A composition for a degradable cup lid, its preparation method, and a cup lid

Abstract

The present invention provides a composition for a degradable cup lid, a preparation method thereof, and a cup lid. The preparation method includes: feeding a lubricant, a compatibilizer, a toughening agent, a first polylactic acid, and a second polylactic acid into a twin-screw extruder to be mixed and stirred evenly; adding glass fiber and modified bamboo fiber to the twin-screw extruder according to the addition amount of the second polylactic acid, and mixing and stirring evenly again and co-extruding and granulating to obtain the composition for a degradable cup lid; wherein, the weight-average molecular weight of the first polylactic acid is 5,000 to 10,000, and the weight-average molecular weight of the second polylactic acid is 250,000 to 300,000; the modified bamboo fiber is surface-modified with calcium carbonate and loaded with an antibacterial agent. The modified bamboo fiber is surface-modified with calcium carbonate and loaded with an antibacterial agent. The composition for a degradable cup lid obtained by the preparation method of the present invention has good degradability, mechanical properties, and heat resistance, and can antibacterial and bacteriostatic.

Description

Technical Field

[0001] The present invention relates to the technical field of degradable polymer materials, and more particularly, to a composition for a degradable cup lid, a preparation method thereof, and a cup lid. Background Art

[0002] Polylactic acid (PLA, Poly lactic acid), also known as poly(lactide), is a new type of biodegradable material and belongs to thermoplastic aliphatic polyester polymers. The main raw material sources of polylactic acid are renewable plant resources such as corn, sugarcane, and cassava. These plants are rich in starch, which is ultimately converted into lactic acid through steps such as starch extraction, saccharification, and fermentation, and then polylactic acid is synthesized through chemical synthesis methods. Polylactic acid has good biocompatibility and biodegradability, and can be completely degraded by microorganisms in nature after use, ultimately generating carbon dioxide and water without polluting the environment. Due to the good transparency and processability of polylactic acid, it is widely used in fields such as food packaging, biodegradable plastic bags, and food containers.

[0003] In recent years, people's consumption demands for beverages such as milk tea and coffee have been increasing continuously, and the market demand for degradable disposable beverage containers has also been expanding continuously. Environmentally friendly polylactic acid is exactly the first choice material for manufacturing such products.

[0004] In order to further improve the degradability of polylactic acid materials, natural substances such as plant fibers and starch are generally added in the preparation process of polylactic acid materials in the prior art. In addition, since polylactic acid materials are brittle and have a low softening point and poor heat resistance, inorganic fillers such as talc powder, calcium carbonate, and montmorillonite are also added in the prior art to improve the mechanical strength and heat resistance of polylactic acid materials.

[0005] In particular, for products such as milk tea cup lids, the wall thickness of the products is small, and the fluidity requirements for the materials are relatively high. Moreover, under the condition of a thin wall thickness, the brittleness of the materials will increase significantly. At the same time, when containing food, disposable tableware is required to have a certain heat resistance. Existing polylactic acid biodegradable materials are difficult to simultaneously meet the usage requirements of rapid degradation, high strength, and heat resistance. Summary of the Invention

[0006] The problem solved by the present invention is how to provide a polylactic acid material with rapid degradation, high mechanical strength, and good heat resistance.

[0007] To solve at least one of the above problems, the present invention provides a preparation method of a composition for a degradable cup lid, and the preparation method includes:

[0008] S100. Feed a lubricant, a compatibilizer, a toughening agent, a first polylactic acid, and a second polylactic acid into a twin-screw extruder and mix them evenly according to a mass ratio of lubricant:compatibilizer:toughening agent:first polylactic acid:second polylactic acid = (1 - 2):(6 - 8):(6 - 8):(8 - 10):100;

[0009] S200. According to a mass ratio of glass fiber:modified bamboo fiber:second polylactic acid = (5 - 10):(15 - 20):100, and based on the addition amount of the second polylactic acid in S100, add glass fiber and modified bamboo fiber to the twin-screw extruder, mix them evenly again and co-extrude and pelletize to obtain a composition for a degradable cup lid;

[0010] Among them, the weight-average molecular weight of the first polylactic acid is 5,000 to 10,000, and the weight-average molecular weight of the second polylactic acid is 250,000 to 300,000; the modified bamboo fiber is surface-modified with calcium carbonate and loaded with an antibacterial agent. The modified bamboo fiber is surface-modified with calcium carbonate and loaded with an antibacterial agent.

[0011] In any of the above technical solutions, the lubricant includes at least one or a combination of fatty acid esters, fatty acid amides, and polyethylene waxes; and / or the compatibilizer includes at least one or a combination of maleic anhydride, methyl diphenyl diisocyanate, lysine triisocyanate, lysine diisocyanate, and glycidyl methacrylate; and / or the toughening agent includes at least one or a combination of polybutylene succinate, polybutylene adipate succinate, polycaprolactone, and polybutylene terephthalate adipate; and / or the glass fiber includes at least one or a combination of silicate glass fiber, aluminosilicate glass fiber, alkali metal aluminosilicate glass fiber, and alkaline earth metal aluminosilicate glass fiber.

