A polypropylene foamed flame retardant material and a method for preparing the same

Abstract

The application discloses a kind of polypropylene foamed flame-retardant materials, belongs to polypropylene foamed flame-retardant material technical field.The polypropylene composite material is prepared by foaming, characterized in that, according to percentage by weight, the polypropylene composite material includes maleic anhydride grafting crystal grain refining polypropylene particles (polypropylene-g-MAH) 85-92 parts, non-crystalline resin 45-62 parts, high molecular weight plasticizer 3-5 parts, inorganic flame retardant 20-35 parts, nucleating agent 5-10 parts, physical foaming agent 2-5 parts.The polypropylene foamed flame-retardant material is still helpful to improve the strength of polypropylene melt in higher than existing foaming temperature range, and the cell uniformity is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polypropylene foaming flame-retardant materials, in particular to a polypropylene foaming flame-retardant material and a preparation method thereof. BACKGROUND

[0002] Polypropylene is one of the five most widely used general-purpose plastics, has the advantages of low density, complete types, easy to process and shape, chemical corrosion resistance, etc., and has been widely used in national life and industrial fields. However, polypropylene has the shortcomings of flammability and poor thermal conductivity, so it is necessary to expand the application range of polypropylene and improve its flame retardant performance.

[0003] Polypropylene is a crystalline polymer, and low-temperature solid-state foaming is limited by crystallization. The crystallinity of polypropylene affects the solubility and uniformity of the dispersion of the foaming agent during solid-state foaming, thereby affecting the uniformity of the cell structure. Uniform cell structure cannot be obtained in polymers with high crystallinity, but it can be obtained in polymers with low crystallinity. At high temperatures, the melt strength of polypropylene decreases, which makes it difficult for the polymer melt to maintain the integrity of the cell structure during high-temperature foaming. When the temperature exceeds the melting point of polypropylene, the melt strength decreases rapidly, and the thin and non-viscoelastic polypropylene melt cannot withstand the tensile stress generated during bubble growth, and the gas is easily broken and the bubbles are easily broken and merged, resulting in the inability to prepare foamed products with uniform cell distribution, small cell size and high foaming ratio, thereby maintaining the integrity and uniformity of the cells. When the temperature decreases, the cells do not have time to grow and a large amount of gas is excluded from the melt, so it is difficult to prepare excellent foamed materials from ordinary polypropylene. The melting point of polypropylene occurs within a range, and the homopolymer is at 160-165℃; the copolymer is at 135-159℃, and the suitable foaming temperature range is within 155-170℃, so the suitable foaming viscosity and temperature range is very narrow, and the estimated suitable foaming temperature of polypropylene is only 4℃, which means that the foaming difficulty is very high.

[0004] During the initial stages of bubble growth in polypropylene extrusion foaming, the polypropylene melt that forms the bubble walls is subjected to biaxial stretching, resulting in strong tensile deformation. This requires a low extensional viscosity to allow for rapid bubble growth. During the subsequent bubble growth process, the extensional viscosity must increase to a sufficiently high level to maintain stable bubble growth. If the extensional viscosity of the melt decreases during this period, the already thinned bubble walls due to stretching will become even thinner under the action of internal pressure, making the bubbles prone to collapse, affecting the uniformity of bubble size and the expansion ratio of the foamed product. Therefore, the extensional viscosity and melt elasticity of the polypropylene melt at different temperatures and strain rates are key to polypropylene extrusion foaming. Excessively low melt viscosity and melt elasticity will narrow the window for polypropylene extrusion foaming, making it impossible to control stable bubble growth and produce a high-quality foamed material.

[0005] During the polypropylene foaming process, the blowing agent dissolves in the polypropylene melt. As the temperature drops, gas begins to diffuse from the melt to form bubbles. If the polypropylene crystallizes before the blowing agent diffuses out of the melt and enters the nucleated bubbles, the early solidification will result in insufficient gas to drive bubble growth. This is because the crystallization of the polypropylene restricts the movement of gas molecules, reducing the diffusion of gas into the bubbles, thereby affecting the growth of the bubbles. Summary of the Invention

[0006] In order to overcome the deficiencies of the prior art, one of the objects of the present invention is to provide a polypropylene foam flame retardant material, which helps to increase the strength of the polypropylene melt and improve the uniformity of the cells within a higher foaming temperature range than the existing foaming temperature range.

[0007] A second object of the present invention is to provide a method for preparing a polypropylene foam flame retardant material, which is simple, convenient and has low economic cost.

[0008] A third object of the present invention is to provide a lithium battery module.

[0009] One of the purposes of the present invention is achieved by the following technical solution:

[0010] A polypropylene foam flame retardant material is prepared by foaming a polypropylene composite material. Calculated by weight percentage, the polypropylene composite material comprises 85-92 parts of maleic anhydride grafted grain-refined polypropylene particles (polypropylene-g-MAH), 3-5 parts of a high molecular weight plasticizer, 20-35 parts of an inorganic flame retardant, 5-10 parts of a nucleating agent, and 2-5 parts of a physical foaming agent.

[0011] Furthermore, the polypropylene composite material includes 85 parts of maleic anhydride grafted grain-refined polypropylene particles, 50 parts of non-crystalline resin, 3 parts of high molecular weight plasticizer, 35 parts of inorganic flame retardant, 10 parts of nucleating agent, and 5 parts of physical foaming agent.

[0012] Further, the inorganic flame retardant is one or more mixtures of inorganic phosphorus flame retardants, aluminum hydroxide, and magnesium hydroxide, and diantimony trioxide.

