Preparation method of degradable butyronitrile latex and application of degradable butyronitrile latex in disposable medical gloves

Abstract

The invention relates to the technical field of degradable butyronitrile gloves, and discloses a preparation method of degradable butyronitrile latex and application of the degradable butyronitrile latex in disposable medical gloves. Comprising the following components in parts by weight: 100 parts of carboxylic butadiene-acrylonitrile latex, 3-15 parts of modified starch grafted polylactic acid emulsion, 2-3 parts of zinc oxide, 1-2 parts of potassium hydroxide, 0.9-1.3 parts of sulfur S, 0.4-0.6 part of accelerant BZ, 0.1-0.3 part of anti-aging agent, 3-5 parts of titanium dioxide and deionized water, and is obtained by uniformly mixing and vulcanizing, wherein the modified starch grafted polylactic acid emulsion is prepared from starch grafted acrylonitrile and methallyl modified star-shaped polylactic acid; the prepared butyronitrile latex gloves can keep good mechanical stability at the initial stage of use, the degradation rate at the later stage of use under different conditions is excellent, the degradation rate reaches 96.5% after the gloves are buried in soil for 8 weeks, and complete degradation of the butyronitrile latex gloves is basically achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of degradable nitrile gloves, and specifically to a preparation method of degradable nitrile latex and its application in disposable medical gloves. Background Art

[0002] In the medical industry, disposable medical gloves are important protective supplies to ensure the safety of medical staff and patients. As an important synthetic rubber latex, nitrile latex is prepared by the polymerization reaction of butadiene and acrylonitrile. It has excellent oil resistance, chemical corrosion resistance, good physical and mechanical properties, and the characteristic of not containing natural latex proteinogen, and will not cause allergic reactions. Therefore, it has been widely used in the field of disposable medical gloves. However, traditional disposable nitrile medical gloves contain a large amount of plastic components, which are difficult to degrade in the natural environment. Long-term accumulation will cause serious pollution to the ecosystem. After a large number of waste gloves are discarded, they not only occupy a large amount of space, but also cause serious pollution to the environment. Therefore, the research and development of biodegradable nitrile gloves has very important practical significance and market prospects.

[0003] As an important synthetic rubber material, nitrile latex occupies a key position in the glove manufacturing field. However, the products produced by existing nitrile latex preparation methods are often difficult to balance in terms of mechanical properties and degradability: some methods use high-temperature polymerization, resulting in too high degree of branching and crosslinking of the products, increasing the gel content, and thus affecting the mechanical properties of the gloves; there are also some methods with complex feeding processes, increasing the difficulty of industrial implementation; at the same time, most of the existing degradable materials cannot meet the use requirements of disposable medical gloves in terms of performance, such as strength, elasticity, chemical resistance, etc. For example, starch-based materials have the advantages of being degradable, low-cost, and widely sourced, but the size of native starch granules is generally between several and dozens of micrometers, which is too large for rubber reinforcement. Such a large particle size results in a small specific surface area, weak binding ability with rubber and latex particles, and is easy to fall off in the latex, thus forming voids and depressions, causing material defects and then stress concentration and other problems. Its mechanical properties and water resistance are poor, and it is difficult to directly meet the performance requirements of gloves. Although polylactic acid is a bio-based biodegradable polymer material, it has problems such as poor toughness, slow and uncontrollable degradation rate, and poor hydrophilicity, which limit its application in the field of disposable medical gloves.

[0004] Patent No. CN116333388A discloses a disposable degradable environmentally friendly nitrile latex glove and its processing technology, including carboxylated nitrile latex, modified starch, hydroxypropyl methyl cellulose ether, etc. Among them, the modified starch is obtained by mixing and reacting starch with bis(3-triethoxysilylpropyl) tetrasulfide. However, the compatibility between starch and polymers such as nitrile latex is poor, and phenomena such as delamination and agglomeration are likely to occur during processing, affecting the quality and performance of the gloves and making it difficult to meet the usage requirements of disposable medical gloves. The present invention aims to utilize the complementarity of starch and polylactic acid in performance. Starch can improve the hydrophobicity of polylactic acid and enhance its compatibility with nitrile latex, while polylactic acid enhances the mechanical properties and degradation properties of starch. By modifying starch and polylactic acid, the problem that nitrile latex is non-degradable and has poor mechanical properties is improved. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a preparation method of degradable nitrile latex and its application in disposable medical gloves, solving the problems that traditional nitrile gloves are difficult to degrade and pollute the environment, and at the same time greatly improving the mechanical properties of the gloves.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A preparation method of degradable nitrile latex is carried out according to the following steps: Step (1): Under a nitrogen atmosphere, add 100 parts of starch and deionized water by weight to a reaction flask, gelatinize at 75 - 90 °C for 20 - 40 min, add 2 - 4 parts of emulsifier OP-10, continue stirring for 5 - 10 min, then add 0.8 - 1.5 parts of initiator ammonium persulfate, then react for 10 - 20 min, add 80 - 90 parts of acrylonitrile and 20 - 35 parts of methacryloyl modified star-shaped polylactic acid, and react at 80 - 100 °C for 3 - 8 h. Cool to room temperature and adjust the pH to 6 - 7 to obtain a modified starch grafted polylactic acid emulsion.

