High-strength flame-retardant PP composite material and preparation method thereof

Abstract

The invention relates to a high-strength flame-retardant PP composite material and a preparation method thereof, and belongs to the technical field of high polymer materials. The high-strength flame-retardant PP composite material comprises the following raw materials in parts by weight: 20-50 parts of isotatic polypropylene, 60-80 parts of modified polypropylene, 10-12 parts of a flame retardant, 1-2 parts of a coupling agent and 0.3-0.5 part of a lubricant. Polysiloxane is adopted to graft polypropylene, the molecular weight and molecular chain of polypropylene are increased, breakage of the molecular chain of polypropylene is inhibited, hydroxyl polyphenyl propyl siloxane forms a stable polysiloxane network structure after cracking, polypropylene is greatly endowed with excellent flame retardance, in addition, the flame retardant is added to release nitrogen to destroy the combustion condition, and the flame retardance is improved. According to the high-strength flame-retardant PP composite material and the preparation method thereof, the composite material is subjected to temperature change stretching in the transverse and longitudinal directions, the trend of crystals is controlled, and the crystals are refined, so that a spatial network structure is formed, and the high-strength flame-retardant PP composite material is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials and relates to a high-strength flame-retardant PP composite material and a preparation method thereof. Background Art

[0002] Polypropylene (PP) is a thermoplastic resin with excellent overall properties, widely used in cables, electrical materials, conventional furniture, chemical-resistant materials, the automotive industry, building materials, interior decoration, children's toys, and other fields. However, unmodified PP has a limiting oxygen index of only 17%, making it highly ignitable in air. Furthermore, melting and dripping occur during heating, exacerbating the spread of fire and limiting its further application across various industries. Summary of the Invention

[0003] The present invention relates to a high-strength flame-retardant PP composite material and a preparation method thereof, belonging to the technical field of polymer materials. The high-strength flame-retardant PP composite material disclosed in the present invention comprises the following raw materials in parts by weight: 20-50 parts of isotactic polypropylene, 60-80 parts of modified polypropylene, 10-12 parts of a flame retardant, 1-2 parts of a coupling agent, and 0.3-0.5 parts of a lubricant. The present invention adopts polysiloxane grafted onto polypropylene to increase the molecular weight and molecular chain of polypropylene, inhibit the breakage of the polypropylene molecular chain, and the hydroxy polyphenyl propyl siloxane forms a stable polysiloxane network structure after cracking, which greatly gives the polypropylene excellent flame retardancy. In addition, the addition of the flame retardant releases nitrogen to destroy the combustion conditions, further enhancing the flame retardant effect of the composite material. The present invention adopts temperature-dependent stretching of the composite material in the horizontal and vertical directions to control the direction of crystallization, refine the crystals, and form a spatial network structure, thereby obtaining a high-strength flame-retardant PP composite material.

[0004] The purpose of the present invention can be achieved through the following technical solutions: A high-strength flame-retardant PP composite material comprises the following raw materials in parts by weight: 20-50 parts of isotactic polypropylene, 60-80 parts of modified polypropylene, 10-12 parts of a flame retardant, 1-2 parts of a coupling agent, and 0.3-0.5 parts of a lubricant. The flame retardant is composed of melamine polyphosphate and toluene diphenyl phosphate in a mass ratio of 1-2:1.

[0005] Furthermore, the preparation method of the modified polypropylene comprises the following steps: A1: Preheat polypropylene, add hydroxypolyphenylpropylsiloxane and acetone, and mix and stir to form a mixture; A2: Add a catalyst to the mixture, heat and stir, cool to room temperature, separate the solid and liquid, and dry the solid to obtain modified polypropylene.

[0006] Furthermore, in step A1, the mass ratio of polypropylene, hydroxypolyphenylpropylsiloxane and acetone is 5-10:3:15-18, the preheating temperature and time are 80-120° C. and 30-60 min respectively, and the stirring time is 30-45 min.

