A packaging film containing degradable porous starch and preparation method thereof

Abstract

The invention discloses a packaging film containing degradable porous starch and a preparation method thereof, belonging to the technical field of polyurethane materials, and is used to solve the technical problem that the renewable polyurethane film containing starch in the prior art has poor heat resistance and mechanical properties, and the renewable polyurethane film for food needs to enhance its own antibacterial effect. The invention comprises the following steps: uniformly mixing a modified polyurethane emulsion and a composite microcapsule, then spin-coating the mixture on a cleaned PE substrate, standing and heating the mixture to obtain a packaging film containing the degradable porous starch, adding acrylate and a modifier A with a polyhydroxyl group and a benzene ring structure to the modified polyurethane emulsion to improve the mechanical properties of the film, introducing a modifier A with a silicon element into the modified polyurethane emulsion to improve the heat resistance of the film, and introducing a porous cross-linked starch modified by a mixed acid and an antibacterial agent into the composite microcapsule to improve the antibacterial property of the film.

Description

Technical Field

[0001] The invention relates to the technical field of plastic packaging films, and in particular to a packaging film containing degradable porous starch and a preparation method thereof. Background Art

[0002] Polyurethane is the abbreviation of polyurethane, which has repeated carbamate groups on its main molecular chain. The raw materials for preparing polyurethane are generally diisocyanates or polyisocyanates and compounds containing active hydrogen. Polyurethane has excellent comprehensive performance and has irreplaceable applications in many fields. In addition, polyurethane packaging film also has the advantage of easy molding and processing. However, traditional polyurethane has the characteristics of high molecular weight and difficulty in degradation, which will cause great pollution to the environment in practical applications. In addition, the recovery rate and reuse rate of polyurethane materials are low, and the environmental protection effect is poor. Therefore, it is of positive practical significance to introduce natural renewable polymers and develop green and environmentally friendly polyurethane materials.

[0003] Patent application CN110655632A discloses a method for preparing a starch-based waterborne polyurethane emulsion, wherein corn and cassava starch are used as raw materials, and the waterborne polyurethane emulsion is prepared through liquefaction, neutralization, prepolymerization, salt formation and phase transfer processes. A large proportion of starch bio-based components are introduced into the polyurethane formate structure to improve the biodegradability of the waterborne polyurethane emulsion; however, the film formed by the above-mentioned bio-based polyurethane emulsion has the problem of decreased mechanical properties and heat resistance compared with general polyurethane films. In addition, food packaging films need to have antibacterial effects.

[0004] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a packaging film containing degradable porous starch, which is used to solve the technical problems in the prior art that the packaging film containing starch bio-based components has poor mechanical properties and heat resistance. In addition, for polyurethane packaging films for food, it is necessary to enhance their own antibacterial effect.

[0006] The object of the present invention can be achieved by the following technical scheme: A method for preparing a packaging film containing degradable porous starch comprises the following steps:

[0007] According to weight parts, 150-200 parts of modified polyurethane emulsion and 10-20 parts of composite microcapsules are uniformly mixed to obtain polyurethane composite emulsion; the PE substrate is wiped with alcohol to obtain a cleaned PE substrate;

[0008] The polyurethane composite emulsion is spin-coated on a cleaned PE substrate with a coating thickness of 5-10 μm; the cleaned PE substrate is then placed at 30-40° C. for 1-2 hours to obtain a polymer film; the polymer film is placed in an oven at 100-110° C. and heated for 3 hours to obtain a packaging film containing degradable porous starch.

[0009] The composite microcapsules are added to the modified polyurethane emulsion to obtain the polyurethane composite emulsion; the polyurethane composite emulsion is evenly coated on the PE substrate to obtain a polymer film, and the polymer film evaporates water to obtain a dry polymer film, which is a packaging film containing degradable porous starch.

[0010] Furthermore, the preparation method of the modified polyurethane emulsion comprises the following steps:

[0011] A1, aminosilane and deionized water are mixed evenly to obtain a silanol solution; diphenolic acid powder is added to the silanol solution, and then mixed and reacted at 70-80° C. for 1-2 hours to obtain a mixed solution; the mixed solution is distilled at 100-110° C. for 1-2 hours under nitrogen protection to obtain a modified substance A;

[0012] Aminosilane reacts with deionized water, and the amino groups in the aminosilane molecules react with water molecules to undergo nucleophilic addition reaction, thereby obtaining an aminosilanol solution containing multiple hydroxyl groups. Under heating conditions, the amino groups in the aminosilanol react with the carboxyl groups of the diphenolic acid to dehydrate, generating amide bonds, thereby obtaining a modified substance A.