[0007] Step (2): According to the dry ratio formula (by weight), add 100 parts of carboxylated nitrile latex, 3 - 15 parts of modified starch grafted polylactic acid emulsion, 2 - 3 parts of zinc oxide, 1 - 2 parts of potassium hydroxide, 0.9 - 1.3 parts of sulfur S, 0.4 - 0.6 parts of accelerator BZ, 0.1 - 0.3 parts of antioxidant, 3 - 5 parts of titanium dioxide and deionized water into the reaction flask. Stir and cure at 20 - 35 °C until evenly dispersed, then filter and remove air bubbles to obtain degradable nitrile latex.

[0008] Further, in step (1), the starch is any one of corn starch, potato starch or sweet potato starch.

[0009] Further, the antioxidant in step (2) is any one of 4-methyl-6-tert-butylphenol, 2-mercaptobenzimidazole or nickel dibutyldithiocarbamate.

[0010] Further, the preparation method of the methacryloyl-modified star-shaped polylactic acid in step (1) is as follows: Step S1: Under a nitrogen atmosphere, lactide and polyol are added to a reaction flask. After stirring evenly, stannous octoate is added. First, the reaction is carried out at 180-200 °C for 1-3 h, then the temperature is lowered to 120-140 °C and the reaction is carried out for 24-48 h. After cooling to room temperature, recrystallization is carried out with methanol, filtered and dried to obtain multi-arm star-shaped polylactic acid.

[0011] Step S2: Under a nitrogen atmosphere, multi-arm star-shaped polylactic acid and tetrahydrofuran are added to a reaction flask. After stirring evenly, triethylamine and methacryloyl chloride are added and stirred for reaction. After the reaction is completed, the white precipitate is filtered off, the filtrate is concentrated, recrystallized with methanol, and dried to obtain methacryloyl-modified star-shaped polylactic acid.

[0012] Further, the polyol in step S1 is any one of glycerol, trimethylolethane or pentaerythritol.

[0013] Further, the weight ratio of lactide, polyol and stannous octoate in step S1 is 100:2-5:0.5-1.

[0014] Further, the weight ratio of multi-arm star-shaped polylactic acid, triethylamine and methacryloyl chloride in step S2 is 100:10-15:12-20.

[0015] Further, the reaction temperature in step S2 is 0-10 °C and the reaction time is 5-12 h.

[0016] Further, the preparation method of the medical glove is as follows: The hand mold is preheated to 90-100 °C, impregnated into the biodegradable nitrile latex mixture, and a segmented heating vulcanization process is adopted. The release agent is impregnated, the edges are curled and cooled and demolded to obtain a disposable medical glove.

[0017] Further, the process of the segmented heating vulcanization process is as follows: First, vulcanize at 100-110 °C for 20-30 min, and then vulcanize at 120-130 °C for 15-25 min.

[0018] Adopting the above technical solutions, the beneficial effects of the present invention are as follows: (1)Excellent mechanical properties: After the starch is copolymerized with star-shaped polylactic acid and acrylonitrile, it contains a structure similar to carboxybutadiene latex. Due to the principle of like dissolves like, the interfacial compatibility is improved. After the modified starch is added to the rubber film, the hydroxyl groups on the surface of its particles and the carboxyl groups of carboxybutadiene latex can form hydrogen bond interactions, enhancing the interaction between starch particles and the rubber matrix. At the same time, due to the decrease in crystallinity of star-shaped polylactic acid, the intermolecular force decreases, and the branched chains show flexibility. The star-shaped polylactic acid is grafted onto the starch molecular chain, and several polymer chains combine to form a cross-linked structure, which overlaps and entangles with each other. The stress can be dispersed and transmitted to other molecular chains through the cross-linking points. When an external force acts, the network-like structure can bear more external forces. In addition, grafting polylactic acid onto starch can also significantly improve its cold water solubility and hydrophilicity, and then it can be uniformly and stably dispersed in the rubber matrix during the compounding and vulcanization processes with latex. Grafting polylactic acid on the surface of starch particles also improves the reaction and bonding ability of starch with other substances, reducing the agglomeration of starch itself. Finally, the mechanical properties of the rubber film are significantly improved. The cross-linked network structure formed by the chemical cross-linking of starch and polylactic acid can complement each other's advantages, making the glove material have both sufficient strength and good toughness, thus improving the durability and service life of the gloves.

