A method for enhancing thermal stability and oxidative stability of ethylene propylene diene rubber by functionalized h-bn nanosheets

Abstract

This invention relates to the field of rubber modification technology, specifically a method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets. The method includes the following steps: S1, preparation of hydroxylated h-BN nanosheets; S2, synthesis of phosphazene-modified boron nitride: Purify hexachlorocyclotriphosphine for later use, then weigh 1g of h-BN-OH powder and grind it. Pour the powder into a three-necked flask containing 100ml acetone and ultrasonically stir for 2h. Then add 0.8g of 4,4-dihydroxybiphenyl and continue stirring for 10min. Next, add an acetone solution of HCCP and 5ml of triethylamine dropwise. After the reaction, add tannic acid. After the reaction is complete, cool to room temperature, wash and dry to obtain phosphazene-modified boron nitride; S3, preparation of phosphazene-modified boron nitride / EPDM composite material. This invention, through the synergistic effect of the P / N groups and phenolic hydroxyl groups in phosphazene-modified boron nitride, enables phosphazene-modified boron nitride to achieve excellent flame retardant effects with a lower amount of flame retardant added, significantly reducing the amount of flame retardant used.

Description

Technical Field

[0001] This invention relates to the field of rubber modification technology, and more specifically, to a method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets. Background Technology

[0002] Ethylene propylene diene monomer (EPDM) rubber is widely used in automotive seals, cable sheaths, and building waterproofing materials due to its excellent weather resistance, high temperature resistance, and insulation properties. However, EPDM still has the following technical limitations in high-temperature, oxidizing, and fire-prone environments:

[0003] 1. Insufficient flame retardant performance: In high-temperature, high-speed operation and fire environments, the flammability and low thermal conductivity of EPDM limit its further application in some high-performance fields. Traditional flame retardants, such as chlorinated flame retardants and brominated flame retardants, although effectively improving flame retardant performance, are often accompanied by environmental pollution, toxicity problems and a decline in the mechanical properties of materials.

[0004] 2. Poor thermal stability: Unmodified EPDM is easily oxidized and degraded at high temperatures (>150℃), with an oxidation induction time (OIT) of less than 1 minute, thus limiting its service life;

[0005] 3. Poor filler dispersibility: When boron nitride (h-BN) is used as a thermally conductive / flame-retardant filler, it tends to agglomerate due to its surface inertness and poor compatibility with the rubber matrix, resulting in limited improvement in thermal conductivity (<10%) and low flame retardant efficiency.

[0006] 4. Insufficient aging performance: After 168 hours of heat aging, the elongation at break of conventional EPDM decreases by more than 80%, which is difficult to meet the requirements for long-term use.

[0007] Meanwhile, in the prior art, Chinese invention patent CN1923884A discloses a method for preparing halogen-free flame-retardant EPDM rubber, which uses aluminum hydroxide or magnesium hydroxide as the main flame retardant and adds a large amount, resulting in increased material hardness, decreased elasticity, and deteriorated extrusion processing performance. Therefore, it fails to solve the problem of balancing flame retardancy and mechanical properties. Chinese invention patent CN118772545B discloses a low-density, high-flame-retardant EPDM rubber composite material and its preparation method, which uses a synergistic flame retardant (containing silicon, nitrogen, and phosphorus elements). Although it reduces the amount of inorganic flame retardant, it requires a complex preparation process (such as multi-step condensation reaction) and has a high cost.

[0008] Therefore, how to improve the flame retardant properties of EPDM without sacrificing other properties, especially mechanical properties, has become a key focus of current research. Summary of the Invention

[0009] The purpose of this invention is to provide a method for enhancing the thermal and oxidative stability of EPDM using functionalized h-BN nanosheets, in order to solve the problems mentioned in the background art, such as insufficient flame retardancy, poor thermal stability, poor filler dispersibility, and insufficient aging performance of unmodified EPDM.

[0010] To achieve the above objectives, the present invention aims to provide a method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets, comprising the following steps:

[0011] S1. Preparation of hydroxylated h-BN nanosheets: h-BN and sodium hydroxide were mixed at a mass ratio of 1:10, and grinding balls were added. The mixture was ball-milled at 600 rpm for 1 hour, then cooled for 1 hour. The process was repeated 5 times. The mixture was filtered and washed until the pH was neutral, and then dried and allowed to stand to obtain h-BN-OH.

