A fully bio-based hydroplastic polymer material based on imine bonds, its preparation method and its application

Abstract

This invention discloses a fully bio-based hydroplastic polymer material based on imine bonds, its preparation method, and its applications. The general structural formula of the fully bio-based hydroplastic polymer based on imine bonds is: where a, b, and c are all positive integers, and 1 ≤ a ≤ 1000, 1 ≤ b ≤ 10, 1 ≤ c ≤ 10; a:b:c = (1-10):(10-1):(10-1); R1 is -NH or -CH2. The fully bio-based hydroplastic polymer based on imine bonds of this invention not only exhibits excellent mechanical strength but also possesses arbitrary molding capability under water assistance, enabling the realization of complex geometric shapes that are difficult to achieve with traditional heat treatment; it also exhibits long-lasting temperature resistance, remaining stable in extremely cold, extremely hot, and alternating cold and hot environments, and possesses strong self-healing properties; furthermore, the material can be effectively decomposed through physical or chemical methods, exhibiting excellent recycling performance; after the end of its service life, it can achieve efficient degradation in the natural environment, which is of great significance for promoting material recycling and reducing resource waste.

Description

Technical Field

[0001] This invention relates to an imine-bonded, fully bio-based hydroplastic polymer material, its preparation method, and its applications, belonging to the field of polymer materials. Background Technology

[0002] Plastics, due to their lightweight and cost-effectiveness, play an indispensable role in modern life, and their demand is growing at an astonishing rate. However, plastic pollution, including its environmental impact during production, use, and disposal, is becoming increasingly serious, making sustainable development a critical issue that urgently needs to be addressed. Currently, a vibrant research area is the development of bio-based materials using renewable resources to replace non-degradable plastics. Furthermore, processing methods and recyclability have received widespread attention in order to extend the lifespan of materials. Hydroplastic molding, as a technology that uses a reversible process triggered by water molecules to shape solid materials, is undoubtedly a green and gentle solution. Nevertheless, the precise structural design of hydroplastic polymers, the complex synthesis pathways, and the high standards required for sustainability, as well as the poor mechanical strength and humidity stability of hydroplastic polymers in existing technologies, limit their potential for practical applications. Summary of the Invention

[0003] To address the problems of poor mechanical property stability and insufficient shape retention in existing hydroplastic polymers, this invention provides a fully bio-based hydroplastic polymer material based on imine bonds, its preparation method, and its applications.

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

[0005] A fully bio-based hydroplastic polymer based on imine bonds, with the following general structural formula:

[0006]

[0007] Where a, b and c are all positive integers, and 1≤a≤1000, 1≤b≤10, 1≤c≤10; a:b:c=(1-10):(10-1):(10-1);

[0008] R1 is either -NH or -CH2.

[0009] The aforementioned hydroplastic polymer material not only exhibits excellent mechanical strength but also possesses the ability to be molded into any shape under water-assisted molding. This material is prepared from renewable biomass and possesses a dense, dynamic imine bond network and a compact, fine microstructure. This unique structural network enables the material to achieve complex geometries that are difficult to achieve with traditional heat treatment during water-assisted molding. Furthermore, the material can be effectively decomposed through physical or chemical methods, exhibiting excellent recyclability. Finally, at the end of its service life, the material can be efficiently degraded in the natural environment, which is of great significance for promoting material recycling and reducing resource waste.

[0010] The above-mentioned method for preparing fully bio-based hydroplastic polymers based on imine bonds involves constructing a three-dimensional imine bond crosslinking network with dynamic reversible properties using amino-grafted cellulose derivatives to obtain fully bio-based hydroplastic polymer materials based on imine bonds.

[0011] To ensure product quality, as a preferred embodiment, the preparation method of the above-mentioned fully bio-based hydroplastic polymer based on imine bonds includes the following steps:

[0012] 1) Amino-grafted nanocellulose fibers are obtained by reacting carboxyl-containing nanocellulose fibers with polyamine compounds of different carbon chain lengths under the catalysis of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl) and N-hydroxysuccinimide (NHS), so that the amino groups on the nanocellulose fibers with carboxyl groups form stable amide bonds.

[0013] 2) An imine-based fully bio-based hydroplastic polymer was prepared by reacting amino-grafted nanocellulose fibers with dialdehydes of different carbon chain lengths via a Schiff base reaction.

