CN110903620A - Fully biodegradable serial crystal high-heat-resistance polylactic acid composite material and preparation method thereof - Google Patents
Fully biodegradable serial crystal high-heat-resistance polylactic acid composite material and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the technical field of processing of high polymer materials, and discloses a full-biodegradable serial-crystal high-heat-resistance polylactic acid composite material and a preparation method thereof. The method comprises the following steps: performing multi-flow field cooperative regulation and control on a polymer microstructure molding on the melt blending granules of PLA and PBAT to obtain a crystallized high-heat-resistance polylactic acid composite material; the molding of the microstructure of the polymer by the cooperation of the multi-flow field and the regulation refers to that the melt of PLA and PBAT is subjected to the action of a push-pull and oscillation composite external force field and then is molded in a mold. According to the invention, the PBAT is added into the PLA substrate, and the oscillation push-pull composite flow field is applied at the same time, so that a large amount of interlocked PLA/PBAT nano hybrid crystal clusters are promoted to be formed. The PLA/PBAT composite material has excellent mechanical and heat-resistant properties, and the forming parameters are simple and easy to control, and has obvious advantages compared with the traditional polymer molding technology.
Description
Technical Field
The invention belongs to the technical field of high polymer material processing, and particularly relates to a full-biodegradable serial-crystal high-heat-resistance polylactic acid composite material and a preparation method thereof.
Background
Since the invention of phenolic resin in the beginning of the last century, petroleum-based plastics have replaced a plurality of metal and inorganic products in the past hundred years and become indispensable materials in life. However, as the demand of people for plastic products is getting larger and larger, the problem of environmental pollution caused by plastics is also getting more and more severe. In the present day when petroleum resources are running out and white pollution is getting more and more intense, fully biodegradable renewable biomass polymers gradually come into the field of vision of people. Nowadays, the new generation of bio-based polymer materials is targeting "renewable carbon" to replace "fossil carbon", and gradually advancing towards practical plastics. The biological plastic is an ideal material applied to high-product iteration speed industries such as medical treatment, electronics, aerospace and the like in the future. Polylactic acid (PLA) has become the best petroleum-based plastic alternative to other biomass materials to date at a relatively low cost, with good processability and excellent strength and modulus. But compared with the engineering plastics widely used in the market at present, the PLA has low crystallinity and poor toughness and heat resistance, which seriously restricts the application range of the PLA. Improving the mechanical property and heat resistance of PLA is always a hot problem in the research of bio-based plastics and is also an important prerequisite basis for the engineering application of PLA. To this end, many researchers at home and abroad have proposed various methods to improve the inherent disadvantages of PLA, including the addition of nanofillers to PLA matrices, blending with other polymers, and the like. Bax et al (Benjamin Bax et al, impact and tension properties of PLA/Cordenka and PLA/flax Composites, Composites Science and Technology, 2008681601 1607.) prepared a PLA/Cordenka700 staple fiber composite material and showed a significant increase in impact properties with fiber addition, but did not increase in tensile strength. Burzic et al (Ivana Burzic et al. Impact modification of PLANTING BIODEGRADABLE PHA biopolymers, European Polymer Journal, 2019, 11432-38) added PHA of different molecular weights to PLA and the injection molded samples were annealed at 100 ℃ for 1h, after testing, it was found that the impact properties and elongation at break of the composites were significantly improved, but tensile strength was slightly reduced after adding appropriate amount of PHA and annealing. Although the addition of the second phase material can complement the PLA matrix in some properties to some extent, the overall property improvement effect of PLA is not ideal because different polymers are often poor in compatibility and interface effect.
A key factor contributing to the imbalance in PLA properties is its low crystallinity due to its slow crystallization rate. PLA belongs to a semi-crystalline polymer, and a molecular chain is semi-rigid, so that the crystallization process has larger time and temperature dependence. When the traditional forming method is used for preparing the PLA product, the temperature gradient of cooling in the cooling stage is large, so that the forming process does not have enough time to form perfect crystals. The preparation of PLA samples by dynamic forming methods can overcome this problem to a large extent. Compared with the traditional static injection molding, the dynamic molding method is a research hotspot for preparing high-performance polymer materials at present due to the simple operation and controllable parameters, the polymer condensed structure can be optimized, and the crystallinity of the materials is improved. Li et al (Zhong-Ming Li et al, Strong Shear Flow-drive Simultaneous Formation of Classic Shift-Kebab, Hybrid Shift-Kebab, and Trans lattice variation in Poly (lactic acid)/Natural fiber Biocomposites, ACS stable Chemistry & Engineering, 2013, 1, 12, 1619-. Researches show that under the action of an external force field, the addition of ramie fibers promotes the formation of shish-kebab crystals, so that the crystallinity of the material is increased. The PEG is added into the PLA and is combined with the oscillation shearing injection molding to prepare the PLA/PEG composite material, the PEG flexible chain segment is favorable for the grain growth of the PLA, a more regular and higher-crystallinity crystal string structure is formed in a sample, and the elongation at break of the material is improved.
