A preparation method of self-reinforced PBAT and its film

Abstract

The present invention discloses a method for preparing self-reinforced PBAT and its film. The method for preparing the self-reinforced PBAT includes the following steps: (1) premixing conventional PBAT particles, crosslinking agent ADR 4468, lubricant, antioxidant, and antiblocking agent in a high-speed mixer, and then extruding and pelletizing in a twin-screw extruder to obtain the PBAT particles to be reinforced; (2) mixing the PBAT particles to be reinforced and conventional PBAT particles evenly and co-extruding and pelletizing in a twin-screw extruder to obtain self-reinforced PBAT particles. The method for preparing the self-reinforced PBAT film provided by the present invention further includes: blowing the self-reinforced PBAT particles to obtain a self-reinforced PBAT film. The method of the present invention is suitable for industrial production, and while improving the mechanical properties of PBAT, it can also maintain its good processing performance.

Description

Technical Field

[0001] The present invention relates to the technical field of biodegradable plastics, and in particular to a self-reinforced PBAT and a method for preparing a film thereof. Background Art

[0002] Biodegradable plastics have attracted widespread attention as alternatives to traditional non-degradable plastics. PBAT (polybutylene terephthalate-adipate) is a 100% biodegradable plastic widely used in film packaging. However, compared to traditional plastics, PBAT is more expensive, has a lower modulus, and exhibits less than ideal mechanical properties. Generally, chain extension can be used to increase PBAT molecular weight, thereby improving the mechanical properties of its films. Patent CN117417507A, for example, discloses a method for increasing PBAT molecular weight through chain extension. However, while higher molecular weight improves mechanical properties, processing performance often deteriorates or even becomes impossible, hindering or even prohibiting industrial production.

[0003] Therefore, it is necessary to develop a method that can improve the mechanical properties of PBAT while maintaining its good processing performance, so as to reduce the difficulty of PBAT film blowing and make it more suitable for industrial production. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing self-reinforced PBAT particles suitable for industrial production, which improves the mechanical properties of PBAT while maintaining good processing performance.

[0005] The second object of the present invention is to provide a method for preparing a self-reinforced PBAT film suitable for industrial production, wherein the prepared PBAT film has good mechanical properties.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a self-reinforced PBAT, comprising the following steps:

[0008] (1) Conventional PBAT particles, crosslinking agent, lubricant, antioxidant, and opening agent are premixed in a high-pressure mixer according to a certain mass ratio, and then extruded and granulated in a twin-screw extruder to obtain the reinforced PBAT particles. The processing temperature range of the twin-screw extruder is 80 o C-145 o C, the mass percentages of the components of the PBAT to be enhanced are: PBAT 95.5-99.6%, cross-linking agent 0.2-3.0%, lubricant 0.1-0.5%, antioxidant 0.1-0.5%, and anti-blocking agent 0.1-0.5%; the cross-linking agent is ADR4468;

[0009] (2) Mix the PBAT particles to be enhanced and the conventional PBAT particles evenly and extrude and pelletize them in a twin-screw extruder to obtain self-reinforced PBAT particles, where the mass percentage of the PBAT particles to be enhanced in the total mass of the PBAT particles to be enhanced and the conventional PBAT particles is 10-40%; the processing temperature range of the twin-screw extruder is 80 o C-185 o C.

[0010] In step (1) of the present invention, the conventional PBAT particles are commercially available PBAT particles without modification treatment. The lubricant can be selected from one or more of PE wax, stearic acid, butyl stearate, monoglyceryl stearate, and oleamide. The antioxidant can be selected from one or more of hindered phenol antioxidants and phosphite antioxidants. The antiblocking agent can be selected from one or more of pentaerythritol stearate and calcined silica.

[0011] In step (1) of the present invention, the mass percentages of the components of the PBAT to be enhanced are preferably: PBAT 98.0-99.4%, crosslinking agent 0.25-1.0%, lubricant 0.1-0.5%, antioxidant 0.1-0.5%, antiblocking agent 0.1-0.5%; further preferably, the mass percentages of the components of the PBAT to be enhanced are: PBAT 98.5-99.0%, crosslinking agent 0.5-0.75%, lubricant 0.1-0.5%, antioxidant 0.1-0.5%, antiblocking agent 0.1-0.5%.

