A preparation method of toughened thermally conductive polylactic acid composite material

Abstract

The present invention discloses a method for preparing a toughened, thermally conductive polylactic acid (PLA) composite material. The method utilizes free radicals generated by an initiator to initiate grafting, dehydration, and crosslinking reactions between polylactic acid and vinylphenylboronic acid. Furthermore, dopamine-coated boron nitride nanosheets are introduced as thermally conductive fillers to produce a PLA composite material containing a borate crosslinked structure. The invention not only significantly improves the toughness of the PLA by introducing borate bonds, but also utilizes the borate bonds and π-π conjugation as a connecting "bridge," reducing the interfacial thermal resistance between the thermally conductive fillers and between the thermally conductive fillers and the PLA matrix. This creates a thermally conductive pathway within the composite matrix, significantly enhancing the thermal conductivity of the composite material.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and particularly relates to a method for preparing a toughened thermally conductive polylactic acid composite material. Background Art

[0002] With the continuous updating and iteration of electronic products, electronic systems and equipment are developing in the direction of integration, miniaturization, high efficiency and reliability. The increase in the integration of electronic systems has led to the dense arrangement of products, and the requirements for the thermal stability and thermal conductivity of electronic packaging materials are becoming increasingly higher. At present, most electronic packaging materials are petroleum-based polymers, and there are varying degrees of environmental pollution in the recycling and comprehensive utilization of electronic waste. Polylactic acid (PLA) is one of the most common bio-based polyesters, with good biocompatibility and mechanical properties, and is biodegradable. However, the shortcomings of PLA, such as high brittleness, low toughness, and low thermal conductivity, limit its application in the electronic packaging industry.

[0003] Methods for toughening PLA can be divided into two main categories: one is to add small molecule plasticizers. Small molecule plasticizers can have a good toughening effect, but the problem of small molecules easily precipitating and migrating can greatly reduce the performance and stability of the material. The other is to blend PLA with high-toughness polymers. On the one hand, the introduction of petroleum-based polymers such as polyethylene makes the material difficult to fully biodegrade. On the other hand, the introduction of blended modified polymers has the problem of poor compatibility between the two phases, which significantly reduces the mechanical properties of PLA. In addition, the crystalline polymer reduces the transparency of the composite material, limiting the further application of PLA.

[0004] The thermal conductivity of polymer materials is relatively low (less than 0.2W / (m·K). In order to improve the thermal conductivity of polylactic acid, functional fillers with high thermal conductivity are usually added to form a thermal conductive path, thereby improving the thermal conductivity of the composite material. However, there are many factors that affect the thermal conductivity of the composite material, such as the filler filling amount, the orientation of the filler in the matrix, and the interface interaction between the polymer matrix and the thermally conductive filler and between the fillers. The existing technology is still not ideal for improving the thermal conductivity of polylactic acid composite materials.

[0005] Therefore, exploring new modification methods for polylactic acid and improving its toughness and thermal conductivity are of great significance for further promoting the application of polylactic acid composite materials in industries such as electronic packaging. Summary of the Invention

[0006] In view of the above problems existing in the prior art, the present invention provides a method for preparing a toughened thermally conductive polylactic acid composite material, aiming to simultaneously improve the toughness and thermal conductivity of polylactic acid.

[0007] To achieve the purpose, the present invention adopts the following technical solutions:

[0008] A method for preparing a toughened and thermally conductive polylactic acid composite material comprises: cross-linking polylactic acid with vinylphenylboronic acid in the presence of an initiator to obtain polylactic acid containing a borate cross-linked structure; dopamine-coated boron nitride nanosheets are then added to the polylactic acid composite material to improve its toughness and thermal conductivity, resulting in a toughened and thermally conductive polylactic acid composite material. The method specifically comprises the following steps:

[0009] Step 1: Place boron nitride, deionized water, and zirconium oxide grinding balls in a reactor and perform ultrasonic treatment for 24 hours. Then, filter through a 200-mesh molecular sieve, centrifuge to obtain a supernatant, filter, and wash with deionized water. The resulting product is dried at 60° C. to obtain exfoliated boron nitride.

