Bio-based degradable plastic and preparation method thereof
By combining polylactic acid with activated cellulose, graphene oxide, and activated montmorillonite to form a multi-network structure, the problems of slow degradation and poor stability of polylactic acid are solved, and the structural stability and strength under high temperature environment are improved, making it suitable for engineering plastics.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HANGZHOU YUNSHANG NEW MATERIALS CO LTD
- Filing Date
- 2023-05-25
- Publication Date
- 2026-04-17
AI Technical Summary
Existing bio-based biodegradable plastics such as polylactic acid degrade slowly in soil, have poor dimensional stability, and poor processing thermal stability, which limits their application as engineering plastics.
By combining polylactic acid with activated cellulose, graphene oxide, and activated montmorillonite to form a multi-network structure, the degradation rate and mechanical properties of plastics can be improved by utilizing the hydrophilicity of graphene oxide and the catalytic activity of nano-titanium dioxide.
It has achieved improved structural stability and strength of bio-based biodegradable plastics in high-temperature environments, accelerated degradation rate, and good thermal stability and mechanical properties.
Smart Images
Figure CN121873518A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of biodegradable plastics technology, and more particularly to a bio-based biodegradable plastic and its preparation method. Background Technology
[0002] Plastics are an indispensable type of synthetic polymer material in human life. However, due to their non-degradability and high recycling costs, only about 9% of plastics can currently be recycled. The world's annual plastic production is enormous, and a large amount of waste plastic is buried underground as garbage, undoubtedly causing great harm to the environment.
[0003] Meanwhile, most ordinary plastics are made from petrochemical raw materials. The extensive application of plastics leads to the rapid extraction and utilization of petroleum for plastic production, directly impacting the unsustainable development of energy. In response, bio-based plastics and biodegradable plastics have emerged, offering solutions to the problem of sustainable material development. Bio-based plastics are an effective way to address the environmental pollution caused by plastic waste.
[0004] Currently, the most common biomass-based thermoplastic polymers include polylactic acid (PLA), polycaprolactone (PVC), and polyhydroxyalkanoates (PHA). PLA, a polymer obtained primarily from lactic acid through copolymerization, can be completely degraded into water and carbon dioxide in soil, meeting green environmental protection requirements and causing minimal environmental damage, thus possessing broad application prospects. PLA's production process is pollution-free, and the product is biodegradable, achieving a natural cycle, making it an ideal green biomass-based thermoplastic polymer.
[0005] Because of its compact overall structure, polylactic acid (PLA) molecules generally have a relatively regular arrangement due to the dipole forces between molecules. As a result, water does not easily penetrate into the tissue, making the hydrolysis process slower. Therefore, its actual degradation rate in soil is slow, generally requiring two to three years to complete the degradation process. In addition, its poor dimensional stability, brittleness, and poor thermal stability during processing limit its application as an engineering plastic.
[0006] Cellulose, as the most abundant natural polymer in nature, is not only renewable but also completely biodegradable. However, the extremely strong hydrogen bonds between cellulose chains make it difficult to dissolve and impossible to thermoform. Furthermore, the synthesis processes of polylactic acid and cellulose are complex and costly.
[0007] How to reinforce polylactic acid resin, especially by using cellulose, has become a new research topic in this industry. Summary of the Invention
[0008] The purpose of this invention is to address the shortcomings of existing technologies by proposing a bio-based biodegradable plastic and its preparation method.
[0009] A method for preparing bio-based biodegradable plastics includes the following steps:
[0010] S1. Add polylactic acid to dichloromethane and stir at 40-50℃ until the system becomes transparent. Let it stand to remove air bubbles, then add it dropwise to the activated cellulose dispersion and stir for 1-2 hours. Add graphene oxide and glyoxal solution and continue stirring for 10-20 minutes to adjust the system to acidity. Stir in an ice-water bath for 1-2 hours, raise the temperature to 100-110℃, stir vigorously for 5-15 minutes, cool to room temperature, freeze dry under vacuum, and pulverize to obtain activated polylactic acid.
[0011] S2. Add montmorillonite to hydrochloric acid, add sodium dithionite and stir for 10-20 hours, filter, wash and add tetrabutyl titanate, ball mill for 1-2 hours, add water and continue milling for 1-2 hours, dehydrate and dry, cool and pulverize to obtain activated montmorillonite.
[0012] S3. Stir polystyrene, polyamide, compatibilizer, antioxidant and activated polylactic acid for 1-5 minutes at a stirring temperature of 150-170℃, cool down to 120-130℃, add activated montmorillonite and stir for 1-2 minutes to obtain premix.
[0013] S4. Extrude the premixed material into granules, and then hot-press the granules. First, preheat at 170-200℃ for 5-10 minutes, vent 1-10 times, and then hold at 5-10MPa for 1-5 minutes to obtain bio-based biodegradable plastic.
[0014] Preferably, in S1, the mass ratio of polylactic acid, activated cellulose dispersion, graphene oxide, and glyoxal solution is 30-60:200-500:1-5:1-2, the solid content of the activated cellulose dispersion is 1-2%, and the concentration of the glyoxal solution is 1-2 mol / L.
