Preparation method of environment-friendly plastic storage box of degradable bio-based composite material

Abstract

The application provides an environment-friendly plastic storage box preparation method of degradable bio-based composite materials, and belongs to the field of plastic products. Specifically, polylactic acid and natural plant fibers are compounded to prepare degradable materials, and the distribution directionality of the fibers is optimized through a melt blending process to improve the mechanical properties of the materials. In addition, a photosensitive catalyst is introduced into the composite materials through an in-situ polymerization reaction to promote the accelerated degradation of the materials under outdoor light conditions. The plastic storage box prepared by the method has excellent mechanical properties and photocatalytic degradation capacity, and can be widely applied in the fields of environment-friendly packaging, household storage and outdoor products.

Description

Technical Field

[0001] This invention relates to the field of plastic products, and in particular to a method for preparing an environmentally friendly plastic storage box made of biodegradable bio-based composite material. Background Technology

[0002] Plastic storage boxes are widely used in homes, offices, logistics, and food packaging due to their lightweight, durability, waterproof, and easy-to-clean properties. However, most plastic storage boxes on the market are currently made of petroleum-based polymers such as polypropylene (PP), polyethylene (PE), or polyvinyl chloride (PVC). These materials are non-biodegradable, and if not effectively recycled after use, they will lead to serious environmental pollution problems. For example, discarded plastic products degrade slowly in the natural environment, often taking hundreds of years to completely decompose, thus causing the problem of "white pollution." In addition, some plastic products may release harmful chemicals, such as plasticizers and leaching monomers, under high temperatures or sunlight, posing potential threats to the ecological environment and human health.

[0003] In recent years, biodegradable plastics have gradually become a research hotspot in order to reduce plastic pollution. Among them, polylactic acid (PLA) has attracted widespread attention due to its renewability, good biocompatibility, and biodegradability. PLA is produced by fermenting lactic acid from biomass resources (such as corn, sugarcane, cassava, etc.) and then synthesized through condensation polymerization or epoxy ring-opening polymerization. Under industrial composting conditions, it can be completely degraded into carbon dioxide and water, exhibiting good environmental friendliness. However, PLA also has certain drawbacks, such as high brittleness, poor heat resistance, easy moisture absorption, and limited processing performance. Therefore, it is necessary to improve its overall performance through blending modification or composite reinforcement.

[0004] Natural plant fibers (such as bamboo fiber, straw fiber, and wood fiber) can be used as reinforcing phases for PLA, not only improving the material's mechanical properties, such as enhancing its impact resistance and reducing brittleness, but also further improving its degradation performance. Bamboo fiber and straw fiber, due to their abundant resources, high mechanical strength, and good biodegradability, are considered ideal reinforcing fillers for PLA modification. However, because natural fibers are highly polar and have poor compatibility with the PLA matrix, they easily lead to problems such as weak interfacial bonding and fiber agglomeration within the composite material, thus affecting its mechanical properties. Therefore, using compatibilizers (such as maleic anhydride-grafted polylactic acid and polyvinyl alcohol) for interfacial modification can effectively improve the interfacial compatibility between PLA and plant fibers, thereby enhancing the overall performance of the composite material.

[0005] Currently, most biodegradable plastic storage boxes on the market are made of pure PLA or PLA / filler blends, but they have the following problems:

[0006] Insufficient mechanical properties: PLA itself is relatively brittle, which makes the products prone to breakage and affects their durability.

[0007] Limited degradation rate: Although PLA can degrade under industrial composting conditions, its degradation rate in the natural environment is slow, making it difficult to meet the environmental protection requirements for rapid degradation. Summary of the Invention

[0008] This invention aims to overcome the shortcomings of existing technologies and provide a method for preparing environmentally friendly plastic storage boxes using biodegradable bio-based composite materials. This invention not only improves the mechanical properties and service life of the storage boxes but also endows them with photocatalytic degradation capabilities, making them more suitable for environmental protection and possessing broad market application prospects.

