Transparent preservative film with oxidative biodegradability and preparation method thereof

Abstract

The invention discloses a transparent preservative film with oxidative biodegradability and a preparation method thereof, and relates to the technical field of degradable polyester materials, the transparent preservative film comprises the following components: 50-65 parts of degradable polyester resin, 25-35 parts of polylactic acid, and 5-20 parts of auxiliary resin; and the auxiliary resin is polyurethane. The degradable polyester and the polylactic acid are compounded to obtain a film body with excellent comprehensive mechanical properties, and the auxiliary resin reactive polyurethane and the modified degradable polyester are added, so that the film body is endowed with more degradation sites, good antibacterial property and a cross-linked network; the comprehensive properties such as mechanical property, oxidation biodegradability and barrier property of the prepared preservative film are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of degradable polyester materials, and particularly relates to a transparent preservative film with oxidative biodegradability and a preparation method thereof. BACKGROUND

[0002] Preservative film is an important packaging material for prolonging the shelf life of packaged goods. With the development of economy, the demand for preservative film is gradually increasing. Traditional preservative film materials include fossil raw materials such as polyethylene, polyvinyl chloride, and polyvinylidene fluoride, which are difficult to dispose after being discarded. Materials with biodegradable properties, such as degradable polyesters, have great potential as environmentally friendly packaging materials in the field of environmentally friendly packaging materials. Degradable polyesters such as polybutylene adipate terephthalate (PBAT) and polybutylene succinate (PBS) have good flexibility, but their texture is soft and they have poor film-forming properties. Therefore, we propose a transparent preservative film with oxidative biodegradability and a preparation method thereof. SUMMARY

[0003] The present application aims to provide a transparent preservative film with oxidative biodegradability and a preparation method thereof to solve the problems raised in the background art.

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

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

[0006] Further, 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] The starch graft copolymer is preferably Starch-g-PLA.

[0008] In the above technical solution, the degradable polyester resin and polylactic acid are compounded as the main resin, and after blending, the brittleness and film forming property of the blend can be effectively improved, and the blend has good transparency and flexibility; and has oxidative biodegradability, and biodegradation enzymes (such as esterase, laccase, lipase, protease, peroxidase, and lignin degradation enzyme) can catalyze ester bond hydrolysis, oxidize fatty chains to generate free radicals, oxidize aromatic terephthalic acid units, and oxidize methylene (-CH2-) to generate ketone / aldehyde structure, and initiate chain scission. The auxiliary resin is added to plasticize, toughen, and promote oxidation / biodegradation. For example, PCL can improve the plasticity of the blend at low temperature and enhance the ductility; PEBA toughens; PHA blending can accelerate microbial degradation; starch graft copolymer has the effects of filling and accelerating degradation. Polyurethane can also toughen, improve barrier property, and control degradation rate; cellulose can be used as a bio-based reinforcing agent to improve mechanical strength, barrier property, and biodegradation performance.

[0009] A preparation method of a transparent preservative film with oxidative biodegradability, comprising the following processes: melt-extruding degradable polyester resin, polylactic acid, and auxiliary resin, and blow molding into a film to obtain the preservative film.

[0010] Further, the melt-extrusion adopts a double-screw extruder with a length-diameter ratio L / D = 40, and the temperature is controlled in sections, and the section temperatures are 160-170℃, 170-175℃, 170-175℃, and the die head temperature is 165-175℃; the rotation speed is 150-250rpm.

[0011] Further, the auxiliary resin is polyurethane, and the polyurethane is prepared by the following process:

[0012] Vacuum dehydration of polytrimethylene ether glycol at 120℃ for 2h, and cooling to 63-67℃; stirring, and adding 1,6-hexane diisocyanate, catalyst, and solvent, and heating to 78-82℃, and reacting for 150-200min until the NCO group content no longer changes to obtain a prepolymer;

[0013] Cooling to 63-67℃, adding glycidyl ether chain extender, stirring, and heating to 88-92℃, and reacting for 100-150min to obtain polyurethane.

