Method for enhancing thermal stability and oxidation stability of EPDM (ethylene propylene diene monomer) rubber by using functionalized h-BN (boron nitride) nanosheets

Abstract

The invention relates to the technical field of rubber modification, in particular to a method for enhancing thermal stability and oxidation stability of ethylene propylene diene monomer rubber by using functionalized h-BN nanosheets. Comprising the following steps: S1, preparing a hydroxylated h-BN nanosheet; s2, synthesizing phosphazene modified boron nitride, namely purifying hexachlorocyclotriphosphazene for later use, then weighing 1g of h-BN-OH powder, grinding, pouring the powder into a three-necked flask containing 100ml of acetone, carrying out ultrasonic stirring for 2 hours, then adding 0.8 g of 4, 4-dihydroxybiphenyl, continuously stirring for 10 minutes, dropwise adding an acetone solution of HCCP and 5ml of triethylamine, adding tannic acid after reaction, cooling to room temperature after the reaction is finished, and filtering to obtain the phosphazene modified boron nitride. Washing and drying to obtain phosphazene modified boron nitride; and S3, preparing the phosphazene modified boron nitride / EPDM composite material. Through the synergistic effect of P / N groups and phenolic hydroxyl groups in the phosphazene modified boron nitride, the phosphazene modified boron nitride can achieve an excellent flame retardant effect under the condition of low flame retardant additive amount, and the use amount of the flame retardant is remarkably reduced.

Description

Technical Field

[0001] The invention relates to the technical field of rubber modification, in particular to a method for enhancing the thermal stability and oxidation stability of ethylene propylene diene monomer rubber by utilizing functionalized h-BN nanosheets. Background Art

[0002] Ethylene propylene diene monomer (EPDM) is widely used in automotive seals, cable sheaths and building waterproof materials due to its excellent weather resistance, high temperature resistance and insulation performance. However, EPDM still has the following technical defects in high temperature, oxidation and fire scenarios:

[0003] 1. Insufficient flame retardancy: EPDM's flammability and low thermal conductivity limit its further application in certain high-performance fields under high temperature, high-speed operation and fire environments. Although traditional flame retardants, such as chlorinated flame retardants and brominated flame retardants, effectively improve flame retardancy, the use of these chemicals is often accompanied by environmental pollution, toxicity problems and a decrease in the mechanical properties of the material;

[0004] 2. Poor thermal stability: Unmodified EPDM is easily oxidized and degraded at high temperatures (>150°C), and the oxidation induction time (OIT) is less than 1 minute, which limits its service life;

[0005] 3. Poor filler dispersion: When boron nitride (h-BN) is used as a thermal conductive / flame retardant filler, it is easy to agglomerate due to its surface inertia 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 >80%, which is difficult to meet long-term use requirements.

[0007] Meanwhile, in the prior art, a method for preparing a halogen-free flame-retardant EPDM rubber is disclosed in a Chinese invention patent with publication number CN1923884A, which uses aluminum hydroxide or magnesium hydroxide as the main flame retardant, and the addition amount is relatively large, resulting in increased hardness and decreased elasticity of the material, and deterioration of the extrusion processing performance, thus failing to solve the problem of balancing flame retardancy and mechanical properties; a Chinese invention patent with authorization announcement number CN118772545B discloses a low-density, high-flame-retardant EPDM rubber composite material and a method for preparing the same, which uses a synergistic flame retardant (containing silicon, nitrogen, and phosphorus elements), which reduces the amount of inorganic flame retardants, but requires a complex preparation process (such as a multi-step condensation reaction) and is relatively costly.

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

[0009] The purpose of the present invention is to provide a method for enhancing the thermal stability and oxidative stability of EPDM rubber by using functionalized h-BN nanosheets, so as to solve the problems of insufficient flame retardancy, poor thermal stability, poor filler dispersibility and insufficient aging performance of unmodified EPDM proposed in the above background technology.