[0015] Preferably, in S1, polylactic acid is obtained by polymerization of bio-based lactic acid, and the melting point of polylactic acid is 160-170℃, and the melt flow index (MFR, 2.16kg, 190℃) is ≤10g / 10min.
[0016] Preferably, in S1, activated cellulose is prepared by the following steps: waste corn stalks are crushed, added to sodium hydroxide solution and soaked at room temperature for 10-30 hours, heated to 40-60℃ and stirred for 1-5 hours, filtered, washed, dried, added to hydrochloric acid, boiled and refluxed and stirred for 1-5 hours, filtered, the filter residue is washed until neutral, and freeze-dried to obtain activated cellulose.
[0017] More preferably, the concentration of the sodium hydroxide solution is 1-2 mol / L and the concentration of the hydrochloric acid is 1-2.5 mol / L.
[0018] More preferably, the degree of polymerization of the obtained activated cellulose is 210-250, the crystallinity is 81.3-84.5%, and the particle size is ≤50μm.
[0019] Preferably, in S2, the mass ratio of montmorillonite, sodium dithionite, and tetrabutyl titanate is 2-10:0.1-1:1-3.
[0020] Preferably, in S3, the mass ratio of polystyrene, polyamide, compatibilizer, antioxidant, activated polylactic acid, and activated montmorillonite is 1-15:15-25:1-3:1-3:35-70:2-12.
[0021] Preferably, in S3, the compatibilizer is a maleic anhydride grafted compatibilizer.
[0022] Preferably, in S3, the antioxidant is at least one of antioxidant BHT, antioxidant DNP, antioxidant DLTP, antioxidant TNP, antioxidant TPP, and antioxidant 1010.
[0023] Preferably, in S4, a twin-screw extruder is used for extrusion granulation. The temperature of the feeding section of the twin-screw extruder is 140-160℃, the temperature of the compression section is 180-200℃, the temperature of the metering section is 190-210℃, the temperature of the die head is 200-220℃, and the screw speed is 60-100 r / min.
[0024] A bio-based biodegradable plastic is prepared using the above-mentioned method for preparing bio-based biodegradable plastics.
[0025] The technical effects of this invention are as follows:
[0026] This application uses polylactic acid as a matrix. With the assistance of graphene oxide, activated cellulose is suspended and uniformly dispersed in the system. Glyoxal crosslinking is used. Polylactic acid undergoes an acetal reaction with the hydroxyl groups on the activated cellulose. Activated cellulose can form a network structure in the system due to the van der Waals forces and hydrogen bonds between its surface hydroxyl groups. After glyoxal crosslinking, a multi-layer network structure is formed. As a long-chain polymer, polylactic acid undergoes an esterification reaction with activated cellulose in a high-temperature environment to form a three-dimensional structure, which becomes more stable and has high strength. However, due to the conversion of a large number of hydrophilic hydroxyl groups into hydrophobic groups, the hydrophilicity is greatly reduced.
[0027] Because of its hydrophilic to hydrophobic distribution from the edge to the center of the sheet, graphene oxide can not only promote the uniform distribution of activated cellulose in the system, but also, in a high-temperature environment, the carboxyl groups on the highly dispersed graphene oxide can react and bind in the above-mentioned three-dimensional network structure, which greatly improves the hydrophilicity. After the plastic degrades, its regular sheet structure can quickly promote the diffusion of water molecules. Graphene oxide can also effectively avoid the phenomenon of thermal stress concentration during high-temperature processes and can quickly promote the uniformity of system temperature, effectively reducing the formation of porous structures in activated polylactic acid.
[0028] This application involves inserting tetrabutyl titanate into the structural layers of layered montmorillonite, then hydrolyzing it to generate titanium hydroxide, followed by calcination at 300-350℃ to generate nano-titanium dioxide particles within the montmorillonite sheets. This not only results in a very high degree of bonding between the nano-titanium dioxide and the montmorillonite sheets, but also enhances its chemical activity.
[0029] When activated polylactic acid is blended with polystyrene and polyamide and subjected to high-temperature treatment, the molecular chains become entangled. This process improves the melt strength and mechanical strength of the blends. Furthermore, when combined with activated montmorillonite, the activated montmorillonite not only has a large specific surface area and excellent hydrophilicity but also contains polar hydroxyl groups that interact with activated polylactic acid to form hydrogen bonds. Meanwhile, titanium dioxide exhibits high bonding strength and catalytic activity within the activated montmorillonite sheets. During degradation, nano-titanium dioxide is not easily released, thus maintaining excellent catalytic activity.
[0030] This invention uses widely available cellulose biomass resources as raw materials, which can be thermally processed and the resulting bioplastics have higher tensile strength and Young's modulus, and are easily degraded after disposal. Attached Figure Description
[0031] Figure 1 The graph shows the change in water absorption rate of the bio-based biodegradable plastics obtained in Example 5 and Comparative Examples 1-2 during the hydrolysis and degradation process.
[0032] Figure 2 The graph shows the weight loss rate of the bio-based biodegradable plastics obtained in Example 5 and Comparative Examples 1-2 during the hydrolysis and degradation process.
[0033] Figure 3 The graph shows the change in weight loss rate of the bio-based biodegradable plastics obtained in Example 5 and Comparative Examples 1-2 during the composting degradation process.