[0010] 0.1 mol / L tris(hydroxymethyl)aminomethane) solution and 0.1 mol / L hydrochloric acid standard solution were mixed and diluted in a volume ratio of 40-60 mL:14-15 mL to obtain a Tris-HCl buffer solution with a pH of 8.5. The exfoliated boron nitride was placed in a Tris-HCl buffer solution with a pH of 8.5 and stirred evenly. Dopamine was then added and stirred for 14-16 hours. The resulting product was washed with ethanol, centrifuged, and filtered. The product was then dried at 60°C to obtain dopamine-coated boron nitride nanosheet powder (PDA@BNNS).

[0011] Step 2: dissolving polylactic acid in a first solvent at room temperature, grinding an initiator into powder, and dissolving vinylphenylboric acid in a second solvent; after the polylactic acid is completely dissolved, adding the initiator and the vinylphenylboric acid dissolved in the second solvent, and then adding dopamine-coated boron nitride nanosheets, fully premixing, and then drying in an oven to evaporate the solvent to obtain a premix;

[0012] Step 3: The premix is ​​crushed into powder in a pulverizer, and then added to an internal mixer at a temperature of 190°C and a speed of 50 r / min for internal mixing. Under heating conditions, the free radicals generated by the initiator are used to initiate a grafting reaction between polylactic acid and vinylphenylboronic acid. At the same time, the boric acids undergo dehydration condensation to form borate ester bonds to obtain a toughened thermally conductive polylactic acid composite material.

[0013] Furthermore, the number average molecular weight of the polylactic acid is 100,000-200,000, preferably the polylactic acid is brand PLA (4032D, Nature Works), and the number average molecular weight is 160,000-180,000.

[0014] Furthermore, the initiator includes at least one of an azo initiator (azobisisobutyronitrile, azobisisoheptanenitrile, azoisobutylcyanamide, etc.) and an organic peroxide initiator (dibenzoyl peroxide, dicumyl peroxide, lauroyl peroxide, etc.).

[0015] Furthermore, the vinylbenzene boronic acid is at least one of 2-vinylbenzene boronic acid, 3-vinylbenzene boronic acid and 4-vinylbenzene boronic acid.

[0016] Furthermore, the boron nitride is at least one of hexagonal boron nitride (HBN), rhombohedral boron nitride (RBN), cubic boron nitride (CBN) and wurtzite boron nitride (WBN).

[0017] Furthermore, in step 1, the usage ratio of boron nitride, deionized water and zirconium oxide grinding balls is 1-2 g: 100-1000 mL: 1-2 g, and the mass ratio of the exfoliated boron nitride to dopamine is 0.1-0.3 g: 0.02-0.04 g.

[0018] Furthermore, in step 2, the mass ratio of polylactic acid, initiator, vinylphenylboric acid, dopamine-coated boron nitride nanosheets, first solvent and second solvent is 100:0.1:0.05-0.6:0.5-2.0:0-400:0-20.

[0019] Furthermore, the first solvent and the second solvent are independently selected from at least one of ethanol, toluene, dichloromethane, chloroform, acetone and tetrahydrofuran. The first solvent is preferably dichloromethane, and the second solvent is preferably acetone.

[0020] Furthermore, in step 2, the temperature for evaporating the solvent is preferably 45°C.

[0021] Furthermore, in step 3, the mixing time is 10 minutes.

[0022] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0023] The present invention utilizes free radicals generated by an initiator to initiate grafting, dehydration and cross-linking reactions between polylactic acid and vinylphenylboronic acid, and introduces dopamine-coated boron nitride nanosheets as thermally conductive fillers to obtain a polylactic acid composite material containing a borate cross-linked structure. The present invention not only significantly improves the toughness of polylactic acid based on the introduction of borate bonds, but also solves the problems of high brittleness and low toughness of polylactic acid. In addition, the borate bonds and π-π conjugation act as a connecting "bridge", reducing the interfacial thermal resistance between thermally conductive fillers and between the thermally conductive fillers and the polylactic acid matrix, forming a thermal conductive path in the composite matrix, and greatly improving the thermal conductivity of the composite material. The method of the present invention is simple in process and easy to industrialize, and has broad application prospects in the "green" electronic devices and electronic packaging industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 (a) and (b) are stress-strain curves of samples obtained from various embodiments of the present invention and comparative examples.

[0025] Figure 2 The graph is a data diagram of the impact strength of samples obtained from various embodiments of the present invention and comparative examples.

