Preparation method of degradable plastic mixed particles

Abstract

The invention discloses a preparation method of degradable plastic mixed particles, belongs to the field of degradable plastic mixed particles, and is used for solving the core problems of pollution caused by random discarding of plastic products and pollution caused by incineration of peasant kitchen stoves due to multiple deficiencies of rural material conditions, management specifications and environmental protection consciousness. The preparation method of the degradable plastic mixed particles comprises the following steps: pretreating the raw materials, mixing and stirring, extruding and granulating, and cooling and drying. A plastic product processed by using the particles has the characteristics of rapid degradation in a rural natural environment, harmlessness in incineration in a peasant kitchen range, suitability for rural use in mechanical property and controllable cost.

Description

Technical Field

[0001] This invention relates to the field of biodegradable plastic mixed granules, and more particularly to a method for preparing biodegradable plastic mixed granules. Background Technology

[0002] In order to protect the environment, plastic products are gradually becoming more environmentally friendly, and are usually biodegradable. They can generally be rendered harmless in industrial composting and formal incineration power generation scenarios. However, due to the lack of a standardized waste recycling system in rural areas, coupled with deficiencies in material conditions, management standards, and environmental awareness, plastic products are often carelessly discarded in soil, ditches, and open environments after use, or burned in rural stoves. Existing biodegradable plastic pellets are mainly developed for urban industrial composting and formal incineration power generation scenarios, making them difficult to adapt to the special usage environment in rural areas. The core defects can be summarized as follows: First, poor adaptability to degradation in the rural natural environment, slow degradation rate, and long residue retention; second, incomplete pollution control of rural stove incineration, lacking targeted harmless design; third, mechanical properties do not match usage requirements, easily damaged, and insufficient heat resistance; fourth, excessively high cost, making it difficult to popularize in the rural market. Summary of the Invention

[0003] To overcome the above problems, this invention aims to propose a method for preparing biodegradable plastic granules, enabling plastic products processed from these granules to possess the characteristics of "rapid degradation in the rural natural environment, harmless burning in rural stoves, mechanical properties adapted for rural use, and controllable cost." This addresses the core issues of pollution caused by the indiscriminate disposal of plastic products and pollution from burning in rural stoves, which are often due to deficiencies in rural material conditions, management standards, and environmental awareness.

[0004] Therefore, the specific technical solution adopted by the present invention is as follows: According to one aspect of the present invention, a method for preparing biodegradable plastic mixed granules is provided, comprising the following steps: S1. Pre-treatment of raw materials, including starch modification, waste edible oil modification, and solid raw material pretreatment, wherein solid raw materials include biochar, wood ash, zeolite powder, and bentonite. S2. Weigh the following components by mass percentage: PHA 48%-52%, modified starch 28%-32%, PBAT 6%-8%, biochar 7%-9%, wood ash 4%-5%, potassium nitrate 1%-1.5%, PEG-1000 2.5%-3%, magnesium hydroxide 8%-10%, talc 3%-4%, powdered activated carbon 1.5%-2%, Artemisia argyi extract 1%-1.5%, zeolite powder 2.5%-3%, bentonite 2%-2.5%, waste edible oil modifier 2%-2.5%, silane coupling agent KH-550 0.5%-0.8%, carbon black 0.5%-0.7%; wherein PHA is a PHB / PHBH copolymer, the mass ratio of PHB to PHBH is 1:1.5-2, and the number average molecular weight is [missing information]. The magnesium hydroxide is hexagonal with a particle size ≤ 5 μm; the zeolite powder has a pore size of 0.5-1 nm; the total flavonoid content of the Artemisia argyi extract is ≥ 15%, as determined by ultraviolet spectrophotometry, and then the mixture is stirred. S3. The mixture is fed into a single-screw extruder with a screw diameter of 35-45 mm and a length-to-diameter ratio of 25:1. The barrel is heated in a gradient manner: 130-135℃ in the feeding section, 140-145℃ in the compression section, and 145-150℃ in the metering section. The screw speed is 40-60 r / min, and the die head pressure is controlled at 10-15 MPa by a pressure sensor. After extrusion through the die, the mixture is pelletized by a water ring with a water temperature of 25℃ and a cutter speed of 1500 r / min to obtain particles with a diameter of 2-3 mm and a roundness ≥0.8. S4. The granules are cooled by an air-cooled conveyor belt at a wind speed of 5 m / s for 3 minutes until they reach ≤40℃. Then, they are sent to a vibrating fluidized bed dryer with a hot air temperature of 60℃ and a wind speed of 1.2 m / s for 30-40 minutes. The final moisture content of the granules is controlled to be ≤0.5%, thus obtaining biodegradable plastic mixed granules.

