Full-bio-based water-plastic polymer material based on imine bond as well as preparation method and application of full-bio-based water-plastic polymer material

Abstract

The invention discloses an imine bond-based full-bio-based water-plastic polymer material as well as a preparation method and application thereof. A, b and c are positive integers, a is greater than or equal to 1 and less than or equal to 1000, b is greater than or equal to 1 and less than or equal to 10, and c is greater than or equal to 1 and less than or equal to 10; a: b: c = (1-10): (10-1): (10-1); in the formula, R1 is-NH or-CH2. The imine bond-based full-bio-based water-plastic polymer disclosed by the invention not only shows excellent mechanical strength, but also has any forming capability under water assistance, and can realize a complex geometric form which is difficult to achieve by traditional heat treatment; the coating is durable in temperature resistance, can be stably used in extremely cold, extremely hot and alternate cold and hot environments, and is high in self-repairing performance; in addition, through a physical or chemical method, the material can be effectively deconstructed and shows excellent recycling performance; and after the service life is ended, high-efficiency degradation can be realized in the natural environment, which is of great significance for promoting the cyclic utilization of materials and reducing the waste of resources.

Description

Technical Field

[0001] The present invention relates to a fully bio-based hydroplastic polymer material with imine bonds, a preparation method thereof, and an application thereof, belonging to the field of polymer materials. Background Art

[0002] Plastics play an indispensable role in modern life due to their light weight and cost-effectiveness, and their demand is growing at an alarming rate. However, the problem of plastic pollution, including the environmental impact during production, use, and disposal, is becoming increasingly severe, making sustainable development a key issue that needs to be addressed urgently. Currently, a vibrant research field is to develop bio-based materials using renewable resources in order to replace non-degradable plastics. In addition, in order to extend the service life of materials, their processing methods and recyclability have also received extensive attention. The hydroforming process, 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 route, and the high standards for sustainability, as well as problems such as poor mechanical strength and humidity stability of hydroplastic polymers in the prior art, limit their potential in practical applications. Summary of the Invention

[0003] In order to solve the problems of poor mechanical property stability and insufficient shape persistence of hydroplastic polymers in the prior art, the present invention provides a fully bio-based hydroplastic polymer material with imine bonds, a preparation method thereof, and an application thereof.

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

[0005] A fully bio-based hydroplastic polymer with imine bonds, the general structural formula of which is:

[0006]

[0007] wherein, 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] R 1 is: -NH or -CH 2 in.

[0009] The above-mentioned water-plastic polymer material not only exhibits excellent mechanical strength but also has the ability to be formed arbitrarily with the assistance of water. This material is prepared from renewable biomass and has a dense dynamic imine bond network and a compact and fine microstructure. This unique structural network endows the material with the ability to achieve complex geometric shapes during water-assisted forming that are difficult to achieve by traditional heat treatment. In addition, through physical or chemical methods, this material can be effectively deconstructed, demonstrating excellent recycling performance. Finally, after the end of its service life, this material can be efficiently degraded in the natural environment, which is of great significance for promoting the recycling of materials and reducing resource waste.

[0010] The preparation method of the above-mentioned imine bond-based all-bio-based water-plastic polymer constructs a three-dimensional imine bond cross-linked network with dynamic reversibility through amino grafted cellulose derivatives to obtain an imine bond-based all-bio-based water-plastic polymer material.

[0011] To ensure product quality, as one of the preferred implementation solutions, the preparation method of the above-mentioned imine bond-based all-bio-based water-plastic polymer includes the following steps:

[0012] 1) A nano-cellulose fiber with a carboxyl group reacts with polyamine compounds with different carbon chain lengths under the catalysis of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (abbreviated as EDC·HCl) and N-hydroxysuccinimide (abbreviated as NHS) to form stable amide bonds between the amino group and the carboxyl group on the nano-cellulose fiber with a carboxyl group, thereby obtaining amino grafted nano-cellulose fiber;

[0013] 2) The amino grafted nano-cellulose fiber reacts with dialdehydes with different carbon chain lengths through a Schiff base reaction to prepare an imine bond-based all-bio-based water-plastic polymer.

[0014] In the above step 1), it is preferably to use a nano-cellulose fiber dispersion with a carboxyl group and a solid content of 1.3-1.8 wt% for the reaction, and the obtained amino grafted nano-cellulose fiber dispersion has a solid content of 2.8-3.4 wt%.

