A transparent food preservation film with oxidative biodegradability and its preparation method

Abstract

This invention discloses a transparent food preservation film with oxidative biodegradability and its preparation method, relating to the field of biodegradable polyester materials technology. The film comprises the following components: 50-65 parts biodegradable polyester resin, 25-35 parts polylactic acid, and 5-20 parts auxiliary resin; the auxiliary resin is polyurethane. This invention obtains a film with excellent comprehensive mechanical properties through the compounding of biodegradable polyester and polylactic acid. The addition of reactive polyurethane and modified biodegradable polyester auxiliary resins endows the film with more degradation sites, good antibacterial properties, and a cross-linking network, thereby improving the overall performance of the prepared food preservation film, including its mechanical properties, oxidative biodegradability, and barrier properties.

Description

Technical Field

[0001] This invention relates to the field of biodegradable polyester materials technology, specifically a transparent food preservation film with oxidative biodegradability and its preparation method. Background Technology

[0002] Plastic wrap is an important packaging material for extending the shelf life of packaged goods, and its demand is gradually increasing with economic development. Traditional plastic wrap materials include fossil fuels such as polyethylene, polyvinyl chloride, and polyvinylidene fluoride, which are difficult to dispose of after disposal. Biodegradable materials, such as biodegradable polyesters, have great potential in the field of environmentally friendly packaging materials. Biodegradable polyesters such as polybutylene terephthalate (PBAT) and polybutylene succinate (PBS) have good flexibility, but their texture is relatively soft and their film-forming properties are poor. Therefore, we propose a transparent plastic wrap with oxidative biodegradability and its preparation method. Summary of the Invention

[0003] The purpose of this invention is to provide a transparent food preservation film with oxidative biodegradability and its preparation method, so as to solve the problems mentioned in the background art.

[0004] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a transparent food preservation film with oxidative biodegradability, comprising the following components: 50-65 parts of biodegradable polyester resin, 25-35 parts of polylactic acid (PLA), and 5-20 parts of auxiliary resin.

[0005] Furthermore, the biodegradable polyester resin is one or a mixture of two of polybutylene terephthalate (PBAT) and polybutylene succinate (PBS).

[0006] Furthermore, the auxiliary resin includes, but is not limited to, one or more of the following: polycaprolactone (PCL), polyether block amide (PEBA), polyhydroxyalkanoate (PHA), starch graft copolymer, polyurethane, and cellulose.

[0007] Starch-g-PLA is the preferred starch graft copolymer.

[0008] In the above technical solution, the compound of biodegradable polyester resin and polylactic acid is used as the main resin. After blending, it can effectively improve the brittleness and film-forming properties of the blend, and has good transparency and flexibility. It also has oxidative biodegradability. Biodegrading enzymes (such as esterase, laccase, lipase, protease, peroxidase, and lignin-degrading enzyme) can catalyze the hydrolysis of ester bonds, oxidize aliphatic chains to generate free radicals, oxidize aromatic terephthalic acid units, and oxidize methylene (-CH2-) to generate ketone / aldehyde structures, initiating chain scission. Auxiliary resins are then added to plasticize, toughen, and promote oxidation / biodegradation. For example, PCL can improve the plasticity of the blend at low temperatures and enhance its ductility; PEBA toughens; PHA blends can accelerate microbial degradation; starch graft copolymers have both filling and degradation-accelerating effects. Polyurethane can also toughen, improve barrier properties, and regulate degradation rate; cellulose can act as a bio-based reinforcing agent to improve mechanical strength, barrier properties, and biodegradability.

[0009] A method for preparing a transparent food preservation film with oxidative biodegradability includes the following process: melt extruding biodegradable polyester resin, polylactic acid, and auxiliary resin, and blow molding them into a film to obtain the food preservation film.

[0010] Furthermore, the melt extrusion adopts a twin-screw extruder with a length-to-diameter ratio L / D = 40, segmented temperature control, and segmented temperatures of 160-170℃, 170-175℃, 170-175℃, and 165-175℃ at the die head; the rotation speed is 150-250 rpm.

[0011] Furthermore, the auxiliary resin is polyurethane, which is prepared by the following process:

[0012] Polytrimethylene ether glycol was dehydrated under vacuum at 120°C for 2 hours, then cooled to 63–67°C. The mixture was stirred, and 1,6-hexamethylene diisocyanate, catalyst, and solvent were added. The temperature was raised to 78–82°C, and the reaction was carried out for 150–200 minutes until the NCO group content no longer changed, thus obtaining the prepolymer.

