1. A preparation method of modified PBAT full-biodegradable plastic is characterized by comprising the following steps:

step one, uniformly mixing raw starch and stearic acid according to a mass ratio of 100:1-3, and crushing to obtain pretreated refined starch;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, carrying out high-speed stirring and water drainage for 30-50min at the temperature of 80-90 ℃, adding polycarbonate-1, 6-hexanediol glycol in batches under a high-speed stirring state, discharging after the polycarbonate-1, 6-hexanediol glycol permeates the surface of the pretreated refined starch, cooling to room temperature, sealing, packaging and standing for 24-48 h; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 3-5% of the mass of the pretreated refined starch;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:4-6, stirring at a high speed, gradually heating to 50 ℃, and stirring for 20-30 min; then adding a chain extender, continuing to stir at a high speed, raising the temperature to 80-90 ℃, stirring for reacting for 45-60min, discharging, sealing and aging for 24-48 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.5-1, and crushing to obtain the micronized modified starch for the bioplastic;

and step five, mixing the micronized modified starch, the inorganic powder, the dispersing agent and the PBAT obtained in the step four in a mass ratio of 20-30:3-5:0.5-1:70-80 in a high-speed mixer, and extruding and granulating in a co-rotating double-screw extruder to obtain the modified PBAT fully biodegradable plastic.

2. The preparation method of the modified PBAT full biodegradable plastic according to claim 1, characterized in that: the grain diameter of the D90 of the pretreated refined starch in the first step is less than 5 mu m.

3. The preparation method of the modified PBAT full biodegradable plastic according to claim 1, characterized in that: in the first step, the raw starch is at least one of corn starch, cassava starch and pea starch.

4. The preparation method of the modified PBAT full biodegradable plastic according to claim 1, characterized in that: crushing by adopting a vortex airflow crusher in the step one; the operation process of the vortex airflow crusher comprises that the rotation speed of a main machine is 1200-1400rpm, the grading rotation speed is 950-1000rpm, and the raw starch is mechanically crushed by the vortex airflow crusher under the dispersion action of stearic acid to obtain the pretreated refined starch with the D90 particle size of less than 5 mu m.

5. The preparation method of the modified PBAT full biodegradable plastic according to claim 1, characterized in that: and in the second step, 3-5 batches of polycarbonate-1, 6-hexanediol glycol with equal mass are added.

6. The preparation method of the modified PBAT full biodegradable plastic according to claim 1, characterized in that: and in the third step, the chain extender is 1, 4-butanediol.

7. The preparation method of the modified PBAT full biodegradable plastic according to claim 1, characterized in that: the inorganic powder is at least one of calcium carbonate, talcum powder, bamboo powder, straw powder and bentonite;

the dispersant is at least one of hard amide, stearic acid monoglyceride, liquid paraffin, microcrystalline paraffin and magnesium stearate.

8. The preparation method of the modified PBAT full biodegradable plastic according to claim 1, characterized in that: the length-diameter ratio of the co-rotating twin-screw extruder in the step five is 46: 1; the processing temperature is 130-160 ℃, and the rotating speed of the main machine is 150-200 rpm.

9. The preparation method of the modified PBAT full biodegradable plastic according to any one of claims 1 to 8, characterized in that: the mixing mass ratio of the raw starch to the stearic acid is 100: 2;

the mixing mass ratio of the material obtained in the step two to 4, 4' -diphenylmethane diisocyanate is 100: 5;

mixing the aged material and the glyceryl monostearate in a mass ratio of 100: 0.8;

the mixing mass ratio of the micronized modified starch, the inorganic powder, the dispersing agent and the PBAT is 25:4:0.8: 75.

10. A modified PBAT full-biodegradable plastic is characterized in that: the modified PBAT full-biodegradable plastic is prepared by the preparation method of any one of claims 1-9.

Background

With the gradual promotion of plastic-limiting policy, the market demand of bioplastics is obviously increased in recent years. The related bioplastic technology breaks through the bottleneck continuously. Through continuous screening, the bio-plastic PBAT (polybutylene terephthalate adipate) suitable for manufacturing the film packaging bag is rapidly developed. PBAT is a flexible aliphatic chain-containing bioplastic, has good ductility and film-forming property, and is the currently preferred bioplastic most suitable for preparing packaging bags.

However, PBAT is affected by raw material supply, and the cost is much higher than that of ordinary plastic films, which affects large-scale use. In addition, films prepared from PBAT have poor stability in blown film, bag making due to lack of rigidity. According to the disclosed technology, in order to increase the rigidity of PBAT films and reduce the cost, inorganic fillers such as calcium carbonate and talc are mainly blended in PBAT at present. However, calcium carbonate and talcum powder are easy to agglomerate, so that a large number of white crystal points are easy to appear in the film, and the film rupture can be seriously influenced by overlarge crystal points. Moreover, in the granulation of calcium carbonate and talc powder blended and dispersed in PBAT, serious agglomeration also occurs with the prolonged storage time during the storage process.

The starch as rigid particles is used for PBAT and has the same rigidity characteristics as calcium carbonate and talcum powder, and the cost of PBAT can be reduced. Most importantly, the surface of the starch particle has abundant hydroxyl groups, and the starch particle can be modified to overcome the problems of agglomeration of common fillers and the like. Thus, starch has great potential for use in PBAT.

The starch is structurally high polysaccharide consisting of a single type of sugar unit, and adjacent molecules of the starch are mutually interacted by hydrogen bonds to form complete particles with a micro structure, so that the starch has high crystallinity and the rigidity as same as that of the inorganic filler. The technical effect is well proved by the technology that if hydrogen bonds in starch fine particles are broken, starch molecules are disorganized and thermoplastic processing characteristics similar to general-purpose plastics are formed. For example, water and glycerol, a polyhydric alcohol and the like are used as plasticizers, and starch is infiltrated under the action of high shearing force and high temperature, so that the microcrystals of the starch can be broken, and macromolecules are randomly and linearly arranged, so that the original natural starch can have thermoplasticity.

