1. A method for improving the heat sealing performance of a PBAT-starch composite bioplastic film is characterized by comprising the following steps of crushing corn raw starch into refined starch, reacting the refined starch with alpha-amylase to obtain microporous starch, dissolving PBAT in dichloromethane to prepare PBAT liquid, mixing the microporous starch with the PBAT liquid at a high speed, volatilizing the dichloromethane, further mixing the dichloromethane with PBAT, hydrogenated terpene resin and inorganic filler at a high speed to obtain a premix, extruding, air cooling and granulating to obtain the PBAT-starch composite bioplastic with good heat sealing performance, and the specific steps are as follows:

(1) refining corn native starch to a particle size of less than 10 μm by a vortex jet mill to obtain refined starch;

(2) adding refined starch into acetic acid-sodium acetate buffer solution with pH of 5.0, heating to 40-50 deg.C in a reaction kettle, slowly stirring, adding alpha-amylase, continuously stirring for reaction for 1-4 hr, adding water for dilution, filtering, oven drying, and further refining to obtain microporous starch;

(3) dissolving PBAT in dichloromethane to prepare PBAT liquid, then adding microporous starch into a high-speed stirrer, starting high-speed stirring, continuously spraying the PBAT liquid, then heating the high-speed mixer to 50 ℃ to continuously volatilize the dichloromethane, then adding the PBAT, hydrogenated terpene resin and inorganic filler into the high-speed mixer, and uniformly stirring to obtain a premix;

(4) feeding the premix into a co-rotating double-screw extruder, and carrying out bracing extrusion, air cooling and grain cutting to obtain the PBAT-starch composite bioplastic.

2. The method for improving the heat sealing performance of the PBAT-starch composite bio-plastic film as claimed in claim 1, wherein the rotational speed of the main machine of the vortex air flow pulverizer in step (1) is 1000-1200rpm, and the rotational speed of the classifier is 800-900 rpm.

3. The method for improving the heat sealing performance of the PBAT-starch composite bioplastic film according to claim 1, wherein the mass ratio of the refined starch to the acetic acid-sodium acetate buffer to the alpha-amylase in the step (2) is 1: 3-4: 0.005-0.01.

4. The method for improving the heat sealing performance of the PBAT-starch composite bioplastic film according to claim 1, wherein the enzyme activity of the alpha-amylase in the step (2) is 2000U/g.

5. The method for improving the heat sealing performance of the PBAT-starch composite biological plastic film as claimed in claim 1, wherein the water diluted by adding water in the step (2) is three times of the mass of the starch slurry.

6. The method for improving the heat sealing performance of the PBAT-starch composite bioplastic film according to claim 1, wherein in the PBAT solution in the step (3), the mass ratio of PBAT to dichloromethane is 1: 5-8.

7. The method for improving the heat sealing performance of the PBAT-starch composite bioplastic film as claimed in claim 1, wherein in the premix in step (3), the mass ratio of PBAT liquid, microporous starch, PBAT, hydrogenated terpene resin and inorganic filler is 5-8: 25-30: 60-70: 1-2: 3-5.

8. The method for improving the heat sealing performance of the PBAT-starch composite bioplastic film according to claim 1, wherein the inorganic filler in the step (3) is at least one of talc powder and calcium carbonate, and the particle size of the inorganic filler is less than 10 μm.

9. The method for improving the heat sealing performance of the PBAT-starch composite bioplastic film as claimed in claim 1, wherein the screw length-diameter ratio of the co-rotating twin-screw extruder in the step (4) is 48: 1.

10. the method for improving the heat sealing performance of the PBAT-starch composite bioplastic film according to claim 1, wherein the temperature of the co-rotating twin-screw extruder in the step (4) is as follows: the first section is 120-130 ℃, the second section is 145-150 ℃, the third section is 135-140 ℃ and the fourth section is 130-140 ℃.