[0012] In any of the above technical solutions, the extrusion and pelletizing temperature of the twin-screw extruder in S200 is: the first stage: 160°C to 170°C, the second stage: 180°C to 190°C, the third stage: 190°C to 200°C, the fourth stage: 160°C to 170°C, and the fifth stage: 140°C to 150°C.

[0013] In any of the above technical solutions, the antibacterial agent is an inorganic non-metallic oxide antibacterial agent.

[0014] In any of the above technical solutions, the preparation steps of the modified bamboo fiber include:

[0015] S110. Use a crusher to crush bamboo fiber into bamboo fiber powder with a target particle size;

[0016] S120. Immerse the bamboo fiber powder in hydrogen peroxide. After the immersion, drop an acetic acid aqueous solution with the same volume as the hydrogen peroxide and stir synchronously. After dropping, let it stand, filter, wash, and dry the bamboo fiber powder;

[0017] S130. Ultrasonically disperse the bamboo fiber powder obtained through S120 uniformly in an aqueous calcium chloride solution, and dropwise add an aqueous sodium hydroxide solution until the pH reaches 11 - 12 to obtain a first mixture;

[0018] S140. Let the first mixture stand for aging and then feed it into a closed reaction kettle. First, evacuate the reaction kettle, and then introduce a gas containing carbon dioxide into the reaction kettle. Stir the first mixture under pressure so that the first mixture reacts with carbon dioxide. After the reaction ends, stop introducing the gas, relieve the pressure, and extract the solid matter, filter, wash, and dry it to obtain modified bamboo fiber.

[0019] In any of the above technical solutions, the target particle size of the bamboo fiber powder in S110 is 400 mesh to 600 mesh; and / or the concentration of hydrogen peroxide in S120 is 20% to 25%; and / or the concentration of the aqueous acetic acid solution in S120 is 14% to 18%; and / or the soaking time in S120 is 2 h to 3 h, and the standing time is 20 min to 40 min; and / or the concentration of the aqueous calcium chloride solution in S130 is 10 wt% to 20 wt%; and / or the concentration of the aqueous sodium hydroxide solution in S130 is 8 wt% to 12 wt%; and / or the aging time in S140 is 12 h to 18 h; and / or the pressure condition in S140 is 4 MPa to 8 MPa; and / or the stirring rate in S140 is 600 r / min to 800 r / min, and the stirring time is 2 h to 5 h.

[0020] In any of the above technical solutions, after S140, the preparation steps of the modified bamboo fiber further include:

[0021] S150. Mix carboxymethyl cellulose and starch uniformly in water, and keep it in a water bath at 75°C to 80°C for heat preservation and stirring for 20 min to 40 min to obtain gelatinized starch;

[0022] S160. Mix maleic anhydride, ammonium persulfate, acrylic acid, and acrylamide to obtain a second mixture;

[0023] S170. Lower the temperature of the water bath to 50°C to 60°C, and add the second mixture to the water bath according to the amount of starch in S150, and continue heat preservation and stirring for 1 h to 2 h to obtain modified starch;

[0024] S180. Mix zinc chloride, the modified starch obtained in S170, and the modified bamboo fiber obtained in S140 in water, stir evenly, stand for 4 h to 6 h, dropwise add an 8 wt% to 12 wt% aqueous sodium hydroxide solution until the pH reaches 11 - 12, stand again for 4 h to 6 h, filter, wash, and dry to obtain bamboo fiber powder loaded with antibacterial agents.

[0025] In any of the above technical solutions, in S150, by mass ratio, carboxymethyl cellulose: starch: water = (2 - 4):(15 - 25):100; and / or in S160, by mass ratio, maleic anhydride: ammonium persulfate: acrylic acid: acrylamide = (0.2 - 0.4):(1 - 1.5):(30 - 40):100; and / or in S170, by mass ratio, the second mixture: starch = (10 - 20):100; and / or in S180, by mass ratio, zinc chloride: modified starch: modified bamboo fiber: water = (6 - 8):(10 - 20):(20 - 30):100.

[0026] The present invention also provides a composition for a degradable cup lid, and the composition for a degradable cup lid is obtained by using the preparation method of any of the above technical solutions.

[0027] The present invention also provides a cup lid, and the cup lid is manufactured by using the composition for a degradable cup lid obtained by the preparation method of any of the above technical solutions.