[0012] S2. Synthesis of Phosphazene-Modified Boron Nitride h-BN@PDT: Purify hexachlorocyclotriphosphazene HCCP for later use. Then weigh 1g of h-BN-OH powder and grind it. Pour the powder into a three-necked flask containing 100ml of acetone and sonicate for 2h. Then add 0.8g of 4,4-dihydroxybiphenyl and continue stirring for 10min. Then add dropwise the acetone solution of HCCP and 5ml of triethylamine. Reflux at 70℃ for 1h. Then add 1.7g of tannic acid and continue the reaction for 10h. After the reaction is completed, cool to room temperature, wash, and then dry to obtain h-BN@PDT.

[0013] Preparation of S3 and h-BN@PDT / EPDM composite materials: EPDM is appropriately plasticized in a two-roll mill until the rubber completely wraps around the rolls. Then, a plasticizer is added, followed by a mixture of silica and calcium carbonate. Then, silica, flame retardant, h-BN@PDT, antioxidant RD, bis-(γ-triethoxysilylpropyl)-tetrasulfide and color masterbatch are added in sequence. Finally, a vulcanizing agent is added. After all materials are mixed evenly, the mixture is thinly passed through a mill and sheeted to obtain the h-BN@PDT / EPDM composite material.

[0014] As a further improvement to this technical solution, the ball milling parameters in step S1 are as follows:

[0015] The grinding balls are made of agate, with a diameter of 3-5mm and a ball-to-material ratio of 2.5:1.

[0016] As a further improvement to this technical solution, the specific steps for purifying HCCP in step S2 are as follows:

[0017] Add 200 mL of anhydrous n-hexane to a beaker, heat in an oil bath to 70 °C, add HCCP to the beaker until it no longer dissolves, prepare a saturated HCCP / n-hexane solution, then filter while hot, collect the filtrate in a glass bottle, crystallize and purify, then place the HCCP in a refrigerator to cool and crystallize, remove the n-hexane, and obtain purified HCCP.

[0018] As a further improvement to this technical solution, the mass-volume concentration of the acetone solution of HCCP in step S2 is 35 g / L.

[0019] As a further improvement to this technical solution, the washing method in step S2 is: washing three times with ethanol and deionized water.

[0020] As a further improvement to this technical solution, the drying method in step S2 is: drying overnight in a vacuum oven at 70°C.

[0021] As a further improvement to this technical solution, the mass ratio of silicon dioxide to calcium carbonate in the mixture of silicon dioxide and calcium carbonate is 2:1, the plasticizer is paraffin oil Sunpar 2280, and the vulcanizing agent is peroxide vulcanizing agent: 101XL45-SP2.

[0022] As a further improvement to this technical solution, the flame retardant is a mixture of ammonium polyphosphate (APP) and melamine-formaldehyde resin (CFA) in a mass ratio of 4:1.

[0023] As a further improvement to this technical solution, the mass fraction formulation of the h-BN@PDT / EPDM composite material in step S3 is as follows:

[0024] 100 parts EPDM, 50 parts silica, 25 parts mixture of silica and calcium carbonate, 5 parts plasticizer, 24 parts flame retardant, 0.1-1.2 parts h-BN@PDT, 1.5 parts antioxidant RD, 1.5 parts bis-(γ-triethoxysilylpropyl)-tetrasulfide, 1 part color masterbatch, and 6 parts vulcanizing agent.

[0025] As a further improvement to this technical solution, the mixing process parameters in step S3 are as follows:

[0026] The temperature of the two-roll mill is 70-80℃, and the mixing time is 5-8 minutes.

[0027] Vulcanization conditions: 160℃ for 15 minutes, pressure 10 MPa.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] 1. In this invention, through the synergistic effect of the P / N groups and phenolic hydroxyl groups in h-BN@PDT, h-BN@PDT can achieve excellent flame retardant effect with a low amount of flame retardant added, thereby enabling EPDM material to meet the UL-94 V-0 level requirements, significantly reducing the amount of flame retardant used and reducing the risk of environmental pollution.

[0030] 2. In this invention, the introduction of h-BN@PDT increases the rigidity of the material to a certain extent, but has little effect on the elongation of EPDM. Especially at low addition levels, the ductility of the material is hardly affected, and good mechanical properties are maintained.

[0031] 3. In this invention, the functionalized h-BN nanosheets not only improve their compatibility with EPDM by introducing phosphazene groups, but also enhance the thermal stability of the material. Experimental results show that the heat release rate (HRR) and total heat release (THR) of the composite material are significantly reduced under high temperature conditions.