Background

The chemical plastic products bring various conveniences to people and bring trouble which is hard to imagine to people. Because some waste plastics can not be degraded under natural conditions, harmful gas can be released after combustion, and pollution which is difficult to treat is caused to the ecological environment. Bioplastics have advantages in performance, practicality, degradability, and the like. In terms of performance, bioplastics can reach or exceed the performance of traditional plastics in certain specific fields; in the aspect of practicability, the bioplastic has similar application performance and sanitary performance to the traditional plastic; in terms of degradability, bioplastics can be rapidly degraded in the natural environment after use. Common bioplastics are PLA, PBS, PBAT, PHA, etc.

PBAT, i.e., poly (butylene adipate/terephthalate), is widely used in plastic packaging films. The PBAT contains flexible aliphatic chains and rigid aromatic bonds, so the PBAT has good toughness and film forming property and is suitable for being used as a plastic packaging film. However, because PBAT is too soft, and is liable to stick to a screw during a blow molding process, and bubble swing is unstable, it is necessary to modify PBAT for application, and most commonly, PBAT is modified by blending with starch, inorganic talc, calcium carbonate, and the like.

Although the stability of the PBAT composite bioplastic during film blowing processing can be improved through blending modification, and the cost is reduced to a certain extent, the PBAT modified by blending belongs to an incompatible system with starch, so that the strength of the PBAT modified by blending is easy to reduce, particularly the heat seal strength is reduced, the heat seal opening of a packaging bag is easy to open, and the requirement of a lifting experiment cannot be met, thereby affecting the use performance.

The Chinese patent application No. 201710352464.2 discloses a lignin modified starch-based PBAT biodegradable film material and a preparation method thereof, wherein the preparation method comprises the following steps: (1) drying PBAT and lignin in vacuum; (2) adding the dried PBAT, the lignin, the chain extender, the antioxidant, the plasticizer, the lubricant and the heat stabilizer into a high-speed mixer, and uniformly mixing; (3) extruding and granulating the obtained mixed material by a double-screw extruder to obtain lignin-starch-based PBAT composite plastic granules; (4) and blowing the composite plastic granules at a certain temperature to prepare the lignin modified starch-based PBAT biodegradable film material. Chinese patent application No. 201810751363.7 discloses a PBAT/modified starch full-biodegradable film with high ductility and high barrier property, a preparation method and application thereof, comprising the following steps: premixing starch and a plasticizer according to the mass ratio of 6:4-8:2 to obtain a premix, adding a polybasic organic acid for mixing, extruding A for granulation to obtain acidified modified thermoplastic starch; then the PBAT/AMTPS blend is prepared by double-screw blending and extrusion B with PBAT, and the PBAT/modified starch full-biodegradable film is prepared by extrusion-film blowing molding. Biodegradable plastic films blended by PBAT and starch have good properties, but the problem of reduced heat seal strength is not solved.

It can be seen that in the prior art, the heat sealing performance is reduced after the PBAT and the starch are blended, and even if the starch is subjected to surface coupling treatment or plasticizing modification, good heat sealing performance is difficult to achieve.

Disclosure of Invention

Aiming at the defect that the good heat sealing performance is difficult to achieve by carrying out surface coupling treatment or plasticizing modification on starch by blending the existing biodegradable plastic PBAT and refined starch, the invention provides a method for improving the heat sealing performance of the PBAT-starch composite biological plastic film, so that the heat sealing strength is improved, and the heat sealing performance is not reduced along with the increase of the starch dosage.

In order to achieve the purpose, the invention adopts the following technical scheme:

a method for improving the heat sealing performance of a PBAT-starch composite bioplastic film comprises the following steps of crushing corn native starch into refined starch, reacting the refined starch with alpha-amylase to obtain microporous starch, dissolving PBAT in dichloromethane to prepare PBAT liquid, mixing the microporous starch with the PBAT liquid at a high speed, volatilizing the dichloromethane, further mixing the microporous starch with PBAT, hydrogenated terpene resin and inorganic filler at a high speed to obtain a premix, extruding, air cooling and cutting into granules to obtain the PBAT-starch composite bioplastic with good heat sealing performance, and specifically comprises the following steps:

(1) refining corn native starch to a particle size of less than 10 μm by a vortex jet mill to obtain refined starch;

(2) adding refined starch into acetic acid-sodium acetate buffer solution with pH of 5.0, heating to 40-50 deg.C in a reaction kettle, slowly stirring, adding alpha-amylase, continuously stirring for reaction for 1-4 hr, adding water for dilution, filtering, oven drying, and further refining to obtain microporous starch;

(3) dissolving PBAT in dichloromethane to prepare PBAT liquid, then adding microporous starch into a high-speed stirrer, starting high-speed stirring, continuously spraying the PBAT liquid, then heating the high-speed mixer to 50 ℃ to continuously volatilize the dichloromethane, then adding the PBAT, hydrogenated terpene resin and inorganic filler into the high-speed mixer, and uniformly stirring to obtain a premix;

(4) feeding the premix into a co-rotating double-screw extruder, and carrying out bracing extrusion, air cooling and grain cutting to obtain the PBAT-starch composite bioplastic.

Preferably, the rotation speed of the main machine of the vortex airflow pulverizer in the step (1) is 1000-1200rpm, and the rotation speed of the classifier is 800-900 rpm.

Preferably, the mass ratio of the refined starch, the acetic acid-sodium acetate buffer and the alpha-amylase in the step (2) is 1: 3-4: 0.005-0.01.

Preferably, the enzyme activity of the alpha-amylase in the step (2) is 2000U/g.

Preferably, the water addition amount of the water dilution in the step (2) is three times of the mass of the starch slurry.

Preferably, in the PBAT solution in step (3), the mass ratio of PBAT to dichloromethane is 1: 5-8.

Preferably, in the premix in step (3), the mass ratio of the PBAT solution, the microporous starch, the PBAT, the hydrogenated terpene resin, and the inorganic filler is 5-8: 25-30: 60-70: 1-2: 3-5.

Preferably, in the step (3), the inorganic filler is at least one of talcum powder and calcium carbonate, and the particle size of the inorganic filler is less than 10 μm.

Preferably, the screw length-diameter ratio of the co-rotating twin-screw extruder in the step (4) is 48: 1.

preferably, the temperature of the co-rotating twin-screw extruder in the step (4) is as follows: the first section is 120-130 ℃, the second section is 145-150 ℃, the third section is 135-140 ℃ and the fourth section is 130-140 ℃.

Starch is known to be a natural high-molecular carbohydrate with polyhydroxy, and as a natural degradable high-molecular material, the starch is rich in source and low in price, but the starch has stronger hydrophilicity and is poorer in compatibility with lipophilic polymers. When the PBAT is modified by adopting the starch, if the starch is subjected to simple micronization treatment, the starch is equivalent to a common filler, a homogeneous system is difficult to form with the PBAT, and the system strength, particularly the heat seal strength, is seriously influenced.

The prior art modifies starch by two ways to improve the compatibility of the starch and PBAT, but the composite film with ideal heat sealing performance is difficult to obtain: firstly, the surface coupling treatment is carried out on starch by adopting a coupling agent, wax and the like so as to increase the interface bonding force between the starch and the PBAT, but once the addition amount of the starch exceeds 10 percent, the heat sealability of the film is seriously influenced, and holes are easy to appear, because the coupling agent and the wax are insulating agents instead under the action of heat, particularly when the high-temperature heat sealing is carried out, the coupling agent and the wax material at the interface between the starch and the PBAT lose efficacy, and the heat sealability is further aggravated to be poor; secondly, the water, the polyhydric alcohol and other plasticizers are adopted to destroy the microcrystals of the starch, so that the starch macromolecules are disorderly and linearly arranged, the thermoplasticity of the starch is improved, the homogeneity of the starch and the PBAT during blending is better, and the processed film is smoother.

