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

Abstract

The invention provides a preparation method of an environment-friendly plastic storage box made of a degradable bio-based composite material, and belongs to the field of plastic products. Specifically, polylactic acid and natural plant fibers are compounded to prepare the degradable material, and the distribution directivity of the fibers is optimized through a melt blending process, so that the mechanical property of the material is improved. In addition, a photosensitive catalyst is introduced into the composite material through an in-situ polymerization reaction, and accelerated degradation of the material is promoted under the outdoor illumination condition. The plastic storage box prepared by the method disclosed by the invention has excellent mechanical properties and photocatalytic degradation capability, and can be widely applied to the fields of environment-friendly packaging, household storage and outdoor articles.

Description

Technical Field

[0001] The present invention relates to the field of plastic products, and particularly to a preparation method of an environmentally friendly plastic storage box made of a degradable bio-based composite material. Background Art

[0002] Plastic storage boxes are widely used in fields such as households, offices, logistics, and food packaging due to their light weight, durability, waterproofness, easy cleaning, etc. However, currently, plastic storage boxes on the market are mainly made of petroleum-based polymer materials such as polypropylene (PP), polyethylene (PE), or polyvinyl chloride (PVC). These materials are non-degradable, and if not effectively recycled after use, they will cause serious environmental pollution problems. For example, waste plastic products degrade slowly in the natural environment and usually take hundreds of years to completely decompose, thus causing the "white pollution" problem. In addition, some plastic products may release harmful chemical substances such as plasticizers and eluted monomers under high temperature or light conditions, posing potential threats to the ecological environment and human health.

[0003] In recent years, in order to reduce plastic pollution, biodegradable plastics have gradually become a research hotspot. Among them, polylactic acid (PLA) has been widely concerned due to its renewable nature, good biocompatibility, and biodegradability. PLA is prepared by fermenting biomass resources (such as corn, sugarcane, cassava, etc.) to produce lactic acid, and then through polycondensation or ring-opening polymerization of epoxy. It can be completely degraded into carbon dioxide and water under industrial composting conditions, showing good environmental friendliness. However, PLA also has certain defects, such as relatively large brittleness, poor heat resistance, easy moisture absorption, and limited processing performance. Therefore, it is necessary to improve its comprehensive performance through blending modification or composite reinforcement means.

[0004] Natural plant fibers (such as bamboo fibers, straw fibers, wood fibers, etc.) as the reinforcing phase of PLA can not only improve the mechanical properties of the material, such as enhancing its impact resistance and reducing brittleness, but also further improve the degradation performance of the material. Bamboo fibers and straw fibers are considered ideal reinforcing fillers for PLA modification due to their rich resource reserves, relatively high mechanical strength, and good biodegradability. However, due to the strong polarity of natural fibers, their compatibility with the PLA matrix is poor, which easily leads to problems such as weak interfacial bonding force and fiber agglomeration inside the composite material, thus affecting the mechanical properties of the material. Therefore, using compatibilizers (such as maleic anhydride grafted polylactic acid, polyvinyl alcohol, etc.) 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, the existing degradable plastic storage boxes on the market mainly use pure PLA or PLA / filler blend materials, but there are the following problems:

[0006] Insufficient mechanical properties: PLA itself has relatively large brittleness, resulting in easy cracking of the products and affecting durability.

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

[0008] The present invention aims to overcome the defects of the prior art and provides a preparation method for an environmentally friendly plastic storage box made of a degradable bio-based composite material. The present invention not only improves the mechanical properties and service life of the storage box, but also endows it with photocatalytic degradation ability, making it more suitable for the environmental protection field and having broad market application prospects.

[0009] The specific solution is as follows:

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

[0011] (1) Raw material mixing: Weigh 60 - 80 parts by mass 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, 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 the plant fiber;

[0013] (3) Injection molding: The modified mixed material is fed into an injection molding machine and injection molding is carried out under set conditions;

[0014] (4) Cooling and solidification: The plastic storage box after hot pressing is cooled to room temperature to obtain the final product;

[0015] The reinforcing agent is prepared by reacting isocyanatopropyltriethoxysilane, allylidene triphenylphosphine, 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 - 500 μm.

[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 nanopowder, or WO3 (sodium tungstate / lithium tungstate) photocatalyst.

[0019] Preferably, the preparation method of the reinforcing agent:

[0020] In a reaction vessel equipped with a stirrer, a thermometer, and a reflux condenser, add 200 - 300 parts by weight of toluene, and start the stirring device; sequentially add 20 - 30 parts of isocyanatopropyltriethoxysilane and 0.2 - 3 parts of allylidene triphenylphosphine into the reaction vessel, control the reaction temperature at 50 - 70 °C, and continuously stir to make the raw materials mix evenly; add 0.5 - 2 parts of dibutyltin dilaurate as a catalyst to the mixed system, and continue stirring and reacting 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 reacting for 1 - 3 hours; after the reaction is completed, perform vacuum distillation on the reaction system to remove toluene, and finally obtain an enhancer for cross - linked polyethylene foaming materials.

