Polypropylene foaming flame-retardant material and preparation method thereof

Abstract

The invention discloses a polypropylene foaming flame-retardant material, and belongs to the technical field of polypropylene foaming flame-retardant materials. The polypropylene composite material is prepared by foaming, and is characterized by comprising the following components in percentage by weight: 85-92 parts of maleic anhydride grafted grain refined polypropylene particles (polypropylene-g-MAH), 45-62 parts of amorphous resin, 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. The polypropylene foaming flame-retardant material is still helpful for improving the strength of polypropylene melt and improving the uniformity of foam holes in a range higher than the existing foaming temperature range.

Description

Technical Field

[0001] The invention relates to the technical field of polypropylene foamed flame retardant materials, and in particular to a polypropylene foamed flame retardant material and a preparation method thereof. Background Art

[0002] As one of the five most widely used general-purpose plastics, polypropylene has the advantages of low density, complete models, easy processing and molding, and chemical corrosion resistance. It has been widely used in national life and industrial fields. However, polypropylene has the disadvantages of being flammable and having poor thermal conductivity. Therefore, in order to expand the application scope of polypropylene, it is very necessary to improve its flame retardant properties.

[0003] Polypropylene is a crystalline polymer. Low-temperature solid-state foaming is limited by crystallization. The crystallinity of polypropylene affects its solubility during solid-state foaming and the uniformity of the dispersion of the foaming agent, thereby affecting the uniformity of the pore structure. A uniform pore structure cannot be obtained in a polymer with high crystallinity, but it can be obtained in a polymer with low crystallinity. Under high temperature conditions, the melt strength of polypropylene will decrease, which makes it impossible for the polymer melt to maintain a complete pore structure during the high-temperature foaming process. When the temperature exceeds the melting point of polypropylene, the melt strength drops rapidly. The thin, non-viscoelastic polypropylene melt at high temperature cannot withstand the tensile stress generated during the growth of bubbles. The gas can easily break out of the pores, which can easily lead to pore rupture and aggregation, resulting in the inability to prepare foam products with uniform pore distribution, small pore size, and high foaming ratio, so that the integrity and uniformity of the pores cannot be maintained. When the temperature drops, crystallization occurs rapidly, and the pores do not have time to grow and a large amount of gas is excluded from the melt. Therefore, it is difficult to use ordinary polypropylene to make excellent foaming materials. The melting point of polypropylene occurs within a range, with the homopolymer at 160℃-165℃ and the copolymer at 135℃-159℃, and the suitable foaming temperature interval is between 155℃ and 170℃. Therefore, the viscosity and temperature range suitable for foaming are very narrow. It is estimated that the suitable foaming temperature of polypropylene is only 4℃. The narrow operating window means that foaming is very difficult.

[0004] In the initial stage of bubble growth in polypropylene extrusion foaming, the polypropylene melt that forms the bubble wall is subjected to biaxial stretching, and the polypropylene melt undergoes strong tensile deformation, requiring the tensile viscosity of the polypropylene melt to be low to allow the bubble to grow rapidly; in the subsequent bubble growth process, the tensile viscosity must be increased to a sufficiently high level to maintain the stable growth of the bubble. If the tensile viscosity of the melt decreases at this time, the bubble wall that has been stretched and thinned will become thinner under the action of internal pressure, and the bubble is prone to collapse, affecting the uniformity of the bubble size and the foaming ratio of the foamed product. Therefore, the tensile viscosity and melt elasticity of the polypropylene melt at different temperatures and strain rates are the key to polypropylene extrusion foaming. Too low melt viscosity and melt elasticity will narrow the window of polypropylene extrusion foaming, and it will be impossible to control the stable growth of bubbles and obtain excellent foaming materials.

[0005] During the polypropylene foaming process, the foaming agent is dissolved in the polypropylene melt. As the temperature decreases, the gas begins to diffuse out of the melt to form bubbles. If the polypropylene crystallizes before the foaming agent diffuses out of the melt and enters the nucleated bubbles, the early solidification will result in insufficient gas to drive the bubble growth. This is because the crystallization of polypropylene will limit the movement of gas molecules and reduce the diffusion of gas into the bubble, thus affecting the growth of the bubble. 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 can still help to improve the strength of the polypropylene melt and improve the uniformity of the cells within a higher foaming temperature range than the existing one.