According to the invention, the PBAT is added into the PLA, so that the material can better absorb and dissipate stress when being subjected to the action of external force, and the impact resistance of the composite material is improved; meanwhile, the PBAT is stretched in the composite shear flow field to form the nano-scale fiber with high length-diameter ratio, so that the PLA can be attached to the fiber crystal to form highly oriented shish-kebab hybrid interlocking crystals, and the heat resistance of the material is improved. Compared with PLA/PEG composite materials and PLA/ramie fiber composite materials, the PLA/PBAT composite materials prepared by the invention have tighter interlocking and crystal stringing structures than the PLA/PEG composite materials and the PLA/ramie fiber composite materials. The structure can effectively form a connecting structure at high temperature so as to resist deformation; meanwhile, due to the introduction of PBAT, the composite material shows more excellent impact resistance. In the case of slightly higher tensile properties than the former two, the impact strength is 1.67 times that of the PLA/PEG composite and 1.81 times that of the PLA/ramie fiber composite.
Disclosure of Invention
Aiming at the defects of the technology, the invention aims to provide a full-biodegradable serial-crystal high-heat-resistance polylactic acid composite material and a preparation method thereof. The invention relates to a method for preparing a crystallized high-heat-resistance PLA/PBAT composite material by utilizing a molding method of a multi-flow field cooperative regulation and control polymer microstructure. The molding forming device for the polymer microstructure by the multi-flow field cooperative regulation and control for preparing the composite material is a circulating oscillation push-pull forming device, namely a dynamic forming device. The device mainly comprises a plunger system, a mould system and a screw system. The plunger and the screw system are respectively positioned at two sides of the mould system, and the two system bottom plates are connected through a rigid connecting rod. When the equipment runs, the mold system is not moved, the screw rod system drives the plunger system to move back and forth, and the melt in the mold is subjected to thrust displacement of the screw rod and the plunger to shear with the cavity. The plunger system outputs high-frequency low-amplitude oscillating force to the melt, and shear stretching of the melt is promoted. According to the invention, the PBAT flexible polymer and the PLA are blended, a push-pull and oscillation composite external force field is introduced in the forming process, the crystallinity of the system is increased, the PBAT is stretched into nano-scale fibers under the action of shearing force, the PLA molecular chain is perpendicular to the fibers to generate oriented platelets, and a hybrid interlocking string crystal superstructure with the PBAT as shish and the PLA platelets as kebab is formed. The structure ensures that the composite material has excellent mechanical property and heat resistance, and greatly widens the application field of PLA-based products.
The technical scheme adopted by the invention is as follows:
a preparation method of a full-biodegradable serial crystal high heat-resistant polylactic acid composite material comprises the following steps: performing multi-flow field cooperative regulation and control on a polymer microstructure molding on the melt blending granules of PLA and PBAT to obtain a crystallized high-heat-resistance polylactic acid composite material; the molding of the microstructure of the polymer by the cooperation of the multi-flow field and the regulation refers to that the melt of PLA and PBAT is subjected to the action of a push-pull and oscillation composite external force field and then is molded in a mold.
The push-pull and oscillation compound external force field is provided by the push-pull and oscillation of the screw rod and the plunger, and the rotation of the screw rod is also included.
The stroke and speed of the push-pull are set to be 45-55 mm and 11-13 mm/s, and the amplitude and frequency of the oscillation are 0.5-0.9 mm and 13-17 Hz respectively. The rotating speed of the screw is 80-140 revolutions per minute.
The temperature of a mold for molding and forming the polymer microstructure is regulated and controlled by the cooperation of the multi-flow field to be 180-200 ℃, and the temperatures of a screw and a plunger are both 180-200 ℃.