[0007] Furthermore, in step A2, the mass ratio of the mixture to the catalyst is 10-16:2-4, wherein the catalyst is dibutyltin dilaurate, the temperature and time of the heating and stirring are 50-60° C. and 1-2 h, respectively, and the drying temperature is 70-80° C.

[0008] Furthermore, the preparation method of the high-strength flame-retardant PP composite material comprises the following steps: (1) Put the coupling agent, lubricant and flame retardant into the mixer and mix them. Then add isotactic polypropylene and modified polypropylene and heat and mix them. Then cool and shape them through metal rollers to form rectangular blocks. (2) The rectangular block is placed on a stretching machine equipped with a temperature control box, and temperature-controlled stretching is performed in the horizontal and vertical directions respectively. After cooling to room temperature, it becomes a high-strength flame-retardant PP composite material.

[0009] Furthermore, the temperature, time and stirring speed of the heating and mixing in step (1) are 240-260° C., 5-10 min and 400-500 r / min respectively, and the ratio of the thickness, length and width of the rectangular block is 0.5-0.8:1.2-1.5:1.

[0010] Furthermore, the stretching speed in step (2) is 3-4 mm / s, and the stretching length elongation is 5-8%.

[0011] Furthermore, the temperature-variable stretching in step (2) is divided into three step-by-step cooling intervals, specifically, the first interval temperature is 150-135°C, the second interval temperature is 125-110°C, and the third interval temperature is 100-85°C, and the cooling rate of the temperature change is 8-10°C / min.

[0012] Beneficial effects of the present invention: 1. The present invention uses polysiloxane grafted onto polypropylene to increase the molecular weight and molecular chain of polypropylene, inhibiting the breakage of the polypropylene molecular chain. The hydroxypolyphenylpropylsiloxane forms a stable polysiloxane network structure after cracking, which greatly gives polypropylene excellent flame retardancy. In addition, the addition of the flame retardant releases nitrogen to destroy the combustion conditions, further enhancing the flame retardant effect of the composite material. 2. The present invention uses temperature-variable stretching of the composite material in the horizontal and vertical directions, and controls the direction of crystallization and refines the crystals by controlling the temperature cooling range to form a spatial network structure, thereby obtaining a high-strength flame-retardant PP composite material. DETAILED DESCRIPTION

[0013] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0014] The isotactic polypropylene involved in the present invention was purchased from Guangdong Xiaoda Chemical Co., Ltd. with a product number of 25085-53-4; the coupling agent was KH550; the lubricant was oleamide; melamine polyphosphate was purchased from Shandong Qiansheng Chemical Co., Ltd. with a CAS number of 15541-60-3; the degree of polymerization of polypropylene was 2000; hydroxypolyphenylpropylsiloxane was purchased from Shanghai Dow Corning Co., Ltd. with an Mn of 2500; dibutyltin dilaurate was purchased from Hunan Qilu New Materials Technology Co., Ltd. with a CAS number of 77-58-7; and hydroxypolydimethylsiloxane was purchased from Yantai Dayi Chemical Co., Ltd. with an Mn of 1000.

[0015] Example 1

[0016] A high-strength flame-retardant PP composite material comprises the following raw materials in parts by weight: 20 parts of isotactic polypropylene, 60 parts of modified polypropylene, 10 parts of a flame retardant, 1 part of a coupling agent, and 0.3 parts of a lubricant. The flame retardant is composed of melamine polyphosphate and toluene diphenyl phosphate in a mass ratio of 1:1.

[0017] The preparation method of the modified polypropylene comprises the following steps: A1: Preheat polypropylene, add hydroxypolyphenylpropylsiloxane and acetone, and mix and stir to form a mixture; A2: Add a catalyst to the mixture, heat and stir, cool to room temperature, separate the solid and liquid, and dry the solid to obtain modified polypropylene.

[0018] In the step A1, the mass ratio of polypropylene, hydroxypolyphenylpropylsiloxane and acetone is 5:3:15, the preheating temperature and time are 80° C. and 30 minutes respectively, and the stirring time is 30 minutes.

