Thermoplastic tough starch-fiber-based bioplastic with hierarchical structure and capable of being printed in 3d and preparation method of thermoplastic tough starch-fiber-based bioplastic

Abstract

The invention belongs to the technical field of high polymer materials, and provides a preparation method of thermoplastic tough starch-fiber-based bioplastic with a hierarchical structure and capable of being printed in 3d, and the preparation method comprises the following steps: mixing gelatinized ball-milled starch with an esterifying agent and a fatty acid lubricant, and reacting to form a complex system; adding carboxylated fiber aqueous dispersion containing a dispersing agent into the complex system, uniformly mixing, drying, embrittling by adopting cold source treatment, grinding, removing redundant esterifying agent and dispersing agent, and drying, thereby obtaining the product. A micro-nano echelon structure assembly strategy is adopted, starch and stearic acid are assembled to form a complex, the regular spiral structure of the starch is kept to improve the chain slippage capacity, then fibers are added, and the dispersion effect of the fibers in a starch matrix is improved to build a micron-sized fiber skeleton. The starch-fiber-based bioplastic prepared by the strategy has considerable mechanical strength while maintaining good flexibility and thermoplasticity, so that the smoothness, the forming precision and the application capability of thermoplastic forming of the material are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and in particular relates to a 3D-printable thermoplastic strong-tough starch-fiber-based bioplastic and a preparation method thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Currently, the development of environmentally friendly and sustainable bioplastics using natural substances as raw materials can not only make up for the shortcomings of petroleum-based plastics, but also has the advantages of abundant reserves, natural degradation, adjustable properties (multiple active hydroxyl groups), and a solid foundation for process research. However, current natural polysaccharide-based materials such as cellulose, starch, chitosan, and sodium alginate have defects such as difficulty in thermoplastic processing and poor product flexibility due to the complex hydrogen bond network formed between molecules. Some studies have achieved durable flexibility of starch-based materials through the synergistic method of starch and stearic acid complexation-starch esterification. However, further research found that the above-mentioned starch-based materials have low material strength due to their strong chain slippage ability, which limits their shape retention and thermoplastic molding capabilities. Summary of the Invention

[0004] To address these issues, the present invention provides a micro-nano hierarchical structure assembly strategy. This involves assembling starch and stearic acid to form a complex, maintaining the starch's regular helical structure to enhance chain slippage. Fibers are then added and their dispersion within the starch matrix is improved to construct a micron-scale fiber skeleton. The starch-fiber-based bioplastic prepared using this strategy maintains excellent flexibility and thermoplasticity while possessing considerable mechanical strength, ensuring the material's smoothness, molding accuracy, and applicability during thermoplastic molding. The present invention also proposes a method for preparing a 3D-printable, thermoplastic, strong-tough starch-fiber-based bioplastic with a hierarchical structure.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: The first aspect of the present invention provides a method for preparing a hierarchical structured 3D-printable thermoplastic tough starch-fiber-based bioplastic, comprising: The gelatinized ball-milled starch is mixed with an esterifying agent and a fatty acid lubricant to react and form a complex system; Add 10%-15% of a carboxylated fiber aqueous dispersion containing a dispersant to the complex system, mix evenly, dry, treat with a cold source to embrittle it, grind to remove excess esterifying agent and dispersant, and dry to obtain the product.

[0006] The present invention carboxylates the fiber and adds it to the complex system together with a dispersant. At this time, the fiber forms hydrogen bonds with the starch hydroxyl groups only through the surface hydroxyl groups. Without destroying the complex structure, the mechanical strength of the bioplastic is improved while the flexibility and thermoplasticity are maintained, ultimately achieving its thermoplastic formability and 3D printability.

[0007] The second aspect of the present invention provides a thermoplastic tough starch-fiber-based bioplastic with a hierarchical structure and 3D printability prepared by the above method.

[0008] The third aspect of the present invention provides a 3D printing method for the above-mentioned thermoplastic tough starch-fiber-based bioplastic, comprising: Extruding and granulating the thermoplastic tough starch-fiber-based bioplastic to obtain 3D printing pellets; The 3D printing pellets are 3D printed to obtain a 3D printed product.

[0009] Preferably, the pellets for printing are prepared by a twin-screw extruder, and the temperatures in the three zones are set to 40, 60, and 80° C., respectively.