However, the existing thermoplastic starch has poor water resistance, limited temperature resistance and limited processing range, and the thermoplastic starch adopts more strongly polar micromolecules to treat hydrogen bonds, so that a plasticizer is easy to diffuse out of a product under a high-humidity environment, and the product is sticky and the water resistance is reduced.

If the starch is micronized, the surface modification can keep the good rigidity of the fine starch and be used for PBAT bioplastic to increase the rigidity of the film on the one hand, and on the other hand, the fine starch particle surface has rich hydroxyl groups and can be modified, thereby not only overcoming the agglomeration problem of the filler, but also enhancing the compatibility and the dispersibility with PBAT.

The micronized modified starch prepared by the prior art is mainly treated by physical crushing such as grinding, jet milling and the like and a surface coupling modifier, the micronized starch can not only greatly change the shape of starch granules, but also change a plurality of physical properties of the starch, such as increase of specific surface area, relaxation of integral molecular structure, reduction of crystallinity, reduction of molecular weight and the like, so that the disorder degree of the starch is increased, the reaction activity is improved, and the filling performance is improved. When the micronized starch is used for the bioplastic, the modification requirement on the starch is high, and the simple coupling is difficult to meet the use requirement. The molecular chains on the surface of the micronized starch are usually in a disordered state, but the molecular chains are easily attracted together by hydrogen bonds, and orderly arranged again to form crystals, so that the agglomeration and hardening of the fine starch particles are gradually caused, and the dispersion and the use in the bioplastic are influenced.

Chinese patent CN201710353482.2 discloses a starch modified full-bio-based PBAT biodegradable plastic, although the starch modified full-bio-based PBAT biodegradable plastic prepared by the method meets the requirement of complete degradation after composite modification, enhances the mechanical property of pure PBAT resin, and reduces the production cost, the modified plastic has poor compatibility and insufficient plastic stability.

Chinese patent publication No. CN202110263740.4 discloses a starch-filled full-biodegradable plastic and a preparation method thereof, wherein the main raw materials comprise poly (butylene adipate/terephthalate), starch, a plasticizer, a reinforcing agent, a surfactant, a dispersant, a lubricant and an antioxidant. The preparation method comprises the steps of mixing the materials by a high-speed mixer, and then extruding and granulating in a double-screw extruder. The full-biodegradable plastic is used in the film blowing industry, and has poor plasticity and stability and insufficient compatibility.

Disclosure of Invention

At present, PBAT needs to be changed by reducing the cost and increasing the stability of a blown film so as to be convenient for use and popularization. When the fine starch is used for PBAT, the compatibility and the dispersibility are problematic, and the prepared granules are continuously recrystallized and agglomerated among starch granules after being stored for a period of time, so that a large number of aggregated crystal points appear during film blowing, the film is easy to break, and the film blowing difficulty and the film product defect are caused.

In view of the defects in the prior art, the invention aims to provide a modified PBAT full-biodegradable plastic, which is modified by adopting micronized modified starch, wherein the micronized modified starch is prepared by permeating polycarbonate-1, 6-hexanediol glycol into the micronized starch and further polymerizing and coating a polymer, so that a firm polymer-coated interface layer is formed on the surface of the micronized starch, the agglomeration and surface crystallization of the micronized starch are effectively overcome, and the modified PBAT full-biodegradable plastic has good dispersibility and compatibility when being applied to the bioplastic.

In order to attain the above and other related objects,

the invention provides a preparation method of modified PBAT full-biodegradable plastic, which comprises the following steps:

step one, uniformly mixing raw starch and stearic acid according to a mass ratio of 100:1-3, and crushing to obtain pretreated refined starch;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, carrying out high-speed stirring and water drainage for 30-50min at the temperature of 80-90 ℃, adding polycarbonate-1, 6-hexanediol glycol in batches under a high-speed stirring state, discharging after the polycarbonate-1, 6-hexanediol glycol permeates the surface of the pretreated refined starch, cooling to room temperature, sealing, packaging and standing for 24-48 h to ensure that the polycarbonate-1, 6-hexanediol glycol on the surface of the refined starch fully and uniformly permeates the starch; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 3-5% of the mass of the pretreated refined starch;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:4-6, stirring at a high speed, gradually heating to 50 ℃, and stirring for 20-30 min; then adding a chain extender, continuing to stir at a high speed, raising the temperature to 80-90 ℃, stirring for reacting for 45-60min, discharging, sealing and aging for 24-48 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.5-1, and crushing to obtain the micronized modified starch for the bioplastic;

and step five, mixing the micronized modified starch, the inorganic powder, the dispersing agent and the PBAT obtained in the step four in a mass ratio of 20-30:3-5:0.5-1:70-80 in a high-speed mixer, and extruding and granulating in a co-rotating double-screw extruder to obtain the modified PBAT fully biodegradable plastic.