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

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

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

[0024] Reaction mechanism of the enhancer: The isocyanate group (-N = C = O) in the isocyanatopropyltriethoxysilane molecule has strong electrophilicity. Due to the large electronegativity of nitrogen and oxygen atoms, the electron cloud density of the carbon atom is low, making it vulnerable to nucleophilic attack. The carbon - carbon double bond connected to 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 to form 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 ureido (-NH - CO-) structure. Dibutyltin dilaurate acts as a catalyst, coordinates with the oxygen or carbon atom of the isocyanate group, changes its electron cloud distribution, reduces the reaction activation energy, and promotes the nucleophilic addition - rearrangement reaction.

[0025] Beneficial effects:

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

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

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

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] Example 1:

[0031] (1) Raw material mixing

[0032] Take materials according to the following mass parts: 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, 0.5 kg of enhancer, and stir and mix evenly.

[0033] The preparation steps of the enhancer in this example are as follows: 1) Add 25000 g of toluene to a reaction vessel equipped with a stirrer, a thermometer and a reflux condenser, and start the stirring device; 2) Add 2500 g of isocyanatopropyltriethoxysilane and 150 g of allylidene triphenylphosphine into the reaction vessel in sequence, control the reaction temperature at 60 °C, and continuously stir to make the raw materials mix evenly; 3) Add 100 g of dibutyltin dilaurate as a catalyst to the mixed system, and continue to stir and react for 2 hours; 4) Then add 1500 g of 2-amino-1,3,5-triazine to the reaction system, raise the reaction temperature to 75 °C, and continue to react for 2 hours; 5) After the reaction is completed, perform a vacuum distillation operation on the reaction system to remove toluene, and finally obtain an enhancer for cross-linked polyethylene foaming material.

[0034] (2) Melt blending

[0035] Use a twin-screw extruder (temperature set at 190 °C), screw speed of 60 rpm, shear rate of 20 s-1, and perform melt blending to optimize fiber dispersion and orientation.

[0036] (3) Injection molding

[0037] Feed the blend into an injection molding machine for injection molding: barrel temperature 185°C, injection pressure 80 MPa, mold temperature set at 70°C, holding pressure time 8 seconds.

[0038] (4) Cooling and solidification

[0039] The storage box is naturally cooled to room temperature and, after demolding, is the final product.

[0040] Example 2:

[0041] (1) Raw material mixing

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

[0043] The preparation steps of the reinforcing agent in this example: 1) In a reaction vessel equipped with a stirrer, a thermometer and a reflux condenser, add 28000 g of toluene and start the stirring device; 2) Sequentially add 3000 g of isocyanatopropyltriethoxysilane and 250 g of allylidene triphenylphosphine into the reaction vessel, control the reaction temperature at 55°C, and continuously stir to make the raw materials mix evenly; 3) Add 200 g of dibutyltin dilaurate as a catalyst to the mixing system and continue stirring and reacting for 3 hours; 4) Then add 2000 g of 2-amino-1,3,5-triazine to the reaction system, raise the reaction temperature to 80°C, and continue reacting for 3 hours; 5) After the reaction is completed, perform a vacuum distillation operation on the reaction system to remove toluene, and finally obtain a reinforcing agent for crosslinking polyethylene foamed materials.

[0044] (2) Melt blending

[0045] Temperature: 195°C, screw speed: 70 rpm, shear rate: 30 s-1, perform blending in a twin-screw extruder.

[0046] (3) Injection molding

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

[0048] (4) Cooling and solidification

[0049] After demolding and cooling for 30 minutes, an environmentally friendly storage box is obtained.

[0050] Example 3:

[0051] (1) Raw material mixing

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

[0053] Steps for preparing the reinforcing agent in this example: 1) Add 22000 g of toluene into a reaction vessel equipped with a stirrer, a thermometer, and a reflux condenser, and start the stirring device; 2) Sequentially add 2200 g of isocyanatopropyltriethoxysilane and 80 g of allylidene triphenylphosphine into the reaction vessel, control the reaction temperature at 65 °C, and continuously stir to make the raw materials evenly mixed; 3) Add 80 g of dibutyltin dilaurate as a catalyst into the mixed system, and continue stirring and reacting for 1.5 hours; 4) Then add 1200 g of 2-amino-1,3,5-triazine into the reaction system, raise the reaction temperature to 70 °C, and continue reacting for 1.5 hours; 5) After the reaction is completed, perform a reduced-pressure distillation operation on the reaction system to remove toluene, and finally obtain a reinforcing agent for crosslinking polyethylene foamed materials.

[0054] (2) Melt blending

[0055] The extrusion temperature is set at 180 °C, the screw speed is 100 rpm, the shear rate is 40 s-1, and continuous blending is carried out.

