Degradable high-strength plastic bag and method for preparing the same

Abstract

The application discloses a degradable high-strength plastic bag and a preparation method thereof, and relates to the technical field of plastic bag preparation.The degradable high-strength plastic bag comprises the following raw materials in parts by mass: 40-60 parts of polylactic acid, 20-35 parts of polybutylene adipate terephthalate, 5-15 parts of modified nano calcium carbonate, 3-8 parts of modified wood fiber, 6-8 parts of chitosan grafted polymethyl methacrylate glycidyl ester nanoparticles, 0.5-2 parts of lubricant, 0.3-1 part of antioxidant, 2-5 parts of degradation accelerator and 0.5-1.5 parts of ultraviolet stabilizer.The prepared degradable high-strength plastic bag adopts polylactic acid and polybutylene adipate terephthalate as base materials, adopts modified nano calcium carbonate and modified fiber as fillers, and adopts chitosan grafted polymethyl methacrylate glycidyl ester nanoparticles as a compatibilizer, so that the balance between high strength and degradability is achieved, and the prepared degradable high-strength plastic bag can be used as a high-performance flexible packaging material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of plastic bag preparation, in particular to a degradable high-strength plastic bag and a preparation method thereof. BACKGROUND

[0002] Plastic bags are bags prepared from plastic as the main raw material. Due to the advantages of low cost, extremely light weight, large capacity, and easy storage, plastic bags are often used to load other objects and are one of the indispensable objects in people's daily life. With people's concern about environmental problems, the impact of discarded plastic bags on human life has also been concerned. A large number of studies have found that discarded plastic bags have brought the problem of white pollution to the living environment of human beings due to their non-degradability. General plastic bags generally take hundreds of years to degrade, which causes long-term harm to the soil, affects the growth of crops, and thus leads to a reduction in crop yield. Meanwhile, scattered plastic can also cause animals to die from mistaken ingestion. Based on the above problems, China officially implemented the plastic restriction order in 2008, that is, the plastic shopping bag paid use system was implemented in all supermarkets, shopping malls, and commodity retail places such as markets, and plastic shopping bags with a thickness of less than 0.025 millimeters were prohibited from being produced, sold, and used nationwide. Based on this, biodegradable plastics emerged as the times require.

[0003] Synthetic plastics have good physical and chemical properties and economic feasibility, and have been widely used in many fields. However, traditional petroleum-based plastics are difficult to degrade, and burning or landfill treatment leads to deterioration of ecological conditions. Therefore, it is necessary to develop biodegradable polymers to reduce the negative impact on the environment. Polylactic acid (PLA) is obtained by polycondensation of small molecule lactic acid after microbial fermentation of biomass raw materials such as corn or sugarcane. It is non-toxic, high-strength, high-modulus, and has good biocompatibility and processability, and can be applied to drug carriers, food packaging, optoelectronic devices, and other fields. It is the most potential biodegradable polymer at present. However, due to the high rigidity of the PLA molecular chain, there are defects such as high brittleness, low toughness, poor thermal stability, and poor impact resistance, which limit its application. SUMMARY

[0004] The purpose of the present application is to provide a degradable high-strength plastic bag and a preparation method thereof, which solves the following technical problems:

[0005] The existing polylactic acid-based degradable plastic bag has the problems of high brittleness, low toughness, and poor impact resistance.

[0006] The purpose of the present application can be achieved by the following technical solutions:

[0007] A degradable high-strength plastic bag, at least comprising the following mass parts of raw materials:

[0008] Polylactic acid 40-60 parts, polybutylene adipate / terephthalate 20-35 parts, modified nano calcium carbonate 5-15 parts, modified wood fiber 3-8 parts, chitosan grafted glycidyl methacrylate nanoparticles 6-8 parts, lubricant 0.5-2 parts, antioxidant 0.3-1 part, degradation accelerator 2-5 parts, ultraviolet stabilizer 0.5-1.5 parts.