Further, more specifically, a preparation method of the modified PBAT full-biodegradable plastic comprises the following steps:

step one, uniformly mixing raw starch and stearic acid according to a mass ratio of 100:1-3, and feeding the mixture into a vortex airflow pulverizer to be refined until the particle size of D90 is less than 5 microns to obtain pretreated refined starch;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, controlling the temperature of the high-speed mixer to be 80-90 ℃, draining water for 30-50min by high-speed stirring, and then adding polycarbonate-1, 6-hexanediol ester diol in batches under a high-speed stirring state; permeating polycarbonate-1, 6-hexanediol diol on the surface of the pretreated refined starch, discharging, cooling to room temperature, sealing, packaging and standing for more than 24 hours, preferably 24-48 hours; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 3-5% of the mass of the pretreated refined starch;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:4-6, stirring at a high speed, gradually increasing the temperature of the high-speed mixer from room temperature to 50 ℃, and stirring for 20-30 min; adding chain extender, continuing to stir at high speed, raising the temperature to 80-90 ℃, stirring for reaction for 45-60min, discharging, sealing and aging for more than 24h, preferably 24-48 h;

step four, uniformly mixing the materials aged in the step three and glyceryl monostearate according to the mass ratio of 100:0.5-1, and feeding the mixture into a vortex airflow pulverizer to refine and disperse to obtain the micronized modified starch for the bioplastic.

And step five, mixing the micronized modified starch, the inorganic powder, the dispersing agent and the PBAT obtained in the step four in a mass ratio of 20-30:3-5:0.5-1:70-80 in a high-speed mixer, and extruding and granulating in a co-rotating double-screw extruder to obtain the modified PBAT fully biodegradable plastic.

In one embodiment of the present invention, the D90 particle size of the pretreated refined starch in step one is less than 5 μm.

In an embodiment of the present invention, in the first step, the raw starch is at least one of corn starch, tapioca starch and pea starch.

In an embodiment of the present invention, in the step one, the pulverization is performed by a vortex airflow pulverizer; the operation process of the vortex airflow crusher comprises that the rotation speed of a main machine is 1200-1400rpm, the grading rotation speed is 950-1000rpm, and the raw starch is mechanically crushed by the vortex airflow crusher under the dispersion action of stearic acid to obtain the pretreated refined starch with the D90 particle size of less than 5 mu m.

In the preparation method, the starch and the stearic acid are mixed and are mechanically crushed by a vortex airflow crusher under the dispersion action of the stearic acid to obtain the pretreated refined starch with the D90 particle size of less than 5 mu m; the treatment not only enables the starch particles to be micronized, but also enables the molecular chain structure on the surface of the starch particles to be disordered and to be in a highly activated state, thereby being beneficial to further modification in the follow-up process.

In one embodiment of the invention, the polycarbonate-1, 6-hexanediol diol in step two is added in 3-5 batches with equal mass.

In the preparation method, the polycarbonate-1, 6-hexanediol glycol ester is white wax, and is gradually melted and permeated on the surface of activated fine starch in a heating state; when the fine starch is added, the fine starch is added in equal batches, so that excessive penetration of local starch caused by concentrated addition is prevented, and limited polycarbonate-1, 6-hexanediol glycol cannot be uniformly penetrated and treated. The amount of polycarbonate-1, 6-hexanediol diol used is limited to penetrate the surface of fine starch, and excessive use of polycarbonate-1, 6-hexanediol diol can completely destroy the rigid particles of starch and easily absorb water.

In an embodiment of the present invention, in step three, 1, 4-butanediol is selected as the chain extender.

In the preparation method, in the third step, the high-temperature mixer is gradually heated to 50 ℃ from room temperature, so that the 4, 4' -diphenylmethane diisocyanate is gradually melted and fused with the polycarbonate-1, 6-hexanediol glycol on the surface of the fine starch, and the chain is further extended under the action of the chain extender, so that the polyurethane tightly-coated and modified fine starch is formed.

In an embodiment of the present invention, the inorganic powder is at least one of calcium carbonate, talc powder, bamboo powder, straw powder, and bentonite;

the dispersant is at least one of hard amide, stearic acid monoglyceride, liquid paraffin, microcrystalline paraffin and magnesium stearate.

In one embodiment of the present invention, the length-diameter ratio of the co-rotating twin-screw extruder in the fifth step is 46: 1; the processing temperature is 130-160 ℃, and the rotating speed of the main machine is 150-200 rpm.

In an embodiment of the present invention, the mixing mass ratio of the native starch to the stearic acid is 100: 2;

the mixing mass ratio of the material obtained in the step two to 4, 4' -diphenylmethane diisocyanate is 100: 5;

mixing the aged material and the glyceryl monostearate in a mass ratio of 100: 0.8;

the mixing mass ratio of the micronized modified starch, the inorganic powder, the dispersing agent and the PBAT is 25:4:0.8: 75.

In the preparation method, in the fourth step, the aged material obtained in the third step is dispersed with the glyceryl monostearate, the aged material and the glyceryl monostearate are refined and dispersed in a vortex airflow pulverizer, and the polyurethane is tightly coated and modified to obtain refined starch adhesive groups, and the refined starch adhesive groups are dispersed and refined.

The second aspect of the invention provides a modified PBAT (polybutylene adipate terephthalate) fully biodegradable plastic, which is prepared by the preparation method. PBAT belongs to thermoplastic biodegradable plastics, is a copolymer of butanediol adipate and butanediol terephthalate, has the characteristics of PBA and PBT, and has better ductility and elongation at break as well as better heat resistance and impact property.

According to the invention, the surface of the starch which is highly activated is permeated with the polycarbonate-1, 6-hexanediol diol by micronizing the starch, 4' -diphenylmethane diisocyanate is further added, and the chain extension reaction is carried out under the action of a chain extender, so that the surface of the micronized starch forms the modified fine starch which is tightly coated with a polyurethane layer. The interface layer is firmly connected with starch and is not easy to fall off, so that the rigidity of the fine starch is kept, meanwhile, the fine starch is not agglomerated, and particularly, the compatibility of the interface after the micronized modified starch is used for PBAT bioplastic is remarkably improved.

