High-temperature-resistant high-strength low-pressure variable halogen-free flame-retardant EPDM rubber and preparation method thereof

Abstract

The application discloses a high-temperature-resistant high-strength low-pressure variable halogen-free flame-retardant EPDM rubber and a preparation method thereof. 2+ The application adopts peroxide vulcanization system to construct a double cross-linking network in the rubber, effectively improves the cross-linking density of the EPDM rubber, improves the rubber elasticity, reduces the rubber compression deformation rate, prolongs the service life of the rubber, realizes the improvement of the flame-retardant effect of the rubber composite material on the premise of maintaining good mechanical properties and service life, achieves smokeless combustion and self-extinguishing, and reasonably solves the key problems of the current halogen-free flame-retardant EPDM, such as large filling amount of the flame retardant, low rubber strength and poor compression performance, and is applied to the fields of new energy automobile battery pack rubber sealing parts, explosion-proof valves, electric wires and cables and household appliances.

Description

Technical Field

[0001] This invention belongs to the field of rubber modification technology, specifically relating to a high-temperature resistant, high-strength, low-pressure variable halogen-free flame-retardant EPDM rubber and its preparation method. Background Technology

[0002] Ethylene propylene rubber (EPM) is a copolymer of ethylene, propylene, and unsaturated dienes. Based on the saturation of the molecular chain and the different types of monomers, it can be divided into binary ethylene propylene rubber (EPM) and EPDM rubber (EPDM). EPM contains only ethylene and propylene monomers in its structural unit, and lacks unsaturated bonds in the main chain and side chains. It requires the addition of a peroxide system to initiate the cross-linking reaction, thus significantly limiting its production and usage. To retain the advantages of EPM and achieve industrialization, EPDM has gained wider applications. EPDM rubber is produced by introducing a small amount of a third monomer (non-conjugated diene) onto the ethylene and propylene monomers. Unlike saturated EPM rubber, EPDM has a low degree of saturation in its main chain, composed of C-C single bonds, making it a non-crystalline rubber. Furthermore, its main chain is copolymerized from saturated ethylene and propylene monomers, resulting in good chemical stability. To date, it is one of the fastest-growing synthetic rubbers in the world. Currently, EPDM rubber is widely used in building waterproofing materials, cable sheaths, heat-resistant rubber hoses, tapes, and automotive seals. Despite its excellent overall performance, EPDM rubber still has some shortcomings. Like all carbon-based rubbers, EPDM rubber is easily combustible at room temperature, with a limiting oxygen index (LOI) of only 17.0%. Furthermore, it burns by dripping fuel, which further intensifies the fire. Therefore, improving the flame retardancy and anti-dripping properties of EPDM rubber is crucial and necessary.

[0003] In recent years, the number of deaths caused by fires has been steadily rising. Modern building materials and household goods burn quickly, are highly toxic, and produce more smoke, posing a significant fire hazard. Developing non-combustible or low-flammability composite materials is imperative. Polymer combustion involves many processes, typically requiring heat, fuel, and oxygen. The combustion process involves two key free radicals: highly reactive hydrogen radicals (H·) and hydroxyl radicals (HO·). These, along with external heat sources and the polymer's own combustion heat, conversely provide heat to the polymer. The polymer can only completely burn and cease combustion when the combustion heat is sufficient to sustain thermal degradation and there are no external obstructions, making it extremely dangerous.