[0028] Beneficial effects

[0029] The present invention provides a preparation method of a composition for a degradable cup lid. The preparation method uses a lubricant, a compatibilizer, a toughening agent, a first polylactic acid, a second polylactic acid, glass fiber, and modified bamboo fiber as raw materials. First, the lubricant, the compatibilizer, the toughening agent, the first polylactic acid, and the second polylactic acid are fed into a twin-screw extruder for mixing and stirring. After the above raw materials are mixed evenly, glass fiber and modified bamboo fiber are added, and the mixing continues, and finally, granulation is carried out by extrusion to obtain the composition for a degradable cup lid. Among them, the difference between the first polylactic acid and the second polylactic acid is that the weight-average molecular weight of the first polylactic acid is 5,000 to 10,000, and the weight-average molecular weight of the second polylactic acid is 250,000 to 300,000. Since the present invention adds two polylactic acids with different weight-average molecular weights, the second polylactic acid with a large weight-average molecular weight is used as the main raw material, and the first polylactic acid with a small weight-average molecular weight is used as a flow promoter, so that when the composition for a degradable cup lid is used to prepare products with a small wall thickness, its melt flow rate can meet the processing requirements of thin-wall injection molding, ensuring the processing accuracy of the products. Glass fiber has good mechanical properties, excellent mechanical properties, good chemical stability, and good heat resistance. Therefore, the addition of glass fiber can improve the mechanical properties and heat resistance of the composition for a degradable cup lid, so that when it is used as a disposable beverage container for holding hot drinks, it is not easily deformed and damaged due to high temperature. Bamboo fiber, as a natural plant fiber, can further improve the degradability of the polylactic acid polymer material and improve its environmental friendliness. In summary, through the above technical solutions, the present invention can provide a composition for a degradable cup lid that can be rapidly degraded, has high mechanical strength, and good heat resistance. In addition, considering that bamboo fiber itself has poor mechanical strength and, as a natural plant fiber, has the disadvantages of being difficult to be compatible with polymers and difficult to be evenly dispersed in polymers, the bamboo fiber used in the present invention has been surface-modified with calcium carbonate. On the one hand, calcium carbonate can improve the mechanical strength of bamboo fiber, and on the other hand, it can also improve the compatibility between bamboo fiber and polymers. Finally, considering the antibacterial and mildew-proof requirements of the composition for a degradable cup lid, the present invention loads an antibacterial agent in the bamboo fiber to ensure that the composition for a degradable cup lid has good degradability, mechanical properties, and heat resistance, and can antibacterial and inhibit bacteria. Detailed Embodiments

[0030] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention is provided.

[0031] Unless otherwise specified, the reagents and raw materials used in the present invention can be purchased through commercial channels. The experimental methods without specific conditions mentioned in the following examples are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0032] Polylactic acid is a green renewable resource. It has good biodegradability and biocompatibility and is an ideal biodegradable polymer material. The present invention provides a composition for a degradable cup lid and a preparation method thereof. The purpose of the present invention is to provide a polylactic acid-based composition for a degradable cup lid that has both good degradability, mechanical properties, and heat resistance, and can antibacterial and inhibit bacteria. The preparation method of the composition for the degradable cup lid of the present invention is as follows:

[0033] S100. According to the mass ratio of lubricant: compatibilizer: toughening agent: first polylactic acid: second polylactic acid = (1 - 2):(6 - 8):(6 - 8):(8 - 10):100, feed the lubricant, compatibilizer, toughening agent, first polylactic acid, and second polylactic acid into a twin-screw extruder and mix and stir evenly;

[0034] S200. According to the mass ratio of glass fiber: modified bamboo fiber: second polylactic acid = (5 - 10):(15 - 20):100, and according to the addition amount of the second polylactic acid in S100, add glass fiber and modified bamboo fiber to the twin-screw extruder, mix and stir evenly again and co-extrude and granulate to obtain the composition for the degradable cup lid;

[0035] Among them, the weight-average molecular weight of the first polylactic acid is 250,000 to 300,000, and the weight-average molecular weight of the second polylactic acid is 5,000 to 10,000; the modified bamboo fiber is surface-modified with calcium carbonate and loaded with an antibacterial agent.

[0036] In the above steps, the functions of each component are as follows. The lubricant can significantly reduce the friction between polymer materials, making the materials flow more smoothly during processes such as mixing, extrusion, and injection molding, and reducing energy loss and equipment wear. In the specific embodiments of the present invention, the lubricant includes at least one or a combination of fatty acid esters, fatty acid amides, and polyethylene waxes. Preferably, the lubricant used in the present invention is butyl stearate. In a polymer blend system, the compatibilizer can effectively reduce the particle size of the dispersed phase, making the dispersed phase more uniformly distributed in the continuous phase, thereby improving the mechanical properties and processing properties of the material. In the specific embodiments of the present invention, the compatibilizer includes at least one or a combination of maleic anhydride, methyl diphenyl diisocyanate, lysine triisocyanate, lysine diisocyanate, and glycidyl methacrylate. Preferably, the compatibilizer used in the present invention is maleic anhydride. The toughening agent can reduce the brittleness of the polymer, improve its toughness, and improve the processing properties of the polymer. In the specific embodiments of the present invention, the toughening agent includes at least one or a combination of polybutylene succinate, polybutylene adipate succinate, polycaprolactone, and polybutylene terephthalate adipate. Preferably, the toughening agent used in the present invention is polybutylene succinate. Glass fiber has the characteristics of high strength and high modulus. Adding it to the polymer can significantly improve the mechanical properties such as tensile strength, flexural strength, and impact strength of the composite material. This makes the glass fiber-reinforced polymer composite more stable when subjected to external forces and less likely to break or deform. In the specific embodiments of the present invention, the glass fiber includes at least one or a combination of silicate glass fiber, aluminosilicate glass fiber, alkali metal aluminosilicate glass fiber, and alkaline earth metal aluminosilicate glass fiber. Preferably, the glass fiber used in the present invention is aluminosilicate glass fiber. Bamboo fiber itself is biodegradable. After combining with a biodegradable polymer, it can further promote the degradation performance of the composite material. During the degradation process, bamboo fiber will degrade first, providing channels and space for the degradation of the polymer, thereby accelerating the degradation process of the entire composite material.

