Process for preparing an antibacterial modified polylactic acid for packaging material

Abstract

The application discloses a preparation method of antibacterial modified polylactic acid for packaging materials and belongs to the technical field of polylactic acid functional modification. The antibacterial and barrier type polylactic acid composite material is prepared through initiator ring-opening polymerization, antibacterial molecule grafting and montmorillonite blending. Ethanolamine and chloroacetyl chloride generate a chloro end group initiator, the initiator initiates the ring-opening polymerization of levorotatory lactide to form an end group active polylactic acid, the end group chlorine is subjected to nucleophilic substitution and covalently grafted with an antibacterial modifier, the polylactic acid is endowed with antibacterial properties, modified montmorillonite is subjected to organic intercalation and silane coupling and then is melt-blended with the modified polylactic acid with antibacterial properties, a layered barrier structure is formed and the interface combination is enhanced, so that the polylactic acid has high barrier property, high tensile strength, excellent bacteriostasis and good degradability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of functional modification of polylactic acid, and specifically relates to a preparation method of antibacterial modified polylactic acid for packaging materials. BACKGROUND

[0002] Polylactic acid is an aliphatic polyester polymer material prepared from natural renewable resources (such as corn, cassava, sugar beet, etc.) as raw materials, through fermentation to obtain lactic acid monomers, and then ring-opening polymerization. Due to its good biodegradability, biocompatibility, transparency and film-forming property, it has rapidly developed into one of the representative materials in bio-based plastics, and is widely used in food packaging, disposable products, 3D printing and biomedical materials, etc. However, traditional polylactic acid has some application limitations, especially in the field of medical packaging, higher requirements are put forward for the mechanical properties, barrier properties, degradability and antibacterial properties of the material.

[0003] Existing antibacterial modification mainly includes inorganic antibacterial agent filling, organic antibacterial agent compounding and surface modification methods. Inorganic antibacterial agents have wide antibacterial activity but are prone to agglomeration and affect transparency. Organic antibacterial agents have poor thermal stability and insufficient antibacterial durability. Surface modification process is complex and the coating is easy to fall off. These shortcomings seriously limit the application of polylactic acid in fields with higher hygiene requirements.

[0004] In the prior art, a kind of chitosan modified high transparent antibacterial polylactic acid film and its preparation method and application are announced in Chinese invention patent with publication number CN118772648B. This method is to chemically graft chlorogenic acid and alpha-lipoic acid onto chitosan molecules through amidation reaction to form modified chitosan with antibacterial activity. The modified chitosan is physically blended with the polylactic acid matrix, so that the antibacterial active groups are stably combined in the polylactic acid matrix, thereby giving the material good degerming performance.

[0005] The phenolic hydroxyl and thiol groups in chlorogenic acid and alpha-lipoic acid containing degerming effect in the above-mentioned patent are easily oxidized and inactivated in high temperature or air, which affects the grafting efficiency of the reaction. The grafting efficiency is too low, the content of active groups is insufficient, the antibacterial effect is weakened, and excessive grafting will destroy the original molecular structure and solubility of chitosan, affect the compatibility with polylactic acid, so that the antibacterial active groups cannot be stably combined in the polylactic acid matrix, and the antibacterial effect of the prepared polylactic acid material is further reduced. SUMMARY

[0006] The application aims to provide a preparation method of antibacterial modified polylactic acid for packaging material, which comprises the following steps: preparing a chlorine end group initiator by reacting ethanolamine with chloroacetyl chloride; initiating ring-opening polymerization of L-lactide by using the chlorine end group initiator to obtain a polylactic acid matrix containing chlorine end groups; reacting the polylactic acid matrix with an antibacterial modifier under the action of triethylamine and potassium iodide to realize covalent grafting of antibacterial groups; and finally melt blending, extruding, granulating and drying the antibacterial composite polylactic acid and modified montmorillonite nanofiller to obtain the antibacterial modified polylactic acid for packaging material.

[0007] The application can be realized by the following technical scheme.

[0008] The application provides a preparation method of antibacterial modified polylactic acid for packaging material, which comprises the following steps.

[0009] Step one: condensing double tert-butyloxycarbonyl-L-lysine with isobutyl chloroformate after activation, and then condensing with polyetheramine T403, and then deprotecting, extracting, drying and purifying to obtain an antibacterial modifier.

[0010] Step two: synthesizing a modified polylactic acid matrix containing chlorine end groups by using L-lactide as raw material, stannous octoate as catalyst and adding the chlorine end group initiator for ring-opening polymerization, and then grafting and modifying the modified polylactic acid matrix containing chlorine end groups with the antibacterial modifier to obtain an antibacterial composite polylactic acid matrix.

[0011] Step three: uniformly mixing the antibacterial composite polylactic acid matrix and modified montmorillonite nanofiller, melt copolymerizing by using a double-screw extruder, extruding and granulating, and then vacuum drying to obtain the antibacterial modified polylactic acid for packaging material.

[0012] Further, the temperature of melt copolymerization is 170-185 DEG C, and the time is 5-10 min.

[0013] Further, the mass ratio of the antibacterial composite polylactic acid matrix and the modified montmorillonite nanofiller is 40-60:1-3.

[0014] Further, the preparation steps of the antibacterial modifier are as follows.

[0015] Placing L-lysine modified polyether amide, ethyl acetate and a 1 mol / L hydrochloric acid ethyl acetate solution in a reaction kettle, stirring at room temperature for 8-12 h, centrifuging to collect the solid after the reaction is completed, washing and drying, extracting the dried product, collecting the organic phase, filtering, and rotary evaporating the filtrate to remove the solvent to obtain the antibacterial modifier.

