A graphene-modified flame-retardant polypropylene material and preparation method thereof

Abstract

The invention discloses a graphene-modified flame-retardant polypropylene material and a preparation method thereof. Graphene is dispersed through maleic anhydride grafted polypropylene to form a master batch, and flame retardants such as piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide) are added; the graphene-modified flame-retardant polypropylene material is prepared by master batch-melting-smelting, the dispersibility of graphene in polypropylene is enhanced, the graphene is evenly dispersed in the mixed system, and the dispersion and combination of the flame retardant in the polypropylene matrix are further enhanced; the good barrier properties of graphene and the intumescent flame retardant produce a good synergistic effect, so that the compactness of the carbon layer formed by combustion is enhanced, and the flame retardant performance of the material is significantly improved.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and particularly relates to a graphene-modified flame-retardant polypropylene material and a preparation method thereof. Background Art

[0002] As a typical thermoplastic polyolefin, polypropylene has been widely used in various civil and industrial fields due to its advantages such as easy processing, excellent mechanical properties, low cost and chemical corrosion resistance. Polypropylene is composed only of carbon and hydrogen elements, so it is highly flammable. The combustion of flammable gases generated by the cracking of polypropylene will promote further pyrolysis and combustion of the material. Under the action of sufficient external heat source, the polypropylene chain is thermally decomposed into low molecular weight volatile products, which will burn after mixing with oxygen on the surface of the matrix. The heat of the burned part will be transferred to the unburned polymer, promoting its further pyrolysis until all the polymer is burned out. The flammability of polypropylene limits its application, and the risk of uncontrolled combustion has also attracted great attention from the government, society and scientific researchers.

[0003] Halogen-containing flame retardants, especially chlorine-containing and bromine-containing compounds, are the most effective flame retardants for polypropylene flame retardancy. However, halogen-containing flame retardants produce toxic and corrosive gases when burned, and some halogen-containing flame retardants can be enriched in the human body and have carcinogenic risks, which pose a potential threat to human health and the environment. These halogen-containing flame retardants are being eliminated. Therefore, with the development of high fire safety of polymer composites and the demand for human health, research on halogen-free flame retardants is booming. Common halogen-free flame retardants can be subdivided into: mineral flame retardants, phosphorus-containing flame retardants, nitrogen-containing flame retardants, intumescent flame retardants, etc. Among these halogen-free flame retardants, intumescent flame retardants with the advantages of low smoke, non-toxicity, and anti-dripping are considered to be the most promising. Intumescent flame retardants are mainly composed of three parts: acid source, carbonizing agent, and foaming agent. The most commonly used and typical intumescent flame retardant is composed of ammonium polyphosphate / pentaerythritol / melamine. However, the formula of this traditional intumescent flame retardant is sensitive to water vapor. The presence of low molecular weight compounds such as pentaerythritol and melamine makes the flame retardant easily seep out, resulting in a serious decrease in flame retardancy. In addition, in most cases, an intumescent flame retardant greater than 30% of the plastic mass must be used to achieve the desired flame retardancy. Such a high intumescent flame retardant loading will damage the mechanical properties and processability of polypropylene.

[0004] Graphene has excellent electrical, mechanical and thermal properties. Compared with other plastic composite material additives, it has a small amount of addition and good dispersibility. Graphene sheets form nano-scale dispersion in the plastic matrix, which has great potential in improving the flame retardant properties, mechanical properties and antistatic properties of plastics.

[0005] Some existing technologies combine graphene and intumescent flame retardants and use their synergistic effect to achieve good results. CN 103387712 A discloses a graphene-modified flame-retardant polypropylene material and a preparation method thereof. Melamine polyphosphate, ammonium polyphosphate, and pentaerythritol are used as the main flame retardant, and modified graphene is added as a flame retardant synergist to prepare a flame retardant polypropylene material, which effectively improves the flame retardant properties and mechanical properties of polypropylene. CN 103012953 A discloses a flame-retardant polypropylene / graphene / carbon nanotube nanocomposite material and a preparation method thereof. Graphene, carbon nanotubes and polypropylene are mixed by a solution method to obtain a polypropylene masterbatch containing graphene and carbon nanotubes, and then an intumescent flame retardant, a polypropylene masterbatch containing graphene and carbon nanotubes and polypropylene are melt blended to obtain a flame-retardant polypropylene / graphene / carbon nanotube nanocomposite material. The intumescent flame retardant, graphene and carbon nanotubes have a synergistic flame retardant effect, thereby improving the flame retardant effect on polymer materials, reducing the amount of flame retardant used in polymer materials, and reducing the cost of flame retardant materials. CN 106947159 A prepares a flame-retardant polypropylene material by mixing 75-89% polypropylene, 10-20% encapsulated ammonium polyphosphate and 1-5% modified graphene oxide. The extremely strong barrier effect of graphene reduces the probability of oxygen entering the substrate and avoiding the overflow of combustible gas after the substrate is heated, greatly reducing the amount of flame retardant used, and effectively improving the flame retardant effect.