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

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

[0012] S2. Synthesis of phosphazene-modified boron nitride h-BN@PDT: Purify hexachlorocyclotriphosphine HCCP for later use, then weigh 1g h-BN-OH powder and grind it, pour the powder into a three-necked flask containing 100ml acetone, ultrasonically stir for 2h, then add 0.8g 4,4-dihydroxybiphenyl and continue stirring for 10min, then drop HCCP acetone solution and 5ml triethylamine, reflux at 70℃ for 1h, add 1.7g tannic acid, and continue to react for 10h, cool to room temperature after the reaction, wash, and then dry to obtain h-BN@PDT;

[0013] S3. Preparation of h-BN@PDT / EPDM composite material: EPDM is properly plasticized in a two-roll mill until the rubber is completely wrapped around the rollers, and then a plasticizer is added, followed by a mixture of silica and calcium carbonate, followed by white carbon black, flame retardant, h-BN@PDT, antioxidant RD, bis-(γ-triethoxysilylpropyl)-tetrasulfide and masterbatch, and finally a vulcanizer is added. After all materials are mixed evenly, thin passes are made and sheets are produced to obtain h-BN@PDT / EPDM composite material.

[0014] As a further improvement of the technical solution, the ball milling parameters in step S1 are:

[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 of the technical solution, the specific operation steps of purifying HCCP in step S2 are:

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

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

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

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

[0021] As a further improvement of the 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 a peroxide vulcanizing agent: 101XL45-SP2.

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

[0023] As a further improvement of the technical solution, the mass formula of the h-BN@PDT / EPDM composite material in step S3 is:

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

[0025] As a further improvement of the technical solution, the mixing process parameters in step S3 are:

[0026] The temperature of the double-roll mill is 70-80°C, and the mixing time is 5-8 minutes;

[0027] Vulcanization conditions: 160°C × 15 minutes, pressure 10 MPa.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. In the present invention, through the synergistic effect of the P / N group and the phenolic hydroxyl group in h-BN@PDT, h-BN@PDT can achieve excellent flame retardant effect at a lower flame retardant addition amount, so that the EPDM material meets the UL-94 V-0 level requirements, significantly reduces the use of flame retardants, and reduces the risk of environmental pollution.

[0030] 2. In the present invention, the rigidity of the material is increased to a certain extent by introducing h-BN@PDT, but its effect on the elongation of EPDM is small, especially when the addition amount is low, the ductility of the material is almost unaffected, and good mechanical properties are maintained.

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

[0032] 4. In the present invention, the functionalization of h-BN@PDT enhances the antioxidant properties of EPDM, especially during long-term high-temperature aging, the tensile strength and elongation at break of EPDM are well maintained, delaying the degradation of the material.

[0033] 5. In the present invention, the introduction of functionalized boron nitride significantly improves the thermal conductivity of EPDM by 19%, improves the heat dissipation capacity of the rubber in a high-temperature working environment, and improves its performance in high-power applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a schematic diagram of the steps of the method for enhancing the thermal stability and oxidative stability of EPDM rubber by using functionalized h-BN nanosheets according to the present invention.

[0035] Figure 2 Schematic diagram of the synthesis of h-BN@PDT of the present invention.

[0036] Figure 3 3 is a characterization analysis diagram 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, and 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 4Figure 3 is a scanning electron microscope (SEM) image of h-BN@PDT of the present invention and an energy spectrum (EDS) surface distribution diagram of different elements, wherein 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; d, e, and f are the dispersion distribution of P, C, and O elements introduced by the surface modifier molecules on the surface of boron nitride particles, respectively.

[0038] Figure 5 is the spectrum of h-BN@PDT of the present invention, g is the X-ray diffraction (XRD) spectrum of different boron nitride (BN) samples, h is the Fourier transform infrared spectrum (FT-IR) 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 C1s XPS spectrum of h-BN@PDT‌.

[0039] Figure 6 The graphs are experimental graphs of the EPDM composite material of the present invention, wherein a is the heat release rate graph (HRR) of the EPDM composite material, b is the total heat release graph (THR) of the EPDM composite material, c is the smoke generation rate graph (SPR) of the EPDM composite material, d is the total smoke release graph (TSR) of the EPDM composite material, e is the carbon monoxide generation graph (COP) of the EPDM composite material, and f is the carbon dioxide generation graph (CO 2 P).