[0010] Preferably, the 3D printing of bioplastics is performed using a screw extrusion or pneumatic extrusion 3D printer, with the screw temperature set at 66°C, the nozzle temperature at 82°C or the sleeve temperature at 82°C, and the extrusion pressure at 0.4 MPa (0.8 mm nozzle).

[0011] The fourth aspect of the present invention provides the use of the above-mentioned thermoplastic strong-tough starch-fiber-based bioplastic in the preparation of 3D printed products.

[0012] Beneficial effects of the present invention (1) The present invention carboxylates the fiber and adds it to the complex system simultaneously with the dispersant. At this time, the fiber forms hydrogen bonds with the starch hydroxyl groups only through the surface hydroxyl groups. Without destroying the complex structure, the mechanical strength of the bioplastic is improved while the flexibility and thermoplasticity are maintained, ultimately achieving its thermoplastic formability and 3D printability. The present invention solves the problem of low mechanical strength of traditional thermoplastic and flexible starch-based materials or the loss of thermoplasticity and flexibility while improving mechanical strength; (2) The present invention solves the problem of uneven dispersion and easy entanglement of fibers in the starch matrix; (3) The thermoplastic starch-fiber-based bioplastic prepared by the present invention can be granulated by extrusion and printed by a screw extrusion 3D printer; (4) The present invention proposes a new path for the preparation of thermoplastic starch-fiber-based bioplastics and the improvement of their large-scale processing capabilities.

[0013] (5) The preparation method of the present invention is simple, practical, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention and do not constitute improper limitations on the present invention.

[0015] Figure 1 XRD patterns of crystallization changes before and after modification of Example 1 of the present invention (crystallization state of reaction complex, fiber, and starch); Figure 2 This is an SEM image of the distribution effect of the fibers in Example 1 of the present invention before and after dispersion in the matrix; Figure 3 is a tensile stress-strain curve of the bioplastic prepared in Example 1 of the present invention; Figure 4 These are photos of the bioplastic of Example 1 of the present invention before and after being compressed by 60%; Figure 5 This is a photograph of the bioplastic of Example 1 of the present invention being broken into various shapes at room temperature; Figure 6 The bioplastic 80 of Example 1 of the present invention o C viscosity at different shear rates; Figure 7 is the extrusion speed of the bioplastic in Example 1 of the present invention under different pressures and nozzles of different diameters; Figure 8 The 3D printing pellets of bioplastics manufactured by a twin-screw extruder according to Example 1 of the present invention; Figure 9 This is a photo of the 3D printing process of the bioplastic in Example 1 of the present invention. DETAILED DESCRIPTION

[0016] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0017] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. The reagents or raw materials used in the present invention can be purchased through conventional channels. Unless otherwise specified, the reagents or raw materials used in the present invention are used in accordance with the conventional manner in the art or in accordance with the product instructions. Similarly, unless otherwise specified, the test method of the present invention is also tested in accordance with the conventional manner in the art or the common methods or standards in the industry. In addition, any method and material similar to or equivalent to the described content can be applied to the inventive method. The preferred implementation methods and materials described in the article are for demonstration purposes only.

[0018] Building a hierarchical structure is a means of simultaneously improving multiple material properties. Each gradient hierarchical structure can play a different role and its interference is controllable. Therefore, constructing another gradient reinforcement structure within the starch matrix without disrupting the complex structure is an effective means to achieve toughening and thermoplastic molding. Natural fibers are biodegradable and biosafe. Their high aspect ratio nanofilaments can form a 3D network within the matrix at low concentrations, significantly strengthening the matrix material. To this end, the present invention has found that while the introduction of natural long fibers does not disrupt the complex structure, their large size and high aspect ratio can significantly increase the melt viscosity of the material, causing entanglement during processing and loss of thermoplasticity. The addition of natural cellulose can disrupt the complex structure, leading to its destruction and loss of thermoplasticity. Therefore, the present invention simultaneously adds carboxylated fibers and a dispersant to the complex system. In this case, the uniform fiber network under the action of the dispersant forms hydrogen bonds with the hydroxyl groups of the starch matrix solely through the surface hydroxyl groups. This improves the mechanical strength of the bioplastic while maintaining its flexibility and thermoplasticity without disrupting the complex structure.

