Halogen-free flame retardant modified TPU composite material and preparation method thereof

Abstract

The invention discloses a halogen-free flame retardant modified TPU (thermoplastic polyurethane) composite material and a preparation method thereof, the prepared material can form a carbon layer protection matrix at the initial stage of combustion to prevent the composite material from generating molten drops in the combustion process, and the flame retardant has good compatibility with the TPU matrix, so that the halogen-free flame retardant modified TPU composite material has good flame retardant property. And the influence of the filler on the mechanical properties of the composite material can be reduced while the relatively good flame retardant property is maintained.

Description

Technical Field

[0001] This invention belongs to the field of organic compound synthesis technology, specifically relating to a halogen-free flame retardant modified TPU composite material and its preparation method. Background Technology

[0002] Polyurethane (TPU), as a versatile polymer synthetic material, is widely used in furniture manufacturing, automotive interiors, building insulation, footwear and apparel, cold chain logistics, and many other fields due to its excellent elastic recovery, wear resistance, impact resistance, good thermal and sound insulation properties, and strong molding adaptability. However, polyurethane produces a large amount of toxic and harmful gases during combustion, which can easily cause poisoning and asphyxiation, accompanied by dense black smoke that severely obstructs escape and rescue visibility. Furthermore, polyurethane has a rapid heat release rate during combustion, resulting in rapid flame propagation. The material itself has poor flame retardancy and is difficult to extinguish on its own, posing a significant challenge to fire prevention and control. Therefore, the development of highly efficient flame-retardant polyurethane materials and their supporting processing technologies is of great significance for expanding the application scenarios of polyurethane and improving its safety.

[0003] Currently, the common method to improve the flame retardant properties of polyurethane is to add flame retardants. Commonly used flame retardants are divided into halogenated flame retardants and halogen-free flame retardants. The limitation of halogenated flame retardants lies in the continuous release of large amounts of toxic and harmful gases during combustion. These gases not only rapidly diffuse at the fire scene, causing poisoning and suffocation, but also severely hinder escape and rescue operations. Their insufficient environmental friendliness contradicts the current development trend of "low toxicity, low smoke, and environmental protection" in flame retardant materials, thus severely restricting the application of halogenated flame retardants in fields with high safety and environmental protection requirements, such as furniture, automotive interiors, and building insulation.

[0004] Halogen-free flame retardants can be divided into intumescent flame retardants, represented by nitrogen and phosphorus-based types, and inorganic flame retardants, represented by hydroxides. Inorganic flame retardants, through decomposition endothermic processes and the generation of H2O, can dilute the concentration of combustible gases in the gas phase, avoiding incomplete combustion caused by excessive gas accumulation, thus significantly improving the flame retardant properties of polyurethane. A common inorganic flame retardant is aluminum hydroxide, which absorbs a large amount of heat and produces a large amount of water when heated. However, inorganic flame retardants have poor compatibility with polyurethane, and large amounts are required to achieve good flame retardant performance. Therefore, adding large amounts of aluminum hydroxide significantly reduces the mechanical properties of the composite material. Huang Yanping of Nantong University of Science and Technology prepared flame-retardant and wear-resistant polyurethane composite materials by introducing magnesium hydroxide particles and nano-copper particles, thereby giving low-density polyurethane better flame retardant properties. However, a high content of magnesium hydroxide is required to impart excellent flame retardancy to the polyurethane, greatly affecting the mechanical properties of the material.

[0005] Therefore, it is of great significance to provide a polyurethane composite material that is simple to prepare, has low production cost, and combines flame retardant and mechanical properties. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a halogen-free flame retardant modified thermoplastic polyurethane composite material.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a halogen-free flame retardant modified thermoplastic polyurethane composite material, characterized in that the composite material is prepared by melt blending of the following components: Thermoplastic polyurethane (TPU) matrix; and a halogen-free flame retardant with a core-shell structure, wherein the halogen-free flame retardant is ammonium polyphosphate modified hydrotalcite-coated expandable graphite EG@LDH-APP.