[0006] Although the prior art provides a method for enhancing the flame retardancy of polypropylene materials by using graphene / intumescent flame retardants, the types of intumescent flame retardants used are very limited, and are generally composed of melamine or melamine derivatives, ammonium polyphosphate, and pentaerythritol. Summary of the invention

[0007] In view of the above-mentioned defects of the prior art, the purpose of the present invention is to provide a graphene-modified flame-retardant polypropylene material and a preparation method thereof. The technical problem to be solved is to provide a new type of compound intumescent flame retardant, which has good synergistic enhancement ability with graphene and can significantly improve the flame retardant properties of polypropylene under the premise of having a low impact on the mechanical properties of polypropylene.

[0008] In order to achieve the purpose of the present invention, a method for preparing a graphene-modified flame-retardant polypropylene material is provided, and the specific steps are: heating and melting polypropylene, then adding graphene and a flame retardant, stirring and mixing, then heating and kneading, and forming a sample under hot pressing, that is, the graphene-modified flame-retardant polypropylene material prepared by the present invention.

[0009] Preferably, the weight ratio of graphene, polypropylene and flame retardant is (0.5-2): (70-100): (10-30), the melting temperature is 180-190°C, the flame retardant is one or a combination of focused piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine), the drum speed is 50-80r / min, the mixing temperature is 190-220°C, and the time is 10-30min; the hot pressing temperature is 190-200°C, and the pressure is 10-12MPa.

[0010] The specific preparation steps of the focused piperazine phosphate are as follows: dissolving 80 to 100 parts by weight of piperazine in 100 to 300 parts by weight of ethanol at a rotation speed of 300 to 500 r / min and a temperature of 40 to 60° C. to form a solution I; dropping the solution I into 100 to 300 parts by weight of phosphoric acid at a rate of 30 to 50 parts by weight / min, filtering the precipitated precipitate, and drying it at 60 to 100° C. for 16 to 24 hours to obtain piperazine pyrophosphate; treating 200 to 250 parts by weight of piperazine pyrophosphate in a nitrogen atmosphere at 250 to 300° C. for 2 to 4 hours, cooling naturally, then washing with water, and drying it at 60 to 100° C. for 16 to 24 hours to obtain the focused piperazine phosphate.

[0011] The preparation method of sulfonylbis(ethane-2,1-diyl)bis(diphenylphosphine oxide) is as follows: 60 to 100 parts by weight of diphenylphosphine oxide and 15 to 30 parts by weight of divinyl sulfone are added to 400 to 600 parts by weight of toluene to obtain a mixed system, the temperature of the mixed system is raised to 120 to 150° C., the mixture is stirred at a stirring speed of 300 to 500 r / min for 16 to 24 hours, the insoluble matter is filtered out, washed three times with acetone or ethanol, and dried at 60 to 80° C. for 6 to 10 hours to obtain sulfonylbis(ethane-2,1-diyl)bis(diphenylphosphine oxide).

[0012] Due to its excellent physical properties, graphene is regarded as a potential multifunctional polymer nanofiller. If graphene can be well dispersed in a polymer matrix, then even if a small amount of graphene is added, the performance of the material will be greatly improved. Due to the chemical inertness of graphene, the strong van der Waals forces and π-π conjugation between the sheets, and the huge differences in polarity and compatibility, it is difficult to achieve good dispersion of graphene in a polypropylene matrix. Maleic acid can usually be used to graft polypropylene to improve the compatibility of graphene and polypropylene, which can inhibit the agglomeration of graphene to a certain extent.