[0016] Further, the ratio of the amount of L-lysine modified polyether amide, the hydrochloric acid ethyl acetate solution and ethyl acetate is 20-40 g:100-200 mL:40-60 mL.

[0017] Further, the preparation steps of the L-lysine modified polyether amide are as follows:

[0018] The double tert-butyloxycarbonyl-L-lysine and dichloromethane are stirred in a reaction kettle protected by nitrogen atmosphere, the reaction kettle is cooled to 0-5℃, triethylamine and isobutyl chloroformate are sequentially added, after stirring at room temperature for 1-3h, polyether amine T403 is added, and the stirring is continued at room temperature for 8-12h, after the reaction is completed, potassium bisulfate is added, and stirred for 10-30min, extraction is performed, the organic phase is collected, filtered, and transferred to a rotary evaporator with a temperature of 50-60℃, and rotary evaporation is performed until the solvent is completely removed, to obtain the L-lysine modified polyether amide.

[0019] Further, the amount ratio of the double tert-butyloxycarbonyl-L-lysine, triethylamine, isobutyl chloroformate, polyether amine T403, potassium bisulfate, and dichloromethane is 30-50g:10-15g:10-15mL:25-45g:10-15g:60-100mL.

[0020] Further, the preparation steps of the antibacterial composite polylactic acid matrix are as follows:

[0021] The modified polylactic acid matrix and N,N dimethylformamide are added to a reaction kettle, heated and dissolved at 40-50℃ until the reaction solution is clear, and then the antibacterial modifier, triethylamine, and potassium iodide are sequentially added, and the reaction is carried out at 50-70℃ for 1-3h under nitrogen protection, and after the reaction is completed, the reaction solution is cooled to room temperature, filtered, and the filtrate is added to anhydrous methanol to precipitate and separate, filtered, washed, and vacuum dried to obtain the antibacterial composite polylactic acid matrix.

[0022] Further, the amount ratio of the modified polylactic acid matrix, the antibacterial modifier, triethylamine, potassium iodide, N,N dimethylformamide, and anhydrous methanol is 60-100g:8-12g:1-1.5g:0.1-0.2g:100-150mL:600-800mL.

[0023] Further, the preparation steps of the modified polylactic acid matrix are as follows:

[0024] The chloro end group initiator and L-lactide are placed in a reaction kettle, and stannous octoate is added, a reduced pressure distillation device is connected and magnetic stirring is performed, and the reaction is carried out at 150-170℃ for 4-6h, after the reaction is completed, the product is dissolved in dichloromethane and then added to anhydrous methanol to precipitate and separate, filtered, washed, and vacuum dried to obtain the modified polylactic acid matrix containing a chlorine end group.

[0025] Further, the amount ratio of the chloro end group initiator, L-lactide, stannous octoate, dichloromethane, and anhydrous methanol is 0.8-1.2g:80-120g:100-120mg:400-600mL:100-200mL.

[0026] Further, the preparation steps of the chloro end group initiator are as follows:

[0027] After the ethanolamine is dissolved in dichloromethane, the reaction kettle is filled with the ethanolamine, and a chloroacetyl chloride solution and a 0.2 mol / L sodium hydroxide aqueous solution are added; stirring is performed at 25-35 DEG C, and the reaction is performed for 10-30 min; after the reaction is completed, the reaction liquid is poured into a separatory funnel to be separated, and the lower dichloromethane liquid is distilled under reduced pressure to remove excess solvent, so that the chloro end group initiator is obtained.

[0028] Further, the amount ratio of the ethanolamine, the chloroacetyl chloride solution, the sodium hydroxide aqueous solution and the dichloromethane is 8-12 g:40-60 mL:40-60 mL:60-80 mL; the chloroacetyl chloride solution is composed of chloroacetyl chloride and dichloromethane in a volume ratio of 1:3.

[0029] Further, the preparation steps of the modified montmorillonite nanofiller are as follows:

[0030] The modified montmorillonite nanofiller is obtained by stirring the modified montmorillonite nanoprecursor, gamma-aminopropyl triethoxysilane, ethanol and deionized water in a reaction kettle, adding a 0.5 mol / L acetic acid aqueous solution, heating the reaction kettle to 50-60 DEG C, and performing heat preservation reaction for 2-4 h; after the reaction is completed, the reaction system is cooled to room temperature, and filtration, washing and vacuum drying are performed.

[0031] Further, the amount ratio of the modified montmorillonite nanoprecursor, gamma-aminopropyl triethoxysilane, the acetic acid aqueous solution, ethanol and deionized water is 5-10 g:0.5-1 g:2-4 mL:50-100 mL:5-10 mL.

[0032] Further, the preparation steps of the modified montmorillonite nanoprecursor are as follows:

[0033] The modified montmorillonite nanoprecursor is obtained by stirring sodium-based montmorillonite and deionized water in a reaction kettle at 70-80 DEG C for 1-2 h, adding tetrabutylphosphonium bromide, and stirring at 75-85 DEG C for 3-5 h; after the reaction is completed, hot filtration, washing and vacuum drying are performed.

[0034] Further, the amount ratio of the sodium-based montmorillonite, tetrabutylphosphonium bromide and deionized water is 10-20 g:3-6 g:100-200 mL.

