Polyurethane filling material based on dynamic crosslinking of boron nitride, method of preparation and tyre

Abstract

The application relates to a polyurethane filling material based on dynamic cross-linking of boron nitride, a preparation method and a tire, the material is formed by mixing and curing of A and B components, the A component comprises a polyether polyol and modified boron nitride nanosheets with surface grafted dynamic disulfide bonds, and the B component is an isocyanate prepolymer; the modified boron nitride nanosheets are treated by hydroxylation, amination, aldehyde group treatment and disulfide bond functionalization, the filling material of the application has high thermal conductivity and high elasticity, can be cured and filled in the tire, and is suitable for fields such as airless tires.

Description

Technical Field

[0001] This invention relates to the field of tire technology, specifically to a polyurethane filler material based on boron nitride dynamic crosslinking, its preparation method, and a tire thereof. Background Technology

[0002] Polyurethane elastomers are widely used as the core filling material for solid filled tires due to their excellent wear resistance, tear resistance, high load-bearing capacity, and injection-curable process. However, polyurethane has an extremely low intrinsic thermal conductivity, typically only around 0.2 W / (m·K), making it a poor conductor of heat. During high-speed or heavy-load rolling, the polyurethane filler layer generates a large amount of heat due to periodic compression deformation and internal friction within the molecular chains. This heat is difficult to conduct to the external environment through the material itself and the tire carcass, causing a rapid increase in the tire's internal temperature. Prolonged high-temperature conditions can lead to thermo-oxidative aging of the polyurethane molecular chains, hydrogen bond dissociation, and damage to the cross-linked structure, causing the material to soften, its load-bearing capacity to decrease, and even resulting in safety accidents such as delamination and bursting. Existing technologies, by adding high thermal conductivity fillers such as boron nitride nanosheets, carbon nanotubes, and graphene to polyurethane, can improve the thermal conductivity to some extent, but the rigid fillers reduce elasticity and worsen shock absorption. Therefore, there is an urgent need for a functional filler that can both construct an efficient thermally conductive network and serve as a dynamic cross-linking point to impart excellent elastic recovery capabilities to the material, which is a technical problem that needs to be solved in this field. Summary of the Invention

[0003] To address the above problems, this invention provides a polyurethane filler material based on dynamic crosslinking of boron nitride. It utilizes boron nitride nanosheets with dynamic disulfide bonds grafted onto their surface, making them both functional fillers and dynamic crosslinking agents. This allows the cured material to simultaneously possess high thermal conductivity and high elasticity, solving the problem of the inability to simultaneously achieve thermal conductivity and elasticity in existing technologies.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A thermally conductive and shock-absorbing polyurethane filler material based on boron nitride dynamic crosslinking, wherein the filler material is formed by mixing and curing components A and B; By weight, component A comprises: 60-80 parts of polyether polyol, 5-15 parts of modified boron nitride nanosheets, 0.1-0.3 parts of catalyst, and 0.5-1 parts of defoamer; Component B is 100 parts of isocyanate prepolymer; The modified boron nitride nanosheets are boron nitride nanosheets whose surfaces have been sequentially hydroxylated, aminated, aldehyde-modified, and disulfide bond-functionalized. Their surfaces are grafted with segments containing dynamic disulfide bonds and have active amino groups at the ends. After curing, the modified boron nitride nanosheets are incorporated into the polyurethane matrix through the participation of their surface-active amino groups in the polyurethane crosslinking reaction; the modified boron nitride nanosheets are in contact with each other or bridged by polyurethane segments to form a three-dimensional thermally conductive channel in the matrix; the disulfide bond segments grafted on the surface of the modified boron nitride nanosheets constitute reversible dynamic crosslinking nodes in the polyurethane network.

[0005] Preferably, the preparation of the modified boron nitride nanosheets includes the following steps: Hexagonal boron nitride powder was ultrasonically exfoliated to obtain few-layer boron nitride nanosheets, which were dispersed in an alkaline / hydrogen peroxide mixed solution, washed with water until neutral after reaction, and freeze-dried to obtain hydroxylated boron nitride nanosheets. Hydroxylated boron nitride nanosheets were dispersed in an organic solvent, a silane coupling agent was added, and after the reaction, the nanosheets were washed and dried to obtain aminolated boron nitride nanosheets. Aminated boron nitride nanosheets were dispersed in a solvent containing excess terephthalaldehyde. After the reaction, the nanosheets were washed and dried to obtain aldehyde-modified boron nitride nanosheets. Aldehyde-modified boron nitride nanosheets were dispersed in a solvent containing an excess of bis(4-aminophenyl)disulfide. After the reaction, the nanosheets were washed and dried to obtain the modified boron nitride nanosheets.

