: The hydroplastic polymer constructed based on nanocellulose in this invention possesses high mechanical strength, high recyclability, and remodeling ability, effectively solving the environmental pollution problem of non-degradable waste. Furthermore, its preparation is simple, environmentally friendly, and easy for large-scale production.

Description

Technical Field

[0001] This invention relates to a tannic acid-modified cellulose-based water-plastic polymer, its preparation method and its application, belonging to the field of polymer materials. Background Technology

[0002] Plastics, with their superior specific strength and excellent processing and molding capabilities, have demonstrated broad application potential in various fields such as packaging materials, textile manufacturing, transportation, building structures, and electronics. Continued concerns about resource scarcity and the environmental challenges posed by petroleum-based plastics have driven the development of sustainable bioplastics derived from natural raw materials. Cellulose nanofibers, characterized by their abundant availability and excellent mechanical properties, have become a candidate for sustainable bioplastics. However, the high crystallinity and strong hydrogen bond network of cellulose nanofibers severely hinder their processing and utilization. While chemical modification can effectively break down their rigid structure and improve the processing flexibility of the molecular chains, this process is often accompanied by an inevitable decrease in the degree of polymerization of cellulose and mechanical property degradation caused by violent chemical reactions. Furthermore, processing and molding are another significant factor contributing to the high production costs in the preparation of cellulose-based bioplastics. Against this backdrop, water-assisted processing strategies for cellulose-based bioplastics have shown significant advantages, opening new avenues for exploring low-cost, low-energy, and sustainable processing methods. Although water-assisted processing improves the plasticity of the molecular chains, achieving large deformation and recombination of cellulose fragments remains challenging. Furthermore, in order to conduct in-depth research on the intrinsic mechanism of hydroplasticity, there is an urgent need for the development and design of innovative hydroplastic materials to further promote technological progress in this field. Summary of the Invention

[0003] To improve the processing flexibility of cellulose-based bioplastics and effectively solve key problems such as the difficulty in molding cellulose-based bioplastics and the insufficient mechanical properties of hydroplastic polymers in the prior art, this invention proposes a cellulose-based hydroplastic polymer based on tannic acid modification, its preparation method and its application.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0005] A tannic acid-modified cellulose-based hydroplastic polymer has the following general structural formula:

[0006]

[0007] Where n is a positive integer, and 1≤n≤10; R is any one of -NH and -CH2.

[0008] The aforementioned tannic acid-modified cellulose-based hydroplastic polymer exhibits superior mechanical properties, with a tensile fracture stress reaching 90.3 MPa. Simultaneously, this material demonstrates excellent plasticity under water-assisted molding conditions, enabling easy processing into various complex two-dimensional and three-dimensional structures. This provides greater flexibility in material design and processing, significantly expanding its application potential in the field of materials design and processing. Furthermore, thanks to the dense dynamic imine bond network and highly ordered microstructure within the material, its recyclability is significantly improved, achieving efficient recycling and reuse under mild conditions. This provides strong support for the development of a circular economy and aligns closely with current circular economy development concepts. More importantly, this material can completely biodegrade in the natural environment within 120 days after the end of its service life, effectively solving the environmental pollution problems of traditional plastics. This unique combination of high strength, excellent moldability, high recyclability, and complete biodegradability not only ensures the material's high performance but also minimizes its environmental impact, 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: firstly, surface-functionalized nanocellulose fibers are prepared by tannic acid grafting reaction, and then the tannic acid modified cellulose-based hydroplastic polymer is constructed based on the dynamic imine bond crosslinking mechanism.

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

[0011] 1) Tannic acid surface grafting: Tannic acid molecules containing phenolic groups are converted into oxidized tannic acid with α-hydroxy-o-quinone structure by nanocellulose fibers and tannic acid in a tri(hydroxymethyl)aminomethane and oxygen-rich environment. This oxidized tannic acid is then modified onto the surface of nanocellulose fibers through non-covalent bonding, thereby obtaining tannic acid modified nanocellulose fibers.

[0012] 2) Construction of dynamic crosslinking network: The tannic acid-modified nanocellulose fibers obtained in step 1) are crosslinked with polyamines through Schiff base reaction to form a dynamic imine bond network, thus obtaining a tannic acid-modified cellulose-based water-plastic polymer.

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

[0014] This application uses renewable tannic acid to modify cellulose, and then reacts it with green monomer diamine to prepare a water-plastic polymer with good biodegradability, which is incomparable to that of polymers using petroleum-based materials such as acrylamide or acrylates as the polymer base.