[0004] Currently, most domestic and international methods improve the flame retardant properties of EPDM rubber by adding flame retardants. Chinese patent application number 202310314913.X discloses a flame-retardant and aging-resistant EPDM rubber waterproof membrane. It uses aluminum diethylphosphinate and expanded graphite to prepare a composite flame retardant of aluminum diethylphosphinate and expanded graphite, and uses chlorosulfonated polyethylene as an antioxidant to prepare the composite EPDM rubber. However, this composite rubber contains halogens, which produce toxic fumes when burned, seriously endangering the environment and human life. Han Linxuan et al. from Sichuan University (Polymer Degradation and Stability, 2022, 201, 19, 109) synthesized poly(2-butene-1,4-dikepiperazine fumaroylphenylphosphonate, PPFPP) oligomers and used ammonium polyphosphate (APP) as a char-forming agent to prepare an intumescent flame retardant. When 20 wt% APP / PPFPP (weight ratio 3:1) was added to EPDM rubber, the flame retardancy of the modified rubber reached V-0 level (UL-94 test) and LOI reached 27.0%. However, the preparation process is complex and costly, making it difficult to achieve industrial production. Chinese patent application number 202010140646.5 discloses a flame-retardant EPDM rubber and its preparation method. It uses crystallized magnesium hydroxide coated with expanded graphite as a flame retardant to prepare EPDM composite rubber. The resulting composite rubber is non-toxic and harmless and will not cause environmental pollution. However, its flame retardant effect is relatively average, and the process is complicated, which is not conducive to large-scale industrial production. Summary of the Invention

[0005] Based on the aforementioned technical problems in the background art, this invention provides a high-temperature resistant, high-strength, low-pressure-deformation, halogen-free flame-retardant EPDM rubber and its preparation method. This invention yields a high-strength, low-pressure-deformation, halogen-free, environmentally friendly, and flame-retardant V-0 grade rubber, effectively solving the problems of low strength, toxicity, and high compression set of flame-retardant EPDM rubber. Simultaneously, it effectively reduces environmental pollution, providing a sustainable development path for building a resource-saving, green, and environmentally friendly society in my country.

[0006] This invention relates to a high-temperature resistant, high-strength, low-pressure variable halogen-free flame-retardant EPDM rubber, the raw materials of which are composed of the following parts by mass:

[0007] EPDM rubber 100 copies Aluminum hydroxide 10-60 servings Ammonium polyphosphate 10-60 servings Methyl methacrylate 10-20 servings Peroxide vulcanizing agent 2-4 portions crosslinking agent 2-4 portions carbon black 30-50 servings Zinc oxide 3-7 portions stearic acid 1-2 portions Anti-aging agents 2-4 portions

[0008] The EPDM rubber grade is K2470S, with a Mooney viscosity ML(1+4) of 20-30 at 125℃, an ethylene content of 60-70%, a third monomer content of 3.0-5.0% ENB, and is unfilled with oil.

[0009] The aluminum hydroxide has a particle size of 200-270 mesh.

[0010] The ammonium polyphosphate has a particle size of 300-350 mesh and a degree of polymerization ≥80, and is a high-polymer ammonium polyphosphate.

[0011] Furthermore, the total amount of flame retardant aluminum hydroxide and ammonium polyphosphate added is 60 parts.

[0012] The methyl methacrylate is a liquid with a density of 0.943 g / cm³. 3 .

[0013] The peroxide vulcanizing agent is dicumyl peroxide (DCP), and the crosslinking agent is triallyl isocyanurate (TAIC).

[0014] The carbon black is N330 with a particle size of 25-45 nm.

[0015] The zinc oxide has a purity of over 99%.

[0016] The stearic acid has a purity of over 98% and a melting point between 69-72°C.

[0017] The antioxidant is one or both of 2,2,4-trimethyl-1,2-dihydroquinoline polymer (RD) and 2-mercaptobenzimidazole (MB), and when two are selected for mixing, the ratio is 1:1.

[0018] The present invention discloses a method for preparing high-temperature resistant, high-strength, low-pressure variable halogen-free flame-retardant EPDM rubber, comprising the following steps:

[0019] 100g of EPDM rubber was added to a mixer and melted at 160℃ for 1min. Then, flame retardants aluminum hydroxide and ammonium polyphosphate were added and sheared at 60r / min for 15min to prepare flame retardant EPDM rubber.

[0020] The prepared flame-retardant EPDM rubber was milled on a two-roll mill. Zinc oxide, methyl methacrylate, stearic acid, antioxidant, and carbon black were added and mixed evenly. Finally, peroxide vulcanizing agent and crosslinking agent were added. The mixture was cut several times to the left and right to ensure that the masterbatch was fully absorbed. Finally, it was thinly sheeted to obtain the masterbatch.

[0021] After the obtained masterbatch is left to stand for 24 hours, it is vulcanized to obtain high-temperature resistant, high-strength, low-pressure variable halogen-free flame-retardant EPDM rubber.