[0019] Therefore, the first aspect of the present invention provides a method for preparing a hierarchical structured 3D-printable thermoplastic tough starch-fiber-based bioplastic, comprising: The gelatinized ball-milled starch is mixed with an esterifying agent and a fatty acid lubricant to react and form a complex system; Add 10%-15% of the carboxylated fiber aqueous dispersion containing a dispersant and the dispersant to the complex system, mix them evenly, dry them, treat them with a cold source to make them brittle, grind them, remove excess esterifying agent and dispersant, and dry them to obtain the product.

[0020] In order to ensure that the introduction of fibers can improve the mechanical strength of the starch matrix without destroying its complex structure, the present invention has studied the types and specifications of modified fibers. Preferably, the diameter of the carboxylated fibers is 0.2-3 μm and the length is 20-200 μm, so as to simultaneously obtain better mechanical properties and maintain thermoplasticity.

[0021] Research has found that higher fiber dry weight leads to higher mechanical strength in bioplastics, but lower thermoplasticity. Therefore, the present invention investigates the dosage of carboxylated fiber, and preferably, the mass ratio of carboxylated fiber to starch is 1:20-25, to achieve both superior mechanical properties and thermoplasticity.

[0022] Simple fiber modification still cannot meet the requirement of improving the mechanical strength of bioplastics without destroying the complex structure. To this end, the present invention further introduces amphiphilic substances with weaker polarity to regulate the binding mode and dispersion state of the modified fiber and the starch matrix. The type of amphiphilic substance has a great influence on the regulation effect. Preferably, the dispersant is propylene glycol methyl ether acetate to simultaneously obtain better mechanical properties and maintain thermoplasticity.

[0023] Studies have found that the higher the dispersant content, the better the fiber dispersion effect and the more obvious the mechanical strengthening effect on the matrix. Therefore, the present invention studies the content of the dispersant. Preferably, the addition amount of the dispersant to the fiber is 1-1.5:2.

[0024] Preferably, the freeze-drying is performed by freezing with liquid nitrogen.

[0025] Preferably, the method for removing excess esterifying agent and dispersant is washing with acetone.

[0026] More specifically, they include: Starch and anhydrous ethanol are added to a ball mill and milled to disrupt its integrity and increase its specific surface area, providing a larger reactive surface for further modification and achieving a more thorough modification. (Ball milling is optional, but the resulting starch will have slightly lower thermoplastic properties.) A small amount of water is added to the dried, ball-milled starch and gelatinized at 85°C. An esterifying agent and a fatty acid lubricant are then thoroughly blended with the gelatinized ball-milled starch and stirred continuously in an 85°C oil bath. The esterifying agent esterifies and breaks the starch chains, and the fatty acid lubricant forms a complex with the starch. After a period of time, carboxylated fiber and a dispersant are added. The mixture is stirred at 100°C to remove any unreacted esterifying agent. After drying, a hierarchically structured, 3D-printable, thermoplastic, tough starch-fiber-based bioplastic is obtained.

[0027] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain the present invention rather than to limit it.

[0028] In the following examples and comparative examples, carboxylated fibers with a diameter of 0.2-3 μm and a length of 20-200 μm were purchased from Shanghai Myril Biochemical Technology Co., Ltd. They were mixed with a dispersant to prepare a 10% dispersion, which was then stirred and sonicated for 2 h to achieve complete dispersion.

[0029] Example 1 Starch and anhydrous ethanol were placed in a ball mill at a mass ratio of 1:2. The ball mill revolution speed was set to 18 r / min, the rotation speed was set to 240 r / min, and the ball milling time was set to 40 min. After ball milling, the ball mill was taken out and dried to obtain ball-milled starch.