[0012] In step (1) of the present invention, the temperature of the high-speed mixer is from room temperature to 80 o C, the rotation speed is 200-1000 rpm, and the mixing time is 2-10 min.

[0013] In step (1) of the present invention, the twin-screw extruder is a co-rotating parallel twin-screw extruder, the screw diameter is 35-75 mm, the screw length-diameter ratio is greater than 20:1 but not exceeding 56:1, the temperature of the first to tenth sections of the extruder is 80-145 o C, the die head temperature is 110-140 o C, and the screw rotation speed is controlled at 150-300 rpm.

[0014] In step (2) of the present invention, the mass percentage of the PBAT particles to be enhanced in the total mass of the PBAT particles to be enhanced and the conventional PBAT particles is 25-35%.

[0015] In step (2) of the present invention, the twin-screw extruder is a co-rotating parallel twin-screw extruder, the screw diameter is 35-75 mm, the screw length-diameter ratio is greater than 20:1 but not exceeding 56:1, the temperature of the first to tenth sections of the extruder is 80-185o C, the die temperature is 150 - 170 o C, and the screw speed is controlled at 250 - 400 rpm.

[0016] The crosslinking agent ADR used in the present invention, also known as a chain extender, contains several equivalent active epoxy groups in its molecular chain, and can react with the terminal carboxyl groups or even terminal hydroxyl groups of PBAT at a relatively high temperature (greater than 170 o C) to form branching or even crosslinking. In the present invention, conventional PBAT particles, a crosslinking agent (ADR), a lubricant, an antioxidant, and an antiblocking agent are first used to prepare enhanced PBAT particles by a high - speed mixer and a twin - screw extruder. At this extrusion temperature, the epoxy groups of the crosslinking agent have low reaction activity and will only react slightly with the terminal carboxyl groups of PBAT or do not react. Subsequently, the enhanced PBAT particles are melt - blended with more conventional PBAT particles in a twin - screw extruder. The conventional PBAT particles form a continuous phase, while the enhanced PBAT particles are easily sheared by the screw / barrel into a dispersed phase. At the same time, due to the relatively high extrusion temperature, the enhanced PBAT particles react in situ with the crosslinking agent ADR4688 inside them to form a dispersed phase, and the ADR4688 located at the interface forms a co - crosslinking at the dispersed - phase / continuous - phase interface, thereby obtaining self - reinforced PBAT. This self - reinforced PBAT is a special multiphase system, and the physical properties of its matrix phase and reinforcing phase are significantly different but the chemical structures are basically the same. In this way, in the continuous phase of conventional PBAT, crosslinked PBAT forms a dispersed - phase network, improving the overall strength of PBAT, while the continuous phase ensures the overall thermoplasticity and better fluidity, making the processing process easier.

[0017] In the second aspect, the present invention provides a method for preparing a self - reinforced PBAT film, which includes the following steps:

[0018] (1) Premix conventional PBAT particles, a crosslinking agent, a lubricant, an antioxidant, and an antiblocking agent in a high - speed mixer according to a certain mass ratio, and then extrude and pelletize in a twin - screw extruder to obtain enhanced PBAT particles. The processing temperature range of the twin - screw extruder is 80 o C - 145 o C. The mass percentages of the components of the enhanced PBAT are: PBAT 95.5 - 99.6%, crosslinking agent 0.2 - 3.0%, lubricant 0.1 - 0.5%, antioxidant 0.1 - 0.5%, antiblocking agent 0.1 - 0.5%; the crosslinking agent is ADR4468;

[0019] (2) Mix the PBAT particles to be enhanced and the conventional PBAT particles evenly and co-extrude and pelletize them in a twin-screw extruder to obtain self-reinforced PBAT particles, where the mass percentage of the PBAT particles to be enhanced in the total mass of the PBAT particles to be enhanced and the conventional PBAT particles is 10-40 wt%; the processing temperature range of the twin-screw extruder is 80 o C-185 o °C;

[0020] (3) Blow the self-reinforced PBAT particles into a film to obtain a self-reinforced PBAT film.

[0021] The preparation details of the above steps (1) and (2) are the same as those in the first aspect and will not be elaborated here.