[0014] Further, the polyurethane comprises the following mass components: 30-60 parts of polytrimethylene ether glycol, 10-20 parts of 1,6-hexane 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; and the catalyst is dibutyltin dilaurate;

[0016] The solvent is one or a mixture of both of ethyl acetate and acetone, with purity ≥99.9%; after the reaction, vacuum degassing is performed, and 80℃ vacuum drying is performed until the solvent residual amount is ≤0.1 mg / kg.

[0017] In the above technical solution, the polytrimethylene ether glycol is reacted with 1,6-hexane diisocyanate HDI to generate a terminal isocyanate prepolymer; the hydroxyl (-OH) in the glycidyl ether chain extender is reacted with the terminal -NCO of the PU prepolymer to form a urethane bond; the low temperature of the reaction system and the selection of the catalyst can avoid the hydrolysis of the epoxy group, so that the epoxy group (-EP) is retained at the end of the PU chain and can be used for subsequent crosslinking or functionalization. The polytrimethylene ether glycol is a flexible segment, which provides elasticity and helps to improve the toughness of polylactic acid, synergistically degrades, and realizes the flexibility-degradation balance; the reactive groups are introduced to participate in subsequent reactions.

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

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

[0020] The maleic anhydride grafted polyester resin and anhydrous N,N-dimethylformamide are mixed, and stirred and dissolved at a temperature of 58-65℃; the temperature is lowered to 30-40℃, and imidate hydrochloride and triethylamine are added, and stirred for 20-30 min for activation; under the protection of nitrogen atmosphere, diamine compound is added, heated to 58-63℃, and reacted for 210-270 min; the temperature is raised to 78-82℃, and the reaction is continued for 6-8 h; the reaction is terminated after the pH of the system is adjusted to neutral; precipitated in ice methanol, filtered, washed, and vacuum dried to obtain the modified polyester resin.

[0021] Further, in the extrusion process, the length-diameter ratio of the twin-screw extruder is ≥40:1, and the partition temperature is 155-160℃, 170-180℃, 190-200℃ and 160-170℃ in turn; the screw rotation speed is 100-200 rpm.

[0022] Further, the maleic anhydride grafted polyester resin includes the following mass components: 100 parts of degradable polyester resin, 1-5 parts of maleic anhydride, 0.1-0.5 parts of initiator and 0.1-0.3 parts of antioxidant;

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

[0024] Further, the modified polyester resin includes the following mass components: 100 parts of maleic anhydride grafted polyester resin, 1.1-5.6 parts of imidate hydrochloride, 1.2-5.4 parts of diamine compound and 0.5-1.0 parts of triethylamine.

[0025] The ratio of anhydrous N,N-dimethylformamide to the maleic anhydride grafted polyester resin is 10-15 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, in the twin-screw extrusion, the initiator DCP decomposes to generate free radicals, attacks α-H in the polyester chain (such as PBAT), and undergoes an addition reaction with the double bond of maleic anhydride (MAH). Then the anhydride of MAH opens a ring with the diamine compound to generate amide-carboxylic acid, and the imidic ester reacts with the remaining amine group to form an imine bond branch, obtaining a modified polyester resin. The modified polyester resin structure introduces multiple imine bonds (-C=NH-) and amide bonds (-CO-NH-), which are easily attacked by oxidase (such as laccase) to accelerate chain scission, can provide enzyme / oxidative degradation sites, and help to improve the oxidative biodegradability of the prepared preservative film; at the same time, the polarity of MAH improves the interfacial adhesion of the polyester resin and PLA / auxiliary resin, which helps to reduce phase separation. Micro-crosslinking occurs in the reaction system, which enhances the intermolecular force, and helps to improve the mechanical properties of the preservative film.

[0028] The binding between the modified polyester resin and the enzyme (such as the negative active center of lipase, Ser / His residues) is enhanced, and electrostatic interaction and hydrogen bonding force occur between the two, which can effectively improve the adsorption and combination of the prepared preservative film to the enzyme; at the same time, the introduction of the modified polyester branched structure disturbs the regularity of the molecular chain, increases the proportion of amorphous region, improves the transparency of the preservative film, and makes the enzyme attack site more easily exposed, which helps to fully realize its oxidative biodegradation properties.