[0030] In terms of mass, 35 parts of water were added to 65 parts of ball-milled starch, the mixture was evenly mixed, sealed, and gelatinized at 85°C for 20 minutes. 72.5 parts of gelatinized starch, 20 parts of esterifying agent (maleic anhydride), and 12.5 parts of lubricant (stearic acid) were mixed evenly, stirred and reacted at 85°C for 8 hours. Subsequently, according to the target thermoplasticity and mechanical strength of the bioplastic, a carboxylated fiber aqueous dispersion containing a dispersant (propylene glycol methyl ether acetate PGMEA) with a mass concentration of 10% was added (the ratio of fiber to starch was 1:20; the ratio of dispersant to fiber was 2:1), and the mixture was heated at 100°C. o C, and dried to remove excess water. The sample was then frozen with liquid nitrogen and ground into powder (particle size below 200 mesh). The powder was washed with acetone to remove excess unreacted esterification agent and dispersant. After washing, the sample was vacuum dried (60 o C), obtaining a bioplastic that combines thermoplasticity, flexibility and mechanical strength.

[0031] At the same time, esterified starch and flexible starch are prepared.

[0032] Among them, the esterified starch was not complexed with stearic acid and no fiber and dispersant were added, no complex was formed, and other process conditions remained unchanged.

[0033] Flexible starch is made without adding fiber and dispersant, and only has flexibility, while other process conditions remain unchanged.

[0034] Example 2 Starch and anhydrous ethanol were placed in a ball mill at a mass ratio of 1:1. The ball mill was set to have an orbital speed of 30 r / min, a rotation speed of 400 r / min, and a ball milling time of 20 min. After ball milling, the ball mill was taken out and dried to obtain ball-milled starch.

[0035] In terms of mass, 20 parts of water were added to 50 parts of ball-milled starch, the mixture was evenly mixed, sealed, and gelatinized at 85°C for 10 minutes. 60 parts of gelatinized starch, 10 parts of esterifying agent (acetic anhydride), and 5 parts of lubricant (stearic acid) were mixed evenly, stirred and reacted at 85°C for 4 hours. Then, according to the target thermoplasticity and mechanical strength of the bioplastic, a carboxylated fiber aqueous dispersion containing a dispersant (propylene glycol methyl ether acetate PGMEA) with a mass concentration of 10% was added (the ratio of fiber to starch was 1:20; the ratio of dispersant to fiber was 2:1), and the mixture was heated at 100°C. o C, and dried to remove excess water. The sample was then frozen with liquid nitrogen and ground into powder (particle size below 200 mesh). The powder was washed with acetone to remove excess unreacted esterification agent and dispersant. After washing, the sample was vacuum dried (60 o C), obtaining a bioplastic that combines thermoplasticity, flexibility and mechanical strength.

[0036] Example 3 Starch and anhydrous ethanol were placed in a ball mill at a mass ratio of 1:3. The ball mill revolution speed was set to 6 r / min, the rotation speed was set to 100 r / min, and the ball milling time was set to 60 min. After ball milling, the ball mill was taken out and dried to obtain ball-milled starch.

[0037] In terms of mass, 50 parts of water were added to 80 parts of ball-milled starch, the mixture was evenly mixed, sealed, and gelatinized at 85°C for 30 minutes. 85 parts of gelatinized starch, 30 parts of esterifying agent (maleic anhydride), and 20 parts of lubricant (stearic acid) were mixed evenly, stirred and reacted at 85°C for 12 hours. Then, according to the target thermoplasticity and mechanical strength of the bioplastic, a carboxylated fiber aqueous dispersion containing a dispersant (propylene glycol methyl ether acetate PGMEA) with a mass concentration of 10% was added (the ratio of fiber to starch was 1:20; the ratio of dispersant to fiber was 2:1), and the mixture was heated at 100°C. o C, and dried to remove excess water. The sample was then frozen with liquid nitrogen and ground into powder (particle size below 200 mesh). The powder was washed with acetone to remove excess unreacted esterification agent and dispersant. After washing, the sample was vacuum dried (60 o C), obtaining a bioplastic that combines thermoplasticity, flexibility and mechanical strength.

[0038] Comparative Example 1 The difference from Example 1 is that no dispersant (propylene glycol methyl ether acetate PGMEA) was added.

[0039] Test results: tensile strength 2.46 MPa (because the fibers agglomerated in the matrix and did not form a uniform reinforcement network), elongation at break 139%; o C. Viscosity 2318 Pa·s at a shear rate of 100 rad / s. (e.g. Figure 2 ) Comparative Example 2 The difference from Example 1 is that polyethylene glycol is used instead of propylene glycol methyl ether acetate PGMEA.