[0022] The film blowing in step (3) can be carried out according to the conventional film blowing process. Preferably, the film blowing conditions are: the temperatures of the first to fourth sections of the film blowing extruder are 140-170 o °C, the blow-up ratio (die diameter: bubble diameter) is 1:2-3, and the film blowing draw ratio is 1.2.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] (1) The present invention prepares self-reinforced PBAT by a two-step method, that is, first prepares the PBAT particles to be enhanced at a lower temperature, and then realizes the dynamic cross-linking / branching / tackifying of the dispersed phase through shearing at a higher temperature. The cross-linked / branched / tackified dispersed phase network improves the overall mechanical properties of PBAT, while the continuous phase ensures good processing (film blowing) process performance of PBAT.

[0025] (2) The present invention adopts high mixing, granulation, and film blowing, and the process flow is simple, easy to operate, and suitable for large-scale production.

[0026] (3) The PBAT film prepared by the present invention has good mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. It should be understood that the following drawings only show some embodiments and comparative examples of the present invention, and therefore should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1This is a schematic diagram of the typical experimental process and mechanism for preparing self-reinforced PBAT by the two-step method of the present invention. The self-reinforced PBAT in the example contains a highly branched reinforcing phase and a continuous phase composed of conventional PBAT. The two-phase structure of the self-reinforced PBAT ensures good mechanical properties while also ensuring good processing performance;

[0029] Figure 2 This is a schematic diagram of the typical experimental process and mechanism for preparing self-reinforced PBAT by the homogeneous reaction method of the comparative example of the present invention. What is obtained in the comparative example is uniformly reinforced PBAT;

[0030] Figure 3 This is a graph showing the changes in complex viscosity and storage modulus with angular frequency measured for PBAT samples prepared in some examples and comparative examples in a rotational rheometer;

[0031] Figure 4 This is the microscopic morphology diagram in a scanning electron microscope (SEM) after brittle fracture of the extruded samples in some examples and comparative examples, as well as the modulus distribution diagram in an atomic force microscope (AFM) on the surface of the film in Example 3. Among them, the SEM diagrams are: (a) Comparative Example 4 (control sample without adding ADR), (b) Comparative Example 1, (c) Example 1, (d) Example 2, (e) Example 3; the AFM phase diagram is: (f) Example 3.

[0032] Figure 5 This is the reaction foaming diagram after extrusion using an extruder with a diameter of 48 mm in Comparative Example 2. Detailed implementation manners

[0033] The present invention will be further described below in conjunction with the detailed implementation manners, but the protection scope of the present invention is not limited thereto.

[0034] In the examples of the present invention, those not specified in detail are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained by conventional technical means or through commercial purchase.

[0035] The conventional PBAT particles are TH801T film coating grade PBAT from Xinjiang Tunhe, with a melt flow rate MF of 6.0 g / 10min (190 o °C, 2.16 kg), and the terminal carboxyl group content < 40 mol / ton.

[0036] Example 1

[0037] By mass percentage, the PBAT particles to be reinforced include 99.15% of conventional PBAT particles, 0.25% of crosslinking agent (ADR 4468), 0.1% of lubricant (white oil), 0.1% of antioxidant (bis(4-octylphenyl) diphosphate), 0.2% of antioxidant (tris(2,4-di-tert-butyl)phenyl phosphite), and 0.2% of antiblocking agent (pentaerythritol stearate).

[0038] By mass percentage, the self-reinforced PBAT particles include 70% of conventional PBAT particles and 30% of PBAT particles to be reinforced.

[0039] Preparation of PBAT particles to be reinforced: Weigh the conventional PBAT particles, crosslinking agent (ADR-4468), lubricant (white oil), antioxidants (bis(4-octylphenyl) diphosphate, tris(2,4-di-tert-butyl)phenyl phosphite), and antiblocking agent (pentaerythritol stearate) according to the formula. Directly put all the raw materials into a 50 L high-speed mixer (SHR-50A, Zhangjiagang Pulasman Machinery Manufacturing Co., Ltd.), and blend them at 40 o °C and 500 rpm for 2 min; then add the mixture into a co-rotating parallel twin-screw extruder (φ36, L / D = 36, Nanjing Keya Chemical Complete Equipment Co., Ltd.) for mixing, plasticizing, and extruding. After strand air cooling and pelletizing, the required PBAT particles to be reinforced are obtained; the temperatures of each section of the extruder are as follows: the temperatures of the first to tenth sections are 80, 120, 130, 135, 140, 140, 145, 140, 145, 145 o °C, and the die head temperature is 140 o °C; the rotation speed is 240 rpm.