[0029] In the blending extrusion process of the preservative film, the epoxy groups in the auxiliary resin can react with the amine groups, terminal hydroxyl groups / carboxyl groups in the prepared modified polyester resin, degradable resin and polylactic acid, crosslinking occurs between the molecular chains, forming a certain crosslinking network, which can effectively improve the mechanical properties and thermal stability of the prepared preservative film, and improve the melt strength, which helps to blow the film body.

[0030] Further, the imidic ester hydrochloride is prepared by the following process:

[0031] The dimethyl cyan compound and anhydrous ethanol are mixed, zinc chloride is added, and hydrogen chloride is added at a temperature of 0-5°C, and then the temperature is raised to 25-30°C, and the reaction is stirred for 6-12h; the pH of the system is adjusted to less than 1 by using hydrogen chloride, and then the system is placed in an ice bath, filtered, washed, recrystallized and vacuum dried to obtain the imidic ester hydrochloride.

[0032] Further, the dimethyl cyan compound is one of p-xylylene cyan, 2,5-dicyanofuran, sebacic dinitrile and succindinitrile.

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

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

[0035] In the above technical solution, the dicyan compound is partially alcoholized with ethanol under the catalysis of HCl / ZnCl2 to generate imidic acid ester hydrochloride, which can exert its direct antibacterial effect when its structure is incorporated into the preservative film component, and impart antibacterial activity to the preservative film. In the process of oxidative biodegradation, the imine bond is easily attacked by oxidase (such as laccase), and the free radicals (·OH) generated in the degradation process assist in sterilization.

[0036] Compared with the prior art, the present application has the following advantages:

[0037] The transparent preservative film with oxidative biodegradability described in the present application is prepared by compounding degradable polyester and polylactic acid to obtain a film body with excellent comprehensive mechanical properties, and adding auxiliary resin reaction type polyurethane and modified degradable polyester to impart more degradation sites, good antibacterial properties and crosslinking network to the film body, thereby improving the comprehensive properties of the prepared preservative film, such as mechanical properties, oxidative biodegradability and barrier properties. The film can be used in the field of non-fat, short-term preservation and other preservation fields, or as one of the film layer structures of a multi-layer preservative film. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0039] In the following specific embodiments, all are laboratory small tests, which can be scaled up proportionally.

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

[0041] The polylactic acid is FY601 from Anhui Fengyuan;

[0042] The polytrimethylene ether glycol is PO3G2000 from South Korea Lotte;

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

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

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

[0046] Mix the dicyan compound and anhydrous ethanol, add zinc chloride, and then add hydrogen chloride at 0°C. Warm up to 25°C and stir for 12 hours. Use hydrogen chloride to adjust the pH of the system to 1, and then place it in an ice bath. Filter, wash, recrystallize, and vacuum dry to obtain the imidate hydrochloride. The dicyan compound is terephthalonitrile. The molar ratio of the dicyan compound, anhydrous ethanol, hydrogen chloride, and zinc chloride is 1:5:2:0.05. The addition rate of hydrogen chloride is 0.5 L / min.

[0047] Mix the degradable polyester resin, maleic anhydride, initiator, and antioxidant in a twin-screw extruder to obtain a maleic anhydride grafted polyester resin. In the extrusion process, the length-diameter ratio of the twin-screw extruder is 40:1, and the partition temperature is 155°C, 170°C, 190°C, and 160°C in sequence. The screw rotation speed is 100 rpm. The maleic anhydride grafted polyester resin includes the following mass components: 100 parts of degradable polyester resin, 1 part of maleic anhydride, 0.1 part of initiator, and 0.1 part of antioxidant.