[0013] Further, the nucleating agent is one of sodium benzoate, talcum powder, sorbitol, TMB-4, TMB-5, STARNU-100, N,N'-dicyclohexyl terephthalamide, and WBG-II.

[0014] The non-crystalline resin is one of polystyrene, acrylonitrile-butadiene-styrene copolymer, polymethyl methacrylate, and polyvinyl chloride.

[0015] Further, the physical foaming agent is one of carbon dioxide, air, and nitrogen.

[0016] The second object of the present application is achieved by using the following technical solution:

[0017] A preparation method of a polypropylene foaming flame-retardant material, comprising the following steps:

[0018] S1, preparation of grain-refined polypropylene particles: in the post-processing step of the preparation of polypropylene particles, the nucleating agent is added to the polypropylene particles after hot air drying, and then cooled to obtain the grain-refined polypropylene particles;

[0019] S2, preparation of the maleic anhydride grafted grain-refined polypropylene particles, comprising the following steps:

[0020] S21, the grain-refined polypropylene particles 100 parts, maleic anhydride 4 parts, and initiator 0.3 parts are added into a mixing kettle in proportion, heated to normal pressure reflux temperature under stirring conditions until completely dissolved, and the normal pressure reflux temperature is usually 120-150℃;

[0021] S22, the mixture is added into a reaction kettle, the temperature is controlled between 170-220℃, and the reaction time is 1-3min to obtain a reaction product;

[0022] S23, the reaction product is discharged after being slowly decompressed to atmospheric pressure, and acetone at room temperature is added as a precipitating agent, and then precipitated and filtered to obtain a grafted product;

[0023] S24, the grafted product is crushed, wrapped with filter paper, and placed in a Soxhlet extractor, ethanol is used as a solvent, and heated to reflux extraction in a water bath for 24h to obtain an extracted grafted product;

[0024] S25, the extracted grafted product is placed in a vacuum oven at 110℃ and dried for 12h to obtain the maleic anhydride grafted grain-refined polypropylene particles;

[0025] S3, blending the maleic anhydride grafted grain-refined polypropylene particles, a non-crystalline resin, a high molecular weight plasticizer, an inorganic flame retardant and a nucleating agent to obtain a blended material, wherein the blending temperature is 180° C.-210° C.;

[0026] S4. Add the physical foaming agent to the blended material for extrusion foaming, wherein the die temperature of the extrusion foaming is 160° C.-175° C. to obtain the polypropylene foamed flame retardant material.

[0027] Furthermore, in step S4, extrusion foaming is performed in a single-screw extruder at an extrusion speed of 60 r / min using a rectangular parallelepiped mold to obtain the polypropylene foam flame retardant material.

[0028] The third object of the present invention is achieved by adopting the following technical solution:

[0029] A lithium battery module comprises the polypropylene foamed flame retardant material.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The polypropylene foam flame retardant material provided by the present invention has a large grain size and uneven distribution when no nucleating agent is added. The large grain size means that the size of the amorphous region is also large, which is not conducive to the dissolution of the physical foaming agent during the foaming process. The uneven size distribution of the amorphous region means that the solubility of the physical foaming agent in different areas of the polypropylene foam is different, which will lead to inconsistent formation and growth of bubbles, and the unevenness of the formed mesopore structure. The invention adds a nucleating agent in the post-processing step of preparing polypropylene particles to obtain polypropylene particles with refined crystal grains, improves the crystallinity of polypropylene, can increase the melting point of polypropylene during the foaming process, and still helps to improve the strength of the polypropylene melt within a temperature range higher than the existing foaming temperature, so that the polypropylene melt is not easily deformed or broken when subjected to external forces; the polypropylene particles with refined crystal grains reduce the movement resistance of gas molecules in the polypropylene melt, thereby improving the diffusion efficiency of gas into bubbles, which helps the bubbles to fully grow during the foaming process and form a uniform pore structure; at a relatively high crystallization temperature, the polypropylene melt maintains good fluidity during the decomposition of the physical foaming agent and the diffusion of gas, which provides more time for gas diffusion, ensures that the gas can fully enter the bubbles and promote the growth of the bubbles, and enables the gas to be evenly dispersed in the polypropylene melt to form uniform bubbles.

[0032] (2) Polypropylene itself is a flammable material, so it is very important to modify polypropylene with flame retardant. Maleic anhydride grafted polypropylene, in which maleic anhydride acts as a compatibilizer, can improve the compatibility between inorganic flame retardant and polypropylene, and reduce the phase size. The maleic anhydride groups on it can form hydrogen bonds with inorganic flame retardants, while the polypropylene groups are compatible with non-polar polymers, thus forming a compatible layer at the interface between polypropylene and inorganic flame retardant, reducing the phase size, enhancing the heterogeneous nucleation of the foaming system, and relatively weakening the homogeneous nucleation. The foaming characteristics of the two phases of polypropylene and inorganic flame retardant are gradually weakened, resulting in a variety of non-uniform cell structures in the foaming system, making the foaming system have more uniform cell structure, and the phase size is reduced, which can improve the foaming temperature after adding inorganic flame retardant, and widen the foaming temperature window of the foaming system. High molecular weight plasticizers such as polyethylene glycol (PEG) and polyvinyl alcohol (PVA) have long molecular chains, which can form entanglement and winding between polypropylene polymers, improve the compatibility of the interface, and reduce the phase size. This entanglement can increase the interaction between molecular chains, improve the strength and elasticity of the melt.

