A dual-fiber network reinforced biodegradable PBAT-based composite material and a preparation method thereof

Abstract

The present application relates to the field of high polymer composite material, and particularly relates to a kind of double-fiber network reinforced biodegradable PBAT-based composite material and preparation method thereof.The present application is based on "melt blending-drum high-speed hot stretching" in-situ fiber forming process, and a kind of PBAT-based composite material is prepared, which takes PBAT as matrix phase, takes polylactic acid as dispersed phase and takes carboxylated modified cellulose nanofiber as reinforcing filler, the material is internally formed by the fiber network structure of carboxylated modified cellulose nanofiber and microfibrillated polylactic acid and the fiber network structure of carboxylated modified cellulose nanofiber itself, and the double-fiber network structure is jointly constructed, so as to synergistically enhance the mechanical properties of PBAT-based composite material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high polymer composite materials, in particular to a double-fiber network reinforced biodegradable PBAT-based composite material and a preparation method thereof. BACKGROUND

[0002] High polymer foam materials are widely used in the fields of automobiles, buildings, packaging, fast-moving consumer goods, etc. due to their light weight, high specific strength, heat insulation, shock absorption and other advantages. Common traditional high polymer foam materials mainly include polystyrene foam, polyethylene foam, polyurethane foam, phenolic resin foam, etc. These materials are difficult to degrade and are discarded after use, causing "white pollution". At the same time, alkane blowing agents, which are harmful to the environment and flammable and explosive, are often used in the preparation of the above-mentioned materials, which seriously affects the construction of China's ecological civilization and high-quality development. The concepts of green low-carbon, environmental protection and sustainable development have become the new development direction of high polymer foam. Developing biodegradable high polymer foam materials is one of the good solutions to the environmental problems caused by the materials.

[0003] Polybutylene adipate terephthalate (PBAT) is one of the best biodegradable materials in the market. As an aliphatic-aromatic copolymer, PBAT contains multiple ester bonds between its molecular backbone structural units, which can be easily degraded by microorganisms in nature. At the same time, the presence of flexible aliphatic chain segments and benzene rings in the molecular chain makes it have good ductility and thermal stability. Compared with amorphous polymers, PBAT is a semi-crystalline polymer with linear molecular chain structure, low molecular weight and low molecular chain entanglement, resulting in low melt strength and poor foaming performance. In addition, the condensed state structure of PBAT and its evolution rule are complex, and it is difficult to regulate the performance by microstructure. These reasons have greatly limited its application.

[0004] To solve the above technical problems in the application of PBAT, the existing technology often improves the performance of PBAT materials through polymerization reaction, chemical modification, physical blending modification, fiber reinforcement modification and inorganic nano-filler modification, etc. However, the existing modification methods generally have the disadvantages of contradiction between process complexity and modification effect, uneven dispersion of the third item, deterioration of PBAT's recyclability and degradability, etc. SUMMARY

[0005] To solve the problems in the prior art, the application prepares a PBAT-based composite material based on a PBAT matrix phase, a polylactic acid (PLA) dispersed phase and carboxyl-modified cellulose nanofiber (CNF) as a reinforcing filler based on a "melt blending-drum high-speed thermal stretching" in-situ fiber forming process, the material has a double-fiber network structure formed by a fiber network structure of the PLA and the carboxyl-modified CNF and a fiber network structure of the carboxyl-modified CNF itself, and the double-fiber network structure can synergistically enhance the mechanical properties of the PBAT-based composite material.

[0006] To achieve the above object, the technical scheme adopted by the application is as follows:

[0007] The application provides a preparation method of a double-fiber network enhanced biodegradable PBAT-based composite material, comprising the following steps:

[0008] S1: melt blending PBAT, PLA and carboxyl-modified CNF to obtain a PBAT / PLA / modified CNF mixture;

[0009] S2: performing thermal stretching on the PBAT / PLA / modified CNF mixture, and obtaining the PBAT / PLA / modified CNF composite material, i.e., the double-fiber network enhanced biodegradable PBAT-based composite material, after molding treatment.

