FA modification method, SBR / FA composite material prepared from modified FA and application of SBR / FA composite material

Abstract

The invention belongs to the technical field of fly ash reutilization, and particularly relates to an FA modification method, an SBR / FA composite material prepared from modified fly ash and application of the SBR / FA composite material. The modification method comprises the following steps: S1, grafting a carboxyl functional group to SSBR by utilizing a thiol-ene click reaction to prepare carboxyl functionalized SSBR; and S2, carrying out ball milling by using a planetary ball mill to prepare the modified fly ash SSBR-coated FA. The SSBR coated FA is filled into the SBR composite material, so that the mechanical property, the flame retardant property and the heat-conducting property of the SBR composite material are remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of fly ash recycling technology, and specifically relates to a method for modifying fly ash (FA), as well as SBR / FA composite materials prepared using modified fly ash and their applications. Background Technology

[0002] Although wind, solar, and biogas power generation are currently viable alternative energy sources, coal-fired power plants still play a crucial role in electricity production, accounting for approximately 41% of global electricity output, a figure projected to rise to 44% by 2030. In a coal-fired power plant, approximately one ton of fly ash (FA) is produced for every four tons of coal burned.

[0003] Microscopically, FA exhibits a spherical particle structure, similar to carbon black, primarily composed of silica and metal oxides, with a low tendency to agglomerate. As a non-synthetic filler, FA is low-cost and carbon-free, making it an ideal alternative for reducing the production cost of rubber composites. Adding unmodified FA to the rubber matrix can shorten the vulcanization time, but its mechanical properties decrease compared to rubber composites filled with silica. This is mainly attributed to the low specific surface area and surface inertness of unmodified FA, which reduce the contact area between the rubber molecular chains and the filler particles, lowering surface wettability and thus weakening interfacial interactions. To overcome this problem, surface treatment is an essential step. Garde et al. used acid-base modification to increase the specific surface area of ​​FA, but even with the addition of Si69, the modified FA-filled polyisoprene still suffered from low binder content and poor mechanical strength. This is due to the large particle size of FA and the lack of reactive hydroxyl groups on its surface. Based on the above analysis, factors such as particle size, structure, specific surface area, and surface activity significantly affect the reinforcing efficiency of FA.

[0004] From a chemical composition perspective, besides silica, fatty acid (FA) contains a large amount of metal oxides, such as calcium oxide, aluminum oxide, and iron oxide. Based on this compositional characteristic, Yang's research group proposed the concept of in-situ grafting-neutralization to improve the performance of FA-filled rubber composites. Through in-situ carboxylate reaction under heating conditions, a fixed nitrile butadiene rubber (XNBR) layer is formed on the surface of FA particles, resulting in better interfacial adhesion. Therefore, the tensile strength of the XNBR / 20FA composite reaches 23.19 MPa, approximately 44.0% higher than that of pure XNBR. The research team also prepared composites by blending sorbic acid (SA) or tannic acid (TA) with rubber and FA that do not contain carboxyl functional groups. One end of these acid molecules reacts with the surface components of the FA particles, and the other end reacts with the rubber chains, thus forming a stronger interfacial interaction between the rubber and FA particles. The tensile strength of the SBR / FA / 15SA composite is approximately 215% higher than that of the SBR / FA composite. Based on the same concept, other research groups have carbonized FA by introducing CO2 into water. Carbonated FA can be used as a reinforcing filler for silicone rubber, effectively improving the flame retardancy of composite materials.

[0005] Despite some progress in using fatty acids (FAs) to reinforce rubber, achieving significant improvements in mechanical properties in rubber composites remains a major challenge, especially with large additions of FAs. Encapsulating FA in hydrophobic polymer coatings effectively addresses these issues, making it an ideal filler candidate for commercial applications in rubber-based composites. Bordoloi et al. prepared a novel surface-modified filler (SuMoFA) by encapsulating FA with a hydrophobic polysulfide coating. SuMoFA exhibits excellent wettability with rubber, effectively reducing dust pollution and heavy metal leaching. Other research teams have also reported similar hydrophobic coatings based on biopolymers for FA encapsulation; these coatings are synthesized from waste sulfur and edible oils.

[0006] As a commonly used matrix in rubber composites, research on the modification and coating of solution-polymerized styrene-butadiene rubber (SSBR) with FA is rarely reported. This invention involves wet ball milling two carboxyl-functionalized SSBRs with FA to prepare hydrophobic FA (SSBR@FA) via an in-situ grafting-neutralization reaction. Ball milling is used to reduce the FA particle size and modify the filler particle morphology. Under the combined effect of ball milling and SSBR modifiers, the SSBR@FA-filled SBR composite material exhibits significant improvements in mechanical properties, thermal conductivity, and flame retardancy, providing a new approach for the large-scale application of FA in rubber materials. Summary of the Invention

[0007] The first objective of this invention is to provide a method for modifying fatty acids (FAs), comprising the following steps: S1. Carboxyl functional groups are grafted onto SSBR using a mercapto-alkene click reaction to prepare carboxyl-functionalized SSBR. Under nitrogen protection, SSBR was dissolved in cyclohexane and stirred until SSBR was completely dissolved. Then, a mercapto compound was added, and a pre-prepared solution of dodecyl peroxide (LPO)cyclohexane was added while the temperature was raised and stirring continued to complete the mercapto-alkene click reaction. S2. Modified fly ash (SSBR@FA) is prepared by ball milling using a planetary ball mill. S2.1. Add the cyclohexane solution of carboxyl-functionalized SSBR and fly ash sequentially into a ball mill jar, and then add cyclohexane; S2.2 Grind the above mixture for 8 hours under alternating forward and reverse rotation conditions. The planetary ball mill has a revolution speed of 260 rpm and a rotation speed of 530 rpm. Use 30 zirconia balls with a diameter of 5 mm and 18 zirconia balls with a diameter of 10 mm. S2.3. Take the ball-milled material, extract it with cyclohexane as a solvent to remove ungrafted SSBR, and then dry it under vacuum to constant weight to obtain the modified fly ash sample SSBR@FA.

[0008] Furthermore, the thiol compound is one of 3-mercaptopropionic acid (MPA) or 11-mercaptoundecanoic acid (MUA).

[0009] Furthermore, the molar ratio of the thiol compound to SSBR in S1 is (0.12-0.2):1.

[0010] Furthermore, the molar ratio of LPO to thiol compound in S1 is 1:(80-150).

[0011] Furthermore, the mass ratio of SSBR to fly ash is (0.01-0.03):1.