[0013] A2, acrylate, diisocyanate, polycaprolactone and dibutyltin dilaurate are mixed evenly, heated in a water bath and mixed under a nitrogen atmosphere to obtain a mixed monomer liquid; the modifier A is added to the mixed monomer liquid, and the mixture is reacted at room temperature to obtain a prepolymer; ethylenediamine is added to the prepolymer for neutralization reaction, and then deionized water is added dropwise and stirred to obtain an emulsion system; the emulsion system is heated to 70-80°C, and an initiator KBS is added dropwise using a peristaltic pump to obtain a composite PUA emulsion.

[0014] The modified substance A contains polyhydroxyl functional groups, and thus can be used as a chain extender for preparing polyurethane and can react with isocyanate to obtain a prepolymer.

[0015] Further, in step A1, the ratio of aminosilane to deionized water is 5-10 g:100 mL, and the ratio of silanol solution to diphenolic acid powder is 105-110 g:20 g;

[0016] Furthermore, in step A1, the aminosilane is any one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, phenylaminopropyltrimethoxysilane, and phenylaminopropyltriethoxysilane, and a combination thereof.

[0017] Further, in step A2, the acrylate is any one of methyl acrylate, ethyl acrylate, methyl 2-methacrylate or ethyl 2-methacrylate; the diisocyanate is any one of diphenylmethane diisocyanate, isophorone diisocyanate or hexamethylene diisocyanate; the amount ratio of acrylate, diisocyanate, polycaprolactone and dibutyltin dilaurate is 10-20g:25-30g:10-20g:0.5g; the amount of modifier A is 10-20g, the amount of ethylenediamine is 10-20mL, the amount of deionized water is 100-200mL, and the amount of initiator is 1-2g.

[0018] Furthermore, in step A2, the temperature of water bath heating is 70-80°C, the speed of mixing reaction is 100-300r / min, and the duration of mixing reaction is 3h; the duration of room temperature reaction is 1-2h, and the speed of room temperature reaction is 100r / min; the temperature of neutralization reaction is 30°C, the speed of neutralization reaction is 500-1000r / min, and the duration of neutralization reaction is 30-60min; the stirring time is 1-2h, and the stirring speed is 1000-1200r / min.

[0019] Furthermore, the preparation method of the composite microcapsule comprises the following steps:

[0020] S1, porous starch and distilled water are mixed to obtain a porous starch solution; the pH value of the porous starch solution is adjusted to 2.5-3.5 with a 0.1 mol / L NaOH solution, and then the porous starch solution and the mixed acid are evenly mixed, reacted at room temperature, and then dried to obtain a solid; the solid is ground, passed through a 100 mesh sieve, and then dried to obtain a porous cross-linked starch;

[0021] The mixed acid is specifically citric acid and malic acid. The hydroxyl groups in the porous starch react with the carboxyl groups in the citric acid and malic acid to form ester bonds, thereby obtaining porous cross-linked starch.

[0022] S2, uniformly mixing gelatin, gum arabic and deionized water, and heating at 50-60° C. until completely melted to obtain a wall material liquid; uniformly mixing benzyl alcohol and 2-benzylphenol to obtain an antibacterial agent; uniformly mixing porous starch and the antibacterial agent to obtain a core material;

[0023] S3, the core material and the wall material liquid are mixed and stirred to obtain an antibacterial agent / wall material liquid; the remaining wall material liquid is added dropwise to the antibacterial agent / wall material liquid, and after the addition is completed, a 10%wt acetic acid solution is used to adjust the pH value to 3-4, and then the temperature is raised to 70-80°C to perform a complex coagulation reaction to obtain a mixed solution; the mixed solution is cooled to room temperature, and then a cold water bath is taken to 5-10°C, and a 1mol / L NaOH solution is used to adjust the pH value of the mixed solution to 8-9, and then 2mL, 3%wt calcium chloride solution is added to solidify for 1h, and filtered to obtain a filter residue; the filter residue is washed 3 times with deionized water, and then dried at 50-60°C for 2h to obtain a composite microcapsule.

