Bioplastic based on cellulose ether deep eutectic solvent and method for synthesizing the same

Abstract

The application discloses a kind of based on cellulose ether eutectic solvent biological plastics and its synthesis method, the synthesis method by cellulose ether hydrogen bond donor and hydrophobic phenolic hydrogen bond acceptor according to predetermined mass ratio under certain temperature condition preparation cellulose ether eutectic solvent;Then homogeneous dynamic boron-oxygen bond chemical modification is carried out to cellulose ether in the eutectic solvent;Finally, add the cellulose ether eutectic solvent mixed solution containing polymerizable monomer, after two kinds of solution are mixed evenly, under certain temperature, stationary for a certain time, biological plastics can be prepared.The preparation process of the application does not need to use any initiator and catalyst, and does not involve organic solvent and VOC, process is simple, green and environmental protection, low in cost;The prepared biological plastics has excellent optical performance, mechanical property, and has the characteristics of recyclability and biodegradability.

Description

Technical Field

[0001] This invention relates to the field of bioplastic materials, and more particularly to a bioplastic based on a cellulose ether eutectic solvent and its synthesis method. Background Technology

[0002] With the increasing depletion of global non-renewable resources, the development of green and sustainable materials has become an urgent need. Cellulose, as a recognized environmentally friendly material, is an ideal choice for replacing petroleum-based resources in the preparation of high-value-added materials due to its low cost, wide availability, easy degradation, and renewability. Paper made from natural cellulose fibers possesses characteristics such as high flexibility, light weight, high thermal stability, renewability, and biodegradability, thus being considered a potential candidate for plastic alternatives. However, the polyhydroxy structure of cellulose gives it strong hydrophilicity, and compared to traditional plastics, paper's porous structure, lower wet strength, and poor barrier properties against water vapor and oxygen make it difficult to directly use as a plastic substitute. Modifying the paper surface, such as by applying waterproof coatings, lamination, or composite nanofillers and natural polymers, can significantly improve its water vapor barrier properties. However, these paper-based composite materials still face limitations such as low recyclability, high cost, and long preparation cycles.

[0003] In recent years, researchers have attempted to develop high-performance cellulose products and realize their high-value utilization by chemically modifying the molecular structure of cellulose at the molecular scale. However, the strong intramolecular and intermolecular hydrogen bonds within cellulose molecules often require large amounts of solvents for modification and involve complex issues related to subsequent separation and recycling. Therefore, developing cellulose-based materials with excellent overall performance, simple processing, recyclability, and reusability remains a pressing challenge.

[0004] Deep eutectic solvents (DES) have attracted considerable attention in recent years in the fields of green solvents and functional material synthesis due to their simple preparation, extremely low vapor pressure, ease of recovery, and strong solubility for both ionic and nonionic compounds. DES consists of hydrogen bond acceptors and hydrogen bond donors, and their components form an electron-delocalized structure through hydrogen bonding, significantly lowering the melting point of the mixture compared to a single component, exhibiting an enthalpy-driven negative deviation from thermodynamic ideals. Because of the diverse molecular structures of hydrogen bond donors and acceptors, DES is also known as a "designable solvent." Based on these characteristics, researchers have attempted to utilize DES as a green solvent for cellulose to prepare high-value-added products. However, despite optimization through molecular structure design, ultrasonic assistance, or the addition of co-solvents, the solubility of cellulose in DES remains relatively limited. Compared to traditional non-derivative solvents such as N-methylmorpholine-N-oxide (solubility up to ~30 wt.%) and ionic liquids (>20 wt.%), the solubility of cellulose in DES remains low.

[0005] The dissolution of cellulose is essentially a process of hydrogen bond breaking. An ideal solvent should have the ability to effectively interrupt intramolecular and intermolecular hydrogen bonds in cellulose. However, taking common diethylsaturated solvents (DES) (such as choline chloride / urea solvents) as an example, although its components can form hydrogen bonds with cellulose, the dense hydrogen bond network between the components within the DES limits its interaction with cellulose molecules, resulting in insufficient permeability to cellulose. The competition between the hydrogen bonds within the DES itself and the hydrogen bonds between the DES and cellulose ultimately reduces the solubility of cellulose in DES. This limitation has become a bottleneck for the preparation of high-value-added cellulose-based functional materials using DES.

