Completely biodegradable plastic bag and preparation method thereof

Abstract

The invention discloses a completely biodegradable plastic bag and a preparation method thereof, and relates to the technical field of plastic products. The completely biodegradable plastic bag is at least prepared from the following raw materials in parts by mass: 30 to 40 parts of polylactic acid, 20 to 30 parts of poly (1, 2-propylene glycol adipate), 10 to 20 parts of poly (butylene succinate), 15 to 25 parts of modified holocellulose, 2 to 5 parts of plasticizer and 1 to 3 parts of maleic anhydride grafted compatilizer. According to the completely biodegradable plastic bag prepared from the water-based industrial coating, poly (1, 2-propylene glycol adipate) is used as a plasticizer, poly (butylene succinate) is used as a flexibilizer, and modified holocellulose is used as a modified filler, so that the mechanical property and heat resistance of the completely biodegradable plastic bag are improved, the completely biodegradable plastic bag can be completely biodegraded, the pollution to the environment is reduced, and the cost is reduced; the method has good economic benefits and wide application prospects, and can be suitable for supermarket shopping bags and express packaging bags.

Description

Technical Field

[0001] The present invention relates to the technical field of plastic products, in particular to a completely biodegradable plastic bag and a preparation method thereof. Background Art

[0002] Since the advent of polymer materials, along with the rapid development of the petroleum industry and rising productivity, plastic products have been increasingly used in all areas of production and life, becoming an indispensable resource for society. However, traditional polymer materials, characterized by excellent stability, chemical resistance, and corrosion resistance, are not easily degraded in the natural environment. Consequently, these refractory plastics pose a significant environmental pollution problem. This social issue has a wide-ranging impact on natural resources and the environment, intertwined with numerous other social issues. For example, the difficulty in recycling plastics leads to the waste of petroleum resources, the "white pollution" caused by non-degradable, single-use plastics, and the air and soil pollution caused by the incineration and landfilling of plastics. To fundamentally and effectively address the environmental pollution caused by discarded plastics, research has begun on biodegradable, environmentally friendly plastics, aiming to address the pollution problem at its source. There are many types of biodegradable plastics, including fully biodegradable plastics, which can be broken down by naturally occurring microorganisms such as bacteria and molds into small molecules that re-enter the natural cycle. These plastics are easily disposed of and pose no environmental risk.

[0003] Fully biodegradable plastics are biodegradable biopolymers that can be completely degraded by microorganisms under natural conditions after use, ultimately breaking down into water and carbon dioxide. Because their raw materials are widely available and their final degradation products are environmentally friendly, biodegradable plastics are also known as "green plastics." Currently, China has successfully developed a variety of methods for producing fully biodegradable plastics. Major biodegradable polymers include β-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV), polycaprolactone (PCL), polybutylene succinate (PBS), polyvinyl alcohol (PVA), starch, carbon dioxide copolymers, polybutylene terephthalate (PBAT), and polylactic acid (PLA). PLA, a thermoplastic aliphatic polyester, is widely available, inexpensive, and biocompatible, exhibiting excellent chemical inertness, biodegradability, and mechanical properties. PLA products possess excellent gloss and transparency and are the only biodegradable plastic with excellent antibacterial and antifungal properties. However, PLA's shortcomings, such as brittleness, poor impact resistance, and poor thermal stability, limit its application. Summary of the Invention

[0004] The purpose of the present invention is to provide a fully biodegradable plastic bag and a preparation method thereof, to solve the following technical problems: Existing polylactic acid-based fully biodegradable plastic bags have the problems of being brittle in use, having poor impact resistance and poor thermal stability.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A completely biodegradable plastic bag, comprising at least the following raw materials in parts by weight: 30-40 parts of polylactic acid, 20-30 parts of poly(1,2-propylene adipate), 10-20 parts of poly(butylene succinate), 15-25 parts of modified holocellulose, 2-5 parts of plasticizer, and 1-3 parts of maleic anhydride grafted compatibilizer.

