A fully biodegradable plastic bag and its preparation method

Abstract

This invention discloses a fully biodegradable plastic bag and its preparation method, relating to the field of plastic products technology. The fully biodegradable plastic bag of this invention comprises at least the following raw materials in parts by weight: 30-40 parts polylactic acid, 20-30 parts poly(1,2-propanediol adipate), 10-20 parts polybutylene succinate, 15-25 parts modified holocellulose, 2-5 parts plasticizer, and 1-3 parts maleic anhydride graft compatibilizer. The prepared fully biodegradable plastic bag uses poly(1,2-propanediol adipate) as a plasticizer, polybutylene succinate as a toughening agent, and modified holocellulose as a modified filler, improving the mechanical properties and heat resistance of the fully biodegradable plastic bag. It is fully biodegradable, reducing environmental pollution, lowering costs, and has good economic benefits. It has broad application prospects and can be used for supermarket shopping bags and express delivery packaging bags.

Description

Technical Field

[0001] This invention relates to the field of plastic products technology, specifically to a fully biodegradable plastic bag and its preparation method. Background Technology

[0002] Since the advent of polymer materials, with the rapid development of the petroleum industry and the improvement of social productivity, plastic products have been increasingly used in various fields of production and life, becoming an indispensable material resource for social production and life. However, traditional polymer materials have characteristics such as good stability, chemical resistance, and corrosion resistance, making them difficult to degrade in the natural environment. This has led to environmental pollution problems caused by these non-degradable plastics. This social problem has a wide-ranging impact on natural resources and the environment, and is related to many other social issues to varying degrees. For example, the difficulty in recycling plastic products leads to the waste of petroleum resources; non-degradable single-use plastic products cause "white pollution"; and the burning and landfilling of plastic products cause air and soil pollution. In order to fundamentally and effectively solve the environmental pollution problem caused by waste plastics, people have begun to study degradable, environmentally friendly plastics, striving to solve the pollution problem at its source. There are many types of degradable plastics, among which fully biodegradable plastics can be degraded into small molecules by bacteria, molds, and other microorganisms in nature and re-enter the natural cycle. After disposal, they are easy to handle and cause no pollution to the environment.

[0003] Fully biodegradable plastics refer to biopolymer materials that are biodegradable and can be completely degraded by microorganisms under natural conditions after use, eventually decomposing into water and carbon dioxide. Because their raw materials are widely available and their final degradation products do not pollute the environment, biodegradable plastics are also known as "green plastics." Currently, China has successfully developed several production methods for fully biodegradable plastics. Among these, biodegradable polymer materials mainly include β-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV), polycaprolactone (PCL), polybutylene succinate (PBS), polyvinyl alcohol (PVA), starches, carbon dioxide copolymers, polybutylene terephthalate (PBAT), and polylactic acid (PLA). PLA, as a thermoplastic aliphatic polyester, is widely available, inexpensive, and has good biocompatibility, as well as good chemical inertness, biodegradability, and mechanical properties. PLA products have good gloss and transparency, and are the only biodegradable plastic with excellent antibacterial and antifungal properties. However, PLA's brittleness, poor impact resistance, and poor thermal stability limit its application range. Summary of the Invention

[0004] The purpose of this invention is to provide a fully biodegradable plastic bag and its preparation method, thereby solving the following technical problems:

[0005] Existing polylactic acid-based fully biodegradable plastic bags suffer from problems such as brittleness, poor impact resistance, and poor thermal stability.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A fully biodegradable plastic bag comprising at least the following parts by weight of raw materials:

[0008] 30-40 parts polylactic acid, 20-30 parts poly(1,2-propanediol adipate), 10-20 parts polybutylene succinate, 15-25 parts modified holocellulose, 2-5 parts plasticizer, and 1-3 parts maleic anhydride graft compatibilizer.