When the mass fraction of PBAT in the string crystallization high heat-resistant polylactic acid composite material is 5-25%, and preferably 8-12%, the improvement effect on the PLA performance is optimal.
The PLA granules have a relative molecular mass of 21-23 kg/mol, and a melt flow rate of preferably 7 g/10 min (2.16 kg, 210 ℃); the relative molecular mass of the PBAT is 6-9 million g/mol.
The melt blending particle of PLA and PBAT refers to the melt blending particle obtained by uniformly mixing dry PLA and PBAT resin raw materials, and then carrying out melt blending, extrusion and granulation.
The melt blending is carried out by adopting a double-screw extruder, and the heating temperatures of the conveying section, the melting section and the metering section of the double-screw extruder are 140-175 ℃, 175-190 ℃ and 170-185 ℃ respectively.
Compared with the traditional forming method, under the combined action of the PBAT and the composite force field, the PLA molecular chain takes the extremely fine PBAT fiber as a crystal nucleus to form shish-kebab highly-oriented hybrid crystal string. The formation of more crystals and the establishment of the shish-kebab superstructure improve the mechanical and thermal properties of the material.
In the invention, an oscillating shear flow field and a push-pull shear flow field are continuously applied to the melt in the pressure maintaining stage of the polymer forming process, so that on one hand, the PBAT is promoted to be sheared and stretched into nano-scale long fibers; on the other hand, the orientation arrangement of PLA molecular chains is accelerated by utilizing a flow field, and the stretched PLA molecular chains are induced to adhere to the surface of the PBAT fiber for crystallization, so that oriented PLA/PBAT hybrid crystal clusters with high crystallinity are formed. The crystallization process of PLA is accelerated by adding PBAT, and the fiberized PBAT and an externally added composite flow field show good synergistic effect in promoting the molecular orientation and crystallization of the PLA, so that the target composite material is endowed with high strength, high toughness and high heat resistance.
According to the invention, the PBAT is added into the PLA substrate, and the oscillation push-pull composite flow field is applied at the same time, so that a large amount of interlocked PLA/PBAT nano hybrid crystal clusters are promoted to be formed. The abundant crystal types and the construction of the hierarchical crystal structure improve the mechanical and thermal properties of the material.
Compared with the prior art, the invention has the advantages that:
(1) in the preparation method, the PBAT in the material in a microspherical shape is refined into a nano-scale fiber shape along the flow field direction by the composite flow field, so that the contact area of the two phases is increased, the PBAT can be used as a stress concentration point to dissipate stress under the stress condition, and the impact resistance of the material is improved.
(2) In the preparation method, PLA is attached to PBAT fibers to form shish-kebab crystal clusters under a composite shear flow field generated by external force during molding, so that the crystal structure is optimized, the crystallinity of the material is improved, and the strength and the heat resistance of the material are enhanced.
(3) The PLA and PBAT material used in the invention is thermoplastic biodegradable plastic, has good biodegradability and is one of biodegradable materials widely active in the market. Therefore, the target product has excellent degradation performance and practically conforms to the design concept of the environment-friendly new material.
(4) The mechanical property, the impact resistance and the heat resistance of the sample prepared by the method are greatly improved. The crystallinity of the polymer microstructure molding material is improved by nearly 4 times compared with a PLA sample prepared by a traditional injection molding method by adding 8-12 wt% of PBAT multi-flow field to cooperatively regulate and control, the tensile strength, Young modulus, elongation at break and impact strength of the polymer microstructure molding material are respectively improved by 36.2%, 12.5%, 181.8% and 253.7%, and the Vicat softening temperature is increased to 104.8 ℃ from 59.6 ℃. In conclusion, the PLA/PBAT composite material molded and formed by cooperatively regulating and controlling the polymer microstructure through the multi-flow field has excellent mechanical and heat-resistant properties, is simple and convenient in forming parameters and easy to control, and has obvious advantages compared with the traditional polymer molding and forming technology.
Drawings
FIG. 1 is a scanning electron microscope image of the crystal morphology of the PLA material prepared in example 1;
FIG. 2 is a scanning electron microscope image of the crystal morphology of the PLA/PBAT composite prepared in example 2;
FIG. 3 is a scanning electron microscope image of the crystal morphology of the PLA/PBAT composite prepared in example 3;
FIG. 4 is a scanning electron microscope image of the crystal morphology of the PLA material prepared in comparative example 1;
FIG. 5 is a scanning electron microscope image of the crystal morphology of the PLA/PBAT composite prepared in comparative example 2;
FIG. 6 is a scanning electron microscope image of the crystal morphology of the PLA/PBAT composite prepared in comparative example 3.