[0019] The mass ratio of the mixture to the catalyst in step A2 is 10:2, wherein the catalyst is dibutyltin dilaurate, the temperature and time of the heating and stirring are 50° C. and 1 hour respectively, and the drying temperature is 70° C.

[0020] The preparation method of the high-strength flame-retardant PP composite material comprises the following steps: (1) Put the coupling agent, lubricant and flame retardant into the mixer and mix them. Then add isotactic polypropylene and modified polypropylene and heat and mix them. Then cool and shape them through metal rollers to form rectangular blocks. (2) The rectangular block is placed on a stretching machine equipped with a temperature control box, and temperature-controlled stretching is performed in the horizontal and vertical directions respectively. After cooling to room temperature, it becomes a high-strength flame-retardant PP composite material.

[0021] The temperature, time and stirring speed of the heating and mixing in step (1) are 240° C., 5 min and 400 r / min respectively, and the ratio of the thickness, length and width of the rectangular block is 0.5:1.2:1.

[0022] The stretching speed in the step (2) is 3 mm / s, and the stretching length elongation is 5%.

[0023] The temperature-changing stretching in step (2) is divided into three step-by-step cooling intervals, specifically, the first interval temperature is 150-135°C, the second interval temperature is 125-110°C, and the third interval temperature is 100-85°C. The cooling rate of the temperature change is 8°C / min.

[0024] Example 2

[0025] A high-strength flame-retardant PP composite material comprises the following raw materials in parts by weight: 35 parts of isotactic polypropylene, 70 parts of modified polypropylene, 11 parts of a flame retardant, 1.5 parts of a coupling agent, and 0.4 parts of a lubricant. The flame retardant is composed of melamine polyphosphate and toluene diphenyl phosphate in a mass ratio of 1.5:1.

[0026] The preparation method of the modified polypropylene comprises the following steps: A1: Preheat polypropylene, add hydroxypolyphenylpropylsiloxane and acetone, and mix and stir to form a mixture; A2: Add a catalyst to the mixture, heat and stir, cool to room temperature, separate the solid and liquid, and dry the solid to obtain modified polypropylene.

[0027] In step A1, the mass ratio of polypropylene, hydroxypolyphenylpropylsiloxane and acetone is 7.5:3:16.5, the preheating temperature and time are 100° C. and 45 minutes respectively, and the stirring time is 40 minutes.

[0028] The mass ratio of the mixture to the catalyst in step A2 is 13:3, wherein the catalyst is dibutyltin dilaurate, the temperature and time of the heating and stirring are 55° C. and 1.5 h respectively, and the drying temperature is 75° C.

[0029] The preparation method of the high-strength flame-retardant PP composite material comprises the following steps: (1) Put the coupling agent, lubricant and flame retardant into the mixer and mix them. Then add isotactic polypropylene and modified polypropylene and heat and mix them. Then cool and shape them through metal rollers to form rectangular blocks. (2) The rectangular block is placed on a stretching machine equipped with a temperature control box, and temperature-controlled stretching is performed in the horizontal and vertical directions respectively. After cooling to room temperature, it becomes a high-strength flame-retardant PP composite material.

[0030] The temperature, time and stirring speed of the heating and mixing in step (1) are 250° C., 7 min and 450 r / min respectively, and the ratio of the thickness, length and width of the rectangular block is 0.65:1.35:1.

[0031] The stretching speed in the step (2) is 3.5 mm / s, and the stretching length elongation is 6.5%.

[0032] The temperature-changing stretching in step (2) is divided into three step-by-step cooling intervals, specifically, the first interval temperature is 150-135°C, the second interval temperature is 125-110°C, and the third interval temperature is 100-85°C. The cooling rate of the temperature change is 9°C / min.