[0005] Optionally, step S1 specifically includes the following sub-steps: S11. Mix starch with propylene oxide and hydrochloric acid at a mass ratio of 100:5:0.8, purge with nitrogen for protection, and stir at room temperature for 2-3 hours. During this period, take samples every 30 minutes to test the degree of crosslinking. Stop the reaction when the degree of crosslinking reaches 15%-20%. Wash with water to remove unreacted hydrochloric acid, and spray dry under air inlet at 180℃ and air outlet at 80℃ to obtain modified starch. The degree of crosslinking is tested by the swelling degree method: the modified starch is soaked in distilled water at 25℃ for 24 hours, and the degree of crosslinking (%) is calculated according to the formula "degree of crosslinking (%) = (mass of insoluble matter after soaking / mass of sample before soaking) × 100%". S12. The waste cooking oil is filtered through an 80-mesh filter to remove impurities. It is then mixed with methanol and sulfuric acid catalyst at a mass ratio of 100:20:1 and reacted at 60℃ and 300r / min for 1 hour. After standing and separating into layers, the upper layer of fatty acid methyl ester is taken. The purity is detected by gas chromatography to be ≥95%, thus obtaining the waste cooking oil modified product. S13. Biochar, wood ash, zeolite powder, and bentonite are pulverized separately using a planetary ball mill with a ball-to-material ratio of 10:1 and a rotation speed of 400 r / min. After pulverization, the materials are passed through an 80-100 mesh sieve and dried at 80℃ and a vacuum of -0.09 MPa for 2 hours, with the moisture content controlled to be ≤1.5%. The biochar is prepared from straw or rice husks through oxygen-limited pyrolysis at 400-500℃ for 2 hours, and the specific surface area measured by BET is ≥300 m² / g.

[0006] Optionally, the mixing process in step S2 is as follows: First, the solid components are put into a high-speed mixer, heated to 60-70°C, and stirred at 800-1000 r / min for 10 minutes to allow the amino group of the silane coupling agent KH-550 to chemically bond with the starch hydroxyl group and the biochar carboxyl group. Then, the liquid components are added, and the stirring speed is reduced to 600 r / min and stirred for another 5-10 minutes. During this period, the material temperature is controlled to not exceed 70°C by an infrared thermometer to obtain a mixed material.

[0007] Optionally, in S11, the starch is corn starch or sweet potato starch, and the degree of crosslinking is strictly controlled between 15% and 20%. When the degree of crosslinking is <15%, the starch is prone to swelling in the humid environment of rural areas, causing the product to break prematurely. When the degree of crosslinking is >20%, the starch is too rigid, resulting in the product's elongation at break being less than 120%, which cannot meet the needs of loading heavy objects in rural areas. In S13, the specific surface area of ​​the biochar is ≥300m² / g, and its porous structure can provide microbial attachment sites. When the specific surface area is <300m² / g, the amount of microbial colonization is reduced by more than 40%, and the degradation rate of the product drops to below 70% after 6 months.

[0008] Optionally, in S2, the mass ratio of the PHB / PHBH copolymer is 1:1.5-2, where PHB provides rigidity (tensile strength ≥25MPa) and PHBH provides low-temperature toughness (elongation at break ≥80% at -10℃), synergistically adapting to rural low-temperature storage and rough use scenarios. The "potassium nitrate-wood ash-PEG" constitutes a composite combustion-supporting system: potassium nitrate releases oxygen when burning, potassium salts in wood ash catalyze the combustion reaction, and PEG lowers the ignition point of the substrate. The three work synergistically to improve combustion completeness by more than 80% and reduce black smoke emissions by 80%.

[0009] Optionally, in S2, the "magnesium hydroxide-talc powder" constitutes a temperature control system: magnesium hydroxide has a thermal decomposition temperature of 340℃ and absorbs a large amount of heat during decomposition, while talc powder stabilizes the combustion temperature. Together, they stabilize the burning temperature of the farm stove at 500-600℃, avoiding the 300-500℃ range where dioxins are generated.

[0010] Optionally, the activated carbon, artemisia extract, and zeolite powder in S2 constitute a deodorization system: activated carbon adsorbs VOCs, and zeolite powder adsorbs... Sulfur-containing gases, flavonoids in Artemisia argyi extract react chemically with odor molecules, and the three work together to ensure that VOC emissions during combustion are ≤10mg / m³, with no pungent odor.

[0011] Optionally, in S3, the die head pressure is controlled at 10-15MPa: when the pressure is <10MPa, the material is not fully plasticized and the product has bubble defects; when the pressure is >15MPa, the screw load exceeds the bearing limit of the small extruder, which can easily lead to equipment failure.

[0012] Optionally, in S2, the amount of silane coupling agent KH-550 added is 0.5%-0.8%. Its amino group undergoes a condensation reaction with the starch hydroxyl group and the biochar carboxyl group to form a -Si-OC- chemical bond, which improves the compatibility of each component. When the amount added is <0.5%, the product is prone to delamination; when the amount added is >0.8%, it will lead to a decrease in the tensile strength of the product.