Detailed Description
The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited thereto.
Drying the PLA (polylactic acid) and the PBAT (poly adipic acid/butylene terephthalate) for 6-12 hours in a blast oven at 50-80 ℃ to remove water. The PLA pellets in the examples had a relative molecular mass of 22.3 kg/mole and a melt flow rate of 7 g/10 min (2.16 kg, 210 ℃); the relative molecular mass of the PBAT was 7.5 kg/mol.
Example 1(PLA + Multi-flow field synergy)
The preparation method of the fully biodegradable serial crystal high heat-resistant polylactic acid composite material provided by the embodiment comprises the following specific preparation steps:
(1) for comparison, the PLA feedstock was placed in a forced air oven for 10h to remove moisture, with the oven temperature set at 70 ℃; melting and extruding the dried PLA by a double-screw extruder, and then carrying out the steps of traction, cooling, grain cutting and the like to obtain PLA particles; the rotating speed of the screw is 80 revolutions per minute, and the rotating speed of the feeding screw is 8 revolutions per minute; drying the obtained particles in a blast oven at 70 ℃ for 10h for later use;
(2) molding and forming a polymer microstructure through multi-flow field cooperative regulation: and (3) drying the particles obtained in the step (1), and then performing multi-flow-field cooperative regulation and control on a polymer microstructure to mold and form to obtain the PLA material. The temperatures of a die, a plunger and a screw of the polymer microstructure molding equipment are all set to be 180 ℃ by the cooperation of multiple flow fields. In addition, the push-pull stroke and speed of the device are set to be 50 mm/s and 12.5 mm/s, and the vibration amplitude are respectively 0.7 mm and 15 Hz. The rotational speed of the screw was 80 revolutions per minute.
Example 2(PLA + PBAT + Multi-flow field synergy)
The fully biodegradable serial crystal high heat-resistant polylactic acid composite material and the preparation method thereof provided by the embodiment comprise the following specific preparation steps:
(1) preparation of PLA/PBAT premix: placing the PLA and PBAT raw materials in a forced air oven for 10h to remove moisture, wherein the oven temperature was set at 70 ℃; mixing PLA and PBAT raw materials according to a mass fraction ratio of 90: 10 adding the mixture into a high-speed mixer for mechanical mixing; wherein, the high-speed mixer is used for mixing for 30 seconds at the speed of 10000 r/min, the machine is stopped for cooling for 1 minute, and the premixed material is obtained after mixing for 30 seconds;
(2) preparation of PLA/PBAT blend: melting and blending the PLA/PBAT premix by a double-screw extruder, and obtaining PLA/PBAT blend particles after the steps of extrusion, traction, cooling, grain cutting and the like; wherein the rotating speed of the screw is 80 revolutions per minute, and the rotating speed of the feeding screw is 8 revolutions per minute; putting the blend particles into a blast oven to be dried for 10 hours at the temperature of 70 ℃;
(3) molding and forming a polymer microstructure through multi-flow field cooperative regulation: drying the granules obtained in the step (2), and then performing molding forming on a polymer microstructure under the cooperative regulation of multiple flow fields to obtain the PLA/PBAT composite material. The temperatures of a die, a screw and a plunger of the polymer microstructure molding equipment are all set to be 180 ℃ by the cooperation of multiple flow fields. In addition, the push-pull stroke and speed of the device are set to be 50 mm/s and 12.5 mm/s, and the vibration amplitude are respectively 0.7 mm and 15 Hz. The rotating speed of the screw is 80 r/min
Example 3(PLA + PBAT + Multi-flow field synergy)
The fully biodegradable serial crystal high heat-resistant polylactic acid composite material and the preparation method thereof provided by the embodiment comprise the following specific preparation steps:
(1) preparation of PLA/PBAT premix: placing the PLA and PBAT raw materials in a forced air oven for 10h to remove moisture, wherein the oven temperature was set at 70 ℃; mixing PLA and PBAT raw materials in a mass fraction ratio of 80: 20 adding into a high-speed mixer for mechanical mixing; wherein, the high-speed mixer is used for mixing for 30 seconds at the speed of 10000 r/min, the machine is stopped for 1 minute for cooling, and the premixed material is obtained after mixing for 30 seconds;
(2) preparation of PLA/PBAT blend: melting and blending the PLA/PBAT premix by a double-screw extruder, and obtaining PLA/PBAT blend particles after the steps of extrusion, traction, cooling, grain cutting and the like; wherein the rotating speed of the screw is 80 revolutions per minute, and the rotating speed of the feeding screw is 8 revolutions per minute; putting the blend particles into a blast oven to be dried for 10 hours at the temperature of 70 ℃;
(3) molding and forming a polymer microstructure through multi-flow field cooperative regulation: drying the granules obtained in the step (2), and then performing molding forming on a polymer microstructure under the cooperative regulation of multiple flow fields to obtain the PLA/PBAT composite material. The temperatures of a die, a screw and a plunger of the polymer microstructure molding equipment are all set to be 180 ℃ by the cooperation of multiple flow fields. In addition, the push-pull stroke and speed of the device are set to be 50 mm/s and 12.5 mm/s, and the vibration amplitude are respectively 0.7 mm and 15 Hz. The rotational speed of the screw was 80 revolutions per minute.