[0040] Test results: tensile strength 3.28 MPa, elongation at break 13% (because the complex structure is destroyed); o C. Viscosity 2081 Pa·s at a shear rate of 100 rad / s. Comparative Example 3 The difference from Example 1 is that ordinary nanofibers are used instead of carboxylated fibers.

[0041] Test results: tensile strength 1.63 MPa, elongation at break 58% (due to poor dispersion of fibers in the group, resulting in entanglement and agglomeration); oC. Viscosity 2635 Pa·s at a shear rate of 100 rad / s. Comparative Example 4 The difference from Example 1 is that alkali-treated kapok fiber is used instead of carboxylated fiber.

[0042] Test results: tensile strength 1.82 MPa, elongation at break 39% (due to poor fiber dispersion, resulting in entanglement and agglomeration); o C. Viscosity 2898 Pa·s at a shear rate of 100 rad / s.

[0043] Experimental Example 1 The above bioplastics were thermoformed into standard samples for various tests and their performance was characterized.

[0044] The XRD crystallization curve ( Figure 1 ) and SEM images ( Figure 2 ) It can be seen that the bioplastic prepared by the present invention not only maintains the complex structure of flexible starch, but also has the crystallization characteristics of fiber, and the fiber is evenly dispersed in the starch matrix. The test results show that the bioplastic with a hierarchical structure prepared by the present invention has a tensile strength of 6.27 MPa and an elongation at break of 103% ( Figure 3 ), no cracks after compression by 60% ( Figure 4 ), and can be bent into various shapes at room temperature ( Figure 5 At the same time, bioplastics maintain good thermoplasticity, 80 o C, the viscosity under shear is less than 2000 Pa·s ( Figure 6 ), which can be smoothly extruded from a 0.8 mm nozzle at a pressure of 0.4 MPa ( Figure 7 In addition, it has excellent 3D printability ( Figure 8 ), the printed products have high shape fidelity, good inter-layer bonding effect, stable and durable shape and size, such as Figure 9 shown.

[0045] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a hierarchical structured 3D-printable thermoplastic tough starch-fiber-based bioplastic, characterized in that: include: The gelatinized ball-milled starch is mixed with an esterifying agent and a fatty acid lubricant to react and form a complex system; Add 10%-15% of the carboxylated fiber aqueous dispersion containing a dispersant and the dispersant to the complex system, mix them evenly, dry them, treat them with a cold source to make them brittle, grind them, remove excess esterifying agent and dispersant, and dry them to obtain the product.

2. The method for preparing a hierarchical 3D printable thermoplastic tough starch-fiber-based bioplastic according to claim 1, wherein: The diameter of the carboxylated fibers is 0.2-3 μm and the length is 20-200 μm.

3. The method for preparing a hierarchical 3D printable thermoplastic tough starch-fiber-based bioplastic according to claim 1, wherein: The mass ratio of the carboxylated fiber to the starch is 1:20-25.

4. The method for preparing a hierarchical 3D printable thermoplastic tough starch-fiber-based bioplastic according to claim 1, wherein: The dispersant is propylene glycol methyl ether acetate.

5. The method for preparing a hierarchical 3D printable thermoplastic tough starch-fiber-based bioplastic according to claim 1, wherein: The added amount of the dispersant and the fiber is 1-1.5:

2.

6. The method for preparing a hierarchical 3D printable thermoplastic tough starch-fiber-based bioplastic according to claim 1, wherein: The freeze-drying method uses liquid nitrogen freezing.

7. The method for preparing a hierarchical 3D printable thermoplastic tough starch-fiber-based bioplastic according to claim 1, wherein: The method for removing excess esterifying agent and dispersant is washing with acetone.

8. A thermoplastic tough starch-fiber-based bioplastic with a hierarchical structure and capable of 3D printing, prepared by the method according to any one of claims 1 to 7.

9. A 3D printing method for the thermoplastic tough starch-fiber-based bioplastic according to claim 8, characterized in that: include: Extruding and granulating the thermoplastic tough starch-fiber-based bioplastic to obtain 3D printing pellets; The 3D printing pellets are 3D printed to obtain a 3D printed product.

10. Use of the thermoplastic tough starch-fiber-based bioplastic according to claim 8 or 9 in the preparation of 3D printed products.

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