[0035] The beneficial effects of the present application are as follows:

[0036] 1. The application constructs a polylactic acid composite material with high barrier property, high strength, excellent antibacterial property and good degradability through multi-step chemical modification. Ethanolamine reacts with chloroacetyl chloride to generate an initiator containing a chlorine end group, which is used as an initiation source for ring-opening polymerization and reacts with L-lactide under stannous octoate catalysis to form an active polylactic acid chain. The chlorine end group of polylactic acid reacts with an antibacterial modifier under the action of triethylamine and potassium iodide to form a stable covalent bond, achieving grafting of the antibacterial molecule on the polylactic acid backbone and imparting long-term antibacterial properties to the material. The material is melt blended with modified montmorillonite nanofiller, the montmorillonite layers are uniformly dispersed in the polylactic acid matrix to form a barrier structure, significantly improving the gas barrier property, the Si-O-Si bond and hydrogen bond between the layers and the polylactic acid enhance the interfacial bonding, improving the tensile strength, and the polylactic acid backbone structure remains intact, still having excellent biodegradability, achieving the synergistic integration of high strength, high barrier, antibacterial and degradability.

[0037] 2. The modified montmorillonite nanofiller prepared in the application has an interlayer structure changed from hydrophilic to organic compatibility through organophosphonium salt intercalation and silane coupling modification, significantly improving the dispersibility and interfacial bonding force with the polylactic acid matrix. In the intercalation reaction, the organophosphonium cation replaces the interlayer sodium ions, expanding the interlayer distance. The hydrolysis of γ-aminopropyltriethoxysilane generates silanol, which condenses with the surface hydroxyl groups of montmorillonite to form Si-O-Si covalent bonds, making the filler surface have an active silane layer that can form hydrogen bonds or van der Waals forces with the polylactic acid molecular chain, forming a uniformly dispersed layered barrier in the material, thereby significantly improving the oxygen and water vapor barrier properties. At the same time, the high rigidity of the montmorillonite layers and the interfacial chemical bonding together improve the stress transfer efficiency and load bearing capacity of the polylactic acid matrix, enhancing the tensile strength and structural stability.

[0038] 3. The application realizes high-efficiency and long-lasting antibacterial performance by introducing an antibacterial modifier to the polylactic acid end group. The nucleophilic substitution of the chlorine end group of polylactic acid is promoted by triethylamine and potassium iodide, forming a stable covalent bond with the antibacterial modifier containing active amino groups, making the antibacterial groups firmly grafted to the polymer backbone, avoiding the problems of easy migration and failure in traditional physical blending. The antibacterial modifier is derived from lysine cationic structure, and its positive charge can produce electrostatic interaction with the anionic groups on the bacterial cell membrane, destroy the cell membrane permeability and cause the loss of cell contents, achieving bactericidal and bacteriostatic effects. At the same time, the grafting structure ensures uniform distribution of the antibacterial components in the polylactic acid matrix, forming a long-acting and stable antibacterial interface, significantly improving the antibacterial rate of the material. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0040] Embodiment 1: The present embodiment provides an antibacterial modifier for packaging materials, which is prepared by the following steps:

[0041] S1: 30g of bis-tert-butyloxycarbonyl-L-lysine and 60mL of dichloromethane were placed in a reaction kettle protected by nitrogen atmosphere and stirred, the reaction kettle was cooled to 0℃, 10g of triethylamine and 10mL of isobutyl chloroformate were added in turn, after stirring at room temperature for 1h, 25g of polyetheramine T403 was added, and the stirring was continued at room temperature for 8h, after the reaction was completed, 10g of potassium bisulfate was added, stirred for 10min, extracted with saturated sodium bicarbonate solution and dichloromethane twice, the organic phase was collected, filtered to remove impurities, and the filtrate was transferred to a rotary evaporator with a temperature of 50℃, rotary evaporation was performed until the solvent was completely removed, and L-lysine modified polyether amide was obtained.

[0042] S2: 20g of L-lysine modified polyether amide and 40mL of ethyl acetate were placed in a reaction kettle, 100mL of 1mol / L hydrochloric acid ethyl acetate solution was added, and stirred at room temperature for 8h, after the reaction was completed, the solid was collected by centrifugation and washed with diethyl ether twice, and vacuum dried at 40℃, the product after vacuum drying was extracted twice with the extraction liquid, the organic phase was collected, filtered to remove impurities, and the filtrate was transferred to a rotary evaporator with a temperature of 50℃, rotary evaporation was performed until the solvent was completely removed, and an antibacterial modifier was obtained.

[0043] The extraction liquid is a mixture of 15% sodium hydroxide aqueous solution and ethyl acetate in a volume ratio of 1:2.

[0044] Embodiment 2: The present embodiment provides an antibacterial modifier for packaging materials, which is prepared by the following steps:

[0045] S1: 40g of bis-tert-butyloxycarbonyl-L-lysine and 80mL of dichloromethane were placed in a reaction kettle protected by nitrogen atmosphere and stirred, the reaction kettle was cooled to 3℃, 12g of triethylamine and 12mL of isobutyl chloroformate were added in turn, after stirring at room temperature for 2h, 35g of polyetheramine T403 was added, and the stirring was continued at room temperature for 10h, after the reaction was completed, 12g of potassium bisulfate was added, stirred for 20min, extracted with saturated sodium bicarbonate solution and dichloromethane three times, the organic phase was collected, filtered to remove impurities, and the filtrate was transferred to a rotary evaporator with a temperature of 55℃, rotary evaporation was performed until the solvent was completely removed, and L-lysine modified polyether amide was obtained.