[0022] The vulcanization treatment is performed at a pressure of 10 MPa, a temperature of 150-180°C, and a time of 500-800 seconds.

[0023] All raw materials used in the formulation of this invention are commercially available. The selected EPDM rubber grade is K2470S, which has high Mooney viscosity and ethylene content, resulting in high tensile and tear strength in the vulcanized rubber compound. The high ethylene content also contributes to the excellent abrasion and heat resistance of the vulcanized rubber, and allows for higher filler content to reduce costs. Furthermore, the higher content of the third monomer results in faster vulcanization, lower costs, and higher production efficiency.

[0024] Because EPDM rubber produces a large amount of smoke when burning, flame retardants can be added to achieve flame retardancy. This invention uses aluminum hydroxide (ATH), an inorganic metal hydroxide flame retardant, in combination with ammonium polyphosphate (APP), a nitrogen-phosphorus flame retardant. Based on the synergistic effect between nitrogen and phosphorus elements, it features low addition amount and high flame retardant efficiency. Moreover, aluminum hydroxide not only improves the heat resistance of the vulcanized rubber but also has a smoke-suppressing effect. The main mechanism is that ammonium polyphosphate, under the action of aluminum hydroxide, generates phospholipids and polymetaphosphate. Polymetaphosphate has a dehydrating effect, accelerating the thermal decomposition of aluminum hydroxide and causing a dehydration reaction. By optimizing the ratio of aluminum hydroxide to ammonium polyphosphate, the flame retardant system is promoted to undergo thermal dehydration, char layer formation, cooling, and oxygen isolation. The resulting modified rubber is environmentally friendly and halogen-free, and the combustion products do not release any toxic gases. The product is green, environmentally friendly, and harmless to the human body.

[0025] Methyl methacrylate (MMA) is added, and it reacts with zinc oxide to produce zinc dimethacrylate (ZDMA) in situ, introducing Zn. 2+ An ionic crosslinking network, combining a peroxide vulcanizing system with carbon black, forms a double crosslinking network within the rubber. Compared to pure EPDM, the introduction of ZDMA improves both tensile strength and elongation at break. Furthermore, during aging, it can delay the increase in compression deformation and the decrease in the contact stress relaxation coefficient, thereby enhancing the sealing elasticity and durability of EPDM. The ZDMA itself exhibits uniform distribution. During vulcanization, a double crosslinking network is constructed, including covalent crosslinking of the peroxide vulcanizing agent and the additive CC, as well as the Zn introduced by ZDMA. 2+ Ionic crosslinking leads to a significant increase in crosslinking density and retention rate during aging, thus exhibiting synergistic reinforcement and stabilization effects.

[0026] Traditional rubber uses sulfur as a vulcanizing agent. While sulfur vulcanization offers a fast vulcanization rate, it easily leads to blooming on the rubber surface, reduced heat resistance, poor resilience at high temperatures, and high permanent compression set. This invention uses DCP peroxide as the rubber vulcanizing agent. The structure of the vulcanized rubber obtained by peroxide vulcanization is composed of C-C crosslinks with short bond lengths and high bond energies. This results in excellent resilience and low permanent compression set. The peroxide vulcanization process produces C-C crosslinks with high bond energies, resulting in strong heat resistance, low permanent compression set, and less blooming, giving EPDM rubber excellent heat resistance and low permanent deformation. Because the initial decomposition temperature of peroxides is very high, the vulcanization temperature of traditional vulcanized rubber needs to be increased accordingly. Increasing the vulcanization temperature also reduces vulcanization time and lowers production costs. This invention uses TAIC as a co-crosslinking agent. TAIC acts as a covalent bridge during peroxide vulcanization, effectively increasing the crosslink density of the vulcanized rubber, shortening the vulcanization time, improving the tensile strength of the rubber, and significantly reducing the permanent compression set. Furthermore, the present invention uses zinc oxide as an activator, which not only accelerates the vulcanization rate of rubber, but also increases the crosslinking density of rubber.