[0013] Cool to 63-67℃, add glycidyl ether chain extender, stir and heat to 88-92℃, react for 100-150 min to obtain polyurethane.

[0014] Furthermore, the polyurethane comprises the following components by weight: 30-60 parts of polytrimethylene ether glycol, 10-20 parts of 1,6-hexamethylene diisocyanate, 3.6-7.2 parts of glycidyl ether chain extender, 0.1-0.2 parts of catalyst, and 28.5-68 parts of solvent;

[0015] The glycidyl ether chain extender is one of glycidyl ether ethanol and p-hydroxyphenyl glycidyl ether; the catalyst is dibutyltin dilaurate.

[0016] The solvent is one or a mixture of ethyl acetate and acetone, with a purity ≥99.9%; after the reaction, the solvent is degassed under vacuum and dried at 80℃ until the residual solvent content is ≤0.1mg / kg.

[0017] In the above technical solution, polytrimethylene ether glycol reacts with 1,6-hexamethylene diisocyanate (HDI) to generate a terminal isocyanate prepolymer. The hydroxyl groups (-OH) in the glycidyl ether chain extender react with the terminal -NCO groups of the PU prepolymer to form urethane bonds. The low temperature of the reaction system and the selection of the catalyst prevent the hydrolysis of epoxy groups, allowing the epoxy groups (-EP) to remain at the ends of the PU chains for subsequent crosslinking or functionalization. Polytrimethylene ether glycol is a flexible segment, providing elasticity and helping to improve the toughness of polylactic acid, synergistically degrading and achieving a balance between flexibility and degradation. It also introduces reactive groups to participate in subsequent reactions.

[0018] Furthermore, the biodegradable polyester resin is modified, and the specific modification process is as follows:

[0019] A biodegradable polyester resin, maleic anhydride, initiator and antioxidant are mixed and extruded in a twin-screw extruder to obtain maleic anhydride-grafted polyester resin.

[0020] Maleic anhydride-grafted polyester resin and anhydrous N,N-dimethylformamide were mixed and heated to 58–65°C with stirring to dissolve. The mixture was then cooled to 30–40°C, and imine hydrochloride and triethylamine were added. The mixture was stirred for 20–30 min to activate the resin. Under a nitrogen atmosphere, a diamine compound was added, and the mixture was heated to 58–63°C for 210–270 min. The mixture was then heated to 78–82°C and the reaction was continued for 6–8 h. The mixture was cooled, and the pH of the system was adjusted to neutral to terminate the reaction. The precipitate was placed in ice-cold methanol, filtered, washed, and vacuum dried to obtain the modified polyester resin.

[0021] Furthermore, in the extrusion process, the length-to-diameter ratio of the twin-screw extruder is ≥40:1, and the zone temperatures are as follows: feeding zone: 155~160℃, 170~180℃, 190~200℃, 160~170℃; screw speed is 100~200rpm.

[0022] Furthermore, the maleic anhydride-grafted polyester resin comprises the following components by weight: 100 parts of biodegradable polyester resin, 1 to 5 parts of maleic anhydride, 0.1 to 0.5 parts of initiator, and 0.1 to 0.3 parts of antioxidant;

[0023] The initiator is dicumyl peroxide (DCP); the antioxidant is antioxidant 1010.

[0024] Furthermore, the modified polyester resin comprises the following components by weight: 100 parts maleic anhydride-grafted polyester resin, 1.1 to 5.6 parts imine ester hydrochloride, 1.2 to 5.4 parts diamine compound, and 0.5 to 1.0 parts triethylamine;

[0025] The ratio of anhydrous N,N-dimethylformamide and maleic anhydride grafted polyester resin is 10 to 15 times (V / W).

[0026] The diamine compound is one of 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, and 1,4-cyclohexanediamine.

[0027] In the above technical solution, during twin-screw extrusion, the initiator DCP decomposes to generate free radicals, which attack the α-H in the polyester chain (such as PBAT) and undergo an addition reaction with the double bond of maleic anhydride (MAH). Subsequently, the MAH anhydride reacts with a diamine compound to form an amide-carboxylic acid, and the imine ester reacts with the remaining amine groups to form imine bond branches, yielding a modified polyester resin. The modified polyester resin structure introduces multiple imine bonds (-C=NH-) and amide bonds (-CO-NH-), making it susceptible to attack by oxidases (such as laccase), accelerating chain breakage and providing enzyme / oxidative degradation sites, thus improving the oxidative biodegradability of the prepared food preservation film. Simultaneously, the polarity of MAH improves the interfacial adhesion between the polyester resin and PLA / auxiliary resin, helping to reduce phase separation. Micro-crosslinking occurs in the reaction system, enhancing the intermolecular forces and contributing to the improvement of the mechanical properties of the food preservation film.