[0009] As a further aspect of the present invention, the method for preparing the modified holocellulose includes the following steps:

[0010] The pH of the ethanol solution of methacryloyloxypropyltrimethoxysilane was adjusted to 3-4, and the solution was stirred to obtain a hydrolysate. Homocellulose was then added, and after the reaction, coupling agent modified homocellulose was obtained.

[0011] The coupling agent-modified holocellulose, water, N,N-dimethylformamide, potassium persulfate, and n-butyl acrylate were mixed and reacted under nitrogen protection to obtain modified holocellulose.

[0012] As a further aspect of the present invention, the mass ratio of the methacryloyloxypropyltrimethoxysilane to the holocellulose is 10-13:1.

[0013] As a further aspect 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.

[0014] As a further aspect of the present invention: the holocellulose is obtained by extracting lignocellulose, wherein the lignocellulose includes at least one of corn cob, rice straw, wheat straw, rapeseed straw, corn straw, bamboo shavings, wood chips, rice husks or sugarcane bagasse.

[0015] As a further aspect of the present invention: the plasticizer is one or more of epoxidized soybean oil, tributyl citrate, or polycaprolactone diol.

[0016] As a further aspect of the present invention: the maleic anhydride graft compatibilizer is one or more of maleic anhydride-grafted poly(1,2-propanediol adipate), maleic anhydride-grafted polylactic acid, or maleic anhydride-grafted poly(butylene succinate).

[0017] A method for preparing a fully biodegradable plastic bag includes at least the following preparation steps:

[0018] Polylactic acid, poly(1,2-propanediol adipate), polybutylene succinate, modified holocellulose, plasticizer and maleic anhydride graft compatibilizer are added to a high-speed mixer to obtain a premix.

[0019] The premixed material is added to a twin-screw extruder and melt-granulated to obtain masterbatch;

[0020] The masterbatch is added to a single-screw blown film machine and cut by a bag-making machine to obtain a fully biodegradable plastic bag.

[0021] As a further aspect of the present invention: the thickness of the fully biodegradable plastic bag is 20-50 μm.

[0022] The beneficial effects of this invention are:

[0023] A fully biodegradable plastic bag was prepared using a melt blending method with poly(1,2-propanediol adipate), polybutylene succinate, polylactic acid, and modified holocellulose, followed by extrusion blown film processing. Poly(1,2-propanediol adipate) was used as a plasticizer, polybutylene succinate as a toughening agent, and modified holocellulose as a filler, which improved the mechanical and heat resistance properties of the fully biodegradable plastic bag. The fully biodegradable plastic bag prepared in this invention exhibits excellent overall performance, meeting the requirements of most packaging bags. It can completely degrade within 180 days under composting conditions, reducing environmental pollution and lowering costs, thus offering good economic benefits and broad application prospects. It is suitable for supermarket shopping bags and express delivery packaging bags.

[0024] In this invention, the addition of polybutylene succinate (PBS) improves the flexibility of polylactic acid (PLA). The two materials complement each other in their blending properties; PBS increases the toughness of PLA, while PLA increases the rigidity of PBS. This results in improved elongation at break and tear strength of the prepared plastic bags. PBS has high crystallinity; when added to PLA, its crystalline phase acts as a nucleating agent, promoting the orderly arrangement of PLA molecular chains and increasing its crystallinity, thereby improving the heat resistance of the blend. Furthermore, the addition of poly(1,2-propanediol adipate) enhances the mobility of PLA molecules, causing PLA to transition from brittle fracture to ductile fracture due to plastic deformation, thus acting as a plasticizer and making the film more flexible. Furthermore, poly(1,2-propanediol adipate) is composed of adipic acid (flexible aliphatic chain) and 1,2-propanediol (containing hydroxyl groups). Its molecular chain combines the flexibility of an aliphatic chain with the polarity of an ester group. This structure allows poly(1,2-propanediol adipate) to act as a "transition phase," reducing the interfacial tension between polylactic acid and polybutylene succinate, promoting the interpenetration of molecular chain segments, and improving the compatibility of polybutylene succinate and polylactic acid. This results in further improvements in the heat resistance, elongation at break, and tear strength of the obtained fully biodegradable plastic bag. The blending of polybutylene succinate, poly(1,2-propanediol adipate), and polylactic acid in this invention can prepare high-performance, low-cost, fully biodegradable plastic bags with promising application prospects, aligning with the concept of green development.

