Process for producing preservative film by using plant-based plasticizer

Abstract

The invention discloses a process for producing a preservative film by using a plant-based plasticizer, and relates to the technical field of preservative films. The preservative film is prepared from the following raw materials in parts by mass: 100 to 120 parts of polylactic acid, 10 to 20 parts of poly (butyl adipate-butylene terephthalate), 2 to 5 parts of the plant-based plasticizer, 0.05 to 0.1 part of an antibacterial agent, 5 to 10 parts of modified corn starch, 2 to 3 parts of corn straw fiber, 10 to 20 parts of polymerized rosin and 2 to 5 parts of triethyl citrate. Wherein the plant-based plasticizer adopts epoxidized soybean oil grafted polylactic acid and ricinoleic acid; the toughness of polylactic acid is synergistically improved, and the prepared preservative film has good mechanical properties and air and moisture permeability.

Description

Technical Field

[0001] The invention relates to the technical field of cling film, in particular to a process for producing cling film by using a plant-based plasticizer. Background Art

[0002] The plasticizer added in the production of cling film is a chemical additive used to improve the performance of plastics and is widely used in food packaging materials. The main function of plasticizers is to make plastics softer and more ductile, thereby improving their processability and performance. However, the type and amount of plasticizers used have an important impact on the safety of food packaging; for example, the use of plasticizers commonly used in industry, including DEHP, in PVC cling film has received some attention because it can easily migrate out when exposed to high temperatures or oils and penetrate into food, which may have adverse effects on human health. In addition, DEHP is also considered to have a carcinogenic risk; therefore, researchers have turned their attention to bio-based materials;

[0003] Bio-based cling film usually uses natural materials such as cellulose, starch, chitosan, etc. These materials come from agricultural waste, such as wood scraps, straw, stalks, bagasse, peels and corn cobs. These materials are not only green and environmentally friendly, but also can improve the high-value utilization of agricultural and forestry waste biomass resources. Bio-based plasticizers are made from biomass materials, such as vegetable oils, animal oils, etc., with low toxicity, low migration and renewability, and can partially or completely replace traditional phthalate plasticizers; bio-based cling film and bio-based plasticizers represent the future development direction of cling film materials. Summary of the invention

[0004] The object of the present invention is to provide a process for producing fresh-keeping film using a plant-based plasticizer to solve the problems raised in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A process for producing a fresh-keeping film using a plant-based plasticizer. The fresh-keeping film comprises the following raw materials in parts by weight: 100-120 parts of polylactic acid, 10-20 parts of poly(butyl adipate-butylene terephthalate), 2-5 parts of a plant-based plasticizer, 0.05-0.1 parts of an antibacterial agent, 5-10 parts of modified corn starch, 2-3 parts of corn stalk fiber, 10-20 parts of polymerized rosin, and 2-5 parts of triethyl citrate.

[0007] The preparation steps of the plant-based plasticizer include:

[0008] S1, vacuum-drying polylactic acid, adding maleic anhydride, epoxy soybean oil, triethanolamine and peroxide initiator, melt-blending at 160-170° C., cooling and crushing to obtain anhydride-modified polylactic acid, and setting aside;

[0009] S2, take graphene oxide and freeze-dry it, place it in epoxy soybean oil for ultrasonic dispersion for 20-24h, and set it aside, take the modified polylactic acid prepared in S1, add xylene, dissolve it by mechanical stirring at 45°C, heat it to 70°C, add the above-prepared graphene oxide soybean oil dispersion and triethanolamine, keep the temperature for reaction for 40-45min, cool it to room temperature, add acetone, wash it 2-3 times, filter and dry it after precipitation, and obtain modified epoxy soybean oil;

[0010] S3. Take ricinoleic acid and p-toluenesulfonic acid and slowly pour them into the modified epoxidized soybean oil prepared in S2, raise the temperature to 120-150° C., react for 3 hours under nitrogen, and continue to vacuum the reaction for 2-4 hours to obtain a plant-based plasticizer.

