A biodegradable plastic and its preparation method and application

Abstract

The present invention discloses a biodegradable plastic, a preparation method and an application thereof. The preparation method of the biodegradable plastic of the present invention comprises the following steps: 1) dissolving onion DNA in water to prepare a DNA solution; 2) injecting the DNA solution into a mold for bidirectional freeze casting to obtain a DNA frozen block; 3) freeze-drying the DNA frozen block to obtain a DNA aerogel block; 4) placing the DNA aerogel block in a water vapor environment for annealing to obtain an annealed DNA aerogel block; 5) stacking a plurality of annealed DNA aerogel blocks and compressing and densifying them to obtain a biodegradable plastic. The biodegradable plastic of the present invention has the characteristics of both high toughness and environmentally friendly degradability, and its raw material source is wide and the preparation method is simple. It can be used in packaging, medical equipment, 3D printing, agricultural tools and environmentally friendly consumer products and other fields, and is suitable for large-scale industrial production and application.

Description

Technical Field

[0001] The present invention relates to the technical field of environmentally friendly materials, and in particular to a biodegradable plastic and a preparation method and application thereof. Background Art

[0002] Plastics (petroleum-based) are ubiquitous in our daily lives and play an important role. However, their recycling is difficult, and the resulting environmental pollution cannot be ignored. Biodegradable plastics are a type of plastic that can be degraded by naturally occurring microorganisms (such as bacteria, mold, and algae). Compared to traditional plastics, they are more environmentally friendly and offer broader application prospects.

[0003] Currently, raw materials such as cellulose, starch, and protein have been used to make biodegradable plastics. However, these materials often face the following challenges during production and use: 1) Processing requires high temperatures and hot pressing, which consumes significant amounts of energy; 2) Modification requires the use of large amounts of organic solvents, which poses environmental risks and produces byproducts; and 3) Raw materials are derived from crops, competing with agricultural resources such as farmland and water. Deoxyribonucleic acid (DNA), a natural polymer with excellent biocompatibility and degradability, is suitable for the preparation of biodegradable plastics. However, the strength of current DNA-based biodegradable plastics is far inferior to that of other biodegradable and petroleum-based plastics, making them difficult to fully meet practical application requirements and significantly limiting their application.

[0004] Therefore, it is of great significance to develop a DNA-based highly tough biodegradable plastic. Summary of the Invention

[0005] The purpose of the present invention is to provide a biodegradable plastic and a preparation method and application thereof.

[0006] The technical solution adopted by the present invention is:

[0007] A method for preparing biodegradable plastics comprises the following steps:

[0008] 1) Dissolve onion DNA in water to prepare a DNA solution;

[0009] 2) Injecting the DNA solution into the mold for bidirectional freezing casting to obtain a DNA frozen block;

[0010] 3) freeze-drying the DNA frozen block to obtain a DNA aerogel block;

[0011] 4) placing the DNA aerogel block in a water vapor environment for annealing to obtain an annealed DNA aerogel block;

[0012] 5) stacking multiple annealed DNA aerogel blocks and then compressing and densifying them to obtain biodegradable plastic.

[0013] Preferably, the onion DNA in step 1) is prepared by a preparation method comprising the following steps: rapidly freezing onions and then crushing them to produce onion powder; adding the onion powder to a mixed solution of CTAB extraction buffer and 2-mercaptoethanol for incubation; adding chloroform and isoamyl alcohol and centrifuging; collecting the supernatant for alcohol precipitation; centrifuging; and collecting the solid matter for washing and drying to obtain the onion DNA.

[0014] Preferably, the rapid freezing comprises the following steps: adding the onions into liquid nitrogen for freezing.

[0015] Preferably, the volume ratio of the CTAB extraction buffer to 2-mercaptoethanol is 20-30:1.

[0016] Preferably, the incubation is carried out at a temperature of 60° C. to 70° C., and the incubation time is 40 min to 60 min.

[0017] Preferably, the volume ratio of chloroform to isoamyl alcohol is 20-30:1.

[0018] Preferably, the washing comprises the following steps: first washing with anhydrous ethanol, then washing with an ethanol solution with a mass fraction of 70% to 80%, and finally washing with water for multiple times.