[0025] Co-grafted modified holocellulose was modified using methacryloyloxypropyltrimethoxysilane and polybutyl acrylate. Methacryloxypropyltrimethoxysilane was used to modify the holocellulose, introducing terminal olefins onto the surface. Subsequently, polybutyl acrylate polymerized with the double bonds introduced by the coupling agent, grafting polybutyl acrylate onto the holocellulose surface to form a bilayer. This bilayer replaces and covers the hydroxyl groups on the surface of the modified holocellulose, reducing its hydrophilicity and improving its thermal stability. The coupling agent / polybutyl acrylate bilayer on the surface of the modified holocellulose exhibits better modification effects than a single coupling agent or polybutyl acrylate, resulting in better interfacial interactions between the modified holocellulose and the polylactic acid (PLA) matrix, improved compatibility, and enhanced dispersibility of the modified holocellulose in the PLA matrix, as well as improved crystallinity, thermal properties, and mechanical properties of the composite material. Homocellulose itself can be degraded by microorganisms, matching the degradation rate of polybutylene succinate, poly(1,2-propanediol adipate) and polylactic acid, thus avoiding residues. Homocellulose is derived from corn cobs, straw, etc., reducing dependence on petroleum-based fillers and lowering production costs. Detailed Implementation

[0026] 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.

[0027] Example 1: The preparation method of modified holocellulose includes the following steps:

[0028] A 1000 mL (v / v) solution of 10% methacryloyloxypropyltrimethoxysilane in ethanol was adjusted to pH 3 with hydrochloric acid and pre-hydrolyzed at room temperature with stirring for 1.5 h. 10 g of holocellulose was added to the hydrolysate, the temperature was raised to 60 °C, and the reaction was continued for 4 h. After the reaction was complete, the mixture was filtered and dried at 60 °C, then calcined at 110 °C for 2 h. The resulting product was then transferred to a Soxhlet extractor and extracted with acetone for 2 h to remove unreacted coupling agent, yielding coupling agent-modified holocellulose.

[0029] 10g of the above-mentioned coupling agent-modified holocellulose, 100mL of water, 100mL of N,N-dimethylformamide, 0.125g of potassium persulfate and 8.5mL of n-butyl acrylate were added to a three-necked flask. Nitrogen gas was purged for 30min to remove oxygen from the reaction system. The temperature was then raised to 65℃ and the reaction was continued for 2h. After the reaction was completed, the reaction solution was filtered and transferred to a Soxhlet extractor for extraction with acetone to remove the polybutyl acrylate homopolymer. The solution was dried at 60℃ to obtain modified holocellulose.

[0030] Example 2: The preparation method of modified holocellulose includes the following steps:

[0031] A 1000 mL solution of 12% (v / v) methacryloyloxypropyltrimethoxysilane in ethanol was adjusted to pH 3 with hydrochloric acid and pre-hydrolyzed at room temperature with stirring for 2 h. 10 g of holocellulose was added to the hydrolysate, the temperature was raised to 60 °C, and the reaction was continued for 5 h. After the reaction was complete, the mixture was filtered and dried at 60 °C, then calcined at 110 °C for 2 h. The resulting product was then transferred to a Soxhlet extractor and extracted with acetone for 2 h to remove unreacted coupling agent, yielding coupling agent-modified holocellulose.