[0007] The second object of the present invention is to provide a method for preparing a polypropylene foamed 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 foamed flame retardant material is prepared by foaming a polypropylene composite material. The polypropylene composite material comprises, by weight percentage, 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] Furthermore, the inorganic flame retardant is a mixture of one or more of an inorganic phosphorus flame retardant, aluminum hydroxide, magnesium hydroxide, and antimony trioxide.

[0013] Furthermore, the nucleating agent is one of sodium benzoate, talc, 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] Furthermore, the physical foaming agent is one of carbon dioxide, air and nitrogen.

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

[0017] A method for preparing a polypropylene foamed flame retardant material comprises the following steps:

[0018] S1. Preparation of grain-refined polypropylene particles: In the post-processing step of preparing the polypropylene particles, the nucleating agent is added to the hot air dried polypropylene particles, and then cooled to obtain the grain-refined polypropylene particles;

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

[0020] S21, adding 100 parts of the grain-refined polypropylene particles, 4 parts of maleic anhydride, and 0.3 parts of initiator into a mixing kettle according to proportion, and heating to the atmospheric reflux temperature under stirring until they are completely dissolved, wherein the atmospheric reflux temperature is usually 120° C.-150° C.;

[0021] S22, adding the mixture into a reaction kettle, controlling the temperature between 170° C. and 220° C., and reacting for 1 min to 3 min to obtain a reaction product;

[0022] S23, the reaction product is decompressed to atmospheric pressure through buffering and then discharged, acetone at room temperature is added as a precipitating agent, and then a grafted product is obtained through precipitation and filtration;

[0023] S24, crushing the grafted product, wrapping it with filter paper, putting it into a Soxhlet extractor, using ethanol as a solvent, heating and refluxing in a water bath for 24 hours to obtain an extracted grafted product;

[0024] S25, placing the extracted grafted product in a vacuum oven at 110° C. and drying for 12 hours to obtain the maleic anhydride grafted polypropylene particles with refined grains;

[0025] S3, blending the maleic anhydride grafted grain-refined polypropylene particles, non-crystalline resin, high molecular weight plasticizer, inorganic flame retardant and 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 carried out in a single-screw extruder at an extrusion speed of 60 r / min and a rectangular mold is used to obtain the polypropylene foamed 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 regions of the polypropylene foam is different, which will lead to inconsistent formation and growth of bubbles and 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 improve the melting point of polypropylene in the foaming process, and is still helpful to improve the strength of polypropylene melt within a temperature range higher than the existing foaming temperature, so that the polypropylene melt is not easy to deform or break when subjected to external force; 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 in the foaming process and form a uniform pore structure; when the polypropylene melt is at a relatively high crystallization temperature, the 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 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 the flame retardant of polypropylene. Maleic anhydride is grafted onto polypropylene, in which maleic anhydride acts as a compatibilizer. Maleic anhydride grafted onto polypropylene can improve the compatibility between inorganic flame retardants and polypropylene and reduce the size of the phase domain. The maleic anhydride groups on it can form hydrogen bonds with inorganic flame retardants, while the polypropylene groups are compatible with non-polar polymers, thereby forming a compatibility layer at the interface between polypropylene and inorganic flame retardants, reducing the size of the phase domain, enhancing the heterogeneous nucleation effect of the foaming system, and relatively weakening the homogeneous nucleation effect. The foaming characteristics of the two phases of polypropylene and inorganic flame retardant are gradually weakened, resulting in the foaming system not having various non-uniform pore structures, making the foaming system have a more uniform pore structure, and the phase domain size is reduced, which can increase the foaming temperature after the addition of inorganic flame retardants, and widen the foaming temperature window of the foaming system. High molecular weight plasticizers such as polyethylene glycol (PEG) and polyvinyl alcohol (PVA) have longer molecular chains, which can form entanglements and entanglements between polypropylene polymers, improve the compatibility of the phase interface, and reduce the phase area size. This entanglement can increase the interaction force between the molecular chains and improve the strength and elasticity of the melt.

