GMA grafting modified pvdf / fkm thermoplastic vulcanizate

Abstract

This invention provides a GMA-grafted modified PVDF / FKM thermoplastic vulcanizate. When the BPO content is 0.3 g and the GMA content is 1.0 g, the equilibrium torque of the PVDF / FKM TPV is 1.52 times and 1.94 times that of pure PVDF, respectively. When the BPO content is 1.0 g, the tensile strength increases by 42.98% year-on-year, while the elongation at break is 108.24% of that of PVDF. At a torque rheometer speed of 120 r / min, the tensile strength of the TPV increases by 48.65%, and the elongation at break increases by 123.92%. DSC analysis results show that GMA contributes to improving the crystallinity of the PVDF / FKM TPV. TG analysis results show that at a speed of 150 r / min, the carbon residue of the PVDF / FKM TPV is 29.10%, which is approximately 94% higher than that of PVDF. When the BPO dosage is 1.0 g, the maximum carbon residue of PVDF / FKM TPV is 25.67%. With the increase of BPO dosage, the carbon residue generally shows an upward trend, and the thermal stability increases. GMA grafting modification significantly improves the performance of PVDF / FKM TPV, making it suitable for cable sheathing and gasket materials.

Description

Technical Field

[0001] This invention relates to the field of fluororubber technology, specifically to a GMA-grafted modified PVDF / FKM thermoplastic vulcanizate. Background Technology

[0002] Global greenhouse gas emissions from fossil fuel combustion have spurred increased demand for environmentally friendly materials. Fluororubber, with its excellent chemical resistance and low permeability, has gained widespread adoption in fuel pipe applications. Traditional vulcanized rubber, which is difficult to recycle, suffers from environmental problems due to its permanently cross-linked structure. Therefore, reusable thermoplastic vulcanized fluororubber is gradually becoming a key research focus.

[0003] Fluororubber (FKM) is a type of synthetic rubber containing fluorine substituents on the carbon atoms of its main or side chains. The unique role of fluorine atoms in the molecular structure endows the material with excellent comprehensive properties. Due to their extremely high electronegativity and strong oxidative stability, fluorine atoms give FKM excellent resistance to chemical degradation. The small size of fluorine atoms allows them to tightly encapsulate the carbon chain, creating a steric hindrance effect that significantly reduces the risk of C-C bond erosion. Simultaneously, the high bond energy of the C-F bonds further strengthens the chemical inertness of the molecular chain. These properties make FKM outstanding in terms of heat resistance, chemical resistance, weather resistance, sealing properties, and self-extinguishing characteristics; however, problems such as poor low-temperature elasticity, high processing difficulty, and high cost limit its application range.

[0004] Both FKM and polyvinylidene fluoride (PVDF) are fluorinated polar polymers, and the interaction of fluorine atoms between their molecular chains promotes their compatibility. Introducing PVDF into the FKM system can not only improve the processing fluidity of fluororubber, but also optimize costs by reducing the proportion of raw materials, while retaining the high chemical resistance and mechanical strength of the blend.

[0005] However, in practical applications, there are increasingly higher requirements for PVDF / FKM thermoplastic vulcanizates (PVDF / FKM TPV). Improving the compatibility, mechanical properties, processing technology, aging and chemical resistance of PVDF / FKM TPV to meet the performance requirements in PVDF / FKM TPV applications is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide a GMA-grafted modified PVDF / FKM thermoplastic vulcanizate.

[0007] The technical solution adopted in this invention is as follows: A GMA-grafted modified PVDF / FKM thermoplastic vulcanizate, the preparation method of which includes the following steps: S1. Set the temperature of the torque rheometer to 150-200℃, add PVDF, GMA and BPO, and process for 3-15 minutes to obtain PVDF-g-GMA. S2. Set the torque rheometer to 150-200℃, add PVDF-g-GMA, fluororubber, and GMA (glycidyl methacrylate) in a mass ratio of 50:(40-60):(1-3), and heat for 5-15 minutes. S3. After heating the sample in step S2, vulcanize it to obtain GMA grafted modified PVDF / FKM thermoplastic vulcanized elastomer.