[0011] The molar ratio of maleic anhydride to total epoxidized soybean oil is 1:(1-2); the peroxide initiator is 2,5-dimethyl-2,5-bis(tert-butylperoxide)hexane; and the graphene oxide soybean oil dispersion contains (0.5-1) wt% graphene oxide.

[0012] The antibacterial agent is one or more combinations of nano silver, nano zinc oxide and nano titanium oxide.

[0013] The preparation steps of the modified corn starch include: mixing and grinding corn starch, lactic acid monomer and stannous octoate, sealing and hydrothermal treatment at 80-100° C., reacting for 1-2 hours, cooling to room temperature, adding acetone, washing 2-3 times, filtering after precipitation, and drying at 55° C.; wherein the mass ratio of corn starch to lactic acid monomer is 1:(0.05-0.2); and the amount of stannous octoate added is 0.03-0.06wt% of the lactic acid monomer.

[0014] The production process of cling film includes:

[0015] The raw materials are weighed, and the corn straw fiber is dried at 80°C for 24 hours, and the polylactic acid and poly(butyl adipate-butylene terephthalate) are dried at 50°C for 24 hours; the treated polylactic acid, corn straw fiber, poly(butyl adipate-butylene terephthalate), plant plasticizer, antibacterial agent, modified corn starch, polymerized rosin and triethyl citrate are mixed, stirred for 10-20 minutes, placed in a twin-screw extruder, blended and extruded into long strips, subjected to water-cooling-granulation-drying to obtain a blended masterbatch, and then blown into a film, and cooled to obtain a fresh-keeping film.

[0016] Among them, the setting parameters of the twin-screw extruder include: temperature settings of 170°C, 175°C, 175°C, 175°C, and a speed of 100-150r·min-1; and a blow molding temperature of 160-170°C.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. The plant-based plasticizer prepared by the present invention adopts epoxy soybean oil to graft polylactic acid, and then esterifies with castor oil acid. Compared with unmodified epoxy soybean oil, the plant-based plasticizer has more active groups, reacts with hydroxyl groups, ester groups, etc. on the polylactic acid molecular chain, improves the compatibility with polylactic acid, and provides a strong interaction between compatible interfaces; the grafting and introduction of castor oil acid synergistically play the role of plasticizer; the addition of graphene oxide as a nanofiller plays a significant role in improving the toughness of PLA blending modification; adding the plant-based plasticizer to the cling film can promote the crystallization of polylactic acid and improve the toughness of polylactic acid;

[0019] 2. Add modified corn starch and graft polymerize corn starch with lactic acid monomer to improve the hydrophobicity of starch and the compatibility of starch and polylactic acid, thereby improving the mechanical properties of polylactic acid;

[0020] 3. Adding a small amount of metal nano antibacterial agent, the prepared polylactic acid cling film has antibacterial effect in practical application, prolonging the food preservation; DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0022] In the experiment, the specification of polylactic acid is Mw ~ 60000, the brand of poly (butylene adipate-terephthalate) is BASF pbat c1200 from Germany, the corn starch is straight-chain corn starch with an active ingredient content of 70%, purchased from Wuhan Huaxiang Kejie Biotechnology Co., Ltd., and the polymerized rosin is purchased from Wuhan Kemik Biomedicine Technology Co., Ltd.; graphene oxide is a 10 mg / ml aqueous dispersion purchased from Aladdin Biochemical Technology Co., Ltd.

[0023] The antibacterial agents are nanosilver and nanozinc oxide, with a mass ratio of 1:1. The particle size of the nanosilver is 20 nm, and the particle size of the nanozinc oxide is 30±10 nm; the corn straw fiber is crushed by a multifunctional crusher, and the 120 mesh particle size is separated by screening;

[0024] Example 1: This example provides a process for producing fresh-keeping film using a plant-based plasticizer. The specific process steps are as follows:

[0025] The raw materials were weighed by mass: 100 parts of polylactic acid, 20 parts of poly(butylene adipate-butylene terephthalate), 3 parts of plant-based plasticizer, 0.05 parts of antibacterial agent, 6 parts of modified corn starch, 2 parts of corn straw fiber, 20 parts of polymerized rosin, and 3 parts of triethyl citrate;