[0019] (2)Excellent degradability: Both polylactic acid and starch are renewable resources. Their blended use can reduce the dependence on non-renewable resources such as petroleum. Since the butadiene nitrile gloves provide energy for the molecular chain movement after receiving external heat, the cross-linking bonds and fragile hydrogen bonds will break. At the same time, there is oxygen during the heating process, and oxygen can accelerate the thermal degradation of starch. Starch dehydrates at high temperature and then undergoes degradation processes such as thermal cracking to generate small molecule substances. Polylactic acid can be degraded into pollution-free substances such as carbon dioxide and water. The cross-linked structure produced by their synergistic effect helps to reduce the generation of microplastics during the degradation process, reducing the risk of incomplete degradation of single materials to produce microplastics, which is more beneficial to environmental protection. At the same time, under natural and buried conditions, affected by natural environments such as light oxygen, ultraviolet rays, and humidity, the moisture inside the gloves also evaporates, forming a large number and size of crystalline regions inside the gloves, increasing the stress concentration effect, reducing the ability of the film to withstand further elongation, and thus accelerating the degradation rate. In this way, the gloves can maintain good stability in the initial stage of use, while in the later stage of use, the synergistic degradation characteristics of starch and polylactic acid can accelerate the overall degradation of the gloves. Detailed implementation manners

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] Unless otherwise specified, the raw materials and reagents used in this application are all commercially available products or can be prepared by known methods.

[0022] Carboxylated nitrile latex: total solids mass fraction 48%, product of Shanghai Xintema Chemical Co., Ltd.

[0023] Starch: commercially available, Jiangsu Baobao Suqian Guomin Biotechnology Co., Ltd.

[0024] Example 1 (1) Under a nitrogen atmosphere, 100 g of lactide and 3 g of glycerol were added to a reaction flask. After stirring evenly, 0.8 g of stannous octoate was added. The reaction was first carried out at 190 °C for 2 h, then cooled to 130 °C and reacted for 32 h. After cooling to room temperature, recrystallization was carried out with methanol, filtered and dried to obtain multi-arm star-shaped polylactic acid.

[0025] (2) Under a nitrogen atmosphere, 100 g of multi-arm star-shaped polylactic acid and 1000 mL of tetrahydrofuran were added to a reaction flask. After stirring evenly, 12 g of triethylamine and 15 g of methacryloyl chloride were added. The reaction was carried out at 5 °C for 8 h. The white precipitate was filtered off, the filtrate was concentrated, recrystallized with methanol, and dried to obtain methacryloyl-modified star-shaped polylactic acid.

[0026] (3) Under a nitrogen atmosphere, 100 g of corn starch and 2300 mL of deionized water were added to a reaction flask. Gelatinization was carried out at 85 °C for 30 min, 34 g of emulsifier OP-10 was added, and stirring was continued for 7 min. Then 1.2 g of initiator ammonium persulfate was added, and the reaction was continued for 15 min. 85 g of acrylonitrile and 30 g of methacryloyl-modified star-shaped polylactic acid were added, and the reaction was carried out at 90 °C for 6 h. After cooling to room temperature, the pH was adjusted to 7 to obtain a modified starch-grafted polylactic acid emulsion.

[0027] (4) According to the dry ratio formula, 100 g of carboxylated nitrile latex, 3 g of modified starch-grafted polylactic acid emulsion, 2.5 g of zinc oxide, 1.6 g of potassium hydroxide, 1.1 g of sulfur S, 0.5 g of accelerator BZ, 0.2 g of 4-methyl-6-tert-butylphenol, 4 g of titanium dioxide and deionized water were added to a reaction flask. After stirring and curing at 25 °C until uniformly dispersed, filtration and degassing were carried out to obtain a degradable nitrile latex.