[0006] Existing research indicates that traditional methods of dissolving cellulose using DES struggle to balance the interaction between hydrogen bonds within DES and those between DES and cellulose. When cellulose is added to DES as a solute, it competes for hydrogen bonds with DES, significantly limiting its solubility. However, by shifting the focus to include cellulose directly as a component of DES in the construction of eutectic solvents, the hydrogen bond competition inherent in the traditional solute role can be avoided, thus achieving a homogeneous cellulose solvent at the molecular scale in one step. Furthermore, functionalizing cellulose molecules through chemical modification (such as introducing dynamic chemical bonds) allows for the convenient preparation of cellulose-based adaptive functional materials. The key here lies in designing cellulose molecules as hydrogen bond donors or acceptors that conform to the characteristics of DES components.

[0007] Furthermore, from a materials design perspective, researchers have explored using DES as a dispersion medium for cellulose, introducing monomers to achieve chemical cross-linking, and preparing reinforced cellulose-based functional materials; or utilizing cellulose dispersed in DES for in-situ chemical modification, grafting active monomers to improve the mechanical properties of cellulose-based gel materials. However, these materials typically exhibit strong hydrophilicity, and their performance still lags behind that of traditional synthetic plastics. Simultaneously, the cellulose-based polymer networks synthesized based on this solvent are difficult to depolymerize under normal conditions, posing challenges to the degradation, recycling, and reuse of these materials. Summary of the Invention

[0008] Purpose of the invention: The present invention aims to provide a biodegradable and recyclable transparent bioplastic based on cellulose ether eutectic solvent and its synthesis method.

[0009] Technical solution: The method for synthesizing bioplastics based on cellulose ether eutectic solvent according to the present invention includes the following steps:

[0010] Step S1: Prepare a cellulose ether eutectic solvent by mixing a cellulose ether hydrogen bond donor and a hydrophobic phenolic hydrogen bond acceptor in a mass ratio of 1:3 to 1:9 at 60 to 90 °C;

[0011] Step S2: Add the active intermediate containing isocyanate groups to the cellulose ether eutectic solvent obtained in step S1, and react at room temperature for 1-4 hours;

[0012] Step S3: Add a small molecule containing phenylboronic acid group to the mixed solvent obtained in step S2, stir at room temperature for 24-48 hours, and the resulting mixture is denoted as solution A;

[0013] Step S4: Prepare a cellulose ether eutectic solvent according to step S1, add a polymerizable monomer and mix thoroughly. The resulting mixture is denoted as solution B. The mass ratio of the polymerizable monomer to the cellulose ether eutectic solvent is 0.5:1 to 1.5:1.

[0014] Step S5: Mix solution A obtained in step S3 with solution B obtained in step S4 until homogeneous, and let stand at 60-90℃ for 8-12 hours to obtain biodegradable and recyclable transparent bioplastic.

[0015] Preferably, in step S1, the cellulose ether hydrogen bond donor is one or more of methylcellulose, ethylcellulose, and methyl ethylcellulose.

[0016] Preferably, in step S1, the hydrophobic phenolic hydrogen bond acceptor is one or more of thymol, carvacrol, vanillin, and eugenol.

[0017] Preferably, in step S2, the active intermediate containing the isocyanate group is one or more of isophorone diisocyanate, cyclohexane-1,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), and 4,4-diisocyanate dicyclohexylmethane.

[0018] Preferably, in step S3, the small molecule containing phenylboronic acid is one or more of 3-carboxyphenylboronic acid, 4-carboxyphenylboronic acid, 2-aminophenylboronic acid, 3-aminophenylboronic acid, and 4-aminophenylboronic acid.

[0019] Preferably, in step S4, the polymerizable monomer is one or more of hydroxyethyl acrylate, hydroxypropyl methacrylate, 2-phenoxyethyl acrylate, isobornyl acrylate, and benzyl acrylate.

[0020] The bioplastic based on cellulose ether eutectic solvent of the present invention is prepared by the above-described synthesis method.

