Modified starch fiber-based degradable plastic and preparation method thereof

Abstract

The invention discloses a modified starch fiber-based degradable plastic and a preparation method thereof, and belongs to the technical field of bioplastics, citric acid is adopted to improve the interaction between starch and epoxidized soybean oil, borax is used as a cross-linking agent to further improve the compatibility between the starch and citric acid-epoxidized soybean oil oligomer, and the modified starch fiber-based degradable plastic is prepared. The modified starch fiber-based degradable plastic is obtained, finally, the degradable plastic film is prepared through a hot press molding method, the degradable plastic film has good tensile strength, elongation at break and degradation capacity, borax serves as a cross-linking agent and can be complexed with hydroxyl of starch to form a ligand, and a multi-core complex of a net structure is formed. The borax can also form a coordinate bond with hydroxyl or carboxyl of citric acid or generate a polymerization reaction, so that the compatibility of the starch and the citric acid-epoxidized soybean oil oligomer is further improved.

Description

Technical Field

[0001] This invention belongs to the field of bioplastics technology, specifically a modified starch fiber-based degradable plastic and its preparation method. Background Technology

[0002] Plastics are widely used in medical, agricultural, and daily life fields, and have become an essential material for economic development. Most traditional plastics are made from petroleum, which is difficult to degrade in the natural environment, causing serious pollution to the ecological environment. Moreover, petroleum is a non-renewable resource. Degradable plastics can replace traditional plastics, thus conserving petroleum resources. Statistics show that degradable plastics account for only 1% of total plastic production. Therefore, the development of high-performance, low-cost degradable plastics is urgently needed. Due to the renewable nature of biological resources, bio-based degradable plastics are currently a research hotspot in the plastics industry.

[0003] Starch is a natural polymer compound, abundant and widely available, with good film-forming properties, renewable, and completely degradable in the natural environment. Because starch is much cheaper than synthetic biodegradable macromolecules, starch-based biodegradable plastics account for the highest proportion of total bioplastics. Lignocellulose is the world's most abundant biomass resource, and its excellent mechanical properties have made it widely used as a reinforcing agent for starch-based plastics. However, due to the large number of hydroxyl groups in starch and its strong hydrophilicity, starch / cellulose-based biodegradable plastics suffer from insufficient water resistance and mechanical properties, which greatly limits their application range.

[0004] Chinese patent CN117186499A discloses a production process for synthesizing starch-based bioplastics from citric acid epoxidized soybean oil oligomers. In order to improve the poor mechanical properties and easy water absorption of starch-based bioplastics, this application prepared citric acid epoxidized soybean oil oligomers and used them to improve the performance of corn starch-based bioplastics. However, the crosslinking temperature of citric acid epoxidized soybean oil oligomers and starch in this method is too high. At this high temperature, citric acid is prone to cause starch acid hydrolysis, which is not conducive to improving the mechanical properties of starch-based bioplastics. Summary of the Invention

[0005] The purpose of this invention is to provide a modified starch fiber-based biodegradable plastic and its preparation method. This method avoids high-temperature crosslinking and uses borax as a crosslinking agent. Borax can complex with the hydroxyl groups of starch to form ligands, forming a polynuclear complex with a network structure. Borax can also form coordination bonds or undergo polymerization reactions with the hydroxyl or carboxyl groups of citric acid, further improving the compatibility of starch and citric acid-epoxidized soybean oil oligomers.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a modified starch cellulose-based biodegradable plastic includes the following steps: Step 1: Dry and grind microcrystalline cellulose to obtain microcrystalline cellulose particles. Then, activate and swell the microcrystalline cellulose particles with sodium hydroxide to obtain activated microcrystalline cellulose particles. Combine the large number of hydroxyl groups on the surface of the activated microcrystalline cellulose particles with the silanol groups generated by the hydrolysis of γ-aminopropyltriethoxysilane to obtain amino-functionalized microcrystalline cellulose particles. Step 2: The amino groups of amino-functionalized microcrystalline cellulose particles and the imidazole groups of 2-methylimidazolium are co-coordinated with titanium ions in titanium nitrate under hydrothermal conditions to obtain titanium-based MOF / microcrystalline cellulose particles. Step 3: Using starch, glycerol, titanium-based MOF / microcrystalline cellulose particles, deionized water, borax, stearic acid, citric acid-epoxidized soybean oil oligomer solution and Tween 80 as raw materials, a modified starch fiber-based degradable plastic is obtained.