[0033] Example 3

[0034] A high-strength flame-retardant PP composite material comprises the following raw materials in parts by weight: 50 parts of isotactic polypropylene, 80 parts of modified polypropylene, 12 parts of a flame retardant, 2 parts of a coupling agent, and 0.5 parts of a lubricant. The flame retardant is composed of melamine polyphosphate and toluene diphenyl phosphate in a mass ratio of 2:1.

[0035] The preparation method of the modified polypropylene comprises the following steps: A1: Preheat polypropylene, add hydroxypolyphenylpropylsiloxane and acetone, and mix and stir to form a mixture; A2: Add a catalyst to the mixture, heat and stir, cool to room temperature, separate the solid and liquid, and dry the solid to obtain modified polypropylene.

[0036] In the step A1, the mass ratio of polypropylene, hydroxypolyphenylpropylsiloxane and acetone is 10:3:18, the preheating temperature and time are 120° C. and 60 min respectively, and the stirring time is 45 min.

[0037] The mass ratio of the mixture to the catalyst in step A2 is 16:4, wherein the catalyst is dibutyltin dilaurate, the temperature and time of the heating and stirring are 60° C. and 2 h respectively, and the drying temperature is 80° C.

[0038] The preparation method of the high-strength flame-retardant PP composite material comprises the following steps: (1) Put the coupling agent, lubricant and flame retardant into the mixer and mix them. Then add isotactic polypropylene and modified polypropylene and heat and mix them. Then cool and shape them through metal rollers to form rectangular blocks. (2) The rectangular block is placed on a stretching machine equipped with a temperature control box, and temperature-controlled stretching is performed in the horizontal and vertical directions respectively. After cooling to room temperature, it becomes a high-strength flame-retardant PP composite material.

[0039] The temperature, time and stirring speed of the heating and mixing in step (1) are 260° C., 10 min and 500 r / min respectively, and the ratio of the thickness, length and width of the rectangular block is 0.8:1.5:1.

[0040] The stretching speed in the step (2) is 4 mm / s, and the stretching length elongation is 8%.

[0041] The temperature-changing stretching in step (2) is divided into three step-by-step cooling intervals, specifically, the first interval temperature is 150-135°C, the second interval temperature is 125-110°C, and the third interval temperature is 100-85°C. The cooling rate of the temperature change is 10°C / min.

[0042] Comparative Example 1 On the basis of Example 2, the isotactic polypropylene in the raw material was removed and replaced with an equal weight portion of modified polypropylene. Other conditions were the same as in Example 2.

[0043] Comparative Example 2 On the basis of Example 2, the hydroxypolyphenylpropylsiloxane was replaced by hydroxypolydimethylsiloxane of equal mass, and other conditions were the same as those in Example 2.

[0044] Comparative Example 3 On the basis of Example 2, the modified polypropylene was replaced by polypropylene of equal mass, and other conditions were consistent with Example 2.

[0045] Comparative Example 4 On the basis of Example 2, melamine polyphosphate was removed and replaced with an equal mass of toluene diphenyl phosphate. Other conditions were the same as those in Example 2.

[0046] Comparative Example 5 On the basis of Example 2, toluene diphenyl phosphate was removed and replaced with melamine polyphosphate of equal mass. Other conditions were the same as those in Example 2.

[0047] Comparative Example 6 Based on Example 2, a high-strength flame-retardant PP composite material is provided. The high-strength flame-retardant PP composite material includes the following raw materials in parts by weight: 35 parts of isotactic polypropylene, 70 parts of modified polypropylene, 11 parts of a flame retardant, 1.5 parts of a coupling agent, and 0.4 parts of a lubricant. The flame retardant is composed of melamine polyphosphate and toluene diphenyl phosphate in a mass ratio of 1.5:1.

[0048] The preparation method of the modified polypropylene comprises the following steps: A1: Preheat polypropylene, add hydroxypolyphenylpropylsiloxane and acetone, and mix and stir to form a mixture; A2: Add a catalyst to the mixture, heat and stir, cool to room temperature, separate the solid and liquid, and dry the solid to obtain modified polypropylene.