[0009] The specific plan is as follows:

[0010] A method for preparing an environmentally friendly plastic storage box made of biodegradable bio-based composite material, characterized by comprising the following steps:

[0011] (1) Raw material mixing: Weigh 60-80 parts of polylactic acid, 20-40 parts of natural plant fiber, 1-5 parts of compatibilizer, 1-3 parts of photosensitive catalyst, and 0.1-2.0 parts of reinforcing agent according to the mass fraction and mix them evenly;

[0012] (2) Melt blending: The mixture obtained in step (1) is melt blended using a twin-screw extruder to optimize the orientation distribution of plant fibers;

[0013] (3) Injection molding: The modified mixture is fed into the injection molding machine and injection molding is performed under the set conditions;

[0014] (4) Cooling and curing: Cool the hot-pressed plastic storage box to room temperature to obtain the final product;

[0015] The reinforcing agent is prepared by reacting propyltriethoxysilane isocyanate, allyltriphenylphosphine, dibutyltin dilaurate, and 2-amino-1,3,5-triazine.

[0016] Preferably, the natural plant fiber is selected from bamboo fiber or straw fiber, and the fiber particle size is 50-500μm.

[0017] Preferably, the compatibilizer is maleic anhydride-grafted polylactic acid (PLA-g-MA) or polyvinyl alcohol (PVA).

[0018] Preferably, the photosensitive catalyst is selected from titanium dioxide mixed crystal powder P25, ZnO nanoparticles, or WO3 (sodium tungstate / lithium tungstate) photocatalyst.

[0019] Preferably, the method for preparing the reinforcing agent is as follows:

[0020] In a reaction vessel equipped with a stirrer, thermometer, and reflux condenser, add 200-300 parts by weight of toluene and turn on the stirrer. Then, add 20-30 parts of propyltriethoxysilane isocyanate and 0.2-3 parts of allylidene triphenylphosphine sequentially to the reaction vessel, maintaining the reaction temperature at 50-70°C and continuously stirring to ensure uniform mixing of the raw materials. Next, add 0.5-2 parts of dibutyltin dilaurate as a catalyst to the mixture and continue stirring for 1-3 hours. Then, add 10-20 parts of 2-amino-1,3,5-triazine to the reaction system, raise the reaction temperature to 70-80°C, and continue the reaction for 1-3 hours. After the reaction is complete, perform vacuum distillation to remove toluene, finally obtaining a reinforcing agent for cross-linked polyethylene foam materials.

[0021] Preferably, the melt blending is carried out using a twin-screw extruder with a melt temperature of 180-200℃, a screw speed of 50-100 rpm, and a shear rate of 10-50 s⁻¹.

[0022] Preferably, the injection temperature is 170-200℃, the injection pressure is 60-100MPa, and the mold temperature is 60-90℃.

[0023] Preferably, the cooling and curing process includes natural cooling or water cooling to bring the plastic storage box to room temperature.

[0024] Mechanism of the reaction: The isocyanate group (-N=C=O) in the propyltriethoxysilane molecule is strongly electrophilic. Due to the high electronegativity of nitrogen and oxygen atoms, the electron cloud density of the carbon atom is low, making it susceptible to nucleophilic attack. The carbon-carbon double bond connected by the phosphorus atom in allylidene triphenylphosphine has a certain electron cloud density and can act as a nucleophile. During the reaction, the π electron cloud of the carbon-carbon double bond attacks the carbon atom of the isocyanate group, forming a transition state. The π bond of the isocyanate group opens, and the lone pair electrons of the phosphorus atom form a new σ bond with the carbon atom. Subsequently, the transition state rearranges to form a stable intermediate containing a carbon-phosphorus bond and a urea group (-NH-CO-). Dibutyltin dilaurate acts as a catalyst, coordinating with the oxygen or carbon atom of the isocyanate group, changing its electron cloud distribution, lowering the activation energy, and promoting the nucleophilic addition-rearrangement reaction.

[0025] Beneficial effects:

[0026] 1. Using PLA and natural plant fiber composites: Optimize fiber distribution orientation through melt blending to improve the mechanical properties of the composite material, reduce the brittleness of PLA, and improve impact resistance.