As mentioned above, the modified PBAT full-biodegradable plastic and the preparation method thereof have the following beneficial effects:

1. the preparation method comprises the steps of mixing starch with stearic acid, and mechanically crushing the mixture by a vortex airflow crusher under the dispersion action of the stearic acid to obtain pretreated refined starch; the treatment not only enables the starch particles to be micronized, but also enables the molecular chain structure on the surface of the starch particles to be disordered and to be in a highly activated state, thereby being beneficial to further modification in the follow-up process.

2. In the preparation method, under the heating state, the white wax substance polycarbonate-1, 6-hexanediol glycol is gradually melted and permeated on the surface of activated fine starch in batches, and the batch addition can effectively prevent the excessive permeation of local starch caused by the concentrated addition, so that the limited polycarbonate-1, 6-hexanediol glycol can not uniformly permeate the fine starch; the dosage of the polycarbonate-1, 6-hexanediol glycol ester is neither too much nor too little, and too little polycarbonate-1, 6-hexanediol glycol ester cannot permeate and wrap the surface of fine starch, so that excessive use can lead to that the rigid particles of the starch are completely damaged by the polycarbonate-1, 6-hexanediol ester glycol ester, and the polycarbonate-1, 6-hexanediol ester glycol ester is easy to absorb water; the activated starch of the surface penetration polycarbonate-1, 6-hexanediol glycol ester diol obtained by the method has excellent thermoplasticity and mechanical property.

3. According to the preparation method, the polycarbonate-1, 6-hexanediol glycol ester diol permeates into the surface of the highly activated starch, 4' -diphenylmethane diisocyanate is further added, chain extension reaction is carried out under the action of a chain extender, so that the modified fine starch tightly coated with a polyurethane layer is formed on the surface of the fine starch, the interface layer is firmly connected with the starch and is not easy to fall off, the fine starch keeps rigidity, meanwhile, the fine starch is not agglomerated, and particularly, the interface compatibility, the tensile strength and the stability of the fine modified starch after the fine modified starch is used for PBAT (poly (butylene adipate-co-terephthalate)) bioplastic are obviously improved.

Drawings

FIG. 1: polarizing microscope images of the micronized modified starch treated in example 1 of the present invention;

FIG. 2: a polarizing microscope picture of pretreated refined starch obtained in the first step of example 1 of the invention.

Detailed Description

The following description of the embodiments of the present invention is provided for illustrative purposes, and other advantages and effects of the present invention will become apparent to those skilled in the art from the present disclosure.

Example 1

A modified PBAT full-biodegradable plastic and a preparation method thereof comprise the following steps:

uniformly mixing raw starch and stearic acid according to a mass ratio of 100:2, crushing, and refining until the grain size of D90 is less than 5 microns to obtain pretreated refined starch, wherein the rotating speed of a main machine is 1300rpm, the grading rotating speed is 980 rpm;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, stirring at a high speed at 85 ℃ for draining for 40min, adding polycarbonate-1, 6-hexanediol glycol in batches under a high-speed stirring state, discharging after the polycarbonate-1, 6-hexanediol glycol permeates the surface of the pretreated refined starch, cooling to room temperature, sealing, packaging and standing for 36h to ensure that the polycarbonate-1, 6-hexanediol glycol on the surface of the refined starch fully and uniformly permeates the starch; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 4 percent of the mass of the pretreated refined starch; adding 4 batches of polycarbonate-1, 6-hexanediol glycol in the second step according to equal mass;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:5, stirring at a high speed, gradually heating to 50 ℃, and stirring for 25 min; then adding chain extender 1, 4-butanediol, wherein the adding amount of the chain extender is 20% of the mass of 4, 4' -diphenylmethane diisocyanate, continuing to stir at a high speed, raising the temperature to 85 ℃, stirring for reacting for 50min, discharging, sealing and aging for 36 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.8, and crushing to obtain the micronized modified starch for the bioplastic;

step five, mixing the micronized modified starch, the inorganic powder, the dispersing agent and the PBAT obtained in the step four in a high-speed mixer according to the mass ratio of 25:4:0.8:75, and extruding and granulating in a co-rotating double-screw extruder to obtain the modified PBAT fully biodegradable plastic; the inorganic powder is calcium carbonate; the dispersant is a hard amide; the length-diameter ratio of the co-rotating twin-screw extruder is 46: 1; the processing temperature is 150 ℃, and the rotating speed of the main machine is 150-.

Example 2

A modified PBAT full-biodegradable plastic and a preparation method thereof comprise the following steps:

uniformly mixing raw starch and stearic acid according to a mass ratio of 100:3, crushing, and refining until the particle size of D90 is less than 5 microns at a main machine rotation speed of 1300rpm and a grading rotation speed of 1000rpm to obtain pretreated refined starch; the raw starch is cassava starch;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, stirring at a high speed at 80 ℃ for draining for 30min, adding polycarbonate-1, 6-hexanediol glycol in batches under a high-speed stirring state, discharging after the polycarbonate-1, 6-hexanediol glycol permeates the surface of the pretreated refined starch, cooling to room temperature, sealing, packaging and standing for 24h to ensure that the polycarbonate-1, 6-hexanediol glycol on the surface of the refined starch fully and uniformly permeates the starch; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 5 percent of the mass of the pretreated refined starch; adding 5 batches of polycarbonate-1, 6-hexanediol glycol in the second step according to equal mass;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:4, stirring at a high speed, gradually heating to 50 ℃, and stirring for 30 min; then adding a chain extender 1, 4-butanediol, wherein the adding amount of the chain extender is 20% of the mass of the 4, 4' -diphenylmethane diisocyanate, continuously stirring at a high speed, raising the temperature to 90 ℃, stirring for reacting for 60min, discharging, sealing and aging for 48 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.5, and crushing to obtain the micronized modified starch for the bioplastic;

step five, mixing the micronized modified starch obtained in the step four, inorganic powder calcium carbonate, dispersant hard amide and PBAT in a high-speed mixer according to the mass ratio of 20:5:0.5:70, and extruding and granulating in a co-rotating double-screw extruder to obtain the modified PBAT fully biodegradable plastic; the length-diameter ratio of the co-rotating twin-screw extruder is 46: 1; the processing temperature is 140 ℃, and the rotating speed of the main machine is 150 rpm.