[0007] Furthermore, the specific preparation steps of the citric acid-epoxidized soybean oil oligomer solution are as follows: Citric acid and deionized water are added to a reaction vessel and stirred for 10-15 minutes at 20-25℃ and 500-600 r / min. Then, epoxidized soybean oil is added, and the mixture is heated to 90-100℃ and reacted under nitrogen protection in a sealed environment for 1-1.5 hours. Glycerol is then added as a dissolving agent, and the mixture is stirred for another 10-12 minutes to obtain a citric acid-epoxidized soybean oil oligomer solution.

[0008] Furthermore, the ratio of citric acid, deionized water, epoxidized soybean oil, and glycerin is 80-90g: 120-130mL: 40-50g: 40-45g.

[0009] Furthermore, the specific preparation steps for activated microcrystalline cellulose particles are as follows: Microcrystalline cellulose was dried at 105-110℃ for 3-4 hours and then ground for 2-3 minutes to obtain microcrystalline cellulose particles with a particle size of 20-30 μm. The microcrystalline cellulose particles were then mixed with NaOH and ground for 2-3 minutes. The mixture was then placed in a reactor containing deionized water and stirred for 2-3 hours at 100-120℃ and 500-600 r / min. The mixture was filtered, and the precipitate was washed 2-3 times with deionized water and anhydrous ethanol. The precipitate was then vacuum dried at 60-80℃ for 1-2 hours to obtain activated microcrystalline cellulose particles.

[0010] Furthermore, the ratio of microcrystalline cellulose particles, NaOH, and deionized water is 80-90g: 3-4g: 180-200mL.

[0011] Furthermore, the specific preparation steps for amino-functionalized microcrystalline cellulose particles are as follows: Activated microcrystalline cellulose particles, anhydrous ethanol, and deionized water were added to a reaction vessel and stirred for 10-15 min at 60-70℃ and 500-600 r / min. Then, γ-aminopropyltriethoxysilane was added, and the pH was adjusted to 3-4 with hydrochloric acid solution. The reaction was continued with stirring for 6-7 h. After filtration, the precipitate was washed 2-3 times with deionized water and anhydrous ethanol and dried under vacuum at 60-80℃ for 1-2 h to obtain amino-functionalized microcrystalline cellulose particles.

[0012] Furthermore, the ratio of activated microcrystalline cellulose particles, anhydrous ethanol, deionized water, and γ-aminopropyltriethoxysilane is 70-80g: 150-170mL: 250-300mL: 50-60g.

[0013] Furthermore, the specific preparation steps for titanium-based MOF / microcrystalline cellulose particles are as follows: Amino-functionalized microcrystalline cellulose particles, titanium nitrate, and deionized water were added to a polytetrafluoroethylene-lined autoclave and stirred for 20-30 minutes at 20-25°C and 500-600 r / min. Then, 2-methylimidazole was added, and the mixture was heated to 120-130°C and reacted for another 20-24 hours. The mixture was then allowed to cool naturally to room temperature, filtered, and the precipitate was washed 2-3 times with deionized water and anhydrous ethanol. The precipitate was then dried under vacuum at 60-80°C for 1-2 hours to obtain titanium-based MOF / microcrystalline cellulose particles.

[0014] Furthermore, the ratio of amino-functionalized microcrystalline cellulose particles, titanium nitrate, deionized water, and 2-methylimidazole is 60-70g: 80-90g: 800-900mL: 150-160g.