[0021] Mechanism: Cellulose molecules, rich in hydroxyl functional groups, theoretically possess the potential to act as hydrogen bond donors in macromolecules. However, the dense intramolecular and intermolecular hydrogen bonds within them limit their hydrogen bond supply capacity. If their hydrogen bond supply capacity is enhanced through appropriate molecular structure modification and combined with matching hydrogen bond acceptors, molecular-scale eutectic solvents of cellulose can be directly constructed without external solvents. Further chemical modification of cellulose using this homogeneous solvent can lead to the construction of cellulose-based bioplastics at the molecular level. Cellulose ethers can have their hydrogen bond supply capacity significantly modulated through etherification modification, and can be combined with different hydrogen bond acceptors by changing functional groups and degrees of substitution to prepare cellulose ether eutectic solvents. This solvent can serve as a medium for in-situ chemical modification, enabling the construction of cellulose-based dynamically adaptive materials through integrated supramolecular interactions and dynamic chemical modification.

[0022] Beneficial Effects: Compared with existing technologies, the significant advantages of this invention are: 1. This invention prepares a cellulose ether eutectic solvent in one step solely through hydrogen bonding between components without the intervention of any external solvent, and utilizes it as an integrated green medium for molecular-scale cellulose structural modification and functionalization, providing a new approach for the development of cellulose-based bioplastic materials; 2. The cellulose ether hydrogen bond donor and hydrophobic phenolic hydrogen bond acceptor in the cellulose ether eutectic solvent used in this invention are both natural biomass and their derivatives, and the preparation process does not involve the generation of any organic solvents or VOCs, making the preparation method and the resulting bioplastics environmentally friendly, simple in process, green, and low-cost; 3. This invention utilizes the cellulose ether eutectic solvent to prepare cellulose ether... 4. The synthesis of the bioplastics of this invention does not require the addition of an initiator, and the self-polymerization and cross-linking of polymerizable monomers is achieved by relying on the high reactivity within the system; 5. The transparent bioplastics prepared by this invention have excellent optical and mechanical properties, and can spontaneously repair themselves by hot pressing after breakage; 6. The bioplastics prepared by this invention can still maintain good mechanical properties even after up to 20 recycling treatments; 7. The bioplastics prepared by this invention can spontaneously degrade in natural environment, and their complete degradation cycle is about 3 months; 8. The bioplastics prepared by this invention have broad application prospects in the fields of future smart packaging, biodegradable and recyclable products. Attached Figure Description

[0023] Figure 1 The synthetic route diagram for the bioplastic prepared in Example 1;

[0024] Figure 2 The infrared spectrum of the bioplastic prepared in Example 1 after dynamic chemical modification.

[0025] Figure 3 An optical photograph of the bioplastic prepared in Example 2;

[0026] Figure 4 The UV-Vis transmittance curve of the bioplastic prepared in Example 2;

[0027] Figure 5 Optical photographs showing the puncture resistance of the bioplastic prepared in Example 3 and its ability to lift heavy objects;

[0028] Figure 6 The DSC curves of the bioplastics prepared in Examples 1-5 are shown.

[0029] Figure 7 The stress-strain curves of the bioplastics prepared in Examples 1-5 are shown.

[0030] Figure 8 The stress-strain curves of the bioplastic prepared in Example 4 after immersion in water for 1 day and 7 days are shown.

[0031] Figure 9 The stress-strain curve of the bioplastic prepared in Example 5 after hot pressing and welding is shown.

[0032] Figure 10 An optical photograph of a water-filled packaging bag made from the bioplastic prepared in Example 5 by hot-press welding.

[0033] Figure 11 The stress curve of the bioplastic prepared in Example 3 after hot pressing and recycling is shown.

[0034] Figure 12 An optical photograph of the bioplastic prepared in Example 5 undergoing outdoor degradation. Detailed Implementation

[0035] The invention will now be further described with reference to the accompanying drawings.

