Biodegradable plastic bag and preparation method thereof

Abstract

The invention relates to the field of plastic bags, and discloses a biodegradable plastic bag and a preparation method thereof, the biodegradable plastic bag comprises polylactic acid, poly (butylene adipate-co-terephthalate), a functional additive, modified starch, a lubricant and an antioxidant; the functional additive is prepared by grafting hydroxylated modified castor oil and isocyanated montmorillonite loaded titanium dioxide; the hydroxylation modified castor oil is prepared by modifying castor oil with chloroethyl isocyanate, then reacting with N-allylimidazole, and then reacting with 6-mercaptohexyl-1-alcohol; the isocyanated montmorillonite loaded titanium dioxide is prepared by reacting montmorillonite loaded titanium dioxide obtained by a sol-gel method with isophorone diisocyanate; the modified starch is prepared by reacting octadecanoyl chloride and acryloyl chloride with starch, then carrying out graft copolymerization with ethyl acrylate and further introducing glycidyl methacrylate, so that the plastic bag is endowed with excellent mechanical properties, biodegradability and antibacterial property.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic bags, and particularly relates to a biodegradable plastic bag and a preparation method thereof. Background Art

[0002] As we all know, plastic products are inexpensive, lightweight, durable, and highly malleable, making them popular in industries such as construction, transportation, packaging, and agricultural production. Disposable plastic bags are the most widely used. With increasing concern about environmental issues, the disposal of discarded plastic bags is gaining increasing attention. Conventional disposal of discarded plastic bags is landfill, but this poses the problem of long-term non-degradability. Consequently, biodegradable plastic bags have attracted considerable attention due to their biodegradability, non-toxicity, and high recyclability.

[0003] Polylactic acid has good film-forming stability, biocompatibility and biodegradability, and is considered to be one of the environmentally friendly polymer matrices in sustainable development. However, due to the lack of antibacterial activity and brittleness of polylactic acid, its application range is limited. The existing technology adds small molecule antibacterial components, but they easily migrate from the matrix to the surface and then come into contact with the packaging contents. Excessive migration will also cause the antibacterial performance of the matrix to decrease, making it difficult to achieve long-term antibacterial properties. In addition, the existing technology mixes starch into the matrix to reduce costs, but the higher the starch content, the worse the mechanical properties of the degradable plastic bag, which limits the application of plastic bag products. Summary of the Invention

[0004] In order to address the deficiencies mentioned in the above background technology, the purpose of the present invention is to provide a biodegradable plastic bag and a preparation method thereof, wherein functional additives and modified starch are added to a polylactic acid / polybutylene terephthalate-adipate based composite material to give the plastic bag excellent mechanical properties, biodegradability and antibacterial properties.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A biodegradable plastic bag comprises the following components in parts by weight: 60-80 parts of polylactic acid, 40-50 parts of polybutylene terephthalate-adipate, 10-20 parts of a functional additive, 5-15 parts of modified starch, 1-3 parts of a lubricant, and 0.1-0.5 parts of an antioxidant; The functional additive is prepared by grafting hydroxylated modified castor oil with isocyanate-modified montmorillonite-loaded titanium dioxide through a chemical reaction; wherein the hydroxylated modified castor oil is prepared by reacting chloroethyl carbamate castor oil ester obtained by modifying castor oil with chloroethyl isocyanate with N-allylimidazole to prepare modified castor oil, and then the modified castor oil is reacted with 6-mercaptohexan-1-ol to undergo a thiol-ene click reaction to prepare the functional additive; and the isocyanate-modified montmorillonite-loaded titanium dioxide is prepared by reacting montmorillonite-loaded titanium dioxide prepared by a sol-gel method with isophorone diisocyanate to undergo a nucleophilic addition reaction; The modified starch is prepared by esterifying starch by esterifying octadecanoyl chloride and acryloyl chloride with starch, then grafting ethyl acrylate and the esterified starch by soap-free emulsion polymerization, and then further introducing glycidyl methacrylate to prepare the modified starch.