[0014] In step 1) above, a nanocellulose fiber dispersion with a solid content of 1.3 to 1.8 wt% is preferably used for the reaction, and the solid content of the obtained amino-grafted nanocellulose fiber dispersion is 2.8 to 3.4 wt%.

[0015] The aforementioned fully bio-based hydroplastic polymer based on imine bonds is a fully bio-based network structure based on dynamic imine bond crosslinking.

[0016] As one specific implementation scheme, the above-mentioned carboxyl-containing nanocellulose fibers are prepared by the following method: using bleached softwood pulp as raw material, the nanocellulose fibers with carboxyl groups are obtained by catalytic oxidation treatment with 2,2,6,6-tetramethylpiperidine oxide.

[0017] To optimize the yield, the specific preparation process of carboxyl-containing cellulose nanofibers was further optimized as follows: At room temperature, sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxo radicals were first dissolved in deionized water, followed by the addition of bleached softwood pulp. Under an alkaline environment maintaining the system pH between 10.0 and 10.2, sodium hypochlorite solution (available chlorine content ≥5%) was slowly added dropwise to ensure sufficient contact and complete reaction with the reactants, thereby obtaining carboxyl-containing cellulose nanofibers. After the reaction, the pulp was repeatedly washed and filtered with deionized water until the pH of the filtrate reached neutral to thoroughly remove residual reaction reagents and byproducts. Finally, the washed pulp was collected and further processed using a homogenizer to obtain uniformly dispersed cellulose nanofibers. The processed cellulose nanofibers were then stored in a refrigerator at 4°C for subsequent experiments.

[0018] Unless otherwise specified, all percentages in this application are percentages by mass.

[0019] To further improve reaction efficiency, the mass ratio of sodium bromide to 2,2,6,6-tetramethylpiperidine-1-oxo radical is preferably controlled within the range of (1–5):(0.1–0.5) to ensure high reaction efficiency and product selectivity. Furthermore, the ratio between the mass (in grams) of bleached softwood pulp and the volume (in milliliters) of sodium hypochlorite solution should be controlled within the range of (0.5–1):(2–4).

[0020] To ensure the quality of the obtained polymer, step 1) is as follows: carboxyl-containing nanocellulose fibers are mixed with polyamine compounds of different carbon chain lengths at a temperature of 20-30°C and stirred for 8-10 minutes. Then, a mixed catalyst of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide is added, and the reaction is stirred for 8-12 hours. After purification, amino-grafted nanocellulose fibers are obtained.

[0021] To further purify the reaction products, a dialysis bag with a molecular weight cutoff of 3.5 kDa was used for dialysis in deionized water for 2–3 days to effectively remove unreacted monomers and catalysts, thereby obtaining high-purity amino-grafted nanocellulose fibers.

[0022] To balance reaction efficiency and product quality, in step 1), the polyamine compound is at least one of 1,4-butanediamine, 1,5-diaminopentane, 1,6-hexanediamine, 1,8-octanediamine, 1,10-diaminodecane, or polyethyleneimine, more preferably polyethyleneimine, 1,8-octanediamine, or 1,10-diaminodecane.

[0023] To balance reaction efficiency and product quality, in step 1), the mass ratio of carboxyl-containing nanocellulose fibers, polyamine compound, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide is (1-5.5):(1.5-10.5):(0.1-3.5):(0.1-4.5).

[0024] To balance reaction efficiency and product quality, step 2) involves mixing amino-grafted nanocellulose fibers with dialdehydes of different carbon chain lengths at a temperature of 20–30°C and stirring for 8–12 hours to ensure that a fully bio-based hydroplastic polymer based on imine bonds is obtained through Schiff base reaction. The polymer is then poured into a mold and dried to form the final product.

[0025] To further improve the quality of the polymer, in step 2), the dialdehyde is at least one of glyoxal, glutaraldehyde, adipaldehyde, or octaldehyde, and more preferably at least one of glyoxal, glutaraldehyde, or octaldehyde; the mass ratio of amino-grafted nanocellulose fibers to dialdehyde is (1-5):(1.5-10.5).

[0026] The aforementioned fully bio-based hydroplastic polymers based on imine bonds can be used to replace traditional plastics.