[0036] Example 1

[0037] A method for synthesizing bioplastics based on cellulose ether eutectic solvents includes the following steps:

[0038] Step S1: Weigh 1g of ethyl cellulose and 9g of thymol, with a mass ratio of 1:9, stir at 60℃ until clear and transparent, then remove and cool to room temperature to complete the preparation of cellulose ether eutectic solvent;

[0039] Step S2: Add 0.6873 g of isophorone diisocyanate to the cellulose ether eutectic solvent prepared in step S1 and react at room temperature for 1 h;

[0040] Step S3: Add 0.4234 g of 3-aminophenylboronic acid to the mixed solvent prepared in step S2, and stir at room temperature for 24 h; the mixture obtained in the above steps is denoted as solution A;

[0041] Step S4: Prepare a cellulose ether eutectic solvent according to the method in step S1, then add 5g of hydroxyethyl acrylate and mix thoroughly; the mixture obtained in the above steps is denoted as solution B;

[0042] Step S5: Mix solution A obtained in step S3 with solution B obtained in step S4 until homogeneous, and let stand at 90°C for 8 hours to prepare a biodegradable and recyclable transparent bioplastic.

[0043] like Figure 2The image shows the infrared spectrum of the cellulose ether eutectic solvent prepared after dynamic chemical modification in steps S1-S3 of Example 1. Comparing the infrared spectrum of the cellulose ether eutectic solvent prepared in step S1, the spectrum obtained in step S2 after the introduction of isophorone diisocyanate is 2267 cm⁻¹. -1 A characteristic absorption peak for the -N=C=O functional group was found at 1717 cm⁻¹. -1 The presence of a characteristic absorption peak for the -C=O photogroup indicates that isophorone diisocyanate reacted with the -OH functional group in the eutectic solvent component of cellulose ether; furthermore, after the introduction of 3-aminophenylboronic acid in step S3, a peak was observed at 2267 cm⁻¹. -1 The absorption peak intensity of the -N=C=O functional group decreased significantly, indicating that the -NH2 in 3-aminophenylboronic acid reacted effectively with the -N=C=O functional group, greatly reducing its content in the system. Furthermore, an absorption peak intensity was observed at 1660 cm⁻¹. -1 A characteristic absorption peak of -NH was found at 711 cm⁻¹. -1 The presence of a characteristic absorption peak for phenyl groups provides evidence that 3-aminophenylboronic acid was effectively grafted onto components in a cellulose ether eutectic solvent via isophorone diisocyanate.

[0044] like Figure 6 As shown, the glass transition temperature of the bioplastic obtained in Example 1 is 26.92°C. Figure 7 As shown, the bioplastic obtained in Example 1 has a deformation of about 37% under stress and a tensile strength of about 5 MPa, exhibiting good mechanical properties.

[0045] Example 2

[0046] A method for synthesizing bioplastics based on cellulose ether eutectic solvents includes the following steps:

[0047] Step S1: Weigh 1g of methylcellulose and 8g of carvacrol in a mass ratio of 1:8, stir at 90°C until clear and transparent, then remove and cool to room temperature to complete the preparation of cellulose ether eutectic solvent;

[0048] Step S2: Add 0.511 g of cyclohexane-1,4-diisocyanate to the eutectic solvent of the cellulose ether prepared in step S1, and react at room temperature for 4 h;

[0049] Step S3: Add 0.513 g of 3-carboxyphenylboronic acid to the mixed solvent prepared in step S2, and stir at room temperature for 48 h; the mixture obtained in the above steps is denoted as solution A;

[0050] Step S4: Prepare a cellulose ether eutectic solvent according to the method in step S1, then add 9g of hydroxypropyl methacrylate and mix thoroughly; the mixture obtained in the above steps is denoted as solution B;

[0051] Step S5: Mix solution A obtained in step S3 with solution B obtained in step S4 until homogeneous, and let stand at 60°C for 12 hours to prepare a biodegradable and recyclable transparent bioplastic.

[0052] like Figure 3 and Figure 4 As shown, optical photographs and UV-Vis transmittance curves of the biodegradable and recyclable transparent bioplastic prepared using the method in Example 2 are presented. The bioplastic can be processed into leaf shapes and exhibits excellent optical transmittance, with an average optical transmittance of approximately ~85%. Figure 6 As shown, the glass transition temperature of the bioplastic obtained in Example 2 was 25.23°C; Figure 7 As shown, the bioplastic obtained in Example 2 exhibits a tensile deformation of approximately 35% and a tensile strength of approximately 9 MPa under stress, demonstrating good mechanical properties.

[0053] Example 3

[0054] A method for synthesizing bioplastics based on cellulose ether eutectic solvents includes the following steps:

[0055] Step S1: Weigh 1g of methyl ethyl cellulose and 5g of vanillin, with a mass ratio of 1:5. Stir at 90°C until clear and transparent, then remove and cool to room temperature to complete the preparation of cellulose ether eutectic solvent.