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

[0041] Figure 8 This is a graph showing the test results of tensile strength and elongation at break of the rubber sample of the present invention after 24h aging.

[0042] Fig. 9 This is a graph showing the test results of tensile strength and elongation at break of the rubber sample of the present invention after 72 hours of aging.

[0043] Fig.10 This is a graph showing the test results of tensile strength and elongation at break of the rubber sample of the present invention after 168h aging.

[0044] Fig.11 This is a schematic diagram of the test results of thermal conductivity of rubber after adding BN and h-BN@PDT in the present invention. DETAILED DESCRIPTION

[0045] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] In a specific embodiment, Figure 1-Figure 11 As shown, the present invention provides a method for enhancing the thermal stability and oxidative stability of EPDM rubber by using functionalized h-BN nanosheets, which specifically comprises the following steps:

[0047] Step 1, preparation of hydroxylated h-BN nanosheets: h-BN and sodium hydroxide were mixed in a mass ratio of 1:10, agate grinding balls with a diameter of 3-5 mm and a ball-to-material ratio of 2.5:1 were added, ball milled at 600 rpm for 1 hour, then cooled for 1 hour, the process was repeated 5 times, filtered and washed to neutral pH, 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 hexachlorocyclotriphosphine HCCP for use, add 200 ml of anhydrous n-hexane into a beaker, heat the oil bath to 70°C, add HCCP into 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, put the HCCP into a refrigerator to cool and crystallize, remove the n-hexane, and obtain purified HCCP.

[0050] Then, 1 g of h-BN-OH powder was weighed and ground, and the powder was poured into a three-necked flask containing 100 ml of acetone and ultrasonically stirred for 2 h. Subsequently, 0.8 g of 4,4-dihydroxybiphenyl was added and stirring was continued for 10 min. Then, an acetone solution of HCCP (‌35 g / L) and 5 ml of triethylamine were dropped. After reflux reaction at 70 °C for 1 h, 1.7 g of tannic acid was added and the reaction was continued for 10 h. After the reaction was completed, it was cooled to room temperature, washed three times with ethanol and deionized water, and dried in a vacuum oven at 70 °C overnight to obtain h-BN@PDT.

[0051] Step 3: Preparation of h-BN@PDT / EPDM composite material: 100 parts of EPDM are properly plasticized in a two-roll mill until the rubber is completely wrapped around the rollers, and then 5 parts of plasticizer (paraffin oil Sunpar 2280) are added, followed by 25 parts of a mixture of silica and calcium carbonate, followed by 50 parts of white carbon black, 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 masterbatch, and finally 6 parts of vulcanizer (oxide vulcanizer: 101XL45-SP2). After all the materials are mixed evenly, thin pass and sheet out to obtain the h-BN@PDT / EPDM composite material.

[0052] The mass ratio of silicon dioxide to calcium carbonate in the mixture of silicon dioxide and calcium carbonate is 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:

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

[0054] The following specific experiments are used to demonstrate the characteristics of h-BN@PDT / EPDM composite materials:

[0055] Wherein, step 1 and step 2 are performed according to the above steps, and the mass formula of the h-BN@PDT / EPDM composite material in step 3 is shown in Table 1 below:

[0056] Table 1. Weight parts formula of h-BN@PDT / EPDM composites

[0057] Taking h-BN@PDT as a variable, the addition amounts were 0.1g, 0.5g, 1g, and 2g, respectively, and the corresponding formula numbers were 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:

[0058] Table 2 Experimental results of h-BN@PDT / EPDM composites

[0059] It can be seen from Table 2 above that h-BN@PDT / EPDM composite material has the following properties:

[0060] 1. Improved thermal stability: At an addition amount of 1g, the oxidation induction time and temperature reach peak values, meeting the requirements of high-temperature applications.

[0061] 2. Balance of mechanical properties: While significantly improving tensile strength, it maintains high elongation at break, breaking through the performance contradiction of traditional flame retardant fillers.

[0062] 3. Breakthrough in aging resistance: The performance retention rate after 168 hours of aging is high, far exceeding that of unmodified EPDM.

[0063] 4. The process window is clear: 1g is the optimal addition amount. Excessive addition will lead to decreased performance and must be strictly controlled within the range of 0.5-1.2 parts.