[0012] Furthermore, the composition of fly ash is as follows: SiO2: 31.72%, CaO: 28.67%, Al2O3: 22.98%, SO3: 4.96%, Na2O: 1.72%, MgO: 1.41%, P2O5: 1.25%, K2O: 1.41%, TiO2: 1.27%, V2O5: 0.06%, MnO: 0.02%, Fe2O3: 3.57%, Co2O3: 0.01%, NiO: 0.01%, CuO: 0.02%, SrO: 0.44%, ZrO2: 0.03%, BaO: 0.38%.

[0013] Furthermore, the number-average molecular weight M of SSBR nThe concentration was 70900 g / mol, the styrene content was 32.4 wt%, and the 1,2-polybutadiene unit accounted for 47.9 wt% of the total polybutadiene unit.

[0014] A second objective of this invention is to provide modified fly ash prepared by the aforementioned modification method.

[0015] A third object of the present invention is to provide an SBR / FA composite material comprising the modified fly ash, comprising the following components: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; SSBR@FA variable 15-30 phr.

[0016] The beneficial technical effects of this invention are as follows: First, this invention successfully grafts carboxyl functional groups onto the solution-polymerized styrene-butadiene rubber (SSBR) molecular chain via a mercapto-olefin click reaction. Then, utilizing the high-energy mechanochemical action of a planetary ball mill, the functionalized SSBR is firmly grafted onto the surface of fly ash (FA) via an in-situ carboxylate reaction, forming a core-shell structured modified filler (SSBR@FA). This method effectively solves the key problems of the original FA surface's inertness, low specific surface area, and weak interfacial interaction with the rubber matrix.

[0017] Secondly, the modified FA exhibits significant performance improvements. Its surface properties change from hydrophilic to hydrophobic, its surface energy is significantly reduced, and its specific surface area is increased. These changes greatly improve the dispersibility and wettability of FA in the SBR matrix, weaken the filler-filler network structure (the Payne effect is significantly reduced), thus laying the foundation for optimizing the composite material's performance.

[0018] Ultimately, incorporating SSBR@FA into SBR composites significantly improved their mechanical properties, flame retardancy, and thermal conductivity. Compared to pure SBR vulcanizates, the composites exhibited simultaneous increases in tensile strength, tear strength, and elongation at break. Furthermore, due to the enhanced flame retardant effects of Al2O3 and SiO2 in FA and the improved thermal conductivity pathways, the composites also showed increases in limiting oxygen index (LOI) and thermal conductivity. Attached Figure Description

[0019] Figure 1 Typical unfunctionalized SSBR and functionalized SSBR 1 HNMR spectrum.

[0020] Figure 2FTIR plots of unfunctionalized and functionalized SSBR.

[0021] Figure 3 FTIR spectra of FA, SSBR, functionalized SSBR and modified FA after extraction.

[0022] Figure 4 The water contact angles of the surfaces of (A) FA, (B) 1PFA, (C) 3PFA, (D) 1UFA and (E) 3UFA.

[0023] Figure 5 Surface energy values ​​of FA, 1PFA, 3PFA, 1UFA and 3UFA.

[0024] Figure 6 Dispersion of FA, BFA, 3PFA and 3UFA in cyclohexane: (A) Initial state; (B) State after ten minutes.

[0025] Figure 7 TGA curves of extracted FA, functionalized SSBR, 1PFA, 3PFA, 1UFA and 3UFA.

[0026] Figure 8 (A) SEM and EDS spectra of 3PFA (B) BET specific surface area (SSA) values ​​of raw fly ash, ball milled fly ash (BFA) and SSBR@FA.

[0027] Figure 9 SEM and EDS spectra of raw fly ash.

[0028] Figure 10 TEM images of 1PFA and 3UFA.

[0029] Figure 11 Stress-strain curves of SBR (Comparative Example 1), SBR / FA (Comparative Examples 2 and 3), and SBR / SSBR@FA (Examples 1-6) vulcanizates.

[0030] Figure 12 Payne effect of SBR / FA and SBR / SSBR@FA compound rubbers.

[0031] Figure 13 Payne effect of SBR / FA and SBR / SSBR@FA vulcanizates.

[0032] Figure 14 Storage modulus-temperature profiles of SBR / FA and SBR / SSBR@FA vulcanizates.

[0033] Figure 15SEM images of SBR / FA15, SBR / 3PFA 15 and SBR / 3UFA 15 at different magnifications. Detailed Implementation

[0034] This invention successfully grafts carboxyl functional groups onto the SSBR molecular chain via a thiol-olefin click reaction under nitrogen protection. The specific process is as follows: SSBR is first dissolved in cyclohexane and stirred at 60°C for 6 hours. Then, a thiol compound, MPA or MUA, is added. The temperature is raised to 80°C, and an LPO initiator is added. The reaction completes the carboxyl functionalization. The functionalized materials obtained are SSBR-g-MPA and SSBR-g-MUA. The number-average molecular weight M of SSBR is... n The concentration is 70900 g / mol, the styrene content is 32.4 wt%, and the 1,2-polybutadiene unit accounts for 47.9 wt% of the polybutadiene unit. The molar ratio of the mercapto compound to SSBR is (0.12-0.2):1. The optimal molar ratio is 0.15:1. The molar ratio of LPO to the mercapto compound is 1:80-150. The optimal ratio is 1:120.

[0035] Functionalized SSBR was synthesized using a planetary ball mill to prepare SSBR@FA modified fly ash via a mechanochemical method. The specific process involved mixing a carboxyl-functionalized SSBR cyclohexane solution with fly ash, adjusting the fly ash concentration to 40%, and milling for 8 hours using multi-sized zirconia balls at a revolution speed of 260 rpm and a rotation speed of 530 rpm. After removing free SSBR through cyclohexane extraction for 72 hours, the mixture was vacuum dried at 50°C, ultimately yielding four core-shell structure modified fly ashes: 1PFA, 3PFA, 1UFA, and 3UFA. This achieved a transformation of the fly ash surface from hydrophilic to hydrophobic. 1PFA represents a 1% mass ratio of SSBR-g-MPA to fly ash, 3PFA represents a 3% mass ratio, 1UFA represents a 1% mass ratio of SSBR-g-MPA to fly ash, and 3UFA represents a 3% mass ratio.

[0036] The obtained SSBR@FA modified fly ash, SBR1502, and other additives were mixed to prepare SBR / FA composite materials, namely SBR / 1PFA15, SBR / 1PFA30, SBR / 3PFA15, SBR / 3PFA30, SBR / 1UFA15, SBR / 1UFA30, SBR / 3UFA15, and SBR / 3UFA30.