[0048] Mix the maleic anhydride grafted polyester resin and anhydrous N,N-dimethylformamide, and stir to dissolve at 58°C. Cool to 30°C, add imidate hydrochloride and triethylamine, and stir for 20 minutes to activate. Under the protection of nitrogen atmosphere, add the diamine compound, heat to 58°C, and react for 210 minutes. Warm up to 78°C and continue to react for 6 hours. Cool down, adjust the pH of the system to neutral, and terminate the reaction. Precipitate in ice methanol, filter, wash, and vacuum dry to obtain the modified polyester resin. The modified polyester resin includes the following mass components: 100 parts of maleic anhydride grafted polyester resin, 1.1 parts of imidate hydrochloride, 1.2 parts of diamine compound, and 0.5 parts of triethylamine. The ratio of anhydrous N,N-dimethylformamide to maleic anhydride grafted polyester resin is 10 times (V / W). The diamine compound is 1,4-butanediamine.

[0049] Step 2: Preparation of auxiliary resin:

[0050] Polytrimethylene ether glycol is vacuum dehydrated at 120℃ for 2h, cooled to 63℃; stirring, and adding 1,6-hexane diisocyanate, catalyst, solvent, warming to 78℃, until the NCO group content does not change, to obtain a prepolymer; cooling to 63℃, adding glycidyl ether chain extender, stirring and warming to 88℃, reacting for 100min to obtain a polyurethane as an auxiliary resin; the polyurethane includes the following mass components: 30 parts of polytrimethylene ether glycol, 10 parts of 1,6-hexane diisocyanate, 3.6 parts of glycidyl ether chain extender, 0.1 part of catalyst, 28.5 parts of solvent; the glycidyl ether chain extender is glycidyl ether ethanol; the catalyst is dibutyltin dilaurate; the solvent is ethyl acetate with a purity of ≥99.9%; after the reaction, vacuum degassing, and vacuum drying at 80℃ until the solvent residue is ≤0.1mg / kg;

[0051] Step 3, preparation of the preservative film:

[0052] 60 parts of the degradable polyester resin (containing 10wt% modified polyester resin), 30 parts of polylactic acid, and 5 parts of auxiliary resin are melt extruded and blown into a film to obtain a preservative film; the melt extrusion uses a double screw extruder with a length-diameter ratio L / D=40, segmented temperature control, and the segmented temperature is 165℃, 172℃, 172℃, and die 170℃ in turn; the rotation speed is 200rpm.

[0053] Example 2: a method for preparing a transparent preservative film with oxidative biodegradability, including the following processes:

[0054] Step 1, modification of the degradable polyester resin:

[0055] The dicyan compound, anhydrous ethanol, and zinc chloride are mixed, and hydrogen chloride is added at a temperature of 2℃, then warmed to 27℃, and stirred for 9h; the pH of the system is adjusted to 1 with hydrogen chloride, and the mixture is placed in an ice bath, filtered, washed, recrystallized, and vacuum dried to obtain imidate hydrochloride; the dicyan compound is 2,5-dicyanofuran; the molar ratio of the dicyan compound, anhydrous ethanol, hydrogen chloride, and zinc chloride is 1:7.5:2.5:0.08; the addition rate of hydrogen chloride is 0.5L / min;

[0056] The degradable polyester resin, maleic anhydride, initiator, and antioxidant are mixed and extruded in a double screw extruder to obtain a maleic anhydride grafted polyester resin; in the extrusion process, the length-diameter ratio of the double screw extruder is 40:1, and the zoned temperature is 158℃, 175℃, 195℃, and 165℃ in turn for the feeding zone; the screw rotation speed is 150rpm; the maleic anhydride grafted polyester resin includes the following mass components: 100 parts of degradable polyester resin, 3 parts of maleic anhydride, 0.3 parts of initiator, and 0.2 parts of antioxidant;

[0057] Maleic anhydride grafted polyester resin, anhydrous N,N-dimethylformamide were mixed, and stirred and dissolved at 60℃; cooled to 35℃, and then imidate hydrochloride, triethylamine were added, and stirred for 25min to activate; under the protection of nitrogen atmosphere, diamine compound was added, heated to 60℃, and reacted for 240min; heated to 80℃, and continued to react for 7h; cooled, adjusted the pH of the system to neutral, and terminated the reaction; precipitated in ice methanol, filtered, washed, and vacuum dried to obtain modified polyester resin; the modified polyester resin comprises the following mass components: 100 parts of maleic anhydride grafted polyester resin, 3.3 parts of imidate hydrochloride, 3.3 parts of diamine compound, and 0.8 parts of triethylamine; the ratio of anhydrous N,N-dimethylformamide to maleic anhydride grafted polyester resin is 12 times (V / W); and the diamine compound is 1,5-pentanediamine;

