Sandwich structure flame-retardant electromagnetic shielding composite material and preparation method thereof

Abstract

The application provides a sandwich structure flame-retardant electromagnetic shielding composite material and a preparation method thereof. The sandwich structure is formed by hot pressing of an electromagnetic shielding carbon fiber cloth intermediate layer and two flame-retardant layers on both sides, wherein the raw material formula of the flame-retardant layer comprises polylactic acid, polybutylene adipate terephthalate, APP@SiO2, and a compatibilizer IPU-PLA-PBA-MXene. In the composite material, the APP@SiO2 after combustion generates a phosphorus-containing component, which can promote the generation of a dense carbon layer of the composite material; the TiO2 generated by the combustion of MXene can hinder the diffusion of heat and smoke and accelerate carbonization; the IPU-PLA-PBA-MXene ensures good mechanical properties of the composite material; the carbon fiber cloth as the intermediate layer ensures high electromagnetic shielding efficiency of the composite material, promotes the carbonization capacity of the composite material, and further improves the mechanical properties of the composite material; the composite material has excellent flame-retardant and electromagnetic shielding properties, is environmentally friendly and safe, and has a wide application prospect in the fields of electronic and electrical materials and automobile materials.

Description

Technical Field

[0001] This invention relates to a sandwich-structured flame-retardant electromagnetic shielding composite material and its preparation method. Background Technology

[0002] In recent years, the development of environmentally friendly biodegradable polymer materials has received widespread attention in order to mitigate the environmental impact of waste plastics. Among biodegradable polymers, polylactic acid (PLA) has attracted considerable attention due to its wide availability and high tensile strength. However, the brittleness and flammability of PLA greatly limit its large-scale application. To overcome the poor toughness of PLA, blending it with flexible polymers has become an effective method for toughening PLA. Polybutylene terephthalate (PBAT) elastomer is considered an effective material for toughening PLA; however, the poor compatibility between PLA and PBAT limits the toughening effect of PBAT. Currently, many studies are exploring the addition of functionalized fillers to improve the compatibility between PLA and PBAT.

[0003] The novel two-dimensional material MXene possesses a unique two-dimensional layered structure, a large specific surface area, and excellent mechanical properties, making it suitable for compatibilization and modification of polymers. However, due to van der Waals interactions, MXene is prone to agglomeration in the polymer matrix, negatively impacting its mechanical properties. Imidazole-based ionic liquids can promote filler dispersion without altering the filler's structural characteristics and physical properties. Therefore, functionalizing MXene with imidazole-based polyurethane can effectively improve the interfacial interaction between PLA and PBAT phases, facilitating stress transfer more efficiently. Furthermore, the sheet-like morphology of MXene acts as a physical barrier, reducing the release of flammable volatiles. The Ti component of MXene also exhibits catalytic activity against most polymers, significantly reducing heat and smoke emissions from the composite material. Xue et al. prepared an MXene-PPDA nanohybrid material by embedding PPDA into an MXene interlayer. Adding 1.0 wt% MXene-PPDA enabled PLA to achieve a UL-94 V-0 rating, reduced the peak exothermic rate by 22.2%, and increased the char yield by 25 times compared to pure PLA (YJ Xue, et al. Chem. Eng.J. 2020, 297:125336). However, MXene alone has poor flame retardant effect and usually needs to be synergistically combined with other flame retardants to achieve effective flame retardancy. Ammonium polyphosphate (APP), a phosphorus / nitrogen type flame retardant, has advantages such as low cost, low smoke, and low toxicity, and is widely used in the flame retardant modification of PLA. However, APP has low flame retardant efficiency, and excessive addition can negatively impact the mechanical properties of PLA. Silane coupling agents are mainly used to improve the compatibility of organic and inorganic materials. APP surface-modified with silica and silane coupling agents exhibits high thermal stability and synergistic effects, effectively improving the flame retardant efficiency of APP and reducing its adverse effects on mechanical properties. Xu et al. prepared SiO2@MAPP modified with SiO2 and KH-570 and applied it as an acid source and gas source in an IFR system. The results showed that the addition of IFR containing SiO2@MAPP / DPER improved the flame retardancy of LDPE composites after coating with SiO2 and KH-570. When the SiO2@MAPP / DPER addition amount was 30 wt%, the limiting oxygen index reached 26.8% and the tensile strength increased by 7.14% (JC Xu, et al. J. Appl. Polym. Sci.2020, 137:49242).