[0034] Figure 4 The graph shows a comparison of the tensile and flexural properties of the bio-based biodegradable plastics obtained in Example 5 and Comparative Examples 1-2.
[0035] Figure 5 Thermogravimetric analysis (TGA) diagrams of the bio-based biodegradable plastics obtained in Example 5 and Comparative Examples 1-2 are shown. Detailed Implementation
[0036] The present invention will be further explained below with reference to specific embodiments.
[0037] Example 1
[0038] A method for preparing bio-based biodegradable plastics includes the following steps:
[0039] S1. Crush waste corn stalks, add them to a 1 mol / L sodium hydroxide solution and soak at room temperature for 10 h, heat to 40℃ and stir for 1 h, filter, wash, dry, add to a 1 mol / L hydrochloric acid solution, boil and then reflux and stir at 50 r / min for 1 h, filter, wash the filter residue until it is neutral, freeze dry to obtain activated cellulose.
[0040] 30 kg of polylactic acid was added to 100 kg of dichloromethane and stirred at 40 °C until the system became transparent. After standing to remove air bubbles, it was added dropwise to 200 kg of activated cellulose dispersion with a solid content of 1% and stirred at 100 r / min for 1 h. Then, 1 kg of graphene oxide and 1 kg of 1 mol / L glyoxal solution were added and stirred for another 10 min to adjust the system to acidity. The mixture was stirred for 20 min and then stirred in an ice-water bath for 1 h. The temperature was raised to 100 °C and stirred vigorously for 5 min at a stirring speed of 1000 r / min. The mixture was then cooled to room temperature, freeze-dried under vacuum, and pulverized to obtain activated polylactic acid.
[0041] S2. Add 2 kg of montmorillonite to 50 kg of 2% hydrochloric acid, add 0.1 kg of sodium dithionite, stir at 1000 r / min for 10 h, filter, wash, add 1 kg of tetrabutyl titanate, ball mill for 1 h, add 5 kg of water and continue grinding for 1 h, dehydrate, dry at 300℃, cool, and pulverize to obtain activated montmorillonite.
[0042] S3. Vacuum dry 1 kg of polystyrene, 15 kg of polyamide, 1 kg of maleic anhydride graft compatibilizer and 1 kg of antioxidant BHT respectively, add them to 35 kg of activated polylactic acid in a mixer and stir for 1 min at a stirring temperature of 150℃. Cool down to 120℃, add 2 kg of activated montmorillonite, and continue stirring at 200 r / min for 1 min to obtain a premix.
[0043] S4. Add the premixed material to a twin-screw extruder for granulation. The temperature of the feeding section is 140℃, the temperature of the compression section is 180℃, the temperature of the metering section is 190℃, the temperature of the die head is 200℃, and the screw speed is 60r / min. Place the granules on the mold and put them in a hot press. Preheat at 170℃ for 5min, vent once, and hold at 5MPa for 1min to obtain bio-based biodegradable plastic.
[0044] Example 2
[0045] A method for preparing bio-based biodegradable plastics includes the following steps:
[0046] S1. Crush waste corn stalks, add them to a 2 mol / L sodium hydroxide solution and soak at room temperature for 30 h, heat to 60℃ and stir for 5 h, filter, wash, dry, add to a 2.5 mol / L hydrochloric acid solution, boil and then reflux and stir at 100 r / min for 5 h, filter, wash the filter residue until it is neutral, freeze dry to obtain activated cellulose.
[0047] 60 kg of polylactic acid was added to 200 kg of dichloromethane and stirred at 50 °C until the system became transparent. After standing to remove air bubbles, it was added dropwise to 500 kg of activated cellulose dispersion with a solid content of 2% and stirred at 500 r / min for 2 h. Then, 5 kg of graphene oxide and 2 kg of 2 mol / L glyoxal solution were added and stirred for another 20 min. The system was adjusted to be acidic and stirred for 50 min. The mixture was then stirred in an ice-water bath for 2 h, heated to 110 °C, and stirred vigorously for 15 min at a stirring speed of 2000 r / min. The mixture was then cooled to room temperature, freeze-dried under vacuum, and pulverized to obtain activated polylactic acid.
[0048] S2. Add 10 kg of montmorillonite to 100 kg of 4% hydrochloric acid, add 1 kg of sodium dithionite, stir at 2000 r / min for 20 h, filter, wash, add 3 kg of tetrabutyl titanate, ball mill for 2 h, add 10 kg of water and continue milling for 2 h, dehydrate, dry at 350℃, cool, and pulverize to obtain activated montmorillonite.
[0049] S3. Vacuum dry 15 kg of polystyrene, 25 kg of polyamide, 3 kg of maleic anhydride graft compatibilizer, and 3 kg of antioxidant 1010 separately. Add them to 70 kg of activated polylactic acid in a mixer and stir for 5 min at a temperature of 170°C. Cool down to 130°C, add 12 kg of activated montmorillonite, and continue stirring at 400 r / min for 2 min to obtain a premix.