[0058] Step 2, preparation of auxiliary resin:

[0059] Polytrimethylene ether glycol was dehydrated at 120℃ for 2h, and then cooled to 65℃; stirred, and then 1,6-hexane diisocyanate, catalyst, and solvent were added, and heated to 80℃, and reacted for 180min until the content of NCO group did not change, to obtain a prepolymer; cooled to 65℃, and then glycidyl ether chain extender was added, and stirred and heated to 90℃, and reacted for 120min to obtain polyurethane as an auxiliary resin; the polyurethane comprises the following mass components: 38 parts of polytrimethylene ether glycol, 15 parts of 1,6-hexane diisocyanate, 5.4 parts of glycidyl ether chain extender, 0.15 parts of catalyst, and 48 parts of solvent; the glycidyl ether chain extender is p-hydroxyphenyl glycidyl ether; the catalyst is dibutyltin dilaurate; and the solvent is ethyl acetate with a purity of ≥99.9%; after the reaction, vacuum degassing was performed, and vacuum drying was performed at 80℃ until the residual amount of solvent was ≤0.1mg / kg;

[0060] Step 3, preparation of preservative film:

[0061] 60 parts of degradable polyester resin (containing 30wt% modified polyester resin), 30 parts of polylactic acid, and 5 parts of auxiliary resin were melt extruded, and blown into a film to obtain a preservative film; melt extrusion was performed by using a double-screw extruder with a length-diameter ratio L / D = 40, and the segmented temperature was 165℃, 172℃, 172℃, and 170℃ of the die in turn; and the rotation speed was 200rpm.

[0062] Example 3: a preparation method of a transparent preservative film with oxidative biodegradability, comprising the following processes:

[0063] Step 1, modification of degradable polyester resin:

[0064] Mixing dicyan compound, anhydrous ethanol, adding zinc chloride, adding hydrogen chloride at 5℃, warming to 30℃, stirring for 6h; using hydrogen chloride to adjust the system pH to 1, ice bath, filtration, washing, recrystallization, vacuum drying, to obtain imidate hydrochloride; dicyan compound is decanedicarbonitrile; the molar ratio of dicyan compound, anhydrous ethanol, hydrogen chloride, zinc chloride is 1:10:3:0.10; the adding rate of hydrogen chloride is 0.5L / min;

[0065] Mixing degradable polyester resin, maleic anhydride, initiator and antioxidant in a twin-screw extruder to obtain maleic anhydride grafted polyester resin; in the extrusion process, the length-diameter ratio of the twin-screw extruder is 40:1, and the partition temperature is 160℃, 180℃, 200℃ and 170℃ in turn; the screw rotation speed is 200rpm; the maleic anhydride grafted polyester resin comprises the following mass components: 100 parts of degradable polyester resin, 5 parts of maleic anhydride, 0.5 parts of initiator and 0.3 parts of antioxidant;

[0066] Mixing maleic anhydride grafted polyester resin and anhydrous N,N-dimethylformamide, stirring and dissolving at 65℃; cooling to 40℃, adding imidate hydrochloride and triethylamine, stirring for 30min to activate; adding diamine compound under nitrogen atmosphere, heating to 63℃, reacting for 270min; warming to 82℃, continuing to react for 8h; cooling, adjusting the system pH to neutral to terminate the reaction; precipitating in ice methanol, filtering, washing, vacuum drying to obtain modified polyester resin; the modified polyester resin comprises the following mass components: 100 parts of maleic anhydride grafted polyester resin, 5.6 parts of imidate hydrochloride, 5.4 parts of diamine compound and 1.0 part of triethylamine; the ratio of anhydrous N,N-dimethylformamide to maleic anhydride grafted polyester resin is 15 times (V / W); the diamine compound is 1,6-hexanediamine;

[0067] Step 2, preparation of auxiliary resin:

[0068] Vacuum dehydrating polytrimethylene ether glycol at 120℃ for 2h, cooling to 67℃; stirring, and adding 1,6-hexane diisocyanate, catalyst, solvent, warming to 82℃, reacting until the NCO group content no longer changes to obtain prepolymer; cooling to 67℃, adding glycidyl ether chain extender, stirring and warming to 92℃, reacting for 150min to obtain polyurethane as auxiliary resin; the polyurethane comprises the following mass components: 45 parts of polytrimethylene ether glycol, 20 parts of 1,6-hexane diisocyanate, 7.2 parts of glycidyl ether chain extender, 0.2 parts of catalyst and 68 parts of solvent; the glycidyl ether chain extender is p-hydroxyphenyl glycidyl ether; the catalyst is dibutyltin dilaurate; the solvent is acetone with purity≥99.9%; after reaction, vacuum degassing, vacuum drying at 80℃ until the solvent residual amount≤0.1mg / kg;

[0069] Step 3, preparation of the preservative film:

[0070] 60 parts of the degradable polyester resin (containing 50wt% modified polyester resin), 30 parts of polylactic acid, 5 parts of auxiliary resin were melt-extruded, blown into a film to obtain a preservative film; the melt-extrusion used a twin-screw extruder with a length-diameter ratio L / D = 40, segmented temperature control, and the segmented temperature was 165℃, 172℃, 172℃, and the die temperature was 170℃; the rotation speed was 200 rpm.

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

[0072] Step 1, modification of the degradable polyester resin:

[0073] The degradable polyester resin, maleic anhydride, initiator and antioxidant were mixed and extruded in a twin-screw extruder to obtain a maleic anhydride grafted polyester resin; in the extrusion process, the length-diameter ratio of the twin-screw extruder was 40:1, and the zone temperature was 155℃, 170℃, 190℃, and 160℃ in turn; the screw rotation speed was 100 rpm; the maleic anhydride grafted polyester resin included the following mass components: 100 parts of degradable polyester resin, 1 part of maleic anhydride, 0.1 part of initiator and 0.1 part of antioxidant;

[0074] The maleic anhydride grafted polyester resin and anhydrous N,N-dimethylformamide were mixed and stirred to dissolve at 58℃; under the protection of nitrogen atmosphere, a diamine compound was added and reacted for 210 min; the temperature was raised to 78℃ and the reaction was continued for 6h; the system was cooled and the pH was adjusted to neutral to terminate the reaction; precipitated in ice methanol, filtered, washed and vacuum dried to obtain a modified polyester resin; the modified polyester resin included the following mass components: 100 parts of maleic anhydride grafted polyester resin, 1.2 parts of 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] Step 2 and Step 3 were the same as Example 1 to obtain a preservative film.

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

[0077] Step 1, modification of the degradable polyester resin:

[0078] The degradable polyester resin, maleic anhydride, initiator and antioxidant are mixed and extruded in a twin-screw extruder to obtain a maleic anhydride grafted polyester resin as a modified polyester resin; in the extrusion process, the length-diameter ratio of the twin-screw extruder is 40:1, the partition temperature is 155℃, 170℃, 190℃ and 160℃ in turn, the screw rotation speed is 100rpm; the maleic anhydride grafted polyester resin comprises the following mass components: 100 parts of degradable polyester resin, 1 part of maleic anhydride, 0.1 part of initiator and 0.1 part of antioxidant;

[0079] Steps 2 and 3 are the same as in Example 1 to obtain a preservative film.

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

[0081] Step 1: Preparation of auxiliary resin:

[0082] Polytrimethylene ether glycol is vacuum dehydrated at 120℃ for 2h and cooled to 63℃; stirring, and adding 1,6-hexane diisocyanate, catalyst, solvent, warming to 78℃, and reacting until the NCO group content no longer changes to obtain a prepolymer; cooling to 63℃, adding 1,4-butanediol, stirring and warming to 88℃, and reacting for 100min to obtain a polyurethane as an auxiliary resin; the polyurethane comprises the following mass components: 30 parts of polytrimethylene ether glycol, 10 parts of 1,6-hexane diisocyanate, 3.6 parts of 1,4-butanediol, 0.1 parts of catalyst, and 28.5 parts of solvent; the catalyst is dibutyltin dilaurate; the solvent is ethyl acetate with a purity of ≥99.9%; after the reaction, vacuum degassing is performed, and vacuum drying is performed at 80℃ until the solvent residue is ≤0.1mg / kg;