[0027] 2. Significant performance improvement: The reinforcing agent of this invention forms a unique chemical structure through the combination and reaction of specific raw materials, which can generate strong interactions with the molecules of cross-linked polyethylene foam material, effectively improving the strength and degree of cross-linking of the material, thereby enhancing the overall performance of the material.

[0028] 3. Optimize process parameters: By controlling process parameters such as melt blending temperature, screw speed, injection molding temperature and time, we ensure high-quality molding and functional optimization of the storage box. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1:

[0031] (1) Mixing raw materials

[0032] Take the following materials in the indicated weight proportions: 70 kg of polylactic acid (PLA), 30 kg of bamboo fiber (particle size 100 μm), 2 kg of maleic anhydride-grafted polylactic acid (PLA-g-MA), 2 kg of P25 type TiO2 photosensitive catalyst, and 0.5 kg of reinforcing agent. Mix them thoroughly.

[0033] The reinforcing agent preparation steps in this embodiment are as follows: 1) Add 25,000 g of toluene to a reaction vessel equipped with a stirrer, thermometer, and reflux condenser, and turn on the stirrer; 2) Add 2,500 g of propyltriethoxysilane isocyanate and 150 g of allylidene triphenylphosphine to the reaction vessel in sequence, control the reaction temperature at 60°C, and continue stirring to ensure uniform mixing of the raw materials; 3) Add 100 g of dibutyltin dilaurate as a catalyst to the mixture and continue stirring for 2 hours; 4) Then add 1,500 g of 2-amino-1,3,5-triazine to the reaction system, raise the reaction temperature to 75°C, and continue the reaction for 2 hours; 5) After the reaction is completed, perform vacuum distillation on the reaction system to remove toluene, and finally obtain the reinforcing agent for cross-linked polyethylene foam materials.

[0034] (2) Melt blending

[0035] A twin-screw extruder (temperature set at 190°C), screw speed at 60 rpm, and shear rate at 20 s⁻¹ were used for melt blending to optimize fiber dispersion and orientation.

[0036] (3) Injection molding

[0037] The blend is fed into an injection molding machine for injection molding: barrel temperature 185℃, injection pressure 80MPa, mold temperature set to 70℃, and holding time 8 seconds.

[0038] (4) Cooling and solidification

[0039] The storage box is allowed to cool naturally to room temperature, and after demolding, it becomes the final product.

[0040] Example 2:

[0041] (1) Mixing raw materials

[0042] Mix 80 kg of polylactic acid (PLA), 20 kg of straw fiber (300 μm particle size), 3 kg of polyvinyl alcohol (PVA), 2.5 kg of ZnO nanopowder, and 1.0 kg of reinforcing agent evenly.

[0043] The reinforcing agent preparation steps in this embodiment are as follows: 1) Add 28,000 g of toluene to a reaction vessel equipped with a stirrer, thermometer, and reflux condenser, and turn on the stirrer; 2) Add 3,000 g of propyltriethoxysilane isocyanate and 250 g of allylidene triphenylphosphine to the reaction vessel in sequence, control the reaction temperature at 55°C, and continue stirring to ensure uniform mixing of the raw materials; 3) Add 200 g of dibutyltin dilaurate as a catalyst to the mixture and continue stirring for 3 hours; 4) Then add 2,000 g of 2-amino-1,3,5-triazine to the reaction system, raise the reaction temperature to 80°C, and continue the reaction for 3 hours; 5) After the reaction is completed, perform vacuum distillation on the reaction system to remove toluene, and finally obtain the reinforcing agent for cross-linked polyethylene foam materials.

[0044] (2) Melt blending

[0045] Temperature: 195℃, screw speed: 70rpm, shear rate: 30s-1, blending was carried out in a twin-screw extruder.

[0046] (3) Injection molding

[0047] Injection temperature 190℃, injection pressure 90MPa, mold temperature set at 80℃, holding pressure for 12 seconds for molding.

[0048] (4) Cooling and solidification

[0049] After demolding and cooling for 30 minutes, you will get an environmentally friendly storage box.

[0050] Example 3:

[0051] (1) Mixing raw materials

[0052] Mix 75kg PLA, 25kg bamboo fiber (particle size 150μm), 4kg PLA-g-MA, 1.5kg WO3 photosensitive catalyst, and 1.5kg reinforcing agent thoroughly.