Example 3

A modified PBAT full-biodegradable plastic and a preparation method thereof comprise the following steps:

uniformly mixing raw starch and stearic acid according to a mass ratio of 100:3, crushing, and refining until the particle size of D90 is less than 5 microns at a main machine rotation speed of 1400rpm and a grading rotation speed of 1000rpm to obtain pretreated refined starch; the raw starch is pea starch;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, carrying out high-speed stirring and water drainage for 45min at the temperature of 90 ℃, adding polycarbonate-1, 6-hexanediol glycol in batches under a high-speed stirring state, discharging after the polycarbonate-1, 6-hexanediol glycol permeates the surface of the pretreated refined starch, cooling to room temperature, sealing, packaging and standing for 30h to ensure that the polycarbonate-1, 6-hexanediol glycol on the surface of the refined starch fully and uniformly permeates the starch; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 5 percent of the mass of the pretreated refined starch; adding 3 batches of polycarbonate-1, 6-hexanediol glycol in the second step according to equal mass;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:6, stirring at a high speed, gradually heating to 50 ℃, and stirring for 20-30 min; then adding a chain extender 1, 4-butanediol, wherein the adding amount of the chain extender is 20% of the mass of the 4, 4' -diphenylmethane diisocyanate, continuously stirring at a high speed, raising the temperature to 85 ℃, stirring for reacting for 45min, discharging, sealing and aging for 48 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.5, and crushing to obtain the micronized modified starch for the bioplastic;

step five, mixing the micronized modified starch obtained in the step four, inorganic powder straw powder, bentonite, dispersant magnesium stearate and PBAT in a high-speed mixer according to the mass ratio of 30:4:0.9:77, and extruding and granulating in a co-rotating double-screw extruder to obtain the modified PBAT fully biodegradable plastic; the length-diameter ratio of the co-rotating twin-screw extruder is 46: 1; the processing temperature is 150 ℃, and the rotating speed of the main machine is 180 rpm.

Example 4

A modified PBAT full-biodegradable plastic and a preparation method thereof comprise the following steps:

uniformly mixing raw starch and stearic acid according to a mass ratio of 100:3, crushing, and refining until the particle size of D90 is less than 5 microns at a main machine rotation speed of 1300rpm and a grading rotation speed of 1000rpm to obtain pretreated refined starch; the raw starch is cassava starch;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, stirring at a high speed at 85 ℃ for draining for 50min, adding polycarbonate-1, 6-hexanediol glycol in batches under a high-speed stirring state, discharging after the polycarbonate-1, 6-hexanediol glycol permeates the surface of the pretreated refined starch, cooling to room temperature, sealing, packaging and standing for 48h to ensure that the polycarbonate-1, 6-hexanediol glycol on the surface of the refined starch fully and uniformly permeates the starch; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 5 percent of the mass of the pretreated refined starch; adding 4 batches of polycarbonate-1, 6-hexanediol glycol in the second step according to equal mass;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:6, stirring at a high speed, gradually heating to 50 ℃, and stirring for 25 min; then adding a chain extender 1, 4-butanediol, wherein the adding amount of the chain extender is 20% of the mass of the 4, 4' -diphenylmethane diisocyanate, continuously stirring at a high speed, raising the temperature to 90 ℃, stirring for reacting for 45min, discharging, sealing and aging for 25 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.9, and crushing to obtain the micronized modified starch for the bioplastic;

step five, mixing the micronized modified starch obtained in the step four, inorganic powder bamboo wood powder, dispersant liquid paraffin and PBAT in a high-speed mixer according to the mass ratio of 30:5:0.8:77, and extruding and granulating in a co-rotating double-screw extruder to obtain modified PBAT fully biodegradable plastic; the length-diameter ratio of the co-rotating twin-screw extruder is 46: 1; the processing temperature is 140 ℃, and the rotating speed of the main machine is 170 rpm.

Example 5

A modified PBAT full-biodegradable plastic and a preparation method thereof comprise the following steps:

step one, uniformly mixing raw starch and stearic acid according to a mass ratio of 100:3, crushing, and refining until the grain size of D90 is less than 5 microns to obtain pretreated refined starch, wherein the main machine rotation speed is 1350rpm and the grading rotation speed is 980 rpm; the raw starch is corn starch;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, stirring at a high speed at 88 ℃ for draining for 35min, adding polycarbonate-1, 6-hexanediol glycol in batches under a high-speed stirring state, discharging after the polycarbonate-1, 6-hexanediol glycol permeates the surface of the pretreated refined starch, cooling to room temperature, sealing, packaging and standing for 40h to ensure that the polycarbonate-1, 6-hexanediol glycol on the surface of the refined starch fully and uniformly permeates the starch; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 3.5 percent of the mass of the pretreated refined starch; adding 3 batches of polycarbonate-1, 6-hexanediol glycol in the second step according to equal mass;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:6, stirring at a high speed, gradually heating to 50 ℃, and stirring for 22 min; then adding a chain extender 1, 4-butanediol, wherein the adding amount of the chain extender is 20% of the mass of the 4, 4' -diphenylmethane diisocyanate, continuously stirring at a high speed, raising the temperature to 82 ℃, stirring for reacting for 48min, discharging, sealing and aging for 30 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.6, and crushing to obtain the micronized modified starch for the bioplastic;

step five, mixing the micronized modified starch obtained in the step four, inorganic powder talcum powder, dispersing agent magnesium stearate and PBAT in a high-speed mixer according to the mass ratio of 28:4:0.8:77, and extruding and granulating in a co-rotating double-screw extruder to obtain modified PBAT fully biodegradable plastic; the length-diameter ratio of the co-rotating twin-screw extruder is 46: 1; the processing temperature is 145 ℃, and the rotation speed of the main machine is 175 rpm.