[0015] The above-mentioned imine bond-based all-bio-based water-plastic polymer is an all-bio-based network structure based on dynamic imine bond cross-linking.

[0016] As one of the specific implementation solutions, the above-mentioned nano-cellulose fiber with a carboxyl group is prepared as follows: Using bleached softwood pulp as the raw material, it is catalytically oxidized by 2,2,6,6-tetramethylpiperidine oxide to obtain a nano-cellulose fiber with a carboxyl group.

[0017] To optimize the yield, the specific preparation process of nano-cellulose fibers with carboxyl groups is further preferably as follows: At room temperature, first dissolve sodium bromide and 2,2,6,6-tetramethylpiperidine-1-oxyl radical in deionized water, and then add bleached softwood pulp. While maintaining the pH value of the system in an alkaline environment of 10.0 to 10.2, slowly dropwise add sodium hypochlorite solution (effective chlorine content ≥ 5%) to ensure its full contact and complete reaction with the reactants, thereby obtaining nano-cellulose fibers containing carboxyl groups. After the reaction is completed, repeatedly wash and filter the slurry with deionized water for multiple times until the pH value of the filtrate reaches neutral to thoroughly remove the residual reaction reagents and by-products. Finally, collect the washed slurry and further process it with a homogenizer to obtain uniformly dispersed nano-cellulose fibers. Finally, store the processed nano-cellulose fibers in a refrigerator at 4°C for subsequent experimental use.

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

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

[0020] To ensure the quality of the resulting polymer, step 1) is: Mix nano-cellulose fibers with carboxyl groups and polyamine compounds with different carbon chain lengths at a temperature of 20 to 30°C, stir for 8 to 10 minutes, and then add a mixed catalyst of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stir and react for 8 to 12 hours, and purify to obtain amino-grafted nano-cellulose fibers.

[0021] To further purify the reaction product, dialysis is carried out for 2 to 3 days in deionized water using a dialysis bag with a cut-off molecular weight of 3.5 kDa to effectively remove the unreacted monomers and catalysts, thereby obtaining high-purity amino-grafted nano-cellulose fibers.

[0022] To balance the 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, and is further preferably polyethyleneimine, 1,8-octanediamine, or 1,10-diaminodecane.

[0023] In order to balance the reaction efficiency and product quality, in step 1), the mass ratio of the carboxyl group-containing nanocellulose fibers, polyamine compounds, 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] In order to balance the reaction efficiency and product quality, step 2) is as follows: The amino-grafted nanocellulose fibers and dialdehydes with different carbon chain lengths are mixed at a temperature of 20-30 °C and stirred for 8-12 hours to ensure the preparation of an imine bond-based all-bioplastic water plastic polymer through a Schiff base reaction, which is then poured into a mold and dried to form a shape.

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

[0026] The above-mentioned imine bond-based all-bioplastic water plastic polymer can be used to replace traditional plastics.

[0027] The above-mentioned imine bond-based all-bioplastic water plastic polymer can be formed under water assistance. The specific steps include: (1) Immerse the water plastic polymer spline in water for 3-5 minutes and use a mold to form the required shape; (2) Air dry for 20-30 minutes at room temperature and a relative humidity of 30-40% to cure and form a shape. The above steps (1)-(2) can be repeated, that is, the steps of forming under water assistance can be repeated as needed. The above steps (1) and (2) are both carried out at room temperature.

[0028] The above-mentioned imine bond-based all-bioplastic water plastic polymer is recycled by a hot pressing method or a depolymerization method; the hot pressing method is to grind the water plastic polymer material activated in water for 20-30 min into fragments and hot press for 8-10 minutes under the conditions of a temperature of 25-35 °C and a pressure of 8-10 MPa; the depolymerization method is as follows: At room temperature, stir the water plastic polymer in a 5 wt% acetic acid aqueous solution for 1.5-2 h, then remove acetic acid by reduced pressure distillation, supplement the dialdehyde, mix at a temperature of 20-30 °C, stir and react for 8-12 hours, re-pour into a mold, and dry to form a shape. The above drying and forming is carried out in an oven at 30-40 °C for 1-3 h. The supplementary amount of the dialdehyde is 10-50 wt% of the mass of the water plastic polymer.