[0027] The aforementioned fully bio-based hydroplastic polymer based on imine bonds can be molded with water assistance. The specific steps include: (1) immersing the hydroplastic polymer sample in water for 3-5 minutes and weaving it into the desired shape using a mold; (2) air-drying it in an environment with room temperature and relative humidity of 30-40% for 20-30 minutes to solidify and shape it. The aforementioned steps (1)-(2) can be repeated repeatedly, that is, the water-assisted molding steps can be repeated as needed. The aforementioned steps (1) and (2) are both performed at room temperature.

[0028] The aforementioned fully bio-based hydroplastic polymer based on imine bonds can be recycled and reused through hot pressing or depolymerization. The hot pressing method involves grinding the hydroplastic polymer material activated in water for 20–30 min into fragments, and then hot-pressing it for 8–10 minutes at a temperature of 25–35°C and a pressure of 8–10 MPa. The depolymerization method involves stirring the hydroplastic polymer in a 5 wt% acetic acid aqueous solution for 1.5–2 h at room temperature, removing the acetic acid by vacuum distillation, adding dialdehyde, mixing at 20–30°C, stirring and reacting for 8–12 hours, then re-casting into a mold and drying. The aforementioned drying and molding process involves drying in an oven at 30–40°C for 1–3 h. The amount of dialdehyde added is 10–50 wt% of the mass of the hydroplastic polymer.

[0029] The mechanical strength of the fully bio-based hydroplastic polymer based on imine bonds remains essentially unchanged after recycling and reuse, just like in its initial state.

[0030] Any techniques not mentioned in this invention are based on existing technologies.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. Simplified and efficient process: The production process covered by the core technology of this invention can be smoothly executed without additional pressure, which greatly simplifies the production process and improves the convenience of operation, thus providing convenient conditions for realizing large-scale industrial production.

[0033] 2. Combining Durability and Environmental Friendliness: Addressing the urgent need for recycling and reusing non-degradable waste, this invention innovatively utilizes nanocellulose as a building block to construct a water-plastic polymer that integrates high mechanical strength, durable temperature resistance, efficient recyclability, and remodeling capabilities. It is stable in extremely cold, extremely hot, and alternating hot and cold environments, and exhibits strong self-healing properties. This material not only provides a solution to environmental pollution problems but also closely aligns with sustainable development economic strategies.

[0034] 3. Flexible and Versatile Morphology: Through precise design, this invention successfully constructs a dynamic imine bond network framework activated by water molecules, thereby creating a high-strength and highly stable hydroplastic polymer material. This material, thanks to a simple wet molding process, can be easily transformed into diverse stable forms and maintains geometrical stability for over 10 months in an environment with 90% relative humidity. It also retains its intact shape in various organic solvents, demonstrating its exceptional shape stability.

[0035] 4. Excellent recyclability: The water-plastic polymer material of this invention can be efficiently recycled through both physical and chemical methods, and the recycled material still has excellent properties, significantly extending the service life of the material and opening up new avenues for resource recycling.

[0036] 5. Naturally degradable, highly efficient and environmentally friendly: The fully bio-based hydroplastic polymer material prepared by this invention can be efficiently degraded in just 150 days under natural conditions, effectively avoiding the accumulation of materials in the environment, which perfectly matches the core concept of sustainable development. Attached Figure Description

[0037] Figure 1 Transmission electron microscopy image of the carboxyl-containing cellulose nanofibers prepared in Example 1.

[0038] Figure 2 The infrared spectrum of the carboxyl-containing cellulose nanofibers prepared in Example 1.

[0039] Figure 3 The infrared spectrum of the amino-grafted cellulose nanofibers prepared in Example 1 is shown.

[0040] Figure 4 Solid-state carbon NMR spectrum of amino-grafted cellulose nanofibers prepared in Example 1.

[0041] Figure 5 The image shows the X-ray diffraction pattern of amino-grafted nanocellulose fibers in Example 1.

[0042] Figure 6 The flowchart shows the preparation process of the fully bio-based hydroplastic polymer material prepared in Example 1.

[0043] Figure 7 This is a schematic diagram of the structure of the fully bio-based hydroplastic polymer material prepared in Example 1.

[0044] Figure 8 The infrared spectrum of the fully bio-based hydroplastic polymer material prepared in Example 1 is shown.