[0033] (3) The addition of non-crystalline resin in the present application can reduce the viscosity of polypropylene melt, so that it can flow at a lower temperature, which not only reduces the softening point, but also allows the bubble to grow rapidly in the initial stage of bubble growth in polypropylene extrusion foaming; and because the non-crystalline resin has high elastic recovery performance, it can quickly recover to its original state when subjected to external force. This elasticity can improve the extension resistance of the melt, thereby increasing the melt strength and enabling it to better maintain the shape of the cell during foaming, preventing cell coalescence and rupture. DETAILED DESCRIPTION

[0034] The present application will be further described in conjunction with specific examples. It should be noted that the following described embodiments or technical features can be combined to form new embodiments without conflict.

[0035] Foaming window: refers to a specific temperature and pressure range in which the foaming process can proceed smoothly, and beyond this range, the foaming effect will be affected, which may result in uneven foaming or failure. Polypropylene is a crystalline polymer, and low-temperature solid-state foaming is limited by crystallization. High-temperature foaming of the polymer melt is not strong enough to maintain the integrity of the cell, so the operable window is narrow.

[0036] Physical meaning of melt strength

[0037] Melt strength: Melt strength refers to the ability of a polymer to support its own weight in the molten state. It reflects the resistance of the melt to tensile deformation. High melt strength means that the melt can withstand greater forces without breaking when stretched by external forces.

[0038] Effect of melt strength on extrusion foaming

[0039] Cell wall stability: During the extrusion foaming process, melt strength directly affects the stability of the cell wall. If the melt strength is too low, the cell wall cannot withstand the tensile stress generated during bubble growth, causing gas to escape and the cell to collapse and break, resulting in small foaming ratio, uneven cell distribution, and low mechanical strength of the foam.

[0040] The detailed steps for preparing polypropylene are as follows:

[0041] 1. Raw material preparation

[0042] Propylene monomer: Propylene monomer is used as raw material for the preparation of polypropylene.

[0043] Catalyst: Common catalysts include Ziegler-Natta catalysts, metallocene catalysts, etc., which can effectively initiate the polymerization of propylene monomer.

[0044] Solvent: Hexane, heptane is needed to dissolve propylene monomer, so as to better control the polymerization reaction.

[0045] 2. Polymerization reaction

[0046] Reactor type: The polymerization reaction of polypropylene can be carried out in various types of reactors, including solution method reactor, slurry method reactor, bulk method reactor and gas phase method reactor.

[0047] Polymerization conditions: Temperature: The temperature of the polymerization reaction is usually between 50℃ to 100℃, the specific temperature depends on the catalyst and process used. Pressure: The reaction pressure is generally between 0.5MPa to 3MPa, the specific pressure also depends on the process used. Reaction time: The residence time of the catalyst in the reactor is usually 1.3 to 3h. Cooling step: During the polymerization reaction, the reactor usually needs to be equipped with a cooling system to control the reaction temperature and prevent overheating. The reaction heat is removed by cooling water or other cooling medium to ensure that the reaction temperature is stable within the set range.

[0048] 3. Post-treatment

[0049] Removal of unreacted monomer: After the polymerization reaction is completed, the unreacted propylene monomer needs to be removed from the reaction system, which is usually achieved by a flash tank. The unreacted propylene is cooled and frozen into a liquid state, and then the pure propylene is recovered from the top of the fractionating column and recycled.

[0050] Catalyst deactivation: To prevent the catalyst from continuing to react during subsequent processing, it is usually necessary to add an alcohol (such as ethanol, propanol or butanol) or acetylacetone to convert the titanium and aluminum in the catalyst to a complex or an alkoxy compound at 60°C.

[0051] Water washing: The catalyst complex is converted into the aqueous phase by water washing, thereby separating it from the polypropylene slurry.

[0052] Drying: The polypropylene filter cake after removal of the solvent and catalyst is dried, usually by hot air drying. If a high-boiling solvent is used, the solvent can be first distilled with steam, and the polypropylene is suspended in the aqueous phase. After centrifugal separation, the polypropylene is dried by hot air to obtain the polypropylene.

[0053] Addition of nucleating agent: A nucleating agent is added to the dried polypropylene particles. The nucleating agent can be an organic nucleating agent (such as sodium benzoate), an inorganic nucleating agent (such as talc) or a rare earth nucleating agent (such as cerium stearate). The addition of the nucleating agent can refine the polypropylene crystal grains, increase the crystallinity, and thus improve the mechanical properties and transparency of the polypropylene.

[0054] Cooling step: During the drying process, the polypropylene particles after hot air drying need to be cooled to ensure the stability and quality of the particles. Cooling is usually achieved by a cooling air or cooling water system.

[0055] Example 1

[0056] This example provides a polypropylene foamed flame-retardant material, which is prepared by foaming a polypropylene composite material. The polypropylene composite material includes, by weight percentage, 85 parts of maleic anhydride grafted crystal grain refined polypropylene particles, 50 parts of non-crystalline resin polystyrene, 3 parts of high molecular weight plasticizer polyethylene glycol, 35 parts of inorganic flame retardant ammonium polyphosphate, 10 parts of nucleating agent sodium benzoate, and 5 parts of physical foaming agent carbon dioxide.

[0057] In this example, the maleic anhydride grafted polypropylene (polypropylene-g-MAH) is used as a compatibilizer. The polypropylene grafting polypropylene can improve the compatibility between the polar flame retardant and the polypropylene, and reduce the phase size. The maleic anhydride groups on it can form hydrogen bonds with the inorganic flame retardant, and the polypropylene groups are compatible with non-polar polymers, thereby forming a compatible layer at the interface between the polypropylene and the inorganic flame retardant, reducing the phase size, enhancing the heterogeneous nucleation of the foaming system, and relatively weakening the homogeneous nucleation. The foaming characteristics of the two phases of polypropylene and inorganic flame retardant are gradually weakened, resulting in a variety of non-uniform cell structures in the foaming system, which makes the foaming system have a more uniform cell structure and a smaller phase size, and can improve the foaming temperature after the addition of the inorganic flame retardant, and widen the foaming temperature window of the foaming system.