[0024] Furthermore, in step S1, the porous starch is any one of potato porous starch, cassava porous starch or sweet potato porous starch and a combination thereof, and the usage ratio of porous starch to distilled water is 3-5g:20mL; the mixed acid is malic acid and citric acid mixed in a mass ratio of 1:1.

[0025] Furthermore, the dosage ratio of gelatin, gum arabic and deionized water is 10-20g:10-20g:100mL, the dosage ratio of benzyl alcohol and 2-benzylphenol is 10-15mL:5-10mL, the dosage ratio of porous starch and antibacterial agent is 10-20g:15mL; the dosage ratio of core material and wall material liquid is 20-30g:50-60mL, and the volume of the remaining wall material liquid is 50-60mL.

[0026] As another aspect of the present invention, a method for preparing a packaging film containing degradable porous starch is provided to prepare a packaging film containing degradable porous starch.

[0027] The present invention has the following beneficial effects:

[0028] 1. In order to improve the antibacterial property of the packaging film of the degradable porous starch prepared by the present invention, benzyl alcohol and 2-benzylphenol are selected as antibacterial agents. Benzyl alcohol has a wide range of antibacterial effects on bacteria, yeasts and molds, and 2-benzylphenol has antibacterial effects on many microorganisms; however, the above two antibacterial materials are easily oxidized and decomposed under light and heat conditions. In order to improve the stability of the antibacterial agent material, porous starch is used as the packaging material. Porous starch has a loose porous structure and can effectively seal the biological activity of the liquid.

[0029] Since the dehydration of intramolecular and intermolecular hydroxyl groups in porous starch is the main reason for its thermal decomposition, the higher the degree of cross-linking between porous starch and organic acid, the fewer hydroxyl groups in the porous starch molecules, and the better the thermal stability; the present invention uses mixed acid to modify porous starch, which can significantly improve the thermal stability of porous starch. In addition, the organic acid itself can be used as a cross-linking agent to bridge two starch molecules together; the organic acid and starch molecules form a three-dimensional network structure between the intramolecular chain and the intermolecular chain, which enhances the interaction between the starch molecular chains, thereby improving the mechanical strength and heat resistance of the porous starch. In summary, the present invention adds composite microcapsules to the prepared modified polyurethane emulsion, which helps to improve the biodegradability, heat resistance and antibacterial properties of the polyurethane film.

[0030] 2. Acrylate is added to the polyurethane emulsion, so that the polyurethane emulsion becomes a high molecular polymer with the advantages of both PU and PA, thereby improving the mechanical properties of the polymer film; in addition, in the synthesis process of the modified polyurethane emulsion, by adding a modifier A containing polyhydroxyl groups and polyphenyl rings, the modifier plays the role of a chain extender, and the polyhydroxyl groups in the modifier and the isocyanate in the diisocyanate undergo multi-addition to obtain polyurethane functional groups, thereby increasing the cross-linking density thereof, and further improving the mechanical properties and heat resistance of the prepared polyurethane film; the modified polyurethane emulsion is spin-coated on a PE substrate and then allowed to stand to form a film, thereby preparing a packaging film containing degradable porous starch. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Example 1

[0032] This embodiment provides a method for preparing a composite microcapsule, comprising the following steps:

[0033] 1. Weigh 3 g of potato porous starch and 20 mL of distilled water and mix them evenly to obtain a porous starch solution. Use 0.1 mol / L NaOH solution to adjust the pH value of the cross-linking agent solution to 2.5; mix the porous starch solution and the mixed acid evenly, react at 100 r / min for 12 h at room temperature, and dry at 60°C for 6 h to obtain a solid; grind the solid in a grinder, pass through a 100-mesh sieve, and dry and react in a 100°C forced air drying oven for 60 min to obtain a porous cross-linked starch.

[0034] 2. Add 10 g of gelatin, 10 g of gum arabic and 100 mL of deionized water into a beaker, then transfer the beaker to an oil bath at 50°C and stir until completely melted to obtain a wall material liquid; mix 10 mL of benzyl alcohol and 5 mL of 2-benzylphenol, stir evenly to obtain an antibacterial agent; mix 10 g of porous starch and 15 mL of the antibacterial agent liquid evenly to obtain a core material.