The invention does not adopt coupling agent, wax and the like to carry out surface coupling treatment on starch, does not adopt water, polyhydric alcohol and the like to carry out plasticizing modification on starch, but thins the starch and then utilizes alpha-amylase to prepare the microporous starch, the microporous starch has large specific surface area and strong adsorption force, can form firm adsorption on PBAT in the starch and on the surface of the starch and then is mixed with a PBAT substrate to form connection of PBAT-PBAT, the compatibility is greatly improved, the heat sealing strength is improved, and the problem of heat sealing property reduction along with the increase of the starch dosage is avoided.

Furthermore, the PBAT is prepared into the PBAT liquid to realize the adsorption compounding with the microporous starch, because the PBAT liquid can be better immersed into micropores of the microporous starch and forms an integral body with the microporous starch, the microporous starch has the PBAT characteristic along with the volatilization removal of dichloromethane, the compatibility with an interface of a PBAT substrate is obviously improved, the interface is not easy to fall off, the heat sealing strength can be effectively prevented from being reduced during heat sealing, and the heat sealing property of a film is ensured during high content of starch. In addition, in order to further improve the heat sealability, a small amount of hydrogenated terpene resin is added into the system, so that the invention has a certain effect on preventing the heat sealability of the film from being reduced during high starch filling.

The existing PBAT-starch composite bioplastic film has poor two-phase compatibility, so that the heat sealing performance is poor, the use requirement cannot be met, and the application of the PBAT-starch composite bioplastic film is limited. In view of the above, the invention provides a method for improving the heat sealing performance of a PBAT-starch composite bioplastic film, which does not adopt coupling agent, wax and the like to carry out surface coupling treatment on starch, does not adopt water, polyhydric alcohol and the like to carry out plasticizing modification on starch, and firstly thins corn native starch to the particle size of less than 10 μm by a vortex airflow crusher to obtain thinned starch; then adding the starch into acetic acid-sodium acetate buffer solution with the pH value of 5.0, heating to 40-50 ℃, adding alpha-amylase for reaction for 1-4h, then adding water for dilution, filtering, drying, and further refining to obtain microporous starch; then preparing PBAT liquid, stirring and mixing the PBAT liquid and the microporous starch at a high speed, heating to 50 ℃ to volatilize dichloromethane, and further mixing the PBAT liquid, the hydrogenated terpene resin and the inorganic filler at a high speed to obtain a premix; and extruding, air-cooling and granulating the premix to obtain the PBAT-starch composite bioplastic. According to the invention, the firm PBAT is formed inside and on the surface of the starch by adsorbing the PBAT liquid by the microporous starch, so that the compatibility of the starch and the PBAT is good, the PBAT-PBAT connection is shown when the film is subjected to heat sealing, the heat sealing strength is high, and the heat sealing property is not reduced along with the increase of the using amount of the starch.

The invention provides a method for improving the heat sealing performance of a PBAT-starch composite bioplastic film, which has the outstanding characteristics and excellent effects compared with the prior art:

1. the invention refines starch and then utilizes alpha-amylase to prepare microporous starch, the microporous starch has large specific surface area, strong adsorption force and firm adsorption to PBAT, and then is mixed with PBAT matrix to represent the connection of PBAT-PBAT, the compatibility is greatly improved, the heat sealing strength is improved, and the problem of heat sealing property reduction along with the increase of the starch dosage can be avoided.

2. The PBAT solution is prepared into the PBAT solution to realize the adsorption and compounding with the microporous starch, the PBAT solution can be better immersed into the starch micropores to form a whole, the microporous starch has the PBAT characteristic, the interface compatibility with a PBAT substrate is obviously improved, the interface is not easy to fall off, the heat sealing strength can be effectively prevented from being reduced during heat sealing, and the heat sealing property of a film is ensured during high content of starch.

3. The invention adds a small amount of hydrogenated terpene resin in the system, has certain effect on preventing the heat sealing performance of the film from being reduced when high starch is filled, and can further improve the heat sealing performance.

Drawings

FIG. 1: example 1 of the invention is a seal diagram after a lifting test.

FIG. 2: comparative example 1 seal after lifting test.

FIG. 3: comparative example 2 seal after lifting test.