[0040] Preparation of self-reinforced PBAT particles and film: Weigh the conventional PABT particles and PBAT particles to be reinforced according to the formula and add them into a co-rotating parallel twin-screw extruder (φ36, L / D = 36, Nanjing Keya Chemical Complete Equipment Co., Ltd.) for mixing, plasticizing, and extruding. After strand air cooling and pelletizing, the self-reinforced PBAT particles are obtained; the temperatures of each section of the extruder are as follows: the temperatures of the first to tenth sections are 80, 135, 150, 160, 165, 175, 180, 185, 185, 170 o °C, and the die head temperature is 160 o °C; the rotation speed is 350 rpm. Use a blown film extruder (SJ-50-850, Dalian Longyao Plastic Machinery Co., Ltd.) to directly blow the obtained self-reinforced PBAT particles to obtain a PBAT film. The temperatures of the first to fourth sections of the blown film extruder are 150, 160, 170, 150 °C in sequence, the blow-up ratio (die diameter: bubble diameter) is 1:3, and the blown film draw ratio is 1.2.

[0041] The obtained PBAT film was subjected to tensile property testing in accordance with GB / T 1040.3-2006 to obtain tensile strength data.

[0042] The melt index of the material was tested using a standardized melt flow index tester. The specific method was as follows: The self-reinforced PBAT particle sample was placed in the heating barrel of the tester. At 190 °C, a load of 2.16 kg was applied to melt the material at the specified temperature and pass it through a standard die. The flow rate within 10 minutes was measured. This flow rate was expressed as grams per 10 minutes (g / 10min). The self-reinforced PBAT particles were compression molded (160 o °C, 5 min) into small discs with a thickness of 1 mm, and their viscosity and storage modulus in the range of 1 - 600 rad / s at 180 o °C were measured. The self-reinforced PBAT particle sample was kneaded in a mixing torque rheometer at 160 °C for 10 min, and the torque was obtained after equilibrium.

[0043] Example 2

[0044] Others were the same as in Example 1, but the dosage of the crosslinking agent in the PBAT particles to be reinforced was increased from 0.25% to 0.5%, and the dosage of PBAT was decreased from 99.15% to 98.9%.

[0045] Example 3

[0046] Others were the same as in Example 1, but the dosage of the crosslinking agent in the PBAT particles to be reinforced was increased from 0.25% to 0.75%, and the dosage of PBAT was decreased from 99.15% to 98.65%.

[0047] Example 4

[0048] Others were the same as in Example 1, but the dosage of the crosslinking agent in the PBAT particles to be reinforced was increased from 0.25% to 1.0%, and the dosage of PBAT was decreased from 99.15% to 98.4%.

[0049] Example 5

[0050] The production of self-reinforced PBAT particles was scaled up, and the extruder was replaced with HK-53 from Nanjing Keya Chemical Complete Equipment Co., Ltd., with a screw diameter of 48 mm and a length-diameter ratio of 40:1. Others were the same as in Example 2.

[0051] Control Example 1

[0052] For comparison with Example 3, uniform reaction extrusion granulation was carried out with the same raw material component contents.

[0053] By mass percentage, the enhanced PBAT particles include 99.595% of conventional PBAT particles, 0.225% of crosslinking agent (ADR-4468), 0.03% of lubricant (white oil), 0.03% of antioxidant (bis(4-octylphenyl) diphosphate), 0.06% of antioxidant (tris(2,4-di-tert-butyl)phenyl phosphite), and 0.06% of antiblocking agent (pentaerythritol stearate).