[0010] As a preferred embodiment of the halogen-free flame retardant modified thermoplastic polyurethane composite material of the present invention, the ratio of the halogen-free flame retardant to the TPU matrix is ​​1:5~10.

[0011] As a preferred embodiment of the halogen-free flame retardant modified thermoplastic polyurethane composite material of the present invention, wherein: the core-shell structure of the halogen-free flame retardant is: expandable graphite EG as the core, and polyphosphate APP modified hydrotalcite LDH as the shell, with polyphosphate APP modified hydrotalcite LDH coating the surface of the expandable graphite.

[0012] As a preferred embodiment of the halogen-free flame retardant modified thermoplastic polyurethane composite material of the present invention, it further includes a compatibilizer, wherein the amount of the compatibilizer is less than 15% of the total amount of the matrix and the halogen-free flame retardant.

[0013] Another objective of this invention is to overcome the shortcomings of the prior art and provide a method for preparing a halogen-free flame retardant modified thermoplastic polyurethane composite material, characterized by comprising the following steps: Preparation of ammonium polyphosphate modified hydrotalcite LDH-APP; Preparation of ammonium polyphosphate modified hydrotalcite coated expandable graphite EG@LDH-APP; The TPU matrix is ​​melt-plasticized, and then expanded graphite EG@LDH-APP coated with ammonium polyphosphate-modified hydrotalcite is added and blended to obtain a halogen-free flame retardant modified thermoplastic polyurethane composite material.

[0014] In a preferred embodiment of the preparation method described in this invention, the blending is performed by melt blending at 180~190°C.

[0015] As a preferred embodiment of the preparation method described in this invention, the preparation method of the ammonium polyphosphate modified hydrotalcite includes, The hydrotalcite was dispersed in anhydrous ethanol, KH550 was added, and a dehydration condensation reaction occurred in an oil bath to obtain an LDH-KH550 solution. Ammonium polyphosphate was dispersed in a 50% aqueous ethanol solution, then added to an LDH-KH550 solution, and reacted in an oil bath to obtain LDH-APP; After being filtered, washed, dried and pulverized in sequence, ammonium polyphosphate modified hydrotalcite LDH-APP is obtained.

[0016] As a preferred embodiment of the preparation method described in this invention, the oil bath heating temperature is 60~70℃ and the time is 8 h.

[0017] As a preferred embodiment of the preparation method described in this invention, the preparation method of the ammonium polyphosphate modified hydrotalcite-coated expandable graphite includes, Ammonium polyphosphate-modified hydrotalcite and expandable graphite were dispersed in water, and then the ammonium polyphosphate-modified hydrotalcite dispersion was added to the expandable graphite dispersion. Electrostatic self-assembly occurred in an oil bath to obtain an ammonium polyphosphate-modified hydrotalcite-coated expandable graphite dispersion. After being filtered, washed, dried and pulverized in sequence, expandable graphite coated with ammonium polyphosphate-modified hydrotalcite is obtained.

[0018] As a preferred embodiment of the preparation method described in this invention, the oil bath heating temperature is 70~80℃ and the time is 6 h.

[0019] Beneficial effects of this invention: This invention uses EG@LDH-APP as a halogen-free flame retardant to give TPU good flame retardant properties. The addition of KH550 can not only improve the agglomeration of inorganic particles, but also provide reaction sites for APP-modified LDH, thereby improving the mechanical properties of flame-retardant TPU materials. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1The images show the microstructures of EG and EG@LDH-APP in Embodiment 1 of the present invention, where a represents EG and b represents EG@LDH-APP. Detailed Implementation

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0022] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0023] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0024] The polyurethane elastomer used in this embodiment was purchased from Covestro AG, model U-90AP10. The hydrotalcite used in this embodiment was purchased from Sinopharm Chemical Reagent Co., Ltd.; the KH550 used in this embodiment was purchased from Sinopharm Chemical Reagent Co., Ltd.; the ammonium polyphosphate used in this embodiment was purchased from Sinopharm Chemical Reagent Co., Ltd.; and the expandable graphite used in this embodiment was purchased from Nanjing Greenfa Carbon Materials Co., Ltd., with a mesh size of 80.