[0019] Preferably, the mold in step 2) is in the shape of a cube or a rectangle, and a polydimethylsiloxane (PDMS) right triangular prism is arranged inside. The bottom surface of the PDMS right triangular prism is a right triangle, and the two right-angled sides of the right triangle are respectively attached to the bottom and side wall of the mold.

[0020] Preferably, the bidirectional freeze casting in step 2) is carried out at a temperature of -80°C to -60°C, and the casting time is 30 minutes to 60 minutes.

[0021] Preferably, the freeze-drying in step 3) is carried out under the conditions of a pressure of 3Pa to 7Pa and a temperature of -70°C to -50°C, and the freeze-drying time is 48h to 72h.

[0022] Preferably, the annealing in step 4) is performed in a water vapor environment with a relative humidity of 60% to 80%, and the annealing time is 15 minutes to 25 minutes.

[0023] Preferably, the compression densification in step 5) is carried out at a pressure of 10 MPa to 15 MPa, and the holding time is 30 min to 40 min.

[0024] A biodegradable plastic is made by the above preparation method.

[0025] An application of the above-mentioned biodegradable plastic in the fields of packaging, medical devices, 3D printing, agricultural tools or environmentally friendly consumer products.

[0026] The beneficial effects of the present invention are: the biodegradable plastic of the present invention has the characteristics of high toughness and environmentally friendly degradability, and its raw material sources are wide and the preparation method is simple. It can be used in packaging, medical devices, 3D printing, agricultural tools and environmentally friendly consumer products and other fields, and is suitable for large-scale industrial production and application.

[0027] Specifically:

[0028] The present invention prepares a DNA-based biodegradable plastic with a structure similar to natural nacre (shell biomaterials have a multi-scale structure, including orderly arranged mineral crystals at the microscopic level and a protein matrix at the macroscopic level. When subjected to external impact, the mineral crystals at the microscopic level can effectively disperse and absorb stress, while the protein matrix helps to prevent crack propagation. The coordination of this multi-scale structural interaction enables shell materials to exhibit excellent toughness and impact resistance) through bidirectional freezing, steam annealing and compression densification. The plastic has a multi-scale hierarchical structure, exhibits excellent toughness and impact resistance, is recyclable and biodegradable, and can be used in many fields such as packaging, medical devices, 3D printing, agricultural tools and environmentally friendly consumer products, and is suitable for large-scale industrial production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The present invention is a flow chart for preparing the biodegradable plastic.

[0030] Figure 2 This is a diagram showing the color change of the onion DNA solution in the example measured by the diphenylamine method.

[0031] Figure 3 It is the ultraviolet absorption spectrum of the onion DNA solution in the embodiment.

[0032] Figure 4 The following are SEM images and physical images of the biodegradable plastics in the examples and comparative examples.

[0033] Figure 5 The stress-strain curves obtained by uniaxial tensile testing of the biodegradable plastics in the examples and comparative examples, as well as the corresponding Young's modulus and tensile work test result diagrams.

[0034] Figure 6 The force-displacement relationship curves are obtained by performing three-point bending fracture tests on the biodegradable plastics in the examples and comparative examples.

[0035] Figure 7Comparative curves of elastic contribution, plastic contribution and toughness of the biodegradable plastics in Examples and Comparative Examples.

[0036] Figure 8 Schematic diagram of the recycling of biodegradable plastics in the embodiment.

[0037] Figure 9 These are optical photographs of the morphological changes of the biodegradable plastic in the examples at different time points during the degradation process and gel electrophoresis band diagrams after complete biodegradation. DETAILED DESCRIPTION

[0038] The present invention will be further explained and illustrated below with reference to specific embodiments.

[0039] Example:

[0040] A biodegradable plastic, the preparation method thereof is as follows (preparation flow chart as shown in Figure 1 shown):

[0041] 1) Add 0.3 g of onion DNA to 10 mL of deionized water and shake at room temperature for 20 minutes to obtain a homogeneous and transparent DNA solution.