[0015] In step 1), the preparation of the nanocellulose matrix is ​​as follows: using bleached needlewood pulp cellulose as raw material, its suspension is dispersed by a high-pressure homogenizer. Under high-pressure shearing and collision, the cellulose is subjected to strong shearing and impact forces, which effectively break and disperse the cellulose bundles, and gradually break them into nano-sized cellulose.

[0016] To optimize the yield, as one of the preferred preparation methods, step 1) involves the following steps in the preparation of the nanocellulose matrix:

[0017] a) The bleached softwood pulp cellulose is subjected to efficient and fine dissociation pretreatment using a fiber dissociator to obtain a cellulose suspension; at the same time, in order to ensure the uniformity of the suspension and avoid possible clogging problems in the subsequent high-pressure homogenization process, the cellulose suspension is ultrasonically treated for 15 to 20 minutes using a (500W power) ultrasonic processor to further disperse the fibers using the ultrasonic cavitation effect.

[0018] b) The cellulose suspension obtained in step a) is subjected to circulating homogenization using a high-pressure homogenizer. After homogenization, centrifugation (10,000 rpm, 10 min) is performed to remove incompletely dissociated fibers or impurities. The concentration of the cellulose nanofiber suspension is adjusted as needed and stored below 4°C for later use to maintain its stability and performance.

[0019] To improve dissociation efficiency, in step a), during the dissociation pretreatment, the rotation speed of the fiber dissociator needs to be adjusted to 2000–3500 rpm, and the treatment time needs to be controlled to 10–40 min, so as to initially dissociate the cellulose fibers through high-speed shear force to form micron-sized fibers; in step b), the operating pressure of the high-pressure homogenizer is set to 500–1500 bar, and the number of homogenization cycles is 10–20 times, so as to ensure that uniformly sized cellulose nanofibers are obtained.

[0020] To ensure reaction quality, as a preferred implementation, step 1) involves preparing tannic acid-modified cellulose nanofibers via a one-pot aqueous method, including the following steps:

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

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

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

[0024] To improve reaction efficiency, as one preferred implementation scheme, step 2) involves mixing the tannic acid-modified nanocellulose fiber suspension with polyamine at room temperature, reacting for 12-18 hours, then degassing, pouring into a mold, and transferring to a forced-air drying oven (40°C, 3h) for drying and molding to obtain the tannic acid-modified cellulose-based hydroplastic polymer.

[0025] To optimize reaction efficiency while ensuring product quality, the polyamine is at least one of 1,4-butanediamine, 1,5-diaminopentane, 1,6-hexanediamine, 1,8-octanediamine, 1,10-diaminodecane, or polyethyleneimine, more preferably at least one of 1,8-octanediamine, 1,10-diaminodecane, or polyethyleneimine; the mass ratio of tannic acid-modified nanocellulose fibers to polyamine is (1-10.5):(1-5.5) to ensure high reaction efficiency and stable product properties.

[0026] The aforementioned tannic acid-modified cellulose-based hydroplastic polymer has excellent mechanical properties and plasticity, is environmentally friendly, self-healing, and can be used as a plastic substitute.

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

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

[0029] The aforementioned tannic acid-modified cellulose-based hydroplastic polymers can be completely recycled and reused through hot pressing or depolymerization.

[0030] The hot pressing method is as follows: the water-plastic polymer material activated in water for 20 to 30 minutes is ground into fragments, and then hot-pressed for 0.1 to 1 hour at a temperature of 70 to 95°C and a pressure of 1 to 8 MPa.

[0031] The depolymerization method is as follows: after stirring the hydroplastic polymer fragments in a 5wt% acetic acid aqueous solution at room temperature for 1.5 to 5 hours, the acetic acid is removed by vacuum distillation, polyamine is added, and the mixture is stirred and reacted at a temperature of 20 to 30°C for 8 to 12 hours. After degassing, the mixture is re-poured into a mold and dried to form the final product. The amount of polyamine added is 5 to 50 wt% of the mass of the hydroplastic polymer.

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

[0033] Any techniques not mentioned in this invention are based on existing technologies.

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

[0035] 1. Solvent-free green process: This invention adopts a solvent-free production process that can be completed efficiently under normal pressure, simplifying the production process, reducing the difficulty of operation, and providing technical support for large-scale industrial production.

