A process for producing fresh-keeping film using plant-based plasticizers

Abstract

The invention discloses a process for producing a fresh-keeping film by using a plant-based plasticizer, and relates to the technical field of fresh-keeping film. The process for producing a fresh-keeping film by using a plant-based plasticizer 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 straw fiber, 10-20 parts of polymerized rosin, and 2-5 parts of triethyl citrate; the plant-based plasticizer is grafted with polylactic acid and ricinoleic acid using epoxy soybean oil; the toughness of the polylactic acid is synergistically improved, and the prepared fresh-keeping film has good mechanical properties and air and moisture permeability.

Description

Technical Field

[0001] The invention relates to the technical field of fresh-keeping films, in particular to a process for producing fresh-keeping films 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 commonly used plasticizers 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 plastic wrap typically uses natural materials such as cellulose, starch, and chitosan, derived from agricultural waste such as wood scraps, straw, stalks, bagasse, fruit peels, and corn cobs. These materials are not only environmentally friendly but also enhance the high-value utilization of agricultural and forestry waste biomass resources. Bio-based plasticizers, derived from biomass materials such as vegetable and animal oils, are low-toxic, low-migration, and renewable, and can partially or completely replace traditional phthalate plasticizers. Bio-based plastic wrap and bio-based plasticizers represent the future development direction of plastic wrap 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, so as 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 mass: 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 straw 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-dry polylactic acid, add maleic anhydride, epoxy soybean oil, triethanolamine and peroxide initiator, melt-blend at 160-170° C., cool and crush to obtain anhydride-modified polylactic acid, and set aside;

[0009] S2, take graphene oxide and freeze-dry it, place it in epoxy soybean oil and ultrasonically disperse it for 20-24h, set aside, take the modified polylactic acid prepared in S1, add xylene, dissolve it with mechanical stirring at 45°C, raise the temperature to 70°C, add the above-prepared graphene oxide soybean oil dispersion and triethanolamine, keep the temperature for reaction for 40-45min, cool to room temperature, add acetone, wash 2-3 times, filter and dry after precipitation to 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 under nitrogen for 3 hours, and continue vacuum 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 corn starch, lactic acid monomer, and stannous octoate, grinding, 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 plastic wrap includes:

[0015] The raw materials are weighed, and the corn straw fiber is placed at 80°C to dry for 24 hours, and the polylactic acid and poly (butyl adipate-butylene terephthalate) are placed at 50°C to dry 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, and subjected to water-cooling-granulation-drying to obtain a blended masterbatch, which is 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 setting at 170℃, 175℃, 175℃, 175℃, speed at 100-150r·min-1; blow molding temperature at 160-170℃.

[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 uses epoxy soybean oil to graft polylactic acid, and then esterifies with ricinoleic acid. Compared with unmodified epoxy soybean oil, it has more active groups, reacts with hydroxyl groups and ester groups on the polylactic acid molecular chain, improves compatibility with polylactic acid, and provides a strong interaction between the compatible interfaces. The grafting of ricinoleic acid synergistically plays the role of a plasticizer. The addition of graphene oxide as a nanofiller has a significant effect on improving the toughness of PLA blending modification. The addition of the plant-based plasticizer to plastic wrap 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 with 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, extending the shelf life of food; DETAILED DESCRIPTION

[0021] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

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

[0023] The antimicrobial agents are nanosilver and nanozinc oxide, with a mass ratio of 1:1. The nanosilver particle size is 20 nm, and the nanozinc oxide particle size is 30 ± 10 nm. Corn straw fiber is crushed by a multifunctional crusher and screened to obtain a 120-mesh particle size.