[0029] The mechanical strength of the recycled and reused imine bond-based all-bioplastic water plastic polymer of the present invention is basically unchanged from the initial state.

[0030] For the technologies not mentioned in the present invention, reference is made to the prior art.

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

[0032] 1. Simplified and efficient process: The production process covered by the core technology of the present invention can be smoothly carried out without additional pressure, greatly streamlining the production process and enhancing the operational convenience, which provides convenient conditions for large-scale industrial production.

[0033] 2. Emphasizing both durability and environmental friendliness: In response to the urgent need for recycling non-degradable waste, the present invention innovatively uses nanocellulose as the cornerstone to construct a water-plastic polymer that combines high mechanical strength, long-term temperature resistance, high-efficiency recyclability, and reshaping ability. It can be stably used in extremely cold, extremely hot, and alternating hot and cold environments, and has strong self-healing performance. This material not only provides a solution to environmental pollution problems but also closely aligns with the economic strategy of sustainable development.

[0034] 3. Flexible and diverse shape shaping: Through precise design, the present invention successfully constructs a dynamic imine bond network framework activated by water molecules, thereby creating a water-plastic polymer material with high strength and excellent stability. With a simple wet forming process, this material can easily transform into various stable shapes and maintain geometric shape stability for more than 10 months in an environment with 90% relative humidity, and can maintain its complete shape in various organic solvents, demonstrating its extraordinary shape stability performance.

[0035] 4. Outstanding recycling performance: The water-plastic polymer material of the present invention can be efficiently recycled by either physical means or chemical methods, and the recycled material still has excellent performance, significantly extending the service life of the material and opening up a new way for the recycling of resources.

[0036] 5. Efficient and environmentally friendly natural degradation: The fully bio-based water-plastic polymer material prepared by the present invention can be efficiently degraded in natural conditions in only 150 days, effectively avoiding the accumulation of materials in the environment and perfectly fitting the core concept of sustainable development. Description of the Drawings

[0037] Figure 1 Transmission electron microscope image of carboxyl-functionalized nanocellulose fibers prepared in Example 1.

[0038] Figure 2 Infrared spectrum of carboxyl-functionalized nanocellulose fibers prepared in Example 1.

[0039] Figure 3 Infrared spectrum of amino-grafted nanocellulose fibers prepared in Example 1.

[0040] Figure 4 Solid-state nuclear magnetic resonance carbon spectrum of the amino-grafted nanocellulose fibers prepared in Example 1.

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

[0042] Figure 6 Preparation flow chart of the fully biobased water-plastic polymer material prepared in Example 1.

[0043] Figure 7 Schematic structural diagram of the fully biobased water-plastic polymer material prepared in Example 1.

[0044] Figure 8 Infrared spectrum of the fully biobased water-plastic polymer material prepared in Example 1.

[0045] Figure 9 Solid-state nuclear magnetic resonance carbon spectrum of the fully biobased water-plastic polymer material prepared in Example 1.

[0046] Figure 10 Surface scanning electron microscope image and energy-dispersive X-ray spectrometer spectrum of the fully biobased water-plastic polymer material prepared in Example 1.

[0047] Figure 11 Dynamic thermomechanical analysis spectrum of the fully biobased water-plastic polymer material prepared in Example 1.

[0048] Figure 12 Physical picture of the fully biobased water-plastic polymer material prepared in Example 1.

[0049] Figure 13 Shape stability of the fully biobased water-plastic polymer material prepared in Example 1 in different humidity environments.

[0050] Figure 14 Stress-strain diagram of the fully biobased water-plastic polymer material prepared in Example 1 in different humidity environments.

[0051] Figure 15 Tensile strength diagram of the fully biobased water-plastic polymer material prepared in Example 1 in different humidity environments.

[0052] Figure 16 Tensile strength comparison diagram of the fully biobased water-plastic polymer material prepared in Example 1 and widely used plastics.

[0053] Figure 17 Stability diagram of the fully biobased water-plastic polymer material prepared in Example 1 in different organic solvents.

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

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

[0056] Figure 20 Schematic diagram of recycling of the fully bio - based hydroplastic polymer material prepared in Example 1.