[0049] In step A1, the mass ratio of polypropylene, hydroxypolyphenylpropylsiloxane and acetone is 7.5:3:16.5, the preheating temperature and time are 100° C. and 45 minutes respectively, and the stirring time is 40 minutes.

[0050] The mass ratio of the mixture to the catalyst in step A2 is 13:3, wherein the catalyst is dibutyltin dilaurate, the temperature and time of the heating and stirring are 55° C. and 1.5 h respectively, and the drying temperature is 75° C.

[0051] The preparation method of the high-strength flame-retardant PP composite material comprises the following steps: (1) The coupling agent, lubricant and flame retardant are put into a mixer and mixed, and then the isotactic polypropylene and modified polypropylene are added and heated and mixed, and then the mixture is extruded into a twin-screw extruder to obtain a high-strength flame-retardant PP composite material.

[0052] The temperature, time and stirring speed of the heating and mixing in step (1) are 250° C., 7 min and 450 r / min respectively.

[0053] Comparative Example 7 Based on Example 2, a high-strength flame-retardant PP composite material is provided. The high-strength flame-retardant PP composite material includes the following raw materials in parts by weight: 35 parts of isotactic polypropylene, 70 parts of modified polypropylene, 11 parts of a flame retardant, 1.5 parts of a coupling agent, and 0.4 parts of a lubricant. The flame retardant is composed of melamine polyphosphate and toluene diphenyl phosphate in a mass ratio of 1.5:1.

[0054] The preparation method of the modified polypropylene comprises the following steps: A1: Preheat polypropylene, add hydroxypolyphenylpropylsiloxane and acetone, and mix and stir to form a mixture; A2: Add a catalyst to the mixture, heat and stir, cool to room temperature, separate the solid and liquid, and dry the solid to obtain modified polypropylene.

[0055] In step A1, the mass ratio of polypropylene, hydroxypolyphenylpropylsiloxane and acetone is 7.5:3:16.5, the preheating temperature and time are 100° C. and 45 minutes respectively, and the stirring time is 40 minutes.

[0056] The mass ratio of the mixture to the catalyst in step A2 is 13:3, wherein the catalyst is dibutyltin dilaurate, the temperature and time of the heating and stirring are 55° C. and 1.5 h respectively, and the drying temperature is 75° C.

[0057] The preparation method of the high-strength flame-retardant PP composite material comprises the following steps: (1) Put the coupling agent, lubricant and flame retardant into the mixer and mix them. Then add isotactic polypropylene and modified polypropylene and heat and mix them. Then cool and shape them through metal rollers to form rectangular blocks. (2) The rectangular block is placed on a stretching machine equipped with a temperature control box, and temperature-controlled stretching is performed in the horizontal and vertical directions respectively. After cooling to room temperature, it becomes a high-strength flame-retardant PP composite material.

[0058] The temperature, time and stirring speed of the heating and mixing in step (1) are 250° C., 7 min and 450 r / min respectively, and the ratio of the thickness, length and width of the rectangular block is 0.65:1.35:1.

[0059] The stretching speed in the step (2) is 3.5 mm / s, and the stretching length elongation is 6.5%.

[0060] The temperature-variable stretching in step (2) is divided into two step-by-step temperature-lowering intervals, specifically, the temperature in the first interval is 150-135°C, and the temperature in the second interval is 100-85°C. The temperature-lowering rate of the temperature-variable stretching is 9°C / min.

[0061] Comparative Example 8 A high-strength flame-retardant PP composite material comprises the following raw materials in parts by weight: 35 parts of isotactic polypropylene, 70 parts of modified polypropylene, 11 parts of a flame retardant, 1.5 parts of a coupling agent, and 0.4 parts of a lubricant. The flame retardant is composed of melamine polyphosphate and toluene diphenyl phosphate in a mass ratio of 1.5:1.