[0028] The modified polyester resin exhibits enhanced binding to enzymes (such as the negatively charged active center of lipase and Ser / His residues). The electrostatic and hydrogen bonding interactions between the two effectively improve the adsorption and binding of enzymes in the prepared plastic wrap. Simultaneously, the introduction of the modified polyester branched structure disrupts the regularity of the molecular chain, increasing the proportion of amorphous regions, improving the transparency of the plastic wrap, and making enzyme attack sites more easily exposed, thus contributing to the full realization of its oxidative biodegradation characteristics.

[0029] In the co-extrusion process of cling film, the epoxy groups in the auxiliary resin can react with the amine groups and terminal hydroxyl / carboxyl groups in the modified polyester resin, biodegradable resin, and polylactic acid, resulting in cross-linking between molecular chains and forming a certain cross-linking network. This can effectively improve the mechanical properties and thermal stability of the cling film, increase melt strength, and facilitate the blowing of the film.

[0030] Furthermore, the imide ester hydrochloride is prepared by the following process:

[0031] The dimethyl nitrile compound and anhydrous ethanol were mixed, and zinc chloride was added. Hydrogen chloride was added at 0–5°C, and the temperature was raised to 25–30°C. The mixture was stirred for 6–12 hours. Hydrogen chloride was used to adjust the pH of the system to <1. The mixture was then allowed to stand in an ice bath, filtered, washed, recrystallized, and dried under vacuum to obtain imine ester hydrochloride.

[0032] Furthermore, the dicarboxylate compound is one of terephthalonitrile, 2,5-dicyanofuran, sebacate, or butadionitrile;

[0033] The molar ratio of xylene nitrile compound, anhydrous ethanol, hydrogen chloride, and zinc chloride is 1:(5-10):(2-3):(0.05-0.10);

[0034] The hydrogen chloride addition rate was 0.5 ± 0.1 L / min.

[0035] In the above technical solution, the dimethyl nitrile compound undergoes partial alcoholysis with ethanol under the catalysis of HCl / ZnCl2 to generate imine ester hydrochloride. When its structure is incorporated into the plastic wrap component, it can exert its direct antibacterial effect, endowing the plastic wrap with antibacterial activity. During the oxidative biodegradation process, its imine bond is easily attacked by oxidases (such as laccase), and the free radicals (·OH) generated during the degradation process assist in sterilization.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] The present invention describes a transparent food preservation film with oxidative biodegradability. By compounding biodegradable polyester and polylactic acid, a film with excellent comprehensive mechanical properties is obtained. The addition of auxiliary resins, reactive polyurethane and modified biodegradable polyester, endows the film with more degradation sites, good antibacterial properties and cross-linking network, thereby improving the comprehensive properties of the prepared food preservation film, such as mechanical properties, oxidative biodegradability, and barrier properties. It can be used in the preservation of non-oil products, short-term preservation and other fields, or as one of the film layer structures of multi-layer food preservation films. Detailed Implementation

[0038] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] In the following specific implementation methods, all are laboratory-scale tests, which can be scaled up proportionally.

[0040] The biodegradable polyester resin is polybutylene terephthalate (PBAT: TH801T, Xinjiang Lanshan Tunhe Chemical Co., Ltd.);

[0041] Polylactic acid: FY601, Fengyuan, Anhui;

[0042] Polytrimethylene ether glycol: PO3G2000, Lotte Korea;

[0043] The initiator is dicumyl peroxide (DCP); the antioxidant is antioxidant 1010.

[0044] Example 1: A method for preparing a transparent food preservation film with oxidative biodegradability, comprising the following processes:

[0045] Step 1: Modification of biodegradable polyester resin:

[0046] A dimethyl phthalonitrile compound and anhydrous ethanol were mixed, and zinc chloride was added. Hydrogen chloride was then added at 0°C, and the mixture was heated to 25°C and stirred for 12 hours. The pH of the system was adjusted to 1 using hydrogen chloride, and the mixture was allowed to stand in an ice bath. The mixture was then filtered, washed, recrystallized, and dried under vacuum to obtain imide hydrochloride. The dimethyl phthalonitrile compound was terephthalonitrile. The molar ratio of dimethyl phthalonitrile compound, anhydrous ethanol, hydrogen chloride, and zinc chloride was 1:5:2:0.05. The hydrogen chloride was added at a rate of 0.5 L / min.