[0004] Studies have found that sandwich structures are effective for electromagnetic interference (EMI) shielding, and the EMI shielding performance of composite materials is closely related to the middle layer of the layered structure. Carbon fiber fabrics have attracted increasing attention due to their lightweight, excellent EMI shielding, and mechanical properties, making them an ideal middle layer material for preparing sandwich structure composite materials. Chinese Patent CN 114261036 A discloses a method for preparing a thermoplastic EMI shielding prepreg, which involves placing a resin-impregnated nickel-plated carbon fiber felt between two layers of thermoplastic resin film and then hot-pressing double-sided impregnation to obtain the thermoplastic EMI shielding prepreg. The sandwich structure composite material made from the thermoplastic EMI shielding prepreg is lightweight, has a wide frequency band, and high EMI shielding effectiveness. Summary of the Invention

[0005] This invention provides a sandwich-structured flame-retardant electromagnetic shielding composite material and its preparation method, aiming to give it both excellent flame-retardant and electromagnetic shielding properties.

[0006] To achieve its objectives, the present invention employs the following technical solution:

[0007] This invention first provides a sandwich-structured flame-retardant electromagnetic shielding composite material, characterized in that: the flame-retardant electromagnetic shielding composite material uses carbon fiber cloth as the middle layer, and flame-retardant layers are provided on both sides of the middle layer to form a sandwich structure. The composition of the flame-retardant layers by mass percentage is as follows:

[0008] Polylactic acid 50-68%;

[0009] Polybutylene terephthalate-butylene adipate 26~48%;

[0010] APP@SiO2 1~8%;

[0011] IPU-PLA-PBA-MXene 1~4%.

[0012] Further, the APP@SiO2 is obtained by dispersing APP and hexadecyltrimethylammonium bromide (CTAB) in a mixture of ammonia, deionized water, and anhydrous ethanol, followed by the addition of tetraethyl orthosilicate and KH-560 for reaction. Specifically, the steps include the following:

[0013] Mix 2 mL of ammonia water, 98.75 mL of deionized water, and 59.25 mL of anhydrous ethanol to obtain 160 mL of ammonia water mixture. Disperse 10 g of APP and 0.5 g of CTAB in the ammonia water mixture and stir mechanically for 10-15 min. Then, slowly add 1.67 g of tetraethyl orthosilicate and 0.47 g of KH-560 under strong mechanical stirring, and continue to react the mixture at 50-60 °C for 20-24 h. After the reaction is complete, wash the obtained precipitate 2-3 times with deionized water and methanol, centrifuge, and finally vacuum dry at 50-60 °C for 36-48 h to obtain the APP@SiO2.

[0014] Furthermore, the preparation method of the IPU-PLA-PBA-MXene specifically includes the following steps:

[0015] 1) Add equimolar amounts of OH-PLA-OH and OH-PBA-OH to two dry three-necked flasks respectively, remove water under vacuum at 150℃ for 0.5-1 h, add appropriate amounts of dimethyl sulfoxide (DMSO) to the two three-necked flasks respectively to fully dissolve the polyol, then add diisocyanate and dibutyltin dilaurate respectively, and react at 150℃ for 0.5-1 h to obtain two prepolymers;

[0016] 2) Mix the two prepolymers synthesized in step 1), then add MXene dispersion dissolved in an appropriate amount of DMSO, N,N-neopentyl glycol p-(N-methylimidazolium) bromide and diisocyanate dissolved in an appropriate amount of DMSO, and react at 140-160 ℃ for 2-3 h.

