A polyurethane outer packaging material synergistically flame-retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane and its preparation method

Abstract

The present invention discloses a polyurethane outer packaging material synergistically flame-retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane, and a preparation method thereof, belonging to the field of development of flame-retardant materials. In the present invention, molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane are added into a polyurethane soft foam system for synergistic flame retardancy, and a flame-retarded polyurethane soft foam is synthesized by a one-step foaming process. The obtained flame-retarded polyurethane soft foam material has extremely good flame-retardant effects, and flame-retardant indexes such as limiting oxygen index, thermal stability, heat release rate and total heat release, smoke production rate and total smoke production, and residual carbon are all greatly improved. Through the synergistic flame-retardant effect of molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane, a polyurethane outer packaging material with extremely outstanding flame-retardant effects is developed, which has excellent application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of flame retardant material development, and particularly relates to a polyurethane outer packaging material synergistically flame retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane, and a preparation method thereof. Background Art

[0002] Due to the flammability of polyurethane flexible foam, flame retardant treatment is required to inhibit its combustion or reduce the combustion rate. In a fire, the toxic gases and particulate matter in the smoke generated by combustion are often more lethal than the fire and heat in the fire. Therefore, developing a highly efficient, halogen-free, low-smoke and low-toxicity flame retardant FPUF is the key to expanding the application fields of FPUF. Ammonium polyphosphate (APP) is widely used as an efficient and non-toxic inorganic phosphorus-based flame retardant. Jiang Haohao et al. prepared polyurethane foam with APP as the flame retardant. After flame retardant treatment, the LOI of the foam reached 23.6%, and the vertical burning reached the UL94 V-0 level. Jiang Changchen et al. added AlPO4 and APP as flame retardants to polyurethane flexible foam. The addition of AlPO4 and APP formed a carbon layer on the foam surface, effectively playing the role of flame retarding combustibles. Xue Jianying et al. expected to enhance the flame retardancy of polyurethane foam through the synergistic flame retardant effect of APP and Mg(OH)2. Li et al. used β-cyclodextrin modified APP as the flame retardant. The flame spread rate of the polyurethane flexible foam decreased by 67.3% compared with that of the pure foam, the extinguishing time decreased by 2.1 s, and the peak heat release rate of the flame retardant foam decreased by 43.8%. More significantly, molybdenum trioxide (MoO3) has a smoke suppression performance. Ma Dengyufeng et al. used APP, C5H 12 O4, and MoO3 as a composite synergistic flame retardant to enhance the flame retardancy of phenolic foam, and found that the oxygen index of the flame retardant phenolic foam increased by about 73%. Liu Xiu et al. studied the smoke suppression effect of MoO3 on expandable EG and APP composite flame retardant polyurethane foam plastics, and found that MoO3 has good flame retardant and smoke suppression effects, and also improves the thermal stability of the foam. Hu Boyuan et al. respectively studied the effects of cuprous oxide and MoO3 on the oxygen index, smoke density, heat release rate and char residue rate of flame retardant polyurethane foam, and found that the smoke generation amount of MoO3 flame retardant polyurethane foam is less and the char residue rate is higher.

[0003] The present invention uses APP, MoO3 and POSS as composite synergistic flame retardants, and uses a one-step foaming synthesis method to prepare flame retardant FPUF. Summary of the Invention

[0004] The object of the present invention is to overcome the shortcomings of the prior art and provide a polyurethane outer packaging material synergistically flame-retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane, and a preparation method thereof, belonging to the field of flame-retardant material development. In the present invention, molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane are added to the polyurethane soft foam system for synergistic flame retardancy, and the flame-retarded polyurethane soft foam is synthesized by a one-step foaming process. The obtained flame-retarded polyurethane soft foam material has extremely good flame retardancy, and its limiting oxygen index, thermal stability, heat release rate and total heat release, smoke production rate and total smoke production, char residue and other flame retardant indexes have been greatly improved. Through the synergistic flame retardant effect of molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane, a polyurethane outer packaging material with extremely prominent flame retardancy has been developed, which has excellent application prospects.