[0013] Optionally, in S13, the bentonite has a montmorillonite content of ≥80%. When burned, the layered structure of montmorillonite binds the ash to form 1-3mm granular ash, avoiding dust pollution. The ash contains potassium and calcium elements and can be directly used as fertilizer for rural farmland.

[0014] Compared with the prior art, this application has the following beneficial effects: 1. A ternary matrix system composed of PHB / PHBH copolymer, cross-linked modified starch, and high specific surface area biochar is formed. By precisely controlling the degree of starch cross-linking and the specific surface area of ​​biochar, a balance between microbial colonization and degradation rate is achieved. The product has a degradation rate of ≥90% in rural environments with fluctuating temperature and humidity of 5-35℃ for 3-6 months. The degradation products are water and carbon dioxide, with no residual pollution. This solves the problem of slow degradation of existing particles and the degradation performance is precisely adapted to the rural environment.

[0015] 2. Through a complete chain system of combustion aid, temperature control, deodorization, and ash modification, the combustion aid system improves combustion completeness, the temperature control system inhibits dioxin formation, the deodorization system eliminates pungent odors, and the ash binding system prevents dust. During incineration, dioxin emissions are ≤0.01ngTEQ / m³, Ringelmann blackness is ≤1, and ash can be directly returned to the field, completely solving the pollution problem of rural household stove incineration. The incineration harmless design is highly targeted.

[0016] 3. By adjusting the PHB / PHBH ratio, using waste cooking oil to modify and toughen the product, and using silane coupling agents to improve compatibility, the product has a tensile strength ≥18MPa, an elongation at break ≥150%, a heat distortion temperature ≥105℃, and can withstand a 1.5m drop without breaking. It can meet the needs of rural areas for carrying heavy objects, holding hot food, and low-temperature storage, and solves the defects of existing biodegradable products that are easy to crack and have poor heat resistance. Its mechanical properties are suitable for rough rural use.

[0017] 4. The modified starch, biochar, wood ash, and artemisia extract in the formula are low-cost raw materials. The modified waste cooking oil realizes the resource utilization of waste. The overall raw material cost is controlled at 1.68-1.78 yuan / kg, which is 20%-30% lower than traditional biodegradable granules. The product price is only 10%-15% higher than traditional plastics, which is acceptable to rural users and conducive to large-scale promotion. The cost is controllable and the raw material sources are wide. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application are clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0019] Example 1 According to an embodiment of the present invention, a method for preparing biodegradable plastic mixed particles is provided.

[0020] According to an embodiment of the present invention, a method for preparing biodegradable plastic mixed granules is provided, comprising the following steps: S1. Pre-treatment of raw materials, including starch modification, waste edible oil modification, and solid raw material pretreatment, wherein solid raw materials include biochar, wood ash, zeolite powder, and bentonite. S2. Weigh the following components by mass percentage: PHA 48%-52%, modified starch 28%-32%, PBAT 6%-8%, biochar 7%-9%, wood ash 4%-5%, potassium nitrate 1%-1.5%, PEG-1000 2.5%-3%, magnesium hydroxide 8%-10%, talc 3%-4%, powdered activated carbon 1.5%-2%, Artemisia argyi extract 1%-1.5%, zeolite powder 2.5%-3%, bentonite 2%-2.5%, waste edible oil modifier 2%-2.5%, silane coupling agent KH-550 0.5%-0.8%, carbon black 0.5%-0.7%; PHA is a PHB / PHBH copolymer, with a PHB to PHBH mass ratio of 1:1.5-2, and a number average molecular weight of [missing information]. Magnesium hydroxide has a hexagonal crystal system and a particle size ≤ 5 μm; the pore size of zeolite powder is 0.5-1 nm; the total flavonoid content of Artemisia argyi extract is ≥ 15%, which is detected by ultraviolet spectrophotometry, and then the mixture is stirred. S3. Feed the mixture into a single-screw extruder with a screw diameter of 35-45mm and a length-to-diameter ratio of 25:1. The barrel uses gradient heating: 130-135℃ for the feeding section, 140-145℃ for the compression section, and 145-150℃ for the metering section. The screw speed is 40-60r / min, and the die head pressure is controlled at 10-15MPa by a pressure sensor. After extrusion through the die, the mixture is pelletized using a water ring with a water temperature of 25℃ and a cutter speed of 1500r / min to obtain particles with a diameter of 2-3mm and a roundness ≥0.8. S4. The granules are cooled by an air-cooled conveyor belt at a wind speed of 5 m / s for 3 minutes until they reach ≤40℃. Then, they are sent to a vibrating fluidized bed dryer with a hot air temperature of 60℃ and a wind speed of 1.2 m / s for 30-40 minutes. The final moisture content of the granules is controlled to be ≤0.5%, thus obtaining biodegradable plastic mixed granules.