[0015] Furthermore, the specific preparation steps for modified starch fiber-based biodegradable plastics are as follows: Starch, glycerol, titanium-based MOF / microcrystalline cellulose granules, and deionized water were added to a reactor and stirred for 30-40 minutes at 60-70℃ and 500-600 rpm. Then, crosslinking agents borax, stearic acid, citric acid-epoxidized soybean oil oligomer solution, and Tween 80 were added and stirred until homogeneous. The mixture was stirred for 1-2 hours at 50-60℃ and 500-600 rpm, sealed, and stored at 20-25℃ for 24-26 hours. The mixture was then transferred to a mixer and heated and plasticized at 150-160℃. The plasticized material was extruded using a twin-screw extruder and then pelletized using a pelletizer to obtain modified starch fiber-based degradable plastic.

[0016] Furthermore, the ratio of starch, glycerol, titanium-based MOF / microcrystalline cellulose particles, deionized water, borax, stearic acid, citric acid-epoxidized soybean oil oligomer solution, and Tween 80 is 120-150g: 25-40g: 60-70g: 90-320mL: 3-4g: 2-4g: 140-145g: 5-8g.

[0017] The beneficial effects of this invention are: 1. The modified starch fiber-based degradable plastic prepared by the present invention uses citric acid to improve the interaction between starch and epoxidized soybean oil, and then uses borax as a crosslinking agent to further improve the compatibility between starch and citric acid-epoxidized soybean oil oligomers to obtain modified starch fiber-based degradable plastic. Finally, a degradable plastic film is prepared by hot pressing. The degradable plastic film has good tensile strength, elongation at break and degradation ability.

[0018] 2. In this invention, citric acid is not used as a curing agent for epoxidized soybean oil. By controlling the ratio of citric acid and epoxidized soybean oil and the reaction time, a citric acid-epoxidized soybean oil oligomer solution is synthesized. Borax can complex with the hydroxyl groups of the swollen starch to form a ligand, forming a polynuclear complex with a network structure. Borax can also form coordination bonds or undergo polymerization reactions with the hydroxyl or carboxyl groups of citric acid, thereby improving the overall crosslinking degree of the degradable plastic.

[0019] 3. In this invention, titanium-based MOF / microcrystalline cellulose particles serve as a reinforcing phase, which, unlike traditional microcrystalline cellulose, can further improve the tensile strength and elongation at break of degradable plastics. The titanium-based MOF / microcrystalline cellulose particles are activated and swollen using NaOH alkali to form a network structure. Furthermore, the swollen microcrystalline cellulose particles are easily oxidized and degraded, meeting the development and application requirements of green and low-carbon technologies. The swollen microcrystalline cellulose particles form a porous network, guiding the orderly growth of titanium-based MOF on its surface, forming a hierarchical pore structure. The titanium-based MOF / microcrystalline cellulose particles of this invention possess excellent photocatalytic activity, endowing modified starch fiber-based degradable plastics with excellent degradability and reducing environmental pollution. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1: A method for preparing a modified starch fiber-based biodegradable plastic, comprising the following steps: S1: Add 80g of citric acid and 120mL of deionized water to the reaction vessel, stir for 10min at 20℃ and 500r / min, then add 140g of epoxidized soybean oil, heat to 90℃, and react in a sealed manner for 1h under nitrogen protection. Then add 40g of glycerol as a dissolving solution and continue stirring for 10min to obtain a citric acid-epoxidized soybean oil oligomer solution.

[0022] The carboxyl groups in citric acid can attack and open the rings of the epoxy groups in epoxidized soybean oil. By controlling the ratio of citric acid to epoxidized soybean oil and the reaction time, a citric acid-epoxidized soybean oil oligomer solution can be obtained.

[0023] S2: 100g of microcrystalline cellulose was dried at 105℃ for 3h and ground for 2min to obtain microcrystalline cellulose particles with a particle size of 20μm; then 80g of microcrystalline cellulose particles and 3g of NaOH were mixed and ground for 2min, and then placed in a reaction vessel containing 180mL of deionized water. The mixture was stirred and reacted at 100℃ and 500r / min for 2h. After filtration, the precipitate was washed twice with deionized water and anhydrous ethanol and dried under vacuum at 60℃ for 1h to obtain activated microcrystalline cellulose particles.