[0006] Preferably, the lubricant is one of stearyl stearate or paraffin.

[0007] Preferably, the antioxidant is one or more combinations of antioxidant 1010, antioxidant 1076, and antioxidant 168.

[0008] Preferably, the preparation method of the functional additive comprises the following steps: (1) Tetrabutyl titanate and anhydrous ethanol are placed in a reactor, montmorillonite and deionized water are added and stirred evenly, and then a mixed solution of acetic acid and deionized water is added, and the mixture is stirred evenly and then allowed to stand for aging. After drying, the mixture is calcined at 550-600°C for 4-6 hours to prepare montmorillonite-loaded titanium dioxide; (2) Montmorillonite-loaded titanium dioxide was ultrasonically dispersed in toluene, and then isophorone diisocyanate and dibutyltin dilaurate were added, and the mixture was stirred at 55-70°C for 4-6 hours. After the reaction was completed, the mixture was filtered, washed, and dried to prepare isocyanate-loaded montmorillonite-loaded titanium dioxide; (3) Castor oil and chloroethyl isocyanate were placed in a reactor, dichloromethane was added to dissolve, and the mixture was reacted at 80-90°C for 68-72 hours. After the reaction was completed, the unreacted product was removed by distillation to prepare chloroethyl castor oil carbamate; (4) Chloroethylcarbamate castor oil ester and N-allylimidazole were placed in a reactor, acetonitrile was added to dissolve, and the mixture was placed at 80-90°C for 30-36 hours under nitrogen protection. After the reaction was completed, the mixture was washed, dried, and rotary evaporated to obtain modified castor oil; (5) Modified castor oil and 6-mercaptohexan-1-ol were placed in a reactor, stirred and mixed evenly, benzoin dimethyl ether photoinitiator was added, and then cured under ultraviolet irradiation for 15-20 minutes, and then heated at 100-110°C for 5-15 minutes to prepare hydroxylated modified castor oil; (6) Isocyanate-treated montmorillonite loaded with titanium dioxide, hydroxylated modified castor oil and toluene were placed in a reactor, and then a mixed solution of dibutyltin dilaurate and toluene was added. The mixture was stirred at 55-70 °C for 10-12 h. After the reaction was completed, the functional additive was prepared by rotary evaporation, washing and drying.

[0009] Preferably, the molar ratio of castor oil to chloroethyl isocyanate in step (3) is 1:3.5-3.8.

[0010] Preferably, in step (4), the molar ratio of castor oil chloroethylcarbamate to N-allylimidazole is 1:4-4.2.

[0011] Preferably, the preparation method of the modified starch comprises the following steps: A. Disperse dry starch in ethyl acetate, add pyridine catalyst, stir at 40-50°C for 0.5-1h, then add octadecanoyl chloride and acryloyl chloride and stir for 2-3h. After the reaction is complete, filter under reduced pressure, wash, and dry to prepare esterified starch; B. Take esterified starch and deionized water in a reactor, place it at 85~90℃ and stir to gelatinize, then cool it to 75~80℃, add ethyl acrylate and stir thoroughly, then add potassium persulfate aqueous solution dropwise, react for 10~12h, cool it to 62~67℃, add glycidyl methacrylate and potassium persulfate aqueous solution, heat it to 78~82℃ and continue to react for 2.5~3h. After the reaction is completed, demulsify to prepare modified starch.

[0012] Preferably, the starch is one of corn starch, potato starch and tapioca starch.

[0013] A method for preparing a biodegradable plastic bag comprises the following steps: weighing raw materials in parts by weight, mixing polylactic acid, polybutylene terephthalate-adipate, functional additives, modified starch, a lubricant and an antioxidant, and performing melt granulation, film blowing and bag making through a twin-screw extruder to prepare the biodegradable plastic bag.

[0014] Preferably, the twin-screw extrusion temperature is 135-170°C.