[0042] 2) The DNA solution was injected into a cube-shaped mold with a PDMS right triangular prism inside. The bottom surface of the PDMS right triangular prism was a right triangle, and the two right-angled sides of the right triangle were respectively attached to the bottom and side walls of the mold. The bottom of the mold was in contact with a cold trap (using liquid nitrogen as the cold source and a copper bridge as the cold source). The mold was bidirectionally frozen at -70°C for 40 minutes to obtain a DNA frozen block.

[0043] 3) The DNA frozen block was removed from the mold and placed in a freeze dryer at a pressure of 5 Pa and a temperature of -60°C for 48 hours to obtain a DNA aerogel block;

[0044] 4) annealing the DNA aerogel block in a water vapor environment with a relative humidity of 70% for 20 minutes to obtain an annealed DNA aerogel block;

[0045] 5) Stacking two annealed DNA aerogel blocks in a hot press and vertically compressing them at room temperature and a pressure of 10 MPa for 35 minutes to obtain biodegradable plastic.

[0046] Note:

[0047] The preparation method of onion DNA is as follows:

[0048] a) immersing onions in liquid nitrogen (-196°C) for rapid freezing, then removing them from the container and grinding them into a fine powder in a sterile mortar to obtain onion powder;

[0049] b) Preheat 250 mL of CTAB extraction buffer to 65°C, add 10 mL of 2-mercaptoethanol, and mix thoroughly. Add onion powder and stir. Incubate in a 65°C water bath for 45 min. Add 240 mL of chloroform and 10 mL of isoamyl alcohol, stir, and centrifuge at 12,000 rpm for 10 min. Collect the supernatant and repeat the centrifugation twice. Add 500 mL of 0°C anhydrous ethanol to precipitate (white flocculent precipitate). Centrifuge again at 5,000 rpm for 5 min. Wash the solid with anhydrous ethanol, then with 75% by mass ethanol solution, and then wash three times with deionized water. Freeze-dry at -60°C for 60 h to obtain onion DNA.

[0050] Comparative Example:

[0051] A biodegradable plastic is prepared in the same manner as in the embodiment except that step 2) is adjusted to "injecting the DNA solution into a mold (without PDMS straight triangular prisms inside) and freeze-molding at -70°C for 40 minutes (the cooling temperature of the mold is random and uniform)".

[0052] Performance testing:

[0053] 1) Add 1 mL of diphenylamine reagent (acidic) to 1 mL of the onion DNA solution in the example, and then observe the color change of the DNA solution under heating conditions. The test results are as follows: Figure 2 (deionized water was used as a reference).

[0054] Depend on Figure 2 It can be seen that after the DNA solution in the example is fully mixed with the diphenylamine reagent, the mixed solution is observed to gradually turn blue. The mechanism of color change is: under acidic heating conditions, the glycosidic bond between the base and the deoxyribose on the DNA molecular chain is broken, and the deoxyribose is dehydrated and condensed under these conditions to generate ω-hydroxy-γ-ketopentanal, which reacts with diphenylamine to undergo a Schiff base reaction, ultimately generating a blue substance 2,5-bis(diphenylamino)pentan-1-ol. As a control, an equal volume of deionized water was used instead of the DNA solution, and the experiment was carried out according to the same steps. It was observed that the mixed solution did not change color, indicating that no DNA was present in the mixed solution.

[0055] 2) The UV absorption spectrum of the DNA solution in the embodiment is shown in FIG. Figure 3 shown.

[0056] Depend on Figure 3It can be seen that: based on the A260 reading on the UV absorption spectrum curve and the conversion factor (1 A260 unit = 50 μg / mL DNA solution), the concentration of the DNA solution in the embodiment is calculated to be 28 ng / μL; the characteristic peaks at 260 nm and 230 nm in the UV absorption spectrum are the identifiers for determining DNA.

[0057] 3) The scanning electron microscope (SEM) images and physical images of the biodegradable plastics in the embodiments and comparative examples are as follows: Figure 4 (a is an embodiment, b is a comparative example; the small pictures in the upper right corner of a and b are the corresponding physical pictures).

[0058] Depend on Figure 4 It can be seen that the cross-section of the biodegradable plastic in the example shows an obvious long-range arranged layered structure, which is formed by compressing and densifying the aerogel, namely the so-called "brick", while the cross-section of the biodegradable plastic in the comparative example is randomly arranged and presents a porous structure, further confirming the significant difference in microstructure between the biodegradable plastic in the example and the biodegradable plastic in the comparative example.