[0009] As a further scheme of the present application: the preparation method of the chitosan grafted glycidyl methacrylate nanoparticles comprises the following steps:

[0010] Add sodium tripolyphosphate solution to the chitosan solution, and obtain chitosan crosslinked nanoparticles after reaction;

[0011] Add glycidyl methacrylate to the chitosan crosslinked nanoparticles, and then add cerium ammonium nitrate nitric acid solution, and obtain chitosan grafted glycidyl methacrylate nanoparticles after reaction.

[0012] As a further scheme of the present application: the mass ratio of the chitosan and the sodium tripolyphosphate is 2-4:1.

[0013] As a further scheme of the present application: the mass ratio of the chitosan crosslinked nanoparticles, the glycidyl methacrylate and the cerium ammonium nitrate is 10:15-20:0.5-1.

[0014] As a further scheme of the present application: the modified nano calcium carbonate is γ-methacryloyloxypropyl trimethoxysilane modified nano calcium carbonate.

[0015] As a further scheme of the present application: the mass ratio of the calcium carbonate and the γ-methacryloyloxypropyl trimethoxysilane is 100:4-6.

[0016] As a further scheme of the present application: the modified wood fiber is γ-methacryloyloxypropyl trimethoxysilane modified wood fiber.

[0017] As a further scheme of the present application: the mass ratio of the wood fiber and the γ-methacryloyloxypropyl trimethoxysilane is 100:3-5.

[0018] As a further scheme of the present application: the lubricant is one or more of stearic acid, stearate, polyvinyl chloride wax, white oil, paraffin, oleic acid amide or erucic acid amide, the antioxidant is one or a mixture of several of antioxidant 1010, antioxidant 1076 or antioxidant 168, the degradation accelerator is one or a mixture of several of citric acid, tartaric acid, malic acid, oxalic acid, malonic acid, succinic anhydride or coconut shell activated carbon, and the ultraviolet stabilizer is one or a mixture of several of 1,2,2,4-tetra (4-carbonyl oxy-2,2,6,6-tetra-methyl pyrrolidine)-amine, 2-benzotriazole-ethyl-4,6-di-tert-butyl phenol or benzoic acid ester ultraviolet stabilizer.

[0019] A preparation method of a degradable high-strength plastic bag, at least comprising the following preparation steps:

[0020] Mixing polylactic acid, polybutylene adipate / terephthalate, modified nano calcium carbonate, modified wood fiber and chitosan grafted glycidyl methacrylate nanoparticles to obtain a premix;

[0021] Double-screw extruding the premix, lubricant, antioxidant, degradation accelerator and ultraviolet stabilizer to obtain composite particles;

[0022] Blowing and packaging the composite particles to prepare an antibacterial high-strength biodegradable plastic bag.

[0023] The present application has the following advantages:

[0024] The present application uses polylactic acid and polybutylene terephthalate adipate as the base material, polybutylene terephthalate adipate can toughen polylactic acid, has excellent degradable performance, is environmentally friendly, and has no pollution and burden to the environment, uses modified nano calcium carbonate and modified fiber as the filler, improves the mechanical properties of the composite material, and uses chitosan grafted glycidyl methacrylate nanoparticle as the compatibilizer, effectively compatibilizes the polylactic acid and polybutylene terephthalate adipate blend.

[0025] The chitosan grafted glycidyl methacrylate nanoparticle is prepared by reducing the particle size of chitosan through ion crosslinking method and then surface-initiated graft polymerization, so that a reactive compatibilization group is introduced into the chitosan, the grafting chain of the chitosan grafted glycidyl methacrylate nanoparticle contains a large number of epoxy side groups, and in the melt blending process, the esterification reaction can occur in situ between the chitosan grafted glycidyl methacrylate nanoparticle and polylactic acid and polybutylene adipate terephthalate to form a polylactic acid-chitosan-polybutylene adipate terephthalate copolymer, thereby playing a reaction compatibilization role, the system strength is increased, and the toughening effect of the polybutylene adipate terephthalate is more obvious, so that the deficiencies of the existing polylactic acid and polybutylene adipate terephthalate blended film, such as poor compatibility of the composite material and poor mechanical properties, are effectively improved, and the comprehensive performance is considered.