[0010] Preferably, the preparation method of the double-fiber network enhanced biodegradable PBAT-based composite material comprises the following steps:

[0011] S1: taking PLA and carboxyl-modified CNF as raw materials, first preparing a PLA / modified CNF composite material by a solution casting method or a melt blending method, and then melt blending PBAT with the PLA / modified CNF composite material to obtain a PBAT / PLA / modified CNF mixture;

[0012] S2: performing thermal stretching on the PBAT / PLA / modified CNF mixture, and obtaining the double-fiber network enhanced biodegradable PBAT-based composite material after molding treatment.

[0013] More preferably, the step of preparing the PLA / modified CNF composite material by the solution casting method comprises the following steps: uniformly dispersing PLA in a N,N-dimethylformamide solution to obtain a PLA solution; mixing the PLA solution with carboxyl-modified CNF in the form of a suspension to obtain a PLA / modified CNF mixed solution; and pouring the PLA / modified CNF mixed solution into a mold and drying to obtain the PLA / modified CNF composite material.

[0014] More preferably, the mass fraction of PLA in the PLA solution is 8% to 12%.

[0015] More preferably, the drying temperature is 60℃, and the drying time is 24 h.

[0016] More preferably, the step of preparing the PLA / modified CNF composite material by melt blending comprises melt blending PLA particles and powdered carboxyl-modified CNF to prepare the PLA / modified CNF composite material.

[0017] More preferably, the melt blending is performed in a twin-screw extruder; the extrusion temperature of the twin-screw extruder is 180℃ to 200℃, and the screw rotation speed is 40 r / min to 80 r / min.

[0018] Preferably, the carboxyl-modified CNF has a diameter of 4 to 10 nm and a length of 0.2 μm to 3 μm.

[0019] The second aspect of the present application provides a double-fiber network reinforced biodegradable PBAT-based composite material prepared by the preparation method according to the first aspect.

[0020] Preferably, the double-fiber network reinforced biodegradable PBAT-based composite material has a double-fiber network structure inside; the double-fiber network structure is constructed by a fiber network structure formed by the carboxyl-modified CNF and the microfibrillated PLA and a fiber network structure formed by the carboxyl-modified CNF itself.

[0021] Preferably, the mass fraction of PLA in the double-fiber network reinforced biodegradable PBAT-based composite material is 10% to 30%, and the mass fraction of the modified CNF is 1% to 3%.

[0022] Preferably, the diameter of the fibers in the double-fiber network structure is 500 nm to 900 nm.

[0023] The present application has the following beneficial effects:

[0024] (1) In the traditional in-situ fiber forming process, the incompatibility between the matrix phase and the dispersed phase reduces the interaction force between the components, reduces the mutual penetration and molecular chain entanglement of the phase interface, which is beneficial to the sliding, orientation and fiber formation of the dispersed phase in the matrix phase. However, the weak interface effect caused by incompatibility will cause stress concentration and peeling at the interface between the microfiber and the matrix, which seriously affects the mechanical properties of the composite material. Therefore, the requirements of microfiber and interface combination for component compatibility are contradictory, and a third component is needed to regulate the interface. CNF is a safe and non-toxic, widely available natural polymer material, which has a large aspect ratio and specific surface area, a high Young's modulus and a high tensile stress. The presence of a large number of hydroxyl groups on the surface of CNF makes it have high surface activity, and the surface hydrophobicity can be enhanced by chemical modification, and the dispersion of CNF in the polymer matrix can be improved. Uniformly dispersed CNF will form a network structure to enhance the matrix.

[0025] In the present application, a certain amount of carboxyl-modified CNF is added when preparing the PBAT-based composite material. On the one hand, the modified CNF will be uniformly attached to the interface between the PBAT matrix phase and the PLA dispersed phase, which is beneficial to the in-situ fiber forming process of PLA microfiber; on the other hand, in the PBAT collective phase, the modified CNF itself will form a three-dimensional fiber network through hydrogen bond interaction. The three-dimensional fiber network formed by the modified CNF itself together with the microfiberized PLA forms a double-fiber network structure in the PBAT matrix phase, which plays a mechanical enhancement effect. At the same time, the double-fiber network structure can also act as a heterogeneous nucleation point in the PBAT crystallization process, accelerating the crystallization nucleation rate, and inducing PBAT molecular chains to crystallize along the fiber orientation direction during the processing process to form transcrystals, thereby synergistically improving the mechanical strength.