[0026] Figure 3 (a) and (b) are scanning electron micrographs of the PLA / 0.1% DCP / 0.2% 4-VPBA / 0.5% BNNS sample and the PLA / 0.1% DCP / 0.2% 4-VPBA / 2.0% BNNS sample obtained in the comparative example of the present invention, respectively; Figure 3 (c) and (d) are scanning electron micrographs of the PLA / 0.1% DCP / 0.2% 4-VPBA / 0.5% PDA@BNNS sample and the PLA / 0.1% DCP / 0.2% 4-VPBA / 2.0% PDA@BNNS sample obtained in the examples of the present invention, respectively.

[0027] Figure 4 Graphs showing the vertical thermal conductivity of samples obtained from various embodiments of the present invention and comparative examples.

[0028] Figure 5 Horizontal thermal conductivity diagrams of samples obtained from various embodiments of the present invention and comparative examples. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further described in detail below through specific examples. This example is implemented on the premise of the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following examples.

[0030] Example 1

[0031] Step 1: 1.2gh-BN, 400mL deionized water, and 1.2g zirconium oxide grinding balls were placed in a solvent bottle and ultrasonicated for 24h. The supernatant was then filtered through a 200-mesh molecular sieve and centrifuged to obtain the supernatant. The supernatant was filtered through a 1μm pore size filter and washed with deionized water. The obtained product was dried at 60°C to obtain exfoliated boron nitride BNNS.

[0032] Mix 50 mL of a 0.1 mol / L tris(hydroxymethyl)aminomethane solution with 14.7 mL of a 0.1 mol / L hydrochloric acid standard solution and dilute to 100 mL with distilled water to obtain a Tris-HCl buffer at pH 8.5. Add 0.2 g of BNNS to 20 mL of Tris-HCl buffer at pH 8.5, stir, and then add 30 mg of dopamine. Stir for 15 hours. The resulting product is washed with ethanol, centrifuged, filtered, and dried at 60°C to obtain PDA@BNNS powder.

[0033] Step 2. Dry PLA in a drying oven at 80°C for 12 h; weigh 50 g of PLA and dissolve it in 200 mL of dichloromethane at room temperature. After it is fully dissolved, add powdered diisopropyl peroxide (DCP) (0.05 g) and 4-vinylphenylboronic acid (4-VPBA) (0.10 g) dissolved in 8 mL of acetone, and then add 0.25 g of PDA@BNNS. After it is fully premixed, place the blend in a drying oven at 45°C and dry overnight to evaporate the solvent to obtain a premixed solid premix.

[0034] Step 3: The obtained solid premix was completely crushed in a grinder, and the crushed powder was added to an internal mixer at a speed of 50 r / min and a temperature of 190°C for 10 min to obtain a PDA@BNNS-filled borate cross-linked polylactic acid composite material (denoted as PLA / 0.1% DCP / 0.2% 4-VPBA / 0.5% PDA@BNNS). The tensile and thermal conductivity test results were as follows: elongation at break was 172.6%, and vertical thermal conductivity was 0.456 Wm -1 K -1 , horizontal thermal conductivity is 0.453Wm -1 K -1 .

[0035] Example 2

[0036] Step 1: 1.2gh-BN, 400mL deionized water, and 1.2g zirconium oxide grinding balls were placed in a solvent bottle and ultrasonicated for 24h. The supernatant was then filtered through a 200-mesh molecular sieve and centrifuged to obtain the supernatant. The supernatant was filtered through a 1μm pore size filter and washed with deionized water. The obtained product was dried at 60°C to obtain exfoliated boron nitride BNNS.

[0037] Mix 50 mL of a 0.1 mol / L tris(hydroxymethyl)aminomethane solution with 14.7 mL of a 0.1 mol / L hydrochloric acid standard solution and dilute to 100 mL with distilled water to obtain a Tris-HCl buffer at pH 8.5. Add 0.2 g of BNNS to 20 mL of Tris-HCl buffer at pH 8.5, stir, and then add 30 mg of dopamine. Stir for 15 hours. The resulting product is washed with ethanol, centrifuged, filtered, and dried at 60°C to obtain PDA@BNNS powder.

[0038] Step 2. Dry PLA in a drying oven at 80°C for 12 h; weigh 50 g of PLA and dissolve it in 200 mL of dichloromethane at room temperature. After it is fully dissolved, add powdered DCP (0.05 g) and 4-VPBA (0.10 g) dissolved in 8 mL of acetone, and then add 0.50 g of PDA@BNNS. After it is fully premixed, place the blend in a drying oven at 45°C and dry overnight to evaporate the solvent to obtain a premixed solid premix.