Comparative example 1
The preparation method of the fully biodegradable serial crystal high heat-resistant polylactic acid composite material comprises the following specific preparation steps:
(1) for comparison, the PLA feedstock was placed in a forced air oven for 10h to remove moisture, with the oven temperature set at 70 ℃; melting and extruding the dried PLA by a double-screw extruder, and then carrying out the steps of traction, cooling, grain cutting and the like to obtain PLA particles; the rotating speed of the screw is 80 revolutions per minute, and the rotating speed of the feeding screw is 8 revolutions per minute; putting the granules into a blast oven to be dried for 10 hours at the temperature of 70 ℃;
(2) traditional injection molding: and (3) carrying out injection molding on the granules obtained in the step (1) by using an injection molding machine, wherein the main molding parameters are as follows: the barrel temperature of the screw was set at 190 ℃ and the die temperature was set at 40 ℃.
Comparative example 2
The preparation method of the fully biodegradable serial crystal high heat-resistant polylactic acid composite material comprises the following specific preparation steps:
(1) preparation of PLA/PBAT premix: placing the PLA and PBAT raw materials in a forced air oven for 10h to remove moisture, wherein the oven temperature was set at 70 ℃; mixing PLA and PBAT raw materials according to a mass fraction ratio of 90: 10 adding the mixture into a high-speed mixer for mechanical mixing; wherein, the high-speed mixer is used for mixing for 30 seconds at the speed of 10000 r/min, the machine is stopped for cooling for 1 minute, and the premixed material is obtained after mixing for 30 seconds;
(2) preparation of PLA/PBAT blend: melting and blending the PLA/PBAT premix by a double-screw extruder, and obtaining PLA/PBAT blend particles after the steps of extrusion, traction, cooling, grain cutting and the like; wherein the rotating speed of the screw is 80 revolutions per minute, and the rotating speed of the feeding screw is 8 revolutions per minute; putting the blend particles into a blast oven to be dried for 10 hours at the temperature of 70 ℃;
(3) traditional injection molding: and (3) carrying out injection molding on the granules obtained in the step (1) by using an injection molding machine, wherein the main molding parameters are as follows: the barrel temperature of the screw was set at 190 ℃ and the die temperature was set at 40 ℃.
Comparative example 3
The preparation method of the fully biodegradable serial crystal high heat-resistant polylactic acid composite material comprises the following specific preparation steps:
(1) preparation of PLA/PBAT premix: placing the PLA and PBAT raw materials in a forced air oven for 10h to remove moisture, wherein the oven temperature was set at 70 ℃; mixing PLA and PBAT raw materials in a mass fraction ratio of 80: 20 adding the mixture into a high-speed mixer for mechanical mixing; wherein, the high-speed mixer is used for mixing for 30 seconds at the speed of 10000 r/min, the machine is stopped for 1 minute for cooling, and the premixed material is obtained after mixing for 30 seconds;
(2) preparation of PLA/PBAT blend: and (3) carrying out melt blending on the PLA/PBAT premix by using a double-screw extruder, and obtaining PLA/PBAT blend particles after the steps of extrusion, traction, cooling, particle cutting and the like. Wherein the rotating speed of the screw is 80 revolutions per minute, and the rotating speed of the feeding screw is 8 revolutions per minute; putting the blend particles into a blast oven to be dried for 10 hours at the temperature of 70 ℃;
(3) traditional injection molding: and (3) carrying out injection molding on the granules obtained in the step (1) by using an injection molding machine, wherein the main molding parameters are as follows: the barrel temperature of the screw was set at 190 ℃ and the die temperature was set at 40 ℃.