[0037] Example 1: Preparation of SBR / 1PFA15 composite material A method for preparing an SBR / FA composite material includes the following steps: S1. A cyclohexane solution of carboxyl-functionalized SSBR is prepared by grafting carboxyl functional groups onto SSBR using a mercapto-olefin click reaction, specifically including the following steps: Under nitrogen protection, a predetermined amount of SSBR (M) was added sequentially to the glass reaction flask. n =70,900 g / mol) and cyclohexane were stirred at 60°C for 6 h until SSBR was completely dissolved, yielding a homogeneous solution with a mass fraction of 10%. Subsequently, a quantitative amount of the mercapto compound 3-mercaptopropionic acid (MPA) was injected, with a molar ratio of MPA to SSBR of 0.15:1. The mixture was heated to 80°C and stirred for 10 min, and a pre-prepared solution of dodecyl peroxide (LPO) in cyclohexane was added. The reaction was continued at 80°C for 1 h with stirring to complete the mercapto-alkene click reaction. The molar ratio of LPO to the mercapto compound was 1:120.

[0038] S2. Modified fly ash (SSBR@FA) of SSBR-g-MPA was prepared using a planetary ball mill, specifically including the following steps: S2.1 First, add the cyclohexane solution of SSBR-g-MPA and fly ash to the ball mill jar. The mass ratio of SSBR to fly ash is 0.01:1. Then add an appropriate amount of cyclohexane to make the fly ash concentration 40%, that is, 40g of fly ash is dissolved in 60g of cyclohexane. S2.2 Grind the above mixture for 8 hours under alternating forward and reverse rotation conditions. The planetary ball mill has a revolution speed of 260 rpm and a rotation speed of 530 rpm. Use 30 zirconia balls with a diameter of 5 mm and 18 zirconia balls with a diameter of 10 mm. S2.3. Take an appropriate amount of the ball-milled material and extract it with cyclohexane as a solvent for 72 hours to remove ungrafted SSBR. Then dry it in a vacuum oven at 50°C to constant weight to obtain the modified fly ash sample SSBR@PFA, named 1PFA.

[0039] S3. The raw materials for the SBR / FA composite material are mixed on a two-roll mill: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; 1 PFA variable 15 phr.

[0040] Example 2: Preparation of SBR / 1PFA30 composite material A method for preparing an SBR / FA composite material includes the following steps: S1. A cyclohexane solution of carboxyl-functionalized SSBR is prepared by grafting carboxyl functional groups onto SSBR using a mercapto-olefin click reaction, specifically including the following steps: Under nitrogen protection, a predetermined amount of SSBR (M) was added sequentially to the glass reaction flask. n =70,900 g / mol) and cyclohexane were stirred at 60°C for 6 h until SSBR was completely dissolved, yielding a homogeneous solution with a mass fraction of 10%. Subsequently, a quantitative amount of the mercapto compound 3-mercaptopropionic acid (MPA) was injected, with a molar ratio of MPA to SSBR of 0.15:1. The mixture was heated to 80°C and stirred for 10 min, and a pre-prepared solution of dodecyl peroxide (LPO) in cyclohexane was added. The reaction was continued at 80°C for 1 h with stirring to complete the mercapto-alkene click reaction. The molar ratio of LPO to the mercapto compound was 1:120.

[0041] S2. SSBR-g-MPA modified fly ash (SSBR@FA) was prepared using a planetary ball mill, specifically including the following steps: S2.1 First, add the cyclohexane solution of SSBR-g-MPA and fly ash to the ball mill jar. The mass ratio of SSBR to fly ash is 0.01:1. Then add an appropriate amount of cyclohexane to make the fly ash concentration 40%, that is, 40g of fly ash is dissolved in 60g of cyclohexane. S2.2 Grind the above mixture for 8 hours under alternating forward and reverse rotation conditions. The planetary ball mill has a revolution speed of 260 rpm and a rotation speed of 530 rpm. Use 30 zirconia balls with a diameter of 5 mm and 18 zirconia balls with a diameter of 10 mm. S2.3. Take an appropriate amount of the ball-milled material and extract it with cyclohexane as a solvent for 72 hours to remove ungrafted SSBR. Then dry it in a vacuum oven at 50°C to constant weight to obtain the modified fly ash sample SSBR@PFA, named 1PFA.

[0042] S3. The raw materials for the SBR / FA composite material are mixed on a two-roll mill: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; 1 PFA variable 30 phr.

[0043] Example 3: Preparation of SBR / 3PFA15 composite material A method for preparing an SBR / FA composite material includes the following steps: S1. A cyclohexane solution of carboxyl-functionalized SSBR is prepared by grafting carboxyl functional groups onto SSBR using a mercapto-olefin click reaction, specifically including the following steps: Under nitrogen protection, a predetermined amount of SSBR (M) was added sequentially to the glass reaction flask. n =70,900 g / mol) and cyclohexane were stirred at 60°C for 6 h until SSBR was completely dissolved, yielding a homogeneous solution with a mass fraction of 10%. Subsequently, a quantitative amount of the mercapto compound 3-mercaptopropionic acid (MPA) was injected, with a molar ratio of MPA to SSBR of 0.15:1. The mixture was heated to 80°C and stirred for 10 min, and a pre-prepared solution of dodecyl peroxide (LPO) in cyclohexane was added. The reaction was continued at 80°C for 1 h with stirring to complete the mercapto-alkene click reaction. The molar ratio of LPO to the mercapto compound was 1:120.

[0044] S2. SSBR-g-MPA modified fly ash (SSBR@FA) was prepared using a planetary ball mill, specifically including the following steps: S2.1 First, add the cyclohexane solution of SSBR-g-MPA and fly ash to the ball mill jar. The mass ratio of SSBR to fly ash is 0.03:1. Then add an appropriate amount of cyclohexane to make the fly ash concentration 40%, that is, 40g of fly ash is dissolved in 60g of cyclohexane. S2.2 Grind the above mixture for 8 hours under alternating forward and reverse rotation conditions. The planetary ball mill has a revolution speed of 260 rpm and a rotation speed of 530 rpm. Use 30 zirconia balls with a diameter of 5 mm and 18 zirconia balls with a diameter of 10 mm. S2.3. Take an appropriate amount of the ball-milled material and extract it with cyclohexane as a solvent for 72 hours to remove ungrafted SSBR. Then dry it in a vacuum oven at 50°C to constant weight to obtain modified fly ash samples SSBR@PFA, which are named 3PFA.

[0045] S3. The raw materials for the SBR / FA composite material are mixed on a two-roll mill: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; 3PFA variable 15 phr.