[0026] The corn straw fiber is placed at 80°C for drying for 24 hours, and the polylactic acid and poly(butyl adipate-butylene terephthalate) are placed at 50°C for drying for 24 hours; the treated polylactic acid, corn straw fiber, poly(butyl adipate-butylene terephthalate), plant plasticizer, antibacterial agent, modified corn starch, polymerized rosin and triethyl citrate are mixed, stirred for 20 minutes, placed in a twin-screw extruder, set the temperature to 170°C, 175°C, 175°C, 175°C, the speed to 150r / min, blended and extruded into long strips, through water-cooling-pelletizing-drying, a blended masterbatch is obtained, and then blown into film at a blowing temperature of 160°C, and cooled to obtain a fresh-keeping film.

[0027] The preparation steps of the plant-based plasticizer include:

[0028] S1, take 100g of polylactic acid and dry it in vacuum, add 2g of maleic anhydride, 5g of epoxy soybean oil, 0.1g of triethanolamine and 0.5g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170°C, and crush after cooling to obtain anhydride-modified polylactic acid for standby use;

[0029] S2, take 0.1g of graphene oxide and freeze-dry it, place it in 20g of epoxy soybean oil and ultrasonically disperse it for 24h, set aside, take the modified polylactic acid prepared in S1, add 200ml of xylene, mechanically stir and dissolve it at 45°C, heat it to 70°C, add the above-prepared graphene oxide soybean oil dispersion and 0.1g of triethanolamine, keep the temperature for reaction for 40min, cool it to room temperature, add acetone, wash it 3 times, filter and dry it after precipitation, and obtain modified epoxy soybean oil;

[0030] S3. Take 20 g of ricinoleic acid and 0.2 g of p-toluenesulfonic acid and slowly pour them into the modified epoxidized soybean oil prepared in S2. Heat to 120° C., react for 3 h under nitrogen, and continue to vacuum react for 3 h to obtain a plant-based plasticizer.

[0031] The preparation steps of modified corn starch include: mixing and grinding 20g corn starch, 2g lactic acid monomer, and 0.001g stannous octoate, sealing and hydrothermal at 80°C, reacting for 2h, cooling to room temperature, adding acetone, washing 3 times, filtering after precipitation, and drying at 55°C.

[0032] Example 2: This example provides a process for producing fresh-keeping film using a plant-based plasticizer. The specific process steps are as follows:

[0033] The raw materials weighed by mass include: 100 parts of polylactic acid, 20 parts of poly(butylene adipate-butylene terephthalate), 4 parts of plant-based plasticizer, 0.05 parts of antibacterial agent, 8 parts of modified corn starch, 3 parts of corn straw fiber, 20 parts of polymerized rosin, and 3 parts of triethyl citrate;

[0034] The corn straw fiber is placed at 80°C for drying for 24 hours, and the polylactic acid and poly(butyl adipate-butylene terephthalate) are placed at 50°C for drying for 24 hours; the treated polylactic acid, corn straw fiber, poly(butyl adipate-butylene terephthalate), plant plasticizer, antibacterial agent, modified corn starch, polymerized rosin and triethyl citrate are mixed, stirred for 20 minutes, placed in a twin-screw extruder, set the temperature to 170°C, 175°C, 175°C, 175°C, and the speed to 150r / min to blend and extrude long strips, after water-cooling-pelletizing-drying, a blended masterbatch is obtained, and then blown into film at a blowing temperature of 160°C, and cooled to obtain a fresh-keeping film.

[0035] The preparation steps of the plant-based plasticizer include:

[0036] S1, take 100g of polylactic acid and dry it in vacuum, add 2g of maleic anhydride, 5g of epoxy soybean oil, 0.1g of triethanolamine and 0.5g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170°C, and crush after cooling to obtain anhydride-modified polylactic acid for standby use;

[0037] S2, 0.1g of graphene oxide was freeze-dried, placed in 20g of epoxy soybean oil for ultrasonic dispersion for 24h, and set aside. The modified polylactic acid prepared in S1 was taken, 200ml of xylene was added, and mechanical stirring was performed to dissolve at 45°C. The temperature was raised to 70°C, and the above-prepared graphene oxide soybean oil dispersion and 0.1g of triethanolamine were added. The reaction was kept warm for 45min, cooled to room temperature, acetone was added, and washed 3 times. After precipitation, it was filtered and dried to obtain modified epoxy soybean oil.