[0054] Preparation of enhanced PBAT particles: Weigh the conventional PABT particles, crosslinking agent, lubricant white oil, antioxidant (bis(4-octylphenyl) diphosphate), antioxidant (tris(2,4-di-tert-butyl)phenyl phosphite), and antiblocking agent (pentaerythritol stearate) according to the above formula. Directly put all the raw materials into a 5 L high-speed mixer (SHR-50A, Zhangjiagang Pulasman Machinery Manufacturing Co., Ltd.), and blend them at 40 o °C and 500 rpm for 2 min; then add the mixture into a co-rotating twin-screw extruder (φ36, L / D = 36, Nanjing Keya Chemical Complete Equipment Co., Ltd.) for premixing by mixing. Obtain the required pellets through strand air cooling and pelletizing; the temperatures of each section of the extruder are as follows: the temperatures of the first to tenth sections are 80, 120, 130, 135, 140, 140, 145, 140, 145, 145 o °C, and the die head temperature is 140 o °C; the rotation speed is 240 rpm. Subsequently, feed the premixed material into the extruder for mixing again to make ADR react with PBAT evenly. The temperatures of each section of the extruder are as follows: the temperatures of the first to tenth sections are 80, 135, 150, 160, 165, 175, 180, 185, 185, 170 o °C, and the die head temperature is 160 o °C; the rotation speed is 350 rpm.

[0055] Preparation of enhanced PBAT film: Use a blown film machine (SJ-50-850, Dalian Longyao Plastic Machinery Co., Ltd.) to directly blow the obtained pellets to obtain a PBAT film. The temperatures of the first to fourth sections of the blown film extruder are 150, 160, 170, 150 °C in sequence, the blow-up ratio (die diameter: film bubble diameter) is 1:3, and the blown film draw ratio is 1.2.

[0056] The performance test methods of the enhanced PBAT particles and films are the same as those in Example 1.

[0057] Comparative Example 2

[0058] Refer to CN 117603481A to prepare a high-starch-content filled PBAT composite film.

[0059] By mass percentage, 97.62% of thermoplastic starch TPS (TPS: grade A302, purchased from Shandong Shouguang Jueneng Jinma Co., Ltd.), 0.2% of peroxide initiator (1,4-bis(tert-butylperoxyisopropyl)benzene, half-life of 1 min at 182 °C), 2% of crosslinking agent (triallyl isocyanurate), 0.03% of lubricant (white oil), 0.03% of antioxidant (bis(4-octylphenyl) diphosphate), 0.06% of antioxidant (tris(2,4-di-tert-butyl)phenyl phosphite), 0.06% of antiblocking agent (pentaerythritol stearate) were mixed in proportion and then put into a 50 L high-speed mixer (SHR-50A, Zhangjiagang Pulasiman Machinery Manufacturing Co., Ltd.). At 60 o °C and a rotation speed of 500 rpm, they were blended for 10 min; then the mixture was added to a co-rotating parallel twin-screw extruder (φ36, L / D = 36, Nanjing Keya Chemical Complete Equipment Co., Ltd.) for mixing, plasticizing and extruding. After being strand-drawn, air-cooled and pelletized, the required pre-crosslinked TPS pellets were obtained; the temperatures of each section of the extruder were as follows: the temperatures of the first to the tenth sections were 80, 85, 90, 100, 110, 120, 110, 100, 95, 90 o °C, and the die head temperature was 100 o °C; the rotation speed was 120 rpm. If an HK-53 extruder with a diameter of 48 mm was used for extrusion in this step, during the extrusion process under the same conditions, due to the strong shear of the screw, the peroxide decomposed, and the surface of the TPS had foamed, and a continuous pre-crosslinked TPS spline could not be produced ( Figure 5 ).

[0060] The pre-crosslinked TPS and conventional PBAT particles were added to a co-rotating parallel twin-screw extruder (φ36, L / D = 36, Nanjing Keya Chemical Complete Equipment Co., Ltd.) according to a mass ratio of 3:7 for mixing, plasticizing and extruding. After being strand-drawn, air-cooled and pelletized, PBAT / TPS composite particles were obtained; the temperatures of each section of the extruder were as follows: the temperatures of the first to the tenth sections were 150, 155, 160, 160, 170, 180, 170, 160, 155, 150 o °C, and the die head temperature was 150 o °C; the rotation speed was 120 rpm. The obtained pellets were directly blown using a blown film extruder (SJ-50-850, Dalian Longyao Plastic Machinery Co., Ltd.) to obtain a PBAT / TPS composite film. The temperatures of the first to the fourth sections of the blown film extruder were 150, 160, 170, 150 °C in sequence, the blow-up ratio (die diameter: bubble diameter) was 1:3, and the blown film draw ratio was 1.2.