[0021] Step S1 specifically includes the following sub-steps: S11. Mix starch with propylene oxide and hydrochloric acid at a mass ratio of 100:5:0.8, purge with nitrogen for protection, and stir at room temperature for 2-3 hours. During this period, take samples every 30 minutes to test the degree of crosslinking. Stop the reaction when the degree of crosslinking reaches 15%-20%. Wash with water to remove unreacted hydrochloric acid, and spray dry under air inlet at 180℃ and air outlet at 80℃ to obtain modified starch. The degree of crosslinking is tested by the swelling degree method: the modified starch is soaked in distilled water at 25℃ for 24 hours, and the degree of crosslinking (%) is calculated according to the formula "degree of crosslinking (%) = (mass of insoluble matter after soaking / mass of sample before soaking) × 100%". S12. The waste cooking oil is filtered through an 80-mesh filter to remove impurities. It is then mixed with methanol and sulfuric acid catalyst at a mass ratio of 100:20:1 and reacted at 60℃ and 300r / min for 1 hour. After standing and separating into layers, the upper layer of fatty acid methyl ester is taken. The purity is detected by gas chromatography to be ≥95%, thus obtaining the waste cooking oil modified product. S13. Biochar, wood ash, zeolite powder, and bentonite are pulverized separately using a planetary ball mill with a ball-to-material ratio of 10:1 and a rotation speed of 400 r / min. After pulverization, the materials are passed through an 80-100 mesh sieve and dried at 80℃ and a vacuum of -0.09 MPa for 2 hours, with the moisture content controlled to be ≤1.5%. Biochar is prepared from straw or rice husks through oxygen-limited pyrolysis at 400-500℃ for 2 hours, and the specific surface area is ≥300 m² / g according to BET testing.

[0022] Step S2 mixing process is as follows: First, put the solid component into a high-speed mixer, heat it to 60-70℃, and stir it at 800-1000r / min for 10 minutes to allow the amino group of silane coupling agent KH-550 to chemically bond with the starch hydroxyl group and the biochar carboxyl group. Then add the liquid component, reduce the speed to 600r / min and continue stirring for 5-10 minutes. During this period, the material temperature is controlled not to exceed 70℃ by an infrared thermometer to obtain a mixture.

[0023] In S11, the starch is corn starch or sweet potato starch, and the degree of cross-linking is strictly controlled between 15% and 20%. When the degree of cross-linking is <15%, the starch is prone to swelling in the humid environment of rural areas, which leads to premature breakage of the product. When the degree of cross-linking is >20%, the starch is too rigid, which leads to the product's elongation at break being less than 120%, which cannot meet the needs of loading heavy objects in rural areas. In S13, the specific surface area of ​​biochar is ≥300m² / g, and its porous structure can provide microbial attachment sites. When the specific surface area is <300m² / g, the amount of microbial colonization is reduced by more than 40%, and the degradation rate of the product drops to below 70% after 6 months.

[0024] In S2, the mass ratio of PHB / PHBH copolymer is 1:1.5-2, where PHB provides rigidity (tensile strength ≥25MPa) and PHBH provides low-temperature toughness (elongation at break ≥80% at -10℃), synergistically adapting to rural low-temperature storage and rough use scenarios. The "potassium nitrate-wood ash-PEG" composite combustion-supporting system: potassium nitrate releases oxygen when burning, potassium salts in wood ash catalyze the combustion reaction, and PEG lowers the ignition point of the substrate. The three work together to improve combustion completeness by more than 80% and reduce black smoke emissions by 80%.

[0025] In S2, "magnesium hydroxide-talc powder" constitutes a temperature control system: magnesium hydroxide has a thermal decomposition temperature of 340℃ and absorbs a large amount of heat during decomposition, while talc powder stabilizes the combustion temperature. Together, they stabilize the burning temperature of the farm stove at 500-600℃, avoiding the 300-500℃ range where dioxins are generated.

[0026] S2 activated carbon, artemisia extract, and zeolite powder constitute the deodorization system: activated carbon adsorbs VOCs, and zeolite powder adsorbs... Sulfur-containing gases, flavonoids in Artemisia argyi extract react chemically with odor molecules, and the three work together to ensure that VOC emissions during combustion are ≤10mg / m³, with no pungent odor.

[0027] In S3, the die head pressure is controlled at 10-15MPa: when the pressure is <10MPa, the material is not fully plasticized and the product has bubble defects; when the pressure is >15MPa, the screw load exceeds the bearing limit of the small extruder, which can easily lead to equipment failure.