[0013] More preferably, a method for preparing a graphene-modified flame-retardant polypropylene material comprises the following steps:

[0014] Step 1: 10 to 50 parts by weight of maleic anhydride grafted polypropylene is heated and melted at 180 to 190° C., 1 to 10 parts by weight of graphene is added, kneaded at a speed of 50 to 80 r / min and a temperature of 190 to 220° C. for 10 to 30 minutes, and hot-pressed at a pressure of 10 to 12 MPa and a temperature of 190 to 200° C. to obtain a maleic anhydride grafted polypropylene masterbatch containing graphene;

[0015] Step 2: 60-100 parts by weight of polypropylene and 5-10 parts by weight of the maleic anhydride grafted polypropylene masterbatch containing graphene obtained in step 1 are heated and melted at 180-190° C., 15-30 parts by weight of a flame retardant are added, and the mixture is kneaded at a speed of 50-80 r / min and 190-220° C. for 10-30 min, and hot-pressed at a pressure of 10-12 MPa and a temperature of 190-200° C. to obtain a finished product, which is the graphene-modified flame-retardant polypropylene material prepared by the present invention.

[0016] In order to better utilize the reinforcing effect of graphene, it is extremely necessary to modify its surface to improve dispersion and control the interface structure. There are two main types of graphene modification: covalent and non-covalent modification. Covalent bond modification is to achieve the grafting of the modifier through the reaction with the oxygen-containing functional groups on the graphene surface. Non-covalent modification is to use a variety of interactions, such as π-π interaction, van der Waals force, electrostatic attraction, etc., to adsorb the modifier to the surface of the graphene sheet. Compared with covalent modification, non-covalent bond modification is simple and does not change the original chemical structure of graphene.

[0017] Further preferably, the graphene in step 1 is modified, and the specific steps are: adding 1 to 2 parts by weight of graphene to 250 to 500 parts by weight of water, ultrasonically treating for 30 to 60 minutes at an ultrasonic power of 50 to 200 W, a frequency of 20 to 130 KHz, and a temperature of 20 to 40 ° C to obtain a graphene suspension a; adding 5 to 20 parts of phosphoric acid to the suspension a stirred at a stirring speed of 300 to 500 r / min, raising the temperature of the suspension a to 60 to 100 ° C, stirring the reaction for 5 to 10 hours, and then centrifuging at 8000 to 10000 r / min for 20 to 30 minutes to collect insoluble matter, washing three times with ethanol and water respectively, and then freeze-drying at -45 to -55 ° C for 24 to 36 hours to obtain modified graphene.

[0018] Further preferably, the flame retardant is composed of focused piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide), and the weight ratio of focused piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide) is (1:1) to (5:1).

[0019] The present invention also provides a graphene-modified flame-retardant polypropylene material, which is prepared according to the above method.

[0020] Beneficial effects of the present invention:

[0021] (1) The graphene-modified flame-retardant polypropylene material prepared by the present invention does not contain halogen, has good flame retardant effect, has a wide range of applications, and meets environmental protection requirements; the preparation operation of the flame-retardant composite material is simple, the raw materials are easily available, and it is easy to industrialize production.

[0022] (2) The present invention forms a masterbatch by dispersing graphene on maleic anhydride grafted polypropylene, and prepares a graphene-modified flame-retardant polypropylene material by masterbatch-melting-blending, thereby enhancing the dispersibility of graphene in polypropylene and making the graphene evenly dispersed in the mixed system; the good barrier properties of graphene and the intumescent flame retardant produce a good synergistic effect, thereby improving the density, degree of graphitization, and thermal stability of the carbon layer formed by combustion, and significantly improving the flame retardant performance of the material; at the same time, the strength of polypropylene decreases within 10%.

[0023] (3) The present invention provides a method for preparing a novel composite intumescent flame retardant, which can achieve a significant flame retardant effect by adding 15% of the amount of polypropylene. The flame retardant has good dispersion in polypropylene and good adhesion to polypropylene. Such a structure can prevent the migration or even overflow of the flame retardant in the polypropylene material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The following are scanning electron micrographs of the tensile section of polypropylene (a) and the product prepared in Example 5 (b). DETAILED DESCRIPTION

[0025] Introduction of some materials in this invention:

[0026] Graphene uses single-layer graphene with a single-layer rate of >99%, a sheet diameter of 0.5-5μm, a thickness of 0.8-1.2nm, and a purity of >99%, and is purchased from Jiangsu Nanjing Xianfeng Nanomaterial Technology Co., Ltd.