[0024] When microcrystalline cellulose particles are placed in an alkaline environment of NaOH, the intermolecular cohesion of the microcrystalline cellulose particles decreases, making them easier to swell. Since the surface of microcrystalline cellulose contains a large number of hydroxyl groups, the particles are prone to agglomeration through hydrogen bonds. The swollen microcrystalline cellulose particles form a network structure, which further improves the strength of the plastic. In addition, the swollen microcrystalline cellulose particles are easy to oxidize and degrade, which improves the degradability of the plastic.

[0025] S3: Add 70g of activated microcrystalline cellulose particles, 150mL of anhydrous ethanol and 250mL of deionized water to a reaction vessel, stir for 10min at 60℃ and 500r / min, then add 50g of γ-aminopropyltriethoxysilane, adjust the pH to 3 with hydrochloric acid solution, continue stirring for 6h, filter, wash the precipitate twice with deionized water and anhydrous ethanol, and vacuum dry at 60℃ for 1h to obtain amino-functionalized microcrystalline cellulose particles.

[0026] The silanol groups generated by the hydrolysis of γ-aminopropyltriethoxysilane combine with the hydroxyl groups of the activated microcrystalline cellulose particles. This prevents the microcrystalline cellulose from agglomerating due to its large hydroxyl content and also imparts amino groups to the activated microcrystalline cellulose particles.

[0027] S4: Add 60g of amino-functionalized microcrystalline cellulose particles, 80g of titanium nitrate, and 800mL of deionized water to a polytetrafluoroethylene-lined autoclave. Stir for 20min at 20℃ and 500r / min. Then add 150g of 2-methylimidazole, heat to 120℃, and continue the reaction for 20h. Cool naturally to room temperature, filter, wash the precipitate twice with deionized water and anhydrous ethanol, and dry under vacuum at 60℃ for 1h to obtain titanium-based MOF / microcrystalline cellulose particles.

[0028] The amino groups on the surface of amino-functionalized microcrystalline cellulose particles can be deprotonated to act as Lewis bases and coordinate with titanium ions. Furthermore, the N atom of the imidazole ring provides a lone pair of electrons to coordinate with titanium ions, resulting in titanium-based MOF / microcrystalline cellulose particles.

[0029] S5: Add 120g starch, 25g glycerol, 60g titanium-based MOF / microcrystalline cellulose granules and 90mL deionized water to a reactor and stir for 30min at 60℃ and 500r / min. Then add 3g crosslinking agent borax, 2g stearic acid, 40g citric acid-epoxidized soybean oil oligomer solution and 5g Tween 80, stir and mix evenly, stir for 1h at 50℃ and 500r / min, seal and store at 20℃ for 24h. Then transfer to a mixer and heat and plasticize at 150℃. Extrude the plasticized material using a twin-screw extruder and then pelletize it using a pelletizer to obtain modified starch fiber-based degradable plastic with a particle size of 0.5±0.2mm.

[0030] Borax is used as a crosslinking agent. After borax is dissolved in water, it undergoes a hydrolysis reaction to form B(OH) ions, which react with some of the hydroxyl groups on starch and titanium-based MOF / microcrystalline cellulose particles to form borate ester bonds, thus forming a three-dimensional crosslinked network.

[0031] Example 2: A method for preparing a modified starch fiber-based biodegradable plastic, comprising the following steps: S1: Add 85g of citric acid and 125mL of deionized water to the reaction vessel and stir for 12.5min at 22.5℃ and 550r / min. Then add 143g of epoxidized soybean oil, heat to 95℃, and react in a sealed manner for 1.25h under nitrogen protection. Then add 42.5g of glycerol as a dissolving solution and continue stirring for 11min to obtain a citric acid-epoxidized soybean oil oligomer solution.