[0057] Figure 21 Physical photos of the degradation process of the fully bio - based hydroplastic polymer material prepared in Example 1. 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, if the temperature is not specifically stated, the operations are carried out at room temperature (20 - 25 °C). If the stirring speed is not specifically stated, the stirring is carried out at a speed of 500 r / min.

[0060] Example 1

[0061] Preparation of cellulose nanofibers: First, weigh 15 g of bleached softwood pulp (UPM Kaukas pulp mill, Finncon softwood pulp), add it to 1000 mL of deionized water, and continuously stir at a speed of 400 rpm for 20 minutes to uniformly disperse the bleached softwood pulp in deionized water. Subsequently, add 1.5 g of sodium bromide and 0.25 g of 2,6,6 - tetramethylpiperidine - 1 - oxyl radical to this system and continuously stir at room temperature until all additives are completely dissolved and uniformly dispersed in the system. Then, use a constant - pressure funnel to dropwise add 40 mL of sodium hypochlorite solution (mass content of available chlorine is 13 wt%) into the above - mentioned mixed solution at a speed of 30 drops / min. At the same time, adjust the pH of the reaction system to 10.0 - 10.2 with 0.1 M sodium hydroxide solution, and stir - react for 8 hours. After the reaction, wash repeatedly with deionized water until the ionic conductivity of the filtrate is less than 50 μS / cm, collect the slurry and treat it with a homogenizer to obtain a carboxyl - containing nanofibrillated cellulose fiber dispersion, which is stored in a refrigerator at 4 °C for later use.

[0062] To verify the morphological characteristics of the prepared carboxyl - containing nanofibrillated cellulose fibers, transmission electron microscopy technology was used for observation, and the results are shown in Figure 1 , and the image clearly shows the typical nanofiber morphology. In addition, through infrared spectroscopy analysis ( Figure 2)Further explored the chemical structure changes of nanocellulose fibers with carboxyl groups, especially after oxidation treatment with 2,2,6,6-tetramethylpiperidine-1-oxyl radical, and an obvious absorption peak was observed at 1604 cm -1 . This peak was attributed to the asymmetric stretching vibration of the carboxyl group (-COO - ), and this finding strongly supported the modification effect of 2,2,6,6-tetramethylpiperidine-1-oxyl radical on the cellulose structure.

[0063] Preparation of amino-grafted cellulose nanofibers: First, 100 g of a nanocellulose fiber dispersion with carboxyl groups (solid content 1.5%) was mixed with 3 g of polyethyleneimine (Shanghai Aladdin Biochemical Technology Co., Ltd., polyethyleneimine: 99%, M.W. 600) at 25 °C and stirred for 10 min for sufficient mixing. Subsequently, a mixed catalyst of 1.5 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.2 g of N-hydroxysuccinimide was added, and stirring was continued for 12 hours. Then, a dialysis bag with a molecular weight cut-off of 3.5 kDa was used to dialyze the reaction product in deionized water for 3 days to remove unreacted monomers and catalysts, obtaining amino-grafted nanocellulose fibers with a solid content of 3.2 wt%. As Figure 3 , the infrared spectrum of the amino-grafted nanocellulose fibers showed characteristic peaks belonging to O=C-NH at 1651 cm -1 and characteristic peaks belonging to -NH -1 at 1457 cm 2 , indicating that polyethyleneimine was successfully grafted onto the cellulose nanofibers. The solid-state nuclear magnetic carbon spectrum of the amino-grafted nanocellulose fibers ( Figure 4 ) demonstrated obvious chemical shifts of the 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). In particular, the appearance of C-8 proved that polyethyleneimine was successfully grafted onto the cellulose nanofibers. The X-ray diffraction pattern of the amino-grafted nanocellulose fibers ( Figure 5 ) showed that the grafting reaction did not change the crystalline structure of the cellulose nanofibers.