[0033] (3) The addition of non-crystalline resin in the present invention reduces the viscosity of the polypropylene melt, allowing it to flow at a lower temperature, which not only reduces the softening point, but also allows the bubbles to grow rapidly in the initial stage of bubble growth during polypropylene extrusion foaming. In addition, since the non-crystalline resin has a high elastic recovery performance and can quickly return to its original shape when subjected to external force, this elasticity can improve the melt's anti-extension property, thereby increasing the melt strength, allowing it to better maintain the shape of the bubbles during the foaming process and prevent the bubbles from merging and rupturing. DETAILED DESCRIPTION

[0034] The present invention is further described below in conjunction with specific embodiments. It should be noted that, under the premise of no conflict, the embodiments or technical features described below can be arbitrarily combined to form a new embodiment.

[0035] Foaming window: refers to the specific temperature and pressure range within which the foaming process can proceed smoothly. Beyond this range, the foaming effect will be affected, which may lead to uneven foaming or failure. Polypropylene is a crystalline polymer. Low-temperature solid foaming is limited by crystallization. High-temperature foaming polymer melt strength is not enough to maintain complete bubbles, so the operating window is narrow.

[0036] Physical meaning of melt strength

[0037] Ability to support its own mass: Melt strength refers to the ability of a polymer to support its own mass in a molten state. It reflects the melt's resistance 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] Stability of cell wall: In 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 the bubble growth process, resulting in gas escape, cell collapse and rupture, resulting in a small foaming ratio, uneven cell distribution and low mechanical strength.

[0040] The detailed steps for the preparation of polypropylene are as follows:

[0041] 1. Raw material preparation

[0042] Propylene monomer: The preparation of polypropylene requires the use of propylene monomer as a raw material.

[0043] Catalyst: Commonly used catalysts include Ziegler-Natta catalysts, metallocene catalysts, etc. These catalysts can effectively initiate the polymerization reaction of propylene monomer.

[0044] Solvent: Hexane and heptane are needed to dissolve the propylene monomer for better control of the polymerization reaction.

[0045] 2. Polymerization

[0046] Reactor Type: Polypropylene polymerization can be carried out in a variety of reactor types, including solution reactors, slurry reactors, bulk reactors and gas phase reactors.

[0047] Polymerization conditions: Temperature: The temperature of the polymerization reaction is usually between 50°C and 100°C, and the specific temperature depends on the catalyst and process used. Pressure: The reaction pressure is generally between 0.5MPa and 3MPa, and 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 the reaction from overheating. The reaction heat is taken away by cooling water or other cooling media to ensure that the reaction temperature is stable within the set range.

[0048] 3. Post-processing

[0049] Removal of unreacted monomers: After the polymerization reaction is completed, the unreacted propylene monomer needs to be removed from the reaction system. This is usually achieved through a flash kettle. After the unreacted propylene is cooled and frozen into a liquid state, pure propylene is recovered from the top of the distillation tower for recycling.

[0050] Catalyst deactivation: In order to prevent the catalyst from continuing to react during subsequent treatment, it is usually necessary to add alcohols (such as ethanol, propanol or butanol) or acetylacetone to convert the titanium and aluminum in the catalyst into complexes or alkoxy compounds at 60°C.

[0051] Water washing: The catalyst complex is transferred into the water phase by water washing, thereby being separated from the polypropylene slurry.

[0052] Drying: After removing the solvent and catalyst, the polypropylene filter cake is dried, usually by hot air drying. If a high boiling point solvent is used, it can be firstly subjected to steam distillation to evaporate the solvent and water vapor, and the polypropylene is suspended in the water phase. After centrifugal separation, it is dried by hot air to obtain polypropylene.

[0053] Adding nucleating agent: Adding nucleating agent 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 nucleating agent can refine the grains of polypropylene and increase the crystallinity, thereby improving the mechanical properties and transparency of polypropylene.