[0006] As a further embodiment of the present invention, the method for preparing the modified holocellulose comprises the following steps: Adjusting the pH of the ethanol solution of methacryloxypropyltrimethoxysilane to 3-4, stirring to obtain a hydrolyzate, adding holocellulose, and reacting to obtain coupling agent-modified holocellulose; The coupling agent-modified holocellulose, water, N,N-dimethylformamide, potassium persulfate and n-butyl acrylate are mixed and reacted under nitrogen protection to obtain modified holocellulose.

[0007] As a further embodiment of the present invention, the mass ratio of the methacryloxypropyltrimethoxysilane to the holocellulose is 10-13:1.

[0008] As a further embodiment of the present invention, the mass ratio of the coupling agent-modified holocellulose, the water, the N,N-dimethylformamide, the potassium persulfate and the n-butyl acrylate is 1:10-15:10-15:0.012-0.015:0.8-0.9.

[0009] As a further embodiment of the present invention, the holocellulose is extracted from lignocellulose, and the lignocellulose includes at least one of corn cobs, rice straw, wheat straw, rape straw, corn straw, bamboo chips, wood chips, rice husks or sugarcane bagasse.

[0010] As a further embodiment of the present invention: the plasticizer is a mixture of one or more of epoxidized soybean oil, tributyl citrate or polycaprolactone diol.

[0011] As a further embodiment of the present invention, the maleic anhydride grafted compatibilizer is a mixture of one or more of maleic anhydride grafted poly(1,2-propylene adipate), maleic anhydride grafted poly(lactic acid) or maleic anhydride grafted poly(butylene succinate).

[0012] A method for preparing a completely biodegradable plastic bag comprises at least the following steps: Adding polylactic acid, poly(1,2-propylene adipate), poly(butylene succinate), modified holocellulose, a plasticizer, and a maleic anhydride grafted compatibilizer into a high-speed mixer to obtain a premix; The premix is ​​added into a twin-screw extruder, melt-granulated, and obtained as a masterbatch; The masterbatch is added into a single-screw film blowing machine and cut into pieces by a bag making machine to obtain completely biodegradable plastic bags.

[0013] As a further solution of the present invention: the thickness of the fully biodegradable plastic bag is 20-50 μm Beneficial effects of the present invention: A water-based industrial coating is used to prepare fully biodegradable plastic bags using a melt blending method and an extrusion blown film process using poly(propylene adipate), poly(butylene succinate), polylactic acid, and modified holocellulose. Poly(propylene adipate) is used as a plasticizer, poly(butylene succinate) as a toughening agent, and modified holocellulose as a modified filler, improving the mechanical and heat resistance of the fully biodegradable plastic bags. The fully biodegradable plastic bags prepared in this invention have excellent overall performance, meeting the requirements of most packaging bags. They can completely degrade within 180 days under composting conditions, reducing environmental pollution and costs. They offer good economic benefits and broad application prospects, including supermarket shopping bags and express delivery bags.

[0014] The addition of polybutylene succinate in the present invention improves the flexibility of polylactic acid, and the blending properties of the two complement each other. Polybutylene succinate increases the toughness of polylactic acid, and polylactic acid increases the rigidity of polybutylene succinate. The elongation at break and tear strength of the prepared plastic bag are both improved. Polybutylene succinate has a high degree of crystallinity. When polybutylene succinate is added to polylactic acid, the crystalline phase of polybutylene succinate can act as a nucleating agent, promoting the regular arrangement of polylactic acid molecular chains and increasing its crystallinity, thereby improving the heat resistance of the blended material. Then, the addition of poly(1,2-propylene adipate) improves the mobility of polylactic acid molecules, causing polylactic acid to change from brittle fracture to tough fracture due to plastic deformation, playing a plasticizing role and making the film soft. Furthermore, poly(1,2-propylene adipate) is composed of adipic acid (a flexible fatty chain) and 1,2-propylene glycol (containing hydroxyl groups). Its molecular chain combines the flexibility of a fatty chain with the polarity of an ester group. This structure allows poly(1,2-propylene adipate) to serve as a "transition phase," reducing the interfacial tension between polylactic acid and poly(butylene succinate), promoting the interpenetration of molecular segments, and improving the compatibility of poly(butylene succinate) and poly(lactic acid). This further enhances the heat resistance, elongation at break, and tear strength of the resulting fully biodegradable plastic bag. The blend of poly(butylene succinate), poly(1,2-propylene adipate), and poly(lactic acid) in the present invention can be used to prepare high-performance, low-cost, fully biodegradable plastic bags, which have promising application prospects and conform to the concept of green development.