[0059] 4) Uniaxial tensile test (tested at room temperature): The biodegradable plastic in the embodiment (denoted as BFA) and the biodegradable plastic in the comparative example (denoted as FI) were cut into standard dumbbell-shaped samples (length 6 mm, width 2 mm, thickness 1.5 mm). The samples were then fixed in the upper and lower clamps of an Instron 5965 electronic universal tensile testing machine (USA), the clamp spacing was adjusted to 8 mm, and a 100N sensor was used to perform a uniaxial tensile test at a rate of 10 mm / min. The test was completed when the sample broke. The stress-strain relationship curve was then generated based on the data recorded by the tensile testing machine, and the corresponding Young's modulus and tensile work test result graphs were obtained. The test results are shown in FIG. Figure 5 (a is the stress-strain relationship curve, b is the Young's modulus and tensile work test results; ∥ indicates that the force is parallel to the sample layer, and ⊥ indicates that the force is perpendicular to the sample layer).

[0060] Depend on Figure 5 It can be seen that the Young's modulus and tensile work of the biodegradable plastic (BFA∥) in the embodiment are 560 MPa and 0.7 MJ / m 3 , which are 1.45 times and 5.2 times that of the biodegradable plastic (FI) in the control example, indicating that the "brick-mud" structure formed in the biodegradable plastic in the embodiment significantly increases the Young's modulus and tensile work of the material, giving the material high toughness.

[0061] 5) Three-point bending fracture test (tested at room temperature): The three-point bending fixture was installed on an Instron 5965 electronic universal tensile testing machine, and a 100N force sensor was used to record the load. The biodegradable plastic in the embodiment (denoted as BFA) and the biodegradable plastic in the comparative example (denoted as FI) were cut into rectangular samples (length 15 mm, width 3 mm, thickness 1.5 mm), and a 1.5 mm long U-shaped notch was polished on the sample. The sample was then placed on the two support rollers of the bending device, and the span was adjusted to 12 mm to ensure that the sample was aligned with the loading device. During the test, the loading head was adjusted to contact the sample but no load was applied. The load was then applied to the set displacement at a constant rate of 0.04 mm / min, and then returned to the starting point at the same rate. The cyclic test (no interval) was performed until the crack propagation was completed and a force-displacement relationship curve was generated. The elastic contribution (J) was calculated based on the crack propagation length. el ), plastic contribution (J pl ) and toughness (J) comparison curve, the test results are as follows Figure 6 (a is a schematic diagram of the three-point bending fracture test, b is the force-displacement curve of the BFA∥ sample, c is the force-displacement curve of the BFA⊥ sample, and d is the force-displacement curve of the FI sample; ∥ indicates that the force is perpendicular to the sample layer, and ⊥ indicates that the force is parallel to the sample layer) and Figure 7 (a is the elastic contribution curve, b is the plastic contribution curve, and c is the toughness curve).

[0062] Toughness includes elastic and plastic parts, and its calculation formula is as follows:

[0063] J=J el +J pl

[0064]

[0065] E′=E / (1-v 2 )

[0066]

[0067]

[0068] Where, J el and J p1 Represent the elastic contribution and plastic contribution of the specimen, E, v and K respectively I They represent the elastic modulus, Poisson's ratio and stress intensity factor of the specimen respectively, P is the load applied to the specimen, S is the span, B is the thickness of the specimen, W is the total width of the specimen 3 mm, a is the crack length, f(a / W) is a geometric shape factor, which is a dimensionless function of a / W (the ratio of crack length to specimen width), Ap1 is the plastic work, and b is the length of the residual unextended crack.

[0069] Depend on Figure 6 and Figure 7 It can be seen that the maximum toughness of the biodegradable plastic in the embodiment can reach 3.78kJ / m 2 , which is about 3 times that of the biodegradable plastic in the comparative example (1.27kJ / m 2 ), indicating that the “brick-mud” structure formed in the biodegradable plastic in the embodiment can induce plastic loss through the deflection of the crack tip during crack propagation, giving the material excellent fracture toughness.