[0046] S2: 20 g of L-lysine modified polyether amide and 40 mL of ethyl acetate were placed in a reaction kettle, 150 mL of ethyl acetate hydrochloric acid solution with a concentration of 1 mol / L was added, stirred at room temperature for 10 h, after the reaction was completed, the solid was collected by centrifugation and washed with ether 3 times, vacuum dried at 45 DEG C, the product after vacuum drying was extracted with the extraction liquid 3 times, the organic phase was collected, filtered to remove impurities, the filtrate was transferred to a rotary evaporator with a temperature of 50 DEG C, and rotary evaporation was performed until the solvent was completely removed to obtain an antibacterial modifier.

[0047] The extraction liquid is mixed by 15% sodium hydroxide aqueous solution and ethyl acetate in a volume ratio of 1:2.

[0048] Example 3: The antibacterial modifier for packaging material is prepared by the following steps:

[0049] S1: 50 g of bis-tert-butoxycarbonyl-L-lysine and 100 mL of dichloromethane were placed in a reaction kettle protected by nitrogen atmosphere and stirred, the reaction kettle was cooled to 5 DEG C, 15 g of triethylamine and 15 mL of isobutyl chloroformate were added in turn, after stirring at room temperature for 3 h, 45 g of polyether amine T403 was added, and the stirring was continued at room temperature for 12 h, after the reaction was completed, 15 g of potassium bisulfate was added, stirred for 30 min, extracted with saturated sodium bicarbonate solution and dichloromethane 4 times, the organic phase was collected, filtered to remove impurities, the filtrate was transferred to a rotary evaporator with a temperature of 60 DEG C, and rotary evaporation was performed until the solvent was completely removed to obtain L-lysine modified polyether amide.

[0050] S2: 20 g of L-lysine modified polyether amide and 40 mL of ethyl acetate were placed in a reaction kettle, 200 mL of ethyl acetate hydrochloric acid solution with a concentration of 1 mol / L was added, stirred at room temperature for 12 h, after the reaction was completed, the solid was collected by centrifugation and washed with ether 4 times, vacuum dried at 50 DEG C, the product after vacuum drying was extracted with the extraction liquid 4 times, the organic phase was collected, filtered to remove impurities, the filtrate was transferred to a rotary evaporator with a temperature of 50 DEG C, and rotary evaporation was performed until the solvent was completely removed to obtain an antibacterial modifier.

[0051] The extraction liquid is mixed by 15% sodium hydroxide aqueous solution and ethyl acetate in a volume ratio of 1:2.

[0052] In the above examples 1-3, the prepared antibacterial agent is an amino acid-polyether type composite antibacterial modifier, which is prepared by activating bis-tert-butoxycarbonyl-L-lysine with isobutyl chloroformate, then reacting with the primary amine group of polyether amine T403 to form a stable C-N bond, and then removing the Boc protecting group by acid to expose the free amino group as an active site for the next reaction.

[0053] Example 4: The modified montmorillonite nanofiller for packaging material is prepared by the following steps:

[0054] S1: 10 g of sodium-based montmorillonite and 100 mL of deionized water were placed in a reaction kettle, stirred at 70°C for 1 h, 3 g of tetrabutylphosphonium bromide was added, stirred at 75°C for 3 h, after the reaction was completed, hot filtration was performed, the filter cake was washed with deionized water and ethanol for 2 times, and was transferred to an oven with a temperature of 50°C, and dried for 12 h to obtain a modified montmorillonite nano precursor.

[0055] S2: 5 g of the modified montmorillonite nano precursor, 0.5 g of γ-aminopropyl triethoxysilane, 50 mL of ethanol and 5 mL of deionized water were placed in a reaction kettle and stirred, 2 mL of 0.5 mol / L acetic acid aqueous solution was added, the reaction kettle was heated to 50°C, and the reaction was kept for 2 h, after the reaction was completed, the reaction system was cooled to room temperature, suction filtration was performed, the filter cake was washed with deionized water and ethanol for 2 times, and was transferred to an oven with a temperature of 50°C, and dried to constant weight to obtain a modified montmorillonite nano filler.

[0056] Example 5: The present example provides a modified montmorillonite nano filler for packaging materials, which is prepared by the following steps:

[0057] S1: 15 g of sodium-based montmorillonite and 150 mL of deionized water were placed in a reaction kettle, stirred at 75°C for 1.5 h, 4.5 g of tetrabutylphosphonium bromide was added, stirred at 80°C for 4 h, after the reaction was completed, hot filtration was performed, the filter cake was washed with deionized water and ethanol for 3 times, and was transferred to an oven with a temperature of 55°C, and dried for 14 h to obtain a modified montmorillonite nano precursor.

[0058] S2: 8 g of the modified montmorillonite nano precursor, 0.8 g of γ-aminopropyl triethoxysilane, 80 mL of ethanol and 8 mL of deionized water were placed in a reaction kettle and stirred, 3 mL of 0.5 mol / L acetic acid aqueous solution was added, the reaction kettle was heated to 55°C, and the reaction was kept for 3 h, after the reaction was completed, the reaction system was cooled to room temperature, suction filtration was performed, the filter cake was washed with deionized water and ethanol for 3 times, and was transferred to an oven with a temperature of 55°C, and dried to constant weight to obtain a modified montmorillonite nano filler.