[0036] 2. Combining high performance and sustainability: This invention is based on a water-plastic polymer constructed from nanocellulose, which combines high mechanical strength, high recyclability and remodeling ability, effectively solving the environmental pollution problem of non-degradable waste.

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

[0038] 4. Rapid natural degradation: The fully 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: This invention utilizes a hydroplastic polymer constructed from nanocellulose, exhibiting excellent mechanical strength and shape stability over a wide humidity range. Even in high humidity environments, it retains superior mechanical properties and shape retention. After being placed in an 80% RH environment for 30 days, its tensile strength remains as high as 74.3 MPa, significantly superior to many commercially available non-degradable plastics. The material's tensile strength after underwater ultrasonic treatment remains as high as 70.4 MPa, demonstrating excellent shape stability and mechanical property retention.

[0040] 6. Aging resistance: The water-plastic polymer constructed based on nanocellulose in this invention exhibits significant resistance to photoaging.

[0041] 7. Strong self-healing properties: The water-plastic polymer constructed based on nanocellulose in this invention exhibits significant self-healing characteristics. After 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 more than 96%. Attached Figure Description

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

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

[0044] Figure 3 The image shows the UV-Vis absorption spectrum of tannic acid-modified nanocellulose fibers in Example 1.

[0045] Figure 4 This is a process flow diagram for the preparation of tannic acid-modified cellulose-based hydroplastic polymer in Example 1.

[0046] Figure 5 The Fourier transform infrared spectrum of the tannic acid-modified cellulose-based hydroplastic polymer of Example 1 is shown.

[0047] Figure 6 Solid-state carbon NMR spectrum of tannic acid-modified cellulose-based hydroplastic polymer in Example 1.

[0048] Figure 7 The images show the surface scanning electron microscope (SEM) image and energy-dispersive X-ray spectroscopy (EDX) spectrum of the tannic acid-modified cellulose-based hydroplastic polymer from Example 1.

[0049] Figure 8 This is a flowchart of the water-assisted molding process for the tannic acid-modified cellulose-based hydroplastic polymer of Example 1.

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

[0051] Figure 10 This is a comparison chart of the tensile strength of the tannic acid-modified cellulose-based hydroplastic polymer and a widely used commercial plastic from Example 1.

[0052] Figure 11 The images and mechanical properties of the tannic acid-modified cellulose-based hydroplastic polymer from Example 1 before and after underwater ultrasonication are shown in the figure.

[0053] Figure 12 The images and mechanical properties of the tannic acid-modified cellulose-based hydroplastic polymer from Example 1 before and after UV aging tests are shown.

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

[0055] Figure 14 This is a diagram illustrating the recycling and reuse of the tannic acid-modified cellulose-based hydroplastic polymer from Example 1.

[0056] Figure 15 This is a physical image of the tannic acid-modified cellulose-based hydroplastic polymer used in Example 1 to monitor its degradation process.

[0057] Figure 16 This is a schematic diagram illustrating the principle of tannic acid surface grafting in this invention. Detailed Implementation

[0058] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0059] Unless otherwise specified, all cases were conducted at room temperature (20–25°C).

[0060] Example 1

[0061] Preparation of nanocellulose fibers:

[0062] 15 grams of bleached softwood pulp cellulose (UPM Kaukas pulp mill, UPM softwood pulp; all sources are the same in the following examples) were pretreated using a fiber dissociator. Mechanical dissociation was performed continuously at 3000 rpm for 30 minutes, initially dissociating the cellulose to the micron level through high-speed shearing, resulting in a cellulose suspension with a concentration of 1.5 wt%. To ensure uniform dispersion of the suspension and prevent clogging during high-pressure homogenization, the suspension was ultrasonically treated for 20 minutes using a 500W ultrasonic processor, utilizing the ultrasonic cavitation effect to further disperse the fibers. Subsequently, the pretreated suspension was placed in a high-pressure homogenizer and homogenized for 15 cycles at 1000 bar to achieve nanoscale dissociation of the cellulose. After homogenization, the suspension was centrifuged at 10000 rpm for 10 minutes to separate and remove incompletely dissociated fibers and impurities. The concentration of the cellulose nanofiber suspension was then adjusted to 1.25 wt% and stored at 4°C to ensure structural stability and performance retention. The morphology of the prepared cellulose nanofibers was characterized by transmission electron microscopy. Figure 1 The images clearly show that the cellulose nanofibers exhibit a typical nanofiber structure with a smooth and uniform surface and an average diameter of approximately 10 nm. This result confirms that high-pressure homogenization successfully dissociates cellulose to the nanoscale, laying a structural foundation for subsequent functionalization modifications and applications.