[0017] 3) Add sodium sulfonate aqueous solution to carry out ion exchange reaction, and react at 70-80℃ for 6-8 hours;

[0018] 4) Using deionized water as a precipitant, the polymer obtained in step 3) is added dropwise to a beaker containing deionized water using a dropper, while stirring continuously and filtering to obtain the IPU-PLA-PBA-MXene.

[0019] Furthermore, the MXene is Ti3C2T x .

[0020] Furthermore, the diisocyanate is at least one selected from isophorone diisocyanate (IPDI), toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and hexamethylene diisocyanate (HDI).

[0021] Furthermore, the sodium sulfonate salt is at least one of sodium p-toluenesulfonate, sodium dodecyl sulfonate, and sodium methanesulfonate.

[0022] This invention also provides a method for preparing the sandwich-structured flame-retardant electromagnetic shielding composite material: polylactic acid, polybutylene terephthalate-adipate, APP@SiO2, and IPU-PLA-PBA-MXene are melt-blended and hot-pressed to obtain a flame-retardant layer; the two flame-retardant layers are then hot-pressed onto both sides of a carbon fiber cloth to obtain the sandwich-structured flame-retardant electromagnetic shielding composite material. Specifically, the method includes the following steps:

[0023] 1) Remove water from polylactic acid in a vacuum drying oven at 50-60℃ for 8-12 h, and remove water from polybutylene terephthalate in a vacuum drying oven at 30-40℃ for 8-12 h.

[0024] 2) Weigh out polylactic acid, polybutylene terephthalate, IPU-PLA-PBA-MXene, and APP@SiO2 according to the formula ratio, disperse and mix them, and then blend them at 180℃ with a torque rheometer at a speed of 50 r / min for 4-6 min to obtain a mixture.

[0025] 3) The obtained mixture is hot-pressed into flame-retardant layer sheets with a thickness of 1-2 mm using a flat vulcanizing apparatus. The hot-pressing temperature is 180-190℃ and the hot-pressing pressure is 5-10 MPa.

[0026] 4) The two flame-retardant layers are hot-pressed onto both sides of the carbon fiber cloth at 180-190℃ and 5-10MPa pressure using a flat vulcanizing apparatus to obtain a sandwich structure flame-retardant electromagnetic shielding composite material.

[0027] The present invention has the following beneficial effects:

[0028] In the flame-retardant electromagnetic shielding composite material of this invention: APP@SiO2 combustion produces phosphorus-containing components, which promote the formation of a dense char layer in the composite material; TiO2 generated by MXene combustion hinders the diffusion of heat and smoke, accelerating carbonization. IPU-PLA-PBA-MXene acts as a compatibilizer, improving the compatibility between the PLA and PBAT phases and ensuring the good mechanical properties of the composite material. Introducing carbon fiber cloth, which has excellent conductivity and carbonization ability, as the middle layer of the sandwich structure composite material ensures high electromagnetic shielding effectiveness while promoting the char formation ability of the composite material. The high strength of carbon fiber further enhances the mechanical properties of the composite material. The sandwich structure flame-retardant electromagnetic shielding composite material possesses both excellent flame-retardant and electromagnetic shielding properties, is environmentally friendly and safe, and has broad application prospects. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of APP@SiO2.

[0030] Figure 2 The infrared spectrum of APP@SiO2.

[0031] Figure 3 For IPU-PLA-PBA-MXene 1 H-NMR spectrum. Detailed Implementation

[0032] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The following embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments. Example

[0033] This embodiment prepares a sandwich-structured flame-retardant electromagnetic shielding composite material according to the following steps:

[0034] 1) Etching of Ti3AlC2 powder using hydrochloric acid and lithium fluoride. LiF powder was slowly dissolved in a 9 mol / L HCl aqueous solution, and then Ti3AlC2 was added to the LiF / HCl solution. The mixture was stirred at 35°C for 36 h. The resulting precipitate was poured into centrifuge tubes and centrifuged at 6000 r / min for 5 min. The supernatant was then removed, and the mixture was washed several times with deionized water until the pH of the supernatant reached 6-7. Finally, the supernatant was concentrated by centrifugation at 10000 rpm for 20 min to obtain highly concentrated Ti3C2T. x Dispersion. Finally, Ti3C2T x The dispersion was freeze-dried for 48 hours to obtain Ti3C2T x Nanoparticle powder.