[0064] At the same time, image analysis was performed for h-BN@PDT characterization, such as Figure 3 As shown in the figure, the SEM images of b, c, and d respectively show the morphology of h-BN, h-BN-OH, and h-BN@PDT. h-BN is a typical flat hexagonal structure with a size of 1-2 μm, a smooth surface, and tight interlayer bonding. Figure 3 Figure b is an electron microscope image under the parameters of SU8220 3.0kV 7.7mmx30.0k SE (UL). Figure 3 Figure c is an electron microscope image under the parameters of SU8220 3.0kV 7.8mmx40.0k SE (UL). Figure 3 Figure d is an electron microscope image under the parameters of SU82203.0kV 7.6mmx35.0k SE (UL).

[0065] During the NaOH-assisted ball milling of h-BN, due to the + and OH - The ions enter the interlayer space during ball milling, inducing hydroxylation reactions, leading to the propagation of defects and the expansion of edges. The BN bonds near the defect site are more susceptible to OH- attack. When the adjacent units are hydroxylated, the defect propagates further until the propagation reaches the edge.

[0066] In addition, NaOH solution as a lubricant effectively reduces impact damage, avoids excessive damage and agglomeration of the sheets, and ensures that the sheets obtain a larger specific surface area while maintaining a certain structural integrity. h-BN-OH consists of thin and folded nanosheets that are aggregated together and randomly overlapped flat nanosheets.

[0067] 4,4-DHB provides phenolic hydroxyl groups. 4,4-DHB is 4,4-dihydroxybiphenyl. After 4,4-DHB reacts with h-BN, it reacts with HCCP through polycondensation to form a P / N synergistic flame retardant structure. In order to enhance the antioxidant effect of the material, tannic acid with multiple phenolic hydroxyl groups is introduced. After the above surface treatment, h-BN@PDT is obtained.

[0068] The surface of h-BN@PDT is obviously rough, the size is larger than that of h-BN-OH, and the outer layer is wrapped by layers. Figure 3 TEM images of e and f can prove that h-BN has a flat hexagonal structure. After ball milling with NaOH, h-BN-OH has an irregular thin and folded nanosheet structure. Mechanical exfoliation reduces the thickness of the sheet and increases the active surface area exposed by the sheet.

[0069] TEM images ( Figure 3 g) The surface of h-BN@PDT after functionalization treatment is significantly roughened, and the thickness and size of the sheets increase. 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.

[0070] Therefore, through functionalization, P / N groups and phenolic hydroxyl groups are added to the surface, making the surface of h-BN@PDT rough and the layered structure larger. This structural change significantly improves the surface activity and compatibility of the material.

[0071] At the same time, as shown in Figure 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, and the obvious aggregation of P, N and O elements confirmed the success of surface modification of 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.

[0072] Figure 5 g XRD spectrum shows that h-BN-OH has a more obvious B-OH peak than h-BN, reflecting the defects introduced by the hydroxylation process. The XRD peak of h-BN@PDT after functionalization is smoother and presents a single peak, indicating that the product has high purity and a complete crystal structure.

[0073] Figure 5 h shows the FT-IR spectra of h-BN, h-BN-OH and h-BN@PDT. h-BN at 1400 cm -1 and 800cm -1 The in-plane and out-of-plane bending peaks correspond to the BNB ring vibrations. -1 The broad peak (-OH) at 800 cm -1 The BN vibration of the functionalized h-BN@PDT is weakened at 980cm -1 and 1200cm -1 P=N and PN peaks appear at the positions respectively, proving the successful introduction of the P / N group.

[0074] Figure 5i TGA results show 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.

[0075] Figure 5 j, k describe the XPS results of h-BN and h-BN@PDT. From the fine spectrum of B1s, it can be seen that the BO peak of h-BN@PDT after surface functionalization is obvious, indicating the success of hydroxylation and functionalization.

[0076] from Figure 5 The C 1s fine spectrum in Figure 1 shows that the C-OH bond is connected to the BN surface, which further confirms the modification of the h-BN surface by tannic acid. The above results confirm that after the h-BN is effectively treated with 4,4-DHB, HCCP and tannic acid, the P / N groups are successfully introduced on the h-BN surface, forming the modified h-BN@PDT containing P / N and OH groups.