[0047] A biodegradable polyester resin, maleic anhydride, initiator, and antioxidant are mixed and extruded in a twin-screw extruder to obtain maleic anhydride-grafted polyester resin. In the extrusion process, the twin-screw extruder has a length-to-diameter ratio of 40:1, and the zone temperatures are sequentially: feeding zone 155℃, 170℃, 190℃, and 160℃; the screw speed is 100 rpm. The maleic anhydride-grafted polyester resin comprises the following components by weight: 100 parts biodegradable polyester resin, 1 part maleic anhydride, 0.1 parts initiator, and 0.1 parts antioxidant.

[0048] Maleic anhydride-grafted polyester resin and anhydrous N,N-dimethylformamide were mixed and heated to 58°C with stirring to dissolve. The mixture was then cooled to 30°C, and imide hydrochloride and triethylamine were added, followed by stirring for 20 min to activate the mixture. Under a nitrogen atmosphere, a diamine compound was added, and the mixture was heated to 58°C and reacted for 210 min. The temperature was then increased to 78°C, and the reaction continued for 6 h. The mixture was cooled, and the pH was adjusted to neutral to terminate the reaction. The precipitate was collected in ice-cold methanol, filtered, washed, and vacuum dried to obtain the modified polyester resin. The modified polyester resin comprised the following components by weight: 100 parts maleic anhydride-grafted polyester resin, 1.1 parts imide hydrochloride, 1.2 parts diamine compound, and 0.5 parts triethylamine. The ratio of anhydrous N,N-dimethylformamide to maleic anhydride-grafted polyester resin was 10 times (V / W). The diamine compound was 1,4-butanediamine.

[0049] Step 2, Preparation of auxiliary resin:

[0050] Polytrimethylene ether glycol was dehydrated under vacuum at 120°C for 2 hours, then cooled to 63°C. The mixture was stirred, and 1,6-hexamethylene diisocyanate, catalyst, and solvent were added. The temperature was raised to 78°C, and the reaction continued until the NCO group content no longer changed, yielding a prepolymer. The temperature was lowered to 63°C, and a glycidyl ether chain extender was added. The mixture was stirred and heated to 88°C, reacting for 100 minutes to obtain polyurethane, which was used as an auxiliary resin. The polyurethane consisted of the following components by mass: 30 parts polytrimethylene ether glycol, 10 parts 1,6-hexamethylene diisocyanate, 3.6 parts glycidyl ether chain extender, 0.1 parts catalyst, and 28.5 parts solvent. The glycidyl ether chain extender was glycidyl ether ethanol; the catalyst was dibutyltin dilaurate; and the solvent was ethyl acetate with a purity ≥99.9%. After the reaction, the mixture was degassed under vacuum and dried at 80°C until the residual solvent content was ≤0.1 mg / kg.

[0051] Step 3, Preparation of plastic wrap:

[0052] 60 parts of biodegradable polyester resin (containing 10 wt% modified polyester resin), 30 parts of polylactic acid, and 5 parts of auxiliary resin were melt-extruded and blow-molded into a film to obtain a cling film. The melt extrusion was carried out using a twin-screw extruder with an L / D ratio of 40 and segmented temperature control. The segment temperatures were 165℃, 172℃, 172℃, and 170℃ at the die head. The rotation speed was 200 rpm.

[0053] Example 2: A method for preparing a transparent food preservation film with oxidative biodegradability, comprising the following processes:

[0054] Step 1: Modification of biodegradable polyester resin:

[0055] A dimethyl nitrile compound and anhydrous ethanol were mixed, and zinc chloride was added. Hydrogen chloride was then added at 2°C, and the mixture was heated to 27°C and stirred for 9 hours. The pH of the system was adjusted to 1 using hydrogen chloride, and the mixture was allowed to stand in an ice bath. The mixture was then filtered, washed, recrystallized, and dried under vacuum to obtain imine ester hydrochloride. The dimethyl nitrile compound was 2,5-dicyanofuran. The molar ratio of dimethyl nitrile compound, anhydrous ethanol, hydrogen chloride, and zinc chloride was 1:7.5:2.5:0.08. The hydrogen chloride was added at a rate of 0.5 L / min.

[0056] A biodegradable polyester resin, maleic anhydride, initiator, and antioxidant are mixed and extruded in a twin-screw extruder to obtain maleic anhydride-grafted polyester resin. In the extrusion process, the twin-screw extruder has a length-to-diameter ratio of 40:1, and the zone temperatures are sequentially: feeding zone 158℃, 175℃, 195℃, and 165℃; the screw speed is 150 rpm. The maleic anhydride-grafted polyester resin comprises the following components by weight: 100 parts biodegradable polyester resin, 3 parts maleic anhydride, 0.3 parts initiator, and 0.2 parts antioxidant.