[0008] Preferably, in step S2, the rotational speed of the torque rheometer is set to 60-100 r / min.

[0009] Preferably, in step S1, the rotational speed of the torque rheometer is set to 50-150 r / min.

[0010] Preferably, in step S1, the mass ratio of PVDF to BPO is 100:(0.3-1).

[0011] Preferably, in step S1, the mass ratio of PVDF to GMA is 100:(3-7).

[0012] Preferably, in step S2, the method for preparing the fluororubber includes the following steps: Raw rubber, magnesium oxide, calcium oxide, mica, TAIC, and Luperox 101-XL-45 in a mass ratio of 100:(2-4):(2-4):(18-22):(1-3):(0.3-0.7):(2-4) were added to an open mill in sequence and mixed evenly to obtain fluororubber.

[0013] Preferably, the roll gap of the open mill is set to 1-1.4 cm and the roll temperature is 40-60 ℃.

[0014] Preferably, in step S3, vulcanization includes the following steps: after the sample heated in step S2 is flattened, it is hot-pressed at 170-210 °C for 4-6 min, and then cold-pressed for 2-4 min.

[0015] The beneficial effects of this invention are as follows: This invention uses GMA grafting to modify PVDF / FKM thermoplastic vulcanizate and studies the effects of GMA dosage, BPO dosage, and rotational speed on the performance of PVDF / FKM TPV. The results show that when the BPO dosage is 0.3 g and the GMA dosage is 1.0 g, the equilibrium torque of PVDF / FKM TPV is 1.52 times and 1.94 times that of pure PVDF, respectively. When the BPO dosage is 1.0 g, the tensile strength increases by 42.98% year-on-year, while the elongation at break is 108.24% of that of PVDF. At a torque rheometer rotational speed of 120 r / min, the tensile strength of TPV increases by 48.65%, and the elongation at break increases by 123.92%. DSC analysis results show that the GMA dosage has a significant impact on the crystallinity of TPV; when the GMA dosage is 1.0 g, the maximum crystallinity can reach 46.72%. TG analysis results show that at a rotation speed of 150 r / min, the residual carbon content of PVDF / FKM TPV is 29.10%, which is approximately 94% higher than that of PVDF. When the BPO dosage is 1.0 g, the residual carbon content of PVDF / FKM TPV reaches a maximum of 25.67%. With increasing BPO dosage, the residual carbon content generally shows an upward trend, indicating improved thermal stability. GMA grafting modification significantly enhances the performance of PVDF / FKM TPV, making it suitable for cable sheathing and gasket materials. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0017] Figure 1 Torque curves for PVDF at different rotational speeds: (a) Torque curves for PVDF / FKM TPV blend; (b) Torque curves for PVDF / FKM TPV blend. Figure 2 Torque curves for PVDF with different BPO dosages: (a) Torque curves for PVDF / FKM TPV blends; Figure 3 Torque curves of PVDF / FKM TPV blends with different GMA dosages Figure 4 Tensile strength and elongation at break curves for PVDF / FKM TPV: (a) different amounts of BPO; (b) different amounts of GMA; (c) different rotational speeds; Figure 5Rockwell hardness curves for PVDF / FKM TPV: (a) different amounts of BPO; (b) different amounts of GMA; (c) different rotation speeds; Figure 6 Volume resistivity curves for PVDF / FKM TPV: (a) different amounts of BPO; (b) different amounts of GMA; (c) different rotational speeds; Figure 7 Melt index curves for PVDF / FKM TPV: (a) different amounts of BPO; (b) different amounts of GMA; (c) different rotation speeds; Figure 8 DSC of PVDF / FKM TPV with different BPO concentrations: (a) crystallization curve; (b) melting curve; Figure 9 DSC of PVDF / FKM TPV with different GMA dosages: (a) crystallization curve; (b) melting curve; Figure 10 DSC of PVDF / FKM TPV at different rotation speeds: (a) Crystallization curve; (b) Melting curve; Figure 11 Infrared spectra of PVDF at different rotation speeds; Figure 12 Infrared spectra of PVDF with different BPO concentrations; Figure 13 Thermogravimetric curves of PVDF / FKM TPV with different BPO dosages. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0019] Example 1 This embodiment provides a GMA-grafted modified PVDF / FKM thermoplastic vulcanizate and its preparation method, the specific steps of which are as follows: (1) Rubber mixing With a roll gap of 1.2 cm and a roll temperature of 50 ℃, raw rubber, magnesium oxide, calcium oxide, mica, TAIC, and Luperox 101-XL-45 in a mass ratio of 100:3:3:20:2:0.5:3 are added sequentially and mixed evenly to obtain fluororubber FKM.