[0028] In S2, the addition amount of silane coupling agent KH-550 is 0.5%-0.8%. Its amino group undergoes a condensation reaction with the starch hydroxyl group and the biochar carboxyl group to form -Si-OC- chemical bonds, which improves the compatibility of each component. When the addition amount is <0.5%, the product is prone to delamination; when the addition amount is >0.8%, it will lead to a decrease in the tensile strength of the product.

[0029] In S13, the bentonite contains ≥80% montmorillonite. During incineration, the layered structure of montmorillonite binds the ash, forming 1-3mm granular ash residue, which avoids dust pollution. In addition, the ash residue contains potassium and calcium elements, which can be directly used as fertilizer for rural farmland.

[0030] Example 2 S1. Raw material pretreatment: S11. Starch modification: Take 100 kg of corn starch, add 5 kg of propylene oxide and 0.8 kg of hydrochloric acid, introduce nitrogen gas, stir at room temperature for 2 hours, and test the degree of crosslinking to 18%. After washing with water, spray dry (inlet air 180℃, outlet air 80℃) to obtain 98 kg of modified starch. S12. Modification of waste cooking oil: Take 100 kg of waste cooking oil, filter it through an 80-mesh filter, add 20 kg of methanol and 1 kg of sulfuric acid, stir and react at 60℃ and 300 r / min for 1 hour, let it stand and separate into layers, take the upper layer, and detect the purity of 96.5% by gas chromatography to obtain 85 kg of modified waste cooking oil. S13. Solid raw material pretreatment: Straw was pyrolyzed at 450℃ under limited oxygen for 2 hours, then pulverized in a planetary ball mill (ball-to-material ratio 10:1, 400 r / min), passed through an 80-mesh sieve, and the BET test showed a specific surface area of ​​320 m² / g to obtain biochar; Wood ash, zeolite powder (0.8 nm), and bentonite (montmorillonite content 85%) were treated in the same way, and after vacuum drying, the moisture content was 1.2%; S2. Mixing and stirring: S21. Weigh out 50 kg of PHB / PHBH copolymer (1:1.5), 30 kg of modified starch, 7 kg of PBAT, 8 kg of biochar, 4.5 kg of wood ash, 1.2 kg of potassium nitrate, 2.8 kg of PEG-1000, 9 kg of magnesium hydroxide (hexagonal crystal system, 5 μm), 3.5 kg of talc, 1.8 kg of activated carbon, 1.2 kg of Artemisia argyi extract (total flavonoids 16%), 2.8 kg of zeolite powder, 2.2 kg of bentonite, 2.3 kg of waste edible oil modified product, 0.6 kg of KH-550, and 0.6 kg of carbon black. S21. Solid components are added to a high-speed mixer and stirred at 65°C and 900 rpm for 10 minutes. Liquid components are added and stirred at 600 rpm for 8 minutes. Infrared temperature measurement shows 68°C to obtain a mixture. S3, Extrusion granulation: The mixture was fed into a 40mm single-screw extruder (length-to-diameter ratio 25:1), with the feed section at 132℃, the compression section at 142℃, the metering section at 148℃, the screw speed at 50r / min, and the die head pressure at 12MPa; it was then pelletized by a water ring (water temperature 25℃, cutter speed 1500r / min) to obtain particles with a diameter of 2.5mm and a roundness of 0.85. S4. Cooling and drying: The mixture is cooled to 35°C in 3 minutes by an air-cooled conveyor belt (5 m / s), and then dried in a vibrating fluidized bed (60°C, 1.2 m / s) for 35 minutes until the moisture content is 0.4%, yielding biodegradable plastic mixed granules. Example 3 S1. Raw material pretreatment: S11, Starch modification: Take 100 kg of sweet potato starch and prepare it according to the steps in Example 2, with a crosslinking degree of 20%; S12, the purity of modified waste cooking oil is 95.2%; S13. Biochar was prepared by pyrolysis of rice husks (specific surface area 310 m² / g), and other solid raw materials were pulverized to 100 mesh with a moisture content of 1.0%. S2. Mixing and stirring: S21. Weigh out 52 kg of PHB / PHBH copolymer (1:2), 28 kg of modified starch, 6 kg of PBAT, 7 kg of biochar, 4 kg of wood ash, 1.0 kg of potassium nitrate, 2.5 kg of PEG-1000, 8 kg of magnesium hydroxide, 3 kg of talc, 1.5 kg of activated carbon, 1.0 kg of Artemisia argyi extract, 2.5 kg of zeolite powder, 2.0 kg of bentonite, 2.0 kg of waste edible oil modifier, 0.5 kg of KH-550, and 0.5 kg of carbon black. S22. Mix according to the process of Example 2 to obtain the mixture; S3, Extrusion granulation: A 35mm single-screw extruder with a feeding section temperature of 130℃, a compression section temperature of 140℃, a metering section temperature of 145℃, a rotation speed of 40r / min, a die head pressure of 10MPa, and a pellet size of 2mm. S4. Cooling and drying: Air-cooled to 38℃, dried for 30 minutes, with a moisture content of 0.5%, the product is obtained.