[0032] S2: 110g of microcrystalline cellulose was dried at 107.5℃ for 3.5h and ground for 2.5min to obtain microcrystalline cellulose particles with a particle size of 25μm; then 85g of microcrystalline cellulose particles and 3.5g of NaOH were mixed and ground for 2.5min, and then placed in a reaction vessel containing 190mL of deionized water. The mixture was stirred and reacted at 110℃ and 550r / min for 2.5h. After filtration, the precipitate was washed 2.5 times with deionized water and anhydrous ethanol and dried under vacuum at 70℃ for 1.5h to obtain activated microcrystalline cellulose particles.

[0033] S3: 75g of activated microcrystalline cellulose particles, 160mL of anhydrous ethanol and 275mL of deionized water were added to a reaction vessel and stirred at 65℃ and 550r / min for 12.5min. Then, 55g of γ-aminopropyltriethoxysilane was added, and the pH was adjusted to 3.5 with hydrochloric acid solution. The reaction was continued to be stirred for 6.5h. After filtration, the precipitate was washed 2.5 times with deionized water and anhydrous ethanol and dried under vacuum at 70℃ for 1.5h to obtain amino-functionalized microcrystalline cellulose particles.

[0034] S4: Add 65g of amino-functionalized microcrystalline cellulose particles, 85g of titanium nitrate, and 850mL of deionized water to a polytetrafluoroethylene-lined autoclave. Stir for 25min at 22.5℃ and 550r / min. Then add 155g of 2-methylimidazole, heat to 125℃, and continue the reaction for 22h. Cool naturally to room temperature, filter, wash the precipitate 2.5 times with deionized water and anhydrous ethanol, and dry under vacuum at 70℃ for 1.5h to obtain titanium-based MOF / microcrystalline cellulose particles.

[0035] S5: Add 135g starch, 32.5g glycerol, 65g titanium-based MOF / microcrystalline cellulose granules and 175mL deionized water to a reactor and stir for 35min at 65℃ and 550r / min. Then add 3.5g crosslinking agent borax, 3g stearic acid, 45g citric acid-epoxidized soybean oil oligomer solution and 6.5g Tween 80, stir and mix evenly, stir for 1.5h at 55℃ and 550r / min, seal and store at 22.5℃ for 25h. Then transfer to a mixer and heat and plasticize at 155℃. Extrude the plasticized material using a twin-screw extruder and then pelletize it using a pelletizer to obtain modified starch fiber-based degradable plastic with a particle size of 0.5±0.2mm.

[0036] Modified starch fiber-based biodegradable plastics were obtained.

[0037] Example 3: A method for preparing a modified starch fiber-based biodegradable plastic, comprising the following steps: S1: Add 90g of citric acid and 130mL of deionized water to a reaction vessel and stir for 15min at 25℃ and 600r / min. Then add 145g of epoxidized soybean oil, heat to 100℃, and react in a sealed manner for 1.5h under nitrogen protection. Then add 45g of glycerol as a dissolving solution and continue stirring for 12min to obtain a citric acid-epoxidized soybean oil oligomer solution.

[0038] S2: 120g of microcrystalline cellulose was dried at 110℃ for 4h and ground for 3min to obtain microcrystalline cellulose particles with a particle size of 30μm; then 90g of microcrystalline cellulose particles and 4g of NaOH were mixed and ground for 3min, and then placed in a reaction vessel containing 200mL of deionized water. The mixture was stirred and reacted at 120℃ and 600r / min for 3h. After filtration, the precipitate was washed three times with deionized water and anhydrous ethanol and dried under vacuum at 80℃ for 2h to obtain activated microcrystalline cellulose particles.

[0039] S3: Add 80g of activated microcrystalline cellulose particles, 170mL of anhydrous ethanol and 300mL of deionized water to a reaction vessel, stir for 15min at 70℃ and 600r / min, then add 60g of γ-aminopropyltriethoxysilane, adjust the pH to 4 with hydrochloric acid solution, continue stirring for 7h, filter, wash the precipitate three times with deionized water and anhydrous ethanol, and vacuum dry at 80℃ for 2h to obtain amino-functionalized microcrystalline cellulose particles.