[0020] (2) PVDF grafting modification Start the torque rheometer, set the temperature to 175℃ and the rotation speed to 50 r / min, add 100g of PVDF, 5g of GMA and 0.3g of BPO, and process for 15 min to prepare PVDF-g-GMA, thus obtaining PVDF-R1.

[0021] (3) Dynamic vulcanization Set the torque rheometer speed to 80 r / min and the temperature to 175℃. Add 50g of preheated fluororubber and 1g of GMA, and process for 9 min. After completion, remove the sample.

[0022] (4) Hot pressing sample The above sample was flattened on an open mill at 160 ℃, then placed in a mold, and hot-pressed on a flat vulcanizing machine at 190 ℃ for 5 min, followed by cold pressing for 3 min. The product was then removed and recorded as TPV-R1.

[0023] Example 2 The only difference between this embodiment and embodiment 1 is that in step (2), the rotation speed is set to 80 r / min to obtain PVDF-R2, and the final product is denoted as TPV-R2.

[0024] Example 3 The only difference between this embodiment and embodiment 1 is that in step (2), the rotation speed is set to 100 r / min to obtain PVDF-R3, and the final product is denoted as TPV-R3.

[0025] Example 4 The only difference between this embodiment and embodiment 1 is that in step (2), the rotation speed is set to 120 r / min to obtain PVDF-R4, and the final product is denoted as TPV-R4.

[0026] Example 5 The only difference between this embodiment and embodiment 1 is that in step (2), the rotation speed is set to 150 r / min to obtain PVDF-R5, and the final product is denoted as TPV-R5.

[0027] Example 6 The only difference between this embodiment and embodiment 2 is that in step (2), the mass of BPO added is 0.5g, and PVDF-B1 is obtained. The final product is denoted as TPV-B1.

[0028] Example 7 The only difference between this embodiment and embodiment 2 is that in step (2), the mass of BPO added is 0.8g, and PVDF-B2 is obtained. The final product is denoted as TPV-B2.

[0029] Example 8 The only difference between this embodiment and embodiment 2 is that in step (2), the mass of BPO added is 1.0g, and PVDF-B3 is obtained. The final product is denoted as TPV-B3.

[0030] Comparative Example 1 The only difference between this embodiment and embodiment 1 is that in step (2), GMA and BPO are not added to obtain PVDF0, and the final product is denoted as TPV-G1.

[0031] Comparative Example 2 The only difference between this embodiment and embodiment 9 is that in step (3), the mass of GMA added is 1.5g, and the final product is denoted as TPV-G2.

[0032] Comparative Example 3 The only difference between this embodiment and embodiment 9 is that in step (3), the mass of GMA added is 2.0g, and the final product is denoted as TPV-G3.

[0033] Comparative Example 4 The only difference between this embodiment and embodiment 9 is that in step (3), the mass of GMA added is 3.0g, and the final product is denoted as TPV-G4.

[0034] Table 1 Formulation and preparation process of PVDF / FKM TPV I. Torque-Time Curve Analysis 1. Torque analysis of PVDF / FKM TPV at different speeds Figure 1 The curve shows the torque versus time during the PVDF / FKM TPV blending process. Figure 1 (a) shows the torque curve within the PVDF. Figure 1 (b) shows the torque curve of the PVDF / FKM TPV. From... Figure 1 In (a), the torque gradually increases during the initial preheating and mixing stages; BPO decomposes at high temperature, generating free radicals that initiate the GMA grafting reaction. The torque stabilizes around 6 minutes, indicating that the grafting reaction is complete and the system has reached dynamic equilibrium.