[0005] To achieve the above technical effects, the following technical solutions are adopted:

[0006] A preparation method of a polyurethane outer packaging material synergistically flame-retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane, comprising the following steps:

[0007] Step S1: Polyether polyol PPO, stannous isooctanoate, triethylenediamine A33, silicone oil L580, deionized water, ammonium polyphosphate APP, molybdenum trioxide MoO3 and organosilsesquioxane POSS are successively added to a reaction vessel, and a stirrer is used to stir and mix evenly to obtain a mixed solution;

[0008] Step S2: Toluene diisocyanate TDI-80 is added to another reaction vessel, and the mixed solution obtained in step S1 is quickly added to toluene diisocyanate TDI-80, and stirred and mixed evenly; after the foaming reaction proceeds for a certain time, the mixture is transferred to a mold to foam naturally; after the foam foams stably, the foam is allowed to stand to obtain a polyurethane soft foam, which is the polyurethane outer packaging material.

[0009] Further, in step S1, the molecular weight of the polyether polyol PPO is 3000-4000.

[0010] Further, in step S1, the mass ratio of the polyether polyol PPO, stannous isooctanoate, triethylenediamine A33, silicone oil L580, deionized water and toluene diisocyanate TDI-80 is 30-40:0.1-0.15:0.1-0.15:0.1-0.15:3-5:15-20.

[0011] Further, in step S1, the total mass of the ammonium polyphosphate APP, molybdenum trioxide MoO3 and organosilsesquioxane POSS accounts for 14%-16% of the total mass of the polyether polyol PPO, stannous isooctanoate, triethylenediamine A33, silicone oil L580, deionized water and toluene diisocyanate TDI-80.

[0012] Further, in the step S1, the mass ratio of ammonium polyphosphate APP, molybdenum trioxide MoO3 and organosilsesquioxane POSS is 13 - 28:14 - 26:3 - 6.

[0013] Further, in the step S2, after the foaming reaction proceeds for 10 - 15 s, the mixture is transferred to a mold to allow it to foam naturally.

[0014] Further, in the step S2, the foam standing temperature is 25°C - 40°C.

[0015] Further, the foam standing time is 24 - 48 h.

[0016] A polyurethane outer packaging material synergistically flame - retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane is prepared by using any one of the above - mentioned preparation methods.

[0017] An application of a polyurethane outer packaging material synergistically flame - retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane in the field of flame - retardant of lithium battery outer packaging.

[0018] The beneficial effects of the present invention are as follows:

[0019] The present invention discloses a polyurethane outer packaging material synergistically flame - retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane and a preparation method, belonging to the field of development of flame - retardant materials. The present invention adds molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane to carry out synergistic flame - retardance in the polyurethane soft foam system, synthesizes flame - retarded polyurethane soft foam through a one - step foaming process. The obtained flame - retarded polyurethane soft foam material has extremely good flame - retardant effects, and its flame - retardant indexes such as limiting oxygen index, thermal stability, heat release rate and total heat release, smoke production rate and total smoke production, char residue, etc. are all greatly improved. Through the synergistic flame - retardant effect of molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane, a polyurethane outer packaging material with extremely prominent flame - retardant effects is developed, which has excellent application prospects. Description of the Drawings

[0020] Figure 1 It is the limiting oxygen index curve graph of the polyurethane soft foam FPUF material in the embodiment of the present invention;

[0021] Figure 2 It is the heat release rate curve of the polyurethane soft foam FPUF material in the embodiment of the present invention;

[0022] Figure 3 It is the total heat release curve of the polyurethane soft foam FPUF material in the embodiment of the present invention;

[0023] Figure 4 It is the smoke production rate curve of the polyurethane soft foam FPUF material in the embodiment of the present invention;

[0024] Figure 5 This is the total smoke production curve of the polyurethane flexible foam FPUF material in the embodiments of the present invention;

[0025] Figure 6 This is a digital photo of the residual char after combustion of the polyurethane flexible foam FPUF material in the cone calorimeter atmosphere in the embodiments of the present invention. Specific embodiments

[0026] The following further describes the present invention with reference to the accompanying drawings. The protection scope of the present invention is not limited to the following:

[0027] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present invention.

[0028] The experimental raw materials for preparing the polyurethane flexible foam FPUF include: polyether polyol (PPO), triethylenediamine (A33), stannous octoate, silicone oil (L580), deionized water, and toluene diisocyanate (TDI-80). The specifications and manufacturer information of the experimental raw materials are shown in Table 1:

[0029] Table 1 Experimental raw materials

[0030]

[0031] The production specifications and manufacturers of the flame retardants used are: ammonium polyphosphate APP (TY-1324), Shandong Yousuo Chemical Technology Co., Ltd.; molybdenum trioxide, Shandong Yousuo Chemical Technology Co., Ltd.; organic sesquisiloxane POSS: industrial grade, with a structural benzene content of 41% - 49% and a structural silicon content of 33% - 44%, BASF Company, Germany.