[0054] Cooling step: During the drying process, the hot air dried polypropylene pellets need to be cooled to ensure the stability and quality of the pellets. Cooling is usually achieved through cooling air or cooling water systems.

[0055] Example 1

[0056] The present embodiment provides a polypropylene foam flame retardant material, which is obtained by foaming a polypropylene composite material. The polypropylene composite material includes, by weight percentage, 85 parts of maleic anhydride grafted 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 embodiment, maleic anhydride grafted polypropylene (polypropylene-g-MAH): maleic anhydride is used as a compatibilizer, and polypropylene grafted polypropylene can improve the compatibility between polar flame retardant and polypropylene, and reduce the phase area size. The maleic anhydride group thereon can form hydrogen bonds with inorganic flame retardants, while the polypropylene group is compatible with non-polar polymers, thereby forming a compatibility layer at the interface between polypropylene and inorganic flame retardants, reducing the phase area size, enhancing the heterogeneous nucleation effect of the foaming system, and relatively weakening the homogeneous nucleation effect. The foaming characteristics of the two phases of polypropylene and inorganic flame retardant are gradually weakened, resulting in the foaming system not having various non-uniform pore structures, making the foaming system have a more uniform pore structure, and the phase area size is reduced, which can increase the foaming temperature after the addition of inorganic flame retardants, and widen the foaming temperature window of the foaming system.

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

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

[0060] Inorganic phosphorus flame retardants: such as phosphate esters, ammonium polyphosphate, etc., are also polar because phosphorus atoms can form polar bonds with oxygen atoms.

[0061] Aluminum hydroxide and magnesium hydroxide: These inorganic flame retardants are highly polar because their surfaces carry a positive charge, are hydrophilic, and have poor compatibility with non-polar polymer materials.

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

[0063] In this embodiment, sodium benzoate is a nucleating agent. The sodium benzoate nucleating agent can reduce the crystallization temperature of polypropylene to about 130°C. This temperature range will neither crystallize prematurely nor delay the 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, talcum powder and sorbitol are α-crystal nucleating agents, which can improve the rigidity and transparency of polypropylene. This type of nucleating agent can refine the crystal structure of polypropylene, thereby increasing the melting point.

[0065] TMB-4, TMB-5, STARNU-100, N,N'-dicyclohexyl terephthalamide, and WBG-II are β-crystal nucleating agents. β-crystal nucleating agents can promote the formation of β-crystals at higher temperatures, thereby increasing the melting point; they can improve the toughness and load deformation temperature of polypropylene materials, and make polypropylene form a loose β-crystal structure. This structure can absorb energy when subjected to external forces, increase impact resistance, and thus improve the toughness of polypropylene products. In order to avoid the excessively fast crystallization rate of α-crystal nucleating agents that may lead to a decrease in the toughness of polypropylene materials, β-crystal nucleating agents are added first. β-crystal nucleating agents can also significantly improve the rigidity of polypropylene materials by mainly increasing the crystal density and refining the grain size.

[0066] Substituted aromatic amide nucleating agents are a class of compounds obtained by chemical synthesis, which have specific substituent groups and can promote the formation of β-crystals in polypropylene (PP). TMB-4 and TMB-5 are one of the substituted aromatic amide nucleating agents.

[0067] Substituted benzamide nucleating agents are a class of compounds obtained by chemical synthesis, with specific substituent groups that can promote the formation of β-crystals in polypropylene (PP). STARNU-100 and N,N'-dicyclohexyl terephthalamide are one of the substituted benzamide nucleating agents.

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

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

[0070] 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 improve the melting point of polypropylene in the foaming process, and is still helpful to improve the strength of polypropylene melt within a temperature range higher than the existing foaming temperature, so that the polypropylene melt is not easy to deform or break when subjected to external force; 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 in the foaming process and form a uniform pore structure; when the polypropylene melt is at a relatively high crystallization temperature, the 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 bubbles and promote the growth of the bubbles, and enables the gas to be evenly dispersed in the polypropylene melt to form uniform bubbles.