[0015] Waterborne industrial coatings utilize methacryloxypropyltrimethoxysilane and polybutyl acrylate to co-graft-modify holocellulose. Methacryloxypropyltrimethoxysilane is used to modify the holocellulose, introducing terminal olefins onto the surface of the modified holocellulose. Subsequently, polybutyl acrylate undergoes a polymerization reaction with the double bonds introduced by the coupling agent, grafting the polybutyl acrylate onto the surface of the holocellulose to form a bilayer. This replaces and covers the hydroxyl groups on the surface of the modified holocellulose, reducing the hydrophilicity of the modified holocellulose and improving its thermal stability. Compared to a single coupling agent or polybutyl acrylate, the coupling agent / polybutyl acrylate bilayer on the surface of the modified holocellulose exhibits a superior modification effect on the holocellulose. This results in a favorable interfacial interaction between the modified holocellulose and the polylactic acid matrix, enhancing compatibility and improving the dispersion of the modified holocellulose in the polylactic acid matrix, as well as the crystallinity, thermal properties, and mechanical properties of the composite. Holocellulose itself can be degraded by microorganisms, matching the degradation rate of polybutylene succinate, poly(1,2-propylene adipate) and polylactic acid to avoid residue. Holocellulose comes from corn cobs, straw, etc., reducing dependence on petroleum-based fillers and lowering production costs. DETAILED DESCRIPTION

[0016] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0017] Example 1 The preparation method of modified holocellulose comprises the following steps: A 1000 mL ethanol solution of 10% methacryloyloxypropyltrimethoxysilane (10%) by volume was adjusted to pH 3 with hydrochloric acid and pre-hydrolyzed at room temperature for 1.5 hours with stirring. 10 g of holocellulose was added to the hydrolyzate, heated to 60°C, and allowed to react for 4 hours. After the reaction, the solution was filtered and dried at 60°C. After drying, it was baked at 110°C for 2 hours. The solution was then transferred to a Soxhlet extractor and extracted with acetone for 2 hours to remove the unreacted coupling agent, yielding coupling agent-modified holocellulose. The above-mentioned 10 g of coupling agent-modified holocellulose, 100 mL of water, 100 mL of N,N-dimethylformamide, 0.125 g of potassium persulfate and 8.5 mL of n-butyl acrylate were added to a three-necked flask, and nitrogen was passed through for 30 minutes to remove oxygen in the reaction system. The temperature was then raised to 65°C and the reaction was continued for 2 hours. After the reaction was completed, the reaction liquid was filtered and transferred to a Soxhlet extractor to extract with acetone to remove polybutyl acrylate homopolymer, and then dried at 60°C to obtain modified holocellulose.

[0018] Example 2 The preparation method of modified holocellulose comprises the following steps: A 1000 mL ethanol solution of 12% methacryloyloxypropyltrimethoxysilane (12%) by volume was adjusted to pH 3 with hydrochloric acid and pre-hydrolyzed at room temperature for 2 hours with stirring. 10 g of holocellulose was added to the hydrolyzate, heated to 60°C, and allowed to react for 5 hours. After the reaction, the solution was filtered and dried at 60°C. After drying, it was baked at 110°C for 2 hours. The solution was then transferred to a Soxhlet extractor and extracted with acetone for 2 hours to remove the unreacted coupling agent, yielding coupling agent-modified holocellulose. The above-mentioned 10 g of coupling agent-modified holocellulose, 100 mL of water, 120 mL of N,N-dimethylformamide, 0.14 g of potassium persulfate and 9 mL of n-butyl acrylate were added to a three-necked flask, and nitrogen was passed through for 30 minutes to remove oxygen in the reaction system. The temperature was then raised to 65°C and the reaction was continued for 2 hours. After the reaction was completed, the reaction liquid was filtered and transferred to a Soxhlet extractor to extract with acetone to remove polybutyl acrylate homopolymer, and then dried at 60°C to obtain modified holocellulose.