[0035] 2) Add 2.5 g of OH-PLA-OH (molecular weight 2000) and 2.5 g of OH-PBA-OH (molecular weight 2000) to two dry three-necked flasks respectively, and remove water under vacuum at 150 °C for 0.5 h. Add appropriate amounts of dimethyl sulfoxide (DMSO) to each of the two three-necked flasks to fully dissolve the polyols, and then add 0.222 g of diisocyanate and 0.02 g of dibutyltin dilaurate to each flask, and react at 150 °C for 0.5 h. Mix the polyurethane synthesized from PLA and PBA polyols, dissolve 2.5 g of MXene and 1.065 g of N,N-neopentyl glycol p-(N-methylimidazole) bromide in an appropriate amount of DMSO and add it to the polyurethane solution, then add 0.645 g of diisocyanate, and react at 150 °C for 2 h. Then, 0.956 g of sodium p-toluenesulfonate was added to carry out an ion exchange reaction, which was carried out at 80 °C for 7 hours. The polymer was added dropwise to a beaker containing deionized water using deionized water as a precipitant, with constant stirring and filtration, to obtain IPU-PLA-PBA-MXene.

[0036] 3) Prepare a 160 mL ammonia solution (2 mL ammonia, 98.75 mL deionized water, and 59.25 mL anhydrous ethanol). Disperse 10 g APP and 0.5 g cetyltrimethylammonium bromide (CTAB) in the ammonia solution and stir mechanically for 10 min. Slowly add 1.67 g tetraethyl orthosilicate (TEOS) and 0.47 g KH-560 under strong mechanical stirring. Continue to react the mixture at 55 °C for 24 h. After the reaction is complete, wash the precipitate three times with deionized water and methanol, centrifuge, and finally vacuum dry at 80 °C for 48 h to obtain APP@SiO2.

[0037] 4) Polylactic acid (PLA) was dehydrated in a vacuum drying oven at 60℃ for 12 h, and polybutylene terephthalate (PET) was dehydrated in a vacuum drying oven at 40℃ for 12 h. 33.6 g PLA, 14.4 g PBAT, 1 g APP@SiO2, and 1 g IPU-PLA-PBA-MXene were weighed according to the formula and dispersed and mixed. The mixture was then blended using a torque rheometer at 50 r / min at 180℃ for 5 min to obtain a final mixture. The mixture was then hot-pressed into a 1.5 mm thick sheet using a flat vulcanizing apparatus at 190℃ and 5 MPa. The two flame-retardant layers were then hot-pressed onto both sides of a carbon fiber cloth using the flat vulcanizing apparatus at 190℃ and 5 MPa pressure to obtain a sandwich-structured flame-retardant electromagnetic shielding composite material.

[0038] Example 2

[0039] In this embodiment, the sandwich structure flame-retardant electromagnetic shielding composite material is prepared according to the same method and steps as in Example 1. The only difference is that the flame-retardant layer raw materials in step 4) are: 32.9 g PLA, 14.1 g PBAT, 2 g APP@SiO2, and 1 g IPU-PLA-PBA-MXene.

[0040] Example 3

[0041] In this embodiment, the sandwich structure flame-retardant electromagnetic shielding composite material is prepared according to the same method and steps as in Example 1. The only difference is that the flame-retardant layer raw materials in step 4) are: 32.2 g PLA, 13.8 g PBAT, 3 g APP@SiO2, and 1 g IPU-PLA-PBA-MXene.

[0042] Example 4

[0043] This embodiment prepares a sandwich-structured flame-retardant electromagnetic shielding composite material according to the same method and steps as in embodiment 1. The only difference is that the flame-retardant layer raw materials in step 4) are: 31.5 g PLA, 13.5 g PBAT, 4 g APP@SiO2, and 1 g IPU-PLA-PBA-MXene.