[0026] (2) The elastic modulus and yield strength of the double-fiber network reinforced biodegradable PBAT-based composite material provided by the present application are significantly improved, which are 3-4 times and 3-4 times of those of pure PBAT material, respectively, and are 3-4 times and 1.5-2 times of those of PBAT / PLA composite material, respectively. At the same time, due to the effect of strain hardening, the double-fiber network reinforced biodegradable PBAT-based composite material provided by the present application still has high tensile strength and high elongation at break. The addition of carboxyl-modified CNF significantly improves the tensile properties of the PBAT-based composite material of the present application.

[0027] (3) The preparation process of the double-fiber network reinforced biodegradable PBAT-based composite material provided by the present application is simple, which can effectively improve the processing performance and mechanical properties of the PBAT-based composite material under the premise of complete biodegradability, non-toxicity and non-pollution. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The microstructure of the composite material in Comparative Example 1;

[0029] Figure 2 Microstructure of the fiber network structure after etching in Example 2;

[0030] Figure 3 Microstructure of the fiber network structure after etching in Example 4;

[0031] Figure 4 Microstructure of the fiber network structure after etching in Example 5;

[0032] Figure 5 Tensile stress test results of the PBAT-based composite material in Example 4. DETAILED DESCRIPTION

[0033] The application will be further described in detail below in combination with specific examples, but the application is not limited to the following specific examples.

[0034] Part of the raw materials in the embodiments of the application are purchased from the following sources:

[0035] Polylactic acid (PLA) is purchased from NatureWorks (4032D); carboxyl-modified cellulose nanofiber (CNF) in the form of suspension is purchased from Guilin Qihong Technology Co., Ltd., with a mass fraction of 1.0%, a diameter of 4-10 nm and a length of 1-3 μm; the carboxyl-modified CNF in powder form is purchased from Macklin, with a diameter of 4-10 nm and a length of 0.2 μm; and the PBAT particles are purchased from China Xinjiang Lanshan Tunhe Polyester Co., Ltd. (TH801T).

[0036] Example 1: Biodegradable PBAT-based composite material and preparation method thereof

[0037] A biodegradable PBAT-based composite material and a preparation method thereof, the preparation method comprising the following steps:

[0038] S1: dissolving PLA in a N,N-dimethylformamide solution to obtain a PLA solution with a mass fraction of 10%;

[0039] S2: mixing the PLA solution with carboxyl-modified CNF in the form of suspension, stirring with a magnetic stirrer for 48 h to make the solution fully mixed; using an ultrasonic cleaner to make the carboxyl-modified CNF fully dispersed to obtain a PLA / modified CNF mixed solution;

[0040] S3: PLA / modified CNF composite material is obtained by using solution casting method, specifically, the PLA / modified CNF mixed solution is poured into a mold (a culture dish), and then is placed in a 60℃ vacuum drying oven for 24 hours to remove water, thereby obtaining the PLA / modified CNF composite material;

[0041] S4: The dried PLA / modified CNF composite material is sheared and granulated by using a granulator, thereby obtaining PLA / modified CNF composite material particles;

[0042] S5: The dried PBAT particles and the dried PLA / modified CNF composite material particles are melt-blended by using a double-screw extruder, the screw temperature of the double-screw extruder is set to 190℃, and the screw rotation speed is 70 r / min; then, a high-speed roller (300 r / min) is used to realize an in-situ fiber forming process of "melting-stretching", thereby obtaining filamentous composite material with a diameter of about 300-400 μm, which is dried in a 60℃ vacuum drying oven for 24 hours to remove water;

[0043] S6: The dried filamentous composite material in S5 is hot-pressed by using a vacuum hot press at a temperature of 140℃, thereby obtaining a PBAT / PLA / modified CNF composite material with a double-fiber network structure, i.e., a biodegradable PBAT-based composite material; in the biodegradable PBAT-based composite material, the mass fractions of PLA and modified CNF are 10% and 1%, respectively.

