Intelligent response type EVOH packaging material as well as preparation method and application thereof

Abstract

The invention discloses an EVOH packaging material with long-acting antibacterial and antioxidant functions and a preparation method of the EVOH packaging material, wherein the EVOH packaging material is obtained on the basis of a dynamic molecular switch and a microcapsule targeted release technology. The material comprises an EVOH matrix (A), an environmental response type molecular switch polymer (B) and an intelligent microcapsule (C) sensitive to at least one putrefying biomarker, and a compatibilizer (D). In a normal state, the molecular switch is turned off, and the release of the active agent is inhibited; when the environment humidity is increased or the concentration of the putrefying biomarker is changed, the molecular switch is turned on, and the microcapsule is disintegrated in a targeted manner, so that the efficient and intelligent release of active substances is realized. The material can prolong the effective period of an active agent by more than 300%, realizes accurate intervention on food spoilage, and is suitable for the field of high-end intelligent packaging.

Description

TECHNICAL FIELD

[0001] The present application relates to an EVOH composite material capable of responding to environmental stimuli and intelligently controlling the release of functional active agents, and a preparation method thereof, which is particularly suitable for packaging scenarios such as food and medicine that require long-term antibacterial and antioxidant protection. BACKGROUND

[0002] Ethylene-vinyl alcohol copolymer (EVOH) is widely used in the packaging field due to its excellent gas barrier properties. In order to endow it with additional functions such as antibacterial and antioxidant properties, the prior art usually directly blends or simply embeds functional active agents (such as silver ions, plant essential oils, etc.) into the EVOH matrix.

[0003] However, this passive release mode has inherent defects:

[0004] 1. Uncontrollable release: the active agents are continuously and indiscriminately released throughout the life cycle of the packaging, resulting in a large amount of loss during the stage when its function is not needed (such as the fresh period of food), and insufficient activity during the stage when its function is needed (such as the early stage of spoilage).

[0005] 2. Low efficiency: more than 60% of the active agents are wasted in the early stage, and the effective action period is short.

[0006] 3. Potential risk: premature or excessive migration of active agents may affect the flavor of the contents or pose a safety risk.

[0007] In the prior art, CN113881100A discloses an antibacterial EVOH film, but does not solve the problem of controllable release. CN105459547A uses microcapsule technology, but its release is still based on a simple diffusion mechanism, lacks the "intelligent switch" feature, and cannot achieve on-demand release.

[0008] Therefore, it is a technical problem to be solved in the field to develop an intelligent response type EVOH material that can sense environmental changes and accurately and controllably release active agents accordingly. SUMMARY

[0009] The purpose of the present application is to overcome the defects of the prior art and provide an intelligent EVOH packaging material capable of dual response to environmental humidity and spoilage biomarkers, achieving "on-demand supply" of functional active agents, thereby achieving long-term antibacterial and antioxidant properties, and a preparation method thereof.

[0010] The core of the present application lies in the construction of a "dual response and synergistic release" mechanism:

[0011] First heavy response (macroscopic switch): PEG-b-PAA is grafted on the molecular chain of EVOH as a humidity response molecular switch. In a low humidity environment, the PAA segment shrinks and combines closely with the EVOH segment, blocking the migration channel of the active agent; in a high humidity environment, the PEG segment absorbs water, the PAA segment ionizes and expands, opening the migration channel.

[0012] Second heavy response (microscopic targeting): the functional active agent is encapsulated in intelligent microcapsules sensitive to spoilage biomarkers. Only when the target marker appears, the microcapsule wall material will chemically react and disintegrate, releasing the active agent.

[0013] To achieve the above purposes, the technical solutions of the present application are as follows:

[0014] An intelligent response EVOH packaging material, comprising the following components:

[0015] An ethylene-vinyl alcohol copolymer EVOH matrix (A); an environmentally responsive molecular switch polymer (B); intelligent microcapsules (C) sensitive to at least one spoilage biomarker; and a compatibilizer (D); wherein, based on 100 parts by weight of the total of (A) and (B), the intelligent response EVOH contains 70 to 95 parts by weight of (A) and 5 to 30 parts by weight of (B), based on 100 parts by weight of (A), the intelligent response EVOH contains 1 to 10 parts by weight of (C) and 1 to 5 parts by weight of (D).