[0031] Test case This test case focuses on Examples 2 and 3, and the test results are shown in Table 1: Table 1: Test Tables for Examples 2 and 3 Comparative Example 1 This comparative example was conducted in the absence of a temperature control system and a deodorization system: (1) Raw material pretreatment: completely consistent with Example 2, starch crosslinking degree 18%, biochar specific surface area 320m² / g; (2) Mixing and stirring: Weigh out 50 kg of PHB / PHBH copolymer (1:1.5), 30 kg of modified starch, 7 kg of PBAT, 8 kg of biochar, 4.5 kg of wood ash, 1.2 kg of potassium nitrate, 2.8 kg of PEG-1000, 3.5 kg of talc, 2.2 kg of bentonite, 2.3 kg of waste edible oil modified product, 0.6 kg of KH-550, and 0.6 kg of carbon black; (Delete the core components of this invention: magnesium hydroxide (core of the temperature control system), powdered activated carbon, Artemisia argyi extract, and zeolite powder (core of the deodorization system)). The mixture was prepared according to the process in Example 2 (stirring at 65°C and 900 rpm for 10 minutes, then stirring at 600 rpm for 8 minutes after adding the liquid component) to obtain the mixture. (3) Extrusion granulation: Same as in Example 2 (40mm single screw extruder, gradient temperature rise 132℃ / 142℃ / 148℃, speed 50r / min, die head pressure 12MPa). (4) Cooling and drying: Same as in Example 2 (air cooling to 35°C, fluidized bed drying for 35 minutes, moisture content 0.4%).

[0032] Comparative analysis Comparative Example 1 (lacking temperature control and deodorization system): Due to the removal of magnesium hydroxide (the core of temperature control), the temperature could not be stabilized at 500-600℃ during incineration, and the dioxin emission reached 0.085 ng TEQ / m³, which is 10.6 times that of Example 2, far exceeding the adaptation requirements; lacking activated carbon, artemisia extract, and zeolite powder (deodorization system), the VOCs emission reached 45.6 mg / m³, which is 5.6 times that of Example 2, producing a distinct pungent odor during incineration, and the Ringelmann blackness rose to level 3, indicating severe pollution.

[0033] Comparative Example 2 This comparative example was conducted under the condition that the degree of starch crosslinking and the specific surface area of ​​biochar did not meet the requirements: (1) Raw material pretreatment: Starch modification: Take 100 kg of corn starch and prepare it according to the steps of Example 2. Stir for only 1 hour and test the degree of crosslinking. The result is 10% (lower than the 15%-20% limit of this invention). Modification of waste cooking oil: Same as in Example 2 (purity 96.5%); Solid raw material pretreatment: Straw is pyrolyzed at 300℃ for 1 hour (lower than the oxygen-limited pyrolysis conditions of 400-500℃ in this invention), crushed and passed through an 80-mesh sieve, and the BET test shows a specific surface area of ​​200m² / g (lower than the ≥300m² / g limit of this invention); other solid raw material treatments are the same as in Example 1; (2) Mixing and stirring: completely consistent with Example 2 (the components, proportions, and processes are all the same); (3) Extrusion granulation: Same as in Example 2; (4) Cooling and drying: Same as in Example 2.

[0034] Comparative analysis Comparative Example 2 (starch crosslinking degree and biochar specific surface area do not meet the standards): The starch crosslinking degree is only 10%, which causes the product to swell and break after 1 month in a humid rural environment. The tensile strength drops to 15.2 MPa and the elongation at break is only 112%, which cannot meet the requirements for loading heavy objects. The biochar specific surface area is 200 m² / g, which is insufficient for microbial attachment sites. The degradation rate after 6 months is only 68.3%, which is far below the suitability requirements. The residue is likely to cause environmental pollution. The dioxin emission is 0.012 ng TEQ / m³ and the VOCs emission is 12.8 mg / m³. Although it is close to the suitability requirements, it does not achieve the optimal effect of the example.

[0035] In summary, this invention, through the synergistic system of "temperature control-deodorization" and the precise control of starch crosslinking degree and biochar specific surface area, enables the product to fully meet the needs of rural scenarios in terms of degradation performance, harmless incineration, and mechanical properties. When the core system is lacking or key parameters exceed the standard, the performance is significantly inferior to that of this invention, which fully demonstrates the inventiveness and necessity of the technical solution of this invention.