[0027] In summary, this invention uses high Mooney viscosity, high ethylene content EPDM rubber K2470S as the matrix to ensure high fillerability, enabling the vulcanizate to achieve high strength and low cost. The addition of flame retardants aluminum hydroxide and ammonium polyphosphate imparts excellent flame retardant properties to the rubber, achieving a V-0 flame retardant rating. The addition of a certain amount of carbon black improves the tensile and tear strength of the rubber. This significantly enhances the physical properties of the vulcanizate, meeting the requirements for high strength, tear strength, and processability. The use of peroxide vulcanizing agent DCP and crosslinking agent TAIC ensures the vulcanization speed and crosslinking density of the compound, thereby improving the resilience and heat resistance of the vulcanizate and reducing permanent compression set.

[0028] The EPDM rubber of this invention features low flame retardant content, high tensile strength, tear strength, high resilience, and low permanent compression set. It achieves smokeless combustion, self-extinguishing upon removal of the flame, and is free of halogens, making it environmentally friendly and pollution-free. It effectively addresses the shortcomings of current flame-retardant rubbers, such as high flame retardant content, low strength, high permanent compression set, and the generation of toxic and harmful substances during combustion. This invention fully complies with EU RoHS requirements and can be widely applied in fields such as new energy vehicle power battery packs, explosion-proof valves, wires and cables, and household appliances. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image of the cross-section of the sample from Example 1.

[0030] Figure 2 This is a scanning electron microscope image of the cross-section of the sample from Example 2.

[0031] Figure 3 This is a scanning electron microscope image of the cross-section of the sample in Example 3.

[0032] Figure 4 These are scanning electron microscope images of the cross-section of a comparative sample. Detailed Implementation

[0033] The present invention will be further described below with reference to embodiments, but the scope of the present invention is not limited to these embodiments.

[0034] Example 1:

[0035] 1. Ingredients

[0036] EPDM rubber: 100 parts

[0037] Aluminum hydroxide: 20 parts

[0038] Ammonium polyphosphate: 40 parts

[0039] Methyl methacrylate: 15 parts

[0040] Peroxide vulcanizing agent DCP: 3 parts

[0041] Crosslinking agent TAIC: 3 parts

[0042] Carbon black: 40 parts

[0043] Zinc oxide: 5 parts

[0044] Stearic acid: 1 part

[0045] Anti-aging agent: 3 parts

[0046] 2. Preparation

[0047] (1) Add 100g of EPDM rubber to a mixer and melt it at 160℃ for 1min. Then add flame retardant aluminum hydroxide and ammonium polyphosphate and shear reaction at 60r / min for 15min to prepare flame retardant EPDM rubber.

[0048] (2) The prepared flame-retardant EPDM rubber is milled on a two-milling machine. Zinc oxide, methyl methacrylate, stearic acid, antioxidant, and carbon black are added and mixed evenly. Finally, peroxide vulcanizing agent and crosslinking agent are added. The masterbatch is cut several times to ensure that the masterbatch is fully absorbed. Finally, it is thinly sheeted to obtain masterbatch A.

[0049] (3) The obtained masterbatch is vulcanized after being left to stand for 24 hours to obtain high-temperature resistant, high-strength, low-pressure variable halogen-free flame-retardant EPDM rubber. The vulcanization treatment is carried out at a pressure of 10 MPa, a temperature of 150-180℃, and a time of 500-800 s.

[0050] Example 2:

[0051] 1. Ingredients

[0052] EPDM rubber: 100 parts

[0053] Ammonium polyphosphate: 60 parts

[0054] Methyl methacrylate: 15 parts

[0055] Peroxide vulcanizing agent DCP: 3 parts

[0056] Crosslinking agent TAIC: 3 parts

[0057] Carbon black: 40 parts

[0058] Zinc oxide: 5 parts

[0059] Stearic acid: 1 part

[0060] Anti-aging agent: 3 parts

[0061] 2. Preparation

[0062] Following the preparation process described in Example 1, halogen-free flame-retardant EPDM rubber was obtained after open mill vulcanization.