[0083] Step 2: Preparation of preservative film:

[0084] 60 parts of degradable polyester resin, 30 parts of polylactic acid and 5 parts of auxiliary resin are melt extruded and blow molded into a film to obtain a preservative film; the melt extrusion is performed using a twin-screw extruder with a length-diameter ratio L / D = 40, segmented temperature control, and the segmented temperature is 165℃, 172℃, 172℃ and die 170℃ in turn; the rotation speed is 200rpm.

[0085] Experiment: The preservative films obtained in Examples 1-3 and Comparative Examples 1-3 are taken to prepare samples, and the performance of the samples is detected and the detection results are recorded:

[0086] Mechanical property test: GB / T 1040.3 is used as a reference standard to detect the tensile strength of the sample; the tensile rate is 50mm / min; GB / T 16578.1 is used as a reference standard to detect the tear strength of the sample;

[0087] Enzymatic degradation performance test: according to ISO 14855-1 as a reference standard, the sample was immersed in a buffer solution containing laccase (10 U / mL, Trametes versicola) and lipase (5 U / mL, CALB) at pH = 7.0, 37℃ oscillation, and the weight loss rate of the sample after 7 days of enzymatic degradation was detected;

[0088] Antibacterial performance test: according to GB / T 31402 as a reference standard, the sample (5x5cm2) was contacted with the bacterial solution (106CFU / mL) for 24 hours (37℃), and the survival colonies were counted by dilution plating, and the antibacterial rate was calculated. The strains are E. coli, S. aureus;

[0089] Barrier performance test: according to GB / T 1037 as a reference standard, the water vapor transmission rate (WVTR) of the sample was detected; according to GB / T 19789 as a reference standard, the oxygen transmission rate (OTR) of the sample was detected;

[0090] Light transmittance test: according to GB / T 2410 as a reference standard, the light transmittance (%) of the sample was detected.

[0091]

[0092] According to the data in the above table, the following conclusions can be clearly obtained:

[0093] The preservative film obtained in Examples 1-3 is compared with the preservative film obtained in Comparative Examples 1-5, and the test results show that,

[0094] Compared with Comparative Example 3, the preservative film obtained in Examples 1-3 has higher tensile strength, tear strength, enzyme degradation weight loss rate, antibacterial rate data, and relatively higher light transmittance, and the water vapor and oxygen transmission rates are reduced. The reason is that: the imine bond crosslinking and polyurethane auxiliary resin introduced in Examples 1-3 significantly improve the tensile strength; the imine bond is easily attacked by laccase, which significantly improves the oxidative degradation rate of Examples 1-3; the cationic effect of imidazolium hydrochloride gives Examples 1-3 significant antibacterial properties, and the antibacterial performance improves with the increase of grafting amount; imidazolium crosslinking and polyurethane auxiliary resin reduce the gap between molecular chains, and the barrier property is improved; appropriate crosslinking can improve the transparency of PLA / PBAT film by inhibiting phase separation and reducing crystallinity. This fully illustrates that the application improves the mechanical properties, oxidative biodegradation performance, antibacterial properties and barrier properties of the prepared preservative film, and maintains good light transmittance.

[0095] The tensile strength, tear strength, enzyme degradation weight loss rate and antibacterial rate of the degradable polyester resin in Comparative Examples 1 and 2 are obviously decreased, and the water vapor and oxygen permeability is increased. It is known that the process and the setting of the components used in the preparation of the preservative film can promote the comprehensive improvement of the mechanical properties, oxidative biodegradation properties, antibacterial properties and barrier properties. In Comparative Example 2, the auxiliary resin maleic anhydride grafted polyester resin can improve the compatibility between PLA / PBAT, and has better transparency, mechanical properties and the like compared with Comparative Example 3.