[0035] from Figure 1(b) PVDF preheating stage (0-6 minutes): Torque gradually increases to a stable value, reflecting the homogenization process of PVDF melt. FKM addition and blending stage (6 minutes): Torque briefly increases, then tends to equilibrium around 7-10 minutes. The secondary addition of 1 g GMA may optimize the interfacial bonding between PVDF and FKM. The first peak appears before 2 minutes. Figure 1 (a) is the case where a peak appears during the PVDF melting process; the second peak appears when the PVDF melting grafting reaction tends to equilibrium, and rises sharply after being added, and then decreases over time and gradually tends to equilibrium.

[0036] In a pure PVDF system, from 0 to 6 minutes, the torque increases with increasing rotational speed, consistent with shear thinning characteristics. This is because at high rotational speeds, the shear rate increases, and the melt viscosity decreases due to shear thinning, but the torque still increases overall due to the increased shear rate. After 6 minutes, the torque tends to stabilize, and the equilibrium torque is higher at high rotational speeds. This is because pure PVDF has no cross-linked network, and the equilibrium torque is entirely determined by the melt viscosity. At high rotational speeds, the viscous resistance of the shear rate plays a dominant role.

[0037] In the blend system, from 0 to 6 minutes, the torque increases with increasing rotational speed, but the increase is less than that in the pure PVDF system. This is because the elastic behavior of FKM partially offsets the viscous resistance, resulting in a slower torque increase. After 7 minutes: the torque rises sharply, and the increase is positively correlated with the rotational speed. This is because high rotational speed accelerates crosslinking kinetics, increases free radical concentration, and increases crosslinking density. Shear-induced network reinforcement: the crosslinked FKM molecular chains align under high shear, enhancing elastic resistance.

[0038] The effect of rotational speed on the torque of the pure PVDF system conforms to pseudoplastic fluid behavior, with viscous dissipation dominating and no crosslinking contribution. The effect of rotational speed on the blend system is significantly stronger than that on the pure PVDF system, with the elastic response of the crosslinked network dominating the torque surge at high rotational speeds. (Comparison) Figure 1 Figures (a) and (b) show that the final equilibrium torque of the system with the rubber phase as the main component is significantly higher than that of the system with the plastic phase as the main component. This is because the cross-linked FKM particles have a certain hindering effect on the rotor, which macroscopically manifests as an increase in torque.

[0039] 2. Torque analysis of PVDF / FKM TPV with different BPO dosages Figure 2 The curve shows the torque variation over time during the PVDF / FKM TPV blending process. Figure 2 (a) shows the torque curve of the PVDF. Figure 2 (b) is the torque curve after PVDF is preheated for 6 minutes and then blended with rubber phase FKM for 9 minutes.

[0040] In a pure PVDF system, the torque generally increases with increasing BPO content. This is because BPO, as a crosslinking agent, decomposes at high temperatures to generate free radicals, promoting the crosslinking of PVDF molecular chains. Increased crosslinking degree leads to increased melt viscosity, resulting in higher torque; however, excessive BPO may cause localized over-crosslinking, slowing down or even decreasing the torque increase rate.

[0041] Figure 2 (b) In the blended system, the torque first increases and then decreases as the amount of BPO increases. An appropriate amount of BPO can optimize the crosslinking network of TPV; however, excessive BPO may lead to excessively high crosslinking density, making the material brittle or causing defects, which in turn reduces performance.

[0042] 3. Torque analysis of PVDF / FKM TPV with different GMA dosages like Figure 3 In the first 4-10 minutes, the torque of the three groups gradually reached a plateau, indicating that the cross-linked network was approaching dynamic equilibrium. In the later stage, TPV-G4 showed a slight decrease in torque, triggering side reactions. In the final equilibrium torque, the final equilibrium torque showed a decreasing trend with increasing GMA dosage. High concentrations of GMA, due to excessive densification of the cross-linked network, limited the relaxation ability of molecular chains, resulting in a slower or decreased torque growth rate. Increasing the GMA dosage shortened the induction period of the cross-linking reaction, but excessive dosage may cause chain termination reactions due to excessively high free radical concentrations, reducing cross-linking efficiency.