[0006] Preferably, the silane coupling agent in step (2) is one or both of 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; The mass ratio of terephthalaldehyde to aminated boron nitride nanosheets in step (3) is 1:(0.5~2); The mass ratio of the bis(4-aminophenyl) disulfide to the aldehyde-based boron nitride nanosheets in step (4) is 1:(1~3).

[0007] Preferably, the polyether polyol is polytetrahydrofuran ether diol with a number average molecular weight of 1000-3000.

[0008] Preferably, the isocyanate prepolymer is prepared by reacting polytetrahydrofuran ether diol with diphenylmethane diisocyanate, and the -NCO mass percentage content is 15%~18%.

[0009] Preferably, the defoamer is selected from at least one of dibutyltin dilaurate and stannous octoate; the defoamer is an organosilicon defoamer.

[0010] Preferably, the components A and B are mixed and cured in a ratio of isocyanate index -NCO / -OH of 0.95 to 1.10.

[0011] A second objective of this invention is to provide a method for preparing the filler material described in any of the above claims, comprising the following steps: (1) Polyether polyol, modified boron nitride nanosheets, catalyst and defoamer are mixed uniformly under vacuum according to the ratio and defoamed to obtain component A; (2) After vacuum dehydration of polytetrahydrofuran ether diol, it is reacted with excess diphenylmethane diisocyanate at 80°C for 2 hours to obtain an isocyanate prepolymer with -NCO content of 15%~18%, which is used as component B. (3) Mix component A and component B at an equivalent ratio of -NCO / -OH of 0.95 to 1.10 and stir until homogeneous to obtain the filler material.

[0012] The third objective of this invention is to provide a thermally conductive and shock-absorbing polyurethane-filled tire, comprising a tire shell and a polyurethane elastomer filled in the tire cavity, wherein the polyurethane elastomer is formed by injecting the aforementioned filling material into the tire cavity and then curing it.

[0013] Preferably, the curing process employs a programmed temperature rise process: (1) The first stage is: temperature 50~70℃, pre-curing time 1~3 hours; (2) The second stage is: temperature 75~90℃, curing time 2~6 hours; (3) The third stage is: temperature 95~115℃, curing time 1~2 hours.

[0014] The fourth objective of this invention is to provide an application of thermally conductive and shock-absorbing polyurethane-filled tires in pneumatic tires, wherein the pneumatic tires are used in low-speed, high-load vehicles, engineering vehicles, military vehicles, or aircraft.

[0015] Compared with the prior art, the advantages of the present invention are as follows: (1) The modified boron nitride nanosheets grafted with dynamic disulfide bonds of the present invention, through molecular-level structural design, enable the tire filling material to have the dual functions of efficient thermal conductivity and dynamic covalent crosslinking, solving the problem that thermally conductive filler and elasticity cannot be obtained simultaneously in the traditional blending method.

[0016] (2) By modifying boron nitride nanosheets, this invention not only achieves uniform and stable dispersion of fillers, but also constructs a network structure that runs through the material by bridging the modified boron nitride nanosheets with extremely short chain segments. This allows for a thermal conductivity that is significantly higher than that of pure polyurethane with a lower filler content, while maintaining the flexibility of the material.

[0017] (3) The disulfide bond segments grafted on the surface of the nanosheets undergo reversible breakage and recombination during the periodic deformation of the tire, giving the material excellent wide-temperature-range damping performance and rapid elastic recovery capability; the heat inside the tire can be quickly discharged through the adjacent thermally conductive nanosheets, avoiding heat accumulation and dynamic bond network instability, thus realizing the synergy of tire thermal conductivity and shock absorption performance.

[0018] (4) The present invention uses a two-component liquid system that can be directly injected into the inner cavity of the tire and cured in situ by programmed temperature rise. The process is simple and suitable for use in urethane-filled tires in pneumatic tires. It has broad industrial application prospects. Attached Figure Description

[0019] Figure 1 : This is a graph showing the rolling heat generation curves of tires in Example 1 and Comparative Examples 1-5 (the change in internal tire temperature over time). Figure 2 : Flowchart of the preparation process of the modified boron nitride nanosheets of this invention. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings. The description in this part is only exemplary and explanatory, and should not be used to limit the scope of protection of the present invention in any way.

[0021] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0022] Raw material source: Hexagonal boron nitride powder: particle size 5-10μm, purity 99.5%, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0023] 3-Aminopropyltriethoxysilane (KH-550): 98% purity, Nanjing Shuguang Chemical Group Co., Ltd.