[0032] 4. In this invention, the functionalization of h-BN@PDT enhances the antioxidant properties of EPDM. In particular, during long-term high-temperature aging, the tensile strength and elongation at break of EPDM remain good, thus delaying the degradation of the material.

[0033] 5. In this invention, the introduction of functionalized boron nitride significantly improves the thermal conductivity of EPDM, increasing the thermal conductivity by 19%, thereby improving the heat dissipation capacity of rubber in high-temperature working environments and enhancing its performance in high-power applications. Attached Figure Description

[0034] Figure 1 This is a schematic diagram illustrating the steps of the method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets, as described in this invention.

[0035] Figure 2 This is a flowchart of the synthesis process of h-BN@PDT of the present invention.

[0036] Figure 3 The above are characterization and analysis diagrams of h-BN@PDT of the present invention, wherein b is a scanning electron microscope (SEM) image of h-BN, c is a scanning electron microscope (SEM) image of hydroxylated h-BN (h-BN-OH), d is a scanning electron microscope (SEM) image of h-BN@PDT, e is a transmission electron microscope (TEM) image of h-BN; f is a transmission electron microscope (TEM) image of h-BN-OH, and g is a scanning electron microscope (SEM) image of h-BN@PDT.

[0037] Figure 4The images show scanning electron microscope (SEM) images and energy dispersive spectroscopy (EDS) distribution diagrams of different elements of the h-BN@PDT of the present invention. In the images, a is a morphology diagram of boron nitride particles; b and c are distribution diagrams of nitrogen and boron elements in boron nitride powder, respectively; and d, e, and f are the dispersion distribution of P, C, and O elements introduced by surface modifier molecules on the surface of boron nitride particles, respectively.

[0038] Figure 5 The image shows the spectrum of h-BN@PDT of the present invention, g is the X-ray diffraction (XRD) pattern of different boron nitride (BN) samples, h is the Fourier transform infrared (FT-IR) spectrum of different BN samples, i is the thermogravimetric analysis (TGA) curve of different BN samples, j is the B 1s X-ray photoelectron spectrum (XPS) of h-BN, k is the B 1s XPS spectrum of h-BN@PDT, and l is the C 1s XPS spectrum of h-BN@PDT.

[0039] Figure 6 The figures shown are experimental diagrams of the EPDM composite material of the present invention, wherein a is the heat release rate (HRR) diagram of the EPDM composite material, b is the total heat release (THR) diagram of the EPDM composite material, c is the smoke generation rate (SPR) diagram of the EPDM composite material, d is the total smoke release (TSR) diagram of the EPDM composite material, e is the carbon monoxide generation (COP) diagram of the EPDM composite material, and f is the carbon dioxide generation (CO2P) diagram of the EPDM composite material.

[0040] Figure 7 This is a schematic diagram of the test results of the mechanical properties of the rubber after aging according to the present invention.

[0041] Figure 8 The graph shows the test results of tensile strength and elongation at break of the rubber sample of this invention after 24 hours of aging.

[0042] Figure 9 The graph shows the test results of tensile strength and elongation at break of the rubber sample of this invention after 72 hours of aging.

[0043] Figure 10 The graph shows the test results of tensile strength and elongation at break of the rubber sample of this invention after 168 hours of aging.

[0044] Figure 11 This is a schematic diagram showing the test results of the thermal conductivity properties of the rubber after adding BN and h-BN@PDT according to the present invention. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] In one specific embodiment, such as Figures 1-11 As shown, this invention provides a method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets, specifically including the following steps:

[0047] Step 1: Preparation of hydroxylated h-BN nanosheets: h-BN and sodium hydroxide were mixed at a mass ratio of 1:10, and agate grinding balls with a diameter of 3-5 mm and a ball-to-material ratio of 2.5:1 were added. The mixture was ball-milled at 600 rpm for 1 hour, then cooled for 1 hour. The process was repeated 5 times. The mixture was then filtered and washed until the pH was neutral, and dried and allowed to stand to obtain h-BN-OH.

[0048] Step 2: Synthesis of phosphazene-modified boron nitride h-BN@PDT:

[0049] First, purify hexachlorocyclotriphosphazene (HCCP) for later use. Add 200 mL of anhydrous n-hexane to a beaker, heat in an oil bath to 70°C, add HCCP to the beaker until it no longer dissolves, prepare a saturated HCCP / n-hexane solution, then filter while hot, collect the filtrate in a glass bottle, crystallize and purify, then place the HCCP in a refrigerator to cool and crystallize, remove the n-hexane, and obtain purified HCCP.