[0046] Example 4: Preparation of SBR / 3PFA30 composite material A method for preparing an SBR / FA composite material includes the following steps: S1. A cyclohexane solution of carboxyl-functionalized SSBR is prepared by grafting carboxyl functional groups onto SSBR using a mercapto-olefin click reaction, specifically including the following steps: Under nitrogen protection, a predetermined amount of SSBR (M) was added sequentially to the glass reaction flask. n =70,900 g / mol) and cyclohexane were stirred at 60°C for 6 h until SSBR was completely dissolved, yielding a homogeneous solution with a mass fraction of 10%. Subsequently, a quantitative amount of the mercapto compound 3-mercaptopropionic acid (MPA) was injected, with a molar ratio of MPA to SSBR of 0.15:1. The mixture was heated to 80°C and stirred for 10 min, and a pre-prepared solution of dodecyl peroxide (LPO) in cyclohexane was added. The reaction was continued at 80°C for 1 h with stirring to complete the mercapto-alkene click reaction. The molar ratio of LPO to the mercapto compound was 1:120.

[0047] S2. SSBR-g-MPA modified fly ash (SSBR@FA) was prepared using a planetary ball mill, specifically including the following steps: S2.1 First, add the cyclohexane solution of SSBR-g-MPA and fly ash to the ball mill jar. The mass ratio of SSBR to fly ash is 0.03:1. Then add an appropriate amount of cyclohexane to make the fly ash concentration 40%, that is, 40g of fly ash is dissolved in 60g of cyclohexane. S2.2 Grind the above mixture for 8 hours under alternating forward and reverse rotation conditions. The planetary ball mill has a revolution speed of 260 rpm and a rotation speed of 530 rpm. Use 30 zirconia balls with a diameter of 5 mm and 18 zirconia balls with a diameter of 10 mm. S2.3. Take an appropriate amount of the ball-milled material and extract it with cyclohexane as a solvent for 72 hours to remove ungrafted SSBR. Then dry it in a vacuum oven at 50°C to constant weight to obtain the modified fly ash sample SSBR@PFA, named 3PFA.

[0048] S3. The raw materials for the SBR / FA composite material are mixed on a two-roll mill: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; 3PFA variable 30 phr.

[0049] Example 5: Preparation of SBR / 1UFA15 composite material A method for preparing an SBR / FA composite material includes the following steps: S1. A cyclohexane solution of carboxyl-functionalized SSBR is prepared by grafting carboxyl functional groups onto SSBR using a mercapto-olefin click reaction, specifically including the following steps: Under nitrogen protection, a predetermined amount of SSBR (M) was added sequentially to the glass reaction flask. n =70,900 g / mol) and cyclohexane were mixed and stirred at 60°C for 6 h until SSBR was completely dissolved, yielding a homogeneous solution with a mass fraction of 10%. Subsequently, a quantitative amount of the thiol compound 11-mercaptoundecanoic acid (MUA) was injected, with a molar ratio of MUA to SSBR of 0.15:1. The mixture was heated to 80°C and stirred for 10 min, and a pre-prepared benzoyl peroxide (LPO) cyclohexane solution was added. The reaction was continued at 80°C for 1 h with stirring to complete the thiol-alkene click reaction. The molar ratio of LPO to the thiol compound was 1:120.

[0050] S2. SSBR-g-MUA modified fly ash (SSBR@FA) was prepared using a planetary ball mill, specifically including the following steps: S2.1 First, add the cyclohexane solution of SSBR-g-MPA and fly ash to the ball mill jar. The mass ratio of SSBR to fly ash is 0.01:1. Then add an appropriate amount of cyclohexane to make the fly ash concentration 40%, that is, 40g of fly ash is dissolved in 60g of cyclohexane. S2.2 Grind the above mixture for 8 hours under alternating forward and reverse rotation conditions. The planetary ball mill has a revolution speed of 260 rpm and a rotation speed of 530 rpm. Use 30 zirconia balls with a diameter of 5 mm and 18 zirconia balls with a diameter of 10 mm. S2.3. Take an appropriate amount of the ball-milled material and extract it with cyclohexane as a solvent for 72 hours to remove ungrafted SSBR. Then dry it in a vacuum oven at 50°C to constant weight to obtain modified fly ash sample SSBR@UFA, which is named 1UFA.

[0051] S3. The raw materials for the SBR / FA composite material are mixed on a two-roll mill: The formulation of the SBR / FA composite material is as follows: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; 1 UFA variable 15 phr.

[0052] Example 6 Preparation of SBR / 1UFA 30 composite material A method for preparing an SBR / FA composite material includes the following steps: S1. A cyclohexane solution of carboxyl-functionalized SSBR is prepared by grafting carboxyl functional groups onto SSBR using a mercapto-olefin click reaction, specifically including the following steps: Under nitrogen protection, a predetermined amount of SSBR (M) was added sequentially to the glass reaction flask. n =70,900 g / mol) and cyclohexane were stirred at 60°C for 6 h until SSBR was completely dissolved, yielding a homogeneous solution with a mass fraction of 10%. Subsequently, a quantitative amount of the thiol compound 11-mercaptoundecanoic acid (MUA) was injected, with a molar ratio of MUA to SSBR of 0.15:1. The mixture was heated to 80°C and stirred for 10 min, and a pre-prepared solution of dodecyl peroxide (LPO) in cyclohexane was added. The reaction was continued at 80°C for 1 h with stirring to complete the thiol-alkene click reaction. The molar ratio of LPO to the thiol compound was 1:120.

[0053] S2. SSBR-g-MUA modified fly ash (SSBR@FA) was prepared using a planetary ball mill, specifically including the following steps: S2.1 First, add the cyclohexane solution of SSBR-g-MPA and fly ash to the ball mill jar. The mass ratio of SSBR to fly ash is 0.01:1. Then add an appropriate amount of cyclohexane to make the fly ash concentration 40%, that is, 40g of fly ash is dissolved in 60g of cyclohexane. S2.2 Grind the above mixture for 8 hours under alternating forward and reverse rotation conditions. The planetary ball mill has a revolution speed of 260 rpm and a rotation speed of 530 rpm. Use 30 zirconia balls with a diameter of 5 mm and 18 zirconia balls with a diameter of 10 mm. S2.3. Take an appropriate amount of the ball-milled material and extract it with cyclohexane as a solvent for 72 hours to remove ungrafted SSBR. Then dry it in a vacuum oven at 50°C to constant weight to obtain the modified fly ash sample SSBR@UFA, named 1UFA.

[0054] S3. The raw materials for the SBR / FA composite material are mixed on a two-roll mill: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; 1 UFA variable 30 phr.