[0045] Figure 9 The solid-state carbon NMR spectrum of the fully bio-based hydroplastic polymer material prepared in Example 1.

[0046] Figure 10 The images show the surface scanning electron microscope (SEM) image and energy-dispersive X-ray spectroscopy (EDX-ray spectroscopy) image of the all-bio-based hydroplastic polymer material prepared in Example 1.

[0047] Figure 11 The image shows the dynamic thermomechanical analysis spectrum of the fully bio-based hydroplastic polymer material prepared in Example 1.

[0048] Figure 12 This is a photograph of the fully bio-based hydroplastic polymer material prepared in Example 1.

[0049] Figure 13 The shape stability of the fully bio-based hydroplastic polymer material prepared in Example 1 under different humidity environments.

[0050] Figure 14 Stress-strain diagrams of the fully bio-based hydroplastic polymer material prepared in Example 1 under different humidity environments.

[0051] Figure 15 The tensile strength diagrams for the fully bio-based hydroplastic polymer material prepared in Example 1 under different humidity conditions are shown.

[0052] Figure 16 This is a comparison chart of the tensile strength of the fully bio-based hydroplastic polymer material prepared in Example 1 and widely used plastics.

[0053] Figure 17 The stability diagram of the fully bio-based hydroplastic polymer material prepared in Example 1 in different organic solvents.

[0054] Figure 18The tensile strength of the fully bio-based hydroplastic polymer material prepared in Example 1 before and after 30 rapid thermal shock cycles.

[0055] Figure 19 This is a schematic diagram of the self-healing process of the fully bio-based hydroplastic polymer material prepared in Example 1, and stress-strain curves before and after self-healing.

[0056] Figure 20 This is a schematic diagram illustrating the recycling and reuse of the fully bio-based hydroplastic polymer material prepared in Example 1.

[0057] Figure 21 This is a photograph of the degradation process of the fully bio-based hydroplastic polymer material prepared in Example 1. 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 examples were conducted at room temperature (20–25°C). Unless otherwise specified, all examples were conducted at a stirring speed of 500 rpm.

[0060] Example 1

[0061] Preparation of cellulose nanofibers: First, 15g of bleached softwood pulp (UPM Kaukas pulp mill, UPM softwood pulp) was weighed and added to 1000mL of deionized water. The mixture was stirred continuously at 400rpm for 20 minutes to ensure uniform dispersion of the bleached softwood pulp in the deionized water. Then, 1.5g of sodium bromide and 0.25g of 2,6,6-tetramethylpiperidine-1-oxo radicals were added to the system, and stirring was continued at room temperature until all additives were completely dissolved and uniformly dispersed in the system. Next, 40mL of sodium hypochlorite solution (with an available chlorine content of 13wt%) was added dropwise to the above mixture at a rate of 30 drops / min using a constant pressure funnel. Simultaneously, the pH of the reaction system was adjusted to 10.0–10.2 using 0.1M sodium hydroxide solution, and the reaction was stirred for 8 hours. After the reaction was completed, the filtrate was repeatedly washed with deionized water until the ionic conductivity of the filtrate was less than 50 μS / cm. The slurry was collected and processed by a homogenizer to obtain a nanocellulose fiber dispersion with carboxyl groups, which was then stored in a refrigerator at 4°C for later use.

[0062] To verify the morphological characteristics of the prepared carboxyl-containing cellulose nanofibers, transmission electron microscopy was used for observation. The results are shown in [Figure number missing]. Figure 1 The images clearly demonstrate the typical morphology of nanofibers. Furthermore, infrared spectroscopy analysis (…) Figure 2The chemical structural changes of cellulose nanofibers with carboxyl groups were further investigated, particularly after oxidation treatment with 2,2,6,6-tetramethylpiperidine-1-oxy radicals, at 1604 cm⁻¹. -1 A distinct absorption peak was observed at [value], which is attributed to the carboxyl group (-COO). - The discovery of asymmetric stretching vibrations strongly supports the modification of cellulose structure by 2,2,6,6-tetramethylpiperidine-1-oxy radicals.