[0016] As a preferred solution, the (A) is an ethylene-vinyl alcohol copolymer with an ethylene content of 15-65 mol% and a saponification degree of 95 mol% or higher.

[0017] As a preferred solution, the (B) is polyethylene glycol-block-polyacrylic acid (PEG-b-PAA) with a weight average molecular weight of 2000-5000 g / mol.

[0018] As a preferred solution, the (C) intelligent microcapsule encapsulates a functional active agent, the wall material is mesoporous silica, and the surface is modified with a chemical group sensitive to spoilage biomarkers; preferably, the spoilage biomarkers are volatile sulfides, ammonia, carbon dioxide and C1-C6 short-chain organic acids such as lactic acid, acetic acid and butyric acid; the functional active agent is an antibacterial agent, an antioxidant and a combination thereof.

[0019] As a preferred solution, the (D) is a maleic anhydride grafted polyolefin elastomer (POE-g-MAH) with a grafting rate of 0.3-0.8%.

[0020] A method for preparing the intelligent response EVOH packaging material, comprising the following steps:

[0021] (1) grafting the environmentally responsive molecular switch polymer (B) to the molecular chain of the ethylene-vinyl alcohol copolymer EVOH matrix (A) by esterification reaction to obtain a smart EVOH resin;

[0022] (2) synthesizing mesoporous silica microcapsules by a sol-gel method, and modifying the surface of the microcapsules with chemical groups sensitive to spoilage biomarkers, and then loading a functional active agent into the pore channels of the microcapsules by a vacuum impregnation method;

[0023] (3) melt blending and granulating the smart EVOH resin obtained in step (1), the smart microcapsules obtained in step (2), and a compatibilizer;

[0024] Optionally, (4) processing the granules into a film or sheet material by a film blowing technique.

[0025] Preferably, in the preparation method, the preparation process of the smart EVOH resin in step (1) is to react 2-10 parts by weight of EVOH-Br or EVOH-Cl with 6-20 parts by weight of PEG-b-PAA under the action of an esterification catalyst and protection of N2 for 24-48 hours, and the reaction temperature is 25-60°C. After the reaction, the solution is filtered, washed, and dried to obtain the smart EVOH resin. In the above preparation process, the preparation method of EVOH-Br or EVOH-Cl is to dissolve 10-30 parts by weight of EVOH particles in 200-400 parts by weight of anhydrous dimethyl sulfoxide DMSO. 20-50 parts by weight of anhydrous dichloromethane DCM solution containing a macromolecular initiator precursor is added dropwise to the solution, and the reaction is carried out at 25-45°C for 8-12 hours. After the reaction is completed, the mixture is poured into a large amount of ice methanol for precipitation, filtered with a Buchner funnel, and washed with methanol three times. The final product is dried in a vacuum oven at 30-50°C for 16-24 hours to obtain EVOH-Br or EVOH-Cl. In the above preparation process, the preferred esterification catalysts include but are not limited to one or more of the carbodiimide condensing agents, and further, N,N-dicyclohexyl carbodiimide is preferred because the by-product dicyclohexyl urea is insoluble in most reaction solvents and is easy to filter out. Further, the preferred amount is 0.1-0.5 parts by weight. In the above preparation process, the preferred macromolecular initiator precursor is 2-bromoisobutyryl bromide or 2-chloroisobutyryl chloride because its structure has the advantages of high initiation efficiency and high controllability. Further, the preferred amount is 1-5 parts by weight.

[0026] Preferably, in the preparation method, the preparation process of the mesoporous silica microcapsule in step (2) is to add 1-10 parts by weight of surfactant into 300-500 parts by weight of alkaline aqueous solution and form micellar template under vigorous stirring at 50-80°C. Then, 5-20 parts by weight of silicon source is added and the reaction is continued at 30-80°C for 2-6 hours, followed by washing with a large amount of deionized water and ethanol. The obtained white powder is stirred and refluxed in ethanol (containing 1-5 wt% HC1) at 40-60°C for 12-24 hours to remove the surfactant. Finally, the product is centrifuged, washed with ethanol, and vacuum dried at 30-60°C to obtain amino-functionalized mesoporous silica (MSN-NH2). In the above preparation process, the preferred alkaline aqueous solution includes but is not limited to aqueous ammonia, aqueous sodium hydroxide, aqueous potassium hydroxide, aqueous ethylenediamine, and aqueous triethylamine. Further, aqueous ammonia is preferred because it can mildly catalyze the reaction and is easy to obtain mesoporous silica with uniform morphology and narrow pore size distribution. In the above preparation process, the preferred surfactant includes but is not limited to one or more of cetyltrimethylammonium bromide, cetyltrimethylammonium chloride, octadecyltrimethylammonium bromide, sodium alkyl carboxylate, and alkyl polyoxyethylene ether. In the above preparation process, the preferred silicon source includes but is not limited to one or more of sodium silicate, methyl orthosilicate, ethyl orthosilicate, and isopropyl orthosilicate.