[0061] The performance test methods of the PBAT / TPS composite particles and the composite film were the same as those in Example 1.

[0062] Comparative Example 3

[0063] Referring to CN 117603481A, peroxide-initiated crosslinking of PBAT was carried out, and self-reinforced PBAT particles and films were prepared by a two-step method.

[0064] Other conditions were the same as in Comparative Example 2, except that the ratio of the PBAT particles to be reinforced was: conventional PBAT particles 97.2%, peroxide initiator (1,4-bis(tert-butylperoxy)cumene, half-life of 1 min at 182 °C) 0.2%, crosslinking agent (triallyl isocyanurate) 2%, lubricant (white oil) 0.1%, antioxidant (bis(4-octylphenyl) diphosphate) 0.1%, antioxidant (tris(2,4-di-tert-butyl)phenyl phosphite) 0.2%, antiblocking agent (pentaerythritol stearate) 0.2%.

[0065] Comparative Example 4

[0066] Other conditions were the same as in Example 1, but the crosslinking agent ADR was not added, and the PBAT content in the PBAT particles to be reinforced was increased to 99.4% to obtain PBAT particles and films.

[0067] Table 1 below shows the performance data of the PBAT films and particles prepared in each example and comparative example:

[0068] Table 1

[0069]

[0070] The tensile strength reflects the mechanical properties of the PBAT film. The melt index can reflect the fluidity during the processing, and the same applies to the torque. Torque refers to the torsional moment required during the processing. The greater the processing torque, the greater the resistance the polymer material encounters during the processing, and the more difficult the processing becomes. As can be seen from Table 1, the PBAT prepared in Comparative Example 4 has good processing performance, but the tensile strength needs to be improved. For the PBAT / TPS composite particles obtained in Comparative Example 2, although the introduction of TPS can reduce the cost of PBAT particles, compared with Comparative Example 4, the mechanical properties are reduced, and the processing performance is significantly reduced. This is because compared with the branching reaction of ADR, the crosslinking network formed by peroxide initiators and crosslinking agents is more dense and intense, which reduces the molecular chain movement ability of PBAT and is not conducive to processing and forming. Moreover, due to the easy decomposition of peroxide initiators, they cannot be used in extruders with large screw diameters, so they are not suitable for industrial large-scale production. Comparative Example 3 refers to Comparative Example 2 and uses peroxide to crosslink PBAT to prepare self-reinforced PBAT particles by a two-step method. Compared with Comparative Example 4, the mechanical properties of PBAT are improved, but similar to Comparative Example 2, the melt index of the self-reinforced PBAT particles is greatly reduced, which is not conducive to processing and forming. Moreover, due to the use of peroxide initiators, there are also problems that are not suitable for industrial large-scale production. Comparative Example 1 selects a relatively mild ADR and uses a homogeneous reaction method to react with PBAT for enhancement. During this reaction process, ADR is used as a chain extender. Therefore, after addition, the mechanical properties will be improved, but the processing performance will also deteriorate. Adding too much chain extender will make its blown film process performance deteriorate (even unable to blow film), and the film quality will also deteriorate, and crystal points are likely to occur, affecting the product appearance. The experimental results also show that compared with Comparative Example 4, the mechanical properties of the enhanced PBAT prepared in Comparative Example 1 are improved, but the melt index of the enhanced PBAT particles decreases, and the torque also increases, and the processing performance deteriorates. In Examples 1-4 of the present invention, self-reinforced particles and films are prepared by a two-step method. Compared with Comparative Example 4, the mechanical properties are significantly improved. The melt index of the prepared self-reinforced PBAT particles only decreases slightly, and the torque only increases slightly, indicating that it maintains the good processing performance of this conventional PBAT; compared with Comparative Example 1, the mechanical properties of PBAT in Example 3 are further improved. Unexpectedly, the processing performance of the self-reinforced PBAT particles obtained by the two-step method is much better than that of the enhanced PBAT particles obtained by the homogeneous reaction method. When using large-scale equipment for production, the self-reinforced PBAT of the present invention (Example 5) also has good mechanical properties and processing performance, indicating that the method of the present invention is suitable for large-scale production.