[0059] Example 6: The present example provides a modified montmorillonite nano filler for packaging materials, which is prepared by the following steps:

[0060] S1: 20 g of sodium-based montmorillonite and 200 mL of deionized water were placed in a reaction kettle, stirred at 80°C for 2 h, 6 g of tetrabutylphosphonium bromide was added, stirred at 85°C for 5 h, after the reaction was completed, hot filtration was performed, the filter cake was washed with deionized water and ethanol for 4 times, and was transferred to an oven with a temperature of 60°C, and dried for 16 h to obtain a modified montmorillonite nano precursor.

[0061] S2: 10 g of modified montmorillonite nanometer precursor, 1 g of γ-aminopropyl triethoxysilane, 100 mL of ethanol and 10 mL of deionized water were placed in a reaction kettle and stirred, 4 mL of 0.5 mol / L acetic acid aqueous solution was added, the reaction kettle was heated to 60℃, and the reaction was kept for 4 h. After the reaction was completed, the reaction system was cooled to room temperature, and then filtered, the filter cake was washed with deionized water and ethanol for 4 times, and then transferred to an oven with a temperature of 60℃, and dried to constant weight to obtain the modified montmorillonite nanofiller.

[0062] In the above examples 4-6, the prepared modified montmorillonite nanofiller is realized by two-step chemical reactions of organic intercalation and silane coupling. The organic phosphonium cation produced by ionization of tetrabutylphosphonium bromide in solution exchanges with sodium ions in the interlayer of montmorillonite, so that the organic cation is inserted into the interlayer, thereby increasing the interlayer spacing and forming organomontmorillonite. The intermediate containing silicon alcohol groups is generated by hydrolysis of γ-aminopropyl triethoxysilane under the catalysis of acetic acid, and the condensation reaction occurs between the silicon alcohol groups and the hydroxyl groups on the surface of the montmorillonite sheet, generating stable Si–O–Si covalent bonds, while the terminal amino propyl group remains active and can interact with the polymer matrix through hydrogen bonding or chemical bonding.

[0063] Example 7: The present example provides an antibacterial modified polylactic acid for packaging material, which is prepared by the following steps:

[0064] S1: 8 g of ethanolamine was dissolved in 60 mL of dichloromethane and then placed in a reaction kettle, 40 mL of chloroacetyl chloride solution and 40 mL of 0.2 mol / L sodium hydroxide aqueous solution were added, and stirring was performed at 25℃ for 10 min. After the reaction was completed, the reaction liquid was poured into a separatory funnel for liquid separation, and the lower dichloromethane liquid was distilled under reduced pressure to remove excess solvent to obtain a chloro-terminated initiator.

[0065] S2: 0.8 g of chloro-terminated initiator and 80 g of L-lactide were added to a reaction kettle, 100 mg of stannous octoate was added, a vacuum distillation device was connected and magnetic stirring was performed, and the reaction was performed at 150℃ for 4 h. After the reaction was completed, the product was dissolved in 400 mL of dichloromethane and then added to 100 mL of anhydrous methanol to precipitate a precipitate, which was filtered, washed with n-heptane for 2 times, and then transferred to an oven with a temperature of 50℃, and dried to constant weight to obtain a modified polylactic acid matrix containing chlorine in the terminal group.

[0066] S3: 60 g of the modified polylactic acid base was added to a reaction kettle, dissolved in 100 mL of N,N-dimethylformamide as a solvent at 40°C until the reaction solution was clear, 8 g of the antibacterial modifier prepared in Example 1 above, 1 g of triethylamine, and 0.1 g of potassium iodide were sequentially added, and the reaction was performed at 50°C for 1 h under nitrogen protection. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was precipitated by adding 600 mL of anhydrous methanol. The precipitate was filtered, washed with n-heptane twice, and dried at 40°C under vacuum for 18 h to obtain an antibacterial composite polylactic acid base.

[0067] S4: 40 g of the antibacterial composite polylactic acid base was uniformly mixed with 1 g of the modified montmorillonite nanofiller prepared in Example 4 above, melt blended in a twin-screw extruder at 170°C for 5 min, extruded, and pelletized. After vacuum drying at 40°C for 8 h, an antibacterial modified polylactic acid for packaging material was obtained.

[0068] Example 8: An antibacterial modified polylactic acid for packaging material was prepared by the following steps:

[0069] S1: 10 g of ethanolamine was dissolved in 70 mL of dichloromethane and then added to a reaction kettle. 50 mL of a chloroacetyl chloride solution and 50 mL of a 0.2 mol / L sodium hydroxide aqueous solution were added, and stirring was performed at 30°C for 20 min. After the reaction was completed, the reaction solution was separated into layers in a separatory funnel, and the lower dichloromethane layer was distilled under reduced pressure to remove excess solvent to obtain a chloro-end group initiator.

[0070] S2: 1 g of the chloro-end group initiator and 100 g of L-lactide were added to a reaction kettle, 110 mg of stannous octoate was added, a vacuum distillation device was connected, and magnetic stirring was performed at 160°C for 5 h. After the reaction was completed, the product was dissolved in 500 mL of dichloromethane and then added to 150 mL of anhydrous methanol to precipitate and separate. The precipitate was filtered, washed with n-heptane three times, and then transferred to an oven at 55°C to dry to constant weight to obtain a modified polylactic acid base having a chloro-end group.