[0063] Preparation of tannic acid-modified cellulose nanofibers:

[0064] 200 g of a 1.25 wt% cellulose nanofiber suspension was placed in a three-necked flask, and 1.0 M tris(hydroxymethyl)aminomethane buffer solution was added dropwise to precisely adjust the pH of the system to 8.5. Then, under continuous oxygen purging (flow rate 25 mL / min), 0.75 g of tannic acid was added, and the mixture was magnetically stirred at 500 rpm in a 25°C constant temperature water bath. After 6 hours of reaction, the suspension gradually turned pale yellow. The resulting 1.6 wt% tannic acid-modified cellulose nanofiber suspension was transferred to a sealed container and stored at 4°C to maintain its stability for subsequent experiments. Infrared spectroscopy analysis of the tannic acid-modified cellulose nanofibers showed a significant C=O characteristic peak at 1712 cm⁻¹. Figure 2 This result confirms that tannic acid has been successfully grafted onto the surface of nanocellulose. Furthermore, such as... Figure 3 As shown, in the UV spectrum of tannic acid-modified cellulose nanofibers, the characteristic absorption peak of tannic acid 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 features provide strong evidence for the effective binding between tannic acid and cellulose nanofibers.

[0065] Synthesis of tannic acid-modified cellulose-based hydroplastic polymers: such as Figure 4 As shown, 200 g of a 1.6 wt% tannic acid-modified nanocellulose fiber suspension was reacted with 0.35 g of 1,10-diaminodecane at a constant temperature of 25 °C for 18 hours. After the reaction, the mixture was placed in a vacuum degassing device and degassed at -0.1 MPa for 10 minutes to eliminate air bubbles. Subsequently, the degassed prepolymer was cast into a polytetrafluoroethylene mold and transferred to a forced-air drying oven for programmed temperature drying (40 °C for 3 hours) to finally obtain a tannic acid-modified cellulose-based hydroplastic polymer with a regular three-dimensional network structure. Figure 5 As shown, infrared spectroscopy analysis of the tannic acid-modified cellulose-based hydroplastic polymer revealed a characteristic peak of an imine bond (C=N) at 1645 cm⁻¹, while the C=O characteristic peak at 1712 cm⁻¹, attributed to the tannic acid-benzoquinone structure, disappeared. This result strongly confirms the successful formation of an imine bond between benzoquinone and the amino group on 1,10-diaminodecane. Furthermore, the solid-state carbon NMR spectrum of the tannic acid-modified cellulose-based hydroplastic polymer (…) Figure 6This is also confirmed. Compared with tannic acid-modified cellulose nanofibers, tannic acid-modified cellulose-based hydroplastic polymers showed a characteristic peak of imine bonds at 162 ppm and a characteristic peak of 1,10-diaminodecane aliphatic carbon chains at 35 ppm, indicating the formation of a dense network of imine bonds in the fully bio-based hydroplastic polymer. Figure 7 As shown in the scanning electron microscope (SEM) images, the tannic acid-modified cellulose-based hydroplastic polymer possesses a dense surface structure. This is due to the densification and cross-linking of tannic acid-modified cellulose nanofibers with 1,10-diaminodecane via imine bonds, forming a stable structural network that exhibits a non-porous, plate-like morphology. Simultaneously, energy-dispersive X-ray spectroscopy (EDS) analysis revealed the uniform distribution of C, O, and N elements within the material, further confirming the successful cross-linking of tannic acid with 1,10-diaminodecane and its uniform dispersion within the material. These results collectively reveal the chemical structure and microstructure characteristics of the tannic acid-modified cellulose-based hydroplastic polymer.