[0050] S4. Add the premixed material to a twin-screw extruder for granulation. The temperature of the feeding section is 160℃, the temperature of the compression section is 200℃, the temperature of the metering section is 210℃, the temperature of the die head is 220℃, and the screw speed is 100r / min. Place the granules on the mold and put them in a hot press. Preheat at 200℃ for 10min, vent 10 times, and hold at 10MPa for 5min to obtain bio-based biodegradable plastic.
[0051] Example 3
[0052] A method for preparing bio-based biodegradable plastics includes the following steps:
[0053] S1. The waste corn stalks were crushed and soaked in a 1.7 mol / L sodium hydroxide solution at room temperature for 15 h. The temperature was raised to 55 °C and stirred for 2 h. The mixture was filtered, washed, dried, added to a 2 mol / L hydrochloric acid solution, boiled, and then refluxed and stirred at 70 r / min for 4 h. The mixture was filtered, the filter residue was washed until neutral, and then freeze-dried to obtain activated cellulose.
[0054] 40 kg of polylactic acid was added to 180 kg of dichloromethane and stirred at 42 °C until the system became transparent. After standing to remove air bubbles, it was added dropwise to 400 kg of activated cellulose dispersion with a solid content of 1.3% and stirred at 400 r / min for 1.3 h. Then, 4 kg of graphene oxide and 1.3 kg of glyoxal solution with a concentration of 1.7 mol / L were added and stirring was continued for 12 min. The system was adjusted to be acidic and stirred for 40 min. The mixture was then stirred in an ice-water bath for 80 min, heated to 108 °C, and stirred vigorously for 8 min at a stirring speed of 1800 r / min. The mixture was then cooled to room temperature, freeze-dried under vacuum, and pulverized to obtain activated polylactic acid.
[0055] S2. Add 4 kg of montmorillonite to 90 kg of 2.5% hydrochloric acid, add 0.8 kg of sodium dithionite, stir at 1300 r / min for 18 h, filter, wash, add 1.5 kg of tetrabutyl titanate, ball mill for 1.8 h, add 6 kg of water and continue milling for 1.7 h, dehydrate, dry at 320℃, cool, and pulverize to obtain activated montmorillonite;
[0056] S3. Vacuum dry 10 kg of polystyrene, 18 kg of polyamide, 2.5 kg of maleic anhydride graft compatibilizer, and 1.5 kg of antioxidant TPP separately. Add them to a mixer with 55 kg of activated polylactic acid and stir for 2 min at a stirring temperature of 165℃. Cool down to 122℃, add 10 kg of activated montmorillonite, and continue stirring at 260 r / min for 1.7 min to obtain a premix.
[0057] S4. Add the premixed material to a twin-screw extruder for granulation. The temperature of the feeding section is 145℃, the temperature of the compression section is 195℃, the temperature of the metering section is 195℃, the temperature of the die head is 215℃, and the screw speed is 70r / min. Place the granules on the die and put them in a hot press. Preheat at 195℃ for 6 minutes, vent 8 times, and hold at a pressure of 7MPa for 4 minutes to obtain bio-based biodegradable plastic.
[0058] Example 4
[0059] A method for preparing bio-based biodegradable plastics includes the following steps:
[0060] S1. Crush waste corn stalks, soak them in a 1.1 mol / L sodium hydroxide solution at room temperature for 25 h, heat to 45 ℃ and stir for 4 h, filter, wash, dry, add to a 1.5 mol / L hydrochloric acid solution, boil, reflux and stir at 90 r / min for 2 h, filter, wash the filter residue until it is neutral, freeze dry to obtain activated cellulose.
[0061] 50 kg of polylactic acid was added to 120 kg of dichloromethane and stirred at 48 °C until the system became transparent. After standing to remove air bubbles, it was added dropwise to 300 kg of activated cellulose dispersion with a solid content of 1.7% and stirred at 200 r / min for 1.7 h. Then, 2 kg of graphene oxide and 1.8 kg of glyoxal solution with a concentration of 1.2 mol / L were added and stirring was continued for 18 min. The system was adjusted to be acidic and stirred for 30 min. The mixture was then stirred in an ice-water bath for 100 min, heated to 102 °C, and stirred vigorously for 12 min at a stirring speed of 1200 r / min. The mixture was then cooled to room temperature, freeze-dried under vacuum, and pulverized to obtain activated polylactic acid.
[0062] S2. Add 8 kg of montmorillonite to 70 kg of 3.5% hydrochloric acid, add 0.2 kg of sodium dithionite, stir at 1700 r / min for 12 h, filter, wash, add 2.5 kg of tetrabutyl titanate, ball mill for 1.2 h, add 8 kg of water and continue milling for 1.3 h, dehydrate, dry at 340℃, cool, and pulverize to obtain activated montmorillonite;
[0063] S3. Vacuum dry 4 kg of polystyrene, 22 kg of polyamide, 1.5 kg of maleic anhydride graft compatibilizer, and 2.5 kg of antioxidant TNP separately, and add them to 45 kg of activated polylactic acid in a mixer and stir for 4 min at a stirring temperature of 155℃. Then cool down to 128℃, add 4 kg of activated montmorillonite, and continue stirring at 340 r / min for 1.3 min to obtain a premix.