[0035] 3. In a 250mL three-necked flask, add 20g of core material to 50mL of wall material liquid, mix and stir at 100r / min for 10min to obtain antibacterial agent / wall material liquid; set a separatory funnel at the port of the three-necked flask, and continue to drip 50mL of wall material liquid through the separatory funnel. After the dripping is completed, adjust the pH value to 3 with 10%wt acetic acid solution, then heat to 70℃, perform complex coagulation reaction, and obtain a mixed solution. Cool the mixed solution to room temperature, then cool it to 5℃, adjust the pH value of the mixed solution to 8 with 1mol / L NaOH solution, then add 2mL, 3%wt calcium chloride solution to solidify for 1h, filter, and obtain filter residue; wash the filter residue with deionized water 3 times, and then dry it at 50℃ for 2h to obtain composite microcapsules. Example 2

[0036] This embodiment provides a method for preparing a composite microcapsule, comprising the following steps:

[0037] 1. Weigh 4 g of cassava porous starch and 20 mL of distilled water and mix them evenly to obtain a porous starch solution. Use 0.1 mol / L NaOH solution to adjust the pH value of the cross-linking agent solution to 3; then mix the cross-linking agent solution and potato porous starch evenly, place it at room temperature at 150 r / min for 12 hours, and then dry it at 60°C for 6 hours to obtain a solid; grind the solid in a grinder, pass it through a 100-mesh sieve, and dry it in a 110°C forced air drying oven for 80 minutes to obtain a porous cross-linked starch.

[0038] 2. Add 15 g of gelatin, 15 g of gum arabic and 100 mL of deionized water into a beaker, then transfer the beaker to an oil bath at 55°C and stir until completely melted to obtain a wall material liquid; mix 12 mL of benzyl alcohol and 6 mL of 2-benzylphenol, stir evenly to obtain an antibacterial agent; mix 10-20 g of porous starch and 15 mL of the antibacterial agent liquid evenly to obtain a core material.

[0039] 3. In a 250mL three-necked flask, add 25g of core material to 57mL of wall material liquid, mix and stir at 100r / min for 10min to obtain antibacterial agent / wall material liquid; set a separatory funnel at the port of the three-necked flask, and continue to drip 58mL of wall material liquid through the separatory funnel. After the dripping is completed, adjust the pH value to 3.5 with 10%wt acetic acid solution, then heat to 75℃, perform complex coagulation reaction, and obtain a mixed solution. Cool the mixed solution to room temperature, then cool it to 6℃, adjust the pH value of the mixed solution to 8.5 with 1mol / L NaOH solution, then add 2mL, 3%wt calcium chloride solution to solidify for 1h, filter, and obtain filter residue; wash the filter residue with deionized water 3 times, and then dry it at 55℃ for 2h to obtain composite microcapsules. Example 3

[0040] This embodiment provides a method for preparing a composite microcapsule, comprising the following steps:

[0041] 1. Weigh 5 g of sweet potato porous starch and 20 mL of distilled water and mix them evenly to obtain a porous starch solution, and use 0.1 mol / L NaOH solution to adjust the pH value of the porous starch solution to 3.5; mix the porous starch solution and the mixed acid evenly, react at 200 r / min at room temperature for 12 h, and dry at 60 ° C for 6 h to obtain a solid; grind the solid in a grinder, pass through a 100-mesh sieve, and dry it in a 120 ° C forced air drying oven for 90 min to obtain a porous cross-linked starch.

[0042] 2. Add 20 g of gelatin, 20 g of gum arabic and 100 mL of deionized water into a beaker, then transfer the beaker to an oil bath at 60°C and stir until completely melted to obtain a wall material liquid; mix 15 mL of benzyl alcohol and 10 mL of 2-benzylphenol, stir evenly to obtain an antibacterial agent; mix 20 g of porous starch and 15 mL of the antibacterial agent evenly to obtain a core material.