[0036] It should be noted that the test methods for Comparative Example 1 and Comparative Example 2 are explained as follows: Soil degradation rate after 6 months: The mass loss rate was measured after 6 months of cultivation in a simulated rural natural soil environment (temperature 25℃, humidity 60%, pH 6.5-7.5). Dioxin emissions from incineration: A tubular furnace was used to simulate the working conditions of a rural stove (temperature 600-800℃, oxygen concentration 15%). After condensation and adsorption, the flue gas was analyzed by GC-MS for 17 dioxin homologs, including 2,3,7,8-TCDD, and the toxicity equivalent was calculated. Incineration Ringelmann blackness: The blackness of the incineration flue gas was observed on-site using a Ringelmann blackness meter; VOC emissions from incineration: The total amount of volatile organic compounds such as benzene, toluene, and xylene in the incineration flue gas was detected using GC-FID. Tensile strength / elongation at break: Refer to GB / T1040.3-2006, process the particles into Class 1A standard specimens, and test them with a universal testing machine (tensile speed 50 mm / min). Heat distortion temperature of lunch boxes: Referring to GB / T1633-2000, the granules were processed into lunch box samples, and the heat distortion temperature under load was tested.

[0037] Although the present invention has been disclosed above with reference to preferred embodiments, the embodiments are merely examples for illustrative purposes and are not intended to limit the present invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present invention. The scope of protection claimed by the present invention should be determined by the claims.

Claims

1. A method for producing degradable plastic mixed particles, characterized by, The method comprises the following steps: S1, pretreatment of raw materials, including starch modification, waste cooking oil modification, solid raw material pretreatment, wherein the solid raw material includes biochar, wood ash, zeolite powder, bentonite; S2, the following components are weighed by mass percentage: PHA 48%-52%, modified starch 28%-32%, PBAT 6%-8%, biochar 7%-9%, wood ash 4%-5%, potassium nitrate 1%-1.5%, PEG-1000 2.5%-3%, magnesium hydroxide 8%-10%, talcum powder 3%-4%, powdered activated carbon 1.5%-2%, wormwood extract 1%-1.5%, zeolite powder 2.5%-3%, bentonite 2%-2.5%, waste cooking oil modifier 2%-2.5%, silane coupling agent KH-550 0.5%-0.8%, carbon black 0.5%-0.7%; the PHA is a PHB / PHBH copolymer, the mass ratio of PHB to PHBH is 1:1.5-2, and the number average molecular weight is ; and then mixing and stirring are performed; S3, the mixture is put into a single screw extruder, the pressure sensor controls the pressure of the machine head to be 10-15 MPa; after extrusion through the mold, water ring cutting is adopted; S4, the particles are cooled by air cooling conveyor belt, and then sent to a vibrating fluidized bed dryer to control the final moisture content of the particles to be ≤0.5%, thereby obtaining the degradable plastic mixed particles.

2. The method of claim 1, wherein the degradable plastic mixed particles are prepared by the steps of: The step S1 specifically comprises the following sub-steps: ​ S11, the starch is mixed with propylene oxide and hydrochloric acid at a mass ratio of 100:5:0.8, nitrogen is introduced for protection, and stirring is performed at room temperature for 2-3 hours; during the stirring, sample detection is performed every 30 minutes; when the crosslinking degree reaches 15%-20%, the reaction is stopped; water washing is performed to remove unreacted hydrochloric acid; and spray drying is performed under the conditions of 180℃ inlet air and 80℃ outlet air, thereby obtaining modified starch; the crosslinking degree is detected by the swelling degree method: the modified starch is soaked in distilled water at 25℃ for 24 hours, and the crosslinking degree is calculated according to the formula "crosslinking degree (%)=(mass of insoluble substances after soaking / mass of sample before soaking)×100%"; S12, the waste cooking oil is filtered through an 80-mesh screen to remove impurities, mixed with methanol and sulfuric acid catalyst at a mass ratio of 100:20:1, and stirred at 60℃ and 300r / min for 1 hour; after standing and separating, the upper layer of fatty acid methyl ester is taken; the purity is detected by gas chromatography to be ≥95%, thereby obtaining waste cooking oil modification; S13, the biochar, wood ash, zeolite powder and bentonite are respectively crushed by a planetary ball mill at a ball-to-material ratio of 10:1 and a rotation speed of 400r / min; after crushing, the materials are sieved through an 80-100 mesh screen; and drying is performed under the conditions of 80℃ and a vacuum degree of-0.09MPa for 2 hours, thereby controlling the water content to be ≤1.5%; the biochar is prepared by limiting oxygen pyrolysis of straw or rice husk at 400-500℃ for 2 hours, and the specific surface area detected by BET is ≥300m² / g.