[0064] S4. Add the premixed material to a twin-screw extruder for granulation. The temperature of the feeding section is 155℃, the temperature of the compression section is 185℃, the temperature of the metering section is 205℃, the temperature of the die head is 205℃, and the screw speed is 90r / min. Place the granules on the mold and put them in a hot press. Preheat at 175℃ for 8 minutes, vent 4 times, and hold at a pressure of 9MPa for 2 minutes to obtain bio-based biodegradable plastic.
[0065] Example 5
[0066] A method for preparing bio-based biodegradable plastics includes the following steps:
[0067] S1. Crush waste corn stalks, soak them in a 1.5 mol / L sodium hydroxide solution at room temperature for 20 h, heat to 50 ℃ and stir for 3 h, filter, wash, dry, add to a 1.8 mol / L hydrochloric acid solution, boil, reflux and stir at 80 r / min for 3 h, filter, wash the filter residue until it is neutral, freeze dry to obtain activated cellulose.
[0068] 45 kg of polylactic acid was added to 150 kg of dichloromethane and stirred at 45 °C until the system became transparent. After standing to remove air bubbles, it was added dropwise to 350 kg of activated cellulose dispersion with a solid content of 1.5% and stirred at 300 r / min for 1.5 h. Then, 3 kg of graphene oxide and 1.5 kg of glyoxal solution with a concentration of 1.5 mol / L were added and stirring was continued for 15 min. The system was adjusted to be acidic and stirred for 35 min. The mixture was then stirred in an ice-water bath for 90 min, heated to 105 °C, and stirred vigorously for 10 min at a stirring speed of 1500 r / min. The mixture was then cooled to room temperature, freeze-dried under vacuum, and pulverized to obtain activated polylactic acid.
[0069] S2. Add 6 kg of montmorillonite to 80 kg of 3% hydrochloric acid, add 0.5 kg of sodium dithionite, stir at 1500 r / min for 15 h, filter, wash, add 2 kg of tetrabutyl titanate, ball mill for 1.5 h, add 7 kg of water and continue milling for 1.5 h, dehydrate, dry at 330℃, cool, and pulverize to obtain activated montmorillonite;
[0070] S3. Vacuum dry 7 kg of polystyrene, 20 kg of polyamide, 2 kg of maleic anhydride graft compatibilizer, and 2 kg of antioxidant DLTP separately. Add them to 50 kg of activated polylactic acid in a mixer and stir for 3 min at a stirring temperature of 160°C. Cool down to 125°C, add 7 kg of activated montmorillonite, and continue stirring at 300 r / min for 1.5 min to obtain a premix.
[0071] S4. Add the premixed material to a twin-screw extruder for granulation. The temperature of the feeding section is 150℃, the temperature of the compression section is 190℃, the temperature of the metering section is 200℃, the temperature of the die head is 210℃, and the screw speed is 80r / min. Place the granules on the mold and put them in a hot press. Preheat at 185℃ for 7 minutes, vent 6 times, and hold at 8MPa for 3 minutes to obtain bio-based biodegradable plastic.
[0072] Comparative Example 1
[0073] A method for preparing bio-based biodegradable plastics includes the following steps:
[0074] S1. Crush waste corn stalks, soak them in a 1.5 mol / L sodium hydroxide solution at room temperature for 20 h, heat to 50 ℃ and stir for 3 h, filter, wash, dry, add to a 1.8 mol / L hydrochloric acid solution, boil, reflux and stir at 80 r / min for 3 h, filter, wash the filter residue until it is neutral, freeze dry to obtain activated cellulose.
[0075] 45 kg of polylactic acid and 3 kg of graphene oxide were mixed and stirred at 300 r / min for 1.5 h. The mixture was then added dropwise to 350 kg of activated cellulose dispersion with a solid content of 1.5% and stirred for another 15 min. The mixture was then freeze-dried under vacuum and pulverized to obtain pretreated polylactic acid.
[0076] S2. Add 6 kg of montmorillonite to 80 kg of 3% hydrochloric acid, add 0.5 kg of sodium dithionite, stir at 1500 r / min for 15 h, filter, wash, add 2 kg of tetrabutyl titanate, ball mill for 1.5 h, add 7 kg of water and continue milling for 1.5 h, dehydrate, dry at 330℃, cool, and pulverize to obtain activated montmorillonite;
[0077] S3. Vacuum dry 7 kg of polystyrene, 20 kg of polyamide, 2 kg of maleic anhydride graft compatibilizer, and 2 kg of antioxidant DLTP separately. Add them to 50 kg of pretreated polylactic acid in a mixer and stir for 3 min at a stirring temperature of 160℃. Cool down to 125℃, add 7 kg of activated montmorillonite, and continue stirring at 300 r / min for 1.5 min to obtain a premix.
[0078] S4. Add the premixed material to a twin-screw extruder for granulation. The temperature of the feeding section is 150℃, the temperature of the compression section is 190℃, the temperature of the metering section is 200℃, the temperature of the die head is 210℃, and the screw speed is 80r / min. Place the granules on the mold and put them in a hot press. Preheat at 185℃ for 7 minutes, vent 6 times, and hold at 8MPa for 3 minutes to obtain bio-based biodegradable plastic.