[0070] 6) Recyclable processing: The biodegradable plastic in the embodiment is added to deionized water and shaken at room temperature for 3 hours. The resulting solution (homogeneous and transparent) is then freeze-dried at a pressure of 5 Pa and a temperature of -80°C for 48 hours to obtain DNA powder. The DNA powder is then used as a raw material to prepare DNA biodegradable plastic, thereby completing a closed-loop recycling process (recycling schematic diagram shown in FIG. Figure 8 shown).

[0071] 7) Degradability test: 0.5 g of the biodegradable plastic in the embodiment was added to 2 mL of an aqueous solution containing DNase I (concentration of 5 U / μL). The biodegradation experiment was carried out at room temperature and the morphological changes were recorded. Optical photographs were taken at the same time. The electrophoretic bands of the degradation solution were then detected by agarose gel electrophoresis. The optical photographs of the morphological changes of the biodegradable plastic at different time points during the degradation process and the gel electrophoresis bands after complete biodegradation were obtained as shown in FIG. Figure 9 (a is an optical photograph of morphological changes, b is a gel electrophoresis band diagram, M1 and M2 in b represent standard DNA gel electrophoresis bands with molecular weights of 23 kp and 5 kp, respectively).

[0072] Depend on Figure 9 It can be seen that: by comparing the number of base pairs with the standard sample, it was found that the DNA band was blurred and the intensity was weakened, indicating that the biodegradable plastic can be completely biodegraded within 8 hours.

[0073] The above embodiments are preferred implementations of the present invention, but the implementations of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing biodegradable plastics, characterized in that: The following steps are involved: 1) Dissolve onion DNA in water to prepare a DNA solution; 2) Injecting the DNA solution into the mold for bidirectional freezing casting to obtain a DNA frozen block; 3) freeze-drying the DNA frozen block to obtain a DNA aerogel block; 4) placing the DNA aerogel block in a water vapor environment for annealing to obtain an annealed DNA aerogel block; 5) stacking multiple annealed DNA aerogel blocks and then compressing and densifying them to obtain biodegradable plastic.

2. The method for preparing biodegradable plastic according to claim 1, wherein: Step 1) The onion DNA is prepared by a preparation method comprising the following steps: rapidly freezing onions and then crushing them to produce onion powder; adding the onion powder to a mixed solution of CTAB extraction buffer and 2-mercaptoethanol for incubation; adding chloroform and isoamyl alcohol and centrifuging the mixture; subjecting the supernatant to alcohol precipitation and centrifugation; and washing and drying the solid matter to obtain the onion DNA.

3. The method for preparing biodegradable plastic according to claim 2, wherein: The incubation is carried out at a temperature of 60° C. to 70° C., and the incubation time is 40 min to 60 min.

4. The method for preparing biodegradable plastic according to claim 2, wherein: The washing comprises the following steps: First wash with anhydrous ethanol, then wash with an ethanol solution with a mass fraction of 70% to 80%, and finally wash with water for multiple times.

5. The method for preparing the biodegradable plastic according to any one of claims 1 to 4, characterized in that: Step 2) The bidirectional freezing casting is carried out at a temperature of -80°C to -60°C, and the casting time is 30 minutes to 60 minutes.

6. The method for preparing a biodegradable plastic according to any one of claims 1 to 4, characterized in that: Step 3) The freeze drying is carried out under the conditions of a pressure of 3Pa to 7Pa and a temperature of -70°C to -50°C, and the freeze drying time is 48h to 72h.

7. The method for preparing a biodegradable plastic according to any one of claims 1 to 4, characterized in that: Step 4) The annealing is performed in a water vapor environment with a relative humidity of 60% to 80%, and the annealing time is 15 minutes to 25 minutes.

8. The method for preparing a biodegradable plastic according to any one of claims 1 to 4, characterized in that: Step 5) The compression densification is carried out at a pressure of 10 MPa to 15 MPa, and the holding time is 30 min to 40 min.

9. A biodegradable plastic, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the biodegradable plastic according to claim 9 in the fields of packaging, medical devices, 3D printing, agricultural tools or environmentally friendly consumer products.

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