[0037] The present invention uses a twin-screw extruder to prepare a composition for a degradable cup lid by extrusion granulation. The process of preparing a polylactic acid material by extrusion granulation belongs to the prior art. Those skilled in the art are capable of selecting and adjusting the equipment and process parameters used in extrusion granulation according to actual needs, and the present invention will not elaborate on it further. Preferably, the extrusion granulation temperature of the twin-screw extruder in S200 is: the first stage: 160°C to 170°C, the second stage: 180°C to 190°C, the third stage: 190°C to 200°C, the fourth stage: 160°C to 170°C, and the fifth stage: 140°C to 150°C.

[0038] Since the present invention adds two kinds of polylactic acid with different weight-average molecular weights, the second polylactic acid with a large weight-average molecular weight is used as the main raw material, and the first polylactic acid with a small weight-average molecular weight is used as a flow promoter, so that when the biodegradable cup lid composition is used to prepare products with a small wall thickness, its melt flow rate can meet the processing requirements of thin-wall injection molding, ensuring the processing accuracy of the products.

[0039] The modified bamboo fiber of the present invention is surface-modified with calcium carbonate, and its purpose is to improve the mechanical strength of the bamboo fiber. Specifically, although bamboo fiber, as a natural plant fiber, can improve the biodegradable performance of polylactic acid materials, its mechanical properties need to be further improved. Calcium carbonate, as an inorganic material, can improve the mechanical properties of bamboo fiber. In addition, existing technologies such as CN111516073A and CN106182298A have also reported that mixing calcium carbonate as a filler with plant fiber powder to fill the resin can prevent the crack propagation of the resin material and play a role in accelerating the dissipation of impact energy through interfacial plastic deformation, so as to achieve the purpose of enhancing the strength of the resin material.

[0040] Therefore, the present invention selects to use calcium carbonate to modify the bamboo fiber. The preparation steps of the modified bamboo fiber include:

[0041] S110. Using a crusher, crushing the bamboo fiber into bamboo fiber powder with a target particle size;

[0042] S120. Soaking the bamboo fiber powder in hydrogen peroxide, after the soaking is completed, dropping an acetic acid aqueous solution with the same volume as the hydrogen peroxide and stirring synchronously, standing still after dropping, filtering, washing, and drying the bamboo fiber powder;

[0043] S130. Ultrasonically dispersing the bamboo fiber powder obtained through S120 evenly in an aqueous calcium chloride solution, dropping an aqueous sodium hydroxide solution until the pH reaches 11 - 12 to obtain a first mixture;

[0044] S140. Standing and aging the first mixture, then feeding it into a closed reaction kettle, first evacuating the reaction kettle, then introducing a gas containing carbon dioxide into the reaction kettle, stirring the first mixture under pressure so that the first mixture reacts with carbon dioxide, stopping introducing the gas after the reaction is completed, releasing the pressure and extracting the solid matter, filtering, washing, and drying to obtain the modified bamboo fiber;

[0045] S150. Mixing carboxymethyl cellulose and starch evenly in water, and keeping it in a water bath at 75°C to 80°C for heat preservation and stirring for 20 min to 40 min to obtain gelatinized starch;

[0046] S160. Mixing maleic anhydride, ammonium persulfate, acrylic acid, and acrylamide to obtain a second mixture;

[0047] S170. Lower the temperature of the water bath to 50°C to 60°C. According to the amount of starch in S150, add the second mixture to the water bath, and continue to keep warm and stir for 1 h to 2 h to obtain modified starch;

[0048] S180. Mix zinc chloride, the modified starch obtained in S170, and the modified bamboo fiber obtained in S140 in water. After stirring evenly, let it stand for 4 h to 6 h. Dropwise add an 8wt% to 12wt% sodium hydroxide aqueous solution until the pH reaches 11 - 12, and let it stand again for 4 h to 6 h. Then filter, wash, and dry to obtain bamboo fiber powder loaded with antibacterial agents.