[0079] Comparative Example 2
[0080] A method for preparing bio-based biodegradable plastics includes the following steps:
[0081] S1. Crush waste corn stalks, soak them in a 1.5 mol / L sodium hydroxide solution at room temperature for 20 h, heat to 50 ℃ and stir for 3 h, filter, wash, dry, add to a 1.8 mol / L hydrochloric acid solution, boil, reflux and stir at 80 r / min for 3 h, filter, wash the filter residue until it is neutral, freeze dry to obtain activated cellulose.
[0082] 45 kg of polylactic acid was added to 150 kg of dichloromethane and stirred at 45 °C until the system became transparent. After standing to remove air bubbles, it was added dropwise to 350 kg of activated cellulose dispersion with a solid content of 1.5% and stirred at 300 r / min for 1.5 h. Then, 3 kg of graphene oxide and 1.5 kg of glyoxal solution with a concentration of 1.5 mol / L were added and stirring was continued for 15 min. The system was adjusted to be acidic and stirred for 35 min. The mixture was then stirred in an ice-water bath for 90 min, heated to 105 °C, and stirred vigorously for 10 min at a stirring speed of 1500 r / min. The mixture was then cooled to room temperature, freeze-dried under vacuum, and pulverized to obtain activated polylactic acid.
[0083] S2. Mix 6 kg of montmorillonite and 2 kg of tetrabutyl titanate and ball mill for 1.5 h. Dry at 330 °C, cool down, and pulverize to obtain pretreated montmorillonite.
[0084] S3. Vacuum dry 7 kg of polystyrene, 20 kg of polyamide, 2 kg of maleic anhydride graft compatibilizer, and 2 kg of antioxidant DLTP separately. Add them to 50 kg of activated polylactic acid in a mixer and stir for 3 min at a stirring temperature of 160℃. Cool down to 125℃, add 7 kg of pretreated montmorillonite, and continue stirring at 300 r / min for 1.5 min to obtain a premix.
[0085] S4. Add the premixed material to a twin-screw extruder for granulation. The temperature of the feeding section is 150℃, the temperature of the compression section is 190℃, the temperature of the metering section is 200℃, the temperature of the die head is 210℃, and the screw speed is 80r / min. Place the granules on the mold and put them in a hot press. Preheat at 185℃ for 7 minutes, vent 6 times, and hold at 8MPa for 3 minutes to obtain bio-based biodegradable plastic.
[0086] The bio-based biodegradable plastics obtained in Example 5 and Comparative Examples 1-2 were subjected to hydrolytic degradation, composting degradation, and ultraviolet degradation experiments, as detailed below:
[0087] 1. Hydrolysis and degradation experiment
[0088] Rectangular samples measuring 10mm × 50mm × 1mm were placed in a vacuum oven and dried at 60℃ for 12 hours until constant weight. The initial mass of each sample was accurately weighed using an electronic balance and recorded as m0. Samples from each group were aliquoted into centrifuge tubes, and 35±5mL of PBS buffer (pH=7.4) was added to completely submerge the samples (8.0g sodium chloride, 0.2g potassium chloride, 2.88g disodium hydrogen phosphate dodecahydrate, and 0.2g potassium dihydrogen phosphate per 1000mL deionized water). The tubes were sealed and labeled, then immersed in a 37℃ constant temperature water bath to begin degradation. The PBS buffer was changed every 3 days. After removing the samples at different times, they were rinsed with deionized water, dried with paper towels, and accurately weighed, recorded as m1. The samples were then placed in a vacuum oven and dried at 60℃ for 12 hours until constant weight, and accurately weighed again, recorded as m2. The water absorption rate and weight loss rate of each group were calculated after weighing.
[0089] Water absorption rate = (m1 - m2) ÷ m2 × 100%
[0090] Weight loss rate = (m0 - m2) ÷ m0 × 100%
[0091] Water absorption rate such as Figure 1 As shown, the water absorption rate increases over time because degradation creates defects in the material, making it easier for water molecules to penetrate. The bio-based biodegradable plastic obtained in Example 5 consistently exhibits the highest water absorption rate.
[0092] weight loss rate Figure 2 As shown, the weight loss rate also increases over time, similar to the water absorption rate. The more water molecules absorbed, the more ester bonds are hydrolyzed on the material's molecular chains, resulting in a higher weight loss rate. The bio-based biodegradable plastic obtained in Example 5 consistently exhibits the highest weight loss rate.
[0093] The applicant believes that this is because graphene oxide exhibits a hydrophilic to hydrophobic distribution from the edge to the center of its sheets. This not only promotes the uniform distribution of activated cellulose in the system, but also allows the highly dispersed graphene oxide to react and bind to the polylactic acid-activated cellulose three-dimensional network structure in a high-temperature environment. This greatly improves the hydrophilicity and, after the plastic degrades, its regular sheet structure rapidly promotes the diffusion of water molecules.
[0094] 2. Composting Degradation Experiments and Tests
[0095] The experiment was conducted in accordance with GB / T 19811-2005, "Determination of the Degree of Disintegration of Plastic Materials under Defined Composting Pilot-Scale Conditions". Rectangular samples of 25mm × 25mm × 1mm were placed in a vacuum oven and dried at 60℃ for 12 hours until constant weight. The initial mass of each sample was accurately weighed using an electronic balance and recorded as m³. Then, each group of samples was buried in a self-made cardboard box containing commercially available potting soil, 5cm deep and spaced 3cm apart. After burying, the boxes were placed in a forced-air drying oven, set to 58℃, and the relative humidity of the soil was adjusted to 60% before degradation began.