[0056] Step S2: Add 0.751 g of 4,4'-methylenebis(phenyl isocyanate) to the eutectic solvent of the cellulose ether prepared in step S1, and react at room temperature for 2 h;

[0057] Step S3: Add 0.513 g of 4-carboxyphenylboronic acid to the mixed solvent prepared in step S2, and stir at room temperature for 24 h; the mixture obtained in the above steps is denoted as solution A;

[0058] Step S4: Prepare a cellulose ether eutectic solvent according to the method in step S1, then add 9g of 2-phenoxyethyl acrylate and mix thoroughly; the mixture obtained in the above steps is denoted as solution B;

[0059] Step S5: Mix solution A obtained in step S3 with solution B obtained in step S4 until homogeneous, and let stand at 80°C for 12 hours to prepare a biodegradable and recyclable transparent bioplastic.

[0060] like Figure 5As shown, an optical photograph of the surface of the biodegradable and recyclable transparent bioplastic prepared using the method of Example 3, obtained by piercing its surface with an iron spike, is shown. Figure 5 As shown in (a), even when the bioplastic undergoes significant deformation, after the sharp object is removed, only a weak dent remains on the surface, without puncturing it, demonstrating excellent puncture resistance. Figure 5 (b) shows an optical photograph of a 4.5 kg weight being lifted using a small piece of bioplastic, demonstrating its strong mechanical properties.

[0061] like Figure 6 As shown, the glass transition temperature of the bioplastic obtained in Example 3 was 28.60℃; Figure 7 As shown, the bioplastic obtained in Example 3 exhibits a tensile deformation of approximately 25% under stress and a tensile strength of approximately 14 MPa, demonstrating good mechanical properties.

[0062] like Figure 11 As shown, the bioplastic obtained in Example 3 can be recycled by hot pressing after being shredded. The hot pressing temperature is 150°C and the pressure is 1 MPa. It can still maintain good mechanical properties after up to 20 recycling cycles.

[0063] Example 4

[0064] A method for synthesizing bioplastics based on cellulose ether eutectic solvents includes the following steps:

[0065] Step S1: Weigh 1g of ethyl cellulose and 3g of eugenol in a mass ratio of 1:3, stir at 90℃ until clear and transparent, then remove and cool to room temperature to complete the preparation of cellulose ether eutectic solvent;

[0066] Step S2: Add 0.751 g of 4,4-diisocyanate dicyclohexylmethane to the eutectic solvent of the cellulose ether prepared in step S1, and react at room temperature for 4 h;

[0067] Step S3: Add 0.4234 g of 2-aminophenylboronic acid to the mixed solvent prepared in step S2, and stir at room temperature for 48 h; the mixture obtained in the above steps is denoted as solution A;

[0068] Step S4: Prepare a cellulose ether eutectic solvent according to the method in step S1, then add 4g of isobornyl acrylate and mix well; the mixture obtained in the above steps is denoted as solution B;

[0069] Step S5: Mix solution A obtained in step S3 with solution B obtained in step S4 until homogeneous, and let stand at 90℃ for 12 hours to prepare a biodegradable and recyclable transparent bioplastic.

[0070] like Figure 6 As shown, the glass transition temperature of the bioplastic obtained in Example 4 was 22.71℃; Figure 7 As shown, the bioplastic obtained in Example 4 exhibits a tensile deformation of approximately 10% and a tensile strength of approximately 19 MPa under stress, demonstrating good mechanical properties.

[0071] like Figure 8 As shown, the stress-strain curves of the bioplastic obtained in Example 4 after immersion in water for 1 day and 7 days are displayed. After immersion in water for 1 day, the mechanical properties of the prepared bioplastic only decreased slightly, indicating that the bioplastic has certain water resistance. After continuous immersion in water for 7 days, the mechanical properties of the bioplastic were significantly reduced due to the dissociation of dynamic boron-oxygen bonds in the network. The tensile strength decreased from approximately 16 MPa initially to approximately 9 MPa, while the tensile deformation increased significantly, reaching approximately 21%. This situation also provides the possibility for natural degradation outdoors.