[0066] Effect evaluation:

[0067] Tannic acid-modified cellulose-based hydroplastic polymers exhibit excellent water-assisted shape programmability, enabling precise transformation from two-dimensional to three-dimensional structures (e.g., Figure 8 (As shown). The water-assisted molding process includes the following three key steps: (1) Water activation stage: At room temperature, the material is immersed in deionized water for 5 minutes to fully activate the dynamic imine bond network inside the material; (2) Shape editing stage: The water-activated material is mechanically molded using a customized mold to prepare a spiral structure with complex geometric features; (3) Dehydration and shaping stage: The molded sample is placed in an environment of 30℃ and 30-40% RH for 30 minutes to dehydrate and shape, and the dynamic imine bond network is re-solidified to achieve shape fixation. The above process can be repeated repeatedly. The shape programmability of the material is mainly attributed to the water-responsive dynamic imine bonds formed between the materials. These bonds can be reversibly broken and recombined in the water environment, thereby achieving controllable molding of the material. Figure 9Stress-strain curves of tannic acid-modified cellulose-based hydroplastic polymer materials under different relative humidity conditions (30–90% RH) were displayed. (The newly prepared tannic acid-modified cellulose-based hydroplastic polymer (without hydroplastic molding) was placed in a humidity-controlled constant temperature and humidity chamber, and after 48 hours of static treatment at the appropriate humidity, tensile performance tests were performed.) These curves reflect the changes in the material's mechanical properties with ambient humidity. Despite relative humidity varying from 30% to 90%, the overall change in the stress-strain curves was relatively small, indicating excellent mechanical strength stability over a wide humidity range. Particularly in the low strain region (<5%), the initial modulus differences under various humidity conditions were small, further demonstrating the material's stiffness stability over a wide humidity range. In the medium strain region (5%–15%), the yield stress of the material fluctuated little with humidity changes under different humidity conditions. Even under high humidity conditions of 90% RH, the yield strength remained at a high level, indicating that the material maintained good resistance to deformation under high humidity, further demonstrating its excellent mechanical property retention under high humidity conditions. Additionally, as... Figure 10 As shown, the tannic acid-modified cellulose-based hydroplastic polymer developed in this study exhibits excellent mechanical property stability. After being placed in an 80% RH environment for 30 days, the hydroplastic polymer still maintains a tensile strength of 74.3 MPa (tensile strength at 30% RH: 90.3 MPa), a value significantly superior to many commercially available non-degradable plastics, including polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), acrylonitrile-butadiene-styrene polymer (ABS), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and polycarbonate (PC). Simultaneously, the mechanical properties of this polymer are also significantly superior to many degradable plastics, including polybutylene adipate-terephthalate coester (PBAT), polyhydroxyalkanoate (PHA), polyhydroxybutyrate-valerate (PHBV), polybutylene succinate (PBS), polycaprolactone (PCL), and polylactic acid (PLA). This discovery highlights the remarkable potential of tannic acid-modified cellulose-based hydroplastic polymers in terms of mechanical properties, and further underscores their enormous potential in replacing traditional petroleum-based plastics, providing new ideas and theoretical basis for the development of high-performance sustainable materials.

[0068] like Figure 11As shown, the tannic acid-modified cellulose-based hydroplastic polymer exhibits excellent shape stability and mechanical property retention after underwater ultrasonic treatment (frequency 40 kHz, power 500 W) for 30 minutes. Quantitative analysis shows that the hydroplastic polymer material did not experience significant mass loss or volume change under intense ultrasonic cavitation, and no depolymerization occurred. This excellent stability is mainly attributed to the three-dimensional dynamic cross-linked network structure formed between tannic acid and cellulose molecules. This network, through reversible imine and hydrogen bond interactions, effectively dissipates the mechanical impact energy and shear stress generated by ultrasonic cavitation. Mechanical property testing further confirms that the tensile strength of the material after underwater ultrasonic treatment remains as high as 70.4 MPa. These results indicate that the tannic acid-modified cellulose-based hydroplastic polymer possesses excellent resistance to mechanical impact and environmental stability. Figure 12 As shown, the tannic acid-modified cellulose-based hydroplastic polymer exhibits significant resistance to photoaging after 100 hours of irradiation with 365 nm ultraviolet light (50 W). Morphological analysis indicates that no obvious discoloration, cracking, or powdering occurred on the material surface, maintaining good structural integrity. Mechanical property testing shows that the stress-strain curves before and after irradiation are highly consistent, with a tensile strength retention rate of 90.3%. This excellent UV resistance is mainly attributed to the catechol structure in the tannic acid molecule, which effectively protects the cellulose matrix from photodegradation by absorbing ultraviolet photons and converting them into heat energy. The material's structural stability and mechanical property retention indicate its significant potential in outdoor applications.