[0044] Comparative Example 1

[0045] This comparative example prepared a sandwich-structured flame-retardant electromagnetic shielding composite material using the same method and steps as in Example 1, except that the flame-retardant layer raw materials in step 4) were 35 g PLA and 15 g PBAT.

[0046] Comparative Example 2

[0047] This comparative example prepared a sandwich-structured flame-retardant electromagnetic shielding composite material using the same method and steps as in Example 1, except that the flame-retardant layer raw materials in step 4) were: 34.3 g PLA, 14.7 g PBAT, and 1 g IPU-PLA-PBA-MXene.

[0048] Comparative Example 3

[0049] This comparative example prepared a sandwich-structured flame-retardant electromagnetic shielding composite material using the same method and steps as in Example 1, except that the flame-retardant layer raw materials in step 4) were: 34.3 g PLA, 14.7 g PBAT, and 1 g MXene.

[0050] Comparative Example 4

[0051] This comparative example prepared a sandwich-structured flame-retardant electromagnetic shielding composite material using the same method and steps as in Example 1, except that the flame-retardant layer materials in step 4) were: 34.3 g PLA, 14.7 g PBAT, and 4 g APP.

[0052] Comparative Example 5

[0053] This comparative example prepared a sandwich-structured flame-retardant electromagnetic shielding composite material using the same method and steps as in Example 1, except that the flame-retardant layer raw materials in step 4) were: 31.5 g PLA, 13.5 g PBAT, 4 g APP, and 1 g MXene.

[0054] Table 1 shows the performance indicators of the sandwich-structured flame-retardant electromagnetic shielding composite materials prepared in each embodiment and comparative example.

[0055] Table 1 Performance Indicators of Sandwich Structure Flame-Retardant Electromagnetic Shielding Composite Material

[0056]

[0057] Table 1 shows that IPU-PLA-PBA-MXene and APP@SiO2 exhibit excellent synergistic effects. The surface SiO2 coating effectively reduces the adverse effects of APP on the mechanical properties of the composite material. IPU grafting promotes the dispersion of MXene in the matrix, inhibits MXene aggregation, and reduces the damage to the matrix's mechanical properties caused by MXene aggregation. The functionalized surface of IPU enables MXene to form covalent bonds with the polymer matrix, ensuring strong interfacial adhesion and good interfacial stress transfer. The excellent char-forming effect of IPU-PLA-PBAT-MXene, synergistically with APP@SiO2, significantly improves the flame retardant properties of the composite material, resulting in an LOI value of 30 and a V-0 rating in the UL-94 test. The sandwich structure design and the selection of the carbon fiber interlayer ensure that the electromagnetic shielding effectiveness of the composite material reaches over 40 dB, far exceeding the requirements for commercial applications.

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sandwich-structured flame-retardant electromagnetic shielding composite material, characterized in that: The flame-retardant electromagnetic shielding composite material uses carbon fiber cloth as the middle layer and flame-retardant layers on both sides of the middle layer to form a sandwich structure. The flame-retardant layer of the flame-retardant electromagnetic shielding composite material is composed of the following components by mass percentage: Polylactic acid 50-68%; Polybutylene terephthalate-butylene adipate 26~48%; APP@SiO2 1~8%; IPU-PLA-PBA-MXene 1~4%; Wherein: APP@SiO2 is obtained by dispersing APP and hexadecyltrimethylammonium bromide (CTAB) in a mixture of ammonia, deionized water and anhydrous ethanol, and then adding ethyl silicate and KH-560 to react; The preparation method of IPU-PLA-PBA-MXene is as follows: diisocyanate is prepolymerized with hydroxyl-terminated polylactic acid OH-PLA-OH and OH-PBA-OH respectively; after the two prepolymers are mixed, MXene, hydroxyl-containing imidazole bromide and IPDI are added for polymerization, and then sodium sulfonate is added for anion exchange to remove bromide ions to obtain the compatibilizer IPU-PLA-PBA-MXene.