[0028] (5) The hand mold was preheated to 95 °C and immersed in the degradable nitrile latex mixture. A segmented heating vulcanization process was used. First, vulcanization was carried out at 105 °C for 28 min, then at 125 °C for 20 min. The release agent was impregnated, the edges were curled, and the mold was cooled and demolded to obtain a disposable medical glove.

[0029] Example 2 (1) Under a nitrogen atmosphere, 100 g of lactide and 2 g of trimethylolethane were added to a reaction flask. After stirring evenly, 0.5 g of stannous octoate was added. The reaction was carried out at 200 °C for 3 h first, then the temperature was lowered to 120 °C and the reaction continued for 48 h. After cooling to room temperature, recrystallization was carried out with methanol, followed by filtration and drying to obtain multi-armed star-shaped polylactic acid.

[0030] (2) Under a nitrogen atmosphere, 100 g of multi-armed star-shaped polylactic acid and 800 mL of tetrahydrofuran were added to a reaction flask. After stirring evenly, 10 g of triethylamine and 12 g of methacryloyl chloride were added. The reaction was carried out at 10 °C for 5 h. The white precipitate was filtered off, the filtrate was concentrated, recrystallized with methanol, and dried to obtain methacryloyl-modified star-shaped polylactic acid.

[0031] (3) Under a nitrogen atmosphere, 100 g of potato starch and 2000 mL of deionized water were added to a reaction flask. Gelatinization was carried out at 90 °C for 20 min, 2 g of emulsifier OP-10 was added, and stirring was continued for 10 min. Then 0.8 g of initiator ammonium persulfate was added, and the reaction continued for 20 min. 80 g of acrylonitrile and 20 g of methacryloyl-modified star-shaped polylactic acid were added, and the reaction was carried out at 100 °C for 3 h. After cooling to room temperature, the pH was adjusted to 6 to obtain a modified starch-grafted polylactic acid emulsion.

[0032] (4) According to the dry ratio formula, 100 g of carboxylated nitrile latex, 6 g of modified starch-grafted polylactic acid emulsion, 2 g of zinc oxide, 1 g of potassium hydroxide, 0.9 g of sulfur S, 0.6 g of accelerator BZ, 0.1 g of 2-mercaptobenzimidazole, 3 g of titanium dioxide and deionized water were added to a reaction flask. After stirring and curing at 35 °C until evenly dispersed, filtration and degassing were carried out to obtain a degradable nitrile latex.

[0033] (5) The hand mold was preheated to 100 °C and immersed in the degradable nitrile latex mixture. A segmented heating vulcanization process was used. First, vulcanization was carried out at 110 °C for 20 min, then at 130 °C for 15 min. The release agent was impregnated, the edges were curled, and the product was cooled and demolded to obtain a disposable medical glove.

[0034] Example 3 (1) Under a nitrogen atmosphere, 100 g of lactide and 5 g of pentaerythritol were added to a reaction flask. After stirring evenly, 1 g of stannous octoate was added. The reaction was carried out at 180 °C for 3 h first, then the temperature was lowered to 120 °C and the reaction continued for 48 h. After cooling to room temperature, recrystallization was carried out with methanol, followed by filtration and drying to obtain multi-armed star-shaped polylactic acid.

[0035] (2) Under a nitrogen atmosphere, 100 g of multi-armed star-shaped polylactic acid and 1200 mL of tetrahydrofuran were added to a reaction flask. After stirring evenly, 15 g of triethylamine and 20 g of methacryloyl chloride were added. The reaction was carried out at 0 °C for 12 h. The white precipitate was filtered off, the filtrate was concentrated, recrystallized with methanol, and dried to obtain methacryloyl-modified star-shaped polylactic acid.

[0036] (3) Under a nitrogen atmosphere, 100 g of sweet potato starch and 2500 mL of deionized water were added to a reaction flask, gelatinized at 75 °C for 40 min, 4 g of emulsifier OP-10 was added, and stirring was continued for 10 min. Then, 1.5 g of initiator ammonium persulfate was added, followed by reaction for 20 min. 90 g of acrylonitrile and 35 g of methacryloyl-modified star-shaped polylactic acid were added, and the reaction was carried out at 80 °C for 8 h. After cooling to room temperature, the pH was adjusted to 6 to obtain a modified starch-grafted polylactic acid emulsion.

[0037] (4) According to the dry ratio formula, 100 g of carboxylated nitrile latex, 9 g of modified starch-grafted polylactic acid emulsion, 3 g of zinc oxide, 2 g of potassium hydroxide, 1.3 g of sulfur S, 0.4 g of accelerator BZ, 0.3 g of nickel dibutyldithiocarbamate, 5 g of titanium dioxide, and deionized water were added to a reaction flask. After stirring and curing at 20 °C until uniformly dispersed, filtration and degassing were carried out to obtain a degradable nitrile latex.