[0015] Beneficial effects of the present invention: The present invention uses a sol-gel method to prepare montmorillonite-loaded titanium dioxide, then uses the highly active isocyanate groups in isophorone diisocyanate to react with the hydroxyl groups on the surface of the montmorillonite-loaded titanium dioxide to prepare isocyanate-loaded montmorillonite-loaded titanium dioxide. At the same time, the present invention uses chloroethyl isocyanate to modify the hydroxyl groups on the castor oil molecular chain to obtain chloroethyl carbamate castor oil ester, which is then reacted with N-allylimidazole to introduce imidazole cationic groups on the castor oil molecular chain to prepare modified castor oil with antibacterial properties, and further reacts the double bonds introduced in the modified castor oil with the thiol groups in 6-mercaptohexan-1-ol to react with the thiol groups. The hydroxylated modified castor oil is prepared by a click reaction of olefins, and then the hydroxylated modified castor oil is grafted with isocyanate montmorillonite-loaded titanium dioxide by a chemical reaction, thereby fixing the modified castor oil on the surface of the montmorillonite-loaded titanium dioxide through a strong chemical bond, thereby obtaining long-lasting antibacterial activity. Nano-titanium dioxide can be used as an inorganic antibacterial agent, so that the prepared functional additive can have the advantages of both inorganic and organic antibacterial materials, exerting complementary and synergistic antibacterial effects. The grafting reaction is beneficial to increasing the interlayer spacing of the montmorillonite-loaded titanium dioxide, promoting the relatively uniform dispersion of the montmorillonite-loaded titanium dioxide in the matrix material, thereby better exerting the mechanical properties.

[0016] The present invention utilizes octadecanoyl chloride and acryloyl chloride to introduce long alkyl chains and carbon-carbon double bonds into starch macromolecular chains to prepare esterified starch. Ethyl acrylate is then graft-copolymerized with the esterified starch using soap-free emulsion polymerization to prepare core-shell particles with starch as the core. Glycidyl methacrylate is then added for further epoxidation modification to prepare modified starch. The core-shell structure of the modified starch improves the mechanical properties of the material to a certain extent. Furthermore, the epoxy groups introduced into the modified starch improve the compatibility of the modified starch with polylactic acid and polybutylene terephthalate-adipate, while also increasing interfacial interactions, further enhancing the mechanical properties of the material. The present invention adds functional additives and modified starch to a polylactic acid / polybutylene terephthalate-adipate-based composite material to impart excellent mechanical properties, biodegradability, and antibacterial properties to the plastic bag. DETAILED DESCRIPTION

[0017] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0018] Example 1 A method for preparing a functional additive comprises the following steps: (1) Take 7 mL of tetrabutyl titanate and 7 mL of anhydrous ethanol in a reactor, add 5 g of montmorillonite and 40 mL of deionized water and stir to mix evenly, then add a mixed solution of 5 mL of acetic acid and 5 mL of deionized water, continue to stir evenly and let it stand for 24 hours, dry and calcine at 600 ° C for 5 hours to prepare montmorillonite-loaded titanium dioxide; (2) 5 g of montmorillonite-loaded titanium dioxide was ultrasonically dispersed in 100 mL of toluene, and then 2.7 g of isophorone diisocyanate and 0.62 g of dibutyltin dilaurate were added. The mixture was stirred at 65 °C for 6 h. After the reaction was completed, the mixture was filtered, washed, and dried to prepare isocyanate-loaded montmorillonite-loaded titanium dioxide. (3) 18.6 g of castor oil and 7.6 g of chloroethyl isocyanate were placed in a reactor, 50 mL of dichloromethane was added to dissolve the mixture, and the mixture was reacted at 85 °C for 72 h. After the reaction was completed, the unreacted product was removed by distillation to prepare chloroethyl castor oil carbamate; (4) 12.5 g of chloroethylcarbamate castor oil ester and 4.3 g of N-allylimidazole were placed in a reactor, 20 mL of acetonitrile was added to dissolve the mixture, and the mixture was placed at 85 °C for 36 h under nitrogen protection. After the reaction was completed, the mixture was washed, dried, and rotary evaporated to obtain modified castor oil; (5) 10.5 g of modified castor oil and 2.2 g of 6-mercaptohexan-1-ol were placed in a reactor, stirred and mixed evenly, 0.04 g of benzoin dimethyl ether photoinitiator was added, and then cured under ultraviolet irradiation for 20 min, and then heated at 110 ° C for 10 min to prepare hydroxylated modified castor oil; (6) 5 g of isocyanate-modified montmorillonite loaded with titanium dioxide, 3 g of hydroxylated modified castor oil and 50 mL of toluene were placed in a reactor, and then a mixed solution of 0.62 g of dibutyltin dilaurate and 10 mL of toluene was added. The mixture was stirred at 65 °C for 12 h. After the reaction was completed, the functional additive was prepared by rotary evaporation, washing and drying.