[0032] Example 1:

[0033] The preparation method is as follows:

[0034] (1) Sequentially add 30 g of polyether polyol PPO, 0.1 g of stannous octoate, 0.1 g of triethylenediamine A33, 0.15 g of silicone oil L580, 3 parts of deionized water, 4.48 g of ammonium polyphosphate APP, 2.24 g of molybdenum trioxide MoO3, and 0.48 g of organic sesquisiloxane POSS into a beaker, and stir with an electric stirrer to make them evenly mixed.

[0035] (2) Add 15 g of TDI to another beaker, and quickly add it to the above mixed solution, stir to make it evenly mixed. After the foaming reaction proceeds for 10 seconds, transfer the mixture to a mold to allow it to foam naturally. After the foam has foamed stably, place the foam in an environment of 25°C - 40°C and let it stand for 24 hours to obtain a flexible polyurethane foam FPUF-A, abbreviated as polyurethane foam A.

[0036] Example 2:

[0037] The preparation method is as follows:

[0038] (1) Sequentially add 30 g of polyether polyol PPO, 0.1 g of stannous octoate, 0.1 g of triethylenediamine A33, 0.15 g of silicone oil L580, 3 parts of deionized water, 2.08 g of ammonium polyphosphate APP, 4.16 g of molybdenum trioxide MoO3, and 0.96 g of organosilsesquioxane POSS into a beaker, and use an electric stirrer to stir to make it evenly mixed.

[0039] (2) Add 15 g of TDI to another beaker, and quickly add it to the above mixed solution, stir to make it evenly mixed. After the foaming reaction proceeds for 10 seconds, transfer the mixture to a mold to allow it to foam naturally. After the foam has foamed stably, place the foam in an environment of 25°C - 40°C and let it stand for 24 hours to obtain a flexible polyurethane foam FPUF-B, abbreviated as polyurethane foam B.

[0040] Comparative Example 1:

[0041] Based on Example 1, the preparation method of Comparative Example 1 is exactly the same as that of Example 1. The only difference is that all 4.48 g of ammonium polyphosphate APP, 2.24 g of molybdenum trioxide MoO3, and 0.48 g of organosilsesquioxane POSS in Example 1 are removed, and other preparation methods are exactly the same as those in the example, to obtain a flexible polyurethane foam FPUF-C, abbreviated as polyurethane foam C.

[0042] Comparative Example 2:

[0043] Based on Example 1, the preparation method of Comparative Example 1 is exactly the same as that of Example 1. The only difference is that the flame retardant formulation in Example 1: 4.48 g of ammonium polyphosphate APP, 2.24 g of molybdenum trioxide MoO3, and 0.48 g of organosilsesquioxane POSS is replaced with: 6.72 g of ammonium polyphosphate APP and 0.48 g of organosilsesquioxane POSS, and other preparation methods are exactly the same as those in the example, to obtain a flexible polyurethane foam FPUF-D, abbreviated as polyurethane foam D.

[0044] Comparative Example 3:

[0045] Based on Example 1, the preparation method of Comparative Example 1 is exactly the same as that of Example 1. The only difference is that the flame retardant formulation in Example 1: 4.48 g of ammonium polyphosphate APP, 2.24 g of molybdenum trioxide MoO3, and 0.48 g of polyhedral oligomeric silsesquioxane POSS is replaced with: 6.72 g of molybdenum trioxide MoO3 and 0.48 g of polyhedral oligomeric silsesquioxane POSS. Other preparation methods are exactly the same as those in the example, obtaining flexible polyurethane foam FPUF-E, abbreviated as polyurethane foam E.

[0046] Comparative Example 4:

[0047] Based on Example 1, the preparation method of Comparative Example 1 is exactly the same as that of Example 1. The only difference is that the flame retardant formulation in Example 1: 4.48 g of ammonium polyphosphate APP, 2.24 g of molybdenum trioxide MoO3, and 0.48 g of polyhedral oligomeric silsesquioxane POSS is replaced with: 4.48 g of ammonium polyphosphate APP, 2.72 g of molybdenum trioxide MoO3. Other preparation methods are exactly the same as those in the example, obtaining flexible polyurethane foam FPUF-F, abbreviated as polyurethane foam F.