3. The method for preparing biodegradable plastic mixed granules according to claim 1, characterized in that, In the step S2, the magnesium hydroxide is in a hexagonal crystal system, and the particle size is ≤5μm; the pore size of the zeolite powder is 0.5-1nm; the total flavone content of the wormwood extract is ≥15%, which is detected by ultraviolet spectrophotometry; and the mixing and stirring process in the step S2 is as follows: first, the solid components are put into a high-speed mixer, heated to 60-70℃, and stirred at a rotation speed of 800-1000r / min for 10 minutes, so that the amino group of the silane coupling agent KH-550 is chemically bonded with the hydroxyl group of the starch and the carboxyl group of the biochar; then, the liquid components are added, and the rotation speed is reduced to 600r / min for continuous stirring for 5-10 minutes; during the stirring, the material temperature is controlled by an infrared temperature detector to be not higher than 70℃, thereby obtaining the mixture.

4. The method for preparing biodegradable plastic mixed granules according to claim 2, characterized in that, In S11, the starch is corn starch or sweet potato starch, and the crosslinking degree is strictly controlled to be 15%-20%; when the crosslinking degree is <15%, the starch is easy to swell in the humid environment in rural areas, which causes the product to break prematurely; when the crosslinking degree is >20%, the starch is too rigid, which causes the elongation rate of the product to be lower than 120%, and the product cannot meet the demand for carrying heavy objects in rural areas. S13, the specific surface area of the biochar is ≥300 m² / g, and the porous structure of the biochar can provide microbial attachment sites. When the specific surface area is <300 m² / g, the amount of microbial colonization is reduced by more than 40%, and the degradation rate of the product is reduced to less than 70% in 6 months.

5. The method for preparing biodegradable plastic mixed granules according to claim 3, characterized in that, In S2, the mass ratio of the PHB / PHBH copolymer is 1:1.5-2, wherein PHB provides rigidity (tensile strength ≥25 MPa), and PHBH provides low-temperature toughness (elongation at break ≥80% at -10°C). The "potassium nitrate-wood ash-PEG" forms a composite combustion-supporting system: potassium nitrate releases oxygen during combustion, the potassium salt in wood ash catalyzes the combustion reaction, and PEG lowers the ignition point of the substrate.

6. The method for preparing biodegradable plastic mixed granules according to claim 3, characterized in that, In S2, the "magnesium hydroxide-talc powder" forms a temperature control system: the thermal decomposition temperature of magnesium hydroxide is 340°C, and it absorbs a large amount of heat during decomposition. Talc powder stabilizes the combustion temperature, and the combination of the two stabilizes the farm stove burning temperature at 500-600°C, avoiding the 300-500°C interval where dioxins are generated.

7. The method for preparing biodegradable plastic mixed granules according to claim 3, characterized in that, S2 The activated carbon, the wormwood extract and the zeolite powder constitute a deodorization system: the activated carbon adsorbs VOCs, the zeolite powder adsorbs sulfur-containing gas, and the flavonoids in the wormwood extract chemically react with odor molecules, so that the VOCs emission during incineration is ≤10 mg / m³ and there is no pungent odor.

8. The method for preparing biodegradable plastic mixed granules according to claim 1, characterized in that, The screw diameter of the extruder in S3 is 35-45 mm, and the length-diameter ratio is 25:

1. The barrel adopts gradient heating: the feeding section is 130-135°C, the compression section is 140-145°C, and the metering section is 145-150°C. The screw rotation speed is 40-60 r / min. The die head pressure is controlled at 10-15 MPa: when the pressure is <10 MPa, the material is not fully plasticized, and the product has air bubble defects; when the pressure is >15 MPa, the screw load exceeds the bearing limit of the small extruder, which can easily cause equipment failure. In the water ring pelletizing in S3, the water temperature is 25°C, and the cutter rotation speed is 1500 r / min, obtaining particles with a diameter of 2-3 mm and a roundness ≥0.

8. In S4, the cooling air speed is 5 m / s, the cooling time is 3 minutes, and the cooling temperature is ≤40°C. Then the product is sent to a vibration fluidized bed dryer, the hot air temperature is 60°C, the air speed is 1.2 m / s, and the drying time is 30-40 minutes.

9. The method for preparing biodegradable plastic mixed granules according to claim 1, characterized in that, In S2, the addition amount of silane coupling agent KH-550 is 0.5%-0.8%. The amino group of KH-550 reacts with the hydroxyl group of starch and the carboxyl group of biochar to form -Si-O-C- chemical bonds, improving the compatibility of each component. When the addition amount is <0.5%, the product is prone to delamination; when the addition amount is >0.8%, the tensile strength of the product decreases.

10. The method of claim 2, wherein the degradable plastic mixed particles are prepared by the steps of: In S13, the montmorillonite content of the bentonite is ≥80%. During incineration, the layered structure of montmorillonite binds the ash, forming 1-3 mm granular ash, which avoids dust pollution, and the ash contains potassium and calcium elements, which can be directly used as a rural farmland fertilizer. ​

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