[0044] Example 2: A biodegradable PBAT-based composite material and a preparation method thereof

[0045] A biodegradable PBAT-based composite material, and a preparation method thereof, includes the following steps:

[0046] S1: PLA particles and powdered carboxyl-modified CNF are dried in a 60℃ vacuum drying oven for 24 hours to sufficiently remove water; the dried PLA particles and the modified CNF are melt-blended by using a micro double-screw extruder, thereby obtaining a PLA / modified CNF composite material; the micro double-screw extrusion temperature is 190℃, and the screw rotation speed is 50 r / min;

[0047] S2: The dried PLA / modified CNF composite material is sheared and granulated by using a granulator, thereby obtaining PLA / modified CNF composite material particles;

[0048] S3: The dried PBAT particles and the dried PLA / modified CNF composite particles are melt-blended by a twin-screw extruder, the twin-screw extrusion temperature is set to 190°C, and the screw rotation speed is 70 r / min; then, a "melt-stretching" in-situ fiber forming process is realized by using a high-speed roller (300 r / min) to obtain filamentous composite materials with a diameter of about 300-400 μm, which are dried in a vacuum drying oven at 60°C for 24 h to remove moisture;

[0049] S4: The dried filamentous composite materials in S3 are hot-pressed by a vacuum hot press at a temperature of 140°C to finally obtain a PBAT / PLA / modified CNF composite material with a double-fiber network structure, i.e., a biodegradable PBAT-based composite material; in the biodegradable PBAT-based composite material, the mass fractions of PLA and modified CNF are 20% and 2%, respectively.

[0050] Example 3: A biodegradable PBAT-based composite material and a preparation method thereof

[0051] A biodegradable PBAT-based composite material, and a preparation method thereof, includes the following steps:

[0052] S1: PLA particles and powdered modified CNF are dried in a vacuum drying oven at 60°C for 24 h to fully remove moisture; the dried PLA particles and powdered carboxylated modified CNF are melt-blended by a micro twin-screw extruder to obtain a PLA / modified CNF composite material; the twin-screw extrusion temperature is 190°C, and the screw rotation speed is 50 r / min;

[0053] S2: The dried PLA / modified CNF composite material is sheared and granulated by using a granulator to obtain PLA / modified CNF composite material particles;

[0054] S3: The dried PBAT particles and the dried PLA / modified CNF composite particles are melt-blended by a twin-screw extruder, the twin-screw extrusion temperature is set to 190°C, and the screw rotation speed is 70 r / min; then, a "melt-stretching" in-situ fiber forming process is realized by using a high-speed roller (300 r / min) to obtain filamentous composite materials with a diameter of about 300-400 μm; which are dried in a vacuum drying oven at 60°C for 24 h to remove moisture;

[0055] S4: The filamentous composite material after drying in S3 is hot-pressed by a vacuum hot press, and the hot-pressing temperature is set to 140℃, and finally a PBAT / PLA / modified CNF composite material with a double-fiber network structure, i.e., a biodegradable PBAT-based composite material, is obtained; in the biodegradable PBAT-based composite material, the mass fractions of PLA and modified CNF are 20% and 4%, respectively.

[0056] Example 4: A biodegradable PBAT-based composite material and a preparation method thereof

[0057] The preparation method of the biodegradable PBAT-based composite material described in this example is basically the same as that in Example 2, and the difference lies in that in the biodegradable PBAT-based composite material, the mass fractions of PBAT, PLA and modified CNF are 67%, 30% and 3%, respectively.

[0058] Example 5: A biodegradable PBAT-based composite material and a preparation method thereof

[0059] A biodegradable PBAT-based composite material, and a preparation method thereof, includes the following steps:

[0060] S1: 300 g of PBAT particles, PLA particles and powdered modified CNF after sufficient drying are mixed in a wide-mouth bottle, and mixed on a roller mixer for 24 h to ensure that the three are fully mixed and uniform, to obtain a raw material mixture;

[0061] S2: The raw material mixture is added to a twin-screw extruder for melt blending, and the twin-screw extrusion temperature is set to 190℃, and the screw rotation speed is 70 r / min; then, a high-speed roller (300 r / min) is used to realize an in-situ fiber-forming process of “melt-stretching”, to obtain a filamentous composite material with a diameter of 200-500 μm;

[0062] S3: The filamentous composite material is hot-pressed by a vacuum film press, and the hot-pressing temperature is set to 140℃, and finally a PBAT / PLA / modified CNF composite material with a double-fiber network structure, i.e., a biodegradable PBAT-based composite material, is obtained; in the biodegradable PBAT-based composite material, the mass fractions of PLA and modified CNF are 30% and 3%, respectively;