[0027] Polypropylene, provided by Sinopec Hainan Refining and Chemical Co., Ltd., grade S1003.

[0028] Phosphoric acid, mass concentration 85%, was purchased from Sinopharm Chemical Reagent Co., Ltd.

[0029] Diphenylphosphine: CAS number is 4559-70-0.

[0030] Divinyl sulfone: CAS number is 77-77-0.

[0031] Introduction and standards of some tests:

[0032] Impact strength is measured by cantilever beam impact tester according to GB / T1843-2008 plastic cantilever beam impact strength test standard, sample size is 10×10×1.5mm3 , Each group of samples was tested five times and the average value was obtained;

[0033] The tensile strength was tested on a universal testing machine according to GB / T 1040.1-2018, the test standard for the tensile properties of plastics. The sample size was 62.5×3.25×0.7mm. 3 Dumbbell-shaped, each group of samples was tested five times to obtain the average value;

[0034] The limiting oxygen index is used to determine the difficulty of a material to burn based on the oxygen index. The limiting oxygen index is measured by a limiting oxygen index tester based on GB / T 2406.2-2009, which uses the oxygen index method to determine the combustion behavior standard; the sample size is 120×10×4mm 3 , Each group of samples was tested five times in parallel to obtain the average value;

[0035] UL-94 vertical combustion test is based on GB / T 2408-2008 Plastics combustion performance determination horizontal and vertical methods standard, and is measured by a vertical combustion instrument. The sample size is 127×12.7×3mm 3 Each group of samples was tested five times in parallel to obtain the average value.

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Example 1 A graphene-modified flame-retardant polypropylene material

[0038] 100 g of polypropylene was put into an open melting machine, and the polypropylene was completely melted at 190° C., 1 g of graphene and 15 g of focused piperazine phosphate were added, the temperature was raised to 210° C., and kneading was performed at a drum speed of 60 r / min for 15 min; hot pressing was performed at a temperature of 200° C. and a pressure of 10 MPa to obtain the product of this embodiment.

[0039] The focused piperazine phosphate is obtained by the following steps: dissolving 90 g of piperazine in 300 g of ethanol at 60° C. and a stirring rate of 300 r / min to form solution I; transferring solution I to a constant pressure funnel, dripping it into 250 g of phosphoric acid at a dripping rate of 30 g / min, filtering the precipitated precipitate, and drying it in a constant temperature oven at 100° C. for 16 hours to obtain piperazine pyrophosphate; treating 200 g of piperazine pyrophosphate in a nitrogen atmosphere at 260° C. for 3 hours to obtain focused piperazine phosphate.

[0040] Example 2 A graphene-modified flame-retardant polypropylene material

[0041] 100 g of polypropylene was put into an open melting machine, and the polypropylene was completely melted at 190° C., 1 g of graphene and 15 g of sulfonylbis(ethane-2,1-diyl)bis(diphenylphosphine) were added, the temperature was raised to 210° C., and kneaded for 15 min at a drum speed of 60 r / min; hot pressing was performed at a temperature of 200° C. and a pressure of 10 MPa to obtain the product of this embodiment.

[0042] The sulfonylbis(ethane-2,1-diyl)bis(diphenylphosphine oxide) is obtained by the following steps: at 25°C, 80g of diphenylphosphine oxide, 20g of divinyl sulfone and 480g of toluene are placed in a dry three-necked round-bottom flask connected with a mechanical stirrer, a nitrogen connection device, a thermometer and a condenser to obtain a mixed system; the temperature of the mixed system is raised to 130°C in a nitrogen atmosphere, the mixture is reacted for 16h, the mixture is naturally cooled to 25°C, an insoluble substance is obtained by suction filtration, the insoluble substance is washed three times with ethanol, and the mixture is dried in a constant temperature oven at 80°C for 10h to obtain sulfonylbis(ethane-2,1-diyl)bis(diphenylphosphine oxide).

[0043] Example 3 A graphene-modified flame-retardant polypropylene material

[0044] 100g of polypropylene was put into an open melting machine, and the polypropylene was completely melted at 190°C. 1g of graphene, 10g of focused piperazine phosphate, and 5g of sulfonylbis(ethane-2,1-diyl)bis(diphenylphosphine) were added, and the temperature was raised to 210°C. The mixture was mixed at a drum speed of 60r / min for 15min. The mixture was hot pressed at a temperature of 200°C and a pressure of 10MPa.