[0071] Blending ordinary polypropylene with other amorphous or low-crystalline resins, elastomers, etc. can increase the melting range and melt strength of polypropylene, thereby increasing the melting point. This method can improve the thermoforming and foaming properties of polypropylene without negatively affecting the foaming.

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

[0073] Polystyrene (PS): Softening temperature: about 120°C; 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 lower temperatures.

[0074] Acrylonitrile-butadiene-styrene copolymer (ABS): Softening temperature: about 120°C; Characteristics: ABS is a terpolymer with good impact strength and chemical resistance. Its softening temperature is low and it is suitable for processing at lower temperatures.

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

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

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

[0078] The addition of non-crystalline resin in the present invention can reduce the viscosity of the polypropylene melt, so that it can flow at a lower temperature, which not only reduces the softening point, but also allows the bubbles to grow rapidly in the initial stage of bubble growth during polypropylene extrusion foaming; and because the non-crystalline resin has a high elastic recovery performance, it can quickly recover to its original shape when subjected to external force. This elasticity can improve the melt's anti-extension property, thereby increasing the melt strength, so that it can better maintain the shape of the pores during the foaming process and prevent the pores from merging and breaking.

[0079] This embodiment also provides a method for preparing a polypropylene foam flame retardant material, comprising the following steps:

[0080] S1. Preparation of grain-refined polypropylene particles: In the post-processing step of preparing the polypropylene particles, a nucleating agent is added to the hot air dried polypropylene particles, and then cooled to obtain grain-refined polypropylene particles;

[0081] S2. The preparation of maleic anhydride grafted grain-refined polypropylene particles comprises the following steps:

[0082] S21, adding 100 parts of crystallized polypropylene particles, 4 parts of maleic anhydride, and 0.3 parts of initiator into a mixing kettle according to the proportion, and heating to the atmospheric reflux temperature under stirring until they are completely dissolved, and the atmospheric reflux temperature is usually 120° C.;

[0083] S22, adding the mixture into a reaction kettle, controlling the temperature at 170° C., and reacting for 2 min to obtain a reaction product;

[0084] S23, the reaction product is decompressed to atmospheric pressure through buffering and then discharged, acetone at room temperature is added as a precipitating agent, and then the grafted product is obtained by precipitation and filtration;

[0085] S24, crushing the grafted product, wrapping it with filter paper, putting it into a Soxhlet extractor, using ethanol as a solvent, heating and refluxing in a water bath for 24 hours to obtain an extracted grafted product;

[0086] S25, placing the extracted grafted product in a vacuum oven at 110° C. and drying for 12 hours to obtain maleic anhydride grafted polypropylene particles with refined grains;

[0087] S3, according to the formula, 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° C.;

[0088] S4. Add carbon dioxide, a physical foaming agent, to the blended material for extrusion foaming. The die head temperature of the extrusion foaming is 175° C. The extrusion foaming is carried out in a single-screw extruder at an extrusion speed of 60 r / min. A rectangular mold is used to obtain a polypropylene foam flame retardant material.

[0089] This embodiment also provides a lithium battery module, including a polypropylene foam flame retardant material.

[0090] Example 2

[0091] The present embodiment provides a polypropylene foam flame retardant material, which is obtained by foaming a polypropylene composite material. The polypropylene composite material includes, by weight percentage, 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] This embodiment also provides a method for preparing a polypropylene foam flame retardant material, comprising the following steps:

[0093] S1. Preparation of grain-refined polypropylene particles: In the post-processing step of preparing the polypropylene particles, a nucleating agent is added to the hot air dried polypropylene particles, and then cooled to obtain grain-refined polypropylene particles;

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

[0095] S21, adding 100 parts of crystallized polypropylene particles, 4 parts of maleic anhydride, and 0.3 parts of initiator into a mixing kettle according to the proportion, and heating to the atmospheric reflux temperature under stirring until they are completely dissolved, the atmospheric reflux temperature being usually 135° C.;