[0071] S3: 80 g of the modified polylactic acid base was added to a reaction kettle, dissolved in 120 mL of N,N-dimethylformamide as a solvent at 45°C until the reaction solution was clear, 10 g of the antibacterial modifier prepared in Example 2 above, 1.2 g of triethylamine, and 0.15 g of potassium iodide were sequentially added, and the reaction was performed at 60°C for 2 h under nitrogen protection. After the reaction was completed, the reaction solution was cooled to room temperature, filtered, and the filtrate was precipitated by adding 700 mL of anhydrous methanol. The precipitate was filtered, washed with n-heptane three times, and dried at 50°C under vacuum for 21 h to obtain an antibacterial composite polylactic acid base.

[0072] S4: 50 g of the antibacterial composite polylactic acid base was uniformly mixed with 2 g of the modified montmorillonite nanofiller prepared in Example 5 above, and melt blended in a twin-screw extruder at 180°C for 8 min. The material was discharged, cooled and extruded into granules. After vacuum drying at 50°C for 10 h, an antibacterial modified polylactic acid for packaging material was obtained.

[0073] Example 9: An antibacterial modified polylactic acid for packaging material was prepared by the following steps:

[0074] S1: 12 g of ethanolamine was dissolved in 80 mL of dichloromethane and placed in a reaction kettle. 60 mL of a chloroacetyl chloride solution and 60 mL of a 0.2 mol / L sodium hydroxide aqueous solution were added, and stirring was performed at 35°C. After 30 min of reaction, the reaction liquid was poured into a separatory funnel for liquid separation. The lower dichloromethane liquid was distilled under reduced pressure to remove excess solvent, and a chloro-end group initiator was obtained.

[0075] S2: 1.2 g of the chloro-end group initiator and 120 g of L-lactide were added to a reaction kettle. 120 mg of stannous octoate was added, a vacuum distillation device was connected, and magnetic stirring was performed at 170°C for 6 h. After the reaction was completed, the product was dissolved in 600 mL of dichloromethane and then added to 200 mL of anhydrous methanol to precipitate a sediment. The sediment was filtered, washed with n-heptane 4 times, and transferred to an oven at 60°C for drying to constant weight. A modified polylactic acid base containing a chloro-end group was obtained.

[0076] S3: 100 g of the modified polylactic acid base was added to a reaction kettle, and 150 mL of N,N-dimethylformamide was used as a solvent to heat and dissolve the reaction liquid until it was clear at 50°C. 12 g of the antibacterial modifier prepared in Example 3 above, 1.5 g of triethylamine, and 0.2 g of potassium iodide were sequentially added. The reaction was performed at 70°C for 3 h under nitrogen protection. After the reaction was completed, the reaction liquid was cooled to room temperature and filtered. The filtrate was added to 800 mL of anhydrous methanol to precipitate and separate out a sediment. The sediment was filtered, washed with n-heptane 4 times, and vacuum dried at 60°C for 24 h. An antibacterial composite polylactic acid base was obtained.

[0077] S4: 60 g of the antibacterial composite polylactic acid base was uniformly mixed with 3 g of the modified montmorillonite nanofiller prepared in Example 6 above, and melt blended in a twin-screw extruder at 185°C for 10 min. The material was discharged, cooled and extruded into granules. After vacuum drying at 60°C for 12 h, an antibacterial modified polylactic acid for packaging material was obtained.

[0078] In Examples 7-9, the antibacterial modified polylactic acid for packaging material is prepared by a reaction process including four chemical stages of initiator preparation, ring-opening polymerization, graft modification and melt blending in sequence. Ethanolamine is amidated with chloroacetyl chloride to form a chloro-terminated initiator, which provides active sites for subsequent polymerization. In the presence of stannous octoate as a catalyst, the initiator initiates ring-opening polymerization of L-lactide to form a chloro-terminated polylactic acid. The chloro-terminated group is covalently bonded to the amino group in the antibacterial modifier through nucleophilic substitution promoted by triethylamine and potassium iodide, achieving stable grafting of the antibacterial group. Finally, the modified montmorillonite is melt blended to form a composite system with both antibacterial properties and high barrier properties through enhanced interfacial interaction by hydrogen bonding and van der Waals forces.

[0079] Comparative Example 1: On the basis of Example 8, ethanolamine in step S1 is used instead of the chloro-terminated initiator in step S2, and the remaining steps remain unchanged, to prepare an antibacterial modified polylactic acid for packaging material.

[0080] Comparative Example 2: On the basis of Example 8, the antibacterial modifier prepared in Example 2 is removed in step S3, and the remaining steps remain unchanged, to prepare an antibacterial modified polylactic acid for packaging material.

[0081] Comparative Example 3: On the basis of Example 8, the modified montmorillonite nanofiller prepared in Example 5 is removed in step S4, and the remaining steps remain unchanged, to prepare an antibacterial modified polylactic acid for packaging material.

[0082] The antibacterial modified polylactic acid for packaging material prepared in Examples 7-9 and Comparative Examples 1-3 is prepared into a film, and then performance testing is carried out. The test results are shown in Table 1.

[0083] Film preparation: 5 g of the antibacterial modified polylactic acid prepared under the above conditions is dissolved in 45 mL of dichloromethane, and stirred magnetically at room temperature for 3 h until clear. After ultrasonic debubbling, the solution is poured onto a glass plate and evenly spread on the glass plate with a glass rod. It is placed in a fume hood for 4 h for preliminary evaporation, and then placed in a 60°C vacuum drying oven for 12 h to remove the remaining solvent. After cooling, it is slowly peeled off from the substrate and cut into a 15 cm x 15 cm film with a thickness of about 20 μm.