[0045] The product of this embodiment can be obtained.

[0046] The preparation method of the focused piperazine phosphate is the same as that of Example 1; the preparation method of the sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine) is the same as that of Example 2.

[0047] Example 4 A graphene-modified flame-retardant polypropylene material

[0048] (1) 50 g of maleic anhydride grafted polypropylene was put into an open melting machine, the maleic anhydride grafted polypropylene was completely melted at 190° C., 10 g of graphene was added, the temperature was raised to 210° C., and kneading was performed at a drum speed of 60 r / min for 30 min; hot pressing was performed at a temperature of 200° C. and a pressure of 10 MPa to obtain a maleic anhydride grafted polypropylene masterbatch containing graphene;

[0049] (2) 95 g of polypropylene and 6 g of the graphene-containing maleic anhydride grafted polypropylene masterbatch obtained in step 1 were put into an open melting machine and completely melted at 190° C., 10 g of focused piperazine phosphate and 5 g of sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine) were added, the temperature was raised to 210° C., and the mixture was mixed at a drum speed of 60 r / min for 15 min; the mixture was hot pressed at a temperature of 200° C. and a pressure of 10 MPa to obtain the product of this embodiment.

[0050] The preparation method of the focused piperazine phosphate is the same as that of Example 1; the preparation method of the sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine) is the same as that of Example 2.

[0051] Example 5 A graphene-modified flame-retardant polypropylene material

[0052] (1) 50 g of maleic anhydride grafted polypropylene was put into an open melting machine, the maleic anhydride grafted polypropylene was completely melted at 190° C., 10 g of modified graphene was added, the temperature was raised to 210° C., and kneading was performed at a drum speed of 60 r / min for 30 min; hot pressing was performed at a temperature of 200° C. and a pressure of 10 MPa to obtain a maleic anhydride grafted polypropylene masterbatch containing graphene;

[0053] (2) 95 g of polypropylene and 6 g of the graphene-containing maleic anhydride grafted polypropylene masterbatch obtained in step 1 were put into an open melting machine and completely melted at 190° C., 10 g of focused piperazine phosphate and 5 g of sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine) were added, the temperature was raised to 210° C., and the mixture was mixed at a drum speed of 60 r / min for 15 min; the mixture was hot pressed at a temperature of 200° C. and a pressure of 10 MPa to obtain the product of this embodiment.

[0054] The preparation method of the modified graphene is as follows: 1 g of graphene is added to 500 g of water, and ultrasonic treatment is performed for 60 min at an ultrasonic power of 100 W, a frequency of 50 KHz, and 25° C. to obtain a graphene suspension a; 10 g of phosphoric acid is added to the suspension a stirred at a stirring rate of 300 r / min, the temperature of the suspension a is increased to 80° C., the suspension is stirred for reaction for 6 h, and then centrifuged at 8000 r / min for 30 min, the collected insoluble matter is washed three times with ethanol and water respectively, and then freeze-dried at -55° C. for 24 h to obtain the modified graphene.

[0055] The preparation method of the focused piperazine phosphate is the same as that of Example 1; the preparation method of the sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine) is the same as that of Example 2.

[0056] Comparative Example 1: A flame retardant polypropylene material

[0057] 95g of polypropylene and 6g of maleic anhydride grafted polypropylene were put into an open melting machine and completely melted at 190°C. 10g of focused piperazine phosphate and 5g of sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine) were added. The temperature was raised to 210°C and mixed at a drum speed of 60r / min for 15min. The mixture was hot pressed at a temperature of 200°C and a pressure of 10MPa to obtain the product of this comparative example.

[0058] The preparation method of the focused piperazine phosphate is the same as that of Example 1; the preparation method of the sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine) is the same as that of Example 2.

[0059] Comparative Example 2: A graphene-modified flame-retardant polypropylene material

[0060] 95g of polypropylene, 5g of maleic anhydride grafted polypropylene, and 1g of graphene were put into an open melting machine and completely melted at 190°C. 10g of focused piperazine phosphate and 5g of sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine) were added, the temperature was raised to 210°C, and the mixture was mixed at a drum speed of 60r / min for 15min. The mixture was hot pressed at a temperature of 200°C and a pressure of 10MPa to obtain the product of this comparative example.