[0027] Preferably, in the preparation method, the preparation process of the mesoporous silica microcapsule in step (2) is to first disperse 1-5 parts by weight of mesoporous silica in 50-150 parts by weight of anhydrous DMF, and then add 1-6 parts by weight of modification compound. Under N2 protection, the reaction is carried out at 45-85°C for 5-12 hours. After the reaction, the solid is collected by centrifugation and washed with DMF and ethanol to obtain MSN-NIm. In the above preparation process, the preferred modification compound includes but is not limited to 4-nitrophthalic anhydride for volatile sulfide, carbon dioxide or specific organic acid, and 4-formylphenylboronic acid for ammonia gas.

[0028] Preferably, in the preparation method, the preparation process of the microcapsule loading the functional active agent in step (2) is to uniformly ultrasonic disperse 0.5-2 parts by weight of MSN-NIm in 50-100 mL of ethanol. Then 2-8 parts by weight of the functional active agent is dissolved in 10-40 parts by weight of ethanol, and it is slowly added to the MSN-NIm dispersion, slowly stirring in the dark for 12-24 hours. Then, the ethanol is removed by a rotary evaporator at 25-40°C to obtain a yellow powder loaded with the functional active agent. In the above preparation process, the preferred functional active agent includes one or more compounds of antioxidants and antibacterial agents, the preferred antioxidant includes but is not limited to vitamin E, vitamin C, rosemary extract, tertiary butyl hydroquinone, tea polyphenol, phytic acid, etc.; the preferred antibacterial agent includes but is not limited to carvacrol, cinnamaldehyde, nisin, lysozyme, nano-silver, nano-zinc oxide, titanium dioxide, etc.

[0029] Preferably, in the preparation method, the preparation method of step (3) is to pre-mix the intelligent EVOH resin, the microcapsule and the POE-g-MAH compatibilizer in a high-speed mixer for 5-30 minutes. The mixture is then melt blended and granulated by a co-rotating twin-screw extruder (for example: Kobe CTE 35). The temperature of each section of the extruder is set as follows: the feeding section 160-190°C, the melting section 165-220°C, the mixing section 185-220°C, the die head 190-200°C, and the screw rotation speed is 50-200 rpm.

[0030] Preferably, in the preparation method, the preparation process of step (4) is to form the obtained granules into a film by a single-screw casting machine (die width 400-600 mm). The casting roll temperature is set to 165-195°C, and the cooling roll temperature is 20-30°C to obtain a film with a thickness of 20-40 μm.

[0031] The positive effects of the present application are:

[0032] 1. Extremely efficient and long-acting: through "on-off" control and targeted release, the active agent waste loss is reduced by more than 80%, and the effective action period is prolonged by 300%.

[0033] 2. High precision and safety: precise intervention in the spoilage process is achieved, unnecessary active agent migration during the fresh period of food is avoided, and it is safer. DETAILED DESCRIPTION

[0034] In order to facilitate the understanding of the present application, the present application lists the following examples. Those skilled in the art should understand that the examples are only to help understand the present application, and should not be regarded as a specific limitation on the present application.

[0035] Example 1:

[0036] 1. Raw materials and formulations

[0037] EVOH-based resin: EVOH F171B produced by Kuraray Co., Ltd., Japan, ethylene content 32 mol%, melt index 1.6 g / 10 min (210°C), saponification degree > 95 mol%.

[0038] PEG-b-PAA: produced by Hangzhou Xinjiao Biotechnology Co., Ltd., with a weight average molecular weight of 3000 g / mol.

[0039] Intelligent microcapsule preparation raw materials: cetyltrimethylammonium bromide (CTAB, 99%), tetraethyl orthosilicate (TEOS, 98%), 3-aminopropyltriethoxysilane (APTES, 99%), 4-nitrophthalic anhydride (97%). Manufacturer: Shanghai Aladdin Biochem Technology Co., Ltd.