[0040] S4: 70g of amino-functionalized microcrystalline cellulose particles, 90g of titanium nitrate and 900mL of deionized water were added to a polytetrafluoroethylene-lined autoclave and stirred for 30min at 25℃ and 600r / min. Then 160g of 2-methylimidazole was added, and the mixture was heated to 130℃ and reacted for 24h. After cooling to room temperature, the mixture was filtered, and the precipitate was washed three times with deionized water and anhydrous ethanol. The precipitate was then dried under vacuum at 80℃ for 2h to obtain titanium-based MOF / microcrystalline cellulose particles.

[0041] S5: Add 150g starch, 40g glycerol, 70g titanium-based MOF / microcrystalline cellulose granules and 320mL deionized water to a reactor and stir for 40min at 70℃ and 600r / min. Then add 4g crosslinking agent borax, 4g stearic acid, 50g citric acid-epoxidized soybean oil oligomer solution and 8g Tween 80, stir and mix evenly, stir for 2h at 60℃ and 600r / min, seal and store at 25℃ for 26h. Then transfer to a mixer and heat at 160℃ for plasticization to obtain thermoplastic starch. Extrude the plasticized material using a twin-screw extruder and then pelletize it using a pelletizer to obtain modified starch fiber-based degradable plastic with a particle size of 0.5±0.2mm.

[0042] Comparative Example 1: Based on Example 3, the titanium-based MOF / microcrystalline cellulose particles in step S5 were replaced with amino-functionalized microcrystalline cellulose particles in step S3, while the other steps remained unchanged, to prepare a modified starch fiber-based degradable plastic.

[0043] Comparative Example 2: Based on Example 3, the amino-functionalized microcrystalline cellulose particles in step S4 were replaced with the activated microcrystalline cellulose particles in step S2 to prepare MOF composite microcrystalline cellulose particles with low binding degree, and the titanium-based MOF / microcrystalline cellulose particles in step S5 were replaced, while the other steps remained unchanged, to prepare a modified starch fiber-based degradable plastic.

[0044] Comparative Example 3: Based on Example 3, the activated microcrystalline cellulose particles in step S3 were replaced with raw material microcrystalline cellulose that had not been treated in step S2, while the other steps remained unchanged, to prepare a modified starch fiber-based degradable plastic.

[0045] Comparative Example 4: Based on Example 3, 4g of crosslinking agent borax, 4g of stearic acid, 50g of citric acid-epoxidized soybean oil oligomer solution and 8g of Tween 80 were added, and after stirring and mixing evenly, the mixture was stirred at 90℃ and 600r / min for 2h, while the other steps remained unchanged, to prepare a modified starch fiber-based degradable plastic.

[0046] In the examples and comparative examples: Microcrystalline cellulose and 2-methylimidazole were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0047] Borax was purchased from Tianjin Jinyaoxiangcheng Technology Co., Ltd.

[0048] The epoxidized soybean oil was purchased from Anhui Yuanyi Chemical Co., Ltd.

[0049] The modified starch fiber-based degradable plastics obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests. The modified starch fiber-based degradable plastics were transferred into a mold and hot-pressed at a pressure of 20 MPa and a temperature of 140°C for 10 min to prepare a degradable plastic film with a thickness of 1 mm. The results are shown in Table 1. 1. Tensile strength and elongation at break tests: The tests shall be conducted in accordance with the standard GB / T 1040.1-2025.

[0050] 2. Degradation time test: The test shall be conducted in accordance with the standard GB / T 19277.1-2025.

[0051] Table 1 Test Table for Degradable Plastic Film Performance project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Tensile strength (MPa) 14.9 15.5 16.2 11.2 11.9 10.1 8.2 Elongation at break (%) 86 89 95 50 48 44 32 Degradation time (days) 55 52 47 80 65 82 48 As can be seen from Table 1, the modified starch fiber-based degradable plastics obtained in Examples 1-3 have significantly better tensile strength and elongation at break than the comparative examples, and their degradation time is significantly shorter than that of the comparative examples. This indicates that the modified starch fiber-based degradable plastics prepared by the present invention have good tensile strength, elongation at break and degradation ability.