[0063] Comparative Example 1: A PBAT-based composite material without carboxylated modified CNF in raw materials and a preparation method thereof

[0064] A PBAT-based composite material without carboxylated modified CNF in raw materials, and a preparation method thereof, includes the following steps:

[0065] S1: dry PBAT particles and PLA particles are melt blended by a twin-screw extruder, the temperature of the twin-screw is set to 190°C, and the screw rotation speed is set to 50 r / min, to obtain a PBAT / PLA composite material;

[0066] S2: the PBAT / PLA composite material is sheared and granulated by a granulator to obtain PBAT / PLA composite material particles;

[0067] S3: the PBAT / PLA composite material particles are hot-pressed by a vacuum film press to form a PBAT-based composite material without carboxyl-modified CNF in the raw material, and the hot-pressing temperature is set to 140°C.

[0068] In the present comparative example, the mass of the PBAT particles accounts for 70% of the total mass of the PBAT particles and the PLA particles; and the mass of the PLA particles accounts for 30% of the total mass of the PBAT particles and the PLA particles.

[0069] Comparative Example 2: a pure PBAT material and a preparation method thereof

[0070] A preparation method of a pure PBAT material, comprising the following steps:

[0071] The dry PBAT particles are sheared and granulated by a granulator after melt blending by a twin-screw extruder; and the obtained particles are hot-pressed by a vacuum film press, and the hot-pressing temperature is set to 140°C, to finally obtain a PBAT material. The temperature of the twin-screw extruder is set to 190°C, and the screw rotation speed is set to 50 r / min.

[0072] After the PBAT-based composite material prepared in Comparative Example 1 is brittle fractured at low temperature by liquid nitrogen, an electron microscope photograph is taken of the fracture surface to observe the micro-morphology, and the results are shown in Figure 1

[0073] The biodegradable PBAT-based composite materials prepared in Example 2, Example 4 and Example 5 are immersed in sufficient tetrahydrofuran solution and stirred, so that the PBAT is completely dissolved in the tetrahydrofuran solution without affecting the fiber network structure, and the undissolved flocculent is collected to take an electron microscope photograph to observe the micro-morphology. The scanning electron microscope photographing results of Example 2, Example 4 and Example 5 are shown in Figure 2 、 Figure 3 、 Figure 4

[0074] Figure 1 ​​​It can be seen that the dispersed phase PLA exists in the PBAT matrix in the form of a ball, and due to poor compatibility between the two, there is a clear gap between the two phases, and when subjected to tensile stress, the spherical PLA cannot withstand the axial tensile force, and due to the gap between the interfaces, local cracks will occur during stretching, accelerating the overall fracture

[0075] By Figures 2-4 It can be seen that the undissolved flocculent (i.e. PLA and modified CNF) presents a clear double-fiber network structure, and the fiber diameter is mainly distributed between 500 nm and 900 nm. This is because there are a large number of hydroxyl groups on the surface of CNF, which makes it have high surface activity, and the surface hydrophobicity can be enhanced by chemical modification, and the dispersion of CNF in the polymer matrix can be improved, and the uniformly dispersed CNF will form a network structure to enhance the matrix. On the one hand, the carboxylated modified CNF is uniformly attached to the interface between the PBAT matrix phase and the PLA dispersed phase, which is beneficial to the microfibrillation of PLA during in-situ fiber formation, and on the other hand, in the PBAT matrix, the carboxylated modified CNF will also form a fiber network through hydrogen bonding interaction; the microfibrillated PLA and the fiber network formed by the carboxylated modified CNF together construct a double-fiber network structure in the PBAT matrix. Therefore, the PBAT-based composite material provided by the present application has a double-fiber network structure inside. Under the condition of uniaxial tensile stress, the fibers will be oriented along the stretching direction, which can effectively improve the elastic modulus; in addition, the PLA fibers and the modified CNF have a synergistic effect, which can further increase the tensile stress.

[0076] The materials finally prepared in all examples, Comparative Example 1 and Comparative Example 2 were made into plate-shaped samples with a length x width x height of 100 mm x 100 mm x 2 mm, and a dumbbell-shaped standard sample was cut using a cutter, and a universal tensile testing machine was used to test the tensile mechanical properties, and the test results are shown in Figure 5 and Table 1.