[0096] S22, adding the mixture into a reaction kettle, controlling the temperature at 180° C., and reacting for 1 min to obtain a reaction product;

[0097] S23, the reaction product is decompressed to atmospheric pressure through buffering and then discharged, acetone at room temperature is added as a precipitating agent, and then the grafted product is obtained by precipitation and filtration;

[0098] S24, crushing the grafted product, wrapping it with filter paper, putting it into a Soxhlet extractor, using ethanol as a solvent, heating and refluxing in a water bath for 24 hours to obtain an extracted grafted product;

[0099] S25, placing the extracted grafted product in a vacuum oven at 110° C. and drying for 12 hours to obtain maleic anhydride grafted polypropylene particles with refined grains;

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

[0101] S4. Adding physical foaming agent air to the blended material for extrusion foaming. The die head temperature of the extrusion foaming is 165° C. The extrusion foaming is carried out in a single-screw extruder at an extrusion speed of 60 r / min. A rectangular mold is used to obtain a polypropylene foam flame retardant material.

[0102] This embodiment also provides a lithium battery module, including a polypropylene foam flame retardant material.

[0103] Example 3

[0104] The present embodiment provides a polypropylene foam flame retardant material, which is obtained by foaming a polypropylene composite material. The polypropylene composite material includes, by weight percentage, 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] This embodiment also provides a method for preparing a polypropylene foam flame retardant material, comprising the following steps:

[0106] S1. Preparation of grain-refined polypropylene particles: In the post-processing step of preparing the polypropylene particles, a nucleating agent is added to the hot air dried polypropylene particles, and then cooled to obtain grain-refined polypropylene particles;

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

[0108] S21, adding 100 parts of crystallized polypropylene particles, 4 parts of maleic anhydride, and 0.3 parts of initiator into a mixing kettle according to the proportion, and heating to the atmospheric reflux temperature under stirring until they are completely dissolved, and the atmospheric reflux temperature is usually 150° C.;

[0109] S22, adding the mixture into a reaction kettle, controlling the temperature at 220° C., and reacting for 3 min to obtain a reaction product;

[0110] S23, the reaction product is decompressed to atmospheric pressure through buffering and then discharged, acetone at room temperature is added as a precipitating agent, and then the grafted product is obtained by precipitation and filtration;

[0111] S24, crushing the grafted product, wrapping it with filter paper, putting it into a Soxhlet extractor, using ethanol as a solvent, heating and refluxing in a water bath for 24 hours to obtain an extracted grafted product;

[0112] S25, placing the extracted grafted product in a vacuum oven at 110° C. and drying for 12 hours to obtain maleic anhydride grafted polypropylene particles with refined grains;

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

[0114] S4. Adding physical foaming agent nitrogen to the blended material for extrusion foaming. The die head temperature of the extrusion foaming is 170° C. The extrusion foaming is carried out in a single screw extruder at an extrusion speed of 60 r / min. A rectangular mold is used to obtain a polypropylene foamed flame retardant material.

[0115] This embodiment also provides a lithium battery module, including a polypropylene foam flame retardant material.

[0116] Example 4

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

[0118] This embodiment also provides a method for preparing a polypropylene foam flame retardant material, comprising the following steps:

[0119] S1. Preparation of grain-refined polypropylene particles: In the post-processing step of preparing the polypropylene particles, a nucleating agent is added to the hot air dried polypropylene particles, and then cooled to obtain grain-refined polypropylene particles;

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

[0121] S21, adding 100 parts of crystallized polypropylene particles, 4 parts of maleic anhydride, and 0.3 parts of initiator into a mixing kettle according to the proportion, and heating to the atmospheric reflux temperature under stirring until they are completely dissolved, the atmospheric reflux temperature being usually 135° C.;

[0122] S22, adding the mixture into a reaction kettle, controlling the temperature at 210° C., and reacting for 2 min to obtain a reaction product;

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

[0124] S24, crushing the grafted product, wrapping it with filter paper, putting it into a Soxhlet extractor, using ethanol as a solvent, heating and refluxing in a water bath for 24 hours to obtain an extracted grafted product;

[0125] S25, placing the extracted grafted product in a vacuum oven at 110° C. and drying for 12 hours to obtain maleic anhydride grafted polypropylene particles with refined grains;

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

[0127] S4. Add carbon dioxide, a physical foaming agent, to the blended material for extrusion foaming. The die head temperature of the extrusion foaming is 160° C. The extrusion foaming is carried out in a single-screw extruder at an extrusion speed of 60 r / min. A rectangular parallelepiped mold is used to obtain a polypropylene foam flame retardant material.