[0038] (5) The hand mold was preheated to 90 °C and immersed in the degradable nitrile latex mixture. Using a segmented heating vulcanization process, vulcanization was first carried out at 100 °C for 30 min, then at 120 °C for 25 min. The release agent was impregnated, the edges were curled, and the mold was cooled and demolded to obtain disposable medical gloves.

[0039] Example 4 (1) Under a nitrogen atmosphere, 100 g of lactide and 4 g of glycerol were added to a reaction flask. After stirring evenly, 0.9 g of stannous octoate was added. The reaction was first carried out at 185 °C for 3 h, then the temperature was lowered to 135 °C and the reaction was carried out for 40 h. After cooling to room temperature, recrystallization from methanol was carried out, and filtration and drying were carried out to obtain multi-arm star-shaped polylactic acid.

[0040] (2) Under a nitrogen atmosphere, 100 g of multi-arm star-shaped polylactic acid and 1100 mL of tetrahydrofuran were added to a reaction flask. After stirring evenly, 11 g of triethylamine and 16 g of methacryloyl chloride were added, and the reaction was carried out at 8 °C for 12 h. The white precipitate was filtered off, the filtrate was concentrated, recrystallized from methanol, and dried to obtain methacryloyl-modified star-shaped polylactic acid.

[0041] (3) Under a nitrogen atmosphere, 100 g of corn starch and 2400 mL of deionized water were added to a reaction flask, gelatinized at 85 °C for 25 min, 3.5 g of emulsifier OP-10 was added, and stirring was continued for 6 min. Then, 1.3 g of initiator ammonium persulfate was added, followed by reaction for 18 min. 88 g of acrylonitrile and 32 g of methacryloyl-modified star-shaped polylactic acid were added, and the reaction was carried out at 95 °C for 5 h. After cooling to room temperature, the pH was adjusted to 7 to obtain a modified starch-grafted polylactic acid emulsion.

[0042] (4)According to the dry ratio formula, 100 g of carboxy nitrile latex, 12 g of modified starch grafted polylactic acid emulsion, 3 g of zinc oxide, 1.6 g of potassium hydroxide, 1.2 g of sulfur S, 0.5 g of accelerator BZ, 0.3 g of 4-methyl-6-tert-butylphenol, 4.2 g of titanium dioxide and deionized water were added to the reaction flask. After stirring and curing at 30 °C until uniformly dispersed, it was filtered and degassed to obtain degradable nitrile latex.

[0043] (5)The hand mold was preheated to 100 °C and impregnated into the degradable nitrile latex mixture. Using a segmented heating vulcanization process, it was first vulcanized at 110 °C for 30 min, then vulcanized at 120 °C for 20 min, impregnated with a release agent, curled, cooled and demolded to obtain disposable medical gloves.

[0044] Example 5 (1)Under a nitrogen atmosphere, 100 g of lactide and 3 g of trimethylolethane were added to the reaction flask. After stirring evenly, 0.7 g of stannous octoate was added. It was first reacted at 195 °C for 3 h, then cooled to 120 °C and reacted for 24 h. After cooling to room temperature, it was recrystallized from methanol, filtered and dried to obtain multi-arm star-shaped polylactic acid.

[0045] (2)Under a nitrogen atmosphere, 100 g of multi-arm star-shaped polylactic acid and 1050 mL of tetrahydrofuran were added to the reaction flask. After stirring evenly, 14 g of triethylamine and 16 g of methacryloyl chloride were added. It was reacted at 0 °C for 9 h, the white precipitate was filtered off, the filtrate was concentrated, recrystallized from methanol, and dried to obtain methacryloyl-modified star-shaped polylactic acid.

[0046] (3)Under a nitrogen atmosphere, 100 g of potato starch and 2250 mL of deionized water were added to the reaction flask. It was gelatinized at 80 °C for 35 min, 3 g of emulsifier OP-10 was added, and stirring was continued for 8 min. Then 1.3 g of initiator ammonium persulfate was added, and the reaction was continued for 15 min. 82 g of acrylonitrile and 25 g of methacryloyl-modified star-shaped polylactic acid were added, and the reaction was carried out at 90 °C for 6 h. After cooling to room temperature, the pH was adjusted to 6 to obtain a modified starch grafted polylactic acid emulsion.