[0038] S3. Take 30 g of ricinoleic acid and 0.2 g of p-toluenesulfonic acid and slowly pour them into the modified epoxidized soybean oil prepared in S2. Heat to 150° C., react for 3 h under nitrogen, and continue to vacuum react for 4 h to obtain a plant-based plasticizer.

[0039] The preparation steps of modified corn starch include: mixing and grinding 20g corn starch, 3g lactic acid monomer, and 0.001g stannous octoate, sealing and hydrothermal at 100°C, reacting for 1h, cooling to room temperature, adding acetone, washing 3 times, filtering after precipitation, and drying at 55°C.

[0040] Example 3: This example provides a process for producing fresh-keeping film using a plant-based plasticizer. The specific process steps are as follows:

[0041] The raw materials weighed by mass include: 100 parts of polylactic acid, 20 parts of poly(butyl adipate-butylene terephthalate), 5 parts of plant-based plasticizer, 0.05 parts of antibacterial agent, 10 parts of modified corn starch, 3 parts of corn straw fiber, 20 parts of polymerized rosin, and 3 parts of triethyl citrate;

[0042] The corn straw fiber is placed at 80°C for drying for 24 hours, and the polylactic acid and poly(butyl adipate-butylene terephthalate) are placed at 50°C for drying for 24 hours; the treated polylactic acid, corn straw fiber, poly(butyl adipate-butylene terephthalate), plant plasticizer, antibacterial agent, modified corn starch, polymerized rosin and triethyl citrate are mixed, stirred for 20 minutes, placed in a twin-screw extruder, set the temperature to 170°C, 175°C, 175°C, 175°C, and the speed to 150r / min to blend and extrude long strips, after water-cooling-pelletizing-drying, a blended masterbatch is obtained, and then blown into film at a blowing temperature of 160°C, and cooled to obtain a fresh-keeping film.

[0043] The preparation steps of the plant-based plasticizer include:

[0044] S1, take 100g of polylactic acid and dry it in vacuum, add 2g of maleic anhydride, 5g of epoxy soybean oil, 0.1g of triethanolamine and 0.5g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170°C, and crush after cooling to obtain anhydride-modified polylactic acid for standby use;

[0045] S2, 0.1g of graphene oxide was freeze-dried, placed in 20g of epoxy soybean oil for ultrasonic dispersion for 24h, and set aside. The modified polylactic acid prepared in S1 was taken, 200ml of xylene was added, and mechanical stirring was performed to dissolve at 45°C. The temperature was raised to 70°C, and the above-prepared graphene oxide soybean oil dispersion and 0.1g of triethanolamine were added. The reaction was kept warm for 45min, cooled to room temperature, acetone was added, and washed 3 times. After precipitation, it was filtered and dried to obtain modified epoxy soybean oil.

[0046] S3. Take 30 g of ricinoleic acid and 0.2 g of p-toluenesulfonic acid and slowly pour them into the modified epoxidized soybean oil prepared in S2. Heat to 150° C., react for 3 h under nitrogen, and continue to vacuum react for 4 h to obtain a plant-based plasticizer.

[0047] The preparation steps of modified corn starch include: mixing and grinding 20g corn starch, 3g lactic acid monomer, and 0.001g stannous octoate, sealing and hydrothermal at 100°C, reacting for 1h, cooling to room temperature, adding acetone, washing 3 times, filtering after precipitation, and drying at 55°C.