[0061] The preparation method of the focused piperazine phosphate is the same as that of Example 1; the preparation method of the sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine) is the same as that of Example 2.

[0062] Test Example 1 Mechanical properties test of polypropylene material

[0063] The tensile strength and impact strength tests were performed on the products obtained in the examples of the present invention and the comparative examples, and polypropylene. The results are shown in Table 1.

[0064] Table 1 Mechanical properties test results

[0065]

[0066]

[0067] The results of Example 1 and Example 2 show that after adding one of the flame retardants, piperazine phosphate or sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide), the tensile strength and impact strength of polypropylene decreased significantly; while adding piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide) as compound flame retardants, the tensile strength and impact strength increased. This may be because the added flame retardant has poor compatibility with polypropylene, and the dispersion is not uniform during the melting process, and agglomerates are formed locally, resulting in excessive local stress, which greatly reduces the mechanical strength of polypropylene; while the mechanical strength of polypropylene increased after adding piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide), which may be because the two substances have a weak interaction, which promotes dispersion in molten polypropylene. However, the mechanical strength of Comparative Example 1 without adding graphene is the lowest, which indicates that the addition of graphene can enhance the dispersion of flame retardants in polypropylene and make the combination of flame retardants and polypropylene stronger; in addition, graphene with excellent mechanical properties also bears external forces.

[0068] The scanning electron microscope images of the tensile cross-section of polypropylene and the product of Example 5 are as follows: Figure 1 As shown, it can be seen that the tensile section of polypropylene is relatively smooth, while the tensile section of Example 5 is relatively rough, and no flame retardant particles can be observed, which indicates that the flame retardant is evenly dispersed and well combined with the polypropylene matrix.

[0069] It can be seen from the results of Examples 4 to 5 and Comparative Example 2 that the polypropylene material prepared by melting graphene and maleic anhydride grafted polypropylene to prepare master batches and then melting it again with polypropylene has better mechanical properties. This is because the chemical inertness of graphene, the strong van der Waals force and π-π conjugation between the sheets, and the huge differences in polarity and compatibility make it difficult to achieve good dispersion of graphene in the polypropylene matrix; maleic acid is grafted with polypropylene to improve the compatibility of graphene and polypropylene, which can inhibit the agglomeration of graphene to a certain extent. The good dispersion of graphene in polypropylene can also promote the interaction between focused piperazine phosphate and sulfonyl bis (ethane-2,1-diyl) bis (diphenylphosphine) and polypropylene, and these factors jointly enhance the mechanical properties of polypropylene. It is worth noting that Example 5 prepared by adding modified graphene has the best mechanical properties, and the mechanical strength decreases within 10% compared with the original polypropylene, which indicates that the modified graphene has a stronger effect on the grafted polypropylene with maleic acid and better dispersibility, further enhancing the dispersion of the focused piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine) in the polypropylene matrix and improving the binding ability.

[0070] Test Example 2 Combustion Performance Test of Polypropylene Material

[0071] The products of the examples of the present invention and the comparative examples were subjected to the limiting oxygen index test and the UL-94 vertical combustion test. The results are shown in Table 2.

[0072] Table 2 Limiting oxygen index and UL-94 vertical burning test results

[0073]

[0074] Generally speaking, a material with a limiting oxygen index lower than 22% is flammable; 22% to 27% is combustible; 27% to 34% is difficult to burn; and above 34% is non-flammable. The limiting oxygen index of polypropylene is 19.5%. From the results of Examples 1 to 3, it can be seen that after adding focused piperazine phosphate or sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide), the limiting oxygen index of polypropylene increases, but is lower than 27%; and the limiting oxygen index of Example 3 obtained by compounding focused piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide) is 28.7%. These results may be because the phosphorus hydroxyl structure in the molecular structure of piperazine phosphate decomposes to produce water to dilute oxygen during combustion, the phosphoric acid produced at a higher temperature can catalyze the formation of a stronger carbon layer to inhibit the overflow of combustible gas, and the ammonia produced by decomposition can also isolate oxygen and dilute combustible gas; sulfonyl bis (ethane-2,1-diyl) bis (diphenyl phosphine oxide) is melted to produce phosphorus and sulfone radicals, these peroxide radicals delay the thermal oxidation degradation of polypropylene and promote the formation of carbon layer; at the same time, the sulfur dioxide produced by decomposition can isolate oxygen. However, sulfonyl bis (ethane-2,1-diyl) bis (diphenyl phosphine oxide) is a low molecular weight substance and has poor dispersibility in polypropylene, so it does not significantly improve the flame retardant properties of polypropylene. Focusing on the compounding of piperazine phosphate and sulfonyl bis (ethane-2,1-diyl) bis (diphenyl phosphine oxide), these combined effects not only enhance their dispersion in polypropylene, but also significantly improve the flame retardant properties of polypropylene by the synergistic effect of combustion decomposition.