[0077] In addition, various performance tests were conducted on h-BN@PDT, and the test results are as follows:

[0078] Flame retardant performance test:

[0079] EPDM-C is a basic formula used for experiments to test the effects of flame retardants and synergists on EPDM performance. This basic formula excludes antioxidants and vulcanizers in order to focus on the effect of flame retardants. The formula design was carried out through UL-94 testing (see Table 3 for specific results).

[0080] Table 3 UL-94 test experimental basic formula

[0081] Table 4 Basic formula of h-BN@PDT / EPDM composites

[0082] The flame retardant addition limit value of 25wt% required for EPDM-C to achieve UL-94 V-1 grade was used as the benchmark. UL-94 experiments of EPDM-Ch-BN@PDT(23+2), EPDM-Ch-BN@PDT(24+1) and EPDM-C-BN(24+1) were subsequently designed, where EPDM-Ch-BN@PDT(23+2) means that the traditional flame retardant addition amount is 23wt% and the h-BN@PDT addition amount is 2wt%.

[0083] Table 5 UL94 test of EPDM rubber with conventional flame retardants added

[0084] Table 6 UL94 test of EPDM rubber with h-BN@PDT flame retardant

[0085] From Table 6, it can be seen that EPDM-Ch-BN@PDT(24+1) self-extinguishes 1 second after the first ignition of 10 seconds, and 2 seconds after the second ignition of 10 seconds. This result is similar to the UL-94 result of EPDM-C-27% in Table 5. Correspondingly, EPDM-Ch-BN(24+1) without surface P / N functionalization has a UL-94 of NR at the same addition amount. From the above results, it can be seen that by introducing h-BN@PDT synergist, not only can the amount of flame retardant used be significantly reduced, but also the flame retardant effect of EPDM can be improved. h-BN@PDT improves the thermal stability of the material by introducing P / N groups and polyphenolic hydroxyl groups, releases phosphoric acid and nitrogen oxides during combustion, and plays the role of expansion flame retardant and free radical capture. The P / N group and phenolic hydroxyl group synergistically improve the flame retardant efficiency, so that the flame retardant grade requirement of UL-94 V-0 can still be met at a lower addition amount than traditional flame retardants.

[0086] Cone calorimeter is an instrument commonly used in fire research, mainly used to evaluate the fire hazard of materials. Heat release rate (HRR) and total heat release (THR) are key parameters for evaluating fire intensity and fire spread. Smoke generation rate (SPR) and total smoke release (TSR) are important indicators of fire smoke, which can help evaluate the concentration of harmful gases and smoke produced when materials burn. Figure 6 a HRR and Figure 6 b THR data shows that the peak shapes of HRR after adding EPDM-C-25% and BN@PDT are basically the same. The peak heat release rate (PHRR) of EPDM-Ch-BN@PDT (23+2) is the lowest, and EPDM-C-25% PHRR is the highest. Surprisingly, after adding only 0.1% BN@PDT, both PHRR and THR are significantly reduced. Figure 6 c SPR and Figure 6 d TSR data shows that the peak shapes of SPR after adding EPDM-C-25% and BN@PDT are basically the same. EPDM-C-25% has the largest TSR. EPDM-Ch-BN@PDT (23+2) has the smallest TSR. EPDM-Ch-BN@PDT (24.9+0.1) has a significant decrease in both SPR and TSR. This proves that BN@PDT has an outstanding flame retardant synergistic effect. Figure 6 e CO release curve and Figure 6 f 2 The release curves of BN@PDT for CO and CO2 There is a certain inhibitory effect, among which EPDM-Ch-BN@PDT (23+2) has the most obvious effect, which is consistent with the previous results.