[0047] (4)According to the dry ratio formula, 100 g of carboxy nitrile latex, 15 g of modified starch grafted polylactic acid emulsion, 2.2 g of zinc oxide, 1.8 g of potassium hydroxide, 1.1 g of sulfur S, 0.45 g of accelerator BZ, 0.25 g of 2-mercaptobenzimidazole, 5 g of titanium dioxide and deionized water were added to the reaction flask. After stirring and curing at 35 °C until uniformly dispersed, it was filtered and degassed to obtain degradable nitrile latex.

[0048] (5) Preheat the hand mold to 90 °C, immerse it in the biodegradable nitrile latex mixture, and use a segmented heating vulcanization process. First, vulcanize at 105 °C for 28 min, then vulcanize at 125 °C for 25 min. Immerse the release agent, crimp the edge, cool and demold to obtain disposable medical gloves.

[0049] Comparative Example 1 (1) According to the dry ratio formula, add 100 g of carboxylated nitrile latex, 3 g of methacrylyl-modified star-shaped polylactic acid (prepared in Example 1), 2.5 g of zinc oxide, 1.6 g of potassium hydroxide, 1.1 g of sulfur S, 0.5 g of accelerator BZ, 0.2 g of 4-methyl-6-tert-butylphenol, 4 g of titanium dioxide and deionized water into the reaction flask. Stir and cure at 25 °C until evenly dispersed, then filter and remove air bubbles to obtain nitrile latex.

[0050] (2) Preheat the hand mold to 95 °C, immerse it in the nitrile latex mixture, and use a segmented heating vulcanization process. First, vulcanize at 105 °C for 28 min, then vulcanize at 125 °C for 20 min. Immerse the release agent, crimp the edge, cool and demold to obtain disposable medical gloves.

[0051] Comparative Example 2 (1) Under a nitrogen atmosphere, add 100 g of corn starch and 2300 mL of deionized water to the reaction flask, gelatinize at 85 °C for 30 min, add 34 g of emulsifier OP-10, continue to stir for 7 min, then add 1.2 g of initiator ammonium persulfate, then react for 15 min, add 85 g of acrylonitrile, and react at 90 °C for 6 h. Cool to room temperature and adjust the pH to 7 to obtain starch-grafted acrylonitrile.

[0052] (2) According to the dry ratio formula, add 100 g of carboxylated nitrile latex, 3 g of starch-grafted acrylonitrile, 2.5 g of zinc oxide, 1.6 g of potassium hydroxide, 1.1 g of sulfur S, 0.5 g of accelerator BZ, 0.2 g of 4-methyl-6-tert-butylphenol, 4 g of titanium dioxide and deionized water into the reaction flask. Stir and cure at 25 °C until evenly dispersed, then filter and remove air bubbles to obtain nitrile latex.

[0053] (3) Preheat the hand mold to 95 °C, immerse it in the nitrile latex mixture, and use a segmented heating vulcanization process. First, vulcanize at 105 °C for 28 min, then vulcanize at 125 °C for 20 min. Immerse the release agent, crimp the edge, cool and demold to obtain disposable medical gloves.

[0054] Comparative Example 3 (1)According to the dry ratio formula, 100 g of carboxylated nitrile latex, 3 g of corn starch, 2.5 g of zinc oxide, 1.6 g of potassium hydroxide, 1.1 g of sulfur S, 0.5 g of accelerator BZ, 0.2 g of 4-methyl-6-tert-butylphenol, 4 g of titanium dioxide and deionized water were added to a reaction flask. After stirring and curing at 25 °C until uniformly dispersed, filtration and degassing were carried out to obtain nitrile latex.

[0055] (2)The hand mold was preheated to 95 °C and immersed in the nitrile latex mixture. A segmented heating vulcanization process was adopted. First, vulcanization was carried out at 105 °C for 28 min, then at 125 °C for 20 min. After impregnating with an isolating agent, curling, cooling and demolding were carried out to obtain disposable medical gloves.

[0056] Mechanical property test: According to the standard of GB / T528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber", the disposable medical gloves were cut into dumbbell-shaped specimens, and the tensile strength, elongation at break and 100% modulus of the specimens were tested. The tensile rate was 500 mm / min.