[0128] This embodiment also provides a lithium battery module, including a polypropylene foam flame retardant material.

[0129] Comparative Example 1

[0130] Different from Example 1, this comparative example provides a polypropylene foam flame retardant material, which is obtained by foaming a polypropylene composite material. The polypropylene composite material includes, by 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] Different from Example 1, this comparative example provides a polypropylene foam flame retardant material, which is obtained by foaming a polypropylene composite material. Calculated by weight percentage, the polypropylene composite material includes 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] Different from Example 1, this comparative example provides a polypropylene foam 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 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.

[0135] Experimental example

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

[0137] Use a melt strength tester (such as Gottfert "Rheotens" melt strength tester) to measure the melt strength of polypropylene foam material. Before the test, ensure that the melt strength tester is in good condition, all components are operating normally, and the sensor is accurately calibrated. Enter the specific extraction rate value through the instrument's control panel or software. In this experiment, the extraction rate is set to 5 mm / s.

[0138] Adding samples: preheating a melt strength tester to a corresponding extrusion foaming die temperature, blending the maleic anhydride grafted grain-refined polypropylene particles, non-crystalline resin, high molecular weight plasticizer, inorganic flame retardant and nucleating agent to obtain a blended material, adding the obtained blended material to an extruder barrel, and keeping the temperature for 6 minutes to ensure the uniformity and stability of the melt.

[0139] Start the test: Then start the extruder, so that the melt is squeezed downward from the die. While the melt is squeezed out of the die, it is pulled by two rollers installed on the balance beam in opposite directions. The rollers move at a lower speed at the beginning, and then gradually accelerate. The rollers accelerate evenly and apply tensile force to the melt bundle. During the stretching process, the stress of the melt bundle is monitored in real time, and the change of tensile force over time is recorded. When the tensile force reaches a certain level, the melt bundle will break. The force recorded at this time when the melt bundle breaks is the "melt strength" of the polymer.

[0140] Data recording: The same sample needs to be tested multiple times, generally at least 3 times, to ensure the accuracy and reliability of the data. The melt strength value of each test is recorded and its average value is calculated as the final melt strength of the sample. The tensile hardness value is usually in centinewton (cN).

[0141] Calculation results: The mass corresponding to a time of 3 minutes is obtained, and this mass can be used as the melt strength at this temperature. The larger the mass value, the higher the melt strength. The melt strength measurement results of the polypropylene foam flame retardant materials 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 measurement results in Table 1 that, compared with the melt strength during the preparation of the polypropylene foam flame retardant material provided in Comparative Examples 1-3, the melt strength during the preparation of the polypropylene foam flame retardant material provided in Examples 1-3 is significantly higher than the melt strength during the preparation of the polypropylene foam flame retardant material provided in Comparative Examples 1-3; compared with the melt strength during the preparation of the polypropylene foam flame retardant material provided in Comparative Example 1, it is shown that polypropylene grafted maleic anhydride can improve the compatibility between the polar flame retardant and polypropylene, reduce the phase region size, and increase the foaming temperature after the addition of the inorganic flame retardant, so that the foaming temperature window of the foaming system becomes wider, and the melt strength increases when foaming at the same temperature; compared with the melt strength during the preparation of the polypropylene foam flame retardant material provided in Comparative Example 2 The comparison of melt strength shows that the present invention adds a nucleating agent in the post-treatment step of preparing polypropylene particles to obtain polypropylene particles with refined grains, and improves the crystallinity of polypropylene, which can increase the melting point of polypropylene during the foaming process. Within a range higher than the existing foaming temperature, it is still helpful to improve the strength of the polypropylene melt, so that it is not easy to deform or break when subjected to external forces; compared with the melt strength in the preparation process of the polypropylene foamed flame retardant material provided in Comparative Example 3, it is shown that the non-crystalline resin has a higher elastic recovery performance and can quickly recover to its original shape when subjected to external forces. This elasticity can improve the anti-extension property of the melt, thereby increasing the melt strength, so that it can better maintain the shape of the pores during the foaming process and prevent the pores from merging and breaking.