[0049] In some embodiments of the present invention, the target particle size of the bamboo fiber powder in S110 is 400 mesh to 600 mesh. Those skilled in the art can select and adjust the particle size of the bamboo fiber according to actual needs.

[0050] In some embodiments of the present invention, the concentration of hydrogen peroxide in S120 is 20% to 25%, the concentration of the acetic acid aqueous solution in S120 is 14% to 18%, the concentration of the calcium chloride aqueous solution in S130 is 10wt% to 20wt%, and the concentration of the sodium hydroxide aqueous solution in S130 is 8wt% to 12wt%.

[0051] Preferably, the concentration of hydrogen peroxide in S120 is 20%, the concentration of the acetic acid aqueous solution in S120 is 15%, the concentration of the calcium chloride aqueous solution in S130 is 12wt%, and the concentration of the sodium hydroxide aqueous solution in S130 is 10wt%.

[0052] In some embodiments of the present invention, the soaking time in S120 is 2 h to 3 h, the standing time is 20 min to 40 min, the aging time in S140 is 12 h to 18 h, the pressure condition in S140 is 4 MPa to 8 MPa, the stirring rate in S140 is 600 r / min to 800 r / min, and the stirring time is 2 h to 5 h.

[0053] Preferably, the soaking time in S120 is 2.5 h, the standing time is 30 min, the aging time in S140 is 15 h, the pressure condition in S140 is 6 MPa, the stirring rate in S140 is 600 r / min, and the stirring time is 3 h.

[0054] In some embodiments of the present invention, in S150, by mass ratio, carboxymethyl cellulose: starch: water = (2 - 4): (15 - 25): 100; in S160, by mass ratio, maleic anhydride: ammonium persulfate: acrylic acid: acrylamide = (0.2 - 0.4): (1 - 1.5): (30 - 40): 100; in S170, by mass ratio, the second mixture: starch = (10 - 20): 100; in S180, by mass ratio, zinc chloride: modified starch: modified bamboo fiber: water = (6 - 8): (10 - 20): (20 - 30): 100.

[0055] Preferably, in S150, by mass ratio, carboxymethyl cellulose: starch: water = 2: 20: 100; in S160, by mass ratio, maleic anhydride: ammonium persulfate: acrylic acid: acrylamide = 0.2: 1: 30: 100; in S170, by mass ratio, the second mixture: starch = 15: 100; in S180, by mass ratio, zinc chloride: modified starch: modified bamboo fiber: water = 6: 10: 30: 100.

[0056] One of the purposes of the above steps is to uniformly and abundantly load calcium carbonate on the bamboo fiber. Specifically, in the present invention, first through S110, the bamboo fiber is broken into powder, and then through S120, the bamboo fiber powder is washed and decontaminated. By soaking the bamboo fiber powder in hydrogen peroxide, the bamboo fiber can be separated and bleached, thereby ensuring that the whiteness and appearance of the bamboo fiber meet the processing requirements. Furthermore, by dropping an acetic acid aqueous solution into the hydrogen peroxide in which the bamboo fiber is immersed, acetic acid and hydrogen peroxide can react to generate active oxygen. Using the active oxygen, the bamboo fiber can be further cleaned to remove bacteria in the bamboo fiber, effectively avoiding mildew during use.

[0057] In S130, by ultrasonically dispersing the bamboo fiber powder uniformly in a calcium chloride aqueous solution and dropping a sodium hydroxide aqueous solution, calcium ions can generate calcium hydroxide under alkaline conditions. The cell structure of the bamboo fiber causes it to produce a capillary effect, enabling calcium ions in the calcium chloride aqueous solution to penetrate through plant cells, fully enter and occupy the cell structure of the bamboo fiber, and deposit on at least part of the interior and surface of the bamboo fiber powder. Under alkaline conditions, calcium ions combine with hydroxyl groups, and calcium hydroxide enters the cell gaps and the interior of the cell cavity of the bamboo fiber, uniformly and abundantly loading calcium hydroxide on at least part of the interior and surface of the bamboo fiber powder. Furthermore, through S140, the calcium hydroxide in the bamboo fiber powder can react with carbon dioxide under high-pressure conditions. Calcium hydroxide reacts with carbon dioxide to form calcium carbonate, and the calcium carbonate precipitate coats at least part of the interior and surface of the bamboo fiber powder, which can improve the mechanical properties of the bamboo fiber.

[0058] Furthermore, the present invention uses zinc oxide as an inorganic non-metallic oxide antibacterial agent and loads it on bamboo fibers in order to improve the antibacterial and bacteriostatic properties of the composition for degradable cup lids. The composition for degradable cup lids of the present invention is particularly suitable for use as cup lids for beverages such as coffee and milk tea. The consumer group of such beverages is constantly expanding. After purchasing beverages such as coffee and milk tea, some consumers will store the remaining unconsumed beverages in the refrigerator. Such beverages contain a lot of sugar and are prone to bacterial growth after being left standing for a long time (especially after being left standing in a complex environment such as a refrigerator where harmful bacteria may exist), which affects food safety. Therefore, the present invention uses an inorganic non-metallic oxide antibacterial agent to endow the composition for degradable cup lids with better antibacterial and bacteriostatic properties, making it more suitable for making cup lids for beverages such as coffee and milk tea.