[0043] 3. In a 250mL three-necked flask, add 30g of core material to 60mL of wall material liquid, mix and stir at 100r / min for 10min to obtain antibacterial agent / wall material liquid; set a separatory funnel at the port of the three-necked flask, and continue to drip 60mL of wall material liquid through the separatory funnel. After the dripping is completed, adjust the pH value to 4 with 10%wt acetic acid solution, then heat it to 80℃, and perform a complex coagulation reaction to obtain a mixed solution. Cool the mixed solution to room temperature, then cool it to 10℃ in a cold water bath, adjust the pH value of the mixed solution to 9 with 1mol / L NaOH solution, then add 2mL, 3%wt calcium chloride solution to solidify for 1h, filter, and obtain a filter residue; wash the filter residue with deionized water 3 times, and then dry it at 60℃ for 2h to obtain a composite microcapsule. Example 4

[0044] This embodiment provides a method for preparing a modified polyurethane emulsion, comprising the following steps:

[0045] 1. Add 5 g of γ-aminopropyltriethoxysilane and 100 mL of deionized water into a beaker, stir at 100 r / min for 10 min at room temperature to obtain a silanol solution; add 20 g of diphenolic acid powder to 105 g of the silanol solution, transfer the beaker to a water bath, and react at 70 ° C for 1 h to obtain a mixed solution; then distill the mixed solution to obtain an organic liquid, which is modified substance A.

[0046] 2. Add 10 g of methyl acrylate, 25 g of diphenylmethane diisocyanate, 10 g of polycaprolactone and 0.5 g of dibutyltin dilaurate into a 1000 mL three-necked flask. A mechanical stirrer is provided at one end of the three-necked flask, a condensation reflux device is provided at one end, and a nitrogen inlet is connected to one end. Under a nitrogen atmosphere, the three-necked flask is transferred to a water bath, heated to 70° C. in a water bath, and mixed at 100 r / min for 3 h to obtain a mixed monomer liquid. Then, 10 g of the modified substance A is added to the mixed monomer liquid, and the mixture is stirred at 100 r / min for 3 h. Continue stirring for 1 hour to obtain a prepolymer; transfer the three-necked flask to a water bath, set the water bath temperature to 30°C, add 10mL of ethylenediamine for neutralization, and react at 500r / min for 30min; add 100mL of deionized water dropwise into the three-necked flask, adjust the rotation speed to 1000r / min, and continue stirring for 1h; then increase the temperature of the three-necked flask to 70°C, use a peristaltic pump to add 1g of KBS initiator dropwise into the emulsion system, and continue stirring at 1200r / min for 1h to obtain a modified polyurethane emulsion. Example 5

[0047] This embodiment provides a method for preparing a modified polyurethane emulsion, comprising the following steps:

[0048] 1. Add 6 g of aminosilane and 100 mL of deionized water into a beaker, stir at room temperature at 150 r / min for 15 min to obtain a silanol solution; add 20 g of diphenolic acid powder into 108 g of the silanol solution, transfer the beaker to a water bath, and react at 76 ° C for 1.5 h to obtain a mixed solution; then distill the mixed solution to obtain an organic liquid, which is modified substance A.

[0049] 2. Add 15 g of ethyl acrylate, 28 g of isophorone diisocyanate, 16 g of polycaprolactone and 0.5 g of dibutyltin dilaurate into a 1000 mL three-necked flask. A mechanical stirrer is provided at one end of the three-necked flask, a condensation reflux device is provided at one end, and a nitrogen inlet is connected to one end. Under a nitrogen atmosphere, the three-necked flask is transferred to a water bath, heated to 75°C in a water bath, and mixed and reacted at 200 r / min for 3 h to obtain a mixed monomer liquid; then, 16 g of the modified substance A is added to the mixed monomer liquid, and the mixture is continuously stirred at 100 r / min. 1.5h to obtain a prepolymer; transfer the three-necked flask to a water bath, set the water bath temperature to 30℃, add 14mL of ethylenediamine for neutralization, and react at 800r / min for 50min; add 180L of deionized water dropwise into the three-necked flask, adjust the rotation speed to 1100r / min, and continue stirring for 1.6h; then raise the temperature of the three-necked flask to 75℃, use a peristaltic pump to add 2g of KBS initiator dropwise into the emulsion system, and continue stirring at 1300r / min for 1.5h to obtain a modified polyurethane emulsion. Example 6

[0050] This embodiment provides a method for preparing a modified polyurethane emulsion, comprising the following steps:

[0051] 1. Add 10g of aminosilane and 100mL of deionized water into a beaker, stir at 200r / min for 20min at room temperature to obtain a silanol solution; add 20g of diphenolic acid powder into 110g of the silanol solution, transfer the beaker to a water bath, mix and react at 80℃ for 2h to obtain a mixed solution. Then distill the mixed solution to obtain an organic liquid, which is the modified substance A.