[0032] 10g of the above-mentioned coupling agent-modified holocellulose, 100mL of water, 120mL of N,N-dimethylformamide, 0.14g of potassium persulfate and 9mL of n-butyl acrylate were added to a three-necked flask. Nitrogen gas was purged for 30min to remove oxygen from the reaction system. The temperature was then raised to 65℃ and the reaction was continued for 2h. After the reaction was completed, the reaction solution was filtered and transferred to a Soxhlet extractor for extraction with acetone to remove the polybutyl acrylate homopolymer. The solution was then dried at 60℃ to obtain the modified holocellulose.

[0033] Example 3: A method for preparing a fully biodegradable plastic bag, comprising the following steps:

[0034] 35 parts by weight of polylactic acid 2003D, 25 parts by weight of poly(1,2-propanediol adipate), 15 parts by weight of polybutylene succinate AZ91TN, 20 parts by weight of the modified holocellulose prepared in Example 1, 3 parts by weight of the plasticizer epoxidized soybean oil, and 2 parts by weight of the compatibilizer maleic anhydride-grafted polylactic acid were added to a high-speed mixer and linearly mixed at 50°C for 15 minutes to obtain a premix.

[0035] The above premixed material was added to a twin-screw extruder, and the temperature gradient was set as follows: polylactic acid section 170℃, poly(1,2-propanediol adipate) section 150℃, poly(butylene succinate) section 140℃, screw speed 200 rpm, melt granulation was performed to obtain masterbatch.

[0036] The above masterbatch was added to a single-screw blown film machine, with the die temperature set at 165℃, the blow-up ratio at 2.5:1, and the traction speed at 12m / min. After being cut by a bag-making machine, a fully biodegradable plastic bag with a thickness of 30μm was obtained.

[0037] Example 4 A method for preparing a fully biodegradable plastic bag, comprising the following steps:

[0038] 35 parts by weight of polylactic acid 2003D, 25 parts by weight of poly(1,2-propanediol adipate), 15 parts by weight of polybutylene succinate AZ91TN, 20 parts by weight of the modified holocellulose prepared in Example 2, 3 parts by weight of the plasticizer epoxidized soybean oil, and 2 parts by weight of the compatibilizer maleic anhydride-grafted polylactic acid were added to a high-speed mixer and linearly mixed at 50°C for 15 minutes to obtain a premix.

[0039] The above premixed material was added to a twin-screw extruder, and the temperature gradient was set as follows: polylactic acid section 170℃, poly(1,2-propanediol adipate) section 150℃, poly(butylene succinate) section 140℃, screw speed 200 rpm, melt granulation was performed to obtain masterbatch.

[0040] The above masterbatch was added to a single-screw blown film machine, with the die temperature set at 165℃, the blow-up ratio at 2.5:1, and the traction speed at 12m / min. After being cut by a bag-making machine, a fully biodegradable plastic bag with a thickness of 30μm was obtained.

[0041] Example 5: A method for preparing a fully biodegradable plastic bag, comprising the following steps:

[0042] 30 parts by weight of polylactic acid 2003D, 25 parts by weight of poly(1,2-propanediol adipate), 15 parts by weight of polybutylene succinate AZ91TN, 25 parts by weight of the modified holocellulose prepared in Example 1, 3 parts by weight of the plasticizer epoxidized soybean oil, and 2 parts by weight of the compatibilizer maleic anhydride-grafted polylactic acid were added to a high-speed mixer and linearly mixed at 50°C for 15 minutes to obtain a premix.

[0043] The above premixed material was added to a twin-screw extruder, and the temperature gradient was set as follows: polylactic acid section 170℃, poly(1,2-propanediol adipate) section 150℃, poly(butylene succinate) section 140℃, screw speed 200 rpm, melt granulation was performed to obtain masterbatch.

[0044] The above masterbatch was added to a single-screw blown film machine, with the die temperature set at 165℃, the blow-up ratio at 2.5:1, and the traction speed at 12m / min. After being cut by a bag-making machine, a fully biodegradable plastic bag with a thickness of 30μm was obtained.