Detailed Description

The present invention will be described in further detail with reference to specific embodiments, but it should not be construed that the scope of the present invention is limited to the following examples. Various substitutions and alterations can be made by those skilled in the art and by conventional means without departing from the spirit of the method of the invention described above.

Example 1

(1) Refining corn native starch to a particle size of less than 10 μm by a vortex jet mill to obtain refined starch; wherein the main machine rotation speed of the vortex air flow pulverizer is 1000rpm, and the rotation speed of the classifier is 800 rpm;

(2) adding refined starch into an acetic acid-sodium acetate buffer solution with the pH value of 5.0, heating to 45 ℃ in a reaction kettle, slowly stirring, then adding alpha-amylase with the enzyme activity of 2000U/g, continuously stirring for reaction for 2 hours, then adding water with the mass being three times that of starch slurry for dilution, filtering, drying, and further refining to obtain microporous starch; wherein the mass ratio of the refined starch to the acetic acid-sodium acetate buffer to the alpha-amylase is 1: 3.5: 0.008;

(3) dissolving PBAT in dichloromethane to prepare PBAT liquid (the mass ratio of PBAT to dichloromethane is 1: 6), then adding microporous starch into a high-speed stirrer, starting high-speed stirring, continuously spraying the PBAT liquid, then heating the high-speed mixer to 50 ℃ to continuously volatilize dichloromethane, then adding PBAT, hydrogenated terpene resin and inorganic filler into the high-speed mixer, and uniformly stirring to obtain a premix; wherein the mass ratio of the PBAT liquid to the microporous starch to the PBAT to the hydrogenated terpene resin to the inorganic filler is 7: 27: 65: 1.5: 4; the inorganic filler is talcum powder with the grain diameter of less than 10 mu m;

(4) feeding the premix into a screw with the length-diameter ratio of 48: 1, setting the temperature of each section to be 125 ℃, 148 ℃, 138 ℃ and 135 ℃ respectively, and carrying out bracing extrusion, air cooling and grain cutting to obtain the PBAT-starch composite bioplastic.

Example 2

(1) Refining corn native starch to a particle size of less than 10 μm by a vortex jet mill to obtain refined starch; wherein the main machine rotation speed of the vortex air flow pulverizer is 1000rpm, and the classifier rotation speed is 900 rpm;

(2) adding refined starch into an acetic acid-sodium acetate buffer solution with the pH value of 5.0, heating to 40 ℃ in a reaction kettle, slowly stirring, then adding alpha-amylase with the enzyme activity of 2000U/g, continuously stirring for reaction for 1h, then adding water with the mass being three times that of starch slurry for dilution, filtering, drying, and further refining to obtain microporous starch; wherein the mass ratio of the refined starch to the acetic acid-sodium acetate buffer to the alpha-amylase is 1: 4: 0.005;

(3) dissolving PBAT in dichloromethane to prepare PBAT liquid (the mass ratio of PBAT to dichloromethane is 1: 8), then adding microporous starch into a high-speed stirrer, starting high-speed stirring, continuously spraying the PBAT liquid, then heating the high-speed mixer to 50 ℃ to continuously volatilize dichloromethane, then adding PBAT, hydrogenated terpene resin and inorganic filler into the high-speed mixer, and uniformly stirring to obtain a premix; wherein the mass ratio of the PBAT liquid to the microporous starch to the PBAT to the hydrogenated terpene resin to the inorganic filler is 5: 30: 60: 2: 3; the inorganic filler is calcium carbonate with the grain diameter of less than 10 mu m;

(4) feeding the premix into a screw with the length-diameter ratio of 48: 1, setting the temperatures of all sections to be 130 ℃, 150 ℃, 140 ℃ and 140 ℃ respectively in a co-rotating double-screw extruder, and carrying out bracing extrusion, air cooling and grain cutting to obtain the PBAT-starch composite bioplastic.