[0075] The limiting oxygen index of comparative example 1 without adding graphene is 26.4%, which shows that graphene has a synergistic effect with the flame retardant in the system. The addition of graphene not only strengthens the dispersion of the flame retardant, but also improves the compactness of the carbon slag due to the extremely strong mechanical properties of graphene, promotes the formation of the carbon slag closed space, and enhances the expansion degree and flame retardant properties of the carbon layer. The effect of graphene and the free radical quenching, catalytic carbon layer formation, and non-flammable gas generated by the flame retardant produce a good synergistic effect. The polypropylene material prepared by melting graphene and maleic anhydride grafted polypropylene and then melting it again with polypropylene is helpful for the dispersion of graphene in polypropylene, and further promotes the dispersion and binding properties of the flame retardant in polypropylene. The surface modification of graphene further enhances its dispersion in polypropylene. The phosphorus-containing functional groups on the graphene surface decompose under high temperature combustion, and in-situ doping on the graphene surface catalyzes the combination of graphene and carbon layer, and further enhances the interaction between graphene and focused piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide). Therefore, Example 5 has the best limiting oxygen index of 33.4%. Based on the above good synergistic effect, the UL-94 vertical combustion rating of the product of Example 5 reaches V-1.

Claims

1. A method for preparing a graphene-modified flame-retardant polypropylene material, characterized in that: The following steps are involved: Step 1: heating and melting 10 to 50 parts by weight of maleic anhydride grafted polypropylene, adding 1 to 10 parts by weight of modified graphene, followed by mixing and hot pressing to obtain a maleic anhydride grafted polypropylene masterbatch containing modified graphene; Step 2: heat and melt 60-100 parts by weight of polypropylene and 5-10 parts by weight of the maleic anhydride grafted polypropylene masterbatch containing modified graphene obtained in step 1, add 15-30 parts by weight of flame retardant, then mix and hot-press to obtain a graphene-modified flame-retardant polypropylene material; The flame retardant is focused piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide); The specific steps of modifying graphene are: adding 1 to 2 parts by weight of graphene to 250 to 500 parts by weight of water, and ultrasonically treating for 30 to 60 minutes at an ultrasonic power of 50 to 200 W, a frequency of 20 to 130 KHz, and a temperature of 20 to 40° C. to obtain a graphene suspension a; adding 5 to 20 parts of phosphoric acid to the suspension a stirred at a stirring speed of 300 to 500 r / min, raising the temperature of the suspension a to 60 to 100° C., stirring for 5 to 10 hours, and then centrifuging at 8000 to 10000 r / min for 20 to 30 minutes to collect insoluble matter, washing with ethanol and water three times each, and then freeze-drying at -45 to -55° C. for 24 to 36 hours to obtain modified graphene; The preparation method of the focused piperazine phosphate is as follows: 80 to 100 parts by weight of piperazine is dissolved in 100 to 300 parts by weight of ethanol at a speed of 300 to 500 r / min and a temperature of 40 to 60° C. to form a solution I; Solution I is added dropwise to 100 to 300 parts by weight of phosphoric acid at a rate of 30 to 50 parts by weight / min, the precipitate is filtered, and dried at 60 to 100° C. for 16 to 24 hours to obtain piperazine pyrophosphate; 200 to 250 parts by weight of piperazine pyrophosphate is treated in a nitrogen atmosphere at 250 to 300° C. for 2 to 4 hours, cooled naturally, then washed with water, and dried at 60 to 100° C. for 16 to 24 hours to obtain focused piperazine phosphate; The preparation method of the sulfonylbis(ethane-2,1-diyl)bis(diphenylphosphine oxide) is as follows: 60 to 100 parts by weight of diphenylphosphine oxide and 15 to 30 parts by weight of divinyl sulfone are added to 400 to 600 parts by weight of toluene to obtain a mixed system, the temperature of the mixed system is raised to 120 to 150° C., the mixture is stirred at a stirring speed of 300 to 500 r / min for 16 to 24 hours, the insoluble matter is filtered out, washed three times with acetone or ethanol, and dried at 60 to 80° C. for 6 to 10 hours to obtain the sulfonylbis(ethane-2,1-diyl)bis(diphenylphosphine oxide).