[0069] like Figure 13 As shown, the tannic acid-modified cellulose-based hydroplastic polymer of this invention exhibits significant self-healing properties. In-situ observation of its self-healing process using an optical microscope revealed that after a mechanical scratch with a length of 310 μm and a width of 10 μm was generated on the material surface, the crack completely disappeared after standing for 1 hour at 25°C and 80% RH. This self-healing behavior is mainly attributed to the reversible recombination mechanism of the dynamic imine bond network within the material. Under suitable temperature and humidity conditions, the breakage-recombination equilibrium of the imine bonds shifts towards recombination, thereby achieving interface repair. Mechanical property tests showed that the tensile strength recovery rate of the repaired material reached 94.7%, confirming its excellent mechanical property recovery capability.

[0070] like Figure 14As shown, tannic acid-modified cellulose-based hydroplastic polymer materials can be reused through physical methods (hot pressing-molding) and chemical methods (depolymerization-recycling). The physical method involves grinding the hydroplastic polymer material activated in water for 30 min into fragments, then reshaping it through hot pressing (3 MPa, 90℃, 1 h), with the mechanical strength remaining essentially unchanged from the initial state (change < 5%). The chemical method involves stirring the hydroplastic polymer material in a 5 wt% acetic acid aqueous solution at room temperature for 2 h, then removing the acetic acid by vacuum distillation (absolute pressure 40 mmHg), supplementing with 25 wt% of 1,10-diaminodecane by mass of the hydroplastic polymer material, mixing at room temperature, stirring for 12 h, degassing at -0.1 MPa for 10 min, then recasting into a mold and drying at 40℃ for 1 h, with the mechanical strength remaining essentially unchanged from the initial state (change < 5%). This demonstrates that tannic acid-modified cellulose-based hydroplastic polymer materials have excellent recycling potential. In addition, soil degradation experiments were conducted to explore the biodegradability of tannic acid-modified cellulose-based hydroplastic polymers. Figure 15 20 mm diameter discs of tannic acid-modified cellulose-based hydroplastic polymer were buried in natural soil (5 cm depth), and their microscopic degradation morphology evolution was observed through periodic sampling. The results showed that with prolonged burial time, the material surface gradually changed from an initial smooth and dense structure to a porous and rough morphology, accompanied by significant crack propagation and fragmentation. After 120 days of burial, the samples were almost completely degraded into debris, with a degradation rate exceeding 95%. This series of morphological changes indicates that the tannic acid-modified cellulose-based hydroplastic polymer material exhibits excellent biodegradability in natural soil environments. The results confirm that this hydroplastic polymer material has good environmental compatibility; 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 g of bleached softwood pulp cellulose was mechanically dissociated at 2500 rpm for 40 minutes to prepare a 1.5 wt% micron-sized cellulose suspension. After ultrasonic treatment at 500 W for 20 minutes, the suspension was homogenized under high pressure at 1200 bar 20 times to achieve nanoscale dissociation. Undissociated fibers were removed by centrifugation (10000 rpm, 10 minutes), the concentration was adjusted to 1.25 wt%, and stored at 4℃.

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

[0074] Synthesis of tannic acid-modified cellulose-based hydroplastic polymer: 200 g of 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 at -0.1 MPa for 10 minutes), the polymer was cast and dried at 40 °C for 3 hours to obtain a three-dimensional network structure hydroplastic polymer.

[0075] The hydroplastic polymer material prepared above exhibits excellent comprehensive properties: its tensile strength reaches 90.6±1.5MPa, demonstrating outstanding mechanical properties; simultaneously, the material has significant hydroplastic molding capability, enabling precise molding of complex shapes under room temperature immersion conditions, and the molding process can be repeated repeatedly, with specific conditions and processes identical to Example 1. Furthermore, the material exhibits excellent self-healing properties; under conditions of 25℃ and 80% relative humidity, it can almost completely repair surface scratches with a length of 350μm and a width of 20μm in just 1 hour, with a repair efficiency exceeding 95%. The hydroplastic polymer material also exhibits good recyclability (method identical to Example 1), and the mechanical strength of the recycled hydroplastic polymer material remains essentially unchanged from its initial state. Degradation performance tests show that the material degrades by more than 95% after being buried in natural soil for 120 days, demonstrating good biodegradability and environmental compatibility.

[0076] Example 3

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

[0078] 200 mL of a 1.25 wt% nanocellulose suspension was adjusted to pH 8.2 with 1.0 M tris(hydroxymethyl)aminomethane buffer, followed by the addition of 0.6 g of tannic acid. The mixture was reacted for 6 hours at a constant temperature of 25°C in a water bath with continuous oxygen flow (25 mL / min) at a stirring speed of 500 rpm, yielding a pale yellow, homogeneous suspension. This suspension was stored at 4°C in the dark for later use.