[0039] Step 3: The obtained solid premix was completely crushed in a grinder, and the crushed powder was added to an internal mixer at a speed of 50 r / min and a temperature of 190°C for 10 min to obtain a PDA@BNNS-filled borate cross-linked polylactic acid composite material (denoted as PLA / 0.1% DCP / 0.2% 4-VPBA / 1.0% PDA@BNNS). The tensile and thermal conductivity test results were as follows: elongation at break was 162.9%, and vertical thermal conductivity was 0.484 Wm -1 K -1 , horizontal thermal conductivity is 0.502Wm -1 K -1 .

[0040] Example 3

[0041] Step 1: 1.2gh-BN, 400mL deionized water, and 1.2g zirconium oxide grinding balls were placed in a solvent bottle and ultrasonicated for 24h. The supernatant was then filtered through a 200-mesh molecular sieve and centrifuged to obtain the supernatant. The supernatant was filtered through a 1μm pore size filter and washed with deionized water. The obtained product was dried at 60°C to obtain exfoliated boron nitride BNNS.

[0042] Mix 50 mL of a 0.1 mol / L tris(hydroxymethyl)aminomethane solution with 14.7 mL of a 0.1 mol / L hydrochloric acid standard solution and dilute to 100 mL with distilled water to obtain a Tris-HCl buffer at pH 8.5. Add 0.2 g of BNNS to 20 mL of Tris-HCl buffer at pH 8.5, stir, and then add 30 mg of dopamine. Stir for 15 hours. The resulting product is washed with ethanol, centrifuged, filtered, and dried at 60°C to obtain PDA@BNNS powder.

[0043] Step 2. Dry PLA in a drying oven at 80°C for 12 h; weigh 50 g of PLA and dissolve it in 200 mL of dichloromethane at room temperature. After it is fully dissolved, add powdered DCP (0.05 g) and 4-VPBA (0.10 g) dissolved in 8 mL of acetone, and then add 0.75 g of PDA@BNNS. After it is fully premixed, place the blend in a drying oven at 45°C and dry overnight to evaporate the solvent to obtain a premixed solid premix.

[0044] Step 3: The obtained solid premix was completely crushed in a grinder, and the crushed powder was added to an internal mixer at a speed of 50 r / min and a temperature of 190°C for 10 min to obtain a PDA@BNNS-filled borate cross-linked polylactic acid composite material (denoted as PLA / 0.1% DCP / 0.2% 4-VPBA / 1.5% PDA@BNNS). The tensile and thermal conductivity test results were as follows: elongation at break was 162.7%, and vertical thermal conductivity was 0.497 Wm -1 K -1 , horizontal thermal conductivity is 0.661Wm -1 K -1 .

[0045] Example 4

[0046] Step 1: 1.2gh-BN, 400mL deionized water, and 1.2g zirconium oxide grinding balls were placed in a solvent bottle and ultrasonicated for 24h. The supernatant was then filtered through a 200-mesh molecular sieve and centrifuged to obtain the supernatant. The supernatant was filtered through a 1μm pore size filter and washed with deionized water. The obtained product was dried at 60°C to obtain exfoliated boron nitride BNNS.

[0047] Mix 50 mL of a 0.1 mol / L tris(hydroxymethyl)aminomethane solution with 14.7 mL of a 0.1 mol / L hydrochloric acid standard solution and dilute to 100 mL with distilled water to obtain a Tris-HCl buffer at pH 8.5. Add 0.2 g of BNNS to 20 mL of Tris-HCl buffer at pH 8.5, stir, and then add 30 mg of dopamine. Stir for 15 hours. The resulting product is washed with ethanol, centrifuged, filtered, and dried at 60°C to obtain PDA@BNNS powder.

[0048] Step 2. Dry PLA in a drying oven at 80°C for 12 h; weigh 50 g of PLA and dissolve it in 200 mL of dichloromethane at room temperature. After it is fully dissolved, add powdered DCP (0.05 g) and 4-VPBA (0.10 g) dissolved in 8 mL of acetone, and then add 1.0 g of PDA@BNNS. After it is fully premixed, place the blend in a drying oven at 45°C and dry overnight to evaporate the solvent to obtain a premixed solid premix.