[0077] By Figure 5It can be seen that the pure PBAT material in Comparative Example 1 exhibits typical characteristics of a ductile material, which starts to yield and enters the strain hardening stage when the strain reaches 10%, and finally the tensile stress reaches 29.4 MPa and breaks at around 1500% strain. However, in practical applications, the standard for evaluating the tensile properties of materials has a higher requirement for yield strength. The lower yield strength and elastic modulus of pure PBAT material greatly affect its application range. Compared with Comparative Example 1, after adding 30% PLA to the raw material to modify PBAT in Comparative Example 2, the PBAT-based composite material prepared has a yield and enters the strengthening stage when the strain reaches 25%. The PBAT-based composite material prepared by adding PLA and carboxylated modified CNF to the raw material in Example 4 has a double-fiber network inside, so that the yield strength reaches 17.05 MPa, and the tensile strength increases to 24.28 MPa. The relevant tensile data are shown in Table 1.

[0078]

[0079] As can be seen from Table 1, compared with the PBAT-based composite material without carboxylated modified CNF in the raw material of Comparative Example 1 and the pure PBAT material of Comparative Example 2, the PBAT-based composite material containing a double-fiber network structure in Examples 1-5 has a significantly improved elastic modulus and yield strength, and due to the effect of strain hardening, it still has a higher tensile strength and a higher elongation at break.

Claims

1. A process for the preparation of a biodegradable PBAT-based composite reinforced with double-fiber networks, characterized in that, The method comprises the following steps: The biodegradable PBAT-based composite material is obtained by melt blending PBAT with polylactic acid / modified cellulose nanofiber composite material, hot stretching the composite material into a filamentous composite material with a diameter of 300-400 μm, and hot pressing; the hot stretching is high-speed roller hot stretching, and the roller rotation speed is 300 r / min; the melt blending temperature is 180-200 ℃; the hot pressing temperature is 130-150 ℃; the polylactic acid / modified cellulose nanofiber composite material is prepared by solution casting or melt blending of polylactic acid and carboxyl-modified cellulose nanofiber; The carboxyl-modified cellulose nanofiber is uniformly attached to the interface between the PBAT matrix phase and the polylactic acid dispersed phase, and the polylactic acid is microfibrillated in situ during the fiber formation; in the PBAT matrix phase, the carboxyl-modified cellulose nanofiber itself forms a three-dimensional fiber network through hydrogen bonding interaction; The three-dimensional fiber network formed by the carboxyl-modified cellulose nanofiber itself and the microfibrillated PLA form a double-fiber network structure in the PBAT matrix phase; the double-fiber network structure acts as a heterogeneous nucleation point in the crystallization process of PBAT, accelerates the crystallization nucleation rate, and induces the PBAT molecular chain to crystallize along the fiber orientation direction during the processing process to form transcrystals.

2. The production method according to claim 1, characterized by, The diameter of the modified cellulose nanofiber is 4-10 nm, and the length is 0.2 μm-3 μm.

3. The production method according to claim 2, characterized by, The melt blending method is that polylactic acid particles and powdered modified cellulose nanofiber are melt blended to prepare a polylactic acid / modified cellulose nanofiber composite material; the melt blending temperature is 180-200 ℃.

4. The production method according to claim 1, characterized by, The solution casting method is that a polylactic acid solution is mixed with a modified cellulose nanofiber suspension to disperse the modified cellulose nanofiber in the polylactic acid solution, and a polylactic acid / modified cellulose nanofiber mixed solution is obtained; The polylactic acid / modified cellulose nanofiber mixed solution is poured into a mold, and a polylactic acid / modified cellulose nanofiber composite material is obtained after drying.

5. The biodegradable PBAT-based composite material prepared by the method according to any one of claims 1-4.

6. The PBAT-based composite material according to claim 5, characterized in that, The mass fraction of polylactic acid in the biodegradable PBAT-based composite material is 10%-30%, and the mass fraction of modified cellulose nanofiber is 1%-3%.

7. The PBAT-based composite material according to claim 6, characterized in that, The fiber diameter in the double-fiber network structure is 500 nm-900 nm.

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