[0052] 2. Add 20 g of methyl 2-methacrylate, 30 g of hexamethylene diisocyanate, 20 g of polycaprolactone and 0.5 g of dibutyltin dilaurate into a 1000 mL three-necked flask. A mechanical stirrer is provided at one end of the three-necked flask, a condensation reflux device is provided at one end, and a nitrogen inlet is connected to one end. Under a nitrogen atmosphere, the three-necked flask is transferred to a water bath, heated to 80°C in a water bath, and mixed at 300 r / min for 3 h to obtain a mixed monomer liquid. Then, 20 g of the modified substance A is added to the mixed monomer liquid, and the mixture is heated at 100 r / min. Continue stirring for 2 hours to obtain a prepolymer; transfer the three-necked flask to a water bath, set the water bath temperature to 30°C, add 20 mL of ethylenediamine for neutralization, and react at 1000 r / min for 60 minutes; add 200 mL of deionized water dropwise into the three-necked flask, adjust the rotation speed to 1200 r / min, and continue stirring for 2 hours; then increase the temperature of the three-necked flask to 80°C, use a peristaltic pump to add 2 g of KBS initiator dropwise into the emulsion system, and continue stirring at 1400 r / min for 2 hours to obtain a modified polyurethane emulsion. Example 7

[0053] This embodiment provides a method for preparing a packaging film containing degradable porous starch, comprising the following steps:

[0054] 1. According to parts by weight, 150 parts of the modified polyurethane emulsion prepared in Example 4 and 10 parts of the composite microcapsules prepared in Example 1 were added to a beaker and mixed evenly to obtain a polyurethane composite emulsion; a PE substrate with a thickness of 200 μm was selected and wiped with alcohol to obtain a cleaned PE substrate.

[0055] 2. Use a rubber-tipped dropper to drop the polyurethane composite emulsion onto the cleaned PE substrate. During the dropping process, rotate the PE substrate to allow the polyurethane composite emulsion to spread evenly on the surface of the substrate to obtain a polyurethane emulsion with a coating thickness of 5 μm; then place the PE substrate at 30°C and let it stand for 1 hour to obtain a polymer film; place the polymer film in an oven at 100°C and heat it for 3 hours to obtain a packaging film containing degradable porous starch. Example 8

[0056] This embodiment provides a method for preparing a packaging film containing degradable porous starch, comprising the following steps:

[0057] 1. According to parts by weight, 180 parts of the modified polyurethane emulsion prepared in Example 5 and 15 parts of the composite microcapsules prepared in Example 2 were added to a beaker and mixed evenly to obtain a polyurethane composite emulsion; a PE substrate with a thickness of 220 μm was selected and wiped with alcohol to obtain a cleaned PE substrate.

[0058] 2. Use a rubber-tipped dropper to drop the polyurethane composite emulsion onto the cleaned PE substrate. During the dropping process, rotate the PE substrate to allow the polyurethane composite emulsion to spread evenly on the surface of the substrate to obtain a polyurethane emulsion with a coating thickness of 6 μm; then place the PE substrate at 35°C and let it stand for 1.5 hours to obtain a polymer film; place the polymer film in an oven at 105°C and heat it for 3 hours to obtain a packaging film containing degradable porous starch. Example 9

[0059] This embodiment provides a method for preparing a packaging film containing degradable porous starch, comprising the following steps:

[0060] 1. According to parts by weight, 200 parts of the modified polyurethane emulsion prepared in Example 6 and 20 parts of the composite microcapsules prepared in Example 3 were added to a beaker and mixed evenly to obtain a polyurethane composite emulsion; a PE substrate with a thickness of 250 μm was selected and wiped with alcohol to obtain a cleaned PE substrate.

[0061] 2. Use a rubber-tipped dropper to drop the polyurethane composite emulsion onto the cleaned PE substrate. During the dropping process, rotate the PE substrate to allow the polyurethane composite emulsion to spread evenly on the surface of the substrate to obtain a polyurethane emulsion with a coating thickness of 10 μm; then place the PE substrate at 40°C and let it stand for 1 hour to obtain a polymer film; place the polymer film in an oven at 100°C and heat it for 3 hours to obtain a packaging film containing degradable porous starch.