[0084] The test methods for each film are as follows:

[0085] Tensile strength determination method: tested by tensile testing machine method according to the standard in “ASTM D882”.

[0086] Barrier property determination method: oxygen transmission rate is tested by coulomb oxygen sensor method according to the standard in “ASTM D3985”, and water vapor transmission rate is tested by modulated infrared sensor method according to the standard in “ASTM F1249”.

[0087] Degradability determination method: according to the standard in ASTM D5338-15, the biodegradation rate of the material is calculated by measuring the amount of carbon dioxide produced by microbial degradation in a composting environment.

[0088] Antibacterial property determination method: tested according to GB / T 21866-200 standard, tested by film covering method, and the strain number of Escherichia coli is ATCC 8739, and the strain number of Staphylococcus aureus is ATCC 6538.

[0089] Table 1 Performance test table of antibacterial modified polylactic acid for packaging materials

[0090]

[0091] It can be seen from Table 1 that the tensile strength, barrier property, degradability and antibacterial property of Comparative Example 1 are lower than those of Examples 7-9, which shows that the chloro end group initiator can introduce active chloro end groups, so that the antibacterial modifier can undergo nucleophilic substitution reaction with polylactic acid to form stable C-N covalent bond, realize chemical grafting of antibacterial component, and the antibacterial component is firmly fixed to prevent migration and loss, the bacteriostatic rate is persistent and stable, and the introduced amino acid and polyether amide structure maintain good biocompatibility, do not affect the degradability of polylactic acid, at the same time, the interface is tightly combined, the barrier property is improved, and the performance of the film material is obviously improved.

[0092] The bacteriostatic rate of Comparative Example 2 decreases significantly, which shows that the amino acid-polyether type composite antibacterial modifier prepared by the application has biological activity and structural stability, the positive charge amino group in the lysine molecule can have electrostatic interaction with the negative charge phospholipid on the surface of the bacterial membrane, destroy the cell membrane structure, lead to leakage of cell contents and realize high-efficiency bacteriostasis, the polyether amine segment endows the molecule with flexibility and good dispersibility, enhances the contact efficiency of the antibacterial group and bacteria, and the two are covalently combined through an amide bond, so that the antibacterial component is not easy to migrate and lose, a persistent and non-releasing antibacterial system is formed, and the antibacterial material has high efficiency, safety and long-acting property, so that the antibacterial performance of the film material is significantly improved.

[0093] The tensile strength and barrier property of Comparative Example 3 decrease significantly, which shows that the montmorillonite nanofiller prepared by the application and synergistically modified by organic phosphonium salt and silane has excellent barrier property and mechanical enhancement effect, the tetrabutyl phosphonium cation enters the interlayer of the montmorillonite through ion exchange, significantly improves the organic compatibility and interlayer spacing of the layer, and enhances the barrier property, the γ-aminopropyl triethoxysilane forms Si-O-Si covalent bond with the surface of the montmorillonite after hydrolysis and condensation, the amino end interacts with the polymer matrix to enhance the interface bonding and stress transfer, and significantly improves the tensile strength and toughness of the composite material.

[0094] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and changes can be made by those skilled in the art without departing from the spirit and principles of the present application.

Claims

1. A method for producing an antibacterial modified polylactic acid for packaging material, characterized by, The method comprises the following steps: Step one: after activation of bis-tert-butyloxycarbonyl-L-lysine with isobutyl chloroformate, condensation with polyether amine T403, deprotection, extraction, drying and purification, an antibacterial modifier is obtained; Step two: using L-lactide as raw material, stannous octoate as catalyst, adding a chloro end group initiator for ring-opening polymerization, a modified polylactic acid matrix containing a chlorine end group is synthesized, and then the modified polylactic acid matrix containing a chlorine end group is grafted with the antibacterial modifier to obtain an antibacterial composite polylactic acid matrix; Step three: after the antibacterial composite polylactic acid matrix and the modified montmorillonite nanofiller are uniformly mixed, they are melt copolymerized through a double-screw extruder, extruded and granulated, and then vacuum dried to obtain an antibacterial modified polylactic acid for packaging materials; The preparation process of the antibacterial modifier in step one is as follows: bis-tert-butyloxycarbonyl-L-lysine and dichloromethane are placed in a reaction kettle under nitrogen atmosphere protection and stirred, the reaction kettle is cooled to 0-5℃, triethylamine and isobutyl chloroformate are sequentially added, stirring at room temperature for 1-3h, polyether amine T403 is added, stirring at room temperature for 8-12h, potassium hydrogen sulfate is added, stirring for 10-30min, extraction, collection of organic phase, filtration, rotary evaporation of the filtrate to remove the solvent, and then L-lysine modified polyether amide is obtained; L-lysine modified polyether amide, ethyl acetate and 1mol / L hydrochloric acid ethyl acetate solution are placed in a reaction kettle, stirring at room temperature for 8-12h, centrifugal collection of solid, washing, drying, extraction of the dried product, collection of organic phase, filtration, rotary evaporation of the filtrate to remove the solvent, and then the antibacterial modifier is obtained; The preparation process of the chloro end group initiator is as follows: ethanolamine is dissolved in dichloromethane and placed in a reaction kettle, a chloroacetyl chloride solution and 0.2mol / L sodium hydroxide aqueous solution are added at the same time, reaction is carried out at 25-35℃ for 10-30min, the reaction liquid is separated, the lower dichloromethane liquid is distilled under reduced pressure to remove the solvent, and then the chloro end group initiator is obtained; The preparation process of the modified montmorillonite nanofiller in step three is as follows: modified montmorillonite nanoprecursor, γ-aminopropyltriethoxysilane, ethanol and deionized water are placed in a reaction kettle and stirred, 0.5mol / L acetic acid aqueous solution is added, reaction is carried out at 50-60℃ for 2-4h, the reaction system is cooled to room temperature, filtration is carried out, washing is carried out, and vacuum drying is carried out until the weight is constant, and then the modified montmorillonite nanofiller is obtained; The preparation process of the modified montmorillonite nanoprecursor is as follows: sodium-based montmorillonite and deionized water are placed in a reaction kettle, reaction is carried out at 70-80℃ for 1-2h, tetrabutylphosphonium bromide salt is added, reaction is carried out at 75-85℃ for 3-5h, hot filtration is carried out, washing is carried out, and vacuum drying is carried out, and then the modified montmorillonite nanoprecursor is obtained.