[0063] Example 3:

[0064] 1. Ingredients

[0065] EPDM rubber: 100 parts

[0066] Aluminum hydroxide: 20 parts

[0067] Ammonium polyphosphate: 40 parts

[0068] Peroxide vulcanizing agent DCP: 3 parts

[0069] Crosslinking agent TAIC: 3 parts

[0070] Carbon black: 40 parts

[0071] Zinc oxide: 5 parts

[0072] Stearic acid: 1 part

[0073] Anti-aging agent: 3 parts

[0074] 2. Preparation

[0075] Following the preparation process described in Example 1, halogen-free flame-retardant EPDM rubber was obtained after open mill vulcanization.

[0076] Comparative example:

[0077] 1. Ingredients

[0078] EPDM rubber: 100 parts

[0079] Peroxide vulcanizing agent DCP: 3 parts

[0080] Crosslinking agent TAIC: 3 parts

[0081] Carbon black: 40 parts

[0082] Zinc oxide: 5 parts

[0083] Stearic acid: 1 part

[0084] Anti-aging agent: 3 parts

[0085] 2. Preparation

[0086] Following the preparation process described in Example 1, halogen-free flame-retardant EPDM rubber was obtained after open mill vulcanization.

[0087] The vulcanizates prepared in Examples 1, 2, and 3, along with the comparative examples, were subjected to physical and flame retardant property tests. Hardness testing was conducted according to GB / T2411-2008; tensile strength and elongation at break testing according to GB / T 528-2009; tear strength testing according to ASTM D624; and heat aging resistance testing according to ASTM D865 (oven drying at 150℃ for 70 hours). Permanent compression set testing was conducted according to GB / T 1683-2018. Flame retardancy testing (limiting oxygen index) was conducted according to GB / T10707-2008. Flame retardancy testing (UL-94) was conducted according to GB / T 2408-2008. Combustion testing (cone calorimetry) was conducted according to ASTM E1354 and ISO 5560. The results are as follows:

[0088] Table 1 Performance Indicators of EPDM Rubber

[0089]

[0090] Table 2 Combustion Performance of EPDM Composite Rubber

[0091] Combustion parameters Example 1 Example 2 Example 3 Comparative Example Thermal decomposition temperature (°C) 431 423 421 435 Ignition time (s) 69 60 58 61 Extinguishing time (s) 328 368 342 651 <![CDATA[Total heat release (MJ / m 2 )]]> 42.8 51.5 50.2 72.0 <![CDATA[Mean heat release rate (kW / m 2 )]]> 148.1 167.2 162.5 182.1 <![CDATA[Peak heat release rate (kW / m 2 )]]> 308.2 452.4 423.6 518.5 Mean mass loss rate (g / s) 0.051 0.047 0.043 0.036 Peak mass loss rate (g / s) 0.317 0.325 0.315 0.383 Average yield of carbon monoxide (kg / kg) 0.002 0.019 0.021 0.032 Average yield of carbon dioxide (kg / kg) 0.20 1.31 1.21 5.78 Carbonization rate (%) 48.1 38.3 37.4 31.5

[0092] The performance of conventional halogen-free flame-retardant rubber needs to meet the following standards: hardness, tensile strength, tear strength, elongation at break, air aging resistance, permanent compression set, and flame retardancy. Hardness assesses the product's ability to resist external stress without change; tensile strength, tear strength, and air aging resistance assess the product's service life; elongation at break assesses the product's assembly performance; permanent compression set assesses the product's operating conditions; and flame retardancy rating assesses the product's flame resistance. Based on the current requirements for flame-retardant materials used in new energy vehicles, the following standards must be met: hardness 75±5 degrees, tensile strength ≥10MPa, elongation at break ≥450%, tear strength ≥5N / mm, permanent compression set ≤40% after hot air aging at 150℃ for 70h, and a loss of ≤25% in tensile strength, elongation at break, and tear strength after oven aging; and a flame retardancy rating of V-0.

[0093] As can be seen from the data in Tables 1 and 2, when the total amount of flame retardant is fixed at 60 parts, adding an appropriate amount of metal hydroxide flame retardant results in better mechanical and flame retardant properties compared to adding all of the ammonium polyphosphate. When the ratio of aluminum hydroxide to ammonium polyphosphate is 20:40 parts, the halogen-free flame-retardant rubber prepared in Example 1 exhibits moderate hardness, high tensile and tear strength, good resistance to hot air aging, low permanent compression set, and a V-0 flame retardant rating, meeting the requirements for use as a sealing material in power battery packs for new energy vehicles. Furthermore, Figures 1-4 These are scanning electron microscope (SEM) images of the interfaces of the samples in Examples 1, 2, 3, and the comparative examples.