[0052] In Comparative Example 1, the titanium-based MOF / microcrystalline cellulose particles in step S5 were replaced with amino-functionalized microcrystalline cellulose particles in step S3. The amino-functionalized microcrystalline cellulose particles improved the interfacial compatibility through silane coupling, but lacked the rigid framework of MOF and could not effectively transfer stress. The porous structure of MOF can absorb deformation energy, while the flexibility of simple amino-functionalized fibers is insufficient. The titanium ions in MOF can catalyze the hydrolysis of ester bonds, and their absence significantly slows down the degradation rate. Furthermore, the amino groups are protonated in an acidic environment, which weakens the crosslinking efficiency with borax, resulting in a loose crosslinking network.

[0053] Comparative Example 2 replaced amino-functionalized microcrystalline cellulose particles with activated microcrystalline cellulose particles. Activated microcrystalline cellulose particles swelled only through alkali treatment, and only hydroxyl groups existed on the surface. They had weak interfacial bonding with starch / citric acid oligomers, and the particles were prone to agglomeration, resulting in stress concentration points. Unfunctionalized microcrystalline cellulose particles had poor compatibility with hydrophobic epoxidized soybean oil, significantly reduced toughness and increased hardness, leading to slow degradation.

[0054] In Comparative Example 3, the activated microcrystalline cellulose particles in step S3 were replaced with raw material microcrystalline cellulose that had not been treated in step S2. This was because the surface of microcrystalline cellulose contains a large number of hydroxyl groups, and the particles are prone to agglomeration through hydrogen bonds. This results in extremely poor compatibility with hydrophobic citric acid-epoxidized soybean oil oligomers, leading to uneven dispersion of microcrystalline cellulose in the matrix, which acts as a brittle fracture point and causes a decrease in mechanical properties.

[0055] In Comparative Example 4, after setting the stirring temperature to 90℃, as shown in Table 1, all properties decreased significantly. This crosslinking temperature is too high, which easily leads to the acid hydrolysis of starch by citric acid, thereby reducing the function of starch and causing a significant decrease in various energy absorption properties.

[0056] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a modified starch fiber-based biodegradable plastic, characterized in that, Includes the following steps: Step 1: Dry and grind microcrystalline cellulose to obtain microcrystalline cellulose particles. Then, activate and swell the microcrystalline cellulose particles with sodium hydroxide to obtain activated microcrystalline cellulose particles. Combine the large number of hydroxyl groups on the surface of the activated microcrystalline cellulose particles with the silanol groups generated by the hydrolysis of γ-aminopropyltriethoxysilane to obtain amino-functionalized microcrystalline cellulose particles. Step 2: The amino groups of amino-functionalized microcrystalline cellulose particles and the imidazole groups of 2-methylimidazolium are co-coordinated with titanium ions in titanium nitrate under hydrothermal conditions to obtain titanium-based MOF / microcrystalline cellulose particles. Step 3: Using starch, glycerol, titanium-based MOF / microcrystalline cellulose particles, deionized water, borax, stearic acid, citric acid-epoxidized soybean oil oligomer solution and Tween 80 as raw materials, a modified starch fiber-based biodegradable plastic is obtained.

2. The method for preparing a modified starch fiber-based degradable plastic according to claim 1, characterized in that, The specific preparation steps of the citric acid-epoxidized soybean oil oligomer solution are as follows: Add citric acid and deionized water to a reaction vessel, stir at 20-25℃ and 500-600r / min for 10-15min, then add epoxidized soybean oil, heat to 90-100℃, and react under nitrogen protection in a sealed environment for 1-1.5h, then add glycerol and continue stirring for 10-12min to obtain a citric acid-epoxidized soybean oil oligomer solution. The ratio of citric acid, deionized water, epoxidized soybean oil, and glycerin is 80-90g: 120-130mL: 40-50g: 40-45g.