[0053] The reinforcing agent preparation steps in this embodiment are as follows: 1) Add 22,000 g of toluene to a reaction vessel equipped with a stirrer, thermometer, and reflux condenser, and turn on the stirrer; 2) Add 2,200 g of propyltriethoxysilane isocyanate and 80 g of allylidene triphenylphosphine to the reaction vessel in sequence, control the reaction temperature at 65°C, and continue stirring to ensure uniform mixing of the raw materials; 3) Add 80 g of dibutyltin dilaurate as a catalyst to the mixture and continue stirring for 1.5 hours; 4) Then add 1,200 g of 2-amino-1,3,5-triazine to the reaction system, raise the reaction temperature to 70°C, and continue the reaction for 1.5 hours; 5) After the reaction is completed, perform vacuum distillation on the reaction system to remove toluene, and finally obtain the reinforcing agent for cross-linked polyethylene foam materials.

[0054] (2) Melt blending

[0055] The extrusion temperature was set to 180℃, the screw speed to 100rpm, the shear rate to 40s-1, and the process was continuous blending.

[0056] (3) Injection molding

[0057] The injection molding machine temperature is set to 170℃, the injection pressure to 70MPa, the mold temperature to 65℃, and the holding time to 10 seconds.

[0058] (4) Cooling and solidification

[0059] After molding, cool for 25 minutes before demolding to obtain the finished product.

[0060] Example 4:

[0061] (1) Mixing raw materials

[0062] Mix 65 kg of PLA, 35 kg of straw fiber (particle size 200 μm), 2 kg of PVA, 3 kg of P25 type TiO2 photosensitizer, and 2.0 kg of reinforcing agent by mechanical stirring for 30 minutes.

[0063] The reinforcing agent preparation steps in this embodiment are as follows: 1) Add 30,000 g of toluene to a reaction vessel equipped with a stirrer, thermometer, and reflux condenser, and turn on the stirrer; 2) Add 2,800 g of propyltriethoxysilane isocyanate and 300 g of allylidene triphenylphosphine to the reaction vessel in sequence, control the reaction temperature at 50°C, and continue stirring to ensure uniform mixing of the raw materials; 3) Add 150 g of dibutyltin dilaurate as a catalyst to the mixture, and continue stirring for 2.5 hours; 4) Then add 1,800 g of 2-amino-1,3,5-triazine to the reaction system, raise the reaction temperature to 78°C, and continue the reaction for 2.5 hours; 5) After the reaction is completed, perform vacuum distillation on the reaction system to remove toluene, and finally obtain the reinforcing agent for cross-linked polyethylene foam materials.

[0064] (2) Melt blending

[0065] The twin-screw extrusion temperature is 200℃, the screw speed is 80rpm, the shear rate is 50s-1, and the processing time is 10 minutes.

[0066] (3) Injection molding

[0067] The injection molding machine is set to a temperature of 200℃, an injection pressure of 100MPa, a mold temperature of 90℃, and a holding time of 12 seconds.

[0068] (4) Cooling and solidification

[0069] After cooling for 30 minutes, the product is demolded to form a dense, heat-resistant, and environmentally friendly storage box.

[0070] Comparative Example 1

[0071] This example is a comparative example of Example 1, the only difference from Example 1 is that no reinforcing agent is added.

[0072] Comparative Example 2

[0073] This example is a comparative example of Example 1. The only difference between this example and Example 1 is that propyltriethoxysilane isocyanate is not added during the preparation of the reinforcing agent.

[0074] Comparative Example 3

[0075] This example is a comparative example of Example 1, and the only difference from Example 1 is that allyl triphenylphosphine is not added during the preparation of the reinforcing agent.

[0076] Test methods and results:

[0077] 1. Mechanical property testing (tensile strength, flexural strength, impact strength)

[0078] Test methods: Tensile strength and flexural strength were determined on an electronic universal testing machine in accordance with GB / T 1040.3-2006 standard; impact strength was tested using a cantilever beam impact test in accordance with GB / T 1843-2008 standard.