[0058] In this embodiment, the high molecular weight plasticizer: high molecular weight plasticizers such as polyethylene glycol (PEG), polyvinyl alcohol (PVA) have longer molecular chains, these molecular chains can form entanglement and winding between polypropylene polymers, improve the compatibility of the phase interface, reduce the phase size, this entanglement can increase the interaction force between the molecular chains, improve the strength and elasticity of the melt.

[0059] In this embodiment, the inorganic flame retardant is a mixture of one or more of inorganic phosphorus flame retardant, aluminum hydroxide and magnesium hydroxide, and antimony trioxide.

[0060] Inorganic phosphorus flame retardant: such as phosphate, ammonium polyphosphate, etc., also has polarity, because the phosphorus atom can form a polar bond with oxygen atom.

[0061] Aluminum hydroxide and magnesium hydroxide: these inorganic flame retardants have strong polarity, because their surface has positive charge, hydrophilic, poor compatibility with non-polar polymer materials.

[0062] Antimony trioxide: as an inorganic flame retardant, also has a certain polarity.

[0063] In this embodiment, sodium benzoate is one of the nucleating agents, and the sodium benzoate nucleating agent can reduce the crystallization temperature of polypropylene to about 130℃, which is neither too early crystallization nor delayed crystallization process. The nucleating agent can also be one of sodium benzoate, talc, sorbitol, TMB-4, TMB-5, STARNU-100, N,N'-dicyclohexyl terephthalamide, WBG-II

[0064] Among them, sodium benzoate, talc, sorbitol are α crystal nucleating agent, which can improve the rigidity and transparency of polypropylene. This kind of nucleating agent can refine the crystalline structure of polypropylene, thereby increasing the melting point.

[0065] TMB-4, TMB-5, STARNU-100, N,N'-dicyclohexyl terephthalamide, WBG-II are β crystal nucleating agent, which can promote the formation of β crystal at high temperature, thereby increasing the melting point; can improve the toughness and load deformation temperature of polypropylene material, so that polypropylene forms loose β crystal structure, which can absorb energy when subjected to external force, increase the impact resistance, thereby improving the toughness of polypropylene products. In order to avoid the possibility of rapid crystallization speed of α crystal nucleating agent leading to the decrease of toughness of polypropylene material, β crystal nucleating agent is preferentially added, which can significantly improve the rigidity of polypropylene material mainly by increasing the crystalline density and refining the grain size.

[0066] Substituted aromatic amide nucleating agent is a kind of compound obtained by chemical synthesis, with specific substituent groups, can promote the formation of β crystal form of polypropylene (PP). TMB-4 and TMB-5 belong to one of the substituted aromatic amide nucleating agent.

[0067] Substituted benzamide nucleating agent is a kind of compound obtained by chemical synthesis, with specific substituent groups, can promote the formation of β crystal form of polypropylene (PP). STARNU-100 and N,N'-dicyclohexyl terephthalamide belong to one of the substituted benzamide nucleating agent.

[0068] Rare earth nucleating agent: WBG-II is used for β crystal nucleation.

[0069] The role of nucleating agent in the present application is as follows:

[0070] The present application is to add nucleating agent in the post-processing step of polypropylene particle preparation, to obtain grain refined polypropylene particles, and improve the crystallinity of polypropylene, which can improve the melting point of polypropylene in the foaming process, and still help to improve the strength of polypropylene melt at higher foaming temperature range, so that it is not easy to deform or break when subjected to external force; grain refined polypropylene particles reduce the resistance of gas molecules in polypropylene melt, thereby improving the diffusion efficiency of gas into the bubble, which helps the bubble to fully grow in the foaming process and form a uniform cell structure; polypropylene melt at a higher crystallization temperature, polypropylene maintains good fluidity in the process of physical foaming agent decomposition and gas diffusion, which provides more time for gas diffusion, ensures that the gas can fully enter the bubble and promote the bubble growth, so that the gas can be uniformly dispersed in the polypropylene melt to form uniform bubbles.

[0071] Blending ordinary polypropylene with other non-crystalline or low crystalline resin, elastomer, etc. can improve the melting range and melt strength of polypropylene, and further improve the melting point. This method can improve the thermoforming performance and foaming performance of polypropylene without negative impact on foaming

[0072] In this embodiment, the non-crystalline resin is as follows:

[0073] Polystyrene (PS): softening temperature: about 120℃; characteristics: PS is a non-crystalline resin with good transparency and processing performance. Its softening temperature is low, and it is suitable for processing at low temperature.

[0074] Acrylonitrile-butadiene-styrene copolymer (ABS): softening temperature: about 120℃; characteristics: ABS is a terpolymer with good impact strength and chemical resistance. Its softening temperature is low, and it is suitable for processing at low temperature.

[0075] Poly(methyl methacrylate) (PMMA): Softening temperature: 105℃; Characteristics: PMMA (commonly known as organic glass) is a non-crystalline resin with high transparency and good optical properties. Its softening temperature is relatively low, suitable for processing at lower temperatures.

[0076] Polyvinyl chloride (PVC): Softening temperature: about 80℃; Characteristics: PVC is a non-crystalline resin with good chemical resistance and mechanical properties. Its softening temperature is relatively low, suitable for processing at lower temperatures.