[0040] Functional active agent: carvacrol (purity > 98%). Manufacturer: Shanghai Aladdin Biochem Technology Co., Ltd.

[0041] Compatibilizer: polyolefin elastomer grafted with maleic anhydride (POE-g-MAH, grafting rate 0.8%). Manufacturer: Keais Chemical Co., Ltd.

[0042] Catalyst and solvent: N,N,N',N",N"-pentamethyldiethylenetriamine (PMDETA, 99%), cuprous bromide (CuBr, 99.999%), N,N-dimethylformamide (DMF, anhydrous), dichloromethane (DCM, anhydrous), 2-bromoisobutyryl bromide (BIBB, 99%), 4-dimethylaminopyridine (DMAP, 99%), N,N-dicyclohexylcarbodiimide (DCC, 99%). Manufacturer: Shanghai Aladdin Biochem Technology Co., Ltd.

[0043] The final intelligent responsive EVOH contains 70 parts by weight of EVOH-based resin, 30 parts by weight of PEG-b-PAA, wherein, based on 100 parts by weight of EVOH-based resin, the intelligent responsive EVOH contains 10 parts by weight of intelligent microcapsules and 5 parts by weight of POE-g-MAH.

[0044] 2. Detailed preparation process

[0045] Step one: synthesis of intelligent EVOH resin (ATRP grafting)

[0046] 1. Preparation of macromolecular initiator (EVOH-Br): In a 500 mL three-necked flask equipped with a magnetic bar, 20 g of dry EVOH F171B granules and 200 mL of anhydrous DMSO were added and stirred at 85 °C under N2protection until complete dissolution. The system was cooled to 0 °C (ice water bath) and a solution containing 2.5 mL of BIBB in 20 mL of anhydrous DCM was added slowly dropwise. After the addition was completed, the ice bath was removed and the reaction was allowed to proceed at 25 °C for 12 h. After the reaction was completed, the mixture was poured into a large amount of ice methanol to precipitate, filtered with a Buchner funnel, and washed with methanol three times. The final product was dried in a vacuum oven at 50 °C for 24 h to obtain EVOH-Br.

[0047] 2. Grafting reaction: 2 g of EVOH-Br and 8.6 g of PEG-b-PAA were dissolved in 50 mL of anhydrous DMF, and 0.1 g of DMAP and 0.25 g of DCC were added as esterification catalysts. The reaction was carried out at 40 °C for 48 h under N2protection. After the reaction, the solution was filtered through a fritted funnel to remove the by-product DCU, and the filtrate was precipitated in a large amount of acetone, filtered, and the product was washed with acetone three times to completely remove the ungrafted copolymer. The final product was dried in a vacuum oven at 50 °C for 48 h to obtain the smart EVOH resin.

[0048] Step two: Preparation of H2S-sensitive microcapsules (MSN-NIm@Carvacrol)

[0049] 1. Synthesis of MSN-NH2: 1.0 g of CTAB was dissolved in 480 mL of deionized water and 3.5 mL of ammonia solution, and stirred vigorously at 80 °C. Then 5.0 mL of TEOS and 0.5 mL of APTES were added slowly in turn. After 2 h of continuous reaction, it was filtered under suction and washed with a large amount of deionized water and ethanol. The obtained white powder was stirred and refluxed in ethanol containing 1 wt% HC1 at 60 °C for 24 h to remove the CTAB template. Finally, the product was centrifuged, washed with ethanol, and dried at 60 °C under vacuum to obtain aminated mesoporous silica (MSN-NH2).

[0050] 2. Surface modification with phthalimide groups (MSN-NIm): 1.0 g of MSN-NH2 was dispersed in 50 mL of anhydrous DMF, and 1.2 g of 4-nitrophthalic anhydride was added. The reaction was carried out at 80 °C for 12 h under N2protection. After the reaction, the solid was collected by centrifugation and washed thoroughly with DMF and ethanol to obtain MSN-NIm.

[0051] 3. Carvacrol-loaded (MSN-NIm@Carvacrol): 0.5 g of MSN-NIm was ultrasonically dispersed uniformly in 50 mL of ethanol. 2.0 g of carvacrol was dissolved in 10 mL of ethanol and was slowly added into the MSN-NIm dispersion, which was slowly stirred at 25 °C in the dark for 24 h. Then, the ethanol was removed by a rotary evaporator at 40 °C to obtain a yellow powder loaded with carvacrol.