[0048] Comparative Example 5:

[0049] Based on Example 1, the preparation method of Comparative Example 1 is exactly the same as that of Example 1. The only difference is that the flame retardant formulation in Example 1: 4.48 g of ammonium polyphosphate APP, 2.24 g of molybdenum trioxide MoO3, and 0.48 g of polyhedral oligomeric silsesquioxane POSS is replaced with: 7.20 g of ammonium polyphosphate APP. Other preparation methods are exactly the same as those in the example, obtaining flexible polyurethane foam FPUF-G, abbreviated as polyurethane foam G.

[0050] Comparative Example 6:

[0051] Based on Example 1, the preparation method of Comparative Example 1 is exactly the same as that of Example 1. The only difference is that the flame retardant formulation in Example 1: 4.48 g of ammonium polyphosphate APP, 2.24 g of molybdenum trioxide MoO3, and 0.48 g of polyhedral oligomeric silsesquioxane POSS is replaced with: 7.20 g of molybdenum trioxide MoO3. Other preparation methods are exactly the same as those in the example, obtaining flexible polyurethane foam FPUF-H, abbreviated as polyurethane foam H.

[0052] Comparative Example 7:

[0053] Taking Example 1 as a reference, the preparation method of Comparative Example 1 is exactly the same as that of Example 1, and the only difference is that the flame retardant formulation in Example 1: 4.48 g of ammonium polyphosphate APP, 2.24 g of molybdenum trioxide MoO3 and 0.48 g of polyhedral oligomeric silsesquioxane POSS is replaced with: 7.20 g of polyhedral oligomeric silsesquioxane POSS, and other preparation methods are exactly the same as those in the example, obtaining flexible polyurethane foam FPUF-I, simply referred to as polyurethane foam I.

[0054] Based on the flexible polyurethane foam FPUF materials prepared in Examples 1-2 and Comparative Examples 1-7, their flame retardant performance was evaluated and characterized:

[0055] Experimental results and analysis:

[0056] 1. Limiting oxygen index (LOI)

[0057] By testing the limiting oxygen index (LOI) of FPUF samples, the flammability of FPUF can be observed. A high oxygen index indicates that the foam is difficult to burn, while a low oxygen index indicates that the foam is easy to burn.

[0058] As Figure 1 shown, it is the limiting oxygen index curve graph of the flexible polyurethane foam FPUF materials (FPUF-A, FPUF-B, FPUF-C, FPUF-D, FPUF-E, FPUF-F, FPUF-G, FPUF-H, FPUF-I) prepared in Examples 1-2 and Comparative Examples 1-7.

[0059] From Figure 1 it can be seen that the oxygen index of the unflame-retarded polyurethane foam FPUF-C is 17.5%; the oxygen index of the polyurethane foam containing only an equal amount of one flame retardant or containing an equal amount of two flame retardants is between 19% and 20%, but when the polyurethane foam system contains three flame retardants, its oxygen index rises significantly to about 40%, having an extremely good flame retardant effect. The three flame retardants act synergistically in the flexible polyurethane foam material, enhancing each other and achieving an excellent flame retardant effect.

[0060] 2. Thermal stability

[0061] Using a thermogravimetric analyzer, the relationship between the mass of the FPUF sample and temperature can be observed, and the thermal stability of FPUF can be studied and analyzed;

[0062] As shown in Table 2, Table 2 is the pyrolysis parameters obtained from the TG curve and DTG curve graph of the FPUF sample, where T -5％ is the initial thermal decomposition temperature, and T max1 , T max2 are the maximum thermal weight loss temperatures.

[0063] As can be seen from Table 2, two weight loss stages occurred in all FPUFs. The first weight loss stage was due to the breaking of polyurethane bonds, resulting in the release of isocyanate and polyol. The second weight loss stage was the degradation and release of residual polyether oligomers and refractory polyols in the foam. The initial thermal decomposition temperature of the unflamed polyurethane flexible foam FPUF-C was 252 °C, the maximum thermal weight loss temperature in the first weight loss stage was 276 °C, and the maximum thermal weight loss temperature in the second weight loss stage was 363 °C. The char residue was only 0.55%. For polyurethane foams containing only equal amounts of one flame retardant or equal amounts of two flame retardants, their respective flame retardant parameters improved, but not significantly. However, when the polyurethane foam system contained three flame retardants, all of its flame retardant parameters increased significantly, showing excellent flame retardant effects. The three flame retardants synergistically interacted and enhanced each other in the polyurethane flexible foam material, achieving excellent flame retardant effects.