2. The method for preparing a graphene-modified flame-retardant polypropylene material according to claim 1, characterized in that: The flame retardant is composed of focused piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide), and the weight ratio of focused piperazine phosphate and sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine oxide) is (1:1) to (5:1).

3. The method for preparing a graphene-modified flame-retardant polypropylene material according to claim 1, characterized in that: The melting temperatures in step 1 and step 2 are each independently 180 to 190°C.

4. The method for preparing a graphene-modified flame-retardant polypropylene material according to claim 1, characterized in that: The mixing parameters in step 1 and step 2 are independently: a rotation speed of 50 to 80 r / min, a temperature of 190 to 220° C., and a time of 10 to 30 min.

5. The method for preparing a graphene-modified flame-retardant polypropylene material according to claim 1, characterized in that: The temperatures during hot pressing in step 1 and step 2 are each independently 190 to 200°C.

6. The method for preparing a graphene-modified flame-retardant polypropylene material according to claim 1, characterized in that: The pressure during hot pressing in step 1 and step 2 is independently 10 to 12 MPa.

7. The method for preparing a graphene-modified flame-retardant polypropylene material according to claim 1, characterized in that: The method comprises the following steps: step 1: putting 50g of maleic anhydride grafted polypropylene into an open melting machine, completely melting the maleic anhydride grafted polypropylene at 190°C, adding 10g of modified graphene, heating to 210°C, and kneading for 30min at a drum speed of 60r / min; hot pressing at a temperature of 200°C and a pressure of 10MPa to obtain a maleic anhydride grafted polypropylene masterbatch containing graphene; Step 2: 95g of polypropylene and 6g of the graphene-containing maleic anhydride grafted polypropylene masterbatch obtained in step 1 are put into an open melting machine, completely melted at 190°C, 10g of focused piperazine phosphate and 5g of sulfonyl bis(ethane-2,1-diyl)bis(diphenylphosphine) are added, the temperature is raised to 210°C, and the mixing is carried out at a drum speed of 60r / min for 15min; hot pressing is carried out at a temperature of 200°C and a pressure of 10MPa to obtain the product of this embodiment; The preparation method of the modified graphene is as follows: 1 g of graphene is added to 500 g of water, and ultrasonic treatment is performed for 60 min at an ultrasonic power of 100 W, a frequency of 50 KHz, and 25° C. to obtain a graphene suspension a; 10 g of phosphoric acid is added to the suspension a stirred at a stirring rate of 300 r / min, the temperature of the suspension a is increased to 80° C., the suspension is stirred for 6 h, and then centrifuged at 8000 r / min for 30 min, the collected insoluble matter is washed three times with ethanol and water respectively, and then freeze-dried at -55° C. for 24 h to obtain the modified graphene; The sulfonylbis(ethane-2,1-diyl)bis(diphenylphosphine oxide) is obtained by the following steps: at 25°C, 80g of diphenylphosphine oxide, 20g of divinyl sulfone and 480g of toluene are placed in a dry three-necked round-bottom flask connected with a mechanical stirrer, a nitrogen connection device, a thermometer and a condenser to obtain a mixed system; the temperature of the mixed system is raised to 130°C in a nitrogen atmosphere, the mixture is reacted for 16h, the mixture is naturally cooled to 25°C, an insoluble substance is obtained by suction filtration, the insoluble substance is washed three times with ethanol, and the mixture is dried in a constant temperature oven at 80°C for 10h to obtain sulfonylbis(ethane-2,1-diyl)bis(diphenylphosphine oxide).

8. A graphene-modified flame-retardant polypropylene material, characterized in that: The flame-retardant polypropylene material is prepared by the method for preparing the graphene-modified flame-retardant polypropylene material according to any one of claims 1 to 7.

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