[0055] Example 7 Preparation of SBR / 3UFA15 composite material A method for preparing an SBR / FA composite material includes the following steps: S1. A cyclohexane solution of carboxyl-functionalized SSBR is prepared by grafting carboxyl functional groups onto SSBR using a mercapto-olefin click reaction, specifically including the following steps: Under nitrogen protection, a predetermined amount of SSBR (M) was added sequentially to the glass reaction flask. n =70,900 g / mol) and cyclohexane were stirred at 60°C for 6 h until SSBR was completely dissolved, yielding a homogeneous solution with a mass fraction of 10%. Subsequently, a quantitative amount of the thiol compound 11-mercaptoundecanoic acid (MUA) was injected, with a molar ratio of MUA to SSBR of 0.15:1. The mixture was heated to 80°C and stirred for 10 min, and a pre-prepared benzoyl peroxide (LPO) cyclohexane solution was added. The reaction was continued at 80°C for 1 h with stirring to complete the thiol-alkene click reaction. The molar ratio of LPO to the thiol compound was 1:120.

[0056] S2. SSBR-g-MUA modified fly ash (SSBR@FA) was prepared using a planetary ball mill, specifically including the following steps: S2.1 First, add the cyclohexane solution of SSBR-g-MUA and fly ash to the ball mill jar. The mass ratio of SSBR to fly ash is 0.03:1. Then add an appropriate amount of cyclohexane to make the fly ash concentration 40%, that is, 40g of fly ash is dissolved in 60g of cyclohexane. S2.2 Grind the above mixture for 8 hours under alternating forward and reverse rotation conditions. The planetary ball mill has a revolution speed of 260 rpm and a rotation speed of 530 rpm. Use 30 zirconia balls with a diameter of 5 mm and 18 zirconia balls with a diameter of 10 mm. S2.3. Take an appropriate amount of the ball-milled material and extract it with cyclohexane as a solvent for 72 hours to remove ungrafted SSBR. Then dry it in a vacuum oven at 50°C to constant weight to obtain the modified fly ash sample SSBR@UFA, named 3UFA.

[0057] S3. The raw materials for the SBR / FA composite material are mixed on a two-roll mill: The formulation of the SBR / FA composite material is as follows: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; 3UFA variable 15 phr.

[0058] Example 8 Preparation of SBR / 3UFA30 composite material A method for preparing an SBR / FA composite material includes the following steps: S1. A cyclohexane solution of carboxyl-functionalized SSBR is prepared by grafting carboxyl functional groups onto SSBR using a mercapto-olefin click reaction, specifically including the following steps: Under nitrogen protection, a predetermined amount of SSBR (M) was added sequentially to the glass reaction flask. n =70,900 g / mol) and cyclohexane were mixed and stirred at 60°C for 6 h until SSBR was completely dissolved, yielding a homogeneous solution with a mass fraction of 10%. Subsequently, a quantitative amount of the thiol compound 11-mercaptoundecanoic acid (MUA) was injected, with a molar ratio of MUA to SSBR of 0.15:1. The mixture was heated to 80°C and stirred for 10 min, and a pre-prepared benzoyl peroxide (LPO) cyclohexane solution was added. The reaction was continued at 80°C for 1 h with stirring to complete the thiol-alkene click reaction. The molar ratio of LPO to the thiol compound was 1:120.

[0059] S2. Modified fly ash (SSBR@FA) of SSBR-g-MUA was prepared using a planetary ball mill, specifically including the following steps: S2.1 First, add the cyclohexane solution of SSBR-g-MUA and fly ash to the ball mill jar. The mass ratio of SSBR to fly ash is 0.03:1. Then add an appropriate amount of cyclohexane to make the fly ash concentration 40%, that is, 40g of fly ash is dissolved in 60g of cyclohexane. S2.2 Grind the above mixture for 8 hours under alternating forward and reverse rotation conditions. The planetary ball mill has a revolution speed of 260 rpm and a rotation speed of 530 rpm. Use 30 zirconia balls with a diameter of 5 mm and 18 zirconia balls with a diameter of 10 mm. S2.3. Take an appropriate amount of the ball-milled material and extract it with cyclohexane as a solvent for 72 hours to remove ungrafted SSBR. Then dry it in a vacuum oven at 50°C to constant weight to obtain modified fly ash sample SSBR@UFA, which is named 3UFA.

[0060] S3. The raw materials for the SBR / FA composite material are mixed on a two-roll mill: The formulation of the SBR / FA composite material is as follows: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; 3UFA variable 30 phr.

[0061] Comparative Example 1: SBR vulcanizate The formula contains only SBR and other additives (no fly ash).

[0062] Specifically: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; Comparative Example 2: SBR / FA15 The formulation contains SBR, 15 parts unmodified fly ash, and other additives.

[0063] Specifically: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; Unmodified fly ash 15 phr.

[0064] Comparative Example 3: SBR / FA30 The formulation contains SBR, 30 parts of unmodified fly ash, and other additives.

[0065] Specifically: SBR1502: 100 phr; Zinc oxide (ZnO): 2.2 phr; Stearic acid (SA): 0.7 phr; N-cyclohexyl-2-benzothiazole sulfenamide (accelerator CBS): 1.1 phr; 2-mercaptobenzothiazole (accelerator MBT): 0.7 phr; Sulfur (S): 1.6 phr; Unmodified fly ash powder 30 phr.

[0066] Results and Discussion (1) Synthesis of functionalized SSBR (SSBR-g-MPA, SSBR-g-MUA) SSBRs with carboxyl functionalization in the chain were obtained by using LPO as an initiator and mercapto-alkene click chemistry under heating conditions. Figure 1 The unfunctionalized SSBR and functionalized SSBR are given. 1HNMR spectra. The mercapto-olefin click reaction mainly occurs between the 1,2-polybutadiene unit (1,2-PB) and the mercapto group. Calculations show that the mass fraction of 1,2-PB (relative to polybutadiene) in the unfunctionalized SSBR decreases from 47.9% to 44.9% in SSBR-g-MPA and 47.3% in SSBR-g-MUA. Furthermore, a new characteristic peak appears in the SSBR-g-MPA spectrum at 2.76–2.88 ppm, attributed to the methylene proton in -SCH2CH2COOH; while in SSBR-g-MUA, the new peak at 2.37–2.41 ppm originates from the methylene proton in -CH2COOH (see [reference needed]). Figure 1 ).

[0067] Based on the above results, it can be concluded that MPA and MUA have been successfully grafted onto the SSBR chain. Calculations show that the thiol grafting rates (ratio of grafted thiol mass to SSBR mass) for MPA and MUA are 6.3% and 4.7%, respectively. Correspondingly, each SSBR-g-MPA molecule contains approximately 42 MPA molecules, and each SSBR-g-MUA molecule contains approximately 16 MUA molecules.