[0087] Mechanical properties test:

[0088] The mechanical properties of EPDM-C were studied using a universal tensile testing machine. Figure 7 a is a comparison chart 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 destroy the cross-linking network of the rubber matrix, resulting in a decrease in mechanical properties. Based on the flame retardant addition limit of 25wt% required for EPDM-C to reach the UL-94 V-1 grade, tensile tests of 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) were designed ( Figure 7 b) Through the UL-94 test, it has been found that a small amount of h-BN@PDT improves the flame retardant efficiency, so that the flame retardant grade requirement of UL-94 V-0 can still be met at a low flame retardant addition. However, in the tensile test, adding a small amount of h-BN@PDT has a certain reduction in tensile strength. This can be attributed to the fact that h-BN@PDT is an inorganic material with high rigidity. The addition of rigid fillers limits the deformation ability of the rubber matrix, destroys the cross-linking structure of EPDM, and reduces the ductility of the material. Figure 7 c and Figure 7 From the elongation results of d, it can be obtained that the elongation decreases with the increase of flame retardant content. Surprisingly, h-BN@PDT has little effect on the elongation of EPDM, especially the introduction of 0.1% h-BN@PDT has a certain improvement in elongation compared with EPDM-C-25%. Compared with traditional flame retardants, h-BN@PDT has little effect on the elongation of EPDM. In particular, when the content of h-BN@PDT 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 a flame retardant effect without significantly affecting the cross-linked network of the matrix, and its high rigidity will not significantly affect the plastic deformation of the matrix. This means that h-BN@PDT can maintain the ductility of the material while maintaining flame retardant properties.

[0089] Aging performance test:

[0090] Aging test is also an essential test for rubber materials. After aging for 24 h, 72 h, and 168 h, the rubber samples were tested for their tensile strength and elongation at break ( Figure 8-Figure 10As shown). The addition of h-BN@PDT greatly improves the aging durability of rubber, and EPDM-Ch-BN@PDT(24+1) shows excellent aging performance. After aging, EPDM-Ch-BN@PDT(24+1) still has high mechanical properties. After 168h aging, the elongation at break of EPDM-C-25% is only 40%, which is 85% lower than before aging; the tensile strength of EPDM-C-25% after 168h aging is only 2.78MPa, which is 68% lower than before aging. However, after 168h aging, the elongation at break of EPDM-Ch-BN@PDT(24+1) is 166%, which is only 35% lower than before aging; after 168h aging, the tensile strength of EPDM-Ch-BN@PDT(24+1) is 11.12MPa, which is only 14.4% lower than the sample aged for 24h. The tensile strength of EPDM-C-25% decreased by 70.7% compared with the corresponding sample aged for 24 hours. The above aging results show that the rubber modified by h-BN@PDT improves the aging performance of the rubber, which can be attributed to the effective capture of free radicals generated during the aging process by the polyphenolic hydroxyl groups in h-BN@PDT, which delays the degradation of the rubber matrix. The layered structure of h-BN and the multi-layer barrier formed by surface modification, the functionalized h-BN@PDT and the matrix form a good interface compatibility, which slows down the destruction of the cross-linked network.

[0091] Thermal analysis:

[0092] BN is an emerging material used as a thermal conductive filler in rubber materials in recent years. Its excellent thermal conductivity and chemical stability make it an ideal choice for improving the thermal conductivity of rubber. The thermal conductivity of pure rubber, rubber after adding BN and h-BN@PDT were compared through thermal conductivity tests ( Fig.11 ). The results show that the thermal conductivity of the rubber material is improved after the introduction of boron nitride, especially after the introduction of h-BN@PDT, the thermal conductivity increases by 19%. This is because boron nitride itself has a high thermal conductivity, and its layered structure helps heat to spread effectively in the rubber matrix. The BN modified with phosphazene enhances the interaction with the matrix and is more conducive to forming a heat conduction path in the rubber matrix, thereby enhancing the heat conduction efficiency. This can be seen from the SEM of the matrix ( Fig.11 ) It can be seen that h-BN@PDT has better uniformity in the matrix, while BN in the rubber matrix has poor uniformity and a rough surface due to its large size.

[0093] Summary: P / N groups and hydroxyl groups were successfully introduced on the surface of boron nitride through NaOH ball milling treatment and functionalization treatment with 4,4-DHB, HCCP and tannic acid.

[0094] SEM, TEM and XPS analyses showed that the surface of the functionalized h-BN@PDT was rough, the layered structure was enlarged, and the compatibility with the rubber matrix was significantly improved.