[0019] Example 2 A method for preparing modified starch comprises the following steps: A. Disperse 90 g of dry corn starch in 270 mL of ethyl acetate, add 4.5 g of pyridine catalyst, and stir at 50° C. for 0.5 h. Then, add 5.4 g of octadecanoyl chloride and 5.4 g of acryloyl chloride, and stir for 2 h. After the reaction is complete, filter under reduced pressure, wash, and dry to prepare esterified starch. B. Take 12g of esterified starch and 50mL of deionized water in a reactor, place it at 90℃ and stir for gelatinization, then cool it to 80℃, add 24g of ethyl acrylate and stir it thoroughly, then add dropwise a mixed solution of 0.36g of potassium persulfate and 6mL of water, react for 12h, cool it to 65℃, add 20g of glycidyl methacrylate and 4mL of 0.08g / mL potassium persulfate aqueous solution, heat it to 80℃ and continue to react for 3h. After the reaction is completed, demulsify to prepare modified starch.

[0020] Example 3 A biodegradable plastic bag comprises the following components in parts by weight: 64 parts of polylactic acid, 42 parts of polybutylene terephthalate-adipate, 11 parts of the functional additive prepared in Example 1, 6 parts of the modified starch prepared in Example 2, 1 part of lubricant octadecyl stearate, and 0.1 part of antioxidant 1010.

[0021] The method for preparing the above-mentioned biodegradable plastic bag includes the following steps: weighing each raw material by weight, mixing polylactic acid, polybutylene terephthalate-adipate, functional additives, modified starch, lubricant and antioxidant, and melt granulating, blowing film and making bags through a twin-screw extruder at a temperature of 165°C to prepare a biodegradable plastic bag.

[0022] Example 4 A biodegradable plastic bag comprises the following components in parts by weight: 70 parts of polylactic acid, 47 parts of polybutylene terephthalate-adipate, 14 parts of the functional additive prepared in Example 1, 8 parts of the modified starch prepared in Example 2, 1.5 parts of lubricant octadecyl stearate, and 0.3 parts of antioxidant 1010.

[0023] The preparation method of the above-mentioned biodegradable plastic bag is the same as that of Example 3.

[0024] Example 5 A biodegradable plastic bag comprises the following components in parts by weight: 77 parts of polylactic acid, 48 parts of polybutylene terephthalate-adipate, 17 parts of the functional additive prepared in Example 1, 12 parts of the modified starch prepared in Example 2, 2.5 parts of lubricant octadecyl stearate, and 0.4 parts of antioxidant 1010.

[0025] The preparation method of the above-mentioned biodegradable plastic bag is the same as that of Example 3.

[0026] Comparative Example 1 A biodegradable plastic bag comprises the following components in parts by weight: 77 parts of polylactic acid, 48 parts of polybutylene terephthalate-adipate, 10 parts of montmorillonite-loaded titanium dioxide prepared in Example 1, 7 parts of castor oil, 12 parts of modified starch prepared in Example 2, 2.5 parts of lubricant octadecyl stearate, and 0.4 parts of antioxidant 1010.

[0027] The preparation method of the above-mentioned biodegradable plastic bag is the same as that of Example 3.