[0043] II. Performance Testing 1. Tensile properties like Figure 4 As shown in (a), the tensile strength initially increases and then decreases with increasing BPO dosage, reaching its peak at TPV-B1 and TPV-B2. This is because an appropriate amount of BPO (0.5 g-0.8 g) initiates cross-linking via free radicals, forming a uniform network and enhancing the material's load-bearing capacity; excessive BPO leads to excessively high cross-linking density, causing localized stress concentration or microcracks, resulting in decreased strength. The elongation at break decreases significantly with increasing BPO dosage, as seen in TPV-B3 where it decreases by approximately 30%. This is because high cross-linking density restricts the slippage ability of molecular chains, reducing material toughness and resulting in brittle fracture.

[0044] like Figure 4 As shown in (b), the overall tensile strength decreased. This is because the increased GMA dosage may have led to improved molecular chain flexibility, incomplete cross-linking network formation, and insufficient interface bonding optimization, resulting in a decrease in load-bearing capacity. The elongation at break increased significantly in TPV-G1, but subsequently showed a decreasing trend. Excessive GMA resulted in excessively high cross-linking density, restricting molecular chain movement; the elongation at break dropped sharply: excessive cross-linking limited the chain segment slippage ability, and the material lost its toughness.

[0045] like Figure 4 As shown in (c), the tensile strength initially increases and then slightly decreases with increasing rotational speed. A moderate rotational speed of 100-120 r / min promotes filler dispersion and interfacial bonding; excessively high rotational speeds (150 r / min) induce shear thermal degradation or phase separation. The elongation at break decreases continuously with increasing rotational speed, decreasing by approximately 35% for TPV-R5 compared to TPV-R1. This is because high shear forces disrupt molecular chain orientation, while thermal degradation leads to chain length shortening and decreased toughness.

[0046] 2. Rockwell hardness As above Figure 5 As shown in (a), the hardness of TPV-R2 was significantly higher than that of the other groups. When the BPO dosage increased, the hardness first decreased and then increased, possibly because the low dosage resulted in insufficient crosslinking, while the high dosage of TPV-B3 partially restored the crosslinking density. This is because an excessively low dosage of TPV-R2 may lead to excessive local crosslinking, resulting in uneven distribution of free radicals and the formation of hard areas; the crosslinking density of TPV-B1 was insufficient, causing the material to soften; and the crosslinking network was strengthened again in TPV-B3, but the uniformity was still poor.

[0047] like Figure 5 As shown in (b), TPV-G4 exhibits the best Rockwell hardness, reaching a critical crosslinking density that forms a denser and more uniform network structure. Excessive GMA leads to excessive molecular chain entanglement, resulting in excessively high local crosslinking density, causing internal stress concentration or microcracks; decreased interfacial compatibility, uneven filler dispersion, and the formation of weak interfacial regions.

[0048] like Figure 5 As shown in (c), TPV-R2 exhibits the highest hardness. At other rotational speeds, the hardness does not show a clear trend with increasing rotational speed, suggesting that shear heat and dispersion efficiency compete with each other. A moderate rotational speed of 80 r / min may optimize the balance between shear force and heat, promoting uniform cross-linking. However, at high rotational speeds (>100 r / min), thermal degradation is triggered, offsetting the dispersion advantage and leading to fluctuations in TPV hardness.

[0049] 3. Volume resistivity like Figure 6 As shown in (a), with increasing BPO dosage, the volume resistivity first decreases and then increases, reaching its peak at TPV-B3. The abnormally low value of TPV-B1 may be due to insufficient crosslinking density, resulting in a large free volume of molecular chains and increased charge mobility; the high resistivity of TPV-B3 indicates that the densification of the crosslinking network significantly inhibits charge migration. Increasing BPO dosage improves the crosslinking density and reduces the free volume inside the material, but a critical degree of crosslinking is required to significantly improve insulation performance.