[0024] Terephthalaldehyde: 99% purity, Sinopharm Chemical Reagent Co., Ltd.

[0025] Bis(4-aminophenyl) disulfide: 97% purity, Beijing Bailingwei Technology Co., Ltd.

[0026] Polytetrahydrofuran ether diol (Mn=2000): Industrial grade, BASF, Germany.

[0027] Diphenylmethane diisocyanate (MDI): Industrial grade, Wanhua Chemical Group Co., Ltd.

[0028] Dibutyltin dilaurate (DBTDL): Chemically pure, Sinopharm Chemical Reagent Co., Ltd.

[0029] Defoamer BYK-A530: BYK Chemical AG, Germany.

[0030] Sodium hydroxide, hydrogen peroxide (30%), anhydrous ethanol, tetrahydrofuran, N,N-dimethylformamide: analytical grade, Sinopharm Chemical Reagent Co., Ltd.

[0031] Preparation of modified boron nitride nanosheets: Examples 1-3 use the same preparation method, with only the amount of boron nitride added differing between examples.

[0032] Step (1): Preparation of hydroxylated boron nitride nanosheets (BN-OH) 10g of hexagonal boron nitride powder was weighed and added to 300mL of isopropanol. The mixture was ultrasonically exfoliated at 300W for 8 hours using an ultrasonic cell disruptor, with the temperature controlled to not exceed 30℃ during the ultrasonication process using an ice-water bath. After ultrasonication, the dispersion was centrifuged at 3000r / min for 15min. The supernatant was collected and vacuum filtered through a 0.22μm polytetrafluoroethylene microporous membrane. The resulting solid was vacuum dried at 60℃ for 12 hours to obtain approximately 6.5g of few-layer boron nitride nanosheets.

[0033] The above-mentioned few-layer boron nitride nanosheets were dispersed in 200 mL of a mixed aqueous solution containing 5 wt% NaOH and 10 wt% H2O2, and the reaction was carried out with magnetic stirring in a constant temperature water bath at 60 °C for 4 hours. After the reaction was completed, the product was repeatedly washed with deionized water until the pH of the washing solution was 7.0 ± 0.2. The product was then freeze-dried at -50 °C and a vacuum degree <10 Pa for 24 hours to obtain hydroxylated boron nitride nanosheets (BN-OH) with a yield of approximately 6.0 g.

[0034] Step (2): Preparation of aminated boron nitride nanosheets (BN-NH2) Weigh 5.0 g of the hydroxylated boron nitride nanosheets (BN-OH) obtained in step (1), add them to 200 mL of anhydrous ethanol, and ultrasonically disperse them for 30 min in an ultrasonic cleaner to obtain a uniform suspension. Under nitrogen protection, add 3.0 mL of 3-aminopropyltriethoxysilane (KH-550) dropwise to the suspension, and stir and reflux in an oil bath at 80 °C for 12 hours. After the reaction is complete, allow it to cool naturally to room temperature, centrifuge at 4000 r / min for 10 min, discard the supernatant, wash the precipitate three times with anhydrous ethanol (100 mL each time), and dry the obtained solid under vacuum at 60 °C for 12 hours to obtain aminolated boron nitride nanosheets (BN-NH2) with a yield of about 4.6 g.

[0035] Step (3): Preparation of aldehyde-modified boron nitride nanosheets (BN-CHO) Weigh 4.0 g of the aminated boron nitride nanosheets (BN-NH2) obtained in step (2), add them to 150 mL of anhydrous tetrahydrofuran, and sonicate for 30 min. Add 5.0 g of terephthalaldehyde (the mass ratio of terephthalaldehyde to aminated boron nitride nanosheets is 1.25:1), and react magnetically for 24 hours at room temperature (25±2℃) in the dark. After the reaction is complete, centrifuge at 4000 r / min for 10 min, discard the supernatant, and wash the precipitate 5 times with anhydrous tetrahydrofuran (80 mL each time) until the washing liquid shows no obvious absorption peak at 270 nm on a UV-Vis spectrophotometer. Dry the obtained solid under vacuum at 60℃ for 12 hours to obtain aldehyde-modified boron nitride nanosheets (BN-CHO), with a yield of about 3.7 g.