[0059] Metal ions such as zinc ions, titanium ions, silver ions, and strontium ions all have good long-term antibacterial and bacteriostatic effects. The oxides of the above metal ions have stable properties, are safe and effective, and are antibacterial agents widely used in food packaging materials. The present invention selects zinc oxide as the antibacterial agent. When zinc oxide comes into contact with bacteria, zinc ions will be released. These zinc ions have redox properties and can bind to the bacterial cell membrane and membrane proteins and react with functional groups such as sulfhydryl, carboxyl, and hydroxyl groups in their structures, thereby destroying the structure of the bacteria. After entering the bacterial cell, zinc ions can also destroy the enzymes in the electron transport system and react with DNA to achieve the purpose of antibacterial.

[0060] The dispersion performance of nano-zinc bactericide in polymer materials is poor and it is prone to agglomeration, thus affecting its bactericidal efficiency. Therefore, in the present invention, zinc ions are uniformly loaded in starch and bamboo fiber. To achieve this purpose, the present invention first prepares a modified starch in a gel state capable of adsorbing metal ions, and then mixes the modified starch and zinc chloride with bamboo fiber, so that the zinc ions are adsorbed by the modified starch and mixed with the bamboo fiber. Specifically, in the present invention, through S150, the starch is gelatinized, so that the starch granules absorb water and expand and destroy their crystal structure, thereby breaking the original morphological structure of the starch granules, making its compatibility with bamboo fiber better. Moreover, the gelatinized starch is more easily decomposed by microorganisms, accelerating the degradation process of polylactic acid plastics. As monomers, acrylic acid and acrylamide can undergo a polymerization reaction at a suitable temperature (50°C to 60°C) under the action of an initiator ammonium persulfate and a cross-linking agent maleic anhydride to generate an acrylic acid copolymer. By mixing the gelatinized starch with maleic anhydride, ammonium persulfate, acrylic acid and acrylamide and reacting at a temperature condition of 50°C to 60°C, a starch modified by an acrylic acid copolymer can be obtained. There are a large number of hydroxyl groups and phosphate groups with obvious cationophilic characteristics in the starch molecule itself. The copolymerization reaction of acrylic acid and acrylamide generates an anionic acrylic acid copolymer, and it contains -COOH groups and -COONa groups. This enables the starch modified by the acrylic acid copolymer to perform electrostatic adsorption with metal cations and load a larger amount of metal ions. Therefore, the present invention prepares a starch modified by an acrylic acid copolymer, mixes it with zinc chloride and modified bamboo fiber, so that a large amount of metal zinc ions are uniformly adsorbed in the starch, and through the dropwise addition of an aqueous sodium hydroxide solution, zinc hydroxide is deposited and loaded in the starch and bamboo fiber to obtain bamboo fiber loaded with an antibacterial agent. Furthermore, in the process of blending and extruding the bamboo fiber with polylactic acid, the high temperature above 150°C oxidizes zinc hydroxide to zinc oxide, which is uniformly and stably dispersed in the bamboo fiber and starch, playing a long-term antibacterial and bacteriostatic role.

[0061] Example 1

[0062] In this example, a modified bamboo fiber sample was prepared, and its preparation process is as follows:

[0063] S1. Using a crusher, the bamboo fiber was crushed into bamboo fiber powder with a mesh size of 400 to 600 meshes;

[0064] S2. The bamboo fiber powder was soaked in hydrogen peroxide with a concentration of 20% for 2.5 h. After the soaking was completed, an acetic acid aqueous solution with a concentration of 15% equal in volume to the hydrogen peroxide was added dropwise and stirred synchronously. After the addition was completed, it was left standing for 30 min, the solid matter was filtered, washed 2 - 3 times with deionized water until odorless, and dried by infrared to obtain bamboo fiber sample 1.

[0065] Example 2

[0066] In this embodiment, the bamboo fiber sample obtained in Embodiment 1 was further processed, and the processing method is as follows:

[0067] S1. According to the mass ratio of bamboo fiber powder: calcium chloride aqueous solution = 20:100, the bamboo fiber powder obtained through Embodiment 1 was ultrasonically dispersed evenly in a calcium chloride aqueous solution with a concentration of 12 wt%, and then an aqueous sodium hydroxide solution with a concentration of 10 wt% was added dropwise until the pH reached 11 - 12 to obtain a first mixture.