[0049] Step 3: The obtained solid premix was completely crushed in a grinder, and the crushed powder was added to an internal mixer at a speed of 50 r / min and a temperature of 190°C for 10 min to obtain a PDA@BNNS-filled borate cross-linked polylactic acid composite material (denoted as PLA / 0.1% DCP / 0.2% 4-VPBA / 2.0% PDA@BNNS). The tensile and thermal conductivity test results were as follows: elongation at break was 129.4%, and vertical thermal conductivity was 0.597 Wm -1 K -1 , horizontal thermal conductivity is 0.779Wm -1 K -1 .

[0050] Comparative Example 1

[0051] Step 1: 1.2gh-BN, 400mL deionized water, and 1.2g zirconium oxide grinding balls were placed in a solvent bottle and ultrasonicated for 24h. The supernatant was then filtered through a 200-mesh molecular sieve and centrifuged to obtain the supernatant. The supernatant was filtered through a 1μm pore size filter and washed with deionized water. The obtained product was dried at 60°C to obtain exfoliated boron nitride BNNS.

[0052] Step 2. Dry PLA in a drying oven at 80°C for 12 h; weigh 50 g of PLA and dissolve it in 200 mL of dichloromethane at room temperature. After it is fully dissolved, add powdered DCP (0.05 g) and 4-VPBA (0.10 g) dissolved in 8 mL of acetone, and then add 0.25 g of BNNS. After it is fully premixed, place the blend in a drying oven at 45°C and dry overnight to evaporate the solvent to obtain a premixed solid premix.

[0053] Step 3: The obtained solid premix was completely crushed in a grinder, and the crushed powder was added to an internal mixer at a speed of 50 r / min and a temperature of 190°C for 10 min to obtain a BNNS-filled borate cross-linked polylactic acid composite material (denoted as PLA / 0.1% DCP / 0.2% 4-VPBA / 0.5% BNNS). The tensile and thermal conductivity test results were as follows: elongation at break was 8.3%, and vertical thermal conductivity was 0.376 Wm -1 K -1 , horizontal thermal conductivity is 0.221Wm -1 K -1 .

[0054] Comparative Example 2

[0055] Step 1: 1.2gh-BN, 400mL deionized water, and 1.2g zirconium oxide grinding balls were placed in a solvent bottle and ultrasonicated for 24h. The supernatant was then filtered through a 200-mesh molecular sieve and centrifuged to obtain the supernatant. The supernatant was filtered through a 1μm pore size filter and washed with deionized water. The obtained product was dried at 60°C to obtain exfoliated boron nitride BNNS.

[0056] Step 2. Dry PLA in a drying oven at 80°C for 12 h; weigh 50 g of PLA and dissolve it in 200 mL of dichloromethane at room temperature. After it is fully dissolved, add powdered DCP (0.05 g) and 4-VPBA (0.10 g) dissolved in 8 mL of acetone, and then add 0.50 g of BNNS. After it is fully premixed, place the blend in a drying oven at 45°C and dry overnight to evaporate the solvent to obtain a premixed solid premix.

[0057] Step 3: The obtained solid premix was completely crushed in a grinder, and the crushed powder was added to an internal mixer at a speed of 50 r / min and a temperature of 190°C for 10 min to obtain a BNNS-filled borate cross-linked polylactic acid composite material (denoted as PLA / 0.1% DCP / 0.2% 4-VPBA / 1.0% BNNS). The tensile and thermal conductivity test results were as follows: elongation at break was 7.3%, and vertical thermal conductivity was 0.438 Wm -1 K -1 , horizontal thermal conductivity is 0.431Wm -1 K -1 .

[0058] Comparative Example 3

[0059] Step 1: 1.2gh-BN, 400mL deionized water, and 1.2g zirconium oxide grinding balls were placed in a solvent bottle and ultrasonicated for 24h. The supernatant was then filtered through a 200-mesh molecular sieve and centrifuged to obtain the supernatant. The supernatant was filtered through a 1μm pore size filter and washed with deionized water. The obtained product was dried at 60°C to obtain exfoliated boron nitride BNNS.