[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 in parts by mass: 100 parts of polylactic acid, 20 parts of poly(butylene adipate-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, subjected to water-cooling-granulation-drying to obtain a blended masterbatch, and then blown into a 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 100 g of polylactic acid and vacuum dry it, add 2 g of maleic anhydride, 5 g of epoxy soybean oil, 0.1 g of triethanolamine and 0.5 g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170° C., cool and crush to obtain anhydride-modified polylactic acid, and set aside;

[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, dissolve it with mechanical stirring at 45°C, raise the temperature 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 to room temperature, add acetone, wash 3 times, filter and dry after precipitation to 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 and react under nitrogen for 3 h. Continue vacuuming and reacting 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 three 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 were weighed in parts by mass: 100 parts of polylactic acid, 20 parts of poly(butylene adipate-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, and after water-cooling-granulation-drying, a blended masterbatch is obtained, and then blown into a 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 100 g of polylactic acid and vacuum dry it, add 2 g of maleic anhydride, 5 g of epoxy soybean oil, 0.1 g of triethanolamine and 0.5 g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170° C., cool and crush to obtain anhydride-modified polylactic acid, and set aside;

[0037] S2, 0.1g of graphene oxide was freeze-dried and 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 at 45°C to dissolve. The temperature was raised to 70°C, and the above-prepared graphene oxide soybean oil dispersion and 0.1g of triethanolamine were added. The mixture was kept warm for 45min, cooled to room temperature, acetone was added, and the mixture was washed three times. After precipitation, it was filtered and dried to obtain modified epoxy soybean oil.

[0038] S3. Take 30g of ricinoleic acid and 0.2g of p-toluenesulfonic acid and slowly pour them into the modified epoxidized soybean oil prepared in S2. Heat to 150°C, react under nitrogen for 3h, and continue vacuum reaction for 4h 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 were weighed in parts by mass: 100 parts of polylactic acid, 20 parts of poly(butylene adipate-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, and after water-cooling-granulation-drying, a blended masterbatch is obtained, and then blown into a 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 100 g of polylactic acid and vacuum dry it, add 2 g of maleic anhydride, 5 g of epoxy soybean oil, 0.1 g of triethanolamine and 0.5 g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170° C., cool and crush to obtain anhydride-modified polylactic acid, and set aside;

[0045] S2, 0.1g of graphene oxide was freeze-dried and 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 at 45°C to dissolve. The temperature was raised to 70°C, and the above-prepared graphene oxide soybean oil dispersion and 0.1g of triethanolamine were added. The mixture was kept warm for 45min, cooled to room temperature, acetone was added, and the mixture was washed three times. After precipitation, it was filtered and dried to obtain modified epoxy soybean oil.

[0046] S3. Take 30g of ricinoleic acid and 0.2g of p-toluenesulfonic acid and slowly pour them into the modified epoxidized soybean oil prepared in S2. Heat to 150°C, react under nitrogen for 3h, and continue vacuum reaction for 4h 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 was not modified, and the specific steps were as follows:

[0049] The raw materials were weighed in parts by mass: 100 parts of polylactic acid, 20 parts of poly(butylene adipate-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, and after water-cooling-granulation-drying, a blended masterbatch is obtained, and then blown into a 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 100 g of polylactic acid and vacuum dry it, add 2 g of maleic anhydride, 5 g of epoxy soybean oil, 0.1 g of triethanolamine and 0.5 g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170° C., cool and crush to obtain anhydride-modified polylactic acid, and set aside;

[0053] S2, 0.1g of graphene oxide was freeze-dried and 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 at 45°C to dissolve. The temperature was raised to 70°C, and the above-prepared graphene oxide soybean oil dispersion and 0.1g of triethanolamine were added. The mixture was kept warm for 45min, cooled to room temperature, acetone was added, and the mixture was washed three times. After precipitation, it was filtered and dried to obtain modified epoxy soybean oil.

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

[0055] Comparative Example 2: No ricinoleic acid was added to the plant-based plasticizer in Example 3, and the specific steps were as follows:

[0056] The raw materials were weighed in parts by mass: 100 parts of polylactic acid, 20 parts of poly(butylene adipate-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, and after water-cooling-granulation-drying, a blended masterbatch is obtained, and then blown into a 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 100 g of polylactic acid and vacuum dry it, add 2 g of maleic anhydride, 5 g of epoxy soybean oil, 0.1 g of triethanolamine and 0.5 g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170° C., cool and crush to obtain anhydride-modified polylactic acid, and set aside;