[0096] During the experiment, the soil was regularly watered to maintain a humidity of approximately 60% and no lower than 40%. Samples were taken in weeks 1, 2, 3, 5, 7, and 9. After sampling, the samples were rinsed with deionized water and then placed in a vacuum oven at 60°C for 12 hours until constant weight was achieved. The samples were then accurately weighed and recorded as m4. The weight loss rate of the samples was calculated after weighing.
[0097] Weight loss rate = (m3 - m4) ÷ m3 × 100%
[0098] like Figure 3 As shown, the weight loss rate of compost degradation increases over time, which is similar to the weight loss rate of hydrolysis degradation. In the early stage of degradation, the degradation rates of each sample are relatively small and not significantly different. This is because compost degradation has a degradation induction period, during which microorganisms mainly attach to the material surface and then begin to decompose and metabolize, thus playing a role in biodegradation. Therefore, during this period, the material mainly degrades under the influence of water and heat. In the middle and late stages of degradation, the material degrades more rapidly under the combined action of water, heat, and microorganisms, resulting in a significant increase in the weight loss rate.
[0099] The weight loss rates of Example 5 and Comparative Example 2 were slightly higher than those of Comparative Example 1 because the graphene oxide reaction combined with the polylactic acid-activated cellulose three-dimensional network structure made it easier for water molecules to penetrate into the material.
[0100] However, comparing the composting degradation weight loss rate of Example 5 and Comparative Example 2 with the hydrolysis degradation weight loss rate, it can be found that the hydrolysis degradation effect is more obvious. Although microorganisms in the soil also play a role in accelerating material degradation, the moisture content in compost soil is low, and the materials of both are more easily broken down by water molecules, thus showing that the composting degradation rate of both is lower than the hydrolysis degradation rate.
[0101] 3. Ultraviolet Degradation Experiment and Testing
[0102] The site and apparatus were set up in accordance with GB / T 18006.2-1999 "Test Method for Degradation Performance of Disposable Biodegradable Tableware". Each group of plastic samples was made into square plates of 4cm×4cm with a thickness of 5mm. Each group of samples was placed under a UV lamp for treatment. The relative humidity was maintained at 30-50% during treatment. The UV lamp power was 60W and the treatment time was 6h. After treatment, the samples were placed in the above-mentioned testing site and observed daily. The number of fragmentation days (i.e., the date when the deformed area reached more than 50% of the total sample area) was recorded.
[0103] The bio-based biodegradable plastic obtained in Example 5 had a fragmentation time of 62 days, compared to 63 days in Comparative Example 1 and 117 days in Comparative Example 2. The applicant believes this is because in Examples 5 and Comparative Example 1, tetrabutyl titanate was inserted into the structural layers of layered montmorillonite, then hydrolyzed to generate titanium hydroxide. After calcination at 300-350℃, nano-titanium dioxide particles were generated within the montmorillonite layers. This not only resulted in a very high degree of bonding between the nano-titanium dioxide and the montmorillonite layers but also provided higher catalytic activity. During degradation, the nano-titanium dioxide was less likely to become free, thus maintaining excellent catalytic activity. This caused the regularly arranged long-chain structure in the plastic to break, generating many fine cracks, which in turn facilitated subsequent degradation.
[0104] The mechanical properties of the bio-based biodegradable plastics obtained in Example 5 and Comparative Examples 1-2 were tested, as follows:
[0105] Referring to GB / T 1040.2-2022 "Determination of Tensile Properties of Plastics - Part 2: Test Conditions for Molded and Extruded Plastics", a computer-controlled electronic universal testing machine was used to test the tensile properties of each group of specimens. The clamp distance was 50 mm, the tensile speed was 5 mm / min, and the specimen thickness was measured and input. Referring to GB / T1843-2008 "Determination of Impact Strength of Plastic Cantilever Beams", a computer-controlled electronic universal testing machine was used to test the bending properties of each group of specimens. The bending speed was 5 mm / min.
[0106] like Figure 4As shown, the tensile and flexural properties of the bio-based biodegradable plastic obtained in Example 5 are superior to those of the comparative example. The applicant believes this is because this application uses polylactic acid (PLA) as the matrix and activated cellulose as the three-dimensional framework. Activated cellulose relies on the van der Waals forces and hydrogen bonds between its surface hydroxyl groups to form a network structure in the system, which further forms a multi-layered network structure after crosslinking with glyoxal. PLA, as a long-chain polymer, undergoes esterification with activated cellulose at high temperatures to form a three-dimensional structure, resulting in a more stable structure and higher strength. Simultaneously, graphene oxide promotes the uniform distribution of activated cellulose in the system, and the carboxyl groups on graphene oxide can react and bind to the aforementioned three-dimensional network structure, further enhancing the system's strength. Furthermore, activated PLA is compounded with polystyrene and polyamide, and after high-temperature treatment, the entanglement of molecular chains helps improve the melt strength of the blends, increasing their mechanical strength.