[0036] Step (4): Preparation of disulfide bond-functionalized boron nitride nanosheets (modified boron nitride nanosheets) Weigh 3.5 g of the aldehyde-modified boron nitride nanosheets obtained in step (3) and add them to 100 mL of anhydrous N,N-dimethylformamide. Disperse the nanosheets by ultrasonication for 30 min. Under nitrogen protection, add 7.0 g of bis(4-aminophenyl)disulfide (the mass ratio of bis(4-aminophenyl)disulfide to aldehyde-modified boron nitride nanosheets is 2:1). Stir the mixture in an oil bath at 60 °C for 12 hours. After the reaction, allow it to cool naturally to room temperature. Centrifuge at 4000 r / min for 10 min, discard the supernatant, and wash the precipitate three times (60 mL each time) with anhydrous N,N-dimethylformamide and three times (60 mL each time) with anhydrous ethanol. Dry the resulting solid under vacuum at 60 °C for 12 hours to obtain modified boron nitride nanosheets (BN-BD-NH2) with dynamic disulfide bonds grafted onto the surface and active amino groups at the ends. The yield is approximately 3.2 g. Thermogravimetric analysis (TGA) determined the surface organic grafting amount to be approximately 18 wt%.

[0037] Preparation of isocyanate prepolymer (component B) Polytetrahydrofuran ether diol (Mn=2000) was dehydrated under vacuum at 110°C for 2 hours. After cooling to 60°C, 100 parts of the dehydrated polytetrahydrofuran ether diol were mixed with 30 parts of diphenylmethane diisocyanate (MDI) under nitrogen protection and reacted at 80°C for 2 hours to obtain a terminal isocyanate prepolymer with a -NCO content of 16.5%, which was then sealed and stored.

[0038] Example 1: 1. Preparation of component A In a stirrer, 70 parts of polytetrahydrofuran ether diol (unprepolymerized portion, Mn=2000, pre-dehydrated under vacuum at 110℃ for 2 hours), 10 parts of modified boron nitride nanosheets (BN-BD-NH2) prepared in step (4), 0.2 parts of dibutyltin dilaurate, and 0.8 parts of defoamer BYK-A530 were added sequentially. The mixture was stirred and mixed for 60 minutes at room temperature and a vacuum of -0.095 MPa to ensure thorough mixing and complete removal of air bubbles. The mixture was then discharged, sealed, and stored.

[0039] 2. Mixing of the combined liquid and tire filling Take 100 parts of the above-mentioned component A and the prepared component B (isocyanate prepolymer), and calculate the actual mixing ratio according to the -NCO / -OH equivalent ratio of 1.05.

[0040] Weighed components A and B were placed in a mixing container and stirred at 2500 rpm for 30 seconds in a high-speed disperser to obtain a homogeneous mixture. The mixture was degassed under a vacuum of -0.095 MPa for 5 minutes and immediately injected into a cleaned and preheated tire cavity. After filling, residual air bubbles were removed by vibration. The tire was then placed in a mold and subjected to programmed temperature curing: pre-curing at 60°C for 2 hours, followed by curing at 80°C for 4 hours, and finally curing at 100°C for 1 hour. After curing, the tire was allowed to cool naturally to room temperature and demolded to obtain a solid tire sample filled with polyurethane elastomer.

[0041] 3. Preparation of test strips The same combination liquid was simultaneously poured into a polytetrafluoroethylene mold preheated to 60°C (mold cavity size 150mm×150mm×2mm and dumbbell-shaped cavity conforming to ASTM D412 standard), and cured using the same programmed temperature rise process as tires. After cooling, the mold was demolded and cut into standard test strips.

[0042] Example 2: The preparation steps of this example are basically the same as those of Example 1, except that the amount of modified boron nitride nanosheets in component A is 7 parts and the amount of polytetrahydrofuran ether diol is 73 parts, so as to keep the total amount of component A unchanged.

[0043] The composition of component A, the formulation and dosage of component B, the mixing process, the tire filling and curing process are all the same as in Example 1, and will not be described again here.

[0044] Example 3: The preparation steps of this example are basically the same as those of Example 1, except that the amount of modified boron nitride nanosheets in component A is 13 parts, and the amount of polytetrahydrofuran ether diol is adjusted to 67 parts accordingly.

[0045] The composition of component A, the formulation and dosage of component B, the mixing process, the tire filling and curing process are all the same as in Example 1.

[0046] Example 4: The preparation steps of this embodiment are basically the same as those of Example 1, except that: the amount of polytetrahydrofuran ether diol in component A is 60 parts, the amount of modified boron nitride nanosheets is 5 parts, the amount of dibutyltin dilaurate is 0.1 parts, and the amount of defoamer is 0.5 parts.

[0047] The composition of component A, the formulation and dosage of component B, the mixing process, the tire filling and curing process are all the same as in Example 1, and will not be described again here.

[0048] Example 5: The preparation steps of this embodiment are basically the same as those of Example 1, except that: the amount of polytetrahydrofuran ether diol in component A is 80 parts, the amount of modified boron nitride nanosheets is 15 parts, the amount of dibutyltin dilaurate is 0.3 parts, and the amount of defoamer is 1 part.