[0062] Comparative Example 1

[0063] The difference between this comparative example and Example 9 is that in step 1, no antibacterial agent is added to the core material of the composite microcapsule prepared in Example 3.

[0064] Comparative Example 2

[0065] The difference between this comparative example and Example 9 is that in step 1, 2-methyl methacrylate is not added to the modified polyurethane emulsion prepared in Example 6.

[0066] Comparative Example 3

[0067] The difference between this comparative example and Example 9 is that in step 1, when preparing the composite microcapsules in Example 3, the porous starch is not cross-linked by mixed acid.

[0068] Performance Test 1:

[0069] 1. According to GB / T1040.3-2006 "Determination of tensile properties of plastics Part 3 Film / sheet test conditions", the packaging films containing degradable porous starch prepared in Examples 1-3 and Comparative Examples 1-3 were tested for tensile strength and elongation at break; wherein the tensile rate was 100 mm / min, the initial clamping distance was 80 mm, the gauge length was 25 mm, and each group of tests was measured five times in parallel.

[0070] 2. The antibacterial activity of the packaging films containing degradable porous starch prepared in Examples 7-9 was tested by the inhibition zone method, and the experimental bacteria selected were Escherichia coli.

[0071] 3. The thermal stability of the packaging films containing degradable porous starch prepared in Examples 7 to 9 was tested by thermogravimetry, wherein the heating rate was 10° C. / min, and the temperature during the first stage of thermal decomposition was tested.

[0072] The specific test results are shown in the table below:

[0073] Table 1

[0074] Group Group Example 7 Example 8 Example 9 Comparative Example 1 Comparative Example 2 Comparative Example 3 Tensile strength / (MPa) 4.10 4.68 5.01 5.00 4.50 4.61 Elongation at break / (%) 35.6 37.8 40.1 39.8 35.6 36.7 Diameter of inhibition zone / (mm) 26 28 31 18 27 30 Thermal decomposition temperature / (℃) 60 63 70 68 60 55

[0075] Data Analysis:

[0076] Analyzing the data in Table 1, the packaging films containing degradable porous starch prepared in Examples 7-9 of the present invention have excellent mechanical properties, antibacterial efficacy and heat resistance. However, in Comparative Example 1, no antibacterial agent was added to the composite microcapsules, thereby reducing the antibacterial property of the packaging film, as shown by a significant decrease in the diameter of the antibacterial zone; in Comparative Example 2, no acrylate was added to the modified polyurethane emulsion, which reduced its own mechanical properties, as shown by a decrease in the tensile strength and elongation at break; in Comparative Example 3, the porous starch was not cross-linked with mixed acid, thereby reducing its own heat resistance stability, as shown by a decrease in the thermal decomposition temperature.