[0063] Preparation of amino-grafted cellulose nanofibers: First, 100g of a dispersion of carboxyl-containing cellulose nanofibers (1.5% solids content) was thoroughly mixed with 3g of polyethyleneimine (Shanghai Aladdin Biochemical Technology Co., Ltd., polyethyleneimine: 99%, MW600) at 25℃ for 10min. Then, a mixed catalyst of 1.5g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.2g of N-hydroxysuccinimide was added, and the mixture was stirred continuously for 12 hours. The reaction product was then dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 3.5kDa to remove unreacted monomers and catalyst, yielding amino-grafted cellulose nanofibers with a solids content of 3.2wt%. Figure 3 Infrared spectroscopy of amino-grafted nanocellulose fibers showed that at 1651 cm⁻¹... -1 The characteristic peaks belonging to O=C-NH and 1457cm appeared at this location. -1 The characteristic peak at the -NH2 position indicates that polyethyleneimine was successfully grafted onto cellulose nanofibers. Solid-state carbon NMR spectrum of amino-grafted cellulose nanofibers ( Figure 4 The study demonstrated significant chemical shifts in cellulose nanofibers at 105.86 ppm (C-1), 72.73 ppm, 74.35 ppm, 76.33 ppm (C-2, C-3, and C-5), 89.98 ppm (C-4), 65.40 ppm (C-6), 173.25 ppm (C-7, -COOH), and 45.21 ppm (C-8). The presence of C-8, in particular, confirms the successful termination of polyethyleneimine onto the cellulose nanofibers. X-ray diffraction patterns of amino-grafted cellulose nanofibers are shown below. Figure 5 The results show that the grafting reaction does not change the crystal structure of cellulose nanofibers.

[0064] Synthesis of fully bio-based hydroplastic polymers based on imine bonds: such as Figure 6As shown, 1g of glutaraldehyde aqueous solution (glutaraldehyde to water volume ratio of 1:1) was dissolved in 10g of amino-grafted cellulose nanofibers (3.2wt% solid content). The mixture was stirred and reacted at room temperature for 12 hours, then poured into a mold and finally dried in an oven at 40℃ for 1 hour to obtain a fully bio-based hydroplastic polymer based on imine bonds, the structure of which is shown below. Figure 7 As shown. Infrared spectrum of the fully bio-based hydroplastic polymer ( Figure 8 The figure shows that at 1637cm -1 The appearance of a new characteristic peak belonging to C=N indicates the successful synthesis of the all-bio-based hydroplastic polymer. Solid-state carbon NMR spectrum of amino-grafted cellulose nanofibers ( Figure 9 A C-9 bond belonging to an imine bond was observed at 148.62 ppm. Additionally, the scanning electron microscope image (...) Figure 10 The prepared water-plastic polymer material showed a smooth and flat surface, and the energy-dispersive X-ray spectroscopy spectrum also showed a uniform distribution of C, O, and N. Dynamic thermomechanical analysis spectrum ( Figure 11 The results show the glass transition temperature (T0) of the synthesized fully bio-based hydroplastic polymer material. g The temperature was 80.23℃.

[0065] Effect evaluation:

[0066] All-bio-based hydroplastic polymer materials based on imine bonds can achieve shape transformation into various two-dimensional or three-dimensional shapes under water-assisted conditions. Figure 12 The water-assisted molding process includes: (1) immersing the hydroplastic polymer sample in water for 5 minutes at room temperature, and then shaping it using a mold while it is wet; (2) air-drying it for 30 minutes in an environment with room temperature and relative humidity of 30-40%. Figure 13 As shown, the shape stability of this hydroplastic polymer material under different humidity environments was evaluated. The hydroplastic polymer material exhibited excellent shape stability under extreme humidity conditions (90% RH), maintaining its shape without deformation for 10 months. Furthermore, the tensile strength of the fully bio-based hydroplastic polymer material based on imine bonds is as follows: Figures 14-16As shown, unlike other water-plastic materials which are highly sensitive to humidity, this material exhibits high mechanical stability over a wide humidity range. It displays a high tensile strength of 93.9 MPa in the Original state (10% humidity), and even after being placed at 90% humidity for 48 hours, the tensile strength remains at 78.6 MPa. It is worth noting that the tensile strength (72.4 MPa) of this hydroplastic polymer material after being placed at 90% humidity for 15 days is far higher than that of currently commercially available non-degradable plastics, such as polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), acrylonitrile-butadiene-styrene polymer (ABS), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and polycarbonate (PC), as well as degradable plastics such as polybutylene adipate-terephthalate coester (PBAT), polyhydroxyalkanoate (PHA), polyhydroxybutyrate-valerate (PHBV), polybutylene succinate (PBS), polycaprolactone (PCL), and polylactic acid (PLA). This material has broad application prospects as a substitute for non-degradable plastics.