[0068] S2. After the first mixture was allowed to stand and age for 15 h, it was fed into a closed reaction kettle. First, the reaction kettle was evacuated, and then a gas was introduced into the reaction kettle. The gas included a mixed gas of carbon dioxide and nitrogen with a volume ratio of 1:9. After the pressure of the mixed gas reached 6 MPa, the first mixture was stirred at a rate of 600 r / min so that the first mixture reacted with carbon dioxide. After maintaining the pressure for 3 h, the gas introduction was stopped, the pressure was released, and the solid was extracted, filtered, washed 2 - 3 times with deionized water, and dried by infrared to obtain bamboo fiber sample 2.

[0069] Embodiment 3

[0070] In this embodiment, the modified bamboo fiber sample obtained in Embodiment 2 was further processed, and the processing method is as follows:

[0071] S1. According to the mass ratio of carboxymethyl cellulose: starch: water = 2:20:100, carboxymethyl cellulose and starch were mixed evenly in water and placed in a water bath at 75 °C for heat preservation and stirring for 20 min to obtain gelatinized starch.

[0072] S2. According to the mass ratio of maleic anhydride: ammonium persulfate: acrylic acid: acrylamide = 0.2:1:30:100, maleic anhydride, ammonium persulfate, acrylic acid, and acrylamide were mixed to obtain a second mixture.

[0073] S3. The temperature of the water bath was lowered to 55 °C. According to the mass ratio of the second mixture: starch = 15:100, based on the amount of starch in S1, after the second mixture was mixed well, it was immediately added to the water bath and continued to be heated and stirred for 1.5 h. After the stirring was completed, the solid was extracted to obtain modified starch in a colloidal state.

[0074] S4. According to the mass ratio of zinc chloride: modified starch: modified bamboo fiber: water = 6:10:30:100, zinc chloride, the modified starch obtained in S3, and the bamboo fiber of Embodiment 2 were mixed in water, stirred evenly, allowed to stand for 6 h, an aqueous sodium hydroxide solution with a concentration of 10 wt% was added dropwise until the pH reached 11 - 12, allowed to stand again for 4 h, filtered, washed 2 - 3 times with deionized water, and dried by infrared to obtain bamboo fiber sample 3.

[0075] Embodiment 4

[0076] In this example, the modified bamboo fiber sample obtained in Example 2 was further processed, and the processing method is as follows:

[0077] S1. According to the mass ratio of carboxymethyl cellulose: starch: water = 2:20:100, mix carboxymethyl cellulose and starch evenly in water, and keep stirring in a water bath at 75 °C for 20 min to obtain gelatinized starch.

[0078] S2. According to the mass ratio of zinc chloride: gelatinized starch: modified bamboo fiber: water = 6:10:30:100, mix zinc chloride, the gelatinized starch obtained in S1, and the bamboo fiber of Example 2 in water. After stirring evenly, let it stand for 6 h, dropwise add 10 wt% sodium hydroxide aqueous solution until the pH reaches 11 - 12, let it stand again for 4 h, filter, wash with deionized water 2 - 3 times, and dry by infrared to obtain Bamboo fiber sample 4.

[0079] Example 5

[0080] In this example, a series of composition samples 1 - 8 for degradable cup lids were prepared. The raw material ratios of composition samples 1 - 8 are listed in Table 1, and the preparation process is as follows:

[0081] S1. Feed butyl stearate, maleic anhydride, poly(butylene succinate), the first polylactic acid with a weight - average molecular weight of 5000 to 10000, and the second polylactic acid with a weight - average molecular weight of 250000 to 300000 into a twin - screw extruder and mix and stir evenly.

[0082] S2. According to the addition amount of the second polylactic acid in S1, add glass fiber and modified bamboo fiber to the twin - screw extruder, mix and stir evenly again and co - extrude and pelletize to obtain the composition for degradable cup lids; among them, the temperature of the first stage of extrusion and pelletizing is 165 °C, the temperature of the second stage is 180 °C, the temperature of the third stage is 195 °C, the temperature of the fourth stage is 165 °C, and the temperature of the fifth stage is 140 °C.

[0083] Table 1

[0084]

[0085] Performance test

[0086] According to GB / T1040, test the tensile strength of composition samples 1 - 8, according to GB / T9341, test the flexural strength of composition samples 1 - 8, and according to GB / T31402 - 2015, test the antibacterial performance of composition samples 1 - 8. The following test results show that, compared with ordinary bamboo fiber, the bamboo fiber modified with calcium carbonate can significantly improve the mechanical properties of the polylactic acid degradable material. In addition, zinc ions as antibacterial agents can improve the antibacterial and bacteriostatic properties of the polylactic acid degradable material.