[0096] It will be apparent to those skilled in the art that the application is not limited to the details of the above-exemplified embodiments and that the application can be implemented in other particular forms without departing from the spirit or essential characteristics of the application. The embodiments should therefore be considered in all respects as illustrative and not restrictive, the scope of the application being indicated by the appended claims rather than by the above description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. A transparent cling film with oxidative biodegradability, characterized by: The invention comprises the following components: 50 to 65 parts of degradable polyester resin, 25 to 35 parts of polylactic acid, and 5 to 20 parts of auxiliary resin; the auxiliary resin is polyurethane.

2. The transparent cling film with oxidative biodegradability according to claim 1, characterized in that: The degradable polyester resin is one of polybutylene terephthalate-adipate and polybutylene succinate, or a mixture of the two.

3. A method for preparing a transparent cling film having oxidative biodegradability, characterized in that: The method comprises the following processes: melting and extruding degradable polyester resin, polylactic acid and auxiliary resin, and blowing the mixture into a film to obtain a fresh-keeping film.

4. The transparent cling film with oxidative biodegradability and the preparation method thereof according to claim 3, characterized in that: The auxiliary resin is polyurethane, which is prepared by the following process: Mixing polytrimethylene ether glycol, 1,6-hexamethylene diisocyanate, a catalyst, and a solvent, heating to 78-82° C., and reacting for 150-200 minutes until the NCO group content no longer changes, thereby obtaining a prepolymer; The temperature was lowered to 63-67° C., a glycidyl ether chain extender was added, the mixture was stirred and heated to 88-92° C., and the reaction was carried out for 100-150 minutes to obtain polyurethane.

5. The transparent cling film with oxidative biodegradability and the preparation method thereof according to claim 4, characterized in that: The polyurethane comprises the following components by mass: 30 to 60 parts of polytrimethylene ether glycol, 10 to 20 parts of 1,6-hexamethylene diisocyanate, 3.6 to 7.2 parts of a glycidyl ether chain extender, 0.1 to 0.2 parts of a catalyst, and 28.5 to 68 parts of a solvent; The glycidyl ether chain extender is one of glycidyl ether ethanol and p-hydroxyphenyl glycidyl ether.

6. The transparent cling film with oxidative biodegradability and the preparation method thereof according to claim 3, characterized in that: The degradable polyester resin is modified, and the specific modification process is as follows: The biodegradable polyester resin, maleic anhydride, an initiator and an antioxidant are mixed and extruded in a twin-screw extruder to obtain a maleic anhydride grafted polyester resin; Mix maleic anhydride grafted polyester resin and anhydrous N,N-dimethylformamide, heat to 58-65°C and stir to dissolve; cool to 30-40°C, add imide ester hydrochloride and triethylamine, and stir for 20-30 minutes to activate; under nitrogen atmosphere, add diamine compound, heat to 58-63°C, react for 210-270 minutes; heat to 78-82°C, continue to react for 6-8 hours to obtain modified polyester resin.

7. The transparent cling film with oxidative biodegradability and the preparation method thereof according to claim 6, characterized in that: The maleic anhydride grafted polyester resin comprises the following components by mass: 100 parts of degradable 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.

8. The transparent cling film with oxidative biodegradability and the preparation method thereof according to claim 6, characterized in that: The modified polyester resin comprises the following components by mass: 100 parts of maleic anhydride grafted polyester resin, 1.1 to 5.6 parts of imide ester hydrochloride, 1.2 to 5.4 parts of diamine compound, and 0.5 to 1.0 part of triethylamine.

9. The transparent cling film with oxidative biodegradability and the preparation method thereof according to claim 6, characterized in that: The imidate hydrochloride is prepared by the following process: Mix the dicarbonitrile compound and anhydrous ethanol, add zinc chloride, add hydrogen chloride at 0-5°C, raise the temperature to 25-30°C, and stir the reaction for 6-12 hours to obtain imidate hydrochloride.

10. The transparent cling film with oxidative biodegradability and the preparation method thereof according to claim 9, characterized in that: The dicarbonitrile compound is one of terephthalonitrile, 2,5-dicyanofuran, sebaconinitrile and succinonitrile.

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