[0057] Maleic anhydride-grafted polyester resin and anhydrous N,N-dimethylformamide were mixed and heated to 60°C with stirring to dissolve. The mixture was then cooled to 35°C, and imide hydrochloride and triethylamine were added, followed by stirring for 25 minutes to activate the mixture. Under a nitrogen atmosphere, a diamine compound was added, and the mixture was heated to 60°C and reacted for 240 minutes. The temperature was then increased to 80°C, and the reaction continued for 7 hours. The mixture was cooled, and the pH was adjusted to neutral to terminate the reaction. The precipitate was collected in ice-cold methanol, filtered, washed, and vacuum dried to obtain the modified polyester resin. The modified polyester resin comprised the following components by weight: 100 parts maleic anhydride-grafted polyester resin, 3.3 parts imide hydrochloride, 3.3 parts diamine compound, and 0.8 parts triethylamine. The ratio of anhydrous N,N-dimethylformamide to maleic anhydride-grafted polyester resin was 12 times (V / W). The diamine compound was 1,5-pentanediamine.

[0058] Step 2, Preparation of auxiliary resin:

[0059] Polytrimethylene ether glycol was dehydrated under vacuum at 120°C for 2 hours, then cooled to 65°C. The mixture was stirred, and 1,6-hexamethylene diisocyanate, catalyst, and solvent were added. The temperature was raised to 80°C, and the reaction was carried out for 180 minutes until the NCO group content no longer changed, yielding a prepolymer. The temperature was lowered to 65°C, and a glycidyl ether chain extender was added. The mixture was stirred and heated to 90°C, and the reaction was carried out for 120 minutes to obtain polyurethane, which was used as an auxiliary resin. The polyurethane consisted of the following components by mass: 38 parts polytrimethylene ether glycol, 15 parts 1,6-hexamethylene diisocyanate, 5.4 parts glycidyl ether chain extender, 0.15 parts catalyst, and 48 parts solvent. The glycidyl ether chain extender was p-hydroxyphenyl glycidyl ether; the catalyst was dibutyltin dilaurate; and the solvent was ethyl acetate with a purity ≥99.9%. After the reaction, the mixture was degassed under vacuum and dried at 80°C until the residual solvent content was ≤0.1 mg / kg.

[0060] Step 3, Preparation of plastic wrap:

[0061] 60 parts of biodegradable polyester resin (containing 30 wt% modified polyester resin), 30 parts of polylactic acid, and 5 parts of auxiliary resin were melt-extruded and blow-molded into a film to obtain a cling film. The melt extrusion was carried out using a twin-screw extruder with an L / D ratio of 40 and segmented temperature control. The segment temperatures were 165℃, 172℃, 172℃, and 170℃ at the die head. The rotation speed was 200 rpm.

[0062] Example 3: A method for preparing a transparent food preservation film with oxidative biodegradability, comprising the following processes:

[0063] Step 1: Modification of biodegradable polyester resin:

[0064] A dimethyl nitrile compound and anhydrous ethanol were mixed, and zinc chloride was added. Hydrogen chloride was then added at 5°C, and the mixture was heated to 30°C and stirred for 6 hours. The pH of the system was adjusted to 1 using hydrogen chloride, and the mixture was allowed to stand in an ice bath. The mixture was then filtered, washed, recrystallized, and dried under vacuum to obtain imide hydrochloride. The dimethyl nitrile compound was sebacate. The molar ratio of dimethyl nitrile compound, anhydrous ethanol, hydrogen chloride, and zinc chloride was 1:10:3:0.10. The hydrogen chloride was added at a rate of 0.5 L / min.

[0065] A biodegradable polyester resin, maleic anhydride, initiator, and antioxidant are mixed and extruded in a twin-screw extruder to obtain maleic anhydride-grafted polyester resin. In the extrusion process, the twin-screw extruder has a length-to-diameter ratio of 40:1, and the zone temperatures are sequentially: feeding zone 160℃, 180℃, 200℃, and 170℃; the screw speed is 200 rpm. The maleic anhydride-grafted polyester resin comprises the following components by weight: 100 parts biodegradable polyester resin, 5 parts maleic anhydride, 0.5 parts initiator, and 0.3 parts antioxidant.