[0050] Then, weigh 1g of h-BN-OH powder and grind it. Pour the powder into a three-necked flask containing 100ml of acetone and sonicate for 2h. Then, add 0.8g of 4,4-dihydroxybiphenyl and continue stirring for 10min. After that, add dropwise an acetone solution of HCCP (35g / L) and 5ml of triethylamine. Reflux at 70℃ for 1h. Then, add 1.7g of tannic acid and continue the reaction for 10h. After the reaction is completed, cool to room temperature, wash three times with ethanol and deionized water, and dry overnight in a vacuum oven at 70℃ to obtain h-BN@PDT.

[0051] Step 3: Preparation of h-BN@PDT / EPDM composite material: 100 parts of EPDM are appropriately plasticized in a two-roll mill until the rubber completely wraps around the rolls. Then, 5 parts of plasticizer (Sunpar 2280 paraffin oil) are added, followed by 25 parts of a mixture of silica and calcium carbonate. Then, 50 parts of silica, 24 parts of flame retardant, 0.1-1.2 parts of h-BN@PDT, 1.5 parts of antioxidant RD, 1.5 parts of bis-(γ-triethoxysilylpropyl)-tetrasulfide, and 1 part of color masterbatch are added in sequence. Finally, 6 parts of vulcanizing agent (oxide vulcanizing agent: 101XL45-SP2) are added. After all materials are mixed evenly, the mixture is thin-passed and sheeted to obtain the h-BN@PDT / EPDM composite material.

[0052] The mixture of silica and calcium carbonate has a mass ratio of 2:1, and the flame retardant is a mixture of ammonium polyphosphate (APP) and melamine-formaldehyde resin (CFA) with a mass ratio of 4:1. The mixing process parameters are as follows:

[0053] The temperature of the two-roll mill is 70-80℃, and the mixing time is 5-8 minutes; the vulcanization conditions are 160℃×15 minutes and the pressure is 10MPa.

[0054] The following experiments demonstrate the properties of the h-BN@PDT / EPDM composite material:

[0055] Steps one and two are performed according to the steps described above. The mass fraction formulation of the h-BN@PDT / EPDM composite material in step three is shown in Table 1 below:

[0056] Table 1. Mass Part Formulation of h-BN@PDT / EPDM Composite Material

[0057]

[0058] Using h-BN@PDT as the variable, the addition amounts were 0.1g, 0.5g, 1g, and 2g, corresponding to formulation numbers 1#, 2#, 3#, and 4#, respectively. The oxidation induction time, oxidation induction temperature, tensile strength, and elongation at break of the h-BN@PDT / EPDM composite materials prepared in each group were compared. The experimental results are shown in Table 2 below:

[0059] Table 2 Experimental results of h-BN@PDT / EPDM composite materials

[0060]

[0061] As shown in Table 2 above, the h-BN@PDT / EPDM composite material possesses the following characteristics:

[0062] 1. Improved thermal stability: With an addition of 1g, the oxidation induction time and temperature reach their peak values, meeting the requirements for high-temperature applications.

[0063] 2. Balance of mechanical properties: While significantly improving tensile strength, it maintains high elongation at break, breaking through the performance contradictions of traditional flame-retardant fillers.

[0064] 3. Breakthrough in anti-aging properties: The performance retention rate is high after 168 hours of aging, far exceeding that of unmodified EPDM.

[0065] 4. Process window is clearly defined: 1g is the optimal addition amount. Excessive addition will lead to a decrease in performance. It must be strictly controlled within the range of 0.5-1.2 parts.

[0066] Simultaneously, image analysis was performed on the h-BN@PDT representation, such as... Figure 3 As shown, SEM images b, c, and d illustrate the morphology of h-BN, h-BN-OH, and h-BN@PDT, respectively. h-BN exhibits a typical flat hexagonal structure with dimensions of 1-2 μm, a smooth surface, and tight interlayer bonding. Figure 3 Image b is an electron microscope image obtained under the parameters SU8220 3.0kV 7.7mm x 30.0k SE (UL). Figure 3 Image c is an electron microscope image obtained under the parameters SU8220 3.0kV 7.8mm x 40.0k SE(UL). Figure 3 Image d is an electron microscope image taken with parameters SU8220 3.0kV 7.6mm x 35.0k SE (UL).

[0067] When NaOH is used to assist in h-BN ball milling, due to Na + and OH - During ball milling, ions enter the interlayer space, inducing hydroxylation reactions, leading to defect propagation and edge expansion. BN bonds near defect sites are more susceptible to OH- attack. As adjacent units undergo hydroxylation, the defects propagate further until they reach the edges.