[0107] The thermal stability of the bio-based biodegradable plastics obtained in Example 5 and Comparative Examples 1-2 was analyzed using a thermogravimetric analyzer. 10 mg of sample was weighed and placed in an alumina crucible, and heated from 30 °C to 600 °C at a heating rate of 10 °C / min in a nitrogen atmosphere.
[0108] like Figure 5 As shown, the bio-based biodegradable plastic obtained in Example 5 has the highest maximum thermal decomposition temperature, which is higher than that of the comparative example. The applicant believes that this is because graphene oxide promotes the uniform distribution of activated cellulose in the system. In a high-temperature environment, the carboxyl groups on graphene oxide can react and bind in the polylactic acid-activated cellulose three-dimensional network structure, effectively avoiding the phenomenon of thermal stress concentration during high-temperature processes, and can quickly promote the uniformity of system temperature, thereby improving thermal stability. At the same time, the activated polylactic acid, polystyrene, polyamide and activated montmorillonite are compounded, and titanium dioxide has a high bonding strength in the activated montmorillonite sheets, which can further slightly improve the thermal stability of the material.
[0109] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for preparing bio-based biodegradable plastics, characterized in that, Includes the following steps: S1. Add polylactic acid to dichloromethane and stir at 40-50℃ until the system becomes transparent. Let it stand to remove air bubbles, then add it dropwise to the activated cellulose dispersion and stir for 1-2 hours. Add graphene oxide and glyoxal solution and continue stirring for 10-20 minutes to adjust the system to acidity. Stir in an ice-water bath for 1-2 hours, raise the temperature to 100-110℃, stir vigorously for 5-15 minutes, cool to room temperature, freeze dry under vacuum, and pulverize to obtain activated polylactic acid. S2. Add montmorillonite to hydrochloric acid, add sodium dithionite and stir for 10-20 hours, filter, wash and add tetrabutyl titanate, ball mill for 1-2 hours, add water and continue milling for 1-2 hours, dehydrate and dry, cool and pulverize to obtain activated montmorillonite. S3. Stir polystyrene, polyamide, compatibilizer, antioxidant and activated polylactic acid for 1-5 minutes at a stirring temperature of 150-170℃, cool down to 120-130℃, add activated montmorillonite and stir for 1-2 minutes to obtain premix. S4. Extrude the premixed material into granules, and then hot-press the granules. First, preheat at 170-200℃ for 5-10 minutes, vent 1-10 times, and then hold at 5-10MPa for 1-5 minutes to obtain bio-based biodegradable plastic.
2. The method for preparing bio-based biodegradable plastics according to claim 1, characterized in that, In S1, the mass ratio of polylactic acid, activated cellulose dispersion, graphene oxide, and glyoxal solution is 30-60:200-500:1-5:1-2, the solid content of activated cellulose dispersion is 1-2%, and the concentration of glyoxal solution is 1-2 mol / L.
3. The method for preparing bio-based biodegradable plastics according to claim 1, characterized in that, In S1, polylactic acid is obtained by polymerization of bio-based lactic acid. The melting point of polylactic acid is 160-170℃ and the melt index is ≤10g / 10min.
4. The method for preparing bio-based biodegradable plastics according to claim 1, characterized in that, In S1, activated cellulose is prepared by the following steps: waste corn stalks are crushed, added to sodium hydroxide solution and soaked at room temperature for 10-30 hours, heated to 40-60℃ and stirred for 1-5 hours, filtered, washed, dried, added to hydrochloric acid, boiled and refluxed and stirred for 1-5 hours, filtered, the filter residue is washed until neutral, and freeze-dried to obtain activated cellulose.
5. The method for preparing bio-based biodegradable plastics according to claim 4, characterized in that, The concentration of sodium hydroxide solution is 1-2 mol / L, and the concentration of hydrochloric acid is 1-2.5 mol / L.
6. The method for preparing bio-based biodegradable plastics according to claim 4, characterized in that, The degree of polymerization of the obtained activated cellulose is 210-250, the crystallinity is 81.3-84.5%, and the particle size is ≤50μm.
7. The method for preparing bio-based biodegradable plastics according to claim 1, characterized in that, In S2, the mass ratio of montmorillonite, sodium dithionite, and tetrabutyl titanate is 2-10: 0.1-1：1-3。 8. The method for preparing bio-based biodegradable plastics according to claim 1, characterized in that, In S3, the mass ratio of polystyrene, polyamide, compatibilizer, antioxidant, activated polylactic acid, and activated montmorillonite is 1-15:15-25:1-3:1-3:35-70:2-12.
9. The method for preparing bio-based biodegradable plastics according to claim 1, characterized in that, In S4, a twin-screw extruder is used for extrusion granulation. The temperature of the feeding section of the twin-screw extruder is 140-160℃, the temperature of the compression section is 180-200℃, the temperature of the metering section is 190-210℃, the temperature of the die head is 200-220℃, and the screw speed is 60-100 r / min.
10. A bio-based biodegradable plastic, characterized in that, It is prepared by the method for preparing bio-based biodegradable plastics according to any one of claims 1-9.