[0066] Maleic anhydride-grafted polyester resin and anhydrous N,N-dimethylformamide were mixed and heated to 65°C with stirring to dissolve. The mixture was then cooled to 40°C, and imide hydrochloride and triethylamine were added, followed by stirring for 30 min to activate the mixture. Under a nitrogen atmosphere, a diamine compound was added, and the mixture was heated to 63°C and reacted for 270 min. The temperature was then increased to 82°C, and the reaction continued for 8 h. The mixture was cooled, and the pH was adjusted to neutral to terminate the reaction. The precipitate was collected in ice-cold methanol, filtered, washed, and vacuum dried to obtain the modified polyester resin. The modified polyester resin comprised the following components by weight: 100 parts maleic anhydride-grafted polyester resin, 5.6 parts imide hydrochloride, 5.4 parts diamine compound, and 1.0 part triethylamine. The ratio of anhydrous N,N-dimethylformamide to maleic anhydride-grafted polyester resin was 15 times (V / W). The diamine compound was 1,6-hexanediamine.

[0067] Step 2, Preparation of auxiliary resin:

[0068] Polytrimethylene ether glycol was dehydrated under vacuum at 120°C for 2 hours, then cooled to 67°C. The mixture was stirred, and 1,6-hexamethylene diisocyanate, catalyst, and solvent were added. The temperature was raised to 82°C, and the reaction continued until the NCO group content no longer changed, yielding a prepolymer. The temperature was lowered to 67°C, and a glycidyl ether chain extender was added. The mixture was stirred and heated to 92°C, reacting for 150 minutes to obtain polyurethane, which was used as an auxiliary resin. The polyurethane consisted of the following components by weight: 45 parts polytrimethylene ether glycol, 20 parts 1,6-hexamethylene diisocyanate, 7.2 parts glycidyl ether chain extender, 0.2 parts catalyst, and 68 parts solvent. The glycidyl ether chain extender was p-hydroxyphenyl glycidyl ether; the catalyst was dibutyltin dilaurate; and the solvent was acetone with a purity ≥99.9%. After the reaction, the mixture was degassed under vacuum and dried at 80°C until the residual solvent content was ≤0.1 mg / kg.

[0069] Step 3, Preparation of plastic wrap:

[0070] 60 parts of biodegradable polyester resin (containing 50 wt% modified polyester resin), 30 parts of polylactic acid, and 5 parts of auxiliary resin were melt-extruded and blow-molded into a film to obtain a cling film. The melt extrusion was carried out using a twin-screw extruder with an L / D ratio of 40 and segmented temperature control. The segment temperatures were 165℃, 172℃, 172℃, and 170℃ at the die head. The rotation speed was 200 rpm.

[0071] Comparative Example 1: A method for preparing a transparent food preservation film with oxidative biodegradability, comprising the following processes:

[0072] Step 1: Modification of biodegradable polyester resin:

[0073] A biodegradable polyester resin, maleic anhydride, initiator, and antioxidant are mixed and extruded in a twin-screw extruder to obtain maleic anhydride-grafted polyester resin. In the extrusion process, the twin-screw extruder has a length-to-diameter ratio of 40:1, and the zone temperatures are sequentially: feeding zone 155℃, 170℃, 190℃, and 160℃; the screw speed is 100 rpm. The maleic anhydride-grafted polyester resin comprises the following components by weight: 100 parts biodegradable polyester resin, 1 part maleic anhydride, 0.1 parts initiator, and 0.1 parts antioxidant.

[0074] Maleic anhydride-grafted polyester resin and anhydrous N,N-dimethylformamide were mixed and heated to 58°C with stirring to dissolve. Under a nitrogen atmosphere, a diamine compound was added, and the reaction was carried out for 210 min. The temperature was then raised to 78°C, and the reaction was continued for 6 h. After cooling, the pH of the system was adjusted to neutral, and the reaction was terminated. The precipitate was placed in ice-cold methanol, filtered, washed, and vacuum dried to obtain the modified polyester resin. The modified polyester resin consisted of the following components by weight: 100 parts maleic anhydride-grafted polyester resin and 1.2 parts diamine compound; the ratio of anhydrous N,N-dimethylformamide to maleic anhydride-grafted polyester resin was 10 times (V / W); the diamine compound was 1,4-butanediamine.

[0075] Steps 2 and 3 are the same as in Example 1, resulting in a plastic wrap.