[0028] Comparative Example 2 A biodegradable plastic bag comprises the following components in parts by weight: 77 parts of polylactic acid, 48 parts of polybutylene terephthalate-adipate, 10 parts of montmorillonite, 7 parts of castor oil, 12 parts of the modified starch prepared in Example 2, 2.5 parts of lubricant octadecyl stearate, and 0.4 parts of antioxidant 1010.

[0029] The preparation method of the above-mentioned biodegradable plastic bag is the same as that of Example 3.

[0030] Comparative Example 3 A biodegradable plastic bag comprises the following components in parts by weight: 77 parts of polylactic acid, 48 parts of polybutylene terephthalate-adipate, 17 parts of the functional additive prepared in Example 1, 12 parts of corn starch, 2.5 parts of lubricant octadecyl stearate, and 0.4 parts of antioxidant 1010.

[0031] The preparation method of the above-mentioned biodegradable plastic bag is the same as that of Example 3.

[0032] Performance testing The plastic bags prepared in Examples 3-5 and Comparative Examples 1-3 were subjected to performance tests: a tensile test was performed on a universal material testing machine in accordance with GB / T 1040.3-2006 at a tensile rate of 2 mm / min, and tensile strength and elongation at break were tested; antibacterial performance was tested in accordance with QB / T 2591-2003, with Staphylococcus aureus and Escherichia coli as the test bacteria; and the biodegradability of the samples after 60 days of landfill was tested in accordance with GB / T 20197-2006. The data results are shown in Table 1.

[0033] Table 1 Sample performance test results As can be seen from the data in Table 1, the plastic bags prepared in Examples 3-5 of the present invention have high tensile strength, are not easy to break, and have excellent antibacterial effects. In Comparative Example 1, montmorillonite loaded with titanium dioxide and castor oil were simply mixed, and in Comparative Example 2, montmorillonite and castor oil were simply mixed. The tensile strength, elongation at break, and antibacterial rate of Comparative Examples 1-2 were lower than those of Examples 3-5, indicating that the addition of functional additives can improve the mechanical properties and antibacterial effect of the material. The decrease in Comparative Example 2 was more significant than that of Comparative Example 1 because the loading of titanium dioxide further improved the mechanical properties and antibacterial effect of the material. In Comparative Example 3, the starch was not modified, and the tensile strength and elongation at break were lower than those of Examples 3-5, indicating that modifying the starch can further improve the mechanical properties of the material.

[0034] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0035] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A biodegradable plastic bag, characterized in that: The invention comprises the following components in parts by weight: 60-80 parts of polylactic acid, 40-50 parts of polybutylene terephthalate-adipate, 10-20 parts of functional additives, 5-15 parts of modified starch, 1-3 parts of lubricant, and 0.1-0.5 parts of antioxidant; The functional additive is prepared by grafting hydroxylated modified castor oil with isocyanate-modified montmorillonite-loaded titanium dioxide through a chemical reaction; wherein the hydroxylated modified castor oil is prepared by reacting chloroethyl carbamate castor oil ester obtained by modifying castor oil with chloroethyl isocyanate with N-allylimidazole to prepare modified castor oil, and then the modified castor oil is reacted with 6-mercaptohexan-1-ol to undergo a thiol-ene click reaction to prepare the functional additive; and the isocyanate-modified montmorillonite-loaded titanium dioxide is prepared by reacting montmorillonite-loaded titanium dioxide prepared by a sol-gel method with isophorone diisocyanate to undergo a nucleophilic addition reaction; The modified starch is prepared by esterifying starch by esterifying octadecanoyl chloride and acryloyl chloride with starch, then grafting ethyl acrylate and the esterified starch by soap-free emulsion polymerization, and then further introducing glycidyl methacrylate to prepare the modified starch.

2. The biodegradable plastic bag according to claim 1, characterized in that: The lubricant is one of stearyl stearate or paraffin.