[0026] In the present application, calcium carbonate and wood fibers are also added. The wood fibers and calcium carbonate particles form a "fiber-particle" dual enhancement network, and the tensile strength is significantly improved. The addition of calcium carbonate and wood fibers to the substrate has a synergistic enhancement effect, forming a "wood fiber-calcium carbonate-matrix" three-dimensional crosslinked network, and the mechanical properties are significantly improved. In the present application, the surface of the calcium carbonate and wood fibers is modified by gamma-methacryloxypropyl trimethoxysilane. The silicon groups in the gamma-methacryloxypropyl trimethoxysilane are hydrolyzed and adsorbed on the surface of the calcium carbonate and wood fibers, forming a chemical bond with high bond energy and strong bonding. The compatibility between the calcium carbonate and wood fibers and polylactic acid is improved to the greatest extent, the toughness of the composite material is relatively obviously improved, and the methacryloxy group of the gamma-methacryloxypropyl trimethoxysilane is covalently crosslinked with the epoxy group in the chitosan grafted glycidyl methacrylate nanoparticle, realizing strong interface bonding between the filler and the matrix, and further improving the toughness and strength of the prepared degradable high-strength plastic bag. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0028] The preparation method of the modified silicon dioxide in Example 1 includes the following steps:

[0029] Chitosan was dissolved in acetic acid with a mass concentration of 1% to prepare a chitosan solution with a concentration of 3 mg / mL. Then, 0.8 mg / mL of sodium tripolyphosphate solution was added to the above solution, and the mass ratio of chitosan CS to sodium tripolyphosphate was controlled to be 3:1. The solution was stirred at room temperature for 1 h, and then centrifuged for 3 times. The precipitate was frozen at -80°C for 2 h and then freeze-dried for 36 h to obtain chitosan cross-linked nanoparticles.

[0030] In a 250 mL single-neck flask, 10 g of chitosan cross-linked nanoparticles were ultrasonically dispersed in 200 mL of deionized water. Nitrogen was slowly bubbled at room temperature for 1 h, then 15 g of glycidyl methacrylate was added and stirred for 30 min. Then, 5 mL of a nitric acid solution (0.5 mol / L) containing 0.5 g of cerium ammonium nitrate was added. The flask was sealed and placed in a constant temperature oil bath at 50°C for continuous stirring for 5 h. After the reaction was completed, the solid product was separated by suction filtration, washed several times with tetrahydrofuran, and finally washed repeatedly with deionized water until neutral. Freeze-drying obtained chitosan grafted glycidyl methacrylate nanoparticles.

[0031] The preparation method of the modified nano calcium carbonate in Example 2 includes the following steps:

[0032] In a 1000 mL single-neck flask, ethanol and water were added in a volume ratio of 9:1, 50 mL of glacial acetic acid was added to adjust the pH of the mixed solution to 8, and then 100 g of nano calcium carbonate, 1 g of hydroquinone and 3 g of γ-methacryloyloxypropyl trimethoxysilane were added in sequence. Ultrasonic for 30 min, heat the oil bath to 80°C, react for 24 h, and cool to room temperature. Low-speed centrifugal separation was performed, and ethanol was used for washing, and the above operation was repeated twice to remove the residual silicon coupling agent. Vacuum drying for 24 h obtained modified nano calcium carbonate.

[0033] The preparation method of the modified wood fiber in Example 3 includes the following steps:

[0034] 100 g of wood fiber (SQMC-3) was soaked in a 5 wt% NaOH solution for 4 h, then washed with deionized water until neutral, air-dried at room temperature, and then placed in a vacuum drying oven at 90°C for 24 h to obtain alkali-treated wood fiber.

[0035] 4 g of γ-methacryloyloxypropyl trimethoxysilane was added to an ethanol aqueous solution containing 180 mL of ethanol and 20 mL of water to prepare a silane coupling agent solution with a concentration of 2%. The pH value was adjusted to 4 with acetic acid, and the hydrolysis was stirred. The above-mentioned alkali-treated wood fiber was added and stirred for 1 h, then washed with distilled water, vacuum dried at 60°C for 12 h, and then dried at 90°C for 24 h to obtain modified wood fiber.