[0049] The composition of component A, the formulation and dosage of component B, the mixing process, the tire filling and curing process are all the same as in Example 1, and will not be described again here.

[0050] Comparative Example 1 (without disulfide bonds, using aminated boron nitride nanosheets instead of modified boron nitride nanosheets): The preparation steps of this comparative example are basically the same as those of Example 1, except that in the preparation of Group A, 10 parts of the aminated boron nitride nanosheets (BN-NH2) obtained in step (2) are used to replace 10 parts of the modified boron nitride nanosheets in Example 1. The aminated boron nitride nanosheets (BN-NH2) have not undergone the aldehyde-based treatment in step (3) and the disulfide bond functionalization treatment in step (4). Their surface only contains amino groups introduced by the silane coupling agent and does not contain dynamic disulfide bond segments.

[0051] The preparation method of component A, the formulation and dosage of component B, the mixing process of components A and B, and the tire filling and curing process are all the same as in Example 1.

[0052] The test strips were prepared in the same manner as in Example 1.

[0053] Comparative Example 2 (without amination, hydroxylated boron nitride nanosheets directly undergoing subsequent reactions): The preparation steps of this comparative example differ fundamentally from those of Example 1 in the preparation process of the modified boron nitride used in component A, as detailed below: Preparation of modified boron nitride used in Comparative Example 2 (omitting the amination treatment in step 2): Take 3.5 g of the hydroxylated boron nitride nanosheets (BN-OH) obtained in step (1), add them to 150 mL of anhydrous tetrahydrofuran and disperse them by ultrasonication. Add 5.0 g of terephthalaldehyde, stir at room temperature in the dark for 24 hours, centrifuge, wash with tetrahydrofuran, and dry. Then disperse the intermediate product in 100 mL of anhydrous DMF, add 7.0 g of bis(4-aminophenyl) disulfide, react at 60 °C for 12 hours, wash and dry to obtain the product without the amination step.

[0054] Filler material preparation: In the A-group allocation, 10 parts of the product obtained above with the amination step omitted were used to replace 10 parts of the modified boron nitride nanosheets in Example 1.

[0055] The composition of component A, the formulation and dosage of component B, the mixing and curing process, etc. are all the same as in Example 1.

[0056] Comparative Example 3 (Irreversible covalent bonds, replaced by an aromatic ring without disulfide bonds): The preparation steps of this comparative example are basically the same as those of Example 1, except that bis(4-aminophenyl) disulfide is replaced with 1,4-phenylenediamine without disulfide bonds to prepare irreversibly covalently linked modified boron nitride nanosheets. Details are as follows: Preparation of modified boron nitride used in Comparative Example 3: 3.5 g of aldehyde-modified boron nitride nanosheets (BN-CHO) obtained in step (3) of the above-mentioned modified boron nitride nanosheet preparation were dispersed in 100 mL of anhydrous N,N-dimethylformamide, and 6.0 g of 1,4-phenylenediamine (equimolar amount with bis(4-aminophenyl)disulfide) was added. The mixture was reacted at 60 °C for 12 hours, washed, and dried to obtain modified boron nitride (BN-BD-NH2) with surface-grafted benzene ring diamine segments and terminal active amino groups. The organic segments on the surface of this product contain only rigid benzene ring structures and do not contain -SS- bonds, thus lacking dynamic reversible exchange capacity.

[0057] Filler material preparation: In the A-group formulation, 10 parts of BN-BD-NH2 were used to replace 10 parts of the modified boron nitride nanosheets in Example 1. The formulations and amounts of the remaining A-group, B-group, mixing and curing processes were the same as in Example 1.

[0058] Comparative Example 4 (Borne Nitride-Free - Pure Polyurethane Blank Control): This comparative example is a pure polyurethane control without any added boron nitride filler. In the preparation of Group A, only 70 parts of polytetrahydrofuran ether diol, 0.2 parts of dibutyltin dilaurate, and 0.8 parts of defoamer BYK-A530 were added; no modified boron nitride nanosheets or any other boron nitride materials were added.

[0059] The formulation and dosage of the remaining component B, the mixing process of components A and B, and the tire filling and curing process are the same as in Example 1.

[0060] Comparative Example 5 (Modified boron nitride nanosheets used at a rate lower than the percolation threshold): The preparation steps of this comparative example are basically the same as those of Example 1, except that the amount of modified boron nitride nanosheets in component A is adjusted to 2 parts, and the amount of polytetrahydrofuran ether diol is adjusted to 78 parts accordingly.