[0077] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

[0078] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0079] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a packaging film containing degradable porous starch, characterized in that: The following steps are involved: According to weight parts, 150-200 parts of modified polyurethane emulsion and 10-20 parts of composite microcapsules are uniformly mixed to obtain a polyurethane composite emulsion; the PE substrate is wiped with alcohol to obtain a cleaned PE substrate; The polyurethane composite emulsion is spin-coated on the cleaned PE substrate, and the coating thickness is 5-10 μm; the cleaned PE substrate is then placed at 30-40° C. for 1-2 hours to obtain a polymer film; the polymer film is placed in an oven at 100-110° C. and heated for 3 hours to obtain a packaging film containing degradable porous starch; The preparation method of the modified polyurethane emulsion comprises the following steps: A1, aminosilane and deionized water are mixed evenly to obtain a silanol solution; diphenolic acid powder is added to the silanol solution, and then mixed and reacted at 70-80° C. for 1-2 hours to obtain a mixed solution; the mixed solution is distilled at 100-110° C. for 1-2 hours under nitrogen protection to obtain a modified substance A; A2, acrylate, diisocyanate, polycaprolactone and dibutyltin dilaurate are mixed evenly, heated in a water bath under a nitrogen atmosphere, mixed and reacted to obtain a mixed monomer liquid; the modifier A is added to the mixed monomer liquid, reacted at room temperature to obtain a prepolymer; ethylenediamine is added to the prepolymer for neutralization reaction, and then deionized water is added dropwise and stirred to obtain an emulsion system; the emulsion system is heated to 70-80°C, and an initiator KBS is added dropwise using a peristaltic pump to obtain a composite PUA emulsion, wherein the acrylate is any one of methyl acrylate, ethyl acrylate, 2-methyl methacrylate or 2-ethyl methacrylate; The preparation method of the composite microcapsule comprises the following steps: S1, porous starch and distilled water are mixed to obtain a porous starch solution; the pH value of the porous starch solution is adjusted to 2.5-3.5 with a 0.1 mol / L NaOH solution, and then the porous starch solution and the mixed acid are evenly mixed, reacted at room temperature, and then dried to obtain a solid; the solid is ground, passed through a 100 mesh sieve, and then dried to obtain a porous cross-linked starch; S2, gelatin, gum arabic and deionized water are mixed evenly, and heated at 50-60°C until completely melted to obtain a wall material liquid; benzyl alcohol and 2-benzylphenol are mixed evenly to obtain an antibacterial agent; porous starch and the antibacterial agent are mixed evenly to obtain a core material, wherein the amount ratio of gelatin, gum arabic and deionized water is 10-20g:10-20g:100mL, the amount ratio of benzyl alcohol and 2-benzylphenol is 10-15mL:5-10mL, and the amount ratio of porous starch and the antibacterial agent is 10-20g:15mL; S3, the core material and the wall material liquid are mixed and stirred to obtain an antibacterial agent / wall material liquid; the remaining wall material liquid is added dropwise to the antibacterial agent / wall material liquid, and after the addition is completed, a 10%wt acetic acid solution is used to adjust the pH value to 3-4, and then the temperature is raised to 70-80°C to perform a complex coagulation reaction to obtain a mixed solution; the mixed solution is cooled to room temperature, and then a cold water bath is taken to 5-10°C, and a 1mol / L NaOH solution is used to adjust the pH value of the mixed solution to 8-9, and then 2mL, 3%wt calcium chloride solution is added to solidify for 1h, and filtered to obtain a filter residue; the filter residue is washed 3 times with deionized water, and then dried at 50-60°C for 2h to obtain a composite microcapsule.

2. The method for preparing a packaging film containing degradable porous starch according to claim 1, characterized in that: In step A1, the ratio of aminosilane to deionized water is 5-10 g:100 mL, and the ratio of silanol solution to diphenolic acid powder is 105-110 g:20 g.

3. The method for preparing a packaging film containing degradable porous starch according to claim 1, characterized in that: In step A1, the aminosilane is any one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, phenylaminopropyltrimethoxysilane, and phenylaminopropyltriethoxysilane, and a combination thereof.

4. The method for preparing a packaging film containing degradable porous starch according to claim 1, characterized in that: In step A2, the diisocyanate is any one of diphenylmethane diisocyanate, isophorone diisocyanate or hexamethylene diisocyanate; the amount ratio of acrylate, diisocyanate, polycaprolactone and dibutyltin dilaurate is 10-20g:25-30g:10-20g:0.5g; the amount of modifier A is 10-20g, the amount of ethylenediamine is 10-20mL, the amount of deionized water is 100-200mL, and the amount of initiator is 1-2g.

5. The method for preparing a packaging film containing degradable porous starch according to claim 1, characterized in that: In step A2, the temperature of water bath heating is 70-80°C, the speed of mixing reaction is 100-300r / min, and the duration of mixing reaction is 3h; the duration of room temperature reaction is 1-2h, and the speed of room temperature reaction is 100r / min; the temperature of neutralization reaction is 30°C, the speed of neutralization reaction is 500-1000r / min, and the duration of neutralization reaction is 30-60min; the stirring time is 1-2h, and the stirring speed is 1000-1200r / min.

6. The method for preparing a packaging film containing degradable porous starch according to claim 1, characterized in that: In step S1, the porous starch is any one of potato porous starch, cassava porous starch or sweet potato porous starch and a combination thereof, and the usage ratio of the porous starch to distilled water is 3-5g:20mL; the mixed acid is malic acid and citric acid mixed in a usage ratio of 10g:10g.

7. The method for preparing a packaging film containing degradable porous starch according to claim 1, characterized in that: In step S3, the usage ratio of the core material and the wall material liquid is 20-30 g:50-60 mL, and the volume of the remaining wall material liquid is 50-60 mL.

8. A packaging film containing degradable porous starch, characterized in that: The packaging film containing degradable porous starch is prepared by the method for preparing a packaging film containing degradable porous starch according to any one of claims 1 to 7.