[0062] The preparation method of the modified polypropylene comprises the following steps: A1: Preheat polypropylene, add hydroxypolyphenylpropylsiloxane and acetone, and mix and stir to form a mixture; A2: Add a catalyst to the mixture, heat and stir, cool to room temperature, separate the solid and liquid, and dry the solid to obtain modified polypropylene.

[0063] In step A1, the mass ratio of polypropylene, hydroxypolyphenylpropylsiloxane and acetone is 7.5:3:16.5, the preheating temperature and time are 100° C. and 45 minutes respectively, and the stirring time is 40 minutes.

[0064] The mass ratio of the mixture to the catalyst in step A2 is 13:3, wherein the catalyst is dibutyltin dilaurate, the temperature and time of the heating and stirring are 55° C. and 1.5 h respectively, and the drying temperature is 75° C.

[0065] The preparation method of the high-strength flame-retardant PP composite material comprises the following steps: (1) Put the coupling agent, lubricant and flame retardant into the mixer and mix them. Then add isotactic polypropylene and modified polypropylene and heat and mix them. Then cool and shape them through metal rollers to form rectangular blocks. (2) The rectangular block is placed on a stretching machine equipped with a temperature control box, and temperature-controlled stretching is performed in the horizontal and vertical directions respectively. After cooling to room temperature, it becomes a high-strength flame-retardant PP composite material.

[0066] The temperature, time and stirring speed of the heating and mixing in step (1) are 250° C., 7 min and 450 r / min respectively, and the ratio of the thickness, length and width of the rectangular block is 0.65:1.35:1.

[0067] The stretching speed in the step (2) is 3.5 mm / s, and the stretching length elongation is 6.5%.

[0068] The temperature range of the temperature-changing stretching in step (2) is 150-85°C, and the cooling rate of the temperature-changing stretching is 9°C / min.

[0069] Performance Testing The high-strength flame-retardant PP composite materials prepared in Examples 1-3 and Comparative Examples 1-8 were used as specimens, and the specimens were cut into: 40 mm long × 5 mm wide × 2 mm thick; the tensile strength of the specimens was tested according to GB / T1040-2006 standard, and the tensile speed was 50 mm / min; the flexural strength of the specimens was tested according to GB / T9341-2008 standard, and the bending speed was 2 mm / min; the notched impact strength of the specimens was tested according to GB / T1843-2008, with a notch bottom radius (mm) of 0.25±0.05 and a notch retained thickness (mm) of 8.0±0.2; the flame retardancy of the specimens was tested according to UL94; the limiting oxygen index of the specimens was tested with reference to GB / T2406-93; the results are shown in Tables 1 and 2.

[0070] Table 1 Test results

[0071] From the results in Table 1, it can be seen that the tensile strength, flexural strength, and notched impact strength of Examples 1-3 are all greater than those of Comparative Examples 1-8, among which Comparative Example 3 has the lowest tensile strength, flexural strength, and notched impact strength. Comparative Example 1 removes isotactic polypropylene, which reduces mechanical strength because isotactic polypropylene can strengthen the interface and refine crystals through heterogeneous nucleation. Comparative Example 2 replaces hydroxypolyphenylpropylsiloxane with hydroxypolydimethylsiloxane, which reduces mechanical strength due to reduced molecular weight and molecular chain. Comparative Example 3 uses unmodified polypropylene, which reduces segment stability and weakens rigidity, resulting in weakened mechanical strength. Comparative Examples 4-5 replace the flame retardant with a minimal effect on the mechanical strength of the material. Comparative Example 6 does not undergo a temperature-dependent stretching process, resulting in disordered crystallization that adversely affects mechanical strength. Comparative Example 7 removes the second temperature interval of the temperature-dependent stretching process, resulting in a large temperature span and poor crystal refinement, resulting in reduced mechanical strength. Comparative Example 8 uses continuous cooling, which leaves no buffer time for crystal growth and easily leads to stacking, reducing mechanical strength.