[0050] like Figure 6As shown in (b), the improvement in the insulation performance of the material is achieved by an appropriate amount of GMA. The sharp increase in the volume resistivity of TPV-G4 is due to the deterioration of the material structure caused by excessive GMA. The excessive densification of the cross-linked network may be caused by excessive GMA, the degree of restriction on molecular chain movement is significantly enhanced, and the formation of microcracks is related to local stress concentration.

[0051] like Figure 6 As shown in (c), the volume resistivity decreases significantly with increasing rotational speed, and TPV-R1 has the best volume resistivity among the samples. This is because the non-uniformity of the filler dispersion is more pronounced under low rotational speed conditions, confirming the formation of more insulating regions. Although a uniform dispersion state is achieved at high rotational speeds, the introduction of defects cannot be ignored, thus reflecting a decrease in insulation performance.

[0052] III. Melt Index Analysis like Figure 7 As shown in (a), the MFR value generally increases with the increase of BPO dosage, indicating that the molecular chain entanglement is reduced in the early stage of crosslinking or that mild crosslinking does not significantly hinder flow. TPV-B3 has the highest MFR because the crosslinking reaction initiated by BPO has not yet formed a dense network at low dosage, and the molecular chain slippage ability is enhanced; at high dosage, thermal degradation or by-product plasticizing effect may accompany it, which offsets the negative impact of crosslinking on flowability.

[0053] The MFR peaked at TPV-G2 and then dropped significantly, indicating that excessive GMA led to an increase in molecular crosslinking density. The MFR dropped sharply in TPV-G3 and TPV-G4 because appropriate amounts of GMA improved dispersibility and reduced entanglement through grafting reactions; when GMA was in excess, it formed a rigid network or increased the interaction of polar groups, restricting molecular chain movement.

[0054] MFR initially decreases and then increases with increasing rotational speed, reaching its lowest point at TPV-R3 and rebounding at TPV-R4. The rebound in MFR at high rotational speeds may be due to molecular chain breakage and thermal degradation caused by shear heat, resulting in partial recovery of fluidity. At medium rotational speeds, shear forces promote cross-linking or molecular chain orientation, reducing fluidity; at high rotational speeds, shear heat leads to chain breakage, reducing molecular weight and improving fluidity. The combined effect of these factors results in the aforementioned changes in MFR values.

[0055] IV. Differential Scanning Calorimetry (DSC) Analysis 1. DSC image analysis of different BPO dosages The formula for calculating crystallinity in the table is: Crystallinity Xc = 100% ΔH PVDF / ΔH lit In the formula, ΔH PVDF This corresponds to the heat of fusion of the sample measured by PVDF. The corresponding enthalpy of fusion in the table is ΔH. TPVThe conversion relationship between the two is: ΔH PVDF= ΔH TPV (100+m) GMA ) / 50, ΔH lit The heat of fusion for PVDF with a crystal structure of 100% purity is 104.7 J / g. The following two sets of calculations using BPO and rotation speed data were obtained using the same formula. The melting temperature decreases by approximately 1.44 ℃ with increasing BPO dosage. This is because BPO acts as a crosslinking agent; its increased dosage restricts the complete melting of the molecular chains through the crosslinking network, resulting in a slight decrease in the energy required for melting.

[0056] Table 2. TPV DSC data for different BPO dosages The crystallization temperature remained stable at 142.34 ℃–142.62 ℃, while the Tc of TPV-B3 decreased significantly to 140.81 ℃. This is because excessive BPO caused excessive cross-linking, which increased the rigidity of the molecular chain, inhibited crystal nucleation and growth, and led to a decrease in the crystallization initiation temperature.

[0057] We can see from Table 2, Figure 8 The data shows that, overall, the enthalpy of fusion and crystallinity both initially increase and then decrease with increasing BPO dosage, indicating that excessive BPO dosage leads to a decrease in crystallinity. TPV-B1 exhibits the highest crystallinity; appropriate surface cross-linking optimizes molecular chain arrangement and promotes the formation of crystalline regions. TPV-R2 may have insufficient cross-linking density, resulting in higher molecular chain disorder. Excessive cross-linking in TPV-B3 restricts chain segment movement, reducing crystallization ability.