[0036] A degradable high-strength plastic bag was made by the following method:

[0037] 40 parts by mass of polylactic acid (4032D), 20 parts by mass of polybutylene adipate / terephthalate (TH801 T), 15 parts by mass of the modified nano calcium carbonate prepared in Example 2, 5 parts by mass of the modified wood fiber prepared in Example 3, and 7 parts by mass of the chitosan grafted polyglycidyl methacrylate nanoparticles prepared in Example 1 were mixed to obtain a premix;

[0038] The above premix, 1 part by mass of stearic acid, 1 part by mass of antioxidant 1010, 2 parts by mass of citric acid, and 1 part by mass of a benzoate-based ultraviolet stabilizer were added to a twin-screw extruder, a length-diameter ratio of 40:1 was set, a rotation speed of 300 rpm was set, a temperature gradient of zone 1 160°C, zone 2 170°C, zone 3 175°C, zone 4 180°C, and a die 175°C were set, and composite particles were obtained;

[0039] The above composite particles were added to a film blowing machine, a temperature machine body zone 1 165°C, zone 2 170°C, zone 3 175°C, and a die 175°C were set, a blow-up ratio of 2.5:1 was set, a pulling speed of 15 m / min was set, a cooling roller temperature of 25°C was set, and a winding tension of 50 N was set, and blowing, packaging were performed, and a degradable high-strength plastic bag was obtained.

[0040] Example 5 A degradable high-strength plastic bag was made by the following method:

[0041] 45 parts by mass of polylactic acid (4032D), 25 parts by mass of polybutylene adipate / terephthalate (TH801 T), 15 parts by mass of the modified nano calcium carbonate prepared in Example 2, 5 parts by mass of the modified wood fiber prepared in Example 3, and 7 parts by mass of the chitosan grafted polyglycidyl methacrylate nanoparticles prepared in Example 1 were mixed to obtain a premix;

[0042] The above premix, 1 part by mass of stearic acid, 1 part by mass of antioxidant 1010, 2 parts by mass of citric acid, and 1 part by mass of a benzoate-based ultraviolet stabilizer were added to a twin-screw extruder, a length-diameter ratio of 40:1 was set, a rotation speed of 300 rpm was set, a temperature gradient of zone 1 160°C, zone 2 170°C, zone 3 175°C, zone 4 180°C, and a die 175°C were set, and composite particles were obtained;

[0043] The above composite particles were added to a film blowing machine, a temperature machine body zone 1 165°C, zone 2 170°C, zone 3 175°C, and a die 175°C were set, a blow-up ratio of 2.5:1 was set, a pulling speed of 15 m / min was set, a cooling roller temperature of 25°C was set, and a winding tension of 50 N was set, and blowing, packaging were performed, and a degradable high-strength plastic bag was obtained.

[0044] Example 6 A degradable high-strength plastic bag was made by the following method:

[0045] A mixture of 50 parts by mass of polylactic acid (4032D), 30 parts by mass of polybutylene adipate / terephthalate (TH801 T), 12 parts by mass of the modified nano calcium carbonate prepared in Example 2, 8 parts by mass of the modified wood fiber prepared in Example 3, and 6 parts by mass of the chitosan-grafted polyglycidyl methacrylate nanoparticles prepared in Example 1 was obtained as a premix;

[0046] The above premix, 1 part by mass of stearic acid, 1 part by mass of antioxidant 1010, 2 parts by mass of citric acid, and 1 part by mass of a benzoate-based ultraviolet stabilizer were added to a twin-screw extruder, which was set to a length-diameter ratio of 40:1, a rotation speed of 300 rpm, and a temperature gradient of 160°C in the first zone, 170°C in the second zone, 175°C in the third zone, 180°C in the fourth zone, and 175°C at the die, to obtain composite particles.

[0047] The above composite particles were added to a film blowing machine, which was set to a temperature of 165°C in the first zone, 170°C in the second zone, 175°C in the third zone, and 175°C at the die, a blow-up ratio of 2.5:1, a pulling speed of 15 m / min, a cooling roller temperature of 25°C, and a winding tension of 50 N, to perform blowing and packaging, thereby obtaining a degradable high-strength plastic bag.