[0064] Synthesis of an imine bond-based all-bioplastic polymer: As Figure 6As shown, 1 g of glutaraldehyde aqueous solution (volume ratio of glutaraldehyde to water is 1:1) was dissolved in the above 10 g of amino-grafted cellulose nanofibers (solid content 3.2 wt%), stirred and reacted at room temperature for 12 hours, poured into a mold, and finally dried in an oven at 40 °C for 1 h to form a fully bio-based hydroplastic polymer based on imine bonds, whose structure is as Figure 7 shown. The infrared spectrum of the fully bio-based hydroplastic polymer ( Figure 8 ) showed that a new characteristic peak belonging to C=N appeared at 1637 cm -1 , which also indicated the successful synthesis of the fully bio-based hydroplastic polymer. The solid-state nuclear magnetic carbon spectrum of the amino-grafted nanofibrillated cellulose ( Figure 9 ) showed a C-9 belonging to the imine bond at 148.62 ppm. In addition, the scanning electron microscope image ( Figure 10 ) showed that the surface of the prepared hydroplastic polymer material was smooth and flat, and the energy-dispersive X-ray spectrometer spectrum also showed a uniform distribution of C, O, and N. The dynamic thermomechanical analysis spectrum ( Figure 11 ) showed that the glass transition temperature (T g ) of the prepared fully bio-based hydroplastic polymer material was 80.23 °C.

[0065] Effect evaluation:

[0066] The fully bio-based hydroplastic polymer material 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 forming process includes: (1) At room temperature, immerse the hydroplastic polymer spline in water for 5 minutes, and edit the shape using a mold in the wet state; (2) Air dry for 30 minutes in an environment with room temperature and relative humidity of 30-40%. As Figure 13 shown, the shape stability of the hydroplastic polymer material in different humidity environments was evaluated. The hydroplastic polymer material showed excellent shape stability under extreme humidity conditions (90% RH) and remained undeformed for 10 months. In addition, the tensile strength of the fully bio-based hydroplastic polymer material is as Figures 14 - 16As shown, different from the high humidity sensitivity of other hydroplastic materials, this material exhibits high mechanical stability within a wide humidity range. It shows a high tensile strength of 93.9 MPa in the Original state (at 10% humidity), and even after being placed at 90% humidity for 48 hours, the tensile strength still remains at 78.6 MPa. Notably, the tensile strength of this hydroplastic polymer material after being placed at 90% humidity for 15 days (72.4 MPa) is much 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 the tensile strength of 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 material has broad application prospects as a substitute for non-degradable plastics.

[0067] As Figure 17 shown, the fully bio-based hydroplastic polymer material was immersed in various high-polarity, medium-polarity, and low-polarity solvents ( Figure 17 in it, a is the initial state, b is the state after 7 days. From left to right in Figures a and b are: N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), ethanol (EtOH), acetone (Ace), tetrahydrofuran (THF), dichloromethane (DCM), n-hexane (n-Hex)). After 7 days, it can still maintain its complete form. As Figure 18 shown, after the fully bio-based hydroplastic polymer material has undergone 30 rapid thermal shock cycles with a large temperature difference (-70 °C to 150 °C), its strength only decreases slightly, indicating that it has strong resistance to thermal shock damage, enabling it to be used in extremely high and low temperature environments.

[0068] The self-healing property of this hydroplastic polymer material Figure 19 demonstrates the self-healing property of the fully bio-based hydroplastic polymer material. Thanks to the abundant imine bonds contained in its dynamic network structure, this material exhibits extraordinary self-healing ability. Scratches were made on the material surface to cause damage (length 800 μm, width 20 μm), and the repair process was monitored using an optical microscope. The damaged hydroplastic polymer material was placed at 25 °C and 90% RH for 24 h, and the damage situation of the material was significantly improved, and the cracks were completely healed. The comparison of the tensile strength after healing with that before damage did not show a significant attenuation (93.4 MPa vs. 87.9 MPa). In addition, the hydroplastic polymer material exhibits excellent recyclability. As Figure 20As shown, the water-plastic polymer material can be reused by physical methods (hot pressing - shaping) and chemical methods (depolymerization - recycling). The physical method is to grind the water-plastic 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 from the initial state (change < 5%). The chemical method is to stir the water-plastic polymer material in a 5 wt% aqueous acetic acid solution at room temperature for 2 hours, then remove acetic acid by vacuum distillation (absolute pressure 30 mmHg), add an aqueous glutaraldehyde solution (the volume ratio of glutaraldehyde to water is 1:1, and the mass of glutaraldehyde is 43 wt% of the mass of the water-plastic polymer material), mix at room temperature, stir and react for 12 hours, re-pour into a mold, and dry at 40 °C for 1 h to form. The mechanical strength is basically unchanged from the initial state (change < 8%). It should be noted that a soil degradation experiment was carried out to explore the biodegradability of the water-plastic polymer material ( Figure 21 ). The water-plastic polymer material (a disc with a diameter of 20 mm) was buried in natural soil (10 cm deep), and the microscopic degradation morphology was monitored over time. The surface of the water-plastic polymer material gradually became rough over time and was almost completely degraded into small pieces after 150 days of soil burial, showing good degradability. The results show that the water-plastic polymer material has excellent biodegradability, can be degraded in natural soil, and can prevent environmental pollution after treatment.