[0077] The role of non-crystalline resin in the present application is as follows:

[0078] In the present application, the addition of non-crystalline resin will reduce the viscosity of the polypropylene melt, allowing it to flow at lower temperatures. This not only lowers the softening point, but also allows the bubbles to grow rapidly during the initial stage of bubble growth in the polypropylene extrusion foaming process. In addition, due to the high elastic recovery performance of non-crystalline resin, it can quickly recover to its original state when subjected to external force. This elasticity can improve the elongation resistance of the melt, thereby increasing the melt strength and allowing it to better maintain the shape of the cells during the foaming process, preventing cell coalescence and rupture.

[0079] The present embodiment also provides a method for preparing a polypropylene foaming flame-retardant material, comprising the following steps:

[0080] S1, preparation of grain-refined polypropylene particles: in the post-treatment step of the preparation of polypropylene particles, a nucleating agent is added to the polypropylene particles after hot air drying, and then cooled to obtain grain-refined polypropylene particles;

[0081] S2, preparation of maleic anhydride grafted grain-refined polypropylene particles, comprising the following steps:

[0082] S21, add grain-refined polypropylene particles 100 parts, maleic anhydride 4 parts, and initiator 0.3 parts into the mixing kettle in proportion, heat to normal pressure reflux temperature under stirring conditions until completely dissolved, and the normal pressure reflux temperature is usually at 120℃;

[0083] S22, add the mixture into the reaction kettle and control the temperature at 170℃, the reaction time is 2min, to obtain the reaction product;

[0084] S23, discharge the reaction product after slowly reducing the pressure to atmospheric pressure, add acetone at room temperature as a precipitating agent, and then filter after precipitation to obtain the grafted product;

[0085] S24, crush the grafted product, wrap it with filter paper, and put it into a Soxhlet extractor, use ethanol as the solvent, heat and reflux extract in the water bath for 24h to obtain the extracted grafted product;

[0086] S25, the extracted graft product is placed in a vacuum oven at 110℃ for drying for 12h to obtain maleic anhydride grafted grain-refined polypropylene particles;

[0087] S3, according to the formula, the maleic anhydride grafted grain-refined polypropylene particles, non-crystalline resin polystyrene, high molecular weight plasticizer polyethylene glycol, inorganic flame retardant ammonium polyphosphate and nucleating agent sodium benzoate are blended to obtain a blended material, and the blending temperature is 180℃;

[0088] S4, the blended material is added with a physical foaming agent carbon dioxide for extrusion foaming, the die temperature for extrusion foaming is 175℃, the extrusion foaming is carried out in a single screw extruder, the extrusion speed is 60r / min, a cuboid mold is used to obtain the polypropylene foaming flame retardant material.

[0089] The embodiment also provides a lithium battery module comprising the polypropylene foaming flame retardant material.

[0090] Embodiment 2

[0091] The embodiment provides a polypropylene foaming flame retardant material, which is prepared from a polypropylene composite material, and according to the weight percentage, the polypropylene composite material comprises 90 parts of maleic anhydride grafted grain-refined polypropylene particles, 45 parts of non-crystalline resin acrylonitrile-butadiene-styrene copolymer, 4 parts of high molecular weight plasticizer polyvinyl alcohol, 20 parts of inorganic flame retardant aluminum hydroxide, 45 parts of nucleating agent TMB, and 2 parts of physical foaming agent air.

[0092] The embodiment also provides a preparation method of the polypropylene foaming flame retardant material, which comprises the following steps:

[0093] S1, preparation of grain-refined polypropylene particles: in the post-treatment step of the preparation of the polypropylene particles, a nucleating agent is added to the polypropylene particles after hot air drying, and then cooled to obtain grain-refined polypropylene particles;

[0094] S2, preparation of maleic anhydride grafted grain-refined polypropylene particles comprises the following steps:

[0095] S21, 100 parts of grain-refined polypropylene particles, 4 parts of maleic anhydride and 0.3 parts of initiator are added into a mixing kettle in proportion, heated to normal pressure reflux temperature under stirring conditions until completely dissolved, and the normal pressure reflux temperature is usually 135℃;

[0096] S22, the mixture is added into a reaction kettle, the temperature is controlled at 180℃, and the reaction time is 1min to obtain a reaction product;

[0097] S23, the reaction product is discharged after being slowly decompressed to atmospheric pressure, and acetone at room temperature is added as a precipitating agent, and then the graft product is obtained by precipitation and filtration.

[0098] S24, after the grafting product is crushed, it is wrapped with filter paper and put into a Soxhlet extractor, ethanol is used as a solvent, and the extraction is carried out in a water bath for 24 h to obtain an extracted grafting product;

[0099] S25, the extracted grafting product is put into a vacuum oven at 110°C and dried for 12 h to obtain maleic anhydride grafted grain-refined polypropylene particles;

[0100] S3, the maleic anhydride grafted grain-refined polypropylene particles, the non-crystalline resin acrylonitrile-butadiene-styrene copolymer, the high molecular weight plasticizer polyvinyl alcohol, the inorganic flame retardant aluminum hydroxide and the nucleating agent TMB-45 are blended to obtain a blended material, and the temperature of the blending is 195°C;

[0101] S4, the physical foaming agent air is added to the blended material to perform extrusion foaming, the die temperature of the extrusion foaming is 165°C, the extrusion foaming is performed in a single screw extruder, the extrusion speed is 60 r / min, a cuboid mold is used, and a polypropylene foaming flame-retardant material is obtained.

[0102] The embodiment also provides a lithium battery module comprising the polypropylene foaming flame-retardant material.