[0068] Furthermore, NaOH solution acts as a lubricant, effectively reducing impact damage and preventing excessive destruction and aggregation of the sheets, thus ensuring that the sheets maintain a certain structural integrity while achieving a larger specific surface area. h-BN-OH is composed of thin, folded nanosheets aggregated together and randomly overlapping flat nanosheets.

[0069] 4,4-DHB provides phenolic hydroxyl groups and is 4,4-dihydroxybiphenyl. After reacting with h-BN, 4,4-DHB is further reacted with HCCP via a condensation reaction to form a P / N synergistic flame-retardant structure. To enhance the material's antioxidant effect, tannic acid with multiple phenolic hydroxyl groups is introduced. After the above surface treatment, h-BN@PDT is obtained.

[0070] The surface of h-BN@PDT is significantly rougher, and its size is larger than that of h-BN-OH, with an outer layer consisting of layers. From Figure 3 TEM images e and f confirm that h-BN has a flat hexagonal structure. After ball milling with NaOH, h-BN-OH exhibits an irregular, thin, folded nanosheet structure. Mechanical exfoliation reduces the sheet thickness and increases the exposed active surface area of ​​the sheets.

[0071] TEM images ( Figure 3 g) shows that the surface of the functionalized h-BN@PDT is significantly rougher, with increased layer thickness and size. This is attributed to the P / N multilayer structure modification formed by HCCP, 4,4-dihydroxybiphenyl, and tannic acid, which significantly improves the surface activity and compatibility of the material.

[0072] Therefore, through functionalization, P / N groups and phenolic hydroxyl groups are added to the surface, resulting in a rougher surface and a larger layered structure in h-BN@PDT. This structural change significantly improves the surface activity and compatibility of the material.

[0073] Meanwhile, as shown in Figures 4a-f, EDS-mapping confirmed the success of surface functionalization. The significant distribution of P, N, and O elements on the h-BN@PDT surface, with obvious aggregation of P, N, and O elements, confirms the successful surface modification by P / N groups and hydroxyl groups. This is closely related to the phenolic hydroxyl groups introduced by 4,4-DHB and the P / N groups provided by HCCP during the functionalization process.

[0074] Figure 5 The gXRD pattern reveals that h-BN-OH exhibits a distinct B-OH peak compared to h-BN, reflecting defects introduced during the hydroxylation process. The functionalized h-BN@PDT XRD peaks are smoother and display a single sharp peak, indicating high product purity and a more complete crystal structure.

[0075] Figure 5 h shows the FT-IR spectra of h-BN, h-BN-OH, and h-BN@PDT. h-BN at 1400 cm⁻¹... -1 and 800cm -1 These correspond to the in-plane and out-of-plane bending peaks of the BNB ring vibration, respectively. After ball milling with NaOH, 3450 cm⁻¹ -1 The broad peak (-OH) at 800 cm⁻¹ is significantly enhanced, indicating the occurrence of hydroxylation. -1 The BN vibration is weakened. The functionalized h-BN@PDT exhibits reduced vibration at 980 cm⁻¹. -1 and 1200cm -1 The appearance of P=N and PN peaks at the locations proves the successful introduction of the P / N group.

[0076] Figure 5 The i TGA results showed that the thermal stability of h-BN@PDT is much higher than that of h-BN, which is closely related to the thermal shielding effect of the P / N groups.

[0077] Figure 5 j and k describe the XPS results of h-BN and h-BN@PDT. The fine B1s spectrum shows a clear BO peak in the surface-functionalized h-BN@PDT, indicating successful hydroxylation and functionalization.

[0078] from Figure 5 The C 1s fine spectrum in l shows that C-OH bonds are attached to the BN surface, further confirming the modification of the h-BN surface by tannic acid. These results confirm that after effectively treating h-BN with 4,4-DHB, HCCP, and tannic acid, P / N groups were successfully introduced onto the h-BN surface, forming a modified h-BN@PDT containing both P / N and OH groups.

[0079] In addition, various performance tests were conducted on h-BN@PDT, and the test results are as follows:

[0080] Flame retardant performance test:

[0081] EPDM-C is the base formulation used in experiments to test the effects of flame retardants and synergists on the performance of EPDM. This base formulation excludes antioxidants and vulcanizing agents to focus on the effectiveness of the flame retardant. The formulation was designed based on UL-94 testing (see Table 3 for results).