[0071] Figure 3Shows the graphs of the complex viscosity and storage modulus of PBAT samples obtained from some examples and control examples varying with the angular frequency in a rotational rheometer. The complex viscosity refers to the difficulty of deformation of the material under shear stress and is related to the rheological stress. The greater the rheological stress, the greater the complex viscosity of the polymer material. The storage modulus is the ability to store energy. The greater the storage modulus, the stronger the elastic behavior of the material. However, if it is too high, flow defects are likely to occur during processing, such as melt fracture and die swell. Therefore, it is not suitable for processing and forming such as blown film if it is too high. From Figure 3 It can be seen that for the PBAT samples prepared in Examples 1-3 of the present invention, with the increase in the content of ADR, PBAT has a higher complex viscosity. This is because the branched structure increases the entanglement of macromolecules, thereby increasing the complex viscosity. In addition, the viscosity of the sample obtained in Example 3 is lower than that of the sample in Control Example 1. This may be attributed to the shear and branching reactions that occur simultaneously in the second step of the two-step process, resulting in the formation of a heterogeneous structure. In this structure, highly branched PBAT regions coexist with low-branched or even unbranched PBAT regions, and the latter act as the continuous phase, giving the composite a lower complex viscosity to ensure better fluidity. This also shows that the self-reinforced PBAT enhanced by this method is more easily processed and formed. Using peroxide to initiate cross-linking of PBAT in Control Example 3 will significantly increase its complex viscosity and storage modulus, and the melt index will also decrease. This is because compared with the branching reaction of ADR, the cross-linking network formed by peroxide initiators and cross-linking agents is more dense and strong, which makes the molecular chain movement ability of PBAT decline and is not conducive to processing and forming.

[0072] From Figure 4 it can be seen that for the self-reinforced PBAT prepared by the two-step method in Examples ( Figure 4 (c), (d), (e)), the samples show obvious surface fluctuations, evolving from initial small protrusions to a sea-island structure with subsequent continuous lamellar structures, while the samples in Control Example 1 ( Figure 4 (b)) do not have obvious surface undulations. In the phase distribution observed by AFM in Figure 4 (f), it can be clearly seen that there is a bicontinuous phase structure in the sample of Example 3. Generally speaking, these observation results confirm the existence of reinforcing phases, which are responsible for enhancing the performance, while the pure PBAT continuous phase maintains fluidity and good processing performance in the self-reinforced PBAT.

Claims

1. A preparation method of self-reinforced PBAT, characterized in that: The preparation method includes the following steps: (1) Premix conventional PBAT particles, crosslinking agent, lubricant, antioxidant, and antiblocking agent in a high-speed mixer according to a certain mass ratio, and then extrude and pelletize in a twin-screw extruder to obtain PBAT particles to be reinforced. The processing temperature range of the twin-screw extruder is 80 o C-145 o °C. The mass percentages of the components of the PBAT to be reinforced are as follows: PBAT 95.5 - 99.6%, crosslinking agent 0.2 - 3.0%, lubricant 0.1 - 0.5%, antioxidant 0.1 - 0.5%, antiblocking agent 0.1 - 0.5%. The sum of the mass percentages of the above components is 100%. The crosslinking agent used is ADR 4468; (2) Mix the PBAT particles to be enhanced and the conventional PBAT particles and extrude and pelletize them in a twin-screw extruder to obtain self-reinforced PBAT particles, where the percentage of the mass of the PBAT particles to be enhanced in the total mass of the PBAT particles to be enhanced and the conventional PBAT particles is 10-40%; the temperature of the first to tenth sections of the twin-screw extruder is 80-185 o °C, and the die temperature is 150-170 o °C.

2. The preparation method according to claim 1, characterized in that: The mass percentages of the components of the PBAT to be reinforced are as follows: PBAT 98.0 - 99.4%, crosslinking agent 0.25 - 1.0%, lubricant 0.1 - 0.5%, antioxidant 0.1 - 0.5%, and antiblocking agent 0.1 - 0.5%.

3. The preparation method according to claim 1, characterized in that: The mass percentages of the components of the PBAT to be reinforced are as follows: PBAT 98.5 - 99.0%, crosslinking agent 0.5 - 0.75%, lubricant 0.1 - 0.5%, antioxidant 0.1 - 0.5%, and antiblocking agent 0.1 - 0.5%.