[0064] Table 2 Pyrolysis parameters of polyurethane flexible foam FPUF

[0065]

[0066] 3. Heat release rate and total heat release

[0067] The flame retardant performance parameters of polyurethane foams can be analyzed using a cone calorimeter. The cone calorimeter is a standard method for testing the combustion performance of polymer materials. It can simulate the combustion of materials under real fire conditions and effectively analyze the flame retardant performance of the polymer materials to be tested.

[0068] As Figure 2 and Figure 3 shown, the heat release rate and total heat release curves of the polyurethane flexible foam FPUF materials (FPUF-A, FPUF-B, FPUF-C, FPUF-D, FPUF-E, FPUF-F, FPUF-G, FPUF-H, FPUF-I) prepared in Examples 1-2 and Comparative Examples 1-7 are presented. Table 3 shows the cone calorimeter parameters (pkHRR and THR) obtained from Figure 2 and Figure 3 . It can be seen from Figure 2 and Figure 3 that the unflamed polyurethane flexible foam FPUF-C not only had the highest pkHRR (480.41 kW / m 2 ), but also the highest THR (27.20 MJ / m 2 ), indicating a high fire hazard. For polyurethane foams containing only equal amounts of one flame retardant or equal amounts of two flame retardants, their pkHRR and THR decreased, but not significantly. However, when the polyurethane foam system contained three flame retardants, their pkHRR and THR decreased significantly, showing excellent flame retardant effects. The three flame retardants synergistically interacted and enhanced each other in the polyurethane flexible foam material, achieving excellent flame retardant effects.

[0069] Table 3 Cone calorimeter parameters (pkHRR and THR)

[0070]

[0071] 4. Smoke production rate and total smoke production

[0072] It should be noted that in a fire, the truly most lethal substances are often the smoke dust and toxic and harmful gases generated by combustion, rather than the flames and heat. Therefore, it is very important to analyze the smoke production rate (SPR) and total smoke production (TSP) during the combustion of flexible polyurethane foam and reduce the release amount of smoke particles generated during the combustion process.

[0073] As Figure 4 and Figure 5 shown, the smoke production rate and total smoke production curves of the flexible polyurethane foam FPUF materials (FPUF-A, FPUF-B, FPUF-C, FPUF-D, FPUF-E, FPUF-F, FPUF-G, FPUF-H, FPUF-I) prepared in Examples 1-2 and Comparative Examples 1-7 are presented. Table 4 shows the cone calorimeter parameters (SPR and TSP) obtained from Figure 4 and Figure 5 . It can be seen from Figure 4 and Figure 5 that the unflamed FPUF still has the highest peak smoke production rate (0.071 m 2 / s) and total smoke production (3.53 m 2 ). For the polyurethane foams containing only an equal amount of one flame retardant or two flame retardants in equal amounts, their SPR and TSP are reduced, but not significantly. However, when the polyurethane foam system contains three flame retardants, their SPR and TSP decrease significantly, showing an extremely good flame retardant effect. The three flame retardants act synergistically in the flexible polyurethane foam material, enhancing each other and achieving an excellent flame retardant effect.

[0074] Table 4 Cone calorimeter parameters (SPR and TSP)

[0075]

[0076] 5. Residual carbon analysis

[0077] Residual carbon is an important basis for analyzing the flame retardant properties of substances. Generally speaking, a dense and continuous residual carbon can significantly reduce the fire hazard of polymer materials. A dense residual carbon can also indicate that the flame-retarded flexible polyurethane foam has good flame retardancy, while the unflamed FPUF will not leave or leave only a small amount of residual carbon after combustion.

[0078] As Figure 6As shown, the digital photos of the residual char after combustion of the polyurethane flexible foam FPUF materials (FPUF-A, FPUF-B, FPUF-C, FPUF-D, FPUF-E, FPUF-F, FPUF-G, FPUF-H, FPUF-I) prepared in Examples 1-2 and Comparative Examples 1-7 in the atmosphere of a cone calorimeter; as Figure 6 shown, the unflamed polyurethane flexible foam FPUF-C has completely burned due to the lack of flame retardant addition and its high flammability, and there is almost no residual char. For the polyurethane foams containing only an equal amount of one flame retardant or containing an equal amount of two flame retardants, the residual char has increased, but not significantly. However, when the polyurethane foam system contains three flame retardants, the residual char increases significantly, and it can be observed that the surface of this char layer is relatively smooth. This char layer plays a role in heat insulation and oxygen isolation, effectively reducing the heat release rate, total heat release, and total smoke production during the combustion of the foam. It has an extremely good flame retardant effect. The three flame retardants act synergistically in the polyurethane flexible foam material, enhancing each other and achieving an excellent flame retardant effect.