[0072] Example 5

[0073] A method for synthesizing bioplastics based on cellulose ether eutectic solvents includes the following steps:

[0074] Step S1: Weigh 1g of ethyl cellulose and 3g of thymol, with a mass ratio of 1:3, stir at 80℃ until clear and transparent, then remove and cool to room temperature to complete the preparation of cellulose ether eutectic solvent.

[0075] Step S2: Add 0.6873 g of isophorone diisocyanate to the cellulose ether eutectic solvent prepared in step S1 and react at room temperature for 2 h;

[0076] Step S3: Add 0.4234 g of 4-aminophenylboronic acid to the mixed solvent prepared in step S2, and stir at room temperature for 24 h; the mixture obtained in the above steps is denoted as solution A;

[0077] Step S4: Prepare a cellulose ether eutectic solvent according to the method in step S1, then add 6g of benzyl acrylate and mix thoroughly; the mixture obtained in the above steps is denoted as solution B;

[0078] Step S5: Mix solution A obtained in step S3 with solution B obtained in step S4 until homogeneous, and let stand at 80°C for 8 hours to prepare a biodegradable and recyclable transparent bioplastic.

[0079] like Figure 5 As shown, the glass transition temperature of the bioplastic obtained in Example 5 is 22.23°C;

[0080] like Figure 6As shown, the bioplastic obtained in Example 5 exhibits a tensile deformation of approximately 8% and a tensile strength of approximately 22 MPa under stress, demonstrating good mechanical properties.

[0081] like Figure 9 and Figure 10 As shown, the bioplastic obtained in Example 5, even after breakage, can be welded together by hot pressing, and the mechanical strength of the welded sample only decreases slightly, demonstrating good hot pressing repair performance. Furthermore, the prepared bioplastic can also be heat-sealed into transparent packaging bags, exhibiting good thermal processing properties.

[0082] like Figure 12 As shown, the bioplastic obtained in Example 5 almost completely disappeared after being placed in an outdoor environment for 90 days, demonstrating good biodegradability.

Claims

1. A method for synthesizing a bio-plastic based on a cellulose ether deep eutectic solvent, characterized by, The method comprises the following steps: Step S1: preparing a cellulose ether eutectic solvent by mixing a cellulose ether hydrogen bond donor and a hydrophobic phenolic hydrogen bond acceptor in a mass ratio of 1:3-1:9 at 60-90°C; Step S2: adding an active intermediate containing an isocyanate group to the cellulose ether eutectic solvent obtained in step S1, and reacting at room temperature for 1-4 h; Step S3: adding a small molecule substance containing a phenylboronic acid group to the mixed solvent obtained in step S2, stirring at room temperature for 24-48 h, and obtaining a mixture, which is recorded as solution A; Step S4: preparing a cellulose ether eutectic solvent according to step S1, and uniformly mixing after adding a polymerizable monomer, and obtaining a mixture, which is recorded as solution B; wherein the mass ratio of the polymerizable monomer to the cellulose ether eutectic solvent is 0.5:1-1.5:1; Step S5: uniformly mixing solution A obtained in step S3 and solution B obtained in step S4, and standing at 60-90°C for 8-12 h to obtain a transparent bioplastic that is degradable and recyclable; In step S1, the cellulose ether hydrogen bond donor is one or more of methyl cellulose, ethyl cellulose, and methyl ethyl cellulose; The hydrophobic phenolic hydrogen bond acceptor is one or more of thymol, carvacrol, vanillin, and eugenol; In step S2, the active intermediate containing an isocyanate group is one or more of isophorone diisocyanate, cyclohexane-1,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), and 4,4-diisocyanate dicyclohexylmethane; In step S3, the small molecule substance containing a phenylboronic acid group is one or more of 3-carboxyphenylboronic acid, 4-carboxyphenylboronic acid, 2-aminophenylboronic acid, 3-aminophenylboronic acid, and 4-aminophenylboronic acid; In step S4, the polymerizable monomer is one or more of hydroxyethyl acrylate, hydroxypropyl methacrylate, 2-phenoxyethyl acrylate, isobornyl acrylate, and benzyl acrylate.

2. A bio-plastic based on a cellulose ether deep eutectic solvent, characterized in that, The bioplastic is prepared by the synthetic method of claim 1.

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