[0069] Example 2

[0070] Weigh 15 grams of bleached softwood pulp and add it to 1 liter of deionized water. Stir continuously at a speed of 400 rpm for 20 minutes. Subsequently, add 1.8 g of sodium bromide and 0.2 g of 2,2,6,6-tetramethylpiperidine-1-oxyl radical to this system and stir continuously at room temperature until the additives are completely dissolved and evenly dispersed. Drop 40 mL of sodium hypochlorite solution (the mass content of available chlorine is 13 wt%) into the mixture at a speed of 30 drops / min through a constant pressure dropping funnel. At the same time, use 0.1 M sodium hydroxide solution to adjust the pH of the reaction system to 10.0 - 10.2 and stir and react for 10 hours. After the reaction is completed, wash repeatedly with deionized water until the ionic conductivity of the filtrate drops below 50 μS / cm, collect the obtained slurry and treat it with a homogenizer. Finally, store the obtained carboxyl-functionalized nanofibrillated cellulose dispersion in a refrigerator at 4 °C for later use.

[0071] Disperse 100 g of a nanofibrillated cellulose fiber dispersion with carboxyl groups and a solids content of 1.5% (1.5% solids) and 2.3 g of 1,8-octanediamine at 25 °C and stir for 10 min for thorough mixing. Then, add a catalyst composed of 1.65 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.5 g of N-hydroxysuccinimide, continue stirring for 10 h, and then use a dialysis membrane with a molecular weight cut-off of 3.5 kDa to dialyze the reaction product in deionized water for 3 days to remove unreacted monomers and the catalyst, obtaining amino-grafted cellulose nanofibers with a solids content of 3.0 wt%.

[0072] Dissolve 1.5 g of glyoxal in 15 g of amino-grafted cellulose nanofibers (3.0 wt% solids content), continuously react at room temperature for 12 h, synthesize a fully biobased hydroplastic polymer by forming imine bonds, pour it into a mold, and dry it in an oven at 40 °C for 1 h to form a shape.

[0073] The tensile strength of the above-prepared hydroplastic polymer material reaches 90.6 MPa; it shows excellent hydroplastic forming (the same method as in Example 1) and long-term shape stability (no deformation occurred after 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 at room temperature in 1 h. The hydroplastic polymer material also exhibits good recycling and reprocessing ability (the same method as in Example 1), and the mechanical strength of the recycled and reprocessed hydroplastic polymer material is basically unchanged from the initial state. It completely degrades within 150 days in the natural environment.

[0074] Example 3

[0075] Add 15 g of bleached softwood pulp to 1 L of deionized water and continuously stir at a speed of 400 rpm for 20 min. Subsequently, add 2.2 g of sodium bromide and 0.23 g of 2,2,6,6-tetramethylpiperidine-1-oxyl radical to the system at room temperature and continuously stir until the additives are completely dissolved and evenly dispersed. Then, dropwise add 42.5 mL of sodium hypochlorite solution (mass content of available chlorine is 13 wt%) to the reaction system at a rate of 30 drops / min through a constant pressure dropping funnel, and finely adjust the pH value of the system between 10 and 10.2 using 0.1 M sodium hydroxide solution. Stir and react for 10 h. After the reaction is completed, wash repeatedly with deionized water until the pH value stabilizes to neutral and the ionic conductivity of the filtrate drops below 45 μS / cm. Collect the resulting slurry and process it with a homogenizer. Finally, store the prepared nanofibrillated cellulose fiber dispersion with carboxyl groups in a 4 °C refrigerator for subsequent experimental use.

[0076] 100 g of carboxyl-containing nanocellulose fiber dispersion (solid content 1.5%) was stirred and mixed with 2.5 g of 1,10-decanediamine at 25°C for 10 min. Subsequently, 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 stirring was continued for 8 hours. Then, the reaction product was 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 solid content of 3.2 wt%.