[0025] Unless otherwise specified, all other raw materials used in the examples were commercially purchased.

[0026] The instruments used in the embodiments of this invention are as follows: Electric thermostatic drying oven: DHG-9146A, Shanghai Jinghong Experimental Equipment Co., Ltd.; Torque rheometer: HAAKE Polylab-OS, HAAKE GmbH, Germany; Film laminating press: GT-7014-E50C, High-speed rail testing instruments (Dongguan) Co., Ltd.; Tensile strength tester: AI-7000-SU1, High-speed rail testing instruments (Dongguan) Co., Ltd.

[0027] Example 1 (1) Take 5 g LDH and add it to 200 mL of anhydrous ethanol. Sonicate for about 30 minutes and then stir at room temperature for 12 hours. Add 2.5 mL of 3-aminopropyltriethoxysilane (KH550) and stir at 65 °C for 8 h to obtain LDH-KH550. Then weigh 5 g of APP and add it to 150 mL of 50% ethanol aqueous solution. Stir at room temperature for 0.5 h and slowly add it to LDH-KH550. After mixing, stir at 60 °C for 5 h to obtain LDH-APP. (2) Take 5g of 80-mesh EG and disperse it in 50ml of water. Slowly add it to LDH-APP and mix. Stir for 6 hours under oil bath heating at 80℃. During this period, EG and LDH-APP undergo electrostatic self-assembly. Then, wash three times with deionized water by centrifugation, dry at 70℃ for 12 hours, and grind to obtain EG@LDH-APP powder. Its SEM is as follows: Figure 1 As shown, it can be clearly seen that the EG core is covered by the LDH-APP shell; (3) Heat the torque rheometer to 190°C, add 40.9 g of TPU raw material, melt and plasticize for 3 min, then add 4.09 g of EG@LDH-APP powder and mix for 7 min to obtain flame-retardant polyurethane composite material product.

[0028] Example 2 The difference between this embodiment and embodiment 1 is that the TPU raw material in step (3) is replaced with 39.13 g and the EG@LDH-APP powder is replaced with 5.87 g. The remaining steps are the same as in embodiment 1, and a flame-retardant polyurethane composite material product is obtained.

[0029] Example 3 The difference between this embodiment and embodiment 1 is that the TPU raw material in step (3) is replaced with 37.5 g and the EG@LDH-APP powder is replaced with 7.5 g. The remaining steps are the same as in embodiment 1, and a flame-retardant polyurethane composite material product is obtained.

[0030] Comparative Example 1 Pure TPU material: The torque rheometer was heated to 190 °C, 45 g of TPU raw material was added, and the mixture was stirred for 10 min to obtain pure TPU material.

[0031] Comparative Example 2 The difference between this comparative example and Example 1 is that the EG powder in step (3) is replaced with 80 mesh, while the other steps are the same as in Example 1, and a flame-retardant polyurethane composite material product is obtained.

[0032] Comparative Example 3 The difference between this comparative example and Example 1 is that the EG powder in step (3) is replaced with 200 mesh, while the rest of the steps are the same as in Example 1, and a flame-retardant polyurethane composite material product is obtained.

[0033] Comparative Example 4 The difference between this comparative example and Example 1 is that the EG@LDH powder in step (3) is replaced with 40.9 g, while the rest of the steps are the same as in Example 1, and a flame-retardant polyurethane composite material product is obtained.

[0034] Comparative Example 5 The difference between this comparative example and Example 1 is that step (3) is replaced by: heating the torque rheometer to 190 °C, first adding 37.5 g of TPU raw material, melting and plasticizing for 3 min, then adding 7.5 g of APP powder, and mixing for 7 min to obtain the flame-retardant polyurethane composite material product.

[0035] Comparative Example 6 The difference between this comparative example and Example 1 is that step (3) is replaced by: heating the torque rheometer to 190 °C, first adding 37.5 g of TPU raw material, melting and plasticizing for 3 min, then adding 3 g of EG powder, 3 g of LDH powder, and 1.5 g of KH550 liquid, and mixing for 7 min to obtain the flame-retardant polyurethane composite material product.