[0060] S2, 0.1g of graphene oxide was freeze-dried, placed in 20g of epoxy soybean oil and ultrasonically dispersed 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 mixture 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 were weighed in parts by mass: 100 parts of polylactic acid, 20 parts of poly(butylene adipate-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, and after water-cooling-granulation-drying, a blended masterbatch is obtained, and then blown into a 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 100 g of polylactic acid and vacuum dry it, add 2 g of maleic anhydride, 5 g of epoxy soybean oil, 0.1 g of triethanolamine and 0.5 g of 2,5-dimethyl-2,5-bis(tert-butyl peroxide)hexane, melt blend at 170° C., cool and crush to obtain anhydride-modified polylactic acid, and set aside;

[0067] S2, take 20g of epoxy soybean oil, add the modified polylactic acid prepared in S1 and 200ml of xylene in sequence, dissolve with 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 and react for 45min, cool to room temperature, add acetone, wash three times, filter and dry after precipitation to obtain modified epoxy soybean oil;

[0068] S3. Take 30g of ricinoleic acid and 0.2g of p-toluenesulfonic acid and slowly pour them into the modified epoxidized soybean oil prepared in S2. Heat to 150°C, react under nitrogen for 3h, and continue vacuum reaction for 4h 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. The mechanical properties of the films were measured using a GBH-1 electronic tensile testing machine in accordance with ISO 1184. The cling films prepared in Examples 1-3 and Comparative Examples 1-3 were cut into 150 mm × 10 mm rectangular strips. The test speed was 50 mm / min and the test clamp distance was 50 mm.

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

[0073] 3. The cling films prepared in Examples 1-3 and Comparative Examples 1-3 were taken and their air permeability was measured using a gas permeability meter using a pressure differential method according to GB / T 1038.

[0074]

[0075] Conclusion: Based on 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. The tensile strength and elongation at break are both reduced, and the air and moisture permeability of the cling film is also reduced accordingly; 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 invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

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 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 straw fiber, 10-20 parts of polymerized rosin, and 2-5 parts of triethyl citrate; The preparation steps of the plant-based plasticizer include: S1. vacuum-dry polylactic acid, add maleic anhydride, epoxy soybean oil, triethanolamine and peroxide initiator, melt-blend at 160-170° C., cool and crush to obtain anhydride-modified polylactic acid, and set aside; S2, take graphene oxide and freeze-dry it, place it in epoxy soybean oil and ultrasonically disperse it for 20-24h, set aside, take the modified polylactic acid prepared in S1, add xylene, dissolve it with mechanical stirring at 45°C, raise the temperature to 70°C, add the above-prepared graphene oxide soybean oil dispersion and triethanolamine, keep the temperature for reaction for 40-45min, cool to room temperature, add acetone, wash 2-3 times, filter and dry after precipitation to obtain modified epoxy soybean oil; S3. Slowly pour ricinoleic acid and p-toluenesulfonic acid into the modified epoxidized soybean oil prepared in S2, raise the temperature to 120-150°C, react under nitrogen for 3 hours, and continue vacuum reaction for 2-4 hours to obtain a plant-based plasticizer; The preparation steps of the modified corn starch include: mixing corn starch, lactic acid monomer and stannous octoate, grinding, 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.

2. The process for producing fresh-keeping film using a plant-based plasticizer according to claim 1, wherein: 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.

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

4. The process for producing fresh-keeping film using a plant-based plasticizer according to claim 1, wherein: 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.

5. The process for producing fresh-keeping film using a plant-based plasticizer according to claim 1, wherein: The process for producing fresh-keeping film comprises: The raw materials are weighed, and the corn straw fiber is placed at 80°C to dry for 24 hours, and the polylactic acid and poly (butyl adipate-butylene terephthalate) are placed at 50°C to dry 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, and subjected to water-cooling-granulation-drying to obtain a blended masterbatch, which is then blown into a film and cooled to obtain a fresh-keeping film.

6. The process for producing fresh-keeping film using a plant-based plasticizer according to claim 5, characterized in that: The twin-screw extruder setting parameters include: temperature setting of 170℃, 175℃, 175℃, 175℃, and speed of 100-150r·min -1 ; Blow molding temperature is 160-170℃.

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