[0077] 1.8 grams of suberaldehyde was dissolved in 25 grams of amino-grafted cellulose nanofibers (solid content of 3.2wt%), reacted continuously at room temperature for 12 hours, and cast into a mold by forming an imine bond. The mold was dried in an oven at 40°C for 1 hour to synthesize a fully bio-based water-plastic polymer.

[0078] The tensile strength of the water-plastic polymer material prepared above is 88.2MPa; it shows excellent water-plastic molding (conditions are the same as in Example 1) and long-term shape stability (maintained for 10 months without deformation at 80% RH). The water-plastic polymer material can completely repair scratches with a length of 300μm, a width of 45μm and a depth of 35μm at room temperature within 1.5 hours. The room temperature self-healing water-plastic film material is plastic after contact with water, and can maintain its shape for a long time in a high humidity environment. The mechanical strength of the recycled and reprocessed (method is the same as in Example 1) water-plastic polymer material is basically unchanged from the initial state. The water-plastic polymer material can achieve efficient degradation within 200 days in a natural environment.

Claims

1. A fully bio-based water-plastic polymer based on imine bonds, characterized in that: Its general structural formula is: Wherein, 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.

2. A method for preparing the all-biobased water-plastic polymer based on imine bonds according to claim 1, characterized in that: By amino-grafting cellulose derivatives, a three-dimensional imine bond cross-linking network with dynamic reversible properties was constructed to obtain a fully bio-based water-plastic polymer material based on imine bonds.

3. The preparation method according to claim 2, characterized in that: The steps include: 1) The amino groups of the nanocellulose fibers with carboxyl groups are reacted with polyamines of different carbon chain lengths under the catalytic action of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to form stable amide bonds with the carboxyl groups on the nanocellulose fibers with carboxyl groups, thereby obtaining amino-grafted nanocellulose fibers; 2) Amino-grafted nanocellulose fibers are reacted with dialdehydes of different carbon chain lengths via Schiff base reaction to prepare fully bio-based water-plastic polymers based on imine bonds.

4. The preparation method according to claim 3, characterized in that: Step 1) is: mixing carboxyl-carboxylated nanocellulose fibers with polyamine compounds of different carbon chain lengths at a temperature of 20 to 30° C., stirring for 8 to 10 minutes, then adding a mixed catalyst of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stirring for reaction for 8 to 12 hours, and purifying to obtain amino-grafted nanocellulose fibers; wherein the purification uses a dialysis bag with a molecular weight cutoff of 3.5 kDa, and performs dialysis treatment in deionized water for 2 to 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, 1,5-diaminopentane, 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 the nanocellulose fibers with carboxyl groups, the 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) is: mixing the amino-grafted nanocellulose fibers with dialdehydes of different carbon chain lengths at a temperature of 20 to 30° C., stirring and reacting for 8 to 12 hours, pouring into a mold, drying and forming, and obtaining a fully bio-based water-plastic polymer based on an imine bond.

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 suberaldehyde; and the mass ratio of the amino-grafted nanocellulose fibers to the dialdehyde is (1-5): (1.5-10.5).

9. An application of the all-biobased water-plastic polymer based on imine bonds according to claim 1, characterized in that: Used to replace plastic.

10. The use according to claim 9, characterized in that: The all-biobased water-plastic polymer based on imine bonds can be formed with the aid of water, and the specific steps include: (1) immersing the water-plastic polymer strip in water for 3 to 5 minutes to form a desired shape; (2) air-drying for 20 to 30 minutes in an environment of room temperature and relative humidity of 30 to 40% to solidify and form, and steps (1) to (2) can be repeated repeatedly; The fully bio-based hydroplastic polymer based on imine bond is recycled and reused through hot pressing method or 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 75 to 95° C. and a pressure of 1 to 8 MPa; The depolymerization method is as follows: after the water-plastic polymer is stirred in a 5wt% acetic acid aqueous solution at room temperature for 1.5 to 2 hours, the acetic acid is removed by reduced pressure distillation, dialdehyde is added, mixed at a temperature of 20 to 30°C, stirred for reaction for 8 to 12 hours, re-cast in a mold, and dried to form; wherein the amount of dialdehyde added is 10 to 50wt% of the mass of the water-plastic polymer.

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