[0036] Comparative Example 7 The difference between this comparative example and Example 1 is that step (3) is replaced by: heating the torque rheometer to 190 °C, first adding 37.5 g of TPU raw material, melting and plasticizing for 3 min, then adding 2 g of EG powder, 2 g of LDH powder, 2 g of APP powder, and 1.5 g of KH550 liquid, and mixing for 7 min to obtain the flame-retardant polyurethane composite material product.

[0037] Tensile properties: The tensile test was conducted using a universal tensile testing machine and in accordance with the standard GB / T1040-2006. The tensile rate was 50 mm / min, and the parallel part of the tensile specimen was 15 mm × 2 mm × 0.5 mm. Each group of samples was tested 5 times and the average value was taken.

[0038] Limiting oxygen index: The sample was prepared into a 100 mm × 8 mm × 4 mm specimen, and the limiting oxygen index of the flame retardant material was determined using a limiting oxygen index meter in accordance with GB / T2406.2-2009.

[0039] UL-94: According to the UL94-2009 standard, the flame retardant properties of composite materials are rated using a vertical burning tester, with ratings of V-0, V-1, V-2, and NR (no rating). The sample size is 100 mm × 8 mm × 4 mm. In the rating system, V-0 indicates that the vertical sample stops burning within 10 seconds with no dripping; V-1 indicates that the vertical sample stops burning within 30 seconds with no dripping; V-2 indicates that the vertical sample stops burning within 30 seconds, and dripping is permitted; NR indicates no rating.

[0040] The density testing method in this invention is as follows: the sample is prepared into a circular piece with a diameter of 27 mm and a thickness of 0.5 mm, the mass of the circular piece is weighed using an analytical balance, and the sample density is obtained by dividing the mass by the volume of the circular piece.

[0041] The flame-retardant TPU composite materials obtained in Examples 1-3 and the TPU materials in Comparative Examples 1-7 were subjected to performance tests. The test results are shown in Tables 1 and 2.

[0042] Table 1 Flame retardant properties of TPU composite materials

[0043] Table 2 Mechanical properties of TPU composite materials

[0044] As can be seen from the data in Tables 1 and 2, compared with the pure TPU material in Comparative Example 1 and the conventional halogen-free flame-retardant TPU composite materials provided in Comparative Examples 2 and 3, the flame-retardant TPU composite material provided by our company, with the same amount of EG@LDH-APP flame retardant, has superior flame-retardant properties and better mechanical properties.

[0045] Comparing the data from Examples 2 and 3, reducing the EG particle size was intended to increase the compatibility of EG with the TPU matrix. It can be seen that reducing the EG particle size increases the self-extinguishing time of the flame-retardant TPU composite material and decreases the limiting oxygen index, but improves the mechanical properties of the flame-retardant TPU composite material. When 10 parts of EG are added, the flame-retardant TPU composite material can self-extinguish without dripping, reaching a V-1 rating, but its mechanical properties are significantly compromised.

[0046] Compared with the data in Example 4, EG@LDH has little impact on the mechanical properties of flame-retardant TPU composites. This may be because modifying LDH with KH550 to form LDH-Si before coating with EG increases the compatibility between the flame retardant and the TPU matrix, reduces damage to the matrix, and maintains good mechanical properties while imparting a certain degree of flame retardancy to the TPU matrix.

[0047] Comparing the data from Examples 2, 5, 6, and 7, APP had a relatively small impact on the mechanical properties of the flame-retardant TPU composite material. This may be because APP has good compatibility with the TPU matrix, causing minimal damage to the matrix, but it cannot impart good flame-retardant properties to the TPU matrix. While a simple blend of EG, LDH, and KH550, compared to adding EG alone, slightly reduced the impact of the flame retardant on the mechanical properties of the flame-retardant TPU composite material, its mechanical properties remained poor, and the flame-retardant rating did not reach V-0.