[0048] Example 7 A degradable high-strength plastic bag was prepared by the following method:

[0049] A mixture of 60 parts by mass of polylactic acid (4032D), 35 parts by mass of polybutylene adipate / terephthalate (TH801 T), 12 parts by mass of the modified nano calcium carbonate prepared in Example 2, 8 parts by mass of the modified wood fiber prepared in Example 3, and 6 parts by mass of the chitosan-grafted polyglycidyl methacrylate nanoparticles prepared in Example 1 was obtained as a premix.

[0050] The above premix, 1 part by mass of stearic acid, 1 part by mass of antioxidant 1010, 2 parts by mass of citric acid, and 1 part by mass of a benzoate-based ultraviolet stabilizer were added to a twin-screw extruder, which was set to a length-diameter ratio of 40:1, a rotation speed of 300 rpm, and a temperature gradient of 160°C in the first zone, 170°C in the second zone, 175°C in the third zone, 180°C in the fourth zone, and 175°C at the die, to obtain composite particles.

[0051] The above composite particles were added to a film blowing machine, which was set to a temperature of 165°C in the first zone, 170°C in the second zone, 175°C in the third zone, and 175°C at the die, a blow-up ratio of 2.5:1, a pulling speed of 15 m / min, a cooling roller temperature of 25°C, and a winding tension of 50 N, to perform blowing and packaging, thereby obtaining a degradable high-strength plastic bag.

[0052] Comparative Example 1 Comparative Example 1 was prepared in the same manner as Example 4, except that the chitosan-grafted polyglycidyl methacrylate nanoparticles prepared in Example 1 were not added.

[0053] Comparative Example 2 is the same as Example 4 except that the modified wood fiber prepared in Example 3 is replaced by the modified calcium carbonate prepared in Example 2.

[0054] Comparative Example 3 is the same as Example 4 except that the modified calcium carbonate prepared in Example 2 is replaced by the modified wood fiber prepared in Example 3.

[0055] Performance testing

[0056] Tensile property test: The tensile strength and elongation at break of the degradable high-strength plastic bag products obtained in Examples 4-7 and Comparative Examples 1-3 were tested by cutting the samples into 150 mm x 25 mm strips and testing at a speed of 20 mm / min and 50 mm / min using a universal testing machine according to GB / T 1040.3-2006 (Determination of tensile properties of plastics, part 3: test conditions for film and sheeting).

[0057] Angle tear strength test: The angle tear strength of the degradable high-strength plastic bag products obtained in Examples 4-7 and Comparative Examples 1-3 was tested by cutting the samples into 100 mm (MD direction) x 25 mm strips, making a 30 mm cut in the middle of the width, and then testing at room temperature using an Instron Model-1211 material testing machine at a tensile rate of 10 mm / min, with n = 3 tests, and the results were expressed as the average value. The test results are shown in Table 1.

[0058] Impact property test: The impact property of the degradable high-strength plastic bag products obtained in Examples 4-7 and Comparative Examples 1-3 was tested by cutting the samples into 80.0 mm x 12.5 mm x 4.0 mm rectangles and milling them into V-shaped notches with a notch depth of 20% of the sample width using a notching machine, and the test results were taken as the average value of 5 samples. The test results are shown in Table 1.

[0059] Degradation test: A sufficient amount of outdoor soil was taken, and a sufficient amount of composite block sample dried to constant weight was placed in the soil. The humidity was maintained by adding an appropriate amount of tap water at regular intervals. After 180 days, the sample was removed, washed clean, dried thoroughly, and weighed to calculate the degradation rate. The test results are shown in Table 1.

[0060] Table 1: Performance test data statistics of plastic bags in Examples 4-7 and Comparative Examples 1-3

[0061]

[0062] As shown in Table 1, the prepared degradable high-strength plastic bag has high strength and high toughness, good degradation performance, and can be applied to high-end packaging, agricultural film and medical field. In the comparative example 1, the chitosan grafted glycidyl methacrylate nanoparticles are not added, and the mechanical properties of the obtained degradable high-strength plastic bag are the worst. In the comparative example 2, only modified calcium carbonate is added, and no modified wood fiber is added, and the tensile properties of the obtained degradable high-strength plastic bag are decreased. In the comparative example 3, only modified wood fiber is added, and no modified calcium carbonate is added, and the impact strength of the obtained degradable high-strength plastic bag is greatly reduced. It is shown that the chitosan grafted glycidyl methacrylate nanoparticles added in the present application can improve the compatibility between polylactic acid and polybutylene adipate / terephthalate, and can improve the dispersibility of the filler, which is beneficial to the mechanical properties of the prepared plastic bag. The modified calcium carbonate and the modified wood fiber have a synergistic effect, and the use of both has a better effect on the modification of the material properties.