[0056] (3) Injection molding

[0057] The temperature of the injection machine is set at 170 °C, the injection pressure is 70 MPa, the mold temperature is 65 °C, and the holding pressure time is 10 seconds.

[0058] (4) Cooling and curing

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

[0060] Example 4:

[0061] (1) Raw material mixing

[0062] 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 are mechanically stirred for 30 minutes to be evenly mixed.

[0063] Steps for preparing the enhancer in this embodiment: 1) Add 30000 g of toluene into a reaction vessel equipped with a stirrer, a thermometer and a reflux condenser, and start the stirring device; 2) Sequentially add 2800 g of isocyanatopropyltriethoxysilane and 300 g of allylidene triphenylphosphine into the reaction vessel, control the reaction temperature at 50 °C, and continuously stir to make the raw materials mix evenly; 3) Add 150 g of dibutyltin dilaurate as a catalyst into the mixed system, and continue stirring and reacting for 2.5 hours; 4) Then add 1800 g of 2-amino-1,3,5-triazine into the reaction system, raise the reaction temperature to 78 °C, and continue reacting for 2.5 hours; 5) After the reaction is completed, perform vacuum distillation on the reaction system to remove toluene, and finally obtain an enhancer for cross-linking polyethylene foamed materials.

[0064] (2) Melt blending

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

[0066] (3) Injection molding

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

[0068] (4) Cooling and curing

[0069] After cooling for 30 minutes, demold to form an environmentally friendly storage box with a dense structure and good heat resistance.

[0070] Comparative example 1

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

[0072] Comparative example 2

[0073] This example is a comparative example of Example 1, and the only difference from Example 1 is that isocyanatopropyltriethoxysilane is not added during the preparation of the enhancer.

[0074] Comparative example 3

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

[0076] Testing methods and results:

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

[0078] Test method: According to the standard of GB / T 1040.3-2006, the tensile strength and flexural strength are measured on an electronic universal testing machine; according to the standard of GB / T 1843-2008, the impact strength is tested by the cantilever beam impact test.

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

[0080]

[0081]

[0082] 2. Photocatalytic degradation test

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

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

[0085] Mass 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] Through the combination of PLA / bamboo fiber composite reinforcement, enhancer design and photocatalytic degradation technology, the comprehensive performance of the plastic storage box is significantly improved, achieving the unity of high strength and photocatalytic degradation function, and having broad market application prospects.

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

Claims

1. A method for preparing an environmentally friendly plastic storage box made of degradable bio-based composite materials, characterized in that: The following steps are involved: (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 enhancer by weight and mix them evenly; (2) melt blending: melt blending the mixture obtained in step (1) using a twin-screw extruder to optimize the orientation distribution of the plant fibers; (3) Injection molding: The modified mixed material is fed into an injection molding machine and injection molding is performed under set conditions; (4) Cooling and curing: cooling the hot-pressed plastic storage box to room temperature to obtain the final product; The reinforcing agent is prepared by reacting propyltriethoxysilane, allyl triphenylphosphine, dibutyltin dilaurate and 2-amino-1,3,5-triazine.

2. The method for preparing an environmentally friendly plastic storage box made of degradable bio-based composite materials 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 degradable bio-based composite materials 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 degradable bio-based composite materials according to claim 1, characterized in that: The photosensitive catalyst is selected from one of titanium dioxide mixed crystal powder P25, ZnO nanopowder or WO3 (sodium tungstate / lithium tungstate) photocatalyst.

5. The method for preparing an environmentally friendly plastic storage box made of degradable bio-based composite materials according to claim 1, characterized in that: The preparation method of the enhancer: In a reaction vessel equipped with a stirrer, a thermometer and a reflux condenser, 200-300 parts by weight of toluene are added, and the stirring device is turned on; 20-30 parts of isocyanatepropyltriethoxysilane and 0.2-3 parts of allyl triphenylphosphine are added to the reaction vessel in sequence, the reaction temperature is controlled at 50-70°C, and stirring is continued to mix the raw materials evenly; 0.5-2 parts of dibutyltin dilaurate are added to the mixed system as a catalyst, and stirring is continued for 1-3 hours; then 10-20 parts of 2-amino-1,3,5-triazine are added to the reaction system, the reaction temperature is increased to 70-80°C, and the reaction is continued for 1-3 hours; after the reaction is completed, the reaction system is subjected to reduced pressure distillation to remove the toluene, and finally a reinforcing agent for cross-linked polyethylene foaming materials is obtained.

6. The method for preparing an environmentally friendly plastic storage box made of degradable bio-based composite materials 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° C., a screw speed of 50-100 rpm, and a shear rate of 10-50 s-1.

7. The method for preparing an environmentally friendly plastic storage box made of degradable bio-based composite materials according to claim 1, characterized in that: The injection molding temperature is 170-200°C, the injection pressure is 60-100MPa, and the mold temperature is 60-90°C.

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

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