[0146] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A polypropylene foamed flame retardant material, obtained by foaming a polypropylene composite material, characterized in that: According to weight percentage, the polypropylene composite material includes 85-92 parts of maleic anhydride grafted grain-refined polypropylene particles, 45-62 parts of non-crystalline resin, 3-5 parts of high molecular weight plasticizer, 20-35 parts of inorganic flame retardant, 5-10 parts of nucleating agent, and 2-5 parts of physical foaming agent.

2. A polypropylene foam flame retardant material as claimed in claim 1, characterized in that: The polypropylene composite material comprises 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.

3. A polypropylene foamed flame retardant material as claimed in claim 1, characterized in that: The inorganic flame retardant is a mixture of one or more inorganic phosphorus flame retardants, aluminum hydroxide, magnesium hydroxide, and antimony trioxide.

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

5. The polypropylene foamed flame retardant material according to claim 1, characterized in that: The nucleating agent is one of sodium benzoate, talc, sorbitol, TMB-4, TMB-5, STARNU-100, N,N'-dicyclohexyl terephthalamide, and WBG-II.

6. A polypropylene foamed flame retardant material as claimed in claim 1, characterized in that: The non-crystalline resin is one of polystyrene, acrylonitrile-butadiene-styrene copolymer, polymethyl methacrylate and polyvinyl chloride.

7. A polypropylene foamed flame retardant material as claimed in claim 1, characterized in that: The physical foaming agent is one of carbon dioxide, air and nitrogen.

8. The method for preparing a polypropylene foamed flame retardant material according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1. Preparation of grain-refined polypropylene particles: In the post-processing step of preparing the polypropylene particles, the nucleating agent is added to the hot air dried polypropylene particles, and then cooled to obtain the grain-refined polypropylene particles; S2, the preparation of the maleic anhydride grafted grain-refined polypropylene particles comprises the following steps: S21, adding 100 parts of the grain-refined polypropylene particles, 4 parts of maleic anhydride, and 0.3 parts of initiator into a mixing kettle according to proportion, and heating to the atmospheric reflux temperature under stirring until they are completely dissolved, wherein the atmospheric reflux temperature is usually 120° C.-150° C.; S22, adding the mixture into a reaction kettle, controlling the temperature between 170° C. and 220° C., and reacting for 1 min to 3 min to obtain a reaction product; S23, the reaction product is decompressed to atmospheric pressure through buffering and then discharged, acetone at room temperature is added as a precipitating agent, and then a grafted product is obtained through precipitation and filtration; S24, crushing the grafted product, wrapping it with filter paper, putting it into a Soxhlet extractor, using ethanol as a solvent, heating and refluxing in a water bath for 24 hours to obtain an extracted grafted product; S25, placing the extracted grafted product in a vacuum oven at 110° C. and drying for 12 hours to obtain the maleic anhydride grafted polypropylene particles with refined grains; S3, blending the maleic anhydride grafted grain-refined polypropylene particles, non-crystalline resin, high molecular weight plasticizer, inorganic flame retardant and nucleating agent to obtain a blended material, wherein the blending temperature is 180° C.-210° C.; 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.

9. The method for preparing a polypropylene foamed flame retardant material according to claim 8, characterized in that: In step S4, extrusion foaming is performed in a single-screw extruder at an extrusion speed of 60 r / min and a rectangular parallelepiped mold is used to obtain the polypropylene foamed flame retardant material.

10. A lithium battery module, characterized in that: A polypropylene foamed flame retardant material comprising any one of claims 1 to 7.

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