[0048] Comparative Example 1: With respect to Example 3, the corn starch is not subjected to modification treatment, and the specific steps are as follows:

[0049] The raw materials weighed by mass include: 100 parts of polylactic acid, 20 parts of poly(butyl adipate-butylene terephthalate), 5 parts of plant-based plasticizer, 0.05 parts of antibacterial agent, 10 parts of corn starch, 3 parts of corn straw fiber, 20 parts of polymerized rosin, and 3 parts of triethyl citrate;

[0050] The corn straw fiber is placed at 80°C for drying for 24 hours, and the polylactic acid and poly(butyl adipate-butylene terephthalate) are placed at 50°C for drying for 24 hours; the treated polylactic acid, corn straw fiber, poly(butyl adipate-butylene terephthalate), plant plasticizer, antibacterial agent, modified corn starch, polymerized rosin and triethyl citrate are mixed, stirred for 20 minutes, placed in a twin-screw extruder, set the temperature to 170°C, 175°C, 175°C, 175°C, and the speed to 150r / min to blend and extrude long strips, after water-cooling-pelletizing-drying, a blended masterbatch is obtained, and then blown into film at a blowing temperature of 160°C, and cooled to obtain a fresh-keeping film.

[0051] The preparation steps of the plant-based plasticizer include:

[0052] S1, take 100g of polylactic acid and dry it in vacuum, add 2g of maleic anhydride, 5g of epoxy soybean oil, 0.1g of triethanolamine and 0.5g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170°C, and crush after cooling to obtain anhydride-modified polylactic acid for standby use;

[0053] S2, 0.1g of graphene oxide was freeze-dried, placed in 20g of epoxy soybean oil for ultrasonic dispersion for 24h, and set aside. The modified polylactic acid prepared in S1 was taken, 200ml of xylene was added, and mechanical stirring was performed to dissolve at 45°C. The temperature was raised to 70°C, and the above-prepared graphene oxide soybean oil dispersion and 0.1g of triethanolamine were added. The reaction was kept warm for 45min, cooled to room temperature, acetone was added, and washed 3 times. After precipitation, it was filtered and dried to obtain modified epoxy soybean oil.

[0054] S3. Take 30 g of ricinoleic acid and 0.2 g of p-toluenesulfonic acid and slowly pour them into the modified epoxidized soybean oil prepared in S2. Heat to 150° C., react for 3 h under nitrogen, and continue to vacuum react for 4 h to obtain a plant-based plasticizer.

[0055] Comparative Example 2: In Example 3, ricinoleic acid is not added to the plant-based plasticizer, and the specific steps are as follows:

[0056] The raw materials weighed by mass include: 100 parts of polylactic acid, 20 parts of poly(butyl adipate-butylene terephthalate), 5 parts of plant-based plasticizer, 0.05 parts of antibacterial agent, 10 parts of modified corn starch, 3 parts of corn straw fiber, 20 parts of polymerized rosin, and 3 parts of triethyl citrate;

[0057] The corn straw fiber is placed at 80°C for drying for 24 hours, and the polylactic acid and poly(butyl adipate-butylene terephthalate) are placed at 50°C for drying for 24 hours; the treated polylactic acid, corn straw fiber, poly(butyl adipate-butylene terephthalate), plant plasticizer, antibacterial agent, modified corn starch, polymerized rosin and triethyl citrate are mixed, stirred for 20 minutes, placed in a twin-screw extruder, set the temperature to 170°C, 175°C, 175°C, 175°C, and the speed to 150r / min to blend and extrude long strips, after water-cooling-pelletizing-drying, a blended masterbatch is obtained, and then blown into film at a blowing temperature of 160°C, and cooled to obtain a fresh-keeping film.

[0058] The preparation steps of the plant-based plasticizer include:

[0059] S1, take 100g of polylactic acid and dry it in vacuum, add 2g of maleic anhydride, 5g of epoxy soybean oil, 0.1g of triethanolamine and 0.5g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170°C, and crush after cooling to obtain anhydride-modified polylactic acid for standby use;

[0060] S2, 0.1g of graphene oxide was freeze-dried, placed in 20g of epoxidized soybean oil and ultrasonically dispersed for 24h, set aside, the modified polylactic acid prepared in S1 was taken, 200ml of xylene was added, mechanically stirred and dissolved at 45°C, the temperature was raised to 70°C, the above-prepared graphene oxide soybean oil dispersion and 0.1g of triethanolamine were added, the reaction was kept warm for 45min, cooled to room temperature, acetone was added, washed 3 times, filtered and dried after precipitation, to obtain a plant-based plasticizer.