[0103] Embodiment 3

[0104] The embodiment provides a polypropylene foaming flame-retardant material, which is prepared by foaming a polypropylene composite material, and the polypropylene composite material comprises, according to the percentage by weight, 92 parts of maleic anhydride grafted grain-refined polypropylene particles, 55 parts of non-crystalline resin polymethyl methacrylate, 5 parts of high molecular weight plasticizer polyvinyl alcohol, 30 parts of inorganic flame retardant magnesium hydroxide, 8 parts of nucleating agent STARNU-100 and 3 parts of physical foaming agent nitrogen.

[0105] The embodiment also provides a preparation method of the polypropylene foaming flame-retardant material, which comprises the following steps.

[0106] S1, preparation of grain-refined polypropylene particles: in a post-treatment step of the preparation of the polypropylene particles, a nucleating agent is added to the polypropylene particles after hot air drying, and then cooled to obtain grain-refined polypropylene particles;

[0107] S2, preparation of maleic anhydride grafted grain-refined polypropylene particles comprises the following steps:

[0108] S21, 100 parts of grain-refined polypropylene particles, 4 parts of maleic anhydride and 0.3 parts of an initiator are added into a mixing kettle in proportion, heated to the normal pressure reflux temperature under stirring conditions until completely dissolved, and the normal pressure reflux temperature is usually 150°C;

[0109] S22, the mixture is added into a reaction kettle, the temperature is controlled at 220℃, and the reaction time is 3 minutes, to obtain a reaction product;

[0110] S23, the reaction product is discharged after being slowly buffered to atmospheric pressure, and acetone at normal temperature is added as a precipitating agent, and then the product is obtained by precipitation and filtration;

[0111] S24, the grafted product is crushed, wrapped with filter paper, and put into a Soxhlet extractor, and ethanol is used as a solvent to extract the grafted product in a water bath for 24 hours, to obtain an extracted grafted product;

[0112] S25, the extracted grafted product is dried in a vacuum oven at 110℃ for 12 hours, to obtain maleic anhydride grafted grain-refined polypropylene particles;

[0113] S3, the maleic anhydride grafted grain-refined polypropylene particles, the non-crystalline resin polymethyl methacrylate, the high molecular weight plasticizer polyvinyl alcohol, the inorganic flame retardant magnesium hydroxide, and the nucleating agent STARNU-1008 are blended, to obtain a blended material, and the blending temperature is 210℃;

[0114] S4, the physical foaming agent nitrogen is added into the blended material to perform extrusion foaming, the die temperature of the extrusion foaming is 170℃, the extrusion foaming is performed in a single screw extruder, the extrusion speed is 60r / min, and a cuboid mold is used, to obtain the polypropylene foaming flame-retardant material.

[0115] The embodiment also provides a lithium battery module comprising the polypropylene foaming flame-retardant material.

[0116] Embodiment 4

[0117] The embodiment provides a polypropylene foaming flame-retardant material, which is prepared from a polypropylene composite material, and the polypropylene composite material comprises, in percentage by weight, 88 parts of maleic anhydride grafted grain-refined polypropylene particles, 62 parts of a non-crystalline resin polyvinyl chloride, 3 parts of a high molecular weight plasticizer polyethylene glycol, 25 parts of an inorganic flame retardant antimony trioxide, 6 parts of a nucleating agent WBG-II, and 4 parts of a physical foaming agent carbon dioxide.

[0118] The embodiment also provides a preparation method of the polypropylene foaming flame-retardant material, which comprises the following steps:

[0119] S1, preparation of grain-refined polypropylene particles: in a post-treatment step of preparation of the polypropylene particles, a nucleating agent is added into the polypropylene particles after hot air drying, and then the polypropylene particles are cooled, to obtain the grain-refined polypropylene particles;

[0120] S2, preparation of maleic anhydride grafted grain-refined polypropylene particles, which comprises the following steps:

[0121] S21, 100 parts of the grain-refined polypropylene particles, 4 parts of maleic anhydride and 0.3 parts of an initiator are added into a mixing kettle in proportion, and heated to normal pressure reflux temperature under stirring until completely dissolved, and the normal pressure reflux temperature is usually 135℃;

[0122] S22, the mixture is added into a reaction kettle, and the temperature is controlled at 210℃, and the reaction time is 2 min to obtain a reaction product;

[0123] S23, the reaction product is discharged after being slowly decompressed to atmospheric pressure, and acetone at normal temperature is added as a precipitating agent, and then the grafted product is obtained by precipitation and filtration;

[0124] S24, the grafted product is crushed, wrapped with filter paper, and placed into a Soxhlet extractor, and ethanol is used as a solvent to extract for 24 h in a water bath under reflux to obtain an extracted grafted product;

[0125] S25, the extracted grafted product is placed into a vacuum oven at 110℃ and dried for 12 h to obtain the maleic anhydride grafted grain-refined polypropylene particles;

[0126] S3, the maleic anhydride grafted grain-refined polypropylene particles, the non-crystalline resin polyvinyl chloride, the high molecular weight plasticizer polyethylene glycol, the inorganic flame retardant antimony trioxide and the nucleating agent WBG-II6 are blended to obtain a blended material, and the blending temperature is 185℃;

[0127] S4, the physical foaming agent carbon dioxide is added into the blended material to perform extrusion foaming, the die temperature of the extrusion foaming is 160℃, the extrusion foaming is performed in a single screw extruder, the extrusion speed is 60 r / min, a cuboid mold is used to obtain the polypropylene foaming flame-retardant material.

[0128] The embodiment also provides a lithium battery module comprising the polypropylene foaming flame-retardant material.