2. The method for preparing an antibacterial modified polylactic acid for a packaging material according to claim 1, characterized by, The amount ratio of the L-lysine modified polyether amide, ethyl acetate solution and ethyl acetate is 20-40g:100-200mL:40-60mL.

3. The method of claim 1, wherein the antibacterial modified polylactic acid for a packaging material is prepared by adding 0.1 to 5 parts by weight of the antibacterial agent to 100 parts by weight of the polylactic acid. The amount ratio of the bis-tert-butoxycarbonyl-L-lysine, triethylamine, isobutyl chloroformate, polyether amine T403, potassium bisulfate and dichloromethane is 30-50 g:10-15 g:10-15 mL:25-45 g:10-15 g:60-100 mL.

4. The method of claim 1, wherein the antibacterial modified polylactic acid for a packaging material is prepared by adding 0.1 to 5 parts by weight of the antibacterial agent to 100 parts by weight of the polylactic acid. The preparation process of the modified polylactic acid matrix in step two is as follows: The chloro end group initiator and L-lactide are put into a reaction kettle, stannous octoate is added, a reduced pressure distillation device is connected and magnetic stirring is conducted, and the reaction is carried out at 150-170 ℃ for 4-6 h, then the product is dissolved in dichloromethane and precipitated by adding anhydrous methanol, filtered, washed and vacuum dried to obtain the modified polylactic acid matrix. The amount ratio of the chloro end group initiator, L-lactide, stannous octoate, dichloromethane and anhydrous methanol is 0.8-1.2 g:80-120 g:100-120 mg:400-600 mL:100-200 mL.

5. The method of claim 1, wherein the antibacterial modified polylactic acid for a packaging material is prepared by adding 0.1 to 5 parts by weight of the antibacterial agent to 100 parts by weight of the polylactic acid. The amount ratio of the ethanolamine, chloroacetyl chloride solution, sodium hydroxide aqueous solution and dichloromethane is 8-12 g:40-60 mL:40-60 mL:60-80 mL; the chloroacetyl chloride solution is composed of chloroacetyl chloride and dichloromethane in a volume ratio of 1:

3.

6. The method of claim 1, wherein the antibacterial modified polylactic acid for a packaging material is prepared by adding 0.1 to 5 parts by weight of the antibacterial agent to 100 parts by weight of the polylactic acid. The preparation process of the antibacterial composite polylactic acid matrix in step two is as follows: The modified polylactic acid matrix and N,N dimethylformamide are added into a reaction kettle, heated and dissolved at 40-50 ℃ until the reaction solution is clear, the antibacterial modifier, triethylamine and potassium iodide are sequentially added, the reaction is carried out at 50-70 ℃ for 1-3 h under nitrogen protection, cooled to room temperature, filtered, the filtrate is precipitated by adding anhydrous methanol, filtered, washed and vacuum dried to obtain the antibacterial composite polylactic acid matrix. The amount ratio of the modified polylactic acid matrix, antibacterial modifier, triethylamine, potassium iodide, N,N dimethylformamide and anhydrous methanol is 60-100 g:8-12 g:1-1.5 g:0.1-0.2 g:100-150 mL:600-800 mL.

7. The method of claim 1, wherein the antibacterial modified polylactic acid for a packaging material is prepared by adding 0.1 to 5 parts by weight of the antibacterial agent to 100 parts by weight of the polylactic acid. The amount ratio of the modified montmorillonite nanometer precursor, γ-aminopropyl triethoxysilane, acetic acid aqueous solution, ethanol and deionized water is 5-10 g:0.5-1 g:2-4 mL:50-100 mL:5-10 mL.

8. The method of claim 1, wherein the antibacterial modified polylactic acid for a packaging material is prepared by adding 0.1 to 5 parts by weight of the antibacterial agent to 100 parts by weight of the polylactic acid. The amount ratio of the sodium-based montmorillonite, tetrabutylphosphonium bromide and deionized water is 10-20 g:3-6 g:100-200 mL.

9. The method for preparing antibacterial modified polylactic acid for packaging materials according to claim 1, characterized in that, The temperature of the melt copolymerization in step three is 170-185 ℃, and the time is 5-10 min.

10. The method for preparing antibacterial modified polylactic acid for packaging materials according to claim 1, characterized in that, The mass ratio of the antibacterial composite polylactic acid matrix and the modified montmorillonite nanofiller is 40-60:1-3.

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