[0061] The formulations and dosages of the remaining components A and B, as well as the mixing and curing processes, are the same as in Example 1.

[0062] Performance Testing and Standards The following performance tests were performed on the filler material samples obtained in the above embodiments and comparative examples: (1) Thermal conductivity: The thermal conductivity was measured using a laser flash thermal conductivity meter (Netzsch LFA 467) according to ASTM E1461 standard. The sample was a circular disc with a diameter of 12.7 mm and a thickness of about 2 mm. Before the test, a thin layer of graphite was evenly sprayed on both sides of the sample. The test temperature was 25℃, and each sample was tested 3 times and the arithmetic mean was taken.

[0063] (2) Tensile properties: determined according to ASTM D412 standard using a universal testing machine (Instron 5966). The specimens were cut with a C-shaped dumbbell cutter, the tensile rate was 500 mm / min, and the gauge length was 25 mm. The tensile strength and elongation at break were recorded, and the average value of at least 5 specimens in each group was taken.

[0064] (3) Dynamic mechanical properties: measured according to ASTM D4065 standard using a dynamic mechanical analyzer (TA DMA Q800). A double cantilever clamp was used, with sample dimensions of 35mm × 12mm × 2mm, frequency of 1Hz, amplitude of 15μm, heating rate of 3℃ / min, and temperature scan range of -80℃ to 100℃. The loss factor tanδ value at 25℃ was recorded.

[0065] (4) Compression set: determined according to ASTM D395 method B. The specimen was a cylinder with a diameter of 29 mm and a thickness of 12.5 mm. It was compressed by 25% in an oven at 70 °C (i.e., compressed to a thickness of 9.375 mm), kept for 24 hours, then depressurized and allowed to recover at room temperature for 30 minutes. The thickness after recovery was measured, and the compression set was calculated according to the standard formula.

[0066] (5) Tire rolling heat generation: On a tire rolling test machine (1.7m diameter drum), the filled tire was installed on a standard rim, inflated to the standard pressure, and continuously rolled for 2 hours at a speed of 50km / h and 80% of the rated load. The temperature was recorded in real time using thermocouples embedded in three locations: the center of the tire crown, the tire shoulder, and the tire sidewall. The highest temperature among the three locations after rolling was taken as the peak internal temperature of the tire. A tire rolling heat generation curve was plotted, see [reference needed]. Figure 1 .

[0067] Table 1 summarizes the performance test results of the filler materials in Examples 1-5.

[0068] Table 2: Summary of performance test results for Comparative Examples 1-5

[0069] Based on Table 1-2 above: (1) As can be seen from Table 1, the thermal conductivity of Examples 1-3 and Example 5 increases with the amount of modified boron nitride nanosheets, and the thermal conductivity of the examples is significantly higher than that of the pure polyurethane set in Comparative Example 4. This indicates that the modified boron nitride nanosheets have constructed a continuous thermal conduction channel in the matrix, which is beneficial to the efficient heat dissipation of the tire.

[0070] As can be seen from Table 2, the thermal conductivity of Comparative Example 5 is only 0.44 W / (m·K), which is much lower than that of Example 1. This indicates that the amount of modified boron nitride nanosheets used did not reach the percolation threshold of the filler and could not form a through-through thermally conductive network.

[0071] Comparative Example 2, lacking an amination step, resulted in poor compatibility and uneven dispersion of the filler with the matrix, leading to a thermal conductivity of only 0.85 W / (m·K). Comparative Examples 1 and 3 both exhibited thermal conductivity of 1.39 W / (m·K), close to that of Example 1. This indicates that the thermal conductivity of the boron nitrogen filler is determined by its intrinsic high thermal conductivity and dispersion state, while the chemical properties of the surface grafted segments have a relatively small impact on thermal conductivity. (2) Example 1 has a tensile strength of 18.7 MPa, an elongation at break of 420%, and a tanδ of 0.21, which shows excellent strength and toughness as well as outstanding shock absorption performance.

[0072] Compared with Example 1, Example 2 has a lower amount of modified boron nitride nanosheets, with a tanδ of 0.19, and its damping performance is slightly worse than that of Example 1, but it is still better than the comparative example. Compared with Example 1, Example 3 has a tanδ as high as 0.24, exhibiting the best damping performance, but its elongation at break drops to 380%, indicating that the addition of excessive modified boron nitride nanosheet filler has a certain negative impact on the material's extensibility.

[0073] (3) Compared with the examples, in Comparative Example 1, when aminated boron nitride nanosheets were used instead of modified boron nitride nanosheets, the loss factor tanδ dropped sharply to 0.11, the compression set increased from 8.4% to 22.5%, and the elongation at break decreased from 420% to 280%. This shows that although BN filler can participate in cross-linking reactions through amino groups, the lack of dynamic covalent bonds significantly reduces the elastic recovery ability and damping performance of the material.