[0129] Comparative Example 1

[0130] Different from Example 1, the comparative example provides a polypropylene foaming flame-retardant material prepared by foaming a polypropylene composite material, and the polypropylene composite material comprises, in terms of weight percentage, 85 parts of grain-refined polypropylene particles, 50 parts of non-crystalline resin polystyrene, 3 parts of high molecular weight plasticizer polyethylene glycol, 35 parts of inorganic flame retardant ammonium polyphosphate, 10 parts of nucleating agent sodium benzoate and 5 parts of physical foaming agent carbon dioxide.

[0131] Comparative Example 2

[0132] Unlike Example 1, this comparative example provides a polypropylene foamed flame retardant material prepared by foaming a polypropylene composite material, which includes, by weight percentage, 85 parts of polypropylene particles, 50 parts of non-crystalline resin polystyrene, 3 parts of high molecular weight plasticizer polyethylene glycol, 35 parts of inorganic flame retardant ammonium polyphosphate, 10 parts of nucleating agent sodium benzoate, and 5 parts of physical foaming agent carbon dioxide.

[0133] Comparative Example 3

[0134] Unlike Example 1, this comparative example provides a polypropylene foamed flame retardant material prepared by foaming a polypropylene composite material, which includes, by weight percentage, 85 parts of polypropylene particles, 50 parts of non-crystalline resin polystyrene, 3 parts of high molecular weight plasticizer polyethylene glycol, 35 parts of inorganic flame retardant ammonium polyphosphate, 10 parts of nucleating agent sodium benzoate, and 5 parts of physical foaming agent carbon dioxide.

[0135] Experimental Example

[0136] The method for measuring the melt strength in the preparation process of the polypropylene foamed flame retardant material provided in Examples 1-4 and Comparative Examples 1-3 is as follows:

[0137] The melt strength of the polypropylene foamed material is measured using a melt strength tester (such as a Gottfert "Rheotens" melt strength tester). Before testing, it is ensured that the melt strength tester is in good condition, that all parts are functioning properly, that the sensor is accurately calibrated, and that the specific take-off speed value is input through the control panel or software of the instrument. In this experiment, the take-off speed is set to 5 mm / s.

[0138] Sample addition: The melt strength tester is preheated to the corresponding die temperature of the extrusion foaming, and the maleic anhydride grafted grain refined polypropylene particles, non-crystalline resin, high molecular weight plasticizer, inorganic flame retardant, and nucleating agent are blended to obtain a blended material. The obtained blended material is added to the extruder barrel and kept for 6 minutes to ensure the uniformity and stability of the melt.

[0139] Start testing: Then the extruder is started to make the melt extrude downward from the die, and at the same time, the melt is pulled by two rollers with opposite directions of motion mounted on a balance beam. The rollers start moving at a low speed and then gradually accelerate. The uniform acceleration of the rollers exerts a stretching force on the melt beam. During the stretching process, the force on the melt beam is monitored in real time, and the change of the stretching force with time is recorded. When the stretching force reaches a certain level, the melt beam will break. The force at which the melt beam breaks at this time is recorded as the "melt strength" of the polymer.

[0140] Data recording: For the same sample, multiple tests are needed, generally at least 3 times to ensure the accuracy and reliability of the data, the melt strength value of each test is recorded and the average value is calculated as the final melt strength of the sample, the tensile hardness value is generally in units of centi-newton (cN).

[0141] Calculation result: the mass corresponding to the time of 3 minutes is calculated, which can be used as the melt strength at this temperature. The larger the mass value, the higher the melt strength. The determination results of the melt strength in the preparation process of the polypropylene foamed flame-retardant material provided in Examples 1-4 and Comparative Examples 1-3 are shown in Table 1.

[0142] Table 1

[0143]

[0144]

[0145] It can be seen from the determination results in Table 1 that compared with the melt strength in the preparation process of the polypropylene foamed flame-retardant material provided in Comparative Examples 1-3, the melt strength in the preparation process of the polypropylene foamed flame-retardant material provided in Examples 1-3 is significantly higher than that in Comparative Examples 1-3; compared with the melt strength in the preparation process of the polypropylene foamed flame-retardant material provided in Comparative Example 1, it shows that the polypropylene grafted maleic anhydride can improve the compatibility between the polar flame retardant and the polypropylene, reduce the phase size, and can increase the foaming temperature after the addition of the inorganic flame retardant, so as to widen the foaming temperature window of the foaming system, and the melt strength is increased under the same foaming temperature; compared with the melt strength in the preparation process of the polypropylene foamed flame-retardant material provided in Comparative Example 2, it shows that the nucleating agent is added in the post-processing step of the preparation of the polypropylene particles to obtain the polypropylene particles with refined crystal grains, and the crystallinity of the polypropylene is improved, which can increase the melting point of the polypropylene in the foaming process, and can still help to increase the strength of the polypropylene melt at a higher foaming temperature range, so that the polypropylene melt is not easy to deform or break under external force; compared with the melt strength in the preparation process of the polypropylene foamed flame-retardant material provided in Comparative Example 3, it shows that the non-crystalline resin has high elastic recovery performance, which can quickly restore to the original state when subjected to external force, and such elasticity can improve the anti-stretching property of the melt, thereby increasing the melt strength, so that the polypropylene melt can better maintain the shape of the cells in the foaming process, and prevent the cells from merging and rupturing.

[0146] The above embodiments are only preferred embodiments of the present application, and cannot be used to limit the protection scope of the present application, and any non-essential changes and substitutions made by those skilled in the art on the basis of the present application shall fall within the protection scope of the present application.