[0082] Table 3 Basic Formulation for UL-94 Test Experiment

[0083]

[0084] Table 4 Basic Formulation of h-BN@PDT / EPDM Composite Material

[0085]

[0086] The baseline was 25 wt%, representing the minimum amount of flame retardant required for EPDM-C to achieve the UL-94 V-1 rating. Subsequent UL-94 tests were designed for EPDM-Ch-BN@PDT(23+2), EPDM-Ch-BN@PDT(24+1), and EPDM-C-BN(24+1), where EPDM-Ch-BN@PDT(23+2) represents a conventional flame retardant addition of 23 wt% and h-BN@PDT addition of 2 wt%.

[0087] Table 5. UL94 test results of EPDM rubber with added conventional flame retardants

[0088]

[0089] Table 6. UL94 test results of EPDM rubber with added h-BN@PDT flame retardant

[0090]

[0091] Table 6 shows that EPDM-Ch-BN@PDT(24+1) self-extinguishes in 1 second after the first ignition (10 seconds) and in 2 seconds after the second ignition (10 seconds). This result is similar to the UL-94 result of EPDM-C-27% in Table 5. In contrast, EPDM-Ch-BN(24+1) without surface P / N functionalization achieves a UL-94 rating of NR at the same addition amount. These results demonstrate that introducing the h-BN@PDT synergist not only significantly reduces the amount of flame retardant used but also enhances the flame retardant effect of EPDM. h-BN@PDT, through the introduction of P / N groups and polyphenolic hydroxyl groups, improves the thermal stability of the material and releases phosphoric acid and nitrogen oxides during combustion, playing a role in expansion flame retardancy and free radical capture. The synergistic effect of the P / N groups and phenolic hydroxyl groups improves the flame retardant efficiency, enabling the UL-94 V-0 flame retardant rating to be met even with lower addition amounts than traditional flame retardants.

[0092] A cone calorimeter is a commonly used instrument in fire research, primarily for assessing the fire hazard of materials. The heat release rate (HRR) and total heat release (THR) are key parameters for evaluating fire intensity and spread. The smoke generation rate (SPR) and total smoke release (TSR) are important indicators of fire smoke, helping to assess the concentration of harmful gases and smoke produced during material combustion. Figure 6 a HRR and Figure 6 The THR data showed that the peak shapes of the HRR for EPDM-C-25% and the BN@PDT-added samples were basically the same. EPDM-Ch-BN@PDT (23+2) had the lowest peak heat release rate (PHRR), while EPDM-C-25% had the highest PHRR. Surprisingly, adding only 0.1% BN@PDT significantly reduced both PHRR and THR. Figure 6 c SPR and Figure 6 The d TSR data show that the peak shapes of the SPR (Signal Retardant Response Rate) are basically the same for EPDM-C-25% and the sample with added BN@PDT. EPDM-C-25% has the highest TSR, while EPDM-Ch-BN@PDT (23+2) has the lowest. EPDM-Ch-BN@PDT (24.9+0.1) shows a significant decrease in both SPR and TSR, demonstrating the outstanding flame retardant synergistic effect of BN@PDT. Figure 6 e CO release curve and Figure 6 The CO2 release curves show that BN@PDT has a certain inhibitory effect on CO and CO2, with EPDM-Ch-BN@PDT (23+2) showing the most significant effect, which is consistent with the previous results.

[0093] Mechanical performance testing:

[0094] The mechanical properties of EPDM-C were studied using a universal tensile testing machine. Figure 7 Figure a shows a comparison of the tensile strength of EPDM with different flame retardant additions. It can be seen that the higher the flame retardant content, the lower the tensile strength. This is because the flame retardant particles disrupt the cross-linking network of the rubber matrix, leading to a decrease in mechanical properties. Based on the 25wt% flame retardant addition threshold required for EPDM-C to achieve the UL-94 V-1 rating, tensile tests were designed for EPDM-Ch-BN@PDT(23+2), EPDM-Ch-BN@PDT(24+1), EPDM-Ch-BN@PDT(24.5+0.5), and EPDM-Ch-BN@PDT(24.9+0.1). Figure 7 (b) UL-94 testing has shown that a small amount of h-BN@PDT improves flame retardant efficiency, allowing the UL-94 V-0 flame retardant rating to be met even with low flame retardant addition. However, in tensile testing, adding a small amount of h-BN@PDT somewhat reduces tensile strength. This can be attributed to the fact that h-BN@PDT is a highly rigid inorganic material; the addition of rigid filler restricts the deformation ability of the rubber matrix, disrupts the cross-linking structure of EPDM, and reduces the material's ductility. Figure 7 c and Figure 7 The elongation results show that increasing the flame retardant content decreases the elongation. Surprisingly, h-BN@PDT has little effect on the elongation of EPDM, especially with 0.1% h-BN@PDT, which shows a slight increase in elongation compared to EPDM-C-25%. Compared to traditional flame retardants, h-BN@PDT has a smaller impact on the elongation of EPDM. In particular, when the h-BN@PDT content is only 0.1%, the elongation of the material is even slightly higher than that of EPDM-C-25%. This may be because a small amount of h-BN@PDT can provide flame retardancy without significantly affecting the crosslinking network of the matrix, and its high rigidity does not significantly affect the plastic deformation of the matrix. This means that h-BN@PDT can maintain the material's ductility while maintaining flame retardant properties.