[0052] Step three: blending, pelletizing and film forming

[0053] The smart EVOH resin, MSN-NIm@Carvacrol microcapsules and POE-g-MAH compatibilizer were pre-mixed in a high-speed mixer for 5 min at the above-mentioned ratio. The mixture was then melt blended and pelletized by a co-rotating twin-screw extruder (Kobe 35). The temperature settings of the extruder were set as follows: feeding section 160 °C, melting section 175 °C, mixing section 185 °C, die head 190 °C, and screw rotation speed 200 rpm.

[0054] The obtained pellets were formed into a film by a casting machine set (die width 600 mm). The casting roll temperature was set at 65 °C and the cooling roll temperature was set at 30 °C to obtain a film with a thickness of 20 pm.

[0055] 3. Performance test and results

[0056] Humidity-responsive release test: The film samples were immersed in airtight containers with different relative humidity (RH) controlled by saturated salt solutions, and samples were taken periodically and the carvacrol concentration released into the headspace was determined by gas chromatography (instrument model: Agilent 7250 GC / Q-TOF, produced by Agilent Technologies). The specific test method is to cut the sample to be tested into a 1 cm * 1 cm square piece, then put it into a 20 ml headspace bottle, seal it and quickly transfer it to a heating table at 60 °C for 15 minutes of equilibrium before testing. The chromatographic column selects HP-5MS capillary column, the carrier gas selects high-purity helium, the flow rate is set to 1 ml / min, the injection port temperature is set to 250 °C, the injection analysis time is set to 5 min, and the temperature rising program is set to 50 °C initially for 2 min, then 10 °C / min to 150 °C, and then 25 °C / min to 280 °C for 5 min.

[0057] Results: Under 55% humidity, the cumulative release rate of carvacrol within 7 days was only 4.5%. When the environment was switched to 95% humidity, the cumulative release rate rapidly increased to 58.7% within 24 hours, proving the successful opening of the molecular switch. Release rate = GC-MS test value / total loading * 100%

[0058] H2S targeted release test: The film sample was placed in a sealed chamber containing 50 ppm H2S gas, with air containing no H2S as a control. The release of carvacol was monitored by GC-MS (instrument model: Agilent 7250 GC / Q-TOF, produced by Agilent Technology Co., Ltd.). The specific test method was to cut the film sample into 1 cm * 1 cm square pieces, place the film sample in a sealed chamber containing 50 ppm H2S gas, and take out the sample to be tested at different times and then place it in a 20 ml headspace bottle. After sealing, it was quickly transferred to a heating table at 60°C for 15 minutes of equilibration before testing. The chromatographic column was selected as an HP-5MS capillary column, the carrier gas was selected as high-purity helium, the flow rate was set to 1 ml / min, the injection port temperature was set to 250°C, the injection analysis time was set to 5 min, and the temperature program was set to an initial 50°C for 2 min, an increase of 10°C / min to 150°C, and then an increase of 25°C / min to 280°C for 5 min.

[0059] Results: In the H2S environment, an explosive release of carvacol was detected within 2 hours, and the release rate was more than 85% in 6 hours. In the control air, the release rate was less than 3% in the same time.

[0060] Active agent effective period test: The samples were divided into two groups, namely the intelligent EVOH film of the application and the traditional blended film (containing an equal amount of uncoated carvacol); the experimental design was to place the two groups of films in a sealed chamber with continuous low-concentration H2S, and take samples every 8 hours, and use GC-MS to determine the release amount of carvacol. The specific test method was to cut the film sample into 1 cm * 1 cm square pieces, place the film sample in a sealed chamber containing 50 ppm H2S gas, and take out the sample to be tested at different times and then place it in a 20 ml headspace bottle. After sealing, it was quickly transferred to a heating table at 60°C for 15 minutes of equilibration before testing. The chromatographic column was selected as an HP-5MS capillary column, the carrier gas was selected as high-purity helium, the flow rate was set to 1 ml / min, the injection port temperature was set to 250°C, the injection analysis time was set to 5 min, and the temperature program was set to an initial 50°C for 2 min, an increase of 10°C / min to 150°C, and then an increase of 25°C / min to 280°C for 5 min.