[0074] Comparative Example 2 showed a tanδ of only 0.13, a compression set of 18.3%, and a significant decrease in thermal conductivity. This indicates that omitting the amination step (2) as an intermediate coupling layer significantly reduces the efficiency of subsequent disulfide bond functionalization, leading to the loss of dynamic crosslinking function and a decline in material properties. This demonstrates the necessity of the amination step. Comparative Example 3, which replaced disulfide bonds with irreversible benzene rings, exhibited the lowest tanδ (0.09), the highest compression set (25.2%), and the worst elastic recovery. When the connection between the filler and the polyurethane matrix was a conventional irreversible covalent bond, the material's energy dissipation and elastic recovery under cyclic loading were significantly lower than those of the dynamic disulfide bond system, further verifying the crucial role of the dynamic reversibility of disulfide bonds in vibration damping performance.

[0075] Comparative Example 4, with pure polyurethane, has a tanδ of only 0.07 and a compression set of 15.1%. Although it has the highest elongation at break (550%), its shock absorption and elastic recovery performance are far inferior to those of Example 1, and its thermal conductivity is extremely low.

[0076] Comparative Example 5, due to a significantly lower amount of modified boron nitride nanosheets than Example 1, had an insufficient number of dynamic crosslinking points, a tanδ of only 0.10, a compression set of 17.7%, and significantly inferior elasticity and damping compared to Example 1. This indicates that the amount of modified boron nitride nanosheets was too low to reach the percolation threshold required to form continuous thermally conductive channels. The preferred amount of modified boron nitride nanosheets in this application is 5 to 15 parts.

[0077] pass Figure 1 We can obtain: Example 1: The initial temperature rise was gradual, stabilizing after about 60 minutes, with the final internal temperature of the tire carcass reaching only 67°C. This is attributed to the highly efficient thermally conductive network of the modified boron nitride nanosheets, which continuously dissipates heat, demonstrating excellent heat dissipation.

[0078] Comparative Example 1 (without disulfide bonds): Although the thermal conductivity is similar to that of Example 1, the temperature rise rate is significantly faster, and the final internal temperature of the tire carcass is 72°C. Due to the lack of dynamic disulfide bonds, the hysteresis heat generated by cyclic deformation cannot be dissipated through dynamic bond exchange, resulting in a higher net heat generation than in Example 1.

[0079] Comparative Example 2 (without amination): The final internal temperature of the tire carcass reached as high as 79°C. Due to its thermal conductivity of only 0.84 W / (m·K), its heat dissipation capacity was insufficient; at the same time, its dynamic cross-linking function was basically lost, resulting in poor elasticity and high internal heat generation.

[0080] Comparative Example 3 (Irreversible Covalent Bonds): The final internal temperature of the tire carcass was 71°C. The thermal conductivity was comparable to that of Example 1, and the initial heat dissipation was acceptable. However, irreversible covalent bonds do not have dynamic reversible energy consumption, resulting in higher internal heat generation than in Example 1, a slightly faster temperature rise, and a slightly higher peak temperature.

[0081] Comparative Example 4 (pure polyurethane): The temperature rise was the most dramatic, exceeding 100℃ in 80 minutes, and the final internal temperature of the tire carcass reached 104℃. This demonstrates that pure polyurethane has extremely poor thermal conductivity and difficulty in dissipating heat, verifying the decisive role of modified boron nitride nanosheets in heat dissipation.

[0082] Comparative Example 5 (Insufficient amount of modified boron nitride nanosheets): The final internal temperature of the tire carcass was 95°C. This indicates that when the amount of modified boron nitride nanosheets is below the percolation threshold, a continuous heat-conducting network cannot be formed, and the heat dissipation effect is significantly reduced compared to the examples.

[0083] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0084] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only for the purpose of helping to understand the method and core ideas of the present invention. The above descriptions are only preferred embodiments of the present invention. It should be noted that due to the limitations of textual expression, while there are objectively infinite specific structures, those skilled in the art can make several improvements, modifications, or changes without departing from the principles of the present invention, and can also combine the above technical features in an appropriate manner. These improvements, modifications, changes, or combinations, or the direct application of the inventive concept and technical solution to other situations without modification, should all be considered within the scope of protection of the present invention.