[0067] like Figure 17 As shown, fully bio-based hydroplastic polymer materials are immersed in various high-polarity, medium-polarity, and low-polarity solvents ( Figure 17 In the figures, a represents the initial state, and b represents the state after 7 days. From left to right in both figures a and b are: N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), ethanol (EtOH), acetone (Ace), tetrahydrofuran (THF), dichloromethane (DCM), and n-hexane (n-Hex). After 7 days, these substances still maintain their intact morphology. Figure 18 As shown, the strength of the fully bio-based hydroplastic polymer material decreased only slightly after undergoing 30 rapid thermal shock cycles with a temperature difference of -70°C to 150°C, indicating that it has a strong resistance to thermal shock damage and can be used in extremely high and low temperature environments.

[0068] The self-healing properties of this hydroplastic polymer material Figure 19 The self-healing properties of a fully bio-based hydroplastic polymer material were demonstrated. Thanks to the abundant imine bonds in its dynamic network structure, this material exhibits remarkable self-healing capabilities. A scratch was applied to the material surface, creating a break (800 μm in length and 20 μm in width), and the repair process was monitored using optical microscopy. After placing the damaged hydroplastic polymer material at 25°C and 90% RH for 24 hours, the damage significantly improved, with the cracks completely healed. The tensile strength after healing showed no significant decrease compared to before the breakage (93.4 MPa vs. 87.9 MPa). Furthermore, the hydroplastic polymer material exhibited excellent recyclability. Figure 20As shown, 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). The mechanical strength remains 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 30 mmHg), adding a glutaraldehyde aqueous solution (glutaraldehyde to water volume ratio 1:1, glutaraldehyde mass being 43 wt% of the hydroplastic polymer material mass), mixing at room temperature, stirring and reacting for 12 h, then recasting into a mold and drying at 40℃ for 1 h. The mechanical strength remains essentially unchanged from the initial state (change < 8%). Notably, soil degradation experiments were conducted to explore the biodegradability of the hydroplastic polymer material. Figure 21 A hydroplastic polymer material (20 mm diameter discs) was buried in natural soil (10 cm deep), and its microscopic degradation morphology was monitored over time. The surface of the hydroplastic polymer material gradually became rougher over time, and it almost completely degraded into small pieces after 150 days of burial in the soil, exhibiting good biodegradability. The results indicate that the hydroplastic polymer material has excellent biodegradability, is degradable in natural soil, and can prevent environmental pollution after treatment.

[0069] Example 2

[0070] Weigh 15 g of bleached softwood pulp and add it to 1 L of deionized water. Stir continuously at 400 rpm for 20 minutes. Then, add 1.8 g of sodium bromide and 0.2 g of 2,2,6,6-tetramethylpiperidine-1-oxo radical to the system and continue stirring at room temperature until the additives are completely dissolved and uniformly dispersed. Add 40 mL of sodium hypochlorite solution (with an available chlorine content of 13 wt%) dropwise to the mixture at a rate of 30 drops / min using a constant-pressure dropping funnel. Simultaneously, adjust the pH of the reaction system to 10.0–10.2 using 0.1 M sodium hydroxide solution and stir the reaction for 10 hours. After the reaction is complete, wash repeatedly with deionized water until the ionic conductivity of the filtrate drops below 50 μS / cm. Collect the resulting pulp and treat it using a homogenizer. Finally, store the resulting carboxyl-containing nanocellulose fiber dispersion at 4°C for later use.

[0071] 100 g of a 1.5% solids dispersion of carboxyl-containing cellulose nanofibers was mixed thoroughly with 2.3 g of 1,8-octanediamine at 25 °C for 10 min. Then, a catalyst consisting of 1.65 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.5 g of N-hydroxysuccinimide was added, and the mixture was stirred continuously for 10 h. The reaction product was then dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 3.5 kDa to remove unreacted monomers and catalyst, yielding amino-grafted cellulose nanofibers with a solids content of 3.0 wt%.