Claims

1. A polypropylene foamed flame retardant material, produced by foaming a polypropylene composite material, characterized in that, The polypropylene composite material comprises maleic anhydride grafted grain refined polypropylene particles 85-92 parts, non-crystalline resin 45-62 parts, high molecular weight plasticizer 3-5 parts, inorganic flame retardant 20-35 parts, nucleating agent 5-10 parts, and physical foaming agent 2-5 parts by weight percentage; the non-crystalline resin is one of polystyrene, acrylonitrile-butadiene-styrene copolymer, polymethyl methacrylate, and polyvinyl chloride; The preparation method of the polypropylene foaming flame-retardant material comprises the following steps: S1, preparation of the grain refined polypropylene particles: in the post-processing step of the preparation of the polypropylene particles, the nucleating agent is added to the polypropylene particles after hot air drying, and then cooled to obtain the grain refined polypropylene particles; S2, preparation of the maleic anhydride grafted grain refined polypropylene particles comprises the following steps: S21, the grain refined polypropylene particles 100 parts, maleic anhydride 4 parts, and initiator 0.3 parts are added into a mixing kettle in proportion, heated to normal pressure reflux temperature under stirring conditions until completely dissolved, and the normal pressure reflux temperature is usually 120-150℃; S22, the mixture is added into a reaction kettle, the temperature is controlled between 170-220℃, and the reaction time is 1-3 min to obtain a reaction product; S23, the reaction product is discharged after being slowly decompressed to atmospheric pressure, acetone at room temperature is added as a precipitating agent, and then the grafted product is obtained by precipitation and filtration; S24, the grafted product is crushed, wrapped with filter paper, placed in a Soxhlet extractor, and extracted by refluxing in a water bath for 24 h using ethanol as a solvent to obtain the extracted grafted product; S25, the extracted grafted product is placed in a 110℃ vacuum oven for drying for 12 h to obtain the maleic anhydride grafted grain refined polypropylene particles; S3, the maleic anhydride grafted grain refined polypropylene particles, non-crystalline resin, high molecular weight plasticizer, inorganic flame retardant, and nucleating agent are blended to obtain a blended material, and the blending temperature is 180-210℃; S4, the physical foaming agent is added to the blended material for extrusion foaming, the die temperature of the extrusion foaming is 160-175℃, and the polypropylene foaming flame-retardant material is obtained.

2. A polypropylene foamed flame retardant material as claimed in claim 1, wherein, The polypropylene composite material comprises maleic anhydride grafted grain refined polypropylene particles 85 parts, non-crystalline resin 50 parts, high molecular weight plasticizer 3 parts, inorganic flame retardant 35 parts, nucleating agent 10 parts, and physical foaming agent 5 parts.

3. A polypropylene foamed flame retardant material as in claim 1, wherein, The inorganic flame retardant is one or a mixture of more than one of inorganic phosphorus-based flame retardant, aluminum hydroxide, and magnesium hydroxide, and antimony trioxide.

4. A polypropylene foamed flame retardant material as in claim 1, wherein, The high molecular weight plasticizer is one of polyethylene glycol (PEG) and polyvinyl alcohol (PVA).

5. A polypropylene foamed flame retardant material as in claim 1 wherein, The nucleating agent is one of sodium benzoate, talcum powder, sorbitol, TMB-4, TMB-5, STARNU-100, N,N'-dicyclohexyl terephthalamide, and WBG-II.

6. A polypropylene foamed flame retardant material as in claim 1 wherein, The physical foaming agent is one of carbon dioxide, air, and nitrogen.

7. A process for the preparation of a polypropylene foamed flame retardant material according to any one of claims 1 to 6, characterized in that, The preparation method comprises the following steps: S1, the preparation of the grain refined polypropylene particles: in the post-processing step of the preparation of the polypropylene particles, the nucleating agent is added to the polypropylene particles after hot air drying, and then cooled to obtain the grain refined polypropylene particles; S2, the preparation of the maleic anhydride grafted grain refined polypropylene particles includes the following steps: S21, the grain refined polypropylene particles 100 parts, maleic anhydride 4 parts, initiator 0.3 parts are added into the mixing kettle according to the proportion, heated to normal pressure reflux temperature under stirring condition to completely dissolve, the normal pressure reflux temperature is usually at 120-150℃; S22, the mixture is added into the reaction kettle, the temperature is controlled between 170-220℃, the reaction time is 1-3min, to obtain the reaction product; S23, the reaction product is discharged after buffer decompression to atmospheric pressure, add acetone at room temperature as the precipitating agent, and then precipitate and filter to obtain the graft product; S24, the graft product is crushed and wrapped with filter paper, put into Soxhlet extractor, use ethanol as solvent, heat reflux extraction in water bath for 24h to obtain the extracted graft product; S25, the extracted graft product is put into 110℃ vacuum oven for drying for 12h to obtain the maleic anhydride grafted grain refined polypropylene particles; S3, the maleic anhydride grafted grain refined polypropylene particles, non-crystalline resin, high molecular weight plasticizer, inorganic flame retardant and nucleating agent are blended to obtain the blended material, the blending temperature is 180-210℃; S4, the physical foaming agent is added to the blended material for extrusion foaming, the extrusion foaming die temperature is 160-175℃, to obtain the polypropylene foaming flame retardant material. In step S4, the extrusion foaming is carried out in a single screw extruder, the extrusion speed is 60r / min, a cuboid mold is used to prepare the polypropylene foaming flame retardant material.

8. A process for the preparation of a polypropylene foamed flame retardant material according to claim 7, characterized in that, A polypropylene foaming flame retardant material comprising any one of claims 1-6.

9. A lithium battery module, characterized by A polypropylene foaming flame retardant material comprising any one of claims 1-6.

Images