[0095] Aging performance test:

[0096] Aging tests are also essential for rubber materials. Rubber samples were aged for 24 hours, 72 hours, and 168 hours, and their tensile strength and elongation at break were tested respectively. Figures 8-10 (As shown). The addition of h-BN@PDT greatly improved the aging durability of rubber, and EPDM-Ch-BN@PDT(24+1) exhibited excellent aging performance. After aging, EPDM-Ch-BN@PDT(24+1) still had high mechanical properties. After 168h aging, the elongation at break of EPDM-C-25% was only 40%, a decrease of 85% compared to before aging; the tensile strength of EPDM-C-25% after 168h aging was only 2.78MPa, a decrease of 68% compared to before aging. However, after 168h aging, the elongation at break of EPDM-Ch-BN@PDT(24+1) was 166%, a decrease of only 35% compared to before aging; the tensile strength of EPDM-Ch-BN@PDT(24+1) after 168h aging was 11.12MPa, a decrease of only 14.4% compared to the 24h aged sample. The tensile strength of EPDM-C-25% decreased by 70.7% compared to its corresponding 24-hour aged sample. These aging results indicate that the rubber modified with h-BN@PDT exhibits improved aging performance. This can be attributed to the effective capture of free radicals generated during aging by the polyphenolic hydroxyl groups in h-BN@PDT, thus delaying the degradation of the rubber matrix. The layered structure of h-BN and the multi-layered barrier formed by surface modification allow the functionalized h-BN@PDT to form good interfacial compatibility with the matrix, mitigating the damage to the crosslinking network.

[0097] Thermal conductivity analysis:

[0098] Bismuth natural nanoparticles (BN) are a relatively new material used as thermally conductive fillers in rubber materials in recent years. Their excellent thermal conductivity and chemical stability make them an ideal choice for improving the thermal conductivity of rubber. Thermal conductivity tests were conducted to compare the thermal conductivity of pure rubber with that of rubber after adding BN and h-BN@PDT. Figure 11 The results showed that the thermal conductivity of the rubber material increased after the introduction of boron nitride, especially after the introduction of h-BN@PDT, the thermal conductivity increased by 19%. This is because boron nitride itself has high thermal conductivity, and its layered structure facilitates the efficient transfer of heat in the rubber matrix. The phosphazene-modified BN enhances its interaction with the matrix, which is more conducive to forming heat conduction paths in the rubber matrix, thereby enhancing the thermal conductivity efficiency. This is evident from the SEM images of the matrix. Figure 11 It can be seen that h-BN@PDT has significantly better uniformity in the matrix, while BN has poor uniformity and rough surface in the rubber matrix due to its larger size.

[0099] In summary, P / N groups and hydroxyl groups were successfully introduced onto the surface of boron nitride through NaOH ball milling and functionalization with 4,4-DHB, HCCP, and tannic acid.

[0100] SEM, TEM and XPS analyses showed that the functionalized h-BN@PDT had a rough surface, increased layered structure, and significantly improved compatibility with the rubber matrix.

[0101] UL-94 test results show that h-BN@PDT can achieve the UL-94 V-0 rating with a lower amount of flame retardant added, significantly improving flame retardant efficiency.

[0102] The results of HRR and THR indicate that the addition of h-BN@PDT significantly improves the flame retardant and smoke-suppressing properties of the rubber. Tensile test results show that while increasing the flame retardant content leads to a decrease in tensile strength, the addition of h-BN@PDT effectively improves the material's ductility with minimal negative impact on mechanical properties.

[0103] Aging tests showed that h-BN@PDT significantly improved the aging resistance of rubber. Thermal conductivity tests indicated that the addition of h-BN@PDT increased the thermal conductivity of rubber by 19%.