[0072] 1.5 g of glyoxal was dissolved in 15 g of amino-grafted cellulose nanofibers (3.0 wt% solids) and reacted continuously at room temperature for 12 hours to synthesize a fully bio-based hydroplastic polymer through the formation of imine bonds. The polymer was then poured into a mold and dried in an oven at 40°C for 1 hour to solidify.

[0073] The hydroplastic polymer material prepared above achieved a tensile strength of 90.6 MPa, exhibiting excellent hydroplastic molding (method as in Example 1) and long-term shape stability (remaining unchanged for 10 months at 80% RH). The hydroplastic polymer material can almost completely repair scratches with a length of 230 μm, a width of 40 μm, and a depth of 50 μm within 1 hour at room temperature. The hydroplastic polymer material also exhibits good recyclability (method as in Example 1), and the mechanical strength of the recycled hydroplastic polymer material remains essentially unchanged from its initial state. It exhibits complete degradation in the natural environment within 150 days.

[0074] Example 3

[0075] 15 g of bleached softwood pulp was added to 1 L of deionized water and stirred continuously at 400 rpm for 20 minutes. Then, 2.2 g of sodium bromide and 0.23 g of 2,2,6,6-tetramethylpiperidine-1-oxo radicals were added to the system at room temperature and stirred continuously until the additives were completely dissolved and uniformly dispersed. Next, 42.5 mL of sodium hypochlorite solution (13 wt% available chlorine) was added dropwise to the reaction system at a rate of 30 drops / min using a constant-pressure dropping funnel, while the pH of the system was finely adjusted between 10 and 10.2 using 0.1 M sodium hydroxide solution. The reaction was stirred for 10 hours. After the reaction was complete, the mixture was repeatedly washed with deionized water until the pH stabilized to neutral and the ionic conductivity of the filtrate decreased to below 45 μS / cm. The resulting pulp was collected and homogenized. Finally, the resulting carboxyl-containing nanocellulose fiber dispersion was stored at 4°C for subsequent experiments.

[0076] 100 g of a dispersion of carboxyl-containing cellulose nanofibers (1.5% solids content) was mixed thoroughly with 2.5 g of 1,10-decanediamine at 25 °C for 10 min. Then, a catalyst consisting of 1.7 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.55 g of N-hydroxysuccinimide was added, and the mixture was stirred continuously for 8 hours. The reaction product was then dialyzed in deionized water for 3 days using a dialysis bag with a molecular weight cutoff of 3.5 kDa to obtain amino-grafted cellulose nanofibers with a solids content of 3.2 wt%.

[0077] 1.8 g of octanedialdehyde was dissolved in 25 g of amino-grafted cellulose nanofibers (3.2 wt% solids) and reacted continuously at room temperature for 12 hours. The reaction was carried out by forming imine bonds, and the mixture was poured into a mold and dried in an oven at 40 °C for 1 hour to form a fully bio-based hydroplastic polymer.

[0078] The hydroplastic polymer material prepared above exhibits a tensile strength of 88.2 MPa, demonstrating excellent hydroplastic molding (under the same conditions as Example 1) and long-term shape stability (remaining unchanged for 10 months at 80% RH). The hydroplastic polymer material can completely repair scratches with a length of 300 μm, a width of 45 μm, and a depth of 35 μm within 1.5 hours at room temperature. This room-temperature self-healing hydroplastic film material becomes malleable upon contact with water and can maintain its shape for a long time in high humidity environments. The mechanical strength of the recycled and reprocessed hydroplastic polymer material remains essentially unchanged from its initial state. The hydroplastic polymer material can achieve efficient degradation in the natural environment within 200 days.

Claims

1. A fully bio-based hydroplastic polymer based on imine bonds, characterized in that: Its general structural formula is: ， Where a, b and c are all positive integers, and 1 < a ≤ 1000, 1 ≤ b ≤ 10, 1 ≤ c ≤ 10; a:b:c = (1-10):(10-1):(10-1); R1 is: -CH2; Alternatively, the general structural formula of a fully bio-based hydroplastic polymer is: ， a is a positive integer, 1 < a ≤ 1000. The preparation method of the fully bio-based hydroplastic polymer includes the following steps: amino-grafted nanocellulose fibers with carboxyl groups are reacted with polyethyleneimine under the catalysis of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to form stable amide bonds between the amino groups and the carboxyl groups on the nanocellulose fibers, thereby obtaining amino-grafted nanocellulose fibers; wherein, polyethyleneimine MW 600; amino-grafted nanocellulose fibers are reacted with dialdehyde via a Schiff base reaction to obtain a fully bio-based hydroplastic polymer based on imine bonds.