[0058] 2. DSC image analysis of different GMA dosages The melting temperature fluctuated little from TPV-G1 to TPV-G4, ranging from 163.99 ℃ to 164.76 ℃, indicating that the amount of GMA had no significant effect on the melting temperature. The crystallization temperature stabilized at 142.5 ℃ to 142.9 ℃ from TPV-G1 to TPV-G3. from Figure 9 As shown in Table 3, the overall melting enthalpy first increased and then decreased, while the crystallinity first decreased and then rebounded overall. This indicates that an appropriate amount of GMA may improve some crystallization ability through interface optimization; excessive GMA leads to excessively high crosslinking density or decreased molecular chain flexibility, inhibiting the orderly arrangement of chain segments.

[0059] Table 3. TPV DSC data for different GMA dosages 3. DSC image analysis at different rotation speeds The melting temperature fluctuates within a relatively small range of 163.42 ℃–164.52 ℃, indicating that the rotation speed has little effect on the melting temperature and the thermal stability of the main chain is not significantly affected. The crystallization temperature, as shown in the table, does not fluctuate much. However, for TPV-R4, the relatively low crystallization temperature is due to shear heat causing localized temperature increases, which slows down the crystallization process.

[0060] from Figure 10 Based on the crystallinity data in Table 4, the overall trend shows that crystallinity generally increases with increasing rotational speed. TPV-R5 has the highest crystallinity and melting enthalpy, indicating the best molecular chain order at high rotational speeds; high rotational speeds are beneficial for improving crystallization ability.

[0061] Table 4. TPV DSC data for different rotation speeds V. Infrared Spectroscopy Analysis 1. Infrared analysis of PVDF at different rotation speeds Figure 11 The image shows the PVDF infrared spectra of the rotational speed groups. From the image, we can see that all six samples are within the range of 3029.5 cm⁻¹. -1 1175.2 cm -1 1066.5 cm -1 973.2 cm -1 872.0 cm -1 481.6 cm -1 A relative infrared characteristic peak appeared; among them, 3029.5 cm⁻¹. -1 It is located at the inverse stretching vibration peak of -CH-; at 872.0 cm⁻¹ -1 1175.2 cm -1 It is located at the -CF2- stretching vibration peak; at 1066.5 cm⁻¹ -1 973.2 cm -1 It is located at the -CH2- stretching vibration peak. In contrast to pure PVDF, the five groups treated with the PVDF torque rheometer all reached 1736.2 cm⁻¹. -1 The characteristic absorption peak of -C=O appears. The appearance of this absorption peak can preliminarily conclude that after adding equal amounts of GMA and BPO to the torque rheometer, PVDF has undergone a grafting reaction to produce PVDF-g-GMA. The position of the wavenumber of this peak will change slightly due to different rotational speeds, but the change is not significant.

[0062] 2. Infrared analysis of PVDF with different BPO dosages Figure 12 The image shows the PVDF infrared spectra of the BPO variable group. From the image, we can see that all six samples are within the range of 1181.3 cm⁻¹. -11071.4 cm -1 978.6 cm -1 874.3 cm -1 487.3 cm -1 A relative infrared characteristic peak appeared; among which, 3023.2 cm⁻¹... -1 It is at the -CH- inverse stretching vibration peak. Unlike the speed group, in the two groups after processing with the PVDF torque rheometer, only the second group with a BPO dosage of 0.3g shows a peak at 1738.4 cm⁻¹. -1 The characteristic absorption peak of -C=O appeared. Such a peak did not appear in pure PVDF. When the amount of BPO was increased to 0.5 g, only a small and relatively long fluctuation was found, but there was no obvious and clear characteristic absorption peak.

[0063] VI. Thermogravimetric Analysis 1. Thermogravimetric analysis of PVDF / FKM TPV at different rotation speeds As shown in Table 5, the overall temperature trend when the sample weight loss rate is 5% is decreasing, while the temperature range from 5% weight loss rate to 10% weight loss rate first increases and then decreases. However, the TPV-R5 has the highest temperature at 5% weight loss rate due to its excessive rotation speed, but the temperature range for each 5% decrease in weight loss rate is relatively small.