2. The sandwich-structured flame-retardant electromagnetic shielding composite material according to claim 1, characterized in that: The preparation method of the APP@SiO2 includes the following steps: Ammonia, deionized water, and anhydrous ethanol were mixed to obtain an ammonia mixture. 10 g of APP and 0.5 g of CTAB were dispersed in the ammonia mixture and mechanically stirred for 10-15 min. Then, 1.67 g of tetraethyl orthosilicate and 0.47 g of KH-560 were added under mechanical stirring, and the mixture was further reacted at 50-60 °C for 20-24 h. After the reaction was completed, the precipitate was washed successively with deionized water and methanol, centrifuged, and finally vacuum dried at 50-60 °C for 36-48 h to obtain the APP@SiO2.

3. The sandwich-structured flame-retardant electromagnetic shielding composite material according to claim 1, characterized in that: The preparation method of the IPU-PLA-PBA-MXene includes the following steps: 1) Add equimolar amounts of OH-PLA-OH and OH-PBA-OH to two dry three-necked flasks respectively, remove water under vacuum at 150 °C for 0.5-1 h, add appropriate amounts of dimethyl sulfoxide (DMSO) to the two three-necked flasks respectively to fully dissolve the polyol, then add diisocyanate and dibutyltin dilaurate respectively, and react at 150 °C for 0.5-1 h to obtain two prepolymers; 2) Mix the two prepolymers synthesized in step 1), then add MXene dispersion dissolved in an appropriate amount of DMSO, N,N-neopentyl glycol p-(N-methylimidazolium) bromide dissolved in an appropriate amount of DMSO and IPDI, and react at 140-160 ℃ for 2-3 h. 3) Add sodium sulfonate aqueous solution to carry out ion exchange reaction, and react at 70-80℃ for 6-8 hours; 4) Using deionized water as a precipitant, the polymer obtained in step 3) is added dropwise to a beaker containing deionized water using a dropper, while stirring continuously and filtering to obtain the IPU-PLA-PBA-MXene.

4. The sandwich-structured flame-retardant electromagnetic shielding composite material according to claim 1 or 3, characterized in that: The MXene mentioned is Ti3C2T x .

5. The sandwich-structured flame-retardant electromagnetic shielding composite material according to claim 1 or 3, characterized in that: The diisocyanate is at least one of isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, and hexamethylene diisocyanate.

6. The sandwich-structured flame-retardant electromagnetic shielding composite material according to claim 1 or 3, characterized in that: The sodium sulfonate salt is at least one of sodium p-toluenesulfonate, sodium dodecyl sulfonate, and sodium methanesulfonate.

7. A method for preparing a sandwich-structured flame-retardant electromagnetic shielding composite material according to any one of claims 1 to 6, characterized in that: Polylactic acid, polybutylene terephthalate, APP@SiO2 and IPU-PLA-PBA-MXene are melt-blended and hot-pressed to obtain a flame-retardant layer. The two flame-retardant layers are then hot-pressed onto both sides of a carbon fiber cloth to obtain a sandwich-structured flame-retardant electromagnetic shielding composite material.

8. The preparation method according to claim 7, characterized in that, Includes the following steps: 1) Remove water from polylactic acid in a vacuum drying oven at 50-60℃ for 8-12 h, and remove water from polybutylene terephthalate in a vacuum drying oven at 30-40℃ for 8-12 h. 2) Weigh out polylactic acid, polybutylene terephthalate, IPU-PLA-PBA-MXene, and APP@SiO2 according to the formula ratio, disperse and mix them, and then blend them at 180℃ with a torque rheometer at a speed of 50 r / min for 4-6 min to obtain a mixture. 3) The obtained mixture is hot-pressed into flame-retardant layer sheets with a thickness of 1-2 mm using a flat vulcanizing apparatus. The hot-pressing temperature is 180-190℃ and the hot-pressing pressure is 5-10 MPa. 4) The two flame-retardant layers are hot-pressed onto both sides of the carbon fiber cloth at 180-190℃ and 5-10MPa pressure using a flat vulcanizing apparatus to obtain a sandwich structure flame-retardant electromagnetic shielding composite material.

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