Claims

1. A thermally conductive and shock-absorbing polyurethane filler material based on boron nitride dynamic crosslinking, characterized in that, The filler material is formed by mixing and curing components A and B. By weight, component A comprises: 60-80 parts of polyether polyol, 5-15 parts of modified boron nitride nanosheets, 0.1-0.3 parts of catalyst, and 0.5-1 parts of defoamer; Component B is 100 parts of isocyanate prepolymer; The modified boron nitride nanosheets are boron nitride nanosheets whose surfaces have been sequentially hydroxylated, aminated, aldehyde-modified, and disulfide bond-functionalized. Their surfaces are grafted with segments containing dynamic disulfide bonds and have active amino groups at the ends. After curing, the modified boron nitride nanosheets are incorporated into the polyurethane matrix through the participation of their surface-active amino groups in the polyurethane crosslinking reaction; the modified boron nitride nanosheets are in contact with each other or bridged by polyurethane segments to form a three-dimensional thermally conductive channel in the matrix; the disulfide bond segments grafted on the surface of the modified boron nitride nanosheets constitute reversible dynamic crosslinking nodes in the polyurethane network.

2. The filler material according to claim 1, characterized in that, The preparation of the modified boron nitride nanosheets includes the following steps: (1) Hexagonal boron nitride powder was ultrasonically exfoliated to obtain few-layer boron nitride nanosheets, which were dispersed in an alkaline / hydrogen peroxide mixed solution, washed with water until neutral after reaction, and freeze-dried to obtain hydroxylated boron nitride nanosheets; (2) Disperse hydroxylated boron nitride nanosheets in an organic solvent, add silane coupling agent, and after reaction, wash and dry to obtain aminolated boron nitride nanosheets; (3) Disperse the aminated boron nitride nanosheets in a solvent containing excess terephthalaldehyde. After the reaction, wash and dry to obtain aldehyde-modified boron nitride nanosheets. (4) The aldehyde-modified boron nitride nanosheets are dispersed in a solvent containing an excess of bis(4-aminophenyl) disulfide. After the reaction, the nanosheets are washed and dried to obtain the modified boron nitride nanosheets.

3. The filler material according to claim 2, characterized in that, The silane coupling agent mentioned in step (2) is one or both of 3-aminopropyltriethoxysilane and 3-aminopropyltrimethoxysilane; The mass ratio of terephthalaldehyde to aminated boron nitride nanosheets in step (3) is 1:(0.5~2); The mass ratio of bis(4-aminophenyl) disulfide to aldehyde-modified boron nitride nanosheets in step (4) is 1:(1~3).

4. The filler material according to claim 1, characterized in that, The polyether polyol is polytetrahydrofuran ether diol with a number average molecular weight of 1000-3000.

5. The filler material according to claim 1, characterized in that, The isocyanate prepolymer is prepared by reacting polytetrahydrofuran ether diol with diphenylmethane diisocyanate, and the -NCO mass percentage content is 15%~18%.

6. The filler material according to claim 1, characterized in that, The catalyst is an organotin catalyst, selected from at least one of dibutyltin dilaurate and stannous octoate; the defoamer is an organosilicon defoamer.

7. The filler material according to claim 1, characterized in that, The components A and B are mixed and cured in a ratio of isocyanate index -NCO / -OH of 0.95 to 1.

10.

8. A method for preparing a filler material according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) Polyether polyol, modified boron nitride nanosheets, catalyst and defoamer are mixed uniformly under vacuum according to the ratio and defoamed to obtain component A; (2) After vacuum dehydration of polytetrahydrofuran ether diol, it is reacted with excess diphenylmethane diisocyanate at 80°C for 2 hours to obtain an isocyanate prepolymer with -NCO content of 15%~18%, which is used as component B. (3) Mix component A and component B at an equivalent ratio of -NCO / -OH of 0.95 to 1.10 and stir until homogeneous to obtain the filler material.

9. A thermally conductive and shock-absorbing polyurethane-filled tire, comprising a tire shell and a polyurethane elastomer filled in the tire cavity, characterized in that, The polyurethane elastomer is formed by injecting the filler material according to any one of claims 1 to 8 into the inner cavity of a tire and then curing it.

10. The thermally conductive and shock-absorbing polyurethane-filled tire according to claim 9, characterized in that, The curing process employs a programmed temperature rise process: (1) The first stage is: temperature 50~70℃, pre-curing time 1~3 hours; (2) The second stage is: temperature 75~90℃, curing time 2~6 hours; (3) The third stage is: temperature 95~115℃, curing time 1~2 hours.

11. The application of the thermally conductive and shock-absorbing polyurethane-filled tire according to claim 9 or 10 in an airless tire, wherein the airless tire is used in low-speed, high-load vehicles, engineering vehicles, military vehicles, or aircraft.

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