3. The biodegradable plastic bag according to claim 1, characterized in that: The antioxidant is one or more combinations of antioxidant 1010, antioxidant 1076, and antioxidant 168.

4. The biodegradable plastic bag according to claim 1, characterized in that: The preparation method of the functional additive comprises the following steps: (1) Tetrabutyl titanate and anhydrous ethanol are placed in a reactor, montmorillonite and deionized water are added and stirred evenly, and then a mixed solution of acetic acid and deionized water is added, and the mixture is stirred evenly and then allowed to stand for aging. After drying, the mixture is calcined at 550-600°C for 4-6 hours to prepare montmorillonite-loaded titanium dioxide; (2) Montmorillonite-loaded titanium dioxide was ultrasonically dispersed in toluene, and then isophorone diisocyanate and dibutyltin dilaurate were added, and the mixture was stirred at 55-70°C for 4-6 hours. After the reaction was completed, the mixture was filtered, washed, and dried to prepare isocyanate-loaded montmorillonite-loaded titanium dioxide; (3) Castor oil and chloroethyl isocyanate were placed in a reactor, dichloromethane was added to dissolve, and the mixture was reacted at 80-90°C for 68-72 hours. After the reaction was completed, the unreacted product was removed by distillation to prepare chloroethyl castor oil carbamate; (4) Chloroethylcarbamate castor oil ester and N-allylimidazole were placed in a reactor, acetonitrile was added to dissolve, and the mixture was placed at 80-90°C for 30-36 hours under nitrogen protection. After the reaction was completed, the mixture was washed, dried, and rotary evaporated to obtain modified castor oil; (5) Modified castor oil and 6-mercaptohexan-1-ol were placed in a reactor, stirred and mixed evenly, benzoin dimethyl ether photoinitiator was added, and then cured under ultraviolet irradiation for 15-20 minutes, and then heated at 100-110°C for 5-15 minutes to prepare hydroxylated modified castor oil; (6) Isocyanate-treated montmorillonite loaded with titanium dioxide, hydroxylated modified castor oil and toluene were placed in a reactor, and then a mixed solution of dibutyltin dilaurate and toluene was added. The mixture was stirred at 55-70 °C for 10-12 h. After the reaction was completed, the functional additive was prepared by rotary evaporation, washing and drying.

5. The biodegradable plastic bag according to claim 4, characterized in that: The molar ratio of castor oil to chloroethyl isocyanate in step (3) is 1:3.5-3.

8.

6. The biodegradable plastic bag according to claim 4, characterized in that: In the step (4), the molar ratio of castor oil chloroethylcarbamate to N-allylimidazole is 1:4-4.

2.

7. The biodegradable plastic bag according to claim 1, characterized in that: The preparation method of the modified starch comprises the following steps: A. Disperse dry starch in ethyl acetate, add pyridine catalyst, stir at 40-50°C for 0.5-1h, then add octadecanoyl chloride and acryloyl chloride and stir for 2-3h. After the reaction is complete, filter under reduced pressure, wash, and dry to prepare esterified starch; B. Take esterified starch and deionized water in a reactor, place it at 85~90℃ and stir to gelatinize, then cool it to 75~80℃, add ethyl acrylate and stir thoroughly, then add potassium persulfate aqueous solution dropwise, react for 10~12h, cool it to 62~67℃, add glycidyl methacrylate and potassium persulfate aqueous solution, heat it to 78~82℃ and continue to react for 2.5~3h. After the reaction is completed, demulsify to prepare modified starch.

8. The biodegradable plastic bag according to claim 7, characterized in that: The starch is one of corn starch, potato starch and tapioca starch.

9. A method for preparing a biodegradable plastic bag according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: weighing raw materials according to weight, mixing polylactic acid, polybutylene terephthalate-adipate, functional additives, modified starch, lubricant and antioxidant, melting and granulating through a twin-screw extruder, blowing film and making bags to prepare biodegradable plastic bags.

10. The method for preparing a biodegradable plastic bag according to claim 9, characterized in that: The temperature of the twin-screw extrusion is 135-170°C.

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