2. A method for preparing the fully bio-based hydroplastic polymer based on imine bonds as described in claim 1, characterized in that: A three-dimensional imine bond crosslinking network with dynamic reversible properties was constructed by amino-grafted cellulose derivatives, resulting in a fully bio-based hydroplastic polymer material based on imine bonds.

3. The preparation method according to claim 2, characterized in that: Includes the following steps: 1) Amino-grafted nanocellulose fibers are obtained by reacting carboxyl-containing nanocellulose fibers with polyamines of different carbon chain lengths under the catalysis of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, so that the amino groups on the carboxyl groups of the nanocellulose fibers form stable amide bonds. 2) An imine-based fully bio-based hydroplastic polymer was prepared by reacting amino-grafted nanocellulose fibers with dialdehydes of different carbon chain lengths via a Schiff base reaction.

4. The preparation method according to claim 3, characterized in that: Step 1) involves mixing carboxyl-containing nanocellulose fibers with polyamine compounds of different carbon chain lengths at 20-30°C and stirring for 8-10 minutes. Subsequently, a mixed catalyst of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide is added, and the mixture is stirred for 8-12 hours. After purification, amino-grafted nanocellulose fibers are obtained. The purification process uses a dialysis bag with a molecular weight cutoff of 3.5 kDa and involves dialysis in deionized water for 2-3 days to obtain amino-grafted nanocellulose fibers.

5. The preparation method according to claim 3 or 4, characterized in that: In step 1), the polyamine compound is at least one of 1,4-butanediamine, 1,6-hexanediamine, 1,8-octanediamine, 1,10-diaminodecane, or polyethyleneimine.

6. The preparation method according to claim 3 or 4, characterized in that: In step 1), the mass ratio of carboxyl-containing nanocellulose fibers, polyamine compound, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide is (1-5.5):(1.5-10.5):(0.1-3.5):(0.1-4.5).

7. The preparation method according to claim 3 or 4, characterized in that: Step 2) involves mixing amino-grafted nanocellulose fibers with dialdehydes of different carbon chain lengths at a temperature of 20-30°C, stirring and reacting for 8-12 hours, pouring the mixture into a mold, drying and shaping it to obtain a fully bio-based hydroplastic polymer based on imine bonds.

8. The preparation method according to claim 3 or 4, characterized in that: In step 2), the dialdehyde is at least one of glyoxal, glutaraldehyde, adipaldehyde, or octaldehyde; the mass ratio of amino-grafted nanocellulose fibers to dialdehyde is (1-5):(1.5-10.5).

9. The application of the fully bio-based hydroplastic polymer based on imine bonds as described in claim 1, characterized in that: Used as a substitute for plastics.

10. The application as described in claim 9, characterized in that: The fully bio-based hydroplastic polymer based on imine bonds can be molded with water assistance. The specific steps include: (1) immersing the hydroplastic polymer sample in water for 3-5 minutes and weaving it into the desired shape; (2) air drying in an environment with room temperature and relative humidity of 30-40% for 20-30 minutes to solidify and form the polymer. Steps (1) and (2) can be repeated. Alternatively, fully bio-based hydroplastic polymers based on imine bonds can be recycled and reused through hot pressing or depolymerization methods; 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 hot-pressed for 0.1 to 1 h at a temperature of 75 to 95°C and a pressure of 1 to 8 MPa. The depolymerization method is as follows: the water-plastic polymer is stirred in a 5wt% acetic acid aqueous solution at room temperature for 1.5-2 h, the acetic acid is removed by vacuum distillation, dialdehyde is added, and the mixture is stirred at 20-30℃ for 8-12 hours. The mixture is then re-poured into a mold and dried to form the final product. The amount of dialdehyde added is 10-50wt% of the mass of the water-plastic polymer.

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