Example 6

A modified PBAT full-biodegradable plastic and a preparation method thereof comprise the following steps:

step one, uniformly mixing raw starch and stearic acid according to a mass ratio of 100:3, crushing, and refining until the grain size of D90 is less than 5 microns at a main machine rotation speed of 1250rpm and a grading rotation speed of 990rpm to obtain pretreated refined starch; the raw starch is corn starch;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, carrying out high-speed stirring and water drainage for 45min at 87 ℃, adding polycarbonate-1, 6-hexanediol glycol in batches under a high-speed stirring state, discharging after the polycarbonate-1, 6-hexanediol glycol permeates the surface of the pretreated refined starch, cooling to room temperature, sealing, packaging and standing for 35h to ensure that the polycarbonate-1, 6-hexanediol glycol on the surface of the refined starch fully and uniformly permeates the starch; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 4 percent of the mass of the pretreated refined starch; adding 5 batches of polycarbonate-1, 6-hexanediol glycol in the second step according to equal mass;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:4, stirring at a high speed, gradually heating to 50 ℃, and stirring for 28 min; then adding a chain extender 1, 4-butanediol, wherein the adding amount of the chain extender is 20% of the mass of the 4, 4' -diphenylmethane diisocyanate, continuously stirring at a high speed, raising the temperature to 88 ℃, stirring for reacting for 55min, discharging, sealing and aging for 35 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.9, and crushing to obtain the micronized modified starch for the bioplastic;

step five, mixing the micronized modified starch obtained in the step four, inorganic powder calcium carbonate, dispersant hard amide and PBAT in a high-speed mixer according to the mass ratio of 27:5:0.8:77, and extruding and granulating in a co-rotating double-screw extruder to obtain the modified PBAT fully biodegradable plastic; the length-diameter ratio of the co-rotating twin-screw extruder is 46: 1; the processing temperature is 150 ℃, and the rotating speed of the main machine is 180 rpm.

Comparative example 1

A modified PBAT full-biodegradable plastic and a preparation method thereof comprise the following steps:

uniformly mixing raw starch and stearic acid according to a mass ratio of 100:2, crushing, and refining until the grain size of D90 is less than 5 microns to obtain pretreated refined starch, wherein the rotating speed of a main machine is 1300rpm, the grading rotating speed is 980 rpm;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, stirring at a high speed at 85 ℃ for draining for 40min, adding polycarbonate-1, 6-hexanediol glycol in batches under a high-speed stirring state, discharging after the polycarbonate-1, 6-hexanediol glycol permeates the surface of the pretreated refined starch, cooling to room temperature, sealing, packaging and standing for 36h to ensure that the polycarbonate-1, 6-hexanediol glycol on the surface of the refined starch fully and uniformly permeates the starch; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 15 percent of the mass of the pretreated refined starch; adding 4 batches of polycarbonate-1, 6-hexanediol glycol in the second step according to equal mass;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:5, stirring at a high speed, gradually heating to 50 ℃, and stirring for 25 min; then adding chain extender 1, 4-butanediol, wherein the adding amount of the chain extender is 20% of the mass of 4, 4' -diphenylmethane diisocyanate, continuing to stir at a high speed, raising the temperature to 85 ℃, stirring for reacting for 50min, discharging, sealing and aging for 36 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.8, and crushing to obtain the micronized modified starch for the bioplastic;

step five, mixing the micronized modified starch, the inorganic powder, the dispersing agent and the PBAT obtained in the step four in a high-speed mixer according to the mass ratio of 25:4:0.8:75, and extruding and granulating in a co-rotating double-screw extruder to obtain the modified PBAT fully biodegradable plastic; the inorganic powder is calcium carbonate; the dispersant is a hard amide; the length-diameter ratio of the co-rotating twin-screw extruder is 46: 1; the processing temperature is 150 ℃, and the rotating speed of the main machine is 150-.

Comparative example 1 polycarbonate-1, 6-hexanediol diol was added in an amount of 15% by mass of the pretreated refined starch, compared to example 1.

Comparative example 2

A modified PBAT full-biodegradable plastic and a preparation method thereof comprise the following steps:

uniformly mixing raw starch and stearic acid according to a mass ratio of 100:2, crushing, and refining until the grain size of D90 is less than 5 microns to obtain pretreated refined starch, wherein the rotating speed of a main machine is 1300rpm, the grading rotating speed is 980 rpm;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, carrying out high-speed stirring and water drainage for 40min at 85 ℃, adding polycarbonate-1, 6-hexanediol glycol at one time under a high-speed stirring state, discharging after the polycarbonate-1, 6-hexanediol glycol permeates the surface of the pretreated refined starch, cooling to room temperature, sealing, packaging and standing for 36h to ensure that the polycarbonate-1, 6-hexanediol glycol on the surface of the refined starch fully and uniformly permeates the starch; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 4 percent of the mass of the pretreated refined starch;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:5, stirring at a high speed, gradually heating to 50 ℃, and stirring for 25 min; then adding chain extender 1, 4-butanediol, wherein the adding amount of the chain extender is 20% of the mass of 4, 4' -diphenylmethane diisocyanate, continuing to stir at a high speed, raising the temperature to 85 ℃, stirring for reacting for 50min, discharging, sealing and aging for 36 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.8, and crushing to obtain the micronized modified starch for the bioplastic;

step five, mixing the micronized modified starch, the inorganic powder, the dispersing agent and the PBAT obtained in the step four in a high-speed mixer according to the mass ratio of 25:4:0.8:75, and extruding and granulating in a co-rotating double-screw extruder to obtain the modified PBAT fully biodegradable plastic; the inorganic powder is calcium carbonate; the dispersant is a hard amide; the length-diameter ratio of the co-rotating twin-screw extruder is 46: 1; the processing temperature is 150 ℃, and the rotating speed of the main machine is 150-.