[0063] The above has carried out the detailed description to one embodiment of the present application, but the content described is only the preferred embodiment of the present application, and cannot be considered for limiting the scope of the present application. Any equivalent changes and improvements made according to the scope of the present application should still belong to the patent coverage range of the present application.

Claims

1. A degradable high-strength plastic bag, characterized by, At least the following quality parts of raw materials: Poly lactic acid 40-60 parts, polybutylene adipate terephthalate 20-35 parts, modified nano calcium carbonate 5-15 parts, modified wood fiber 3-8 parts, chitosan grafted poly glycidyl methacrylate nanoparticles 6-8 parts, lubricant 0.5-2 parts, antioxidant 0.3-1 part, degradation promoter 2-5 parts, ultraviolet stabilizer 0.5-1.5 parts; The preparation method of the chitosan grafted poly glycidyl methacrylate nanoparticles comprises the following steps: Sodium tripolyphosphate solution is added to the chitosan solution, and after reaction, chitosan crosslinked nanoparticles are obtained; Glycidyl methacrylate is added to the chitosan crosslinked nanoparticles, and then cerium nitrate nitric acid solution is added, and after reaction, chitosan grafted poly glycidyl methacrylate nanoparticles are obtained; The modified nano calcium carbonate is γ-methacryloyloxypropyl trimethoxysilane modified nano calcium carbonate; The modified wood fiber is γ-methacryloyloxypropyl trimethoxysilane modified wood fiber.

2. The degradable high-strength plastic bag according to claim 1, wherein, The mass ratio of the chitosan and the sodium tripolyphosphate is 2-4:

1.

3. The degradable high-strength plastic bag according to claim 1, wherein, The mass ratio of the chitosan crosslinked nanoparticles, the glycidyl methacrylate and the cerium nitrate is 10:15-20:0.5-1.

4. The degradable high-strength plastic bag according to claim 1, wherein, The mass ratio of the calcium carbonate and the γ-methacryloyloxypropyl trimethoxysilane is 100:4-6.

5. The degradable high-strength plastic bag according to claim 1, wherein, The mass ratio of the wood fiber and the γ-methacryloyloxypropyl trimethoxysilane is 100:3-5.

6. The degradable high-strength plastic bag according to claim 1, wherein, The lubricant is one or more of stearic acid, stearate, polyvinyl chloride wax, white oil, paraffin, oleic acid amide or erucic acid amide, the antioxidant is one or a mixture of several of antioxidant 1010, antioxidant 1076 or antioxidant 168, the degradation promoter is one or a mixture of several of citric acid, tartaric acid, malic acid, oxalic acid, malonic acid, succinic anhydride or coconut shell activated carbon, and the ultraviolet stabilizer is one or a mixture of several of 1,2,2,4-tetra(4-carbonyloxy-2,2,6,6-tetra-methylpyrrolidine)-amine, 2-benzotriazole-ethyl-4,6-di-tert-butyl phenol or benzoic acid ester ultraviolet stabilizer.

7. A process for the production of a degradable high-strength plastic bag as claimed in any one of claims 1 to 6, characterized in that, At least the following preparation steps are included: Mixing poly lactic acid, polybutylene adipate terephthalate, modified nano calcium carbonate, modified wood fiber and chitosan grafted poly glycidyl methacrylate nanoparticles to obtain a premix; Double screw extrusion of the premix, lubricant, antioxidant, degradation promoter and ultraviolet stabilizer to obtain composite particles; Blowing and packaging the composite particles to prepare an antibacterial high-strength biodegradable plastic bag.

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