[0060] Step 2. Dry PLA in a drying oven at 80°C for 12 h; weigh 50 g of PLA and dissolve it in 200 mL of dichloromethane at room temperature. After it is fully dissolved, add powdered DCP (0.05 g) and 4-VPBA (0.10 g) dissolved in 8 mL of acetone, and then add 0.75 g of BNNS. After it is fully premixed, place the blend in a drying oven at 45°C and dry overnight to evaporate the solvent to obtain a premixed solid premix.

[0061] Step 3: The obtained solid premix was completely crushed in a grinder, and the crushed powder was added to an internal mixer at a speed of 50 r / min and a temperature of 190°C for 10 min to obtain a BNNS-filled borate cross-linked polylactic acid composite material (denoted as PLA / 0.1% DCP / 0.2% 4-VPBA / 1.5% BNNS). The tensile and thermal conductivity test results were as follows: elongation at break was 6.7%, and vertical thermal conductivity was 0.453 Wm -1 K -1 , horizontal thermal conductivity is 0.440Wm -1 K -1 .

[0062] Comparative Example 4

[0063] Step 1: 1.2gh-BN, 400mL deionized water, and 1.2g zirconium oxide grinding balls were placed in a solvent bottle and ultrasonicated for 24h. The supernatant was then filtered through a 200-mesh molecular sieve and centrifuged to obtain the supernatant. The supernatant was filtered through a 1μm pore size filter and washed with deionized water. The obtained product was dried at 60°C to obtain exfoliated boron nitride BNNS.

[0064] Step 2. Dry PLA in a drying oven at 80°C for 12 h; weigh 50 g of PLA and dissolve it in 200 mL of dichloromethane at room temperature. After it is fully dissolved, add powdered DCP (0.05 g) and 4-VPBA (0.10 g) dissolved in 8 mL of acetone, and then add 1.0 g of BNNS. After it is fully premixed, place the blend in a drying oven at 45°C and dry overnight to evaporate the solvent to obtain a premixed solid premix.

[0065] Step 3: The obtained solid premix was completely crushed in a grinder, and the crushed powder was added to an internal mixer at a speed of 50 r / min and a temperature of 190°C for 10 min to obtain a BNNS-filled borate cross-linked polylactic acid composite material (denoted as PLA / 0.1% DCP / 0.2% 4-VPBA / 2.0% BNNS). The tensile and thermal conductivity test results were as follows: elongation at break was 5.8%, and vertical thermal conductivity was 0.513 Wm -1 K -1 , horizontal thermal conductivity is 0.599Wm -1 K -1 .

[0066] Comparative Example 5

[0067] Step 1. Dry PLA in a drying oven at 80°C for 12 hours; weigh 50 g of PLA and dissolve it in 200 mL of dichloromethane at room temperature. After it is fully dissolved, add powdered DCP (0.05 g) and 4-VPBA (0.10 g) dissolved in 8 mL of acetone. After it is fully premixed, place the blend in a drying oven at 45°C to dry and evaporate the solvent to obtain a premixed solid premix.

[0068] Step 2: The obtained solid premix was completely crushed in a grinder, and the crushed powder was added to an internal mixer at a speed of 50 r / min and a temperature of 190° C. for 10 min to obtain a borate cross-linked polylactic acid material (denoted as PLA / 0.1% DCP / 0.2% 4-VPBA). The tensile test results and thermal conductivity test results were: elongation at break was 223.0%, and vertical thermal conductivity was 0.275 Wm -1 K -1 , horizontal thermal conductivity is 0.275Wm -1 K -1 .

[0069] Comparative Example 6

[0070] Step 1. Dry PLA in a drying oven at 80°C for 12 hours; weigh 50g PLA and dissolve it in 200mL dichloromethane at room temperature. After it is fully dissolved, place it in a drying oven at 45°C to dry and evaporate the solvent to obtain a uniform solid premix.

[0071] Step 2: The obtained solid premix was completely crushed in a grinder, and the crushed powder was added to an internal mixer at a speed of 50 r / min and a temperature of 190°C for 10 min to obtain a pure polylactic acid material (denoted as PLA). The tensile test results and thermal conductivity test results were: elongation at break was 6.5%, and vertical thermal conductivity was 0.234 Wm -1 K -1 , horizontal thermal conductivity is 0.275Wm -1 K -1 .