[0104] In conclusion, h-BN@PDT, as a synergistic agent, not only improves the flame retardant properties of EPDM, but also enhances its thermal stability, mechanical properties, and thermal conductivity, showing promising application prospects.

[0105] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets, characterized in that, Includes the following steps: S1. Preparation of hydroxylated h-BN nanosheets: h-BN and sodium hydroxide were mixed at a mass ratio of 1:10, and grinding balls were added. The mixture was ball-milled at 600 rpm for 1 hour, then cooled for 1 hour. The process was repeated 5 times. The mixture was filtered and washed until the pH was neutral, and then dried and allowed to stand to obtain h-BN-OH. S2. Synthesis of Phosphazene-Modified Boron Nitride h-BN@PDT: Purified hexachlorocyclotriphosphazene (HCCP) was prepared for use; then 1g of h-BN-OH powder was weighed and ground, and the powder was poured into a three-necked flask containing 100ml of acetone. The mixture was ultrasonically stirred for 2h, followed by the addition of 0.8g of 4,4-dihydroxybiphenyl and stirring for another 10min. Then, an acetone solution of HCCP and 5ml of triethylamine were added dropwise, and the mixture was refluxed at 70℃ for 1h. After that, 1.7g of tannic acid was added, and the reaction was continued for another 10h. After the reaction was completed, the mixture was cooled to room temperature, washed, and then dried to obtain h-BN@PDT; the mass-volume concentration of the acetone solution of HCCP was 35g / L. Preparation of S3 and h-BN@PDT / EPDM composite materials: EPDM is appropriately plasticized in a two-roll mill until the rubber completely wraps around the rolls. Then, a plasticizer is added, followed by a mixture of silica and calcium carbonate. Then, silica, flame retardant, h-BN@PDT, antioxidant RD, bis-(γ-triethoxysilylpropyl)-tetrasulfide and color masterbatch are added in sequence. Finally, a vulcanizing agent is added. After all materials are mixed evenly, the mixture is thinly passed through a mill and sheeted to obtain the h-BN@PDT / EPDM composite material.

2. The method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets according to claim 1, characterized in that, The ball milling parameters in step S1 are: The grinding balls are made of agate, with a diameter of 3-5mm and a ball-to-material ratio of 2.5:

1.

3. The method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets according to claim 1, characterized in that, The specific steps for purifying HCCP in step S2 are as follows: Add 200 mL of anhydrous n-hexane to a beaker, heat in an oil bath to 70 °C, add HCCP to the beaker until it no longer dissolves, prepare a saturated HCCP / n-hexane solution, then filter while hot, collect the filtrate in a glass bottle, crystallize and purify, then place the HCCP in a refrigerator to cool and crystallize, remove the n-hexane, and obtain purified HCCP.

4. The method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets according to claim 1, characterized in that, The washing method in step S2 is as follows: washing three times with ethanol and deionized water.

5. The method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets according to claim 1, characterized in that, The drying method in step S2 is: drying overnight in a vacuum oven at 70°C.

6. The method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets according to claim 1, characterized in that, The mass ratio of silicon dioxide to calcium carbonate in the mixture of silicon dioxide and calcium carbonate is 2:1, the plasticizer is paraffin oil Sunpar 2280, and the vulcanizing agent is peroxide vulcanizing agent: 101XL45-SP2.

7. The method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets according to claim 1, characterized in that, The flame retardant is a mixture of ammonium polyphosphate (APP) and melamine-formaldehyde resin (CFA) in a mass ratio of 4:

1.

8. The method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets according to claim 1, characterized in that, The mass fraction formulation of the h-BN@PDT / EPDM composite material in step S3 is as follows: 100 parts EPDM, 50 parts silica, 25 parts mixture of silica and calcium carbonate, 5 parts plasticizer, 24 parts flame retardant, 0.1-1.2 parts h-BN@PDT, 1.5 parts antioxidant RD, 1.5 parts bis-(γ-triethoxysilylpropyl)-tetrasulfide, 1 part color masterbatch, and 6 parts vulcanizing agent.

9. The method for enhancing the thermal and oxidative stability of EPDM rubber using functionalized h-BN nanosheets according to claim 1, characterized in that, The mixing process parameters in step S3 are as follows: The temperature of the two-roll mill is 70-80℃, and the mixing time is 5-8 minutes. Vulcanization conditions: 160℃ for 15 minutes, pressure 10 MPa.

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