3. The method for preparing a modified starch fiber-based biodegradable plastic according to claim 2, characterized in that, The specific preparation steps for the activated microcrystalline cellulose particles are as follows: Microcrystalline cellulose was dried at 105-110℃ for 3-4 hours and then ground for 2-3 minutes to obtain microcrystalline cellulose particles with a particle size of 20-30 μm. The microcrystalline cellulose particles were then mixed with NaOH and ground for 2-3 minutes. The mixture was then placed in a reactor containing deionized water and stirred for 2-3 hours at 100-120℃ and 500-600 r / min. The mixture was filtered, and the precipitate was washed 2-3 times with deionized water and anhydrous ethanol. The precipitate was then vacuum dried at 60-80℃ for 1-2 hours to obtain activated microcrystalline cellulose particles.

4. The method for preparing a modified starch fiber-based degradable plastic according to claim 3, characterized in that, The ratio of microcrystalline cellulose particles, NaOH, and deionized water is 80-90g: 3-4g: 180-200mL.

5. The method for preparing a modified starch fiber-based degradable plastic according to claim 1, characterized in that, The specific preparation steps for the amino-functionalized microcrystalline cellulose particles are as follows: Activated microcrystalline cellulose particles, anhydrous ethanol, and deionized water were added to a reaction vessel and stirred at 60-70℃ and 500-600 r / min for 10-15 min. Then, γ-aminopropyltriethoxysilane was added, and the pH was adjusted to 3-4 with hydrochloric acid solution. The reaction was continued to be stirred for 6-7 h. After filtration, washing, and vacuum drying, amino-functionalized microcrystalline cellulose particles were obtained.

6. The method for preparing a modified starch fiber-based degradable plastic according to claim 5, characterized in that, The ratio of activated microcrystalline cellulose particles, anhydrous ethanol, deionized water, and γ-aminopropyltriethoxysilane is 70-80g: 150-170mL: 250-300mL: 50-60g.

7. The method for preparing a modified starch fiber-based degradable plastic according to claim 1, characterized in that, The specific preparation steps for the titanium-based MOF / microcrystalline cellulose particles are as follows: Amino-functionalized microcrystalline cellulose particles, titanium nitrate, and deionized water were added to a polytetrafluoroethylene-lined autoclave and stirred for 20-30 min at 20-25℃ and 500-600 r / min. Then, 2-methylimidazole was added, and the mixture was heated to 120-130℃ and reacted for 20-24 h. The mixture was then allowed to cool naturally to room temperature, filtered, and the precipitate was washed 2-3 times with deionized water and anhydrous ethanol. The precipitate was then dried under vacuum to obtain titanium-based MOF / microcrystalline cellulose particles. The ratio of amino-functionalized microcrystalline cellulose particles, titanium nitrate, deionized water, and 2-methylimidazole is 60-70g: 80-90g: 800-900mL: 150-160g.

8. The method for preparing a modified starch fiber-based degradable plastic according to claim 1, characterized in that, The specific preparation steps of the modified starch fiber-based biodegradable plastic are as follows: Starch, glycerol, titanium-based MOF / microcrystalline cellulose particles, and deionized water were added to a reactor and stirred at 60-70℃ and 500-600 rpm for 30-40 minutes. Then, crosslinking agents borax, stearic acid, citric acid-epoxidized soybean oil oligomer solution, and Tween 80 were added and stirred until homogeneous. The mixture was stirred at 50-60℃ and 500-600 rpm for 1-2 hours, sealed, and stored at 20-25℃ for 24-26 hours. The mixture was then transferred to an internal mixer and heated and plasticized at 150-160℃. The plasticized material was extruded and pelletized to obtain modified starch fiber-based degradable plastic.

9. The method for preparing a modified starch fiber-based degradable plastic according to claim 8, characterized in that, The ratio of starch, glycerol, titanium-based MOF / microcrystalline cellulose particles, deionized water, borax, stearic acid, citric acid-epoxidized soybean oil oligomer solution, and Tween 80 is 120-150g: 25-40g: 60-70g: 90-320mL: 3-4g: 2-4g: 140-145g: 5-8g.

10. A modified starch fiber-based biodegradable plastic, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.