[0079] In summary, the present invention discloses a polyurethane outer packaging material synergistically flame-retarded by molybdenum trioxide, ammonium polyphosphate, and organosilsesquioxane, and a preparation method thereof, belonging to the field of flame-retardant material development. The present invention adds molybdenum trioxide, ammonium polyphosphate, and organosilsesquioxane to the polyurethane flexible foam system for synergistic flame retardancy, and synthesizes the flame-retarded polyurethane flexible foam through a one-step foaming process. The obtained flame-retarded polyurethane flexible foam material has an extremely good flame retardant effect, and its flame retardant indexes such as limiting oxygen index, thermal stability, heat release rate and total heat release, smoke production rate and total smoke production, and residual char have been greatly improved. Through the synergistic flame retardant effect of molybdenum trioxide, ammonium polyphosphate, and organosilsesquioxane, a polyurethane outer packaging material with extremely outstanding flame retardant effect has been developed, which has excellent application prospects.

[0080] Up to this point, those skilled in the art recognize that although the embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the content disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and determined to cover all these other variations or modifications.

Claims

1. A preparation method of a polyurethane outer packaging material synergistically flame-retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane, characterized in that, The preparation method includes the following steps: Step S1: Sequentially add polyether polyol PPO, stannous octoate, triethylenediamine A33, silicone oil L580, deionized water, ammonium polyphosphate APP, molybdenum trioxide MoO3, and organosilsesquioxane POSS into a reaction vessel, and stir with a stirrer to mix evenly to obtain a mixed solution; Step S2: Add toluene diisocyanate TDI-80 into another reaction vessel, and quickly add the mixed solution obtained in Step S1 into toluene diisocyanate TDI-80, and stir to mix evenly; after the foaming reaction proceeds for a certain time, transfer the mixture to a mold to allow it to foam naturally; after the foam foams stably, let the foam stand still to obtain a polyurethane flexible foam, which is the polyurethane outer packaging material; In the said Step S1, the mass ratio of polyether polyol PPO, stannous octoate, triethylenediamine A33, silicone oil L580, deionized water, and toluene diisocyanate TDI-80 is 30-40:0.1-0.15:0.1-0.15:0.1-0.15:3-5:15-20; In the said Step S1, the total mass of ammonium polyphosphate APP, molybdenum trioxide MoO3, and organosilsesquioxane POSS accounts for 14%-16% of the total mass of polyether polyol PPO, stannous octoate, triethylenediamine A33, silicone oil L580, deionized water, and toluene diisocyanate TDI-80; In the said Step S1, the mass ratio of ammonium polyphosphate APP, molybdenum trioxide MoO3, and organosilsesquioxane POSS is 13-28:14-26:3-6.

2. The preparation method of a polyurethane outer packaging material with synergistic flame retardancy of molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane as described in claim 1, characterized in that, In the said Step S1, the molecular weight of polyether polyol PPO is 3000-4000.

3. The preparation method of a polyurethane outer packaging material with synergistic flame retardancy of molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane as described in claim 1, characterized in that, In the said Step S2, after the foaming reaction proceeds for 10-15 s, transfer the mixture to a mold to allow it to foam naturally.

4. The preparation method of a polyurethane outer packaging material synergistically flame-retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane as described in claim 1, characterized in that, In the said Step S2, the standing temperature of the foam is 25°C-40°C.

5. The preparation method of a polyurethane outer packaging material synergistically flame-retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane as described in claim 1, characterized in that, In the said Step S2, the standing time of the foam is 24-48 h.

6. A polyurethane outer packaging material synergistically flame-retarded by molybdenum trioxide, ammonium polyphosphate and organosilsesquioxane, characterized in that, Prepared by using the preparation method according to any one of claims 1-5.

7. Application of a polyurethane outer packaging material with synergistic flame retardancy of molybdenum trioxide, ammonium polyphosphate, and organosilsesquioxane in the field of flame retardancy of lithium battery outer packaging as claimed in claim 6.

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