[0072] Figure 1 and Figure 2 The results of tensile and impact strength tests of dynamically cross-linked PLA are shown. It can be seen that after adding 0.1% DCP and 0.2% 4-VPBA into the melt blending reaction, the comprehensive performance of the composite material is the best, with tensile toughness increased by 216.5% and impact strength increased by 3.3KJ / m 2 , and the tensile strength remains almost unchanged.

[0073] From the performance data of the above examples and comparative examples, it can be seen that the filling of BNNS reduces the mechanical properties of polylactic acid; compared with the borate cross-linked polylactic acid composite material filled with BNNS, the PDA@BNNS-filled borate cross-linked polylactic acid composite material has better toughness, and both the vertical and horizontal thermal conductivities are greatly improved.

[0074] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a toughened thermally conductive polylactic acid composite material, characterized by: Vinylbenzeneboronic acid is used to crosslink and modify polylactic acid under the action of an initiator to obtain polylactic acid containing a borate crosslinked structure, and dopamine-coated boron nitride nanosheets are filled to improve the toughness and thermal conductivity of the polylactic acid composite material to obtain a toughened thermally conductive polylactic acid composite material. The specific steps include: Step 1: Place boron nitride, deionized water, and zirconium oxide grinding balls in a reactor and perform ultrasonic treatment for 24 hours. Then, filter through a 200-mesh molecular sieve, centrifuge to obtain a supernatant, filter, and wash with deionized water. The resulting product is dried at 60° C. to obtain exfoliated boron nitride. The exfoliated boron nitride was placed in a Tris-HCl buffer solution at pH 8.5, stirred evenly, and then dopamine was added and stirred for 14-16 hours. The obtained product was washed with ethanol, centrifuged, and filtered, and dried at 60°C to obtain dopamine-coated boron nitride nanosheet powder; Step 2: dissolving polylactic acid in a first solvent at room temperature, grinding an initiator into powder, and dissolving vinylphenylboric acid in a second solvent; after the polylactic acid is completely dissolved, adding the initiator and the vinylphenylboric acid dissolved in the second solvent, and then adding dopamine-coated boron nitride nanosheets, fully premixing, and then drying and evaporating the solvent in an oven to obtain a premix; wherein the mass ratio of polylactic acid, initiator, vinylphenylboric acid, dopamine-coated boron nitride nanosheets, first solvent, and second solvent is 100:0.1:0.05-0.6:0.5-2.0:0-400:0-20; Step 3: The premix is ​​crushed into powder in a pulverizer, and then added to an internal mixer at a temperature of 190°C and a speed of 50 r / min for internal mixing. Under heating conditions, the free radicals generated by the initiator are used to initiate a grafting reaction between polylactic acid and vinylphenylboronic acid. At the same time, the boric acids undergo dehydration condensation to form borate ester bonds, thereby obtaining a toughened thermally conductive polylactic acid composite material.

2. The method for preparing a toughened thermally conductive polylactic acid composite material according to claim 1, wherein: The number average molecular weight of the polylactic acid is 100,000-200,000.

3. The method for preparing a toughened thermally conductive polylactic acid composite material according to claim 1, wherein: The initiator includes at least one of an azo initiator and an organic peroxide initiator.

4. The method for preparing a toughened thermally conductive polylactic acid composite material according to claim 1, wherein: The vinylbenzene boronic acid is at least one of 2-vinylbenzene boronic acid, 3-vinylbenzene boronic acid and 4-vinylbenzene boronic acid.

5. The method for preparing a toughened thermally conductive polylactic acid composite material according to claim 1, wherein: The boron nitride is at least one of hexagonal boron nitride, rhombohedral boron nitride, cubic boron nitride and wurtzite boron nitride.

6. The method for preparing a toughened thermally conductive polylactic acid composite material according to claim 1, characterized in that: In step 1, the usage ratio of boron nitride, deionized water and zirconium oxide grinding balls is 1-2 g:100-1000 mL:1-2 g.

7. The method for preparing a toughened thermally conductive polylactic acid composite material according to claim 1, characterized in that: In step 1, the mass ratio of the exfoliated boron nitride to dopamine is 0.1-0.3 g: 0.02-0.04 g.

8. The method for preparing a toughened thermally conductive polylactic acid composite material according to claim 1, characterized in that: The first solvent and the second solvent are independently selected from at least one of ethanol, toluene, dichloromethane, chloroform, acetone and tetrahydrofuran.

Images