[0068] To further verify the mercapto-olefin addition reaction between MPA or MUA and SSBR, Figure 2 FTIR spectra of unfunctionalized and functionalized SSBRs are presented. It can be clearly observed that in SSBR-g-MPA, the 1709 cm⁻¹... -1 And in SSBR-g-MUA 1698cm -1 The absorption peaks are attributed to the stretching vibrations of the carboxyl group in the acid dimer state of hydrogen bonding.

[0069] Because the alkyl chain of MUA is longer, the carboxyl groups are farther from the SSBR backbone, thus reducing the number of carboxyl groups embedded within the rubber matrix. This increases the probability of hydrogen bonding between carboxyl groups and exerts stronger constraint on them. Therefore, compared to SSBR-g-MPA, the vibrational absorption peak of the carboxyl groups in SSBR-g-MUA appears 11 cm⁻¹ due to the aforementioned structural differences. -1 The redshift.

[0070] (2) Grafting carboxyl-functionalized SSBR onto FA by ball milling Under heating conditions, carboxyl groups can chemically react with metal oxides on the surface of fly ash to form carboxyl-metal bonds. During the grinding process, planetary ball mills generate significant friction and impact forces. Compared to simple stirring and heating, planetary ball mills can provide higher energy input and faster chemical reaction rates, thereby achieving mechanochemical activation and completing the chemical reaction at lower temperatures. Therefore, realizing carboxyl-metal chemical reactions under ball milling conditions is theoretically feasible. Figure 3 The corresponding spectra of the SSBR@FA hybrid fillers are presented. After ball milling with fly ash, the stretching vibration peak of the carboxyl group in the hydrogen-bonded acid dimer state of SSBR-g-MPA and SSBR-g-MUA disappeared, indicating that the carboxyl group underwent a chemical reaction. Furthermore, compared with fly ash (FA), the characteristic peaks of Si-O-Si in 3PFA and 3UFA became sharper, and the characteristic peak of Si-O-Si in 3UFA showed a slight red shift (from 1105 cm⁻¹). -1 Moved to 1103cm -1 This can be attributed to the interaction between the Si-O-Si groups and carboxyl-metallic bond groups on the fly ash surface, which restricts the vibrational movement of Si-O-Si. Furthermore, at 2915 cm⁻¹... -1 The absorption peak at this location is attributed to the stretching vibration of the methylene group in SSBR. This characteristic peak can still be observed in the FTIR spectra of the extracted 3PFA and 3UFA samples. In summary, both SSBR-g-MPA and SSBR-g-MUA can be grafted onto the surface of fly ash under ball milling.

[0071] The significant polarity difference between rubber and filler leads to poor wettability, which not only hinders filler particle dispersion but also limits the improvement of the overall performance of the composite material. Static contact angle measurements were used to investigate the polarity change of fly ash before and after modification. Figure 4 As shown, water spreads rapidly on the surface of the original fly ash, with a water contact angle (WCA) of 38.3°, indicating significant hydrophilicity. After SSBR treatment, water forms spherical droplets on the modified fly ash surface, with a WCA consistently greater than 90°, demonstrating significant hydrophobicity and a marked change in surface properties. The surface energy of the fly ash was calculated using the Owens-Wendt equation by measuring the contact angles between fly ash and water and diiodomethane. The surface energy values ​​of FA, 1PFA, 3PFA, 1UFA, and 3UFA are shown below. Figure 5 As shown in the figure. The results indicate that the surface energy of the modified fly ash is significantly reduced; for example, the surface energy of 1UFA decreased by 35.9%. This reduction in surface energy helps improve the wettability between fly ash and rubber, thereby enhancing the interfacial interaction between the SSBR@FA hybrid filler and the SBR rubber matrix. To visually demonstrate the hydrophobicity of the modified fly ash, we immersed samples of raw fly ash, ball-milled fly ash (BFA), 3PFA, and 3UFA in cyclohexane (…). Figure 6Initially, all samples were well dispersed in cyclohexane and formed a turbid suspension; after ten minutes, the original fly ash and BFA gradually settled to the bottom of the container, the supernatant became transparent, while 3PFA and 3UFA remained partially dispersed, and the solution maintained a turbid appearance.

[0072] Figure 7 Thermogravimetric curves (TGA) of FA, modified FA, SSBR-g-MPA, and SSBR-g-MUA are presented. SSBR-g-MPA and SSBR-g-MUA mainly decompose in the range of 220-490℃. The TGA curve of FA shows three weight loss intervals (…). Figure 7 The first temperature range (40–210℃) corresponds to the evaporation of unbound water on the surface; the second temperature range (210–450℃) corresponds to the desorption of hydrated water accompanied by volatilization; and the final stage (450–780℃) corresponds to the decomposition of residual coal in FA. In the TGA curves of modified FA, significant weight loss occurs above 300℃, corresponding to the decomposition of functionalized SSBR. The resulting grafting rates of FA-based modified SSBR (ratio of grafted modified SSBR mass to unmodified FA mass) were: 0.2% (1PFA), 2.1% (3PFA), 0.7% (1UFA), and 2.4% (3UFA). Even after 72 hours of extraction, SSBR was not completely removed, confirming that SSBR is firmly adsorbed onto the FA surface through chemical bonds. The grafting rate increased with increasing amounts of carboxyl-functionalized SSBR, indicating that the solution mechanochemical method is beneficial for the in-situ carboxylate reaction between intrachain carboxyl-functionalized SSBR and FA. Furthermore, the grafting efficiency of FA-based SSBR-g-MUA is higher than that of SSBR-g-MPA.

[0073] The chemical composition obtained by EDS further confirmed the SSBR molecular chains grafted onto the fly ash surface. SEM and EDS spectra of 3PFA are shown below. Figure 8 As shown in (A), the SEM and EDS spectra of the original fly ash are as follows: Figure 9 As shown, the content of carbon (C), sulfur (S), and oxygen (O) increased compared to the original fly ash, indicating that the SSBR coating of fly ash changed its surface from hydrophilic to hydrophobic.

[0074] In addition, the specific surface area (SSA) of the original fly ash and SSBR@FA was determined using the BET method, and the results are shown in [Figure number missing]. Figure 8(B). Since ball milling can reduce the particle size and alter the morphology of fly ash, the surface area separation (SSA) of ball-milled fly ash (BFA) was also measured. After ball milling, the SSA of BFA increased from 3.38 m² / g to 5.21 m² / g, a 54.1% increase compared to the original fly ash. The SSA of the modified fly ash was lower than that of BFA because the grafted SSBR macromolecules hindered nitrogen from entering the pores of the fly ash. However, the SSA of PFA and UFA remained higher than that of the original fly ash, which facilitates the easier penetration of the rubber matrix into the pores of SSBR@FA, enhancing the interfacial interaction between the SSBR@FA hybrid filler and the rubber matrix.