[0087] Table 2

[0088]

[0089] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A method for preparing a composition for a degradable cup cover, characterized in that: S100, feeding the lubricant, the compatibilizer, the toughening agent, the first polylactic acid and the second polylactic acid into a twin-screw extruder and mixing and stirring them uniformly according to the mass ratio of lubricant: compatibilizer: toughening agent: first polylactic acid: second polylactic acid = (1-2): (6-8): (6-8): (8-10): 100; S200, adding the glass fiber and the modified bamboo fiber to the twin-screw extruder according to the mass ratio of glass fiber: modified bamboo fiber: second polylactic acid = (5-10): (15-20): 100 and the amount of the second polylactic acid added in S100, mixing and stirring them evenly again and extruding and granulating them together to obtain the composition for the degradable cup cover; The weight average molecular weight of the first polylactic acid is 5000 to 10000, and the weight average molecular weight of the second polylactic acid is 250000 to 300000; the modified bamboo fiber is surface-modified with calcium carbonate and loaded with an antibacterial agent; The preparation steps of the modified bamboo fiber include: S110, using a crusher to crush the bamboo fibers into bamboo fiber powder of target particle size; S120, soaking the bamboo fiber powder in hydrogen peroxide, adding an acetic acid aqueous solution of the same volume as the hydrogen peroxide after soaking and stirring simultaneously, leaving the mixture to stand after the addition is completed, filtering, washing, and drying the bamboo fiber powder; S130, uniformly dispersing the bamboo fiber powder obtained in S120 by ultrasonic dispersion in a calcium chloride aqueous solution, and dripping a sodium hydroxide aqueous solution until the pH reaches 11-12, to obtain a first mixture; S140, placing the first mixture in a closed reactor for aging, first evacuating the reactor, then introducing a gas including carbon dioxide into the reactor, stirring the first mixture under pressure to allow the first mixture to react with the carbon dioxide, stopping the introduction of the gas after the reaction is completed, releasing the pressure, extracting the solids, filtering, washing, and drying, to obtain the modified bamboo fiber; After S140, the step of preparing the modified bamboo fiber further includes: S150, mixing the carboxymethyl cellulose and the starch in water, and placing the mixture in a water bath at 75° C. to 80° C. and stirring for 20 to 40 minutes to obtain gelatinized starch; S160, mixing maleic anhydride, ammonium persulfate, acrylic acid and acrylamide to obtain a second mixture; S170, lowering the temperature of the water bath to 50° C. to 60° C., adding the second mixture to the water bath according to the amount of starch in S150, and continuing to keep warm and stir for 1 h to 2 h to obtain modified starch; S180, mixing zinc chloride, the modified starch obtained in S170, and the modified bamboo fiber obtained in S140 in water, stirring evenly and then standing for 4 to 6 hours, adding 8wt% to 12wt% of sodium hydroxide aqueous solution until the pH reaches 11-12, standing again for 4 to 6 hours, filtering, washing, and drying to obtain the bamboo fiber powder loaded with an antibacterial agent; In S150, by mass ratio, carboxymethyl cellulose: starch: water = (2-4): (15-25): 100; In S160, by mass ratio, maleic anhydride: ammonium persulfate: acrylic acid: acrylamide = (0.2-0.4): (1-1.5): (30-40): 100; In S170, by mass ratio, the second mixture: starch = (10-20): 100; In S180, by mass ratio, zinc chloride: modified starch: modified bamboo fiber: water = (6-8): (10-20): (20-30):

100.

2. The preparation method according to claim 1, characterized in that: The lubricant comprises at least one of fatty acid ester, fatty acid amide and polyethylene wax or a combination thereof; and / or The compatibilizer comprises at least one of maleic anhydride, methyl diphenyl diisocyanate, lysine triisocyanate, lysine diisocyanate, glycidyl methacrylate or a combination thereof; and / or The toughening agent includes at least one of polybutylene succinate, polybutylene succinate adipate, polycaprolactone, polybutylene adipate terephthalate or a combination thereof.

3. The preparation method according to claim 1, characterized in that: The extrusion granulation temperature of the twin-screw extruder described in S200 is: first section: 160°C to 170°C, second section: 180°C to 190°C, third section: 190°C to 200°C, fourth section: 160°C to 170°C, and fifth section: 140°C to 150°C.

4. The preparation method according to claim 1, characterized in that: The target particle size of the bamboo fiber powder in S110 is 400 mesh to 600 mesh; and / or The concentration of hydrogen peroxide in S120 is 20% to 25%; and / or The concentration of the acetic acid aqueous solution in S120 is 14% to 18%; and / or The soaking time in S120 is 2 hours to 3 hours, and the standing time is 20 minutes to 40 minutes; and / or The concentration of the calcium chloride aqueous solution in S130 is 10wt% to 20wt%; and / or The concentration of the sodium hydroxide aqueous solution in S130 is 8wt% to 12wt%; and / or The aging time in S140 is 12 to 18 hours; and / or The pressurization condition in S140 is 4 MPa to 8 MPa; and / or The stirring rate in S140 is 600 r / min to 800 r / min, and the stirring time is 2 h to 5 h.

5. A composition for a degradable cup cover, characterized in that: The composition for degradable cup lids is obtained by the preparation method according to any one of claims 1 to 4.

6. A cup cover, characterized in that: The cup cover is manufactured using the degradable cup cover composition obtained by the preparation method according to any one of claims 1 to 4.

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