Comparative example 2 polycarbonate-1, 6-hexanediol diol was not added in portions, but in one portion, compared to example 1.

Comparative example 3

A modified PBAT full-biodegradable plastic and a preparation method thereof comprise the following steps:

uniformly mixing raw starch and stearic acid according to a mass ratio of 100:2, crushing, and refining until the grain size of D90 is less than 5 microns to obtain pretreated refined starch, wherein the rotating speed of a main machine is 1300rpm, the grading rotating speed is 980 rpm;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, stirring at a high speed at 85 ℃ for draining water for 40min, adding polycarbonate-1, 6-hexanediol glycol in batches under a high-speed stirring state, discharging after the polycarbonate-1, 6-hexanediol glycol permeates the surface of the pretreated refined starch, cooling to room temperature, sealing, packaging and standing for 2 h; wherein the adding amount of the polycarbonate-1, 6-hexanediol glycol is 4 percent of the mass of the pretreated refined starch; adding 4 batches of polycarbonate-1, 6-hexanediol glycol in the second step according to equal mass;

step three, adding the material obtained in the step two after being placed for 2 hours and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:5, stirring at a high speed, gradually heating to 50 ℃, and stirring for 25 min; then adding chain extender 1, 4-butanediol, wherein the adding amount of the chain extender is 20% of the mass of 4, 4' -diphenylmethane diisocyanate, continuing to stir at a high speed, raising the temperature to 85 ℃, stirring for reacting for 50min, discharging, sealing and aging for 36 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.8, and crushing to obtain the micronized modified starch for the bioplastic;

step five, mixing the micronized modified starch, the inorganic powder, the dispersing agent and the PBAT obtained in the step four in a high-speed mixer according to the mass ratio of 25:4:0.8:75, and extruding and granulating in a co-rotating double-screw extruder to obtain the modified PBAT fully biodegradable plastic; the inorganic powder is calcium carbonate; the dispersant is a hard amide; the length-diameter ratio of the co-rotating twin-screw extruder is 46: 1; the processing temperature is 150 ℃, and the rotating speed of the main machine is 150-.

Comparative example 3 compared with example 1, the refined starch is pretreated by the penetration treatment of the polycarbonate-1, 6-hexanediol glycol, and the starch is placed for more than 24 hours without a sealed package, and is used in the next procedure after being placed for only 2 hours.

Comparative example 4

A modified PBAT full-biodegradable plastic and a preparation method thereof comprise the following steps:

uniformly mixing raw starch and stearic acid according to a mass ratio of 100:2, crushing, and refining until the grain size of D90 is less than 5 microns to obtain pretreated refined starch, wherein the rotating speed of a main machine is 1300rpm, the grading rotating speed is 980 rpm;

step two, adding the pretreated refined starch obtained in the step one into a high-speed mixer, stirring at a high speed at 85 ℃ for 40min, draining, stirring at a high speed, discharging, cooling to room temperature, sealing, packaging and standing for 36 h;

step three, adding the material obtained in the step two and 4, 4' -diphenylmethane diisocyanate into a high-speed mixer according to the mass ratio of 100:5, stirring at a high speed, gradually heating to 50 ℃, and stirring for 25 min; then adding chain extender 1, 4-butanediol, wherein the adding amount of the chain extender is 20% of the mass of 4, 4' -diphenylmethane diisocyanate, continuing to stir at a high speed, raising the temperature to 85 ℃, stirring for reacting for 50min, discharging, sealing and aging for 36 h;

step four, uniformly mixing the aged material obtained in the step three and glyceryl monostearate according to the mass ratio of 100:0.8, and crushing to obtain the micronized modified starch for the bioplastic;

step five, mixing the micronized modified starch, the inorganic powder, the dispersing agent and the PBAT obtained in the step four in a high-speed mixer according to the mass ratio of 25:4:0.8:75, and extruding and granulating in a co-rotating double-screw extruder to obtain the modified PBAT fully biodegradable plastic; the inorganic powder is calcium carbonate; the dispersant is a hard amide; the length-diameter ratio of the co-rotating twin-screw extruder is 46: 1; the processing temperature is 150 ℃, and the rotating speed of the main machine is 150-.

Comparative example 4 No polycarbonate-1, 6-hexanediol diol was added compared to example 1.

The modified PBAT full-biodegradable plastics prepared in examples 1 to 6 and comparative examples 1 to 4 were tested as follows, and the test results are shown in Table 1, and the specific test method is as follows:

1. and (4) testing the storage stability:

blowing the modified PBAT full-biodegradable plastics obtained in the examples 1-6 and the comparative examples 1-4 into a film by a 45-type film blowing machine, and cutting a sample; the extruded pellets were stored for 14 days, blown again, samples were taken, and the blown film crystal point was observed. Testing the mechanical property (the stretching speed is 50 mm/min) by referring to the measurement of the stretching property of the GB/T1040-2018 plastic; as shown in table 1.

Table 1

As can be seen from the data in table 1, the modified PBAT fully biodegradable plastic prepared in examples 1 to 6 has high tensile strength, good film blowing effect, high tensile strength after being placed for 14 days, no difference in film blowing effect, good processability, and significantly improved interface compatibility after being used for PBAT bio-plastic.