[0075] Figure 10 TEM images of 1PFA and 3UFA are shown. In the TEM images, the dark areas represent fly ash (FA), and the light areas represent SSBR. This figure shows that SSBR is adsorbed on the FA surface, and the ball-milled FA exhibits a core-shell structure, thereby improving the wettability between FA and the rubber matrix.

[0076] (3) FA-reinforced SBR composite material Table 1. Mechanical properties of SBR (Comparative Example 1), SBR / FA (Comparative Examples 2 and 3) and SBR / SSBR@FA (Examples 1-6) vulcanizates.

[0077]

[0078] The mechanical properties of all vulcanizates are as follows: Figure 11 As shown in the figure, and summarized in Table 1, compared with pure vulcanized SBR, the addition of virgin fly ash to SBR increased the tensile strength from 1.69 MPa to 1.95 MPa, while decreasing the elongation at break from 345% to 284%. Further increasing the fly ash content to 30 phr resulted in a further decrease in both the tensile strength and elongation at break of the FA, indicating that virgin fly ash acts as a non-reinforcing filler in the rubber.

[0079] In contrast, compared to pure SBR vulcanizates, the tensile strength, tear strength, and elongation at break of SBR / SSBR@FA vulcanizates all increased simultaneously, indicating that the fly ash grafted onto the SSBR molecular chains not only acted as a reinforcing filler but also further improved the elastic properties of the rubber-based composite material in this system. For example, compared to SBR vulcanizates, the tensile strength, tear strength, and elongation at break of SBR / 3PFA-30 vulcanizates increased by 66.3%, 52.9%, and 17.7%, respectively. More interestingly, despite the addition of modified fly ash to the SBR matrix, the modulus at 100% strain remained almost unchanged, indicating that the decisive variable in the low-strain region is mainly dominated by the bond angle changes of the rubber molecular chains. Compared to pure SBR, the modulus of SBR / MFA increased in the 300% high-strain region, and this reinforcing effect became more significant with increasing MFA dosage, indicating that the grafted modified fly ash acted as a reinforcing filler.

[0080] Table 2. Payne effect in SBR / FA and SBR / SSBR@FA composites sample <![CDATA[∆G' (compounds) a (KPa)]]> <![CDATA[∆G' (vulcanizates) b (KPa)]]> SBR / FA-15 174.65 80.79 SBR / 1PFA-15 168.33 45.17 SBR / 3PFA-15 167.58 31.95 SBR / 1UFA-15 168.31 36.5 SBR / 3UFA-15 127.84 55.61 SBR / FA-30 280.31 159.32 SBR / 1PFA-30 211.15 87.78 SBR / 3PFA-30 204.51 89.87 SBR / 1UFA-30 178.94 46.4 SBR / 3UFA-30 182.49 62.94 Payne's research shows that the storage modulus (G') of composite materials decreases with increasing strain; this phenomenon is widely known as the Payne effect. A lower Payne effect indicates a weaker filler-filler network structure and better filler dispersion. The effect of ball milling grafting modification on the network structure and dispersion of FA fillers was investigated using the RPA (Rubber Processing Analyzer) testing method. The obtained G'-strain curves are shown below. Figure 12 and Figure 13 As shown, the corresponding data is listed in Table 2.

[0081] In this invention, the SBR / FA compound and vulcanizate exhibit the highest initial G' value and the most significant Payne effect, indicating a strong filler-filler network structure formed due to the weak SBR-FA interfacial interaction. After chemically grafting functionalized SSBR onto the FA surface, the initial G' value of the SBR / SSBR@FA composite material decreases, while the Payne effect weakens. For example, the initial G' values ​​of the SBR / 1UFA-30 compound and vulcanizate decreased by 28.4% and 39.4%, respectively.

[0082] like Figure 13 As shown, compared to SBR / FA, the G' value, indicating the onset of filler-filler structure disruption, is higher in SBR / SSBR@FA vulcanizates. This suggests a decrease in the strain dependence of the storage modulus, further demonstrating that the FA-FA filler network structure was disrupted after graft modification.

[0083] The dynamic mechanical properties of vulcanized rubber, such as Figure 14As shown in the figure, the G' value of the vulcanized rubber in the rubbery plateau region can be used to evaluate the filler-filler network structure. A higher storage modulus value in the rubbery plateau region indicates a stronger filler-filler network structure and poorer filler dispersibility. As shown in the figure, regardless of whether 15 phr or 30 phr of SSBR@FA is added, the storage modulus value of the SBR / SSBR@FA vulcanizate in the rubbery plateau region is lower than that of the corresponding SBR / FA. This indicates that ball-milled grafted FA reduces the filler-filler network structure and improves its dispersibility in the SBR matrix.

[0084] Figure 15 The results show that the cross-section of the SBR / FA composite material after liquid nitrogen brittle fracture exhibits a multi-layered structure with pits. These pits may be traces left by FA detachment under stress, indicating poor interfacial bonding between SBR and FA. Furthermore, FA agglomeration is clearly observed in the micrographs, which is detrimental to the improvement of the composite material's mechanical properties. Most FA particles are mainly dispersed on the surface of the SBR matrix, indicating minimal interfacial contact.

[0085] The SBR / SSBR@FA composite exhibits a reduced multilayer structure and fewer pits in its cross-section, resulting in a relatively smooth fracture surface—a morphology significantly different from its SBR / FA counterpart. Furthermore, the SSBR@FA particles are embedded within the SBR matrix, reducing interfacial color contrast. This enhanced compatibility stems from the combined effects of ball milling and SSBR modification: increasing the specific surface area of ​​FA and reducing its surface energy, thereby optimizing the interfacial contact area and wettability with the rubber matrix. This observation is consistent with the aforementioned BET specific surface area and surface energy results.

[0086] To gain a clearer understanding of the interfacial interaction between FA and rubber and the dispersion state of FA, the following is given: Figure 15 The magnified image of a local area shows that the original FA particles have smooth surfaces, most of which are exposed to the environment and show a clear color contrast with the rubber matrix. In contrast, the SSBR@FA has a rough surface morphology and a seamless interface with the rubber, with most particles encapsulated within the matrix. This encapsulation effectively delays the leaching of heavy metals from the FA.