[0064] The residual carbon rate was lowest among the five groups when the rotation speed was 80 r / min, and highest when the rotation speed was 150 r / min. The overall trend was not very obvious, but the residual carbon rate was generally high, indicating that the prepared PVDF / FKM TPV material has good high temperature resistance. Compared with the original PVDF residual carbon rate of 15%, it is improved by about 94%, and the thermal stability of PVDF / FKM TPV has been greatly improved.

[0065] Table 5. Thermogravimetric parameters of TPV at different rotation speeds. 2. Thermogravimetric analysis of PVDF / FKM TPV with different BPO dosages from Figure 13 As shown in Table 6, the 5% weight loss temperature of TPV-R1 first increases and then decreases with the increase of BPO, with TPV-B1 showing the highest value. This indicates that there is an optimal range for the initial decomposition temperature of PVDF / FKM TPV based on the amount of BPO. With the increase of BPO, both the 50% weight loss temperature and the residual carbon rate increase, indicating that the use of BPO may increase the crosslinking degree of PVDF / FKM TPV and ultimately improve its thermal stability.

[0066] Table 6. TPV thermogravimetric parameters for different BPOs In summary, this invention successfully prepared PVDF / FKM TPV using dynamic GMA grafting modification technology with a rubber-to-plastic ratio of 50:50. The changes in performance indicators under various modification conditions were further investigated, and the specific conclusions are as follows: The interfacial bonding performance of PVDF / FKM TPV grafted with GMA was significantly enhanced. Under variations in rotational speed and the amount of BPO initiator, the matching degree between shear force and crosslinking reaction kinetics was achieved. The data show that an optimal BPO dosage of 0.3 g yielded the best balance torque, which was 1.52 times that of pure PVDF; an optimal GMA dosage of 1.0 g yielded the best balance torque, which was 1.94 times that of pure PVDF, demonstrating good grafting modification results.

[0067] The mechanical property curves show an overall positive correlation and upward trend. With the combined effect of appropriate amounts of initiator BPO in the TPV-R2 group and the optimal grafting agent ratio in the TPV-G1 group, as the amount of BPO increases, the tensile strength of BPO increases by 42.98% year-on-year, and the elongation at break is also 1.08 times higher than before. At the optimal rotational speed of 120 r / min, the tensile strength of TPV-R4 is increased by 48.65% compared to TPV-R1, and the elongation at break is increased by 123.92%.

[0068] DSC analysis showed that the melting temperature range of PVDF / FKM TPV material was stable in the range of 163-164 ℃. Appropriate amounts of BPO and rotation speed helped to increase the crystallinity of TPV, and increasing the amount of GMA also helped to increase the crystallinity of TPV.

[0069] Thermogravimetric analysis revealed that the TPV residual carbon rate was highest at a rotation speed of 150 r / min, reaching 29.10%; the highest TPV residual carbon rate was 25.67% when the BPO dosage was 1.0 g. Overall, the residual carbon rate and thermal stability increased with the increase of BPO dosage.

[0070] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A GMA-grafted modified PVDF / FKM thermoplastic vulcanizate, characterized in that, Its preparation method includes the following steps: S1. Set the temperature of the torque rheometer to 150-200℃, add PVDF, GMA and BPO, and process for 3-15 minutes to obtain PVDF-g-GMA. S2. Set the torque rheometer to 150-200℃, add PVDF-g-GMA, fluororubber and GMA in a mass ratio of 50:(40-60):(1-3), and then dynamically vulcanize for 5-15 minutes. S3. After heating the sample in step S2, hot press it to obtain GMA grafted modified PVDF / FKM thermoplastic vulcanizate.

2. The GMA-grafted modified PVDF / FKM thermoplastic vulcanizate according to claim 1, characterized in that: In step S2, the rotational speed of the torque rheometer is set to 60-100 r / min.

3. The GMA-grafted modified PVDF / FKM