As can be seen from the data in table 1, the modified PBAT fully biodegradable plastic prepared in examples 1 to 6 has higher tensile strength, which indicates that after starch micronization treatment, the highly activated starch surface is permeated with polycarbonate-1, 6-hexanediol diol, and 4, 4' -diphenylmethane diisocyanate and a chain extender are further added to carry out chain extension, so that after the modified fine starch tightly coated with a polyurethane layer is formed on the surface of the micronized starch, the tensile strength of the modified plastic can be significantly improved, the processability of the PBAT fully biodegradable plastic is improved, and the application range of the PBAT fully biodegradable plastic product is widened.

Comparative example 1 polycarbonate-1, 6-hexanediol diol was added in an amount of 15% by mass of the pretreated refined starch, compared to example 6. The polycarbonate-1, 6-hexanediol glycol in the comparative example 1 is added in an excessively high amount, so that the excessive polycarbonate-1, 6-hexanediol glycol thoroughly destroys the rigid particles of the starch and easily absorbs water, and therefore the tensile strength is reduced, the blown film is stable and has no crystal point, the film is soft, and the film absorbs water and is sticky after being placed for 1 day; film blowing effect after storage for 14 days after granulation: the blown film is stable and has no crystal point, the film is soft, the film absorbs water and is sticky after being placed for 1 day, and the tensile strength is greatly reduced; it is demonstrated that although the effect of breaking crystallinity is improved by sufficient penetration of the micronized starch, the water absorption of the obtained starch is increased, and the film rigidity is poor, which affects the product performance.

Comparative example 2 polycarbonate-1, 6-hexanediol diol was not added in portions, but in one portion, compared to example 6. Because the polycarbonate-1, 6-hexanediol glycol ester diol is not added in batches and is intensively added to enable local starch to be excessively permeated, limited polycarbonate-1, 6-hexanediol glycol cannot uniformly permeate and process fine starch, the tensile strength and the film forming performance of the fine starch are affected to a certain extent, the tensile strength of the fine starch is reduced to a certain extent, and the film blowing effect is poor; after the film is placed for 14 days, the tensile strength is reduced greatly, crystal points and film breakage appear in the blown film, the film has rigidity, and the film is dry and comfortable after being placed for 1 day. Therefore, the polycarbonate-1, 6-hexanediol glycol is added at one time, so that local starch is excessively permeated by the polycarbonate-1, 6-hexanediol glycol, part of starch is not treated, the treatment uniformity of the starch is influenced, and the agglomeration crystallization is easy to occur.

Comparative example 3 compared with example 6, the polycarbonate-1, 6-hexanediol glycol ester penetration treatment pretreated refined starch is placed for more than 24 hours without a sealed package, and is used in the next procedure after being placed for only 2 hours. Because the polycarbonate-1, 6-hexanediol diol does not well permeate the fine starch, the subsequently obtained polyurethane coating layer has poor bonding tightness with the starch, the function of an interface layer is weakened when the coating layer is used for PBAT, the starch is agglomerated, and the compatibility with the PBAT is poor. Therefore, the modified PBAT full-biodegradable plastic obtained in the comparative example 3 has lower tensile strength and poorer film blowing effect, but the blown film is stable and has no crystal point, the film has rigidity, and the film is dry and comfortable after being placed for 1 day; after the film is placed for 14 days, the tensile strength is reduced greatly, a large number of crystal points and broken films appear in the blown film, the film has rigidity, and the film is dry and comfortable after being placed for 1 day.

Comparative example 4 No polycarbonate-1, 6-hexanediol diol was added compared to example 6. The polycarbonate-1, 6-hexanediol glycol is not added in the comparative example 4, the surface of the highly activated starch is not permeated and coated with the polycarbonate-1, 6-hexanediol glycol, and a tightly coated polyurethane layer cannot be formed subsequently, so that the stretching effect is poor, the blown film is stable and has no crystal point, the film has no rigidity, and the film is dry and comfortable after being placed for 1 day; after the film is placed for 14 days, the tensile strength of the film is reduced greatly, a large number of crystal points and film breakage appear in the blown film, the film has no rigidity, and the film is dry and comfortable after being placed for 1 day.

And observing and analyzing the crystallinity of the fine starch:

observing the crystal cross of the starch granules of the micronized modified starch obtained in the fourth step of the example 1 under a polarization microscope, wherein the cross is a typical starch granule crystal; observing the crystal cross in the initial preparation period and standing for 1 week, wherein a is a polarization microscope image of the initial preparation period, and the starch crystal cross is uniform dispersed particles; b is a polarizing microscope image of 1 week standing, and the crystalline cross is still a uniform dispersed particle.

Observing the crystal cross of the starch granules of the pretreated refined starch obtained in the first step of the example 1 under a polarization microscope, as shown in the attached figure 2, wherein c is a polarization microscope picture of the initial preparation stage, and the crystal cross of the starch is uniform dispersed granules; d is a polarizing microscope picture of the crystal which is placed for 1 week, and the cross-shaped accumulation of the crystal shows that the fine particles are agglomerated.

In conclusion, the invention makes the surface of the starch which is highly activated permeate polycarbonate-1, 6-hexanediol glycol through micronization of the starch, and further adds 4, 4' -diphenylmethane diisocyanate and a chain extender for chain extension, thereby forming the modified fine starch which is tightly coated with a polyurethane layer on the surface of the micronized starch. The interface layer is firmly connected with starch and is not easy to fall off, so that the fine starch keeps rigidity, meanwhile, the fine starch is not agglomerated, particularly, after the micronized modified starch is used for PBAT (poly (butylene adipate-co-terephthalate)) bioplastic, the interface compatibility is obviously improved, the tensile strength of the film is high, and the stability of the film is still good after the film is placed for 14 days. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.