Example 3

(1) Refining corn native starch to a particle size of less than 10 μm by a vortex jet mill to obtain refined starch; wherein the main machine rotating speed of the vortex air flow pulverizer is 1200rpm, and the rotating speed of the classifier is 800 rpm;

(2) adding refined starch into an acetic acid-sodium acetate buffer solution with the pH value of 5.0, heating to 40 ℃ in a reaction kettle, slowly stirring, then adding alpha-amylase with the enzyme activity of 2000U/g, continuously stirring for reaction for 4 hours, then adding water with the mass being three times that of starch slurry for dilution, filtering, drying, and further refining to obtain microporous starch; wherein the mass ratio of the refined starch to the acetic acid-sodium acetate buffer to the alpha-amylase is 1: 3: 0.01;

(3) dissolving PBAT in dichloromethane to prepare PBAT liquid (the mass ratio of PBAT to dichloromethane is 1: 5), then adding microporous starch into a high-speed stirrer, starting high-speed stirring, continuously spraying the PBAT liquid, then heating the high-speed mixer to 50 ℃ to continuously volatilize dichloromethane, then adding PBAT, hydrogenated terpene resin and inorganic filler into the high-speed mixer, and uniformly stirring to obtain a premix; wherein the mass ratio of the PBAT liquid to the microporous starch to the PBAT to the hydrogenated terpene resin to the inorganic filler is 8: 25: 70: 1: 5; the inorganic filler is talcum powder with the grain diameter of less than 10 mu m;

(4) feeding the premix into a screw with the length-diameter ratio of 48: 1, setting the temperature of each section to be 120 ℃, 145 ℃, 135 ℃ and 130 ℃ respectively, and carrying out bracing extrusion, air cooling and grain cutting to obtain the PBAT-starch composite bioplastic.

Example 4

(1) Refining corn native starch to a particle size of less than 10 μm by a vortex jet mill to obtain refined starch; wherein the main machine rotation speed of the vortex air flow pulverizer is 1100rpm, and the classifier rotation speed is 850 rpm;

(2) adding refined starch into an acetic acid-sodium acetate buffer solution with the pH value of 5.0, heating to 50 ℃ in a reaction kettle, slowly stirring, then adding alpha-amylase with the enzyme activity of 2000U/g, continuously stirring for reaction for 2 hours, then adding water with the mass being three times that of starch slurry for dilution, filtering, drying, and further refining to obtain microporous starch; wherein the mass ratio of the refined starch to the acetic acid-sodium acetate buffer to the alpha-amylase is 1: 4: 0.005;

(3) dissolving PBAT in dichloromethane to prepare PBAT liquid (the mass ratio of PBAT to dichloromethane is 1: 5), then adding microporous starch into a high-speed stirrer, starting high-speed stirring, continuously spraying the PBAT liquid, then heating the high-speed mixer to 50 ℃ to continuously volatilize dichloromethane, then adding PBAT, hydrogenated terpene resin and inorganic filler into the high-speed mixer, and uniformly stirring to obtain a premix; wherein the mass ratio of the PBAT liquid to the microporous starch to the PBAT to the hydrogenated terpene resin to the inorganic filler is 7: 28: 62: 2: 3; the inorganic filler is calcium carbonate with the grain diameter of less than 10 mu m;

(4) feeding the premix into a screw with the length-diameter ratio of 48: 1, setting the temperature of each section to be 120 ℃, 145 ℃, 135 ℃ and 130 ℃ respectively, and carrying out bracing extrusion, air cooling and grain cutting to obtain the PBAT-starch composite bioplastic.

Example 5

(1) Refining corn native starch to a particle size of less than 10 μm by a vortex jet mill to obtain refined starch; wherein the main machine rotating speed of the vortex air flow pulverizer is 1100rpm, and the rotating speed of the classifier is 900 rpm;

(2) adding refined starch into an acetic acid-sodium acetate buffer solution with the pH value of 5.0, heating to 45 ℃ in a reaction kettle, slowly stirring, then adding alpha-amylase with the enzyme activity of 2000U/g, continuously stirring for reaction for 3 hours, then adding water with the mass being three times that of starch slurry for dilution, filtering, drying, and further refining to obtain microporous starch; wherein the mass ratio of the refined starch to the acetic acid-sodium acetate buffer to the alpha-amylase is 1: 3: 0.01;