4. The preparation method according to claim 1, characterized in that: In step (1), the lubricant is selected from one or more of PE wax, stearic acid, butyl stearate, monoglyceryl stearate, and oleamide; the antioxidant is selected from one or more of hindered phenol antioxidants and phosphite antioxidants; the antiblocking agent is selected from one or more of pentaerythritol stearate and calcined silica.

5. The preparation method according to claim 1, characterized in that: In step (1), the twin-screw extruder is a co-rotating parallel twin-screw extruder, with a screw diameter of 35 - 75 mm, a screw length-diameter ratio greater than 20:1 but not exceeding 56:

1. The temperature of the first to tenth sections of the extruder is 80 - 145 o °C, and the die head temperature is 110 - 140 o °C. The screw rotation speed is controlled at 150 - 300 rpm; In step (2), the twin-screw extruder is a co-rotating parallel twin-screw extruder, the screw diameter is 35 - 75 mm, the screw length-diameter ratio is greater than 20:1 but not exceeding 56:1, and the screw rotation speed is controlled at 250 - 400 rpm.

6. A preparation method of a self-reinforced PBAT film, which includes the following steps: (1) Premix conventional PBAT particles, crosslinking agent, lubricant, antioxidant, and antiblocking agent in a high-speed mixer according to a certain mass ratio, and then extrude and pelletize in a twin-screw extruder to obtain PBAT particles to be reinforced. The processing temperature range of the twin-screw extruder is 80 o C-145 o °C. The mass percentages of the components of the PBAT to be reinforced are as follows: PBAT 95.5 - 99.6%, crosslinking agent 0.2 - 3.0%, lubricant 0.1 - 0.5%, antioxidant 0.1 - 0.5%, antiblocking agent 0.1 - 0.5%. The sum of the mass percentages of the above components is 100%; the crosslinking agent is ADR 4468; (2) Mix the PBAT particles to be enhanced and the conventional PBAT particles and extrude and pelletize them in a twin-screw extruder to obtain self-reinforced PBAT particles, where the percentage of the mass of the PBAT particles to be enhanced in the total mass of the PBAT particles to be enhanced and the conventional PBAT particles is 10-40 wt%; the temperature of the first to tenth sections of the twin-screw extruder is 80-185 o °C, and the die head temperature is 150-170 o °C; (3) Blow-mold the self-reinforced PBAT particles to obtain a self-reinforced PBAT film.

7. The preparation method according to claim 6, characterized in that: The mass percentages of the components of the PBAT to be reinforced are as follows: PBAT 98.0 - 99.4%, crosslinking agent 0.25 - 1.0%, lubricant 0.1 - 0.5%, antioxidant 0.1 - 0.5%, and antiblocking agent 0.1 - 0.5%.

8. The preparation method according to claim 6, characterized in that: The mass percentages of the components of the PBAT to be reinforced are as follows: PBAT 98.5 - 99.0%, crosslinking agent 0.5 - 0.75%, lubricant 0.1 - 0.5%, antioxidant 0.1 - 0.5%, and antiblocking agent 0.1 - 0.5%.

9. The preparation method according to claim 6, characterized in that: In step (1), the lubricant is selected from one or more of PE wax, stearic acid, butyl stearate, monoglyceryl stearate, and oleamide; the antioxidant is selected from one or more of hindered phenol antioxidants and phosphite antioxidants; the antiblocking agent is selected from one or more of pentaerythritol stearate and calcined silica.

10. The preparation method according to claim 6, characterized in that: In step (1), the twin-screw extruder is a co-rotating parallel twin-screw extruder, with a screw diameter of 35 - 75 mm, a screw length-to-diameter ratio greater than 20:1 but not exceeding 56:

1. The temperature of the first to tenth sections of the extruder is 80 - 145 o °C, and the die head temperature is 110 - 140 o °C. The screw speed is controlled at 150 - 300 rpm; In step (2), the twin-screw extruder is a co-rotating parallel twin-screw extruder, the screw diameter is 35 - 75 mm, the screw length-diameter ratio is greater than 20:1 but not exceeding 56:1, and the screw rotation speed is controlled at 250 - 400 rpm.

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