[0095] The UL-94 test results show that h-BN@PDT can reach the UL-94 V-0 level at a lower flame retardant addition, significantly improving the flame retardant efficiency.

[0096] The results of HRR and THR show that the flame retardant and smoke suppression properties of rubber are significantly improved after the addition of h-BN@PDT. The tensile test results show that the increase in flame retardant content leads to a decrease in tensile strength, but the addition of h-BN@PDT effectively improves the ductility of the material and has little negative impact on the mechanical properties.

[0097] Aging tests show that h-BN@PDT significantly improves the aging resistance of rubber. Thermal conductivity tests show that the addition of h-BN@PDT increases the thermal conductivity of rubber by 19%.

[0098] In summary, h-BN@PDT, as a synergistic enhancer, not only improves the flame retardant properties of EPDM, but also enhances its thermal stability, mechanical properties and thermal conductivity, and has good application prospects.

[0099] The above shows and describes 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 by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A method for enhancing the thermal stability and oxidative stability of EPDM rubber using functionalized h-BN nanosheets, characterized in that: The following steps are involved: S1. Preparation of hydroxylated h-BN nanosheets: h-BN and sodium hydroxide were mixed in a mass ratio of 1:10, and grinding balls were added. The mixture was ball-milled at 600 rpm for 1 hour, and then cooled for 1 hour. The process was repeated 5 times, filtered and washed until the pH was neutral, and dried and allowed to stand to obtain h-BN-OH. S2. Synthesis of phosphazene-modified boron nitride h-BN@PDT: Purify hexachlorocyclotriphosphine HCCP for later use, then weigh 1g h-BN-OH powder and grind it, pour the powder into a three-necked flask containing 100ml acetone, ultrasonically stir for 2h, then add 0.8g 4,4-dihydroxybiphenyl and continue stirring for 10min, then drop HCCP acetone solution and 5ml triethylamine, reflux at 70℃ for 1h, add 1.7g tannic acid, and continue to react for 10h, cool to room temperature after the reaction, wash, and then dry to obtain h-BN@PDT; S3. Preparation of h-BN@PDT / EPDM composite material: EPDM is properly plasticized in a two-roll mill until the rubber is completely wrapped around the rollers, and then a plasticizer is added, followed by a mixture of silica and calcium carbonate, followed by white carbon black, flame retardant, h-BN@PDT, antioxidant RD, bis-(γ-triethoxysilylpropyl)-tetrasulfide and masterbatch, and finally a vulcanizer is added. After all materials are mixed evenly, thin passes are made and sheets are produced to obtain h-BN@PDT / EPDM composite material.

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

4. The method for enhancing the thermal stability and oxidative stability of EPDM rubber by using functionalized h-BN nanosheets according to claim 1, characterized in that: The mass volume concentration of the acetone solution of HCCP in step S2 is 35 g / L.

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

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

7. The method for enhancing the thermal stability and oxidative stability of EPDM rubber by 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 a peroxide vulcanizing agent: 101XL45-SP2.

8. The method for enhancing the thermal stability and oxidative stability of EPDM rubber by 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, with a mass ratio of 4:

1.

9. The method for enhancing the thermal stability and oxidative stability of EPDM rubber by using functionalized h-BN nanosheets according to claim 1, characterized in that: The mass formula of the h-BN@PDT / EPDM composite material in step S3 is: 100 parts of EPDM, 50 parts of white carbon black, 25 parts of a mixture of silicon dioxide and calcium carbonate, 5 parts of a plasticizer, 24 parts of a flame retardant, 0.1-1.2 parts of h-BN@PDT, 1.5 parts of an antioxidant RD, 1.5 parts of bis-(γ-triethoxysilylpropyl)-tetrasulfide, 1 part of a masterbatch, and 6 parts of a vulcanizing agent.

10. The method for enhancing the thermal stability and oxidative stability of EPDM rubber by using functionalized h-BN nanosheets according to claim 1, characterized in that: The mixing process parameters in step S3 are: The temperature of the double-roll mill is 70-80°C, and the mixing time is 5-8 minutes; Curing conditions: 160°C × 15 minutes, pressure 10 MPa.

Images