[0057] Table 1 Mechanical property test

[0058] From the test results in the above table, it can be seen that with the increase in the content of the modified starch-grafted polylactic acid emulsion, the mechanical properties of the nitrile gloves gradually increase. Among them, the tensile strength in Example 4 reaches 45.7 MPa, the elongation at break is 542.5%, and the 100% tensile stress reaches 2.8 MPa. This is because after starch copolymerizes with star-shaped polylactic acid and acrylonitrile, it contains a structure similar to that of carboxylated nitrile latex. Due to the similar compatibility, the interfacial compatibility is improved. After the modified starch is added to the rubber film, on the one hand, the hydroxyl groups on the particle surface of the starch and the carboxyl groups of the carboxylated nitrile latex can form hydrogen bond interactions, enhancing the interaction between the starch particles and the rubber matrix. At the same time, due to the decrease in crystallinity of star-shaped polylactic acid, the intermolecular force decreases, and the branched chains show flexibility. Star-shaped polylactic acid is grafted onto the starch molecular chain, and several polymer chains combine to form a cross-linked structure, which overlaps and entangles with each other. The stress can be dispersed and transmitted to other molecular chains through the cross-linking points. When an external force acts, the network-like structure can bear more external forces. On the other hand, grafting polylactic acid onto starch can also significantly improve its cold water solubility and hydrophilicity, and then be uniformly and stably dispersed in the rubber matrix during the mixing and vulcanization with latex. Grafting polylactic acid on the surface of starch particles also improves the reaction and bonding ability of starch with other substances, reducing the agglomeration of starch itself, and finally significantly improving the mechanical properties of the rubber film. The cross-linked network structure formed by chemical cross-linking of starch and polylactic acid can form complementary advantages, making the glove material have both sufficient strength and good toughness, thus improving the durability and service life of the gloves.

[0059] In Comparative Example 1, the added material was methylallyl-modified star-shaped polylactic acid, which had a structural similarity to carboxybutadiene latex and good toughness, but did not contain starch and had a low tensile strength; in Comparative Example 2, the added material was starch-grafted acrylonitrile, which had a similar structure to butadiene latex, but the starch had poor water resistance and low toughness; in Comparative Example 3, the added material was unmodified starch, and direct blending led to phase separation in the system, and it did not contain polylactic acid, with insufficient toughness and the worst mechanical properties.

[0060] Thermal oxidative degradation test: Cut dumbbell-shaped specimens were placed in an oven at 120 °C for thermal oxidation for 72 h, and then the specimens were taken out for tensile strength test and the change rate of tensile strength was calculated.

[0061] Natural degradation test: The prepared gloves were hung on an iron rack exposed outdoors, taken down after hanging for 4 weeks, and subjected to tensile strength test and the change rate of tensile strength was calculated.

[0062] Soil burial degradation performance test: The prepared gloves were buried in the soil at a depth of 5 cm, ensuring a soil humidity of 70%. After being buried for 8 weeks, they were taken out, washed and air-dried naturally. The specimens were taken out for tensile strength test and the change rate of tensile strength was calculated.

[0063] Among them, the change rate of tensile strength = (initial tensile strength - tensile strength after degradation) / initial tensile strength × 100%. The larger the change rate of tensile strength, the higher the degree of degradation, that is, the better the degradation performance.

[0064] Table 2 Degradation performance test

[0065] As can be seen from the test results in the above table, with the increase in the content of the modified starch-grafted polylactic acid emulsion, the performance of the nitrile gloves in terms of thermal-oxidative degradation, natural degradation, and soil burial degradation gradually improves. This is because both polylactic acid and starch are renewable resources, and their blended use can reduce the dependence on non-renewable resources such as petroleum. When heat is applied to the nitrile gloves, it provides energy for the molecular chain movement, causing the cross-linking bonds and fragile hydrogen bonds to break. At the same time, there is oxygen during the heating process, and oxygen can accelerate the thermal degradation of starch. Starch dehydrates at high temperatures and then undergoes thermal cracking and other degradation processes to generate small-molecule substances. Polylactic acid can be degraded into pollution-free substances such as carbon dioxide and water. The cross-linked structure produced by the synergistic effect of the two helps to reduce the generation of microplastics during the degradation process, reducing the risk of incomplete degradation of single materials and generating microplastics, which is more conducive to environmental protection. At the same time, under natural and soil burial conditions, affected by natural environments such as light oxygen, ultraviolet rays, and humidity, the moisture inside the gloves also evaporates, forming a large number and size of crystal regions inside the gloves, increasing the stress concentration effect and reducing the ability of the film to withstand further elongation, thereby accelerating the degradation rate. In this way, the gloves can maintain good stability in the initial stage of use, while in the later stage of use, the synergistic degradation characteristics of starch and polylactic acid can accelerate the overall degradation of the gloves.