The scanning electron microscope images of the crystal structures of the PLA/PBAT composite materials prepared in the above examples 1-3 are shown in FIGS. 1-3, respectively. The scanning electron microscope images of the crystal structures of the PLA/PBAT composite materials prepared in the comparative examples 1-3 are respectively shown in FIGS. 4-6.
FIG. 1 is a scanning electron microscope image of the crystal morphology of the PLA material prepared in example 1; FIG. 2 is a scanning electron microscope image of the crystal morphology of the PLA/PBAT composite prepared in example 2; FIG. 3 is a scanning electron microscope image of the crystal morphology of the PLA/PBAT composite prepared in example 3; FIG. 4 is a scanning electron microscope image of the crystal morphology of the PLA material prepared in comparative example 1; FIG. 5 is a scanning electron microscope image of the crystal morphology of the PLA/PBAT composite prepared in comparative example 2; FIG. 6 is a scanning electron microscope image of the crystal morphology of the PLA/PBAT composite prepared in comparative example 3.
The comparison results of the mechanical properties and Vicat softening temperatures of the composite materials prepared in comparative examples 1-3 and examples 1-3 are shown in Table 1.
Table 1 shows the mechanical properties and Vicat softening temperatures of the composites prepared in examples 1-3 and comparative examples 1-3
Claims (8)
1. A preparation method of a full-biodegradable serial crystal high heat-resistant polylactic acid composite material is characterized by comprising the following steps: the method comprises the following steps: performing multi-flow field cooperative regulation and control on a polymer microstructure molding on the melt blending granules of PLA and PBAT to obtain a crystallized high-heat-resistance polylactic acid composite material; the molding of the microstructure of the polymer by the cooperation of the multi-flow field and the regulation refers to that the melt of PLA and PBAT is subjected to the action of a push-pull and oscillation composite external force field and then is molded in a mold.
2. The preparation method of the fully biodegradable serial crystal high heat-resistant polylactic acid composite material according to claim 1, which is characterized in that: the push-pull and oscillation composite external force field is provided by the push-pull and oscillation of the screw and the plunger;
the stroke and speed of the push-pull are set to be 45-55 mm and 11-13 mm/s, and the amplitude and frequency of the oscillation are 0.5-0.9 mm and 13-17 Hz respectively.
3. The preparation method of the fully biodegradable serial crystal high heat-resistant polylactic acid composite material according to claim 1, which is characterized in that: the temperature of a mold for molding and forming the polymer microstructure is regulated and controlled by the cooperation of the multi-flow field to be 180-200 ℃, and the temperature of a screw and a plunger is 180-200 ℃; the rotating speed of the screw is 80-140 revolutions per minute.
4. The preparation method of the fully biodegradable serial crystal high heat-resistant polylactic acid composite material according to claim 1, which is characterized in that: the mass fraction of PBAT in the serial crystallization high heat-resistant polylactic acid composite material is 5-25%.
5. The preparation method of the fully biodegradable serial crystal high heat-resistant polylactic acid composite material according to claim 4, which is characterized in that: the mass fraction of PBAT in the string crystallization high heat-resistant polylactic acid composite material is 8-12%.
6. The preparation method of the fully biodegradable serial crystal high heat-resistant polylactic acid composite material according to claim 1, which is characterized in that: the relative molecular mass of the PLA granules is 21-23 million grams/mole; the relative molecular mass of the PBAT is 6-9 million g/mol.
7. The preparation method of the fully biodegradable serial crystal high heat-resistant polylactic acid composite material according to claim 1, which is characterized in that: the melt blending particle of PLA and PBAT refers to the melt blending particle obtained by uniformly mixing dry PLA and PBAT resin raw materials, and then carrying out melt blending, extrusion and granulation.
8. A fully biodegradable and cross-crystallized polylactic acid composite material obtained by the preparation method of any one of claims 1 to 7.
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