[0076] Comparative Example 2: A method for preparing a transparent food preservation film with oxidative biodegradability, comprising the following processes:

[0077] Step 1: Modification of biodegradable polyester resin:

[0078] Biodegradable polyester resin, maleic anhydride, initiator, and antioxidant are mixed and extruded in a twin-screw extruder to obtain maleic anhydride-grafted polyester resin, which is used as a modified polyester resin. In the extrusion process, the twin-screw extruder has a length-to-diameter ratio of 40:1, and the zone temperatures are as follows: feeding zone: 155℃, 170℃, 190℃, 160℃; screw speed: 100 rpm. The maleic anhydride-grafted polyester resin comprises the following components by mass: 100 parts biodegradable polyester resin, 1 part maleic anhydride, 0.1 parts initiator, and 0.1 parts antioxidant.

[0079] Steps 2 and 3 are the same as in Example 1, resulting in a plastic wrap.

[0080] Comparative Example 3: A method for preparing a transparent food preservation film with oxidative biodegradability, comprising the following processes:

[0081] Step 1: Preparation of auxiliary resin:

[0082] Polytrimethylene ether glycol was dehydrated under vacuum at 120°C for 2 hours, then cooled to 63°C. The mixture was stirred, and 1,6-hexamethylene diisocyanate, catalyst, and solvent were added. The temperature was raised to 78°C, and the reaction continued until the NCO group content no longer changed, yielding a prepolymer. The temperature was lowered to 63°C, and 1,4-butanediol was added. The mixture was stirred and heated to 88°C, reacting for 100 minutes to obtain polyurethane, which was used as an auxiliary resin. The polyurethane consisted of the following components by mass: 30 parts polytrimethylene ether glycol, 10 parts 1,6-hexamethylene diisocyanate, 3.6 parts 1,4-butanediol, 0.1 parts catalyst, and 28.5 parts solvent. The catalyst was dibutyltin dilaurate; the solvent was ethyl acetate with a purity ≥99.9%. After the reaction, the mixture was degassed under vacuum and dried at 80°C until the residual solvent content was ≤0.1 mg / kg.

[0083] Step 2, Preparation of plastic wrap:

[0084] 60 parts of biodegradable polyester resin, 30 parts of polylactic acid, and 5 parts of auxiliary resin were melt-extruded and blow-molded into a film to obtain a cling film. The melt extrusion was carried out using a twin-screw extruder with an length-to-diameter ratio of L / D = 40 and segmented temperature control. The segment temperatures were 165℃, 172℃, 172℃, and 170℃ at the die head. The rotation speed was 200 rpm.

[0085] Experiment: Samples were prepared from the plastic wrap obtained in Examples 1-3 and Comparative Examples 1-3, and their performance was tested and the results were recorded.

[0086] Mechanical property testing: The tensile strength of the specimen was tested with reference to GB / T 1040.3 at a tensile rate of 50 mm / min; the tear strength of the specimen was tested with reference to GB / T 16578.1.

[0087] Enzyme-catalyzed degradation performance test: Using ISO 14855-1 as the reference standard, the sample was immersed in a pH 7.0 buffer solution containing laccase (10 U / mL, Trametes versicola) and lipase (5 U / mL, CALB), shaken at 37°C, and the weight loss rate of the sample was detected after 7 days of enzyme degradation.

[0088] Antibacterial performance test: Based on GB / T 31402, the sample (5×5cm2) was contacted with bacterial solution (106CFU / mL) for 24 hours (37℃), the plate was diluted and the surviving colonies were counted, and the inhibition rate was calculated. The bacterial species were Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus).

[0089] Barrier performance test: The water vapor transmission rate (WVTR) of the sample was tested with reference to GB / T 1037; the oxygen transmission rate (OTR) of the sample was tested with reference to GB / T 19789.

[0090] Transmittance test: The transmittance (%) of the sample is tested with reference to GB / T 2410.

[0091]

[0092] Based on the data in the table above, the following conclusions can be clearly drawn:

[0093] The plastic wraps obtained in Examples 1-3 were compared with those obtained in Comparative Examples 1-5. The test results show that...

[0094] Compared to Comparative Example 3, the preservation films obtained in Examples 1-3 exhibit higher tensile strength, tear strength, enzymatic degradation weight loss rate, and antibacterial rate, with relatively higher light transmittance and lower water vapor and oxygen transmittance. This is because Examples 1-3 introduce imine crosslinking and polyurethane-assisted resin, significantly improving tensile strength; imine bonds are easily attacked by laccase, which significantly increases the oxidative degradation rate of Examples 1-3; the cationic effect of imine ester hydrochloride endows Examples 1-3 with significant antibacterial properties, which improve with increasing grafting amount; imine crosslinking and polyurethane-assisted resin reduce molecular chain gaps, improving barrier properties; and appropriate crosslinking can improve the transparency of the PLA / PBAT film by inhibiting phase separation and reducing crystallinity. This fully demonstrates that the present invention improves the mechanical properties, oxidative biodegradability, antibacterial properties, and barrier properties of the prepared preservation film while maintaining good light transmittance.