[0019] Example 3 A method for preparing a completely biodegradable plastic bag is prepared by the following method: 35 parts by mass of polylactic acid 2003D, 25 parts by mass of poly(1,2-propylene adipate), 15 parts by mass of poly(butylene succinate AZ91TN), 20 parts by mass of the modified holocellulose prepared in Example 1, 3 parts by mass of epoxy soybean oil as a plasticizer, and 2 parts by mass of maleic anhydride-grafted polylactic acid as a compatibilizer were added to a high-speed mixer and mixed at 50° C. for 15 minutes to obtain a premix; The premix was added to a twin-screw extruder, and the temperature gradient was set as follows: polylactic acid section 170°C, poly(1,2-propylene adipate) section 150°C, poly(butylene succinate) section 140°C, and the screw speed was 200 rpm. Melt granulation was performed to obtain masterbatch. The above masterbatch was added into a single-screw film blowing machine, and the die temperature was set to 165°C, the blow-up ratio to 2.5:1, and the pulling speed to 12 m / min. The bag was cut into pieces by a bag making machine to obtain a fully biodegradable plastic bag with a thickness of 30 μm.

[0020] Example 4 A method for preparing a completely biodegradable plastic bag is prepared by the following method: 35 parts by mass of polylactic acid 2003D, 25 parts by mass of poly(1,2-propylene adipate), 15 parts by mass of poly(butylene succinate AZ91TN), 20 parts by mass of the modified holocellulose prepared in Example 2, 3 parts by mass of epoxy soybean oil as a plasticizer, and 2 parts by mass of maleic anhydride-grafted polylactic acid as a compatibilizer were added to a high-speed mixer and mixed at 50° C. for 15 minutes to obtain a premix; The premix was added to a twin-screw extruder, and the temperature gradient was set as follows: polylactic acid section 170°C, poly(1,2-propylene adipate) section 150°C, poly(butylene succinate) section 140°C, and the screw speed was 200 rpm. Melt granulation was performed to obtain masterbatch. The above masterbatch was added into a single-screw film blowing machine, and the die temperature was set to 165°C, the blow-up ratio to 2.5:1, and the pulling speed to 12 m / min. The bag was cut into pieces by a bag making machine to obtain a fully biodegradable plastic bag with a thickness of 30 μm.

[0021] Example 5 A method for preparing a completely biodegradable plastic bag is prepared by the following method: 30 parts by mass of polylactic acid 2003D, 25 parts by mass of poly(1,2-propylene adipate), 15 parts by mass of poly(butylene succinate AZ91TN), 25 parts by mass of the modified holocellulose prepared in Example 1, 3 parts by mass of epoxy soybean oil as a plasticizer, and 2 parts by mass of maleic anhydride-grafted polylactic acid as a compatibilizer were added to a high-speed mixer and mixed at 50° C. for 15 minutes to obtain a premix; The premix was added to a twin-screw extruder, and the temperature gradient was set as follows: polylactic acid section 170°C, poly(1,2-propylene adipate) section 150°C, poly(butylene succinate) section 140°C, and the screw speed was 200 rpm. Melt granulation was performed to obtain masterbatch. The above masterbatch was added into a single-screw film blowing machine, and the die temperature was set to 165°C, the blow-up ratio to 2.5:1, and the pulling speed to 12 m / min. The bag was cut into pieces by a bag making machine to obtain a fully biodegradable plastic bag with a thickness of 30 μm.