[0061] Results: In the same low-concentration H2S environment, the time for the traditional blended film to release carvacol to the minimum effective concentration was 4 days, while the time for the intelligent EVOH film to release carvacol to the minimum effective concentration was 12 days, with an effective period increased by 300%.

[0062] Example 2:

[0063] The main difference between this example and Example 1 is the composition of the smart EVOH film. The smart responsive EVOH comprises 95 parts by weight of EVOH-based resin, 5 parts by weight of PEG-b-PAA, wherein the smart responsive EVOH comprises 1 part by weight of smart microcapsules and 1 part by weight of POE-g-MAH based on 100 parts by weight of the EVOH-based resin. The preparation method is the same as Example 1.

[0064] Performance test and result

[0065] Humidity-responsive release test: Film samples were immersed in airtight containers with different relative humidity (RH) controlled by saturated salt solutions, and samples were taken periodically to measure the concentration of carvacol released into the headspace by gas chromatography (GC).

[0066] Result: Under 55% humidity, the cumulative release rate of carvacol within 7 days was 20.5%. When the environment was switched to 95% humidity, the cumulative release rate rapidly increased to 78.7% within 24 hours, demonstrating the successful opening of the molecular switch.

[0067] H2S-targeted release test: Film samples were placed in an airtight chamber containing 50 ppm H2S gas, with air containing no H2S as a control. Carvacol release was monitored by GC-MS.

[0068] Result: In the H2S environment, an explosive release of carvacol was detected within 4.5 hours, with a release rate of over 85% within 13 hours. In the control air, the release rate was less than 10% within the same time.

[0069] Active agent shelf-life test: Samples were divided into two groups, namely the smart EVOH film of the application and the traditional blended film (containing an equal amount of uncoated carvacol); experimental design: Place the two groups of films in an airtight chamber with continuous low-concentration H2S, take samples every 8 hours, and use GC-MS to determine the release amount of carvacol.

[0070] Result: In the same low-concentration H2S environment, the traditional blended film took 4 days to release carvacol to the minimum effective concentration, while the smart EVOH film took 12 days to release carvacol to the minimum effective concentration, with an effective period increased by 300%.

[0071] Example 3:

[0072] The main difference between this example and Example 1 is the response mechanism of the microcapsules to address the ammonia gas produced during the spoilage of aquatic products (leading to an increase in pH).

[0073] The preparation method is the same as Example 1, except that in Step 2, Schiff Base is used as the pH-sensitive "gate". The specific steps are as follows: after the synthesis of MSN-NH2, it is reacted with 4-formylphenylboronic acid to form a phenylboronic acid ester-protected Schiff Base structure on the surface of the microcapsule. This structure is stable at pH < 7.5, and when pH > 8.0 (local pH increases due to amine substances produced by the spoilage of aquatic products), the Schiff Base hydrolyzes and the microcapsule "gate" opens. The functional active agent is a complex of Nisin and tea polyphenol, which simultaneously targets the common gram-positive bacteria and oxidation problems in aquatic products.

[0074] Test results: In a buffer at pH 7.0, the Nisin release rate is < 5% in 48 hours. When transferred to a buffer at pH 8.2, the Nisin release rate exceeds 70% within 6 hours.

[0075] Comparative Example 1 (traditional blended film)

[0076] Formulation: 100 parts by weight of ordinary EVOH F171B, 10 parts by weight of uncoated pure carvacrol, and 5 parts by weight of POE-g-MAH.

[0077] Preparation and testing: the same processing conditions and test methods as Example 1.

[0078] Results:

[0079] Processing loss: During the granulation process, thermogravimetric analysis showed that about 25% of the carvacrol was lost due to high temperature and volatilization.

[0080] Release behavior: carvacrol shows a rapid initial release (burst effect) under any humidity. Under 95% humidity, the release is close to 100% within 8 hours.

[0081] Fresh-keeping effect: In the fresh-keeping experiment of chilled pork, the antibacterial effect is equivalent to that of Example 1 in the first 2 days, but from the 4th day, the antibacterial ability decreases sharply, and the pork has spoiled by the 6th day, showing no significant difference from ordinary packaging.