[0087] It is generally believed that the mechanical properties of rubber composites depend not only on the morphology and structure of the filler and the adhesion between the rubber and filler surfaces, but also on chemical crosslinking and constraint. Both ball milling and grafting can affect these factors. First, the intense friction generated during milling roughens the FA surface, increasing its specific surface area and thus increasing the contact area between FA and the SBR matrix. Second, SSBR molecular chains grafted onto the FA surface via solution mechanochemical grafting form a rubber constraint layer around the FA particles. The grafted SSBR also acts as a bridge between SBR and FA, further enhancing the interfacial interaction between rubber and FA. Third, the micro-network structure formed by the physical entanglement between the grafted SSBR and the SBR matrix enhances constraint, thereby improving mechanical properties.

[0088] When SBR / FA composites are subjected to external forces, stress is transmitted along the rubber macromolecular chains to prevent stress concentration. Due to the increased contact area between SSBR@FA and the SBR matrix, interfacial interactions are enhanced, thereby reducing the probability of SSBR@FA particles debonding at the interface. This facilitates more efficient transmission of external forces through the interface and lengthens the propagation path of tear cracks. Therefore, SBR / MFA can withstand greater external forces and exhibits improved mechanical properties.

[0089] The thermal conductivity and flame retardant properties of SBR composites were investigated by measuring thermal conductivity and limiting oxygen index (LOI), and the relevant data are shown in Table 3. Compared with pure SBR, the thermal conductivity of SBR / 3PFA-15, SBR / 3PFA-30, SBR / 3UFA-15, and SBR / 3UFA-30 increased by 8.9%, 18.4%, 6.5%, and 16.7%, respectively, and the LOI values ​​increased by 8.6%, 11.1%, 10.1%, and 13.6%, respectively. This improvement is attributed to the ball milling grafting modification improving the dispersion of FA in the composite, thereby effectively utilizing the thermal conductivity and flame retardant effects of Al2O3 and SiO2 in FA. In addition, the increased specific surface area of ​​SSBR@FA promotes the distribution of CO2 generated during combustion in the pores of the FA surface, blocking oxygen and further improving the flame retardant properties.

[0090] Table 3. Thermal conductivity and limiting oxygen index of SBR and SBR / SSBR@FA composites sample SBR SBR / 3PFA-15 SBR / 3PFA-30 SBR / 3UFA-15 SBR / 3UFA-30 Thermal conductivity (W / mk) 0.2293 0.2497 0.2716 0.2443 0.2677 LOI(100%) 19.8 21.5 22.0 21.8 22.5 Conclusion: Mechanochemical activation achieved through ball milling promotes in-situ carboxylate reactions between the carboxyl functional groups on the SSBR chain and the metal oxides on the FA surface. FTIR results confirm that SSBR-g-MPA and SSBR-g-MUA have been successfully grafted onto FA, with maximum grafting rates of 2.1% and 2.4%, respectively. This effectively alleviates dust pollution caused by FA during use and helps reduce the leaching of heavy metals.

[0091] Under the combined effects of ball milling and grafting, the modified FA exhibits hydrophobicity, increased specific surface area, and decreased surface energy. Since SSBR-g-MPA / SSBR-g-MUA acts as both a dispersant and a rubber matrix, the wet properties of SSBR@FA and SBR are improved, a fact confirmed by SEM results.

[0092] With enhanced interfacial interactions and the rubber constraint layer formed around the FA particles, external forces can be transmitted more efficiently at the interface, thereby improving the mechanical strength of the SBR / MFA composite. Even with the addition of 30 phr of MFA, the mechanical properties are still significantly improved.

Claims

1. A method for modifying fly ash, characterized in that, Includes the following steps: S1. Carboxyl functional groups are grafted onto SSBR using a mercapto-alkene click reaction to prepare carboxyl-functionalized SSBR. Under nitrogen protection, SSBR was dissolved in cyclohexane and stirred until the SSBR was completely dissolved. Then, a mercapto compound was added, and the mixture was heated and stirred before adding a pre-prepared solution of dodecyl peroxide LPO cyclohexane. Stirring was continued to complete the mercapto-alkene click reaction. S2. Modified fly ash SSBR@FA was prepared by ball milling using a planetary ball mill. S2.

1. Add the cyclohexane solution of carboxyl-functionalized SSBR and fly ash sequentially into a ball mill jar, and then add cyclohexane; S2.2 Grind the above mixture using a planetary ball mill under alternating forward and reverse rotation conditions; S2.

3. Take the ball-milled material, extract it with cyclohexane as a solvent to remove ungrafted SSBR, and then dry it under vacuum to constant weight to obtain the modified fly ash sample SSBR@FA.

2. The modification method according to claim 1, characterized in that, In step S1, the thiol compound is 3-mercaptopropionic acid (MPA) or 11-mercaptoundecanoic acid (MUA); the molar ratio of the thiol compound to SSBR is (0.12-0.2):

1.

3. The modification method according to claim 1, characterized in that, In step S1, the molar ratio of LPO to the thiol compound is 1:(80-150).

4. The modification method according to claim 1, characterized in that, In step S2.1, the mass ratio of carboxyl-functionalized SSBR to fly ash is (0.01-0.03):

1.

5. The modification method according to claim 1, characterized in that, The ball milling process involves a revolution speed of 260 rpm, a rotation speed of 530 rpm, and a grinding time of 8 hours.

6. The modification method according to claim 1, characterized in that, In step S2.2, the grinding conditions are that the ball mill's revolution speed is 260 rpm and its rotation speed is 530 rpm, using 30 zirconia balls with a diameter of 5 mm and 18 zirconia balls with a diameter of 10 mm.

7. A modified fly ash prepared by the method according to any one of claims 1 to 6, characterized in that, The modified fly ash has a core-shell structure, with fly ash as the core and carboxyl-functionalized SSBR as the shell. Its surface has a water contact angle greater than 90°, making it hydrophobic.

8. An SBR / FA composite material comprising the modified fly ash of claim 7, characterized in that, It contains the following components by weight: SBR1502: 100 phr; SSBR@FA: 15-30 phr; Zinc oxide: 2.2 phr; Stearic acid: 0.7 phr; Accelerator CBS: 1.1 phr; Accelerator MBT: 0.7 phr; Sulfur: 1.6 phr; The above components are mixed on a two-roll mill to obtain the SBR / FA composite material.

9. The SBR / FA composite material according to claim 8, characterized in that, The composite material has a tensile strength of not less than 2.16 MPa, a tear strength of not less than 13.9 KN / m, an elongation at break of not less than 357%, a limiting oxygen index (LOI) of not less than 21.5%, and a thermal conductivity of not less than 0.2443 W / m·K.

10. The use of the SBR / FA composite material as described in claim 8 or 9 in the preparation of tires, conveyor belts, seals or flame-retardant rubber products.

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