[0048] Data from Examples 1-3 show that EG@LDH-APP can efficiently impart good flame retardancy to the TPU matrix with minimal impact on mechanical properties. This is likely because the addition of APP promotes the formation of a dense char layer to protect the matrix during the composite material's combustion process. Furthermore, the modification of LDH-APP with KH550 followed by EG coating increases the flame retardant efficiency and compatibility with the TPU matrix, thus maintaining good mechanical properties while imparting excellent flame retardancy to the TPU matrix.

[0049] Compared to conventional halogen-free flame retardants using EG, this patent utilizes a novel halogen-free flame retardant, EG@LDH-APP. This flame retardant can form a char layer to protect the matrix in the early stages of combustion, preventing the composite material from generating molten droplets during combustion. Furthermore, this flame retardant has good compatibility with the TPU matrix, which can maintain good flame retardant performance while reducing the impact of fillers on the mechanical properties of the composite material.

[0050] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A halogen-free flame retardant modified thermoplastic polyurethane composite material, characterized in that, The composite material is made by melt blending the following components: Thermoplastic polyurethane (TPU) matrix; and a halogen-free flame retardant with a core-shell structure, wherein the halogen-free flame retardant is ammonium polyphosphate modified hydrotalcite-coated expandable graphite EG@LDH-APP.

2. The halogen-free flame retardant modified thermoplastic polyurethane composite material as described in claim 1, characterized in that: The mass ratio of the halogen-free flame retardant to the TPU matrix is ​​1:5~10.

3. The halogen-free flame retardant modified thermoplastic polyurethane composite material as described in claim 1, characterized in that: The core-shell structure of the halogen-free flame retardant is as follows: expandable graphite EG is used as the core, and polyphosphate APP-modified hydrotalcite LDH is used as the shell, with polyphosphate APP-modified hydrotalcite LDH coating the surface of the expandable graphite.

4. The method for preparing the halogen-free flame retardant modified thermoplastic polyurethane composite material according to any one of claims 1 to 3, characterized in that, Includes the following steps: Preparation of ammonium polyphosphate modified hydrotalcite LDH-APP; Preparation of ammonium polyphosphate modified hydrotalcite coated expandable graphite EG@LDH-APP; The TPU matrix is ​​melt-plasticized, and then expanded graphite EG@LDH-APP coated with ammonium polyphosphate-modified hydrotalcite is added and blended to obtain a halogen-free flame retardant modified thermoplastic polyurethane composite material.

5. The preparation method according to claim 4, characterized in that: The blending is performed by melt blending at 180~190°C.

6. The preparation method according to claim 4, characterized in that, The preparation method of the ammonium polyphosphate modified hydrotalcite includes, The hydrotalcite was dispersed in anhydrous ethanol, KH550 was added, and a dehydration condensation reaction occurred in an oil bath to obtain an LDH-KH550 solution. Ammonium polyphosphate was dispersed in a 50% aqueous ethanol solution, then added to an LDH-KH550 solution, and reacted in an oil bath. After filtration, washing, drying and pulverization, ammonium polyphosphate modified hydrotalcite LDH-APP was obtained.

7. The preparation method according to claim 6, characterized in that: The oil bath heating temperature is 60~70℃, and the time is 8 hours.

8. The preparation method according to claim 4, characterized in that: The preparation method of the ammonium polyphosphate modified hydrotalcite-coated expandable graphite includes, Ammonium polyphosphate-modified hydrotalcite and expandable graphite were dispersed in water, and then the ammonium polyphosphate-modified hydrotalcite dispersion was added to the expandable graphite dispersion. Electrostatic self-assembly occurred in an oil bath to obtain an ammonium polyphosphate-modified hydrotalcite-coated expandable graphite dispersion. After being filtered, washed, dried and pulverized in sequence, expandable graphite coated with ammonium polyphosphate-modified hydrotalcite is obtained.

9. The preparation method according to claim 8, characterized in that: The oil bath heating temperature is 70~80℃, and the time is 6 hours.

10. Application of the halogen-free flame retardant modified thermoplastic polyurethane composite material prepared by the preparation method according to claims 4 to 9.

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