[0045] Example 6 A method for preparing a fully biodegradable plastic bag, comprising the following steps:

[0046] 30 parts by weight of polylactic acid 2003D, 25 parts by weight of poly(1,2-propanediol adipate), 15 parts by weight of polybutylene succinate AZ91TN, 25 parts by weight of the modified holocellulose prepared in Example 2, 3 parts by weight of the plasticizer epoxidized soybean oil, and 2 parts by weight of the compatibilizer maleic anhydride-grafted polylactic acid were added to a high-speed mixer and linearly mixed at 50°C for 15 minutes to obtain a premix.

[0047] The above premixed material was added to a twin-screw extruder, and the temperature gradient was set as follows: polylactic acid section 170℃, poly(1,2-propanediol adipate) section 150℃, poly(butylene succinate) section 140℃, screw speed 200 rpm, melt granulation was performed to obtain masterbatch.

[0048] The above masterbatch was added to a single-screw blown film machine, with the die temperature set at 165℃, the blow-up ratio at 2.5:1, and the traction speed at 12m / min. After being cut by a bag-making machine, a fully biodegradable plastic bag with a thickness of 30μm was obtained.

[0049] Comparative Example 1: The preparation method of polybutyl acrylate modified holocellulose includes the following steps:

[0050] 10g holocellulose, 100mL water, 120mL N,N-dimethylformamide, 0.125g potassium persulfate and 8.5mL n-butyl acrylate were added to a three-necked flask. Nitrogen gas was purged for 30min to remove oxygen from the reaction system. The temperature was then raised to 65℃ and the reaction was continued for 2h. After the reaction was completed, the reaction solution was filtered and transferred to a Soxhlet extractor for extraction with acetone to remove the polybutyl acrylate homopolymer. The solution was dried at 60℃ to obtain polybutyl acrylate modified holocellulose.

[0051] Compared with Example 3, Comparative Example 2 only replaced the modified holocellulose prepared in Example 1 with the coupling agent modified holocellulose prepared in Example 1. The other components and preparation methods were completely the same as those in Example 3.

[0052] Compared with Example 3, Comparative Example 2 only replaced the modified holocellulose prepared in Example 1 with the polybutyl acrylate modified holocellulose prepared in Comparative Example 1 in the same mass as that in Example 3. The other components and preparation methods were completely the same as those in Example 3.

[0053] Compared with Example 3, Comparative Example 4 only replaced the poly(1,2-propanediol adipate) added in Example 3 with the plasticizer epoxidized soybean oil. The remaining components and preparation methods were completely the same as those in Example 3.

[0054] Compared with Example 3, Comparative Example 4 only replaced the polybutylene succinate added in Example 3 with polylactic acid, while the other components and preparation methods were completely the same as in Example 3.

[0055] Performance testing

[0056] Mechanical properties: The fully biodegradable plastic bags obtained in Examples 3-6 and Comparative Example 2- were cut into dumbbell shapes with dimensions of 20mm × 4mm × 0.025mm. Tensile strength was tested according to ASTM D882-2010 at a rate of 50mm / min; the right-angle tear test of the film was conducted according to QB / T 1130-1991 at a speed of 200mm / min; the test results are shown in Table 1.

[0057] Heat distortion temperature test: According to GB / T 1633—2000 standard, the heat distortion temperature of the fully biodegradable plastic bags obtained in Examples 3-6 and Comparative Examples 2-5 was measured using a heat distortion and Vicat softening point temperature analyzer. The test sample size was 10.0 mm × 10.0 mm × 4.0 mm. The heat transfer medium was silicone oil, the heating rate was set to 120 °C / h, the applied load was 10 N, and the maximum deformation of the sample was 1 mm. The test results are shown in Table 1.