[0066] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. In addition, it should be noted that in the above specific embodiments, the various specific technical features described can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

Claims

1. A preparation method of degradable nitrile latex, characterized in that, The preparation method is carried out according to the following steps: Step (1): Under a nitrogen atmosphere, 100 parts by weight of starch and deionized water are added to a reaction flask, gelatinized at 75 - 90 °C for 20 - 40 min, 2 - 4 parts of emulsifier OP - 10 are added, and stirring is continued for 5 - 10 min. Then, 0.8 - 1.5 parts of initiator ammonium persulfate are added, and the reaction continues for 10 - 20 min. Next, 80 - 90 parts of acrylonitrile and 20 - 35 parts of methacrylyl - modified star - shaped polylactic acid are added, and the reaction is carried out at 80 - 100 °C for 3 - 8 h. After cooling to room temperature, the pH is adjusted to 6 - 7 to obtain a modified starch - grafted polylactic acid emulsion; Step (2): According to the dry - ratio formula (by weight), 100 parts of carboxylated nitrile latex, 3 - 15 parts of modified starch - grafted polylactic acid emulsion, 2 - 3 parts of zinc oxide, 1 - 2 parts of potassium hydroxide, 0.9 - 1.3 parts of sulfur S, 0.4 - 0.6 parts of accelerator BZ, 0.1 - 0.3 parts of antioxidant, 3 - 5 parts of titanium dioxide and deionized water are added to a reaction flask. After stirring and curing at 20 - 35 °C until uniformly dispersed, filtration and degassing are carried out to obtain a degradable nitrile latex.

2. The preparation method of the degradable nitrile latex according to claim 1, characterized in that, In the step (1), the starch is any one of corn starch, potato starch or sweet potato starch.

3. The preparation method of the degradable nitrile latex according to claim 1, characterized in that, In the step (2), the antioxidant is any one of 4 - methyl - 6 - tert - butylphenol, 2 - mercaptobenzimidazole or nickel dibutyldithiocarbamate.

4. The preparation method of the degradable nitrile latex according to claim 1, characterized in that, The preparation method of the methacrylyl - modified star - shaped polylactic acid in the step (1) is as follows: Step S1: Under a nitrogen atmosphere, lactide and polyol are added to a reaction flask. After stirring evenly, stannous octoate is added. First, the reaction is carried out at 180 - 200 °C for 1 - 3 h, and then the temperature is lowered to 120 - 140 °C for 24 - 48 h. After cooling to room temperature, recrystallization with methanol is carried out, and filtration and drying are carried out to obtain multi - arm star - shaped polylactic acid; Step S2: Under a nitrogen atmosphere, multi - arm star - shaped polylactic acid and tetrahydrofuran are added to a reaction flask. After stirring evenly, triethylamine and methacryloyl chloride are added, and stirring reaction is carried out. After the reaction ends, the white precipitate is filtered off, the filtrate is concentrated, recrystallized with methanol, and dried to obtain methacrylyl - modified star - shaped polylactic acid.

5. The preparation method of the degradable nitrile latex according to claim 4, characterized in that, In the step S1, the polyol is any one of glycerol, trimethylolethane or pentaerythritol.

6. The preparation method of the degradable nitrile latex according to claim 4, characterized in that, In the step S1, the weight ratio of lactide, polyol and stannous octoate is 100:2 - 5:0.5 - 1.

7. The preparation method of the degradable nitrile latex according to claim 4, characterized in that, In the step S2, the weight ratio of multi - arm star - shaped polylactic acid, triethylamine and methacryloyl chloride is 100:10 - 15:12 - 20.

8. The preparation method of the degradable nitrile latex according to claim 4, characterized in that, In the step S2, the reaction temperature is 0 - 10 °C, and the reaction time is 5 - 12 h.

9. Use of the degradable nitrile latex obtained by the preparation method according to any one of claims 1-8 in disposable medical gloves, characterized in that, The preparation method of the medical glove is as follows: The hand mold is pre - heated to 90 - 100 °C, dipped into the degradable nitrile latex mixture, and a segmented heating vulcanization process is adopted. After dipping the release agent, curling and cooling and demolding are carried out to obtain a disposable medical glove.

10. The application of the degradable nitrile latex according to claim 9 in disposable medical gloves, characterized in that, The process of the segmented heating vulcanization process is as follows: First, vulcanization is carried out at 100 - 110 °C for 20 - 30 min, and then vulcanization is carried out at 120 - 130 °C for 15 - 25 min.

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