[0095] The biodegradable polyester resins in Comparative Examples 1 and 2 were modified using different methods, resulting in a significant decrease in tensile strength, tear strength, enzymatic degradation weight loss rate, and antibacterial rate, while water vapor and oxygen permeability increased. This indicates that the process and components used in the prepared food preservation film of this invention can comprehensively improve its mechanical properties, oxidative biodegradability, antibacterial properties, and barrier properties. In Comparative Example 2, the maleic anhydride-grafted polyester resin as an auxiliary resin improves the compatibility between PLA and PBAT, exhibiting better transparency and mechanical properties compared to Comparative Example 3.

[0096] 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 implemented 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 exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A transparent food preservation film with oxidative biodegradability, characterized in that, It includes the following components: 50-65 parts biodegradable polyester resin, 25-35 parts polylactic acid, and 5-20 parts auxiliary resin; the auxiliary resin is polyurethane. The polyurethane is prepared by the following process: Polytrimethylene ether glycol, 1,6-hexamethylene diisocyanate, catalyst, and solvent are mixed and heated to 78–82°C. The mixture is reacted for 150–200 min until the NCO group content no longer changes, thus obtaining the prepolymer. Cool the temperature to 63-67℃, add glycidyl ether chain extender, stir and heat to 88-92℃, react for 100-150 min to obtain polyurethane; The biodegradable polyester resin is modified, and the specific modification process is as follows: A biodegradable polyester resin, maleic anhydride, initiator and antioxidant are mixed and extruded in a twin-screw extruder to obtain maleic anhydride-grafted polyester resin. Maleic anhydride-grafted polyester resin and anhydrous N,N-dimethylformamide were mixed and heated to 58–65°C and stirred to dissolve. The mixture was then cooled to 30–40°C, and imide hydrochloride and triethylamine were added. The mixture was stirred for 20–30 min to activate the resin. Under a nitrogen atmosphere, a diamine compound was added, and the mixture was heated to 58–63°C and reacted for 210–270 min. The mixture was then heated to 78–82°C and the reaction was continued for 6–8 h to obtain the modified polyester resin.

2. The transparent food preservation film with oxidative biodegradability according to claim 1, characterized in that, The biodegradable polyester resin is one or a mixture of two of polybutylene terephthalate and polybutylene succinate.

3. The transparent food preservation film with oxidative biodegradability according to claim 1, characterized in that, The polyurethane comprises the following components by weight: 30-60 parts of polytrimethylene ether glycol, 10-20 parts of 1,6-hexamethylene diisocyanate, 3.6-7.2 parts of glycidyl ether chain extender, 0.1-0.2 parts of catalyst, and 28.5-68 parts of solvent; Glycidyl ether chain extenders are one of glycidyl ether ethanol and p-hydroxyphenyl glycidyl ether.

4. The transparent food preservation film with oxidative biodegradability according to claim 1, characterized in that, The maleic anhydride-grafted polyester resin comprises the following components by weight: 100 parts of biodegradable polyester resin, 1 to 5 parts of maleic anhydride, 0.1 to 0.5 parts of initiator, and 0.1 to 0.3 parts of antioxidant.

5. A transparent food preservation film with oxidative biodegradability according to claim 1, characterized in that, The modified polyester resin comprises the following components by weight: 100 parts maleic anhydride-grafted polyester resin, 1.1 to 5.6 parts imine ester hydrochloride, 1.2 to 5.4 parts diamine compound, and 0.5 to 1.0 parts triethylamine.

6. The transparent food preservation film with oxidative biodegradability according to claim 1, characterized in that, The imine ester hydrochloride is prepared by the following process: A dimethyl nitrile compound and anhydrous ethanol were mixed, zinc chloride was added, hydrogen chloride was added at 0–5°C, the temperature was raised to 25–30°C, and the mixture was stirred for 6–12 hours to obtain imine ester hydrochloride.

7. A transparent food preservation film with oxidative biodegradability according to claim 6, characterized in that, The dicarboxylic acid compound is one of terephthalonitrile, 2,5-dicyanofuran, sebacate, or butadionitrile.

8. A method for preparing a transparent food preservation film with oxidative biodegradability according to any one of claims 1-7, characterized in that, The process includes the following steps: melt extrusion of biodegradable polyester resin, polylactic acid, and auxiliary resin, followed by blow molding to form a film, thus obtaining a food preservation film.

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