[0061] The preparation steps of modified corn starch include: mixing and grinding 20g corn starch, 3g lactic acid monomer, and 0.001g stannous octoate, sealing and hydrothermal at 100°C, reacting for 1h, cooling to room temperature, adding acetone, washing 3 times, filtering after precipitation, and drying at 55°C.

[0062] Comparative Example 3: With respect to Example 3, graphene oxide is not added, and the specific steps are as follows:

[0063] The raw materials weighed by mass include: 100 parts of polylactic acid, 20 parts of poly(butyl adipate-butylene terephthalate), 5 parts of plant-based plasticizer, 0.05 parts of antibacterial agent, 10 parts of modified corn starch, 3 parts of corn straw fiber, 20 parts of polymerized rosin, and 3 parts of triethyl citrate;

[0064] The corn straw fiber is placed at 80°C for drying for 24 hours, and the polylactic acid and poly(butyl adipate-butylene terephthalate) are placed at 50°C for drying for 24 hours; the treated polylactic acid, corn straw fiber, poly(butyl adipate-butylene terephthalate), plant plasticizer, antibacterial agent, modified corn starch, polymerized rosin and triethyl citrate are mixed, stirred for 20 minutes, placed in a twin-screw extruder, set the temperature to 170°C, 175°C, 175°C, 175°C, and the speed to 150r / min to blend and extrude long strips, after water-cooling-pelletizing-drying, a blended masterbatch is obtained, and then blown into film at a blowing temperature of 160°C, and cooled to obtain a fresh-keeping film.

[0065] The preparation steps of the plant-based plasticizer include:

[0066] S1, take 100g of polylactic acid and dry it in vacuum, add 2g of maleic anhydride, 5g of epoxy soybean oil, 0.1g of triethanolamine and 0.5g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170°C, and crush after cooling to obtain anhydride-modified polylactic acid for standby use;

[0067] S2, take 20g of epoxy soybean oil, add the modified polylactic acid prepared in S1 and 200ml of xylene in sequence, dissolve under mechanical stirring at 45°C, heat to 70°C, add the above-prepared graphene oxide soybean oil dispersion and 0.1g of triethanolamine, keep warm for 45min, cool to room temperature, add acetone, wash 3 times, filter and dry after precipitation to obtain modified epoxy soybean oil;

[0068] S3. Take 30 g of ricinoleic acid and 0.2 g of p-toluenesulfonic acid and slowly pour them into the modified epoxidized soybean oil prepared in S2. Heat to 150° C., react for 3 h under nitrogen, and continue to vacuum react for 4 h to obtain a plant-based plasticizer.

[0069] The preparation steps of modified corn starch include: mixing and grinding 20g corn starch, 3g lactic acid monomer, and 0.001g stannous octoate, sealing and hydrothermal at 100°C, reacting for 1h, cooling to room temperature, adding acetone, washing 3 times, filtering after precipitation, and drying at 55°C.

[0070] Detection test

[0071] 1. According to ISO 1184, the mechanical properties of the film were measured using a GBH-1 electronic tensile testing machine. The cling films prepared in Examples 1-3 and Comparative Examples 1-3 were cut into rectangular strips of 150 mm×10 mm, with an experimental test speed of 50 mm / min and a test clamp distance of 50 mm.

[0072] 2. The cling film prepared in Examples 1-3 and Comparative Examples 1-3 was taken, and the moisture permeability of the cling film was measured by a water vapor transmission rate meter using the moisture permeability cup method in accordance with GB / T 1037.

[0073] 3. Take the cling film prepared in Example 1-3 and Comparative Example 1-3, and measure the air permeability of the cling film by a gas permeability tester using a pressure difference method according to GB / T 1038.

[0074]

[0075] Conclusion: Through the above experimental data, Example 3 is a set of data with relatively excellent mechanical properties among Examples 1-3. According to the data of Example 3, the corn starch is adjusted without modification to obtain a set of data of Comparative Example 1, in which the tensile strength and elongation at break are both reduced, and the air permeability and moisture permeability of the cling film are also reduced; Comparative Example 2 does not add ricinoleic acid, which affects the performance of the plasticizer and reduces the toughness of the cling film; Comparative Example 3 does not add graphene oxide, which has a slight effect on the cling film.