Claims

1. A smart responsive EVOH packaging material, characterized in that, Includes the following components: The ethylene-vinyl alcohol copolymer (EVOH) matrix (A); an environmentally responsive molecular switch polymer (B); a smart microcapsule sensitive to at least one putrefaction biomarker (C); and a compatibilizer (D); wherein, based on a total of 100 parts by weight of (A) and (B), the smart responsive EVOH comprises 70 to 95 parts by weight of (A) and 5 to 30 parts by weight of (B), and based on 100 parts by weight of (A), the smart responsive EVOH comprises 1 to 10 parts by weight of (C) and 1 to 5 parts by weight of (D).

2. The packaging material according to claim 1, characterized in that, The (A) mentioned above is an ethylene-vinyl alcohol copolymer with an ethylene content of 15-65 mol% and a saponification degree of 95 mol% or more.

3. The packaging material according to claim 1 or 2, characterized in that, The (B) mentioned above is polyethylene glycol-block-polyacrylic acid (PEG-b-PAA), with a weight-average molecular weight of 2000-5000 g / mol.

4. The packaging material according to any one of claims 1-3, characterized in that, The (C) smart microcapsule encapsulates a functional active agent, its wall material is mesoporous silica, and its surface is modified with chemical groups sensitive to putrefactive biomarkers; preferably, the putrefactive biomarkers are volatile sulfides, ammonia, carbon dioxide, and C1-C6 short-chain organic acids, such as lactic acid, acetic acid, and butyric acid; the functional active agent is an antibacterial agent, an antioxidant, or a combination thereof.

5. The packaging material according to claim 4, characterized in that, The antibacterial agent is selected from at least one of carvacrol, cinnamaldehyde, nisin, lysozyme, nano silver, nano zinc oxide, and titanium dioxide, and the antioxidant is selected from at least one of vitamin E, vitamin C, rosemary extract, tert-butylhydroquinone, tea polyphenols, and phytic acid.

6. The packaging material according to claim 4 or 5, characterized in that, The surface of the wall material of the smart microcapsule is modified with chemical groups sensitive to different putrefactive biomarkers. The phthalimide group modified on the wall material surface breaks down in the presence of volatile sulfides, preferably hydrogen sulfide, carbon dioxide, and C1-C6 short-chain organic acids, leading to microcapsule disintegration. The wall material surface is also modified with a Schiff base structure, which hydrolyzes when pH>8.0, causing microcapsule disintegration.

7. The packaging material according to any one of claims 1-6, characterized in that, The aforementioned (D) is a maleic anhydride-grafted polyolefin elastomer (POE-g-MAH) with a grafting rate of 0.3-0.8%.

8. A method for preparing the smart responsive EVOH packaging material according to any one of claims 1-7, characterized in that, Includes the following steps: (1) An environmentally responsive molecular switch polymer (B) is grafted onto the molecular chain of an ethylene-vinyl alcohol copolymer EVOH matrix (A) via esterification to obtain a smart EVOH resin. (2) Mesoporous silica microcapsules were synthesized by sol-gel method and their surface was modified with chemical groups sensitive to putrefactive biomarkers. Then, functional active agents were loaded into the microcapsule channels by vacuum impregnation method to obtain smart microcapsules. (3) The smart EVOH resin obtained in step (1), the smart microcapsules obtained in step (2) and the compatibilizer are melt-blended and granulated. Optionally, (4) the granules are processed into film or sheet materials by blown film technology.

9. The method according to claim 8, characterized in that, In step (1), the smart EVOH resin is prepared by reacting EVOH-Br or EVOH-Cl with PEG-b-PAA under the action of an esterification catalyst. Preferably, the preparation method of EVOH-Br or EVOH-Cl is to dissolve EVOH resin in a solvent and add macromolecular initiator precursor 2-bromoisobutyryl bromide or 2-chloroisobutyryl chloride to react.

10. The method according to claim 8 or 9, characterized in that, In step (2), the chemical groups sensitive to putrefactive biomarkers on the surface of the mesoporous silica microcapsules are modified by dispersing mesoporous silica in a solvent and adding a modifying compound to react. Preferably, the modifying compound includes, but is not limited to, 4-nitrophthalic anhydride for volatile sulfides, carbon dioxide or specific organic acids, and 4-formylphenylboronic acid for ammonia.

11. The use of a smart responsive EVOH packaging material according to any one of claims 1-6 or a packaging material prepared by any one of claims 7-10 in the packaging of food, pharmaceuticals or medical devices.