[0094] After the addition of methyl dimethacrylate, ZDMA is generated and polymerized in situ. ZDMA is uniformly dispersed in the matrix and rapidly polymerizes during the vulcanization process to form a Zn-containing matrix. 2+ Ions, tightly embedded in the matrix, exhibit strong interfacial interactions. This introduces an ionic crosslinking network. Simultaneously, grafting ZDMA onto the EPDM molecular chains via peroxide initiation also contributes to increasing the covalent crosslinking network, forming a composite rubber with a multi-layered crosslinking network. Compared to pure EPDM rubber, the thermo-oxidative aging process of the EPDM composite rubber is delayed with increasing oxidation induction time. The multi-layered crosslinking network is constructed through the crosslinking of the EPDM chains and the introduction of Zn... 2+ The formation of covalent cross-linked networks by ions significantly enhances the mechanical, durable sealing, and resilience properties of EPDM composite rubber.

[0095] The high-temperature resistant, high-strength, low-pressure variable halogen-free flame-retardant EPDM rubber prepared by this invention can effectively compensate for the defects of halogen-free flame-retardant rubber, such as large flame retardant filling amount, low strength, and high compression deformation rate. At the same time, it expands the application range of halogen-free flame-retardant rubber and is widely used in the fields of new energy vehicle power battery packs, explosion-proof valves, wires and cables, and household appliances.

[0096] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope stated in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high temperature resistant, high strength, low pressure, halogen-free, flame retardant EPDM rubber, characterized in that The raw materials are composed of the following components by mass fraction: The EPDM rubber is K2470S, the Mooney viscosity ML(1+4)125℃ is 20-30, the ethylene content is 60-70%, the third monomer is ENB with a content of 3.0-5.0%, and it is not oil-extended; The particle size of the aluminum hydroxide is 200-270 mesh; The polyammonium phosphate is high-polymer polyammonium phosphate with a polymerization degree of ≥80 and a particle size of 300-350 mesh. 2.The high-temperature-resistant high-strength low-pressure variable halogen-free flame-retardant EPDM rubber according to claim 1, characterized in that: The peroxide vulcanizing agent is dicumyl peroxide, and the auxiliary crosslinking agent is triallyl isocyanurate. 3.The high-temperature-resistant high-strength low-pressure variable halogen-free flame-retardant EPDM rubber according to claim 1, characterized in that: The carbon black is N330. 4.The high-temperature-resistant high-strength low-pressure variable halogen-free flame-retardant EPDM rubber according to claim 1, characterized in that: The antioxidant is one or both of 2,2,4-trimethyl-1,2-dihydroquinoline polymer and 2-mercaptobenzimidazole.

5. Process for the production of high temperature resistant, high strength, low pressure, halogen-free flame retardant EPDM rubber according to any one of claims 1 to 4, characterized in that The method comprises the following steps: 100g of EPDM rubber is added to a mixer and melted at 160℃ for 1min, then the flame retardant aluminum hydroxide and polyammonium phosphate are added, and the mixture is sheared at 60r / min for 15min to prepare flame-retardant EPDM rubber; The prepared flame-retardant EPDM rubber is mixed on an open mill, and zinc oxide, methyl methacrylate, stearic acid, antioxidant, and carbon black are added and mixed uniformly, and finally peroxide vulcanizing agent and auxiliary crosslinking agent are added, and the left and right knives are cut several times to make the masterbatch completely eat the material, and finally the sheet is thin-passed to obtain the masterbatch; The obtained masterbatch is stored for 24h and then subjected to vulcanization treatment to obtain the high-temperature-resistant high-strength low-pressure variable halogen-free flame-retardant EPDM rubber. 6.The preparation method according to claim 5, characterized in that: The pressure of the vulcanization treatment is 10MPa, the temperature is 150-180℃, and the time is 500-800s.

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