[0076] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A process for producing fresh-keeping film using a plant-based plasticizer, characterized in that: The fresh-keeping film comprises the following raw materials in parts by weight: 100-120 parts of polylactic acid, 10-20 parts of poly(butyl adipate-butylene terephthalate), 2-5 parts of plant-based plasticizer, 0.05-0.1 parts of antibacterial agent, 5-10 parts of modified corn starch, 2-3 parts of corn straw fiber, 10-20 parts of polymerized rosin, and 2-5 parts of triethyl citrate.

2. A process for producing fresh-keeping film using a plant-based plasticizer according to claim 1, characterized in that: The preparation steps of plant-based plasticizers include: S1, vacuum-drying polylactic acid, adding maleic anhydride, epoxy soybean oil, triethanolamine and peroxide initiator, melt blending at 160-170° C., cooling and crushing to obtain anhydride-modified polylactic acid, and setting aside; S2, take graphene oxide and freeze-dry it, place it in epoxy soybean oil for ultrasonic dispersion for 20-24h, and set it aside, take the modified polylactic acid prepared in S1, add xylene, dissolve it by mechanical stirring at 45°C, heat it to 70°C, add the above-prepared graphene oxide soybean oil dispersion and triethanolamine, keep the temperature for reaction for 40-45min, cool it to room temperature, add acetone, wash it 2-3 times, filter and dry it after precipitation, and obtain modified epoxy soybean oil; S3. Take ricinoleic acid and p-toluenesulfonic acid and slowly pour them into the modified epoxidized soybean oil prepared in S2, raise the temperature to 120-150° C., react for 3 hours under nitrogen, and continue to vacuum the reaction for 2-4 hours to obtain a plant-based plasticizer.

3. A process for producing fresh-keeping film using a plant-based plasticizer according to claim 2, characterized in that: The molar ratio of maleic anhydride to total epoxidized soybean oil is 1:(1-2); the graphene oxide soybean oil dispersion contains (0.5-1) wt% graphene oxide.

4. A process for producing fresh-keeping film using a plant-based plasticizer according to claim 1, characterized in that: The antibacterial agent is one or more combinations of nano silver, nano zinc oxide and nano titanium oxide.

5. A process for producing fresh-keeping film using a plant-based plasticizer according to claim 1, characterized in that: The preparation steps of the modified corn starch include: mixing and grinding corn starch, lactic acid monomer and stannous octoate, sealing and hydrothermal treatment at 80-100° C., reacting for 1-2 hours, cooling to room temperature, adding acetone, washing 2-3 times, filtering after precipitation, and drying at 55° C.

6. A process for producing fresh-keeping film using a plant-based plasticizer according to claim 5, characterized in that: The mass ratio of corn starch to lactic acid monomer is 1:(0.05-0.2); the added amount of stannous octoate is 0.03-0.06wt% of the lactic acid monomer.

7. A process for producing fresh-keeping film using a plant-based plasticizer according to claim 1, characterized in that: The process for producing fresh-keeping film comprises: The raw materials are weighed, and the corn straw fiber is dried at 80°C for 24 hours, and the polylactic acid and poly(butyl adipate-butylene terephthalate) are dried at 50°C for 24 hours; the treated polylactic acid, corn straw fiber, poly(butyl adipate-butylene terephthalate), plant plasticizer, antibacterial agent, modified corn starch, polymerized rosin and triethyl citrate are mixed, stirred for 10-20 minutes, placed in a twin-screw extruder, blended and extruded into long strips, subjected to water-cooling-granulation-drying to obtain a blended masterbatch, and then blown into a film, and cooled to obtain a fresh-keeping film.

8. A process for producing fresh-keeping film using a plant-based plasticizer according to claim 7, characterized in that: The twin-screw extruder setting parameters include: temperature settings of 170°C, 175°C, 175°C, 175°C, and speed of 100-150r·min -1 ; Blow molding temperature is 160-170℃.

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