[0058] Compost degradation test: The compost soil was stirred evenly, spread evenly on a tray and placed in a 55℃ forced-air drying oven until constant weight. 300g of 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 1cm×1cm. 50g of film was weighed. The compost degradation experiment was carried out in a biodegradable tester, and the degradation rate was tested after 6 months. The test results are shown in Table 1.

[0059] Table 1: Statistical Table of Performance Test Data for Plastic Bags in Examples 3-6 and Comparative Examples 2-5

[0060]

[0061] As shown in Table 1, the fully biodegradable plastic bags prepared in Examples 3-6 have good mechanical properties, heat resistance and full biodegradability. In Comparative Example 1, holocellulose was modified only with a coupling agent, and in Comparative Example 2, holocellulose was modified only with polybutyl acrylate. The mechanical properties and initial thermal decomposition temperature of the resulting fully biodegradable plastic bags both decreased, indicating that the coupling agent and polybutyl acrylate jointly modified holocellulose and effectively improved the compatibility of the components of the composite material, thus enhancing its performance. In Comparative Example 3, when poly(1,2-propanediol adipate) was replaced with the plasticizer epoxidized soybean oil, the tensile strength and elastic modulus of the resulting fully biodegradable plastic bags decreased significantly. In Comparative Example 4, when polybutylene succinate was not added, the fracture growth rate and tear strength of the resulting fully biodegradable plastic bags decreased significantly, indicating that poly(1,2-propanediol adipate) acts as a plasticizer while also promoting the compatibility of polylactic acid and polybutylene succinate, and that polybutylene succinate has a good toughening effect on polylactic acid.

[0062] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A fully biodegradable plastic bag, characterized in that, It shall include at least the following parts by weight of raw materials: 30-40 parts of polylactic acid, 20-30 parts of 1,2-propanediol adipate, 10-20 parts of polybutylene succinate, 15-25 parts of modified holocellulose, 2-5 parts of plasticizer, and 1-3 parts of maleic anhydride graft compatibilizer. The method for preparing the modified holocellulose includes the following steps: The pH of the ethanol solution of methacryloyloxypropyltrimethoxysilane was adjusted to 3-4, and the solution was stirred to obtain a hydrolysate. Homocellulose was then added, and after the reaction, coupling agent modified homocellulose was obtained. The coupling agent-modified holocellulose, water, N,N-dimethylformamide, potassium persulfate, and n-butyl acrylate were mixed and reacted under nitrogen protection to obtain modified holocellulose.

2. The fully biodegradable plastic bag according to claim 1, characterized in that, The mass ratio of the methacryloyloxypropyltrimethoxysilane to the holocellulose is 10-13:

1.

3. The fully biodegradable plastic bag according to claim 1, 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.

4. A fully biodegradable plastic bag according to claim 1, characterized in that, The holocellulose is extracted from lignocellulose, which includes at least one of corn cob, rice straw, wheat straw, rapeseed straw, corn straw, bamboo shavings, sawdust, rice husk, or sugarcane bagasse.

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

6. A fully biodegradable plastic bag according to claim 1, characterized in that, Maleic anhydride graft compatibilizer is one or a mixture of maleic anhydride-grafted poly(1,2-propanediol adipate), maleic anhydride-grafted polylactic acid, or maleic anhydride-grafted polybutylene succinate.

7. A method for preparing a fully biodegradable plastic bag as described in any one of claims 1-6, characterized in that, It includes at least the following preparation steps: Polylactic acid, poly(1,2-propanediol adipate), polybutylene succinate, modified holocellulose, plasticizer and maleic anhydride graft compatibilizer are added to a high-speed mixer to obtain a premix. The premixed material is added to a twin-screw extruder and melt-granulated to obtain masterbatch; The masterbatch is added to a single-screw blown film machine and cut by a bag-making machine to obtain a fully biodegradable plastic bag.

8. The method for preparing a fully biodegradable plastic bag according to claim 7, characterized in that, The thickness of the fully biodegradable plastic bag is 20-50 μm.

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