[0022] Example 6 A method for preparing a completely biodegradable plastic bag is prepared by the following method: 30 parts by mass of polylactic acid 2003D, 25 parts by mass of poly(1,2-propylene adipate), 15 parts by mass of poly(butylene succinate AZ91TN), 25 parts by mass of the modified holocellulose prepared in Example 2, 3 parts by mass of epoxy soybean oil as a plasticizer, and 2 parts by mass of maleic anhydride-grafted polylactic acid as a compatibilizer were added to a high-speed mixer and mixed at 50° C. for 15 minutes to obtain a premix; The premix was added to a twin-screw extruder, and the temperature gradient was set as follows: polylactic acid section 170°C, poly(1,2-propylene adipate) section 150°C, poly(butylene succinate) section 140°C, and the screw speed was 200 rpm. Melt granulation was performed to obtain masterbatch. The above masterbatch was added into a single-screw film blowing machine, and the die temperature was set to 165°C, the blow-up ratio to 2.5:1, and the pulling speed to 12 m / min. The bag was cut into pieces by a bag making machine to obtain a fully biodegradable plastic bag with a thickness of 30 μm.

[0023] Comparative Example 1 The preparation method of polybutyl acrylate modified holocellulose comprises the following steps: 10 g of holocellulose, 100 mL of water, 120 mL of N,N-dimethylformamide, 0.125 g of potassium persulfate and 8.5 mL of n-butyl acrylate were added to a three-necked flask, and nitrogen was passed through for 30 minutes to remove oxygen in the reaction system. The temperature was then raised to 65°C and the reaction was continued for 2 hours. After the reaction was completed, the reaction liquid was filtered and transferred to a Soxhlet extractor to extract with acetone to remove polybutyl acrylate homopolymer, and then dried at 60°C to obtain polybutyl acrylate-modified holocellulose.

[0024] Comparative Example 2 Compared with Example 3, Comparative Example 2 only replaces the mass of the modified holocellulose prepared in Example 1 added in Example 3 with the coupling agent-modified holocellulose prepared in Example 1, and the other components and preparation methods are exactly the same as those in Example 3.

[0025] Comparative Example 3 Compared with Example 3, Comparative Example 2 only replaces the modified holocellulose prepared in Example 1 added in Example 3 with the polybutyl acrylate modified holocellulose prepared in Comparative Example 1. The other components and preparation methods are exactly the same as those in Example 3.

[0026] Comparative Example 4 Compared with Example 3, Comparative Example 4 only replaces the poly(1,2-propylene adipate) added in Example 3 with the plasticizer epoxidized soybean oil. The other components and preparation method are completely consistent with those of Example 3.

[0027] Comparative Example 5 Compared with Example 3, Comparative Example 4 only replaces the polybutylene succinate added in Example 3 with polylactic acid. The other components and preparation method are completely consistent with Example 3.

[0028] Performance testing Mechanical Properties: The fully biodegradable plastic bags obtained in Examples 3-6 and Comparative Example 2 were cut into dumbbell shapes measuring 20 mm × 4 mm × 0.025 mm. Testing was performed according to ASTM D882-2010 at a tensile rate of 50 mm / min. The film's right-angle tear test was performed according to QB / T 1130-1991 at a test speed of 200 mm / min. The test results are shown in Table 1. Heat Deformation Temperature Test: The heat deformation temperatures of the fully biodegradable plastic bags obtained in Examples 3-6 and Comparative Examples 2-5 were measured using a heat deformation and Vicat softening point thermometer according to GB / T 1633-2000. The test samples measured 10.0 mm × 10.0 mm × 4.0 mm. The heat transfer medium was silicone oil, the heating rate was set at 120°C / h, the applied load was 10 N, and the maximum deformation of the samples was 1 mm. The test results are shown in Table 1.