[0079] Table 1: Mechanical property test results of the examples and comparative examples

[0080]

[0081]

[0082] 2. Photocatalytic degradation test

[0083] Test method: Each sample was exposed to a UV lamp (wavelength 365nm, power 50W), and the mass loss rate was measured after 60 days to evaluate the degradation performance.

[0084] Table 2: Photocatalytic degradation test results of the examples and comparative examples

[0085] Quality loss rate (60 days, %) Example 1 76.6 Example 2 78.5 Example 3 78.9 Example 4 79.4 Comparative Example 1 76.4 Comparative Example 2 76.6 Comparative Example 3 76.5

[0086] This invention significantly improves the overall performance of plastic storage boxes by combining PLA / bamboo fiber composite reinforcement, reinforcing agent design, and photocatalytic degradation technology. It achieves a balance between high strength and photocatalytic degradation function, and has broad market application prospects.

[0087] In this specification, the invention has been described with reference to specific embodiments thereof. However, it will be apparent that various modifications and variations can be made without departing from the spirit and scope of the invention. Therefore, this specification is to be considered illustrative rather than restrictive.

Claims

1. A method for preparing an environmentally friendly plastic storage box made of biodegradable bio-based composite material, characterized in that, Includes the following steps: (1) Raw material mixing: Weigh 60-80 parts of polylactic acid, 20-40 parts of natural plant fiber, 1-5 parts of compatibilizer, 1-3 parts of photosensitive catalyst, and 0.1-2.0 parts of reinforcing agent according to the mass fraction and mix them evenly; (2) Melt blending: The mixture obtained in step (1) is melt blended using a twin-screw extruder to optimize the orientation distribution of plant fibers; (3) Injection molding: The modified mixture is fed into the injection molding machine and injection molding is performed under the set conditions; (4) Cooling and curing: Cool the thermo-pressed plastic storage box to room temperature to obtain the final product; The reinforcing agent is prepared by reacting propyltriethoxysilane isocyanate, allyltriphenylphosphine, dibutyltin dilaurate, and 2-amino-1,3,5-triazine. The preparation method of the reinforcing agent: In a reaction vessel equipped with a stirrer, thermometer, and reflux condenser, add 200-300 parts by weight of toluene and turn on the stirrer. Then, add 20-30 parts of propyltriethoxysilane isocyanate and 0.2-3 parts of allylidene triphenylphosphine sequentially to the reaction vessel, maintaining the reaction temperature at 50-70°C and continuously stirring to ensure uniform mixing of the raw materials. Next, add 0.5-2 parts of dibutyltin dilaurate as a catalyst to the mixture and continue stirring for 1-3 hours. Then, add 10-20 parts of 2-amino-1,3,5-triazine to the reaction system, raise the reaction temperature to 70-80°C, and continue the reaction for 1-3 hours. After the reaction is complete, perform vacuum distillation to remove toluene, finally obtaining a reinforcing agent for cross-linked polyethylene foam materials.

2. The method for preparing an environmentally friendly plastic storage box made of biodegradable bio-based composite material according to claim 1, characterized in that: The natural plant fiber is selected from bamboo fiber or straw fiber, and the fiber particle size is 50-500 μm.

3. The method for preparing an environmentally friendly plastic storage box made of biodegradable bio-based composite material according to claim 1, characterized in that: The compatibilizer is maleic anhydride-grafted polylactic acid (PLA-g-MA) or polyvinyl alcohol (PVA).

4. The method for preparing an environmentally friendly plastic storage box made of biodegradable bio-based composite material according to claim 1, characterized in that: The melt blending is carried out using a twin-screw extruder with a melt temperature of 180-200℃, a screw speed of 50-100 rpm, and a shear rate of 10-50 s⁻¹.

5. The method for preparing an environmentally friendly plastic storage box made of biodegradable bio-based composite material according to claim 1, characterized in that: The injection temperature is 170-200℃, the injection pressure is 60-100 MPa, and the mold temperature is 60-90℃.

6. The method for preparing an environmentally friendly plastic storage box made of biodegradable bio-based composite material according to claim 1, characterized in that: The cooling and curing process includes natural cooling or water cooling to bring the plastic storage box down to room temperature.

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