(3) dissolving PBAT in dichloromethane to prepare PBAT liquid (the mass ratio of PBAT to dichloromethane is 1: 8), then adding microporous starch into a high-speed stirrer, starting high-speed stirring, continuously spraying the PBAT liquid, then heating the high-speed mixer to 50 ℃ to continuously volatilize dichloromethane, then adding PBAT, hydrogenated terpene resin and inorganic filler into the high-speed mixer, and uniformly stirring to obtain a premix; wherein the mass ratio of the PBAT liquid to the microporous starch to the PBAT to the hydrogenated terpene resin to the inorganic filler is 8: 25: 60: 2: 3; the inorganic filler is calcium carbonate with the grain diameter of less than 10 mu m;

(4) feeding the premix into a screw with the length-diameter ratio of 48: 1, setting the temperatures of all sections to be 130 ℃, 150 ℃, 140 ℃ and 140 ℃ respectively in a co-rotating double-screw extruder, and carrying out bracing extrusion, air cooling and grain cutting to obtain the PBAT-starch composite bioplastic.

Comparative example 1

(1) Refining corn native starch to a particle size of less than 10 μm by a vortex jet mill to obtain refined starch; wherein the main machine rotation speed of the vortex air flow pulverizer is 1000rpm, and the rotation speed of the classifier is 800 rpm;

(2) dissolving PBAT in dichloromethane to prepare PBAT liquid (the mass ratio of PBAT to dichloromethane is 1: 6), adding refined starch into a high-speed stirrer, starting high-speed stirring, continuously spraying the PBAT liquid, heating the high-speed mixer to 50 ℃ to continuously volatilize dichloromethane, adding PBAT, hydrogenated terpene resin and inorganic filler into the high-speed mixer, and uniformly stirring to obtain a premix; wherein the mass ratio of the PBAT liquid to the refined starch to the PBAT to the hydrogenated terpene resin to the inorganic filler is 7: 27: 65: 1.5: 4; the inorganic filler is talcum powder with the grain diameter of less than 10 mu m;

(3) feeding the premix into a screw with the length-diameter ratio of 48: 1, setting the temperature of each section to be 125 ℃, 148 ℃, 138 ℃ and 135 ℃ respectively, and carrying out bracing extrusion, air cooling and grain cutting to obtain the PBAT-starch composite bioplastic.

Comparative example 1 compared to example 1, a thinned starch was used instead of a microporous starch, the others being exactly the same as in example 1.

Comparative example 2

(1) Refining corn native starch to a particle size of less than 10 μm by a vortex jet mill to obtain refined starch; wherein the main machine rotation speed of the vortex air flow pulverizer is 1000rpm, and the rotation speed of the classifier is 800 rpm;

(2) adding refined starch into an acetic acid-sodium acetate buffer solution with the pH value of 5.0, heating to 45 ℃ in a reaction kettle, slowly stirring, then adding alpha-amylase with the enzyme activity of 2000U/g, continuously stirring for reaction for 2 hours, then adding water with the mass being three times that of starch slurry for dilution, filtering, drying, and further refining to obtain microporous starch; wherein the mass ratio of the refined starch to the acetic acid-sodium acetate buffer to the alpha-amylase is 1: 3.5: 0.008;

(3) adding microporous starch, PBAT, hydrogenated terpene resin and inorganic filler into a high-speed mixer, and uniformly stirring to obtain a premix; wherein the mass ratio of the microporous starch to the PBAT to the hydrogenated terpene resin to the inorganic filler is 27: 65: 1.5: 4; the inorganic filler is talcum powder with the grain diameter of less than 10 mu m;

(4) feeding the premix into a screw with the length-diameter ratio of 48: 1, setting the temperature of each section to be 125 ℃, 148 ℃, 138 ℃ and 135 ℃ respectively, and carrying out bracing extrusion, air cooling and grain cutting to obtain the PBAT-starch composite bioplastic.