[0079] Synthesis of tannic acid-modified cellulose-based hydroplastic polymer: 200 g of tannic acid-modified nanocellulose suspension was reacted with 0.65 g of 1,8-octanediamine at 25 °C for 18 h. After degassing (degassing treatment at -0.1 MPa for 10 min), it was cast into molds and dried at 40 °C for 3 h to obtain a three-dimensional network structure hydroplastic polymer.

[0080] The resulting hydroplastic polymer material exhibits a tensile strength of 89.3 MPa, demonstrating excellent mechanical properties. It also exhibits excellent hydroplastic molding capability, achieving precise molding of complex shapes under room temperature immersion conditions. The molding process can be repeated repeatedly, with specific conditions and procedures identical to those in Example 1. The material can repair surface scratches of 350 μm × 20 μm within one hour at 25°C and 80% relative humidity, with a repair efficiency exceeding 96%. The hydroplastic polymer material demonstrates good recyclability (method as in Example 1), and its mechanical strength remains essentially equivalent to the initial material after recycling and reprocessing (retention rate > 95%). Furthermore, the material exhibits a degradation rate exceeding 95% after burial in natural soil for 120 days, demonstrating good biodegradability and environmental compatibility.

Claims

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

2. A method for preparing the tannic acid-modified cellulose-based hydroplastic polymer according to claim 1, characterized in that: Includes the following steps: First, surface-functionalized cellulose nanofibers were prepared via tannic acid grafting reaction, and then tannic acid-modified cellulose-based hydroplastic polymers were constructed based on a dynamic imine bond crosslinking mechanism.

3. The preparation method according to claim 2, characterized in that: Includes the following steps: 1) Tannic acid surface grafting: Tannic acid is grafted onto nanocellulose fibers in a tris(hydroxymethyl)aminomethane and oxygen-rich environment to convert tannic acid molecules containing phenolic groups into oxidized tannic acid with an α-hydroxy-orthoquinone structure, thereby obtaining tannic acid modified nanocellulose fibers. 2) Construction of dynamic crosslinking network: The tannic acid-modified nanocellulose fibers obtained in step 1) are crosslinked with polyamines through Schiff base reaction to form a dynamic imine bond network, thus 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 includes the following steps: a) Use a fiber dissociator to dissociate and pretreat bleached softwood pulp cellulose to obtain a cellulose suspension, and then sonicate it for 15-20 minutes. b) The cellulose suspension obtained in step a) is subjected to cyclic homogenization using a high-pressure homogenizer. After homogenization, it is centrifuged, and the concentration of the cellulose nanofiber suspension is adjusted as needed and stored below 4°C for later use.

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

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

7. The preparation method according to any one of claims 3-5, characterized in that: Step 2) involves mixing a tannic acid-modified nanocellulose fiber suspension with a polyamine at room temperature, reacting for 12–18 hours, then degassing, pouring the mixture into a mold, and drying to obtain a tannic acid-modified cellulose-based hydroplastic 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 tannic acid-modified nanocellulose fibers to polyamine is (1-10.5):(1-5.5).

9. The application of the tannic acid-modified cellulose-based hydroplastic polymer according to claim 1, characterized in that: Used as a substitute for plastics.

10. The application according to claim 9, characterized in that: The method for shaping or recycling tannic acid-modified cellulose-based hydroplastic polymers is as follows: at room temperature, soak in water for 3-5 minutes, then shape into the desired shape, and dry and cure at a temperature of 25-35°C. The above steps can be repeated repeatedly. Tannic acid-modified cellulose-based hydroplastic polymers can be recycled and reused through hot pressing or depolymerization. The hot pressing method is as follows: the water-plastic polymer material activated in water for 20 to 30 minutes is ground into fragments, and then 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: after stirring the hydroplastic polymer fragments in a 5wt% acetic acid aqueous solution at room temperature for 1.5 to 5 hours, the acetic acid is removed by vacuum distillation, polyamine is added, and the mixture is stirred and reacted at a temperature of 20 to 30°C for 8 to 12 hours. After degassing, the mixture is re-poured into a mold and dried to form the final product. The amount of polyamine added is 5 to 50 wt% of the mass of the hydroplastic polymer.

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