[0029] Compost degradation test: Compost soil was stirred evenly, spread on a tray, and placed in a 55°C forced air drying oven until constant weight was achieved. 300 g of the compost soil was weighed. The fully biodegradable plastic bags obtained in Examples 3-6 and Comparative Examples 2-5 were cut into small pieces with a maximum surface area not exceeding 1 cm x 1 cm. 50 g of the film was weighed. A compost degradation test was conducted in a biodegradable tester, and the degradation rate was measured after 6 months. The test results are shown in Table 1. Table 1: Statistical table of plastic bag performance test data for Examples 3-6 and Comparative Examples 2-5

[0030] As shown in Table 1, the fully biodegradable plastic bags prepared in Examples 3-6 in the water-based industrial coatings have good mechanical properties, heat resistance and complete biodegradability. In comparative example 1, the holocellulose was only modified with a coupling agent, and in comparative example 2, the holocellulose was only modified with polybutyl acrylate. The mechanical properties and initial thermal decomposition temperature of the obtained fully biodegradable plastic bag were reduced, indicating that the coupling agent and polybutyl acrylate jointly modified the holocellulose, and effectively improved the compatibility of the components of the composite material, thereby improving the performance. In comparative example 3, poly(1,2-propylene adipate) was replaced with plasticizer epoxy soybean oil, and the tensile strength and elastic modulus of the obtained fully biodegradable plastic bag were greatly reduced. In comparative example 4, no poly(butylene succinate) was added, and the fracture growth rate and tear strength of the obtained fully biodegradable plastic bag were greatly reduced, indicating that poly(1,2-propylene adipate) can not only act as a plasticizer but also promote the compatibility between polylactic acid and poly(butylene succinate), and poly(butylene succinate) has a good toughening effect on polylactic acid.

[0031] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A fully biodegradable plastic bag, characterized in that: At least include the following raw materials by mass: 30-40 parts of polylactic acid, 20-30 parts of poly(1,2-propylene adipate), 10-20 parts of poly(butylene succinate), 15-25 parts of modified holocellulose, 2-5 parts of plasticizer, and 1-3 parts of maleic anhydride grafted compatibilizer.

2. A fully biodegradable plastic bag according to claim 1, characterized in that: The preparation method of the modified holocellulose comprises the following steps: Adjusting the pH of the ethanol solution of methacryloxypropyltrimethoxysilane to 3-4, stirring to obtain a hydrolyzate, adding holocellulose, and reacting to obtain coupling agent-modified holocellulose; The coupling agent-modified holocellulose, water, N,N-dimethylformamide, potassium persulfate and n-butyl acrylate are mixed and reacted under nitrogen protection to obtain modified holocellulose.

3. A fully biodegradable plastic bag according to claim 2, characterized in that: The mass ratio of the methacryloxypropyltrimethoxysilane to the holocellulose is 10-13:

1.

4. A fully biodegradable plastic bag according to claim 2, characterized in that: The mass ratio of the coupling agent-modified holocellulose, the water, the N,N-dimethylformamide, the potassium persulfate and the n-butyl acrylate is 1:10-15:10-15:0.012-0.015:0.8-0.

9.

5. A fully biodegradable plastic bag according to claim 2, characterized in that: The holocellulose is extracted from lignocellulose, and the lignocellulose includes at least one of corn cobs, rice straw, wheat straw, rape straw, corn straw, bamboo chips, wood chips, rice husks or sugarcane bagasse.

6. A fully biodegradable plastic bag according to claim 1, characterized in that: The plasticizer is a mixture of one or more of epoxidized soybean oil, tributyl citrate or polycaprolactone diol.

7. A fully biodegradable plastic bag according to claim 1, characterized in that: The maleic anhydride grafted compatibilizer is a mixture of one or more of maleic anhydride grafted poly(1,2-propylene adipate), maleic anhydride grafted polylactic acid or maleic anhydride grafted poly(butylene succinate).

8. A method for preparing a completely biodegradable plastic bag, characterized in that: The method comprises at least the following preparation steps: Adding polylactic acid, poly(1,2-propylene adipate), poly(butylene succinate), modified holocellulose, a plasticizer, and a maleic anhydride grafted compatibilizer into a high-speed mixer to obtain a premix; The premix is ​​added into a twin-screw extruder, melt-granulated, and obtained as a masterbatch; The masterbatch is added into a single-screw film blowing machine and cut into pieces by a bag making machine to obtain completely biodegradable plastic bags.

9. The method for preparing a completely biodegradable plastic bag according to claim 8, characterized in that: The thickness of the completely biodegradable plastic bag is 20-50 μm.

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