Comparative example 2 in comparison to example 1, microporous starch was not treated with PBAT solution, but was directly blended with PBAT, otherwise exactly as in example 1.

Comparative example 3

(1) Refining corn native starch to a particle size of less than 10 μm by a vortex jet mill to obtain refined starch; wherein the main machine rotation speed of the vortex air flow pulverizer is 1000rpm, and the rotation speed of the classifier is 800 rpm;

(2) adding refined starch into an acetic acid-sodium acetate buffer solution with the pH value of 5.0, heating to 45 ℃ in a reaction kettle, slowly stirring, then adding alpha-amylase with the enzyme activity of 2000U/g, continuously stirring for reaction for 2 hours, then adding water with the mass being three times that of starch slurry for dilution, filtering, drying, and further refining to obtain microporous starch; wherein the mass ratio of the refined starch to the acetic acid-sodium acetate buffer to the alpha-amylase is 1: 3.5: 0.008;

(3) dissolving PBAT in dichloromethane to prepare PBAT liquid (the mass ratio of PBAT to dichloromethane is 1: 6), then adding microporous starch into a high-speed stirrer, starting high-speed stirring, continuously spraying the PBAT liquid, then heating the high-speed mixer to 50 ℃ to continuously volatilize dichloromethane, then adding PBAT and an inorganic filler into the high-speed mixer, and uniformly stirring to obtain a premix; wherein the mass ratio of the PBAT liquid to the microporous starch to the PBAT to the inorganic filler is 7: 27: 65: 4; the inorganic filler is talcum powder with the grain diameter of less than 10 mu m;

(4) feeding the premix into a screw with the length-diameter ratio of 48: 1, setting the temperature of each section to be 125 ℃, 148 ℃, 138 ℃ and 135 ℃ respectively, and carrying out bracing extrusion, air cooling and grain cutting to obtain the PBAT-starch composite bioplastic.

Comparative example 3 compared to example 1, no hydrogenated terpene resin was used to improve heat sealability, otherwise identical to example 1.

Testing of heat seal strength: the composite bioplastic blown films obtained in examples 1 to 5 and comparative examples 1 to 3 were heat-sealed into bags, and the sealing strength was tested according to QB/T2358 at a test speed of 300mm/min, with the test results shown in Table 1;

table 1:

performance index	Sealing strength (N/15 mm)
		Example 1	9.6
Example 2	9.4
		Example 3	9.5
Example 4	9.7
		Example 5	9.6
Comparative example 1	4.3
		Comparative example 2	6.1
Comparative example 3	8.3

Lifting test: the prepared plastic bag is subjected to a lifting experiment according to GB/T38082-2019, sand with the volume of 2/3 is filled in the plastic bag, the damage condition of the packaging bag is observed according to vibration with the amplitude of 30mm and the vibration frequency of 2Hz, and the test result is shown in Table 2.

FIG. 1 is a view showing the seal after the lifting test of example 1. As can be seen from FIG. 1, the plastic bag obtained in example 1 has good heat sealability.

FIG. 2 is a diagram showing a seal after a lifting test in comparative example 1, and it can be seen from FIG. 2 that in comparative example 1, the bonding property of PBAT and starch is affected by using thinned starch instead of microporous starch, thereby affecting the heat sealability.

Fig. 3 is a seal diagram after a lifting test of comparative example 2, and as can be seen from fig. 3, in comparative example 2, because the microporous starch is not treated by the PBAT solution, but is directly blended with the PBAT, and because of the micropores, part of the hot-melt PBAT enters the micropores, which is helpful for improving the heat sealability, but is not obvious, and the heat sealability is poorer than that of example 1.

Table 2:

performance index	Oscillation damage condition
		Example 1	2000 times sealing without damage
Example 2	2000 times sealing without damage
		Example 3	2000 times sealing without damage
Example 4	2000 times sealing without damage
		Example 5	2000 times sealing without damage
Comparative example 1	35 times of seal breakage
		Comparative example 2	263 times sealing is broken
Comparative example 3	2000 times of sealing withoutBreakage of