[0072] Table 2 Test results

[0073] As can be seen from Table 2, the flame retardancy ratings of Examples 1-3 and Comparative Examples 1-8 are both V-0, and the limiting oxygen index of Example 1-3 is greater than that of Comparative Examples 2-8. In Comparative Examples 2-3, the hydroxypolyphenylpropylsiloxane is removed or replaced with hydroxypolydimethylsiloxane. This prevents the hydroxypolyphenylpropylsiloxane from forming a stable polysiloxane network structure after cracking, leading to a decrease in the limiting oxygen index. In Comparative Examples 4-5, a single flame retardant reduces the limiting oxygen index. In Comparative Example 6, the temperature-dependent stretching step is omitted, resulting in a disordered crystal arrangement that is easily exposed to air and reduces the limiting oxygen index. In Comparative Examples 7-8, the temperature-dependent stretching step involves a large or continuous temperature drop, causing crystal coarsening and stacking, which provides conditions for combustion and reduces the limiting oxygen index.

[0074] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A high-strength flame-retardant PP composite material, characterized in that: The high-strength flame-retardant PP composite material includes the following raw materials in parts by weight: 20-50 parts of isotactic polypropylene, 60-80 parts of modified polypropylene, 10-12 parts of flame retardant, 1-2 parts of coupling agent, and 0.3-0.5 parts of lubricant. The flame retardant is composed of melamine polyphosphate and toluene diphenyl phosphate in a mass ratio of 1-2:

1.

2. The high-strength flame-retardant PP composite material according to claim 1, characterized in that: The preparation method of the modified polypropylene comprises the following steps: A1: Preheat polypropylene, add hydroxypolyphenylpropylsiloxane and acetone, and mix and stir to form a mixture; A2: Add a catalyst to the mixture, heat and stir, cool to room temperature, separate the solid and liquid, and dry the solid to obtain modified polypropylene.

3. The high-strength flame-retardant PP composite material according to claim 2, characterized in that: In the step A1, the mass ratio of polypropylene, hydroxypolyphenylpropylsiloxane and acetone is 5-10:3:15-18, the preheating temperature and time are 80-120° C. and 30-60 min respectively, and the stirring time is 30-45 min.

4. The high-strength flame-retardant PP composite material according to claim 2, characterized in that: The mass ratio of the mixture to the catalyst in step A2 is 10-16:2-4, wherein the catalyst is dibutyltin dilaurate, the temperature and time of the heating and stirring are 50-60° C. and 1-2 hours respectively, and the drying temperature is 70-80° C.

5. A method for preparing the high-strength flame-retardant PP composite material according to claim 1, characterized in that: The preparation method of the high-strength flame-retardant PP composite material comprises the following steps: (1) Put the coupling agent, lubricant and flame retardant into the mixer and mix them. Then add isotactic polypropylene and modified polypropylene and heat and mix them. Then cool and shape them through metal rollers to form rectangular blocks. (2) The rectangular block is placed on a stretching machine equipped with a temperature control box, and temperature-controlled stretching is performed in the horizontal and vertical directions respectively. After cooling to room temperature, it becomes a high-strength flame-retardant PP composite material.

6. The method for preparing a high-strength flame-retardant PP composite material according to claim 5, characterized in that: The temperature, time and stirring speed of the heating and mixing in step (1) are 240-260° C., 5-10 min and 400-500 r / min respectively, and the ratio of the thickness, length and width of the rectangular block is 0.5-0.8:1.2-1.5:

1.

7. The method for preparing a high-strength flame-retardant PP composite material according to claim 5, characterized in that: The stretching speed in the step (2) is 3-4 mm / s, and the stretching length elongation is 5-8%.

8. The method for preparing a high-strength flame-retardant PP composite material according to claim 5, characterized in that: The temperature-changing stretching in step (2) is divided into three step-by-step cooling intervals, specifically, the first interval temperature is 150-135°C, the second interval temperature is 125-110°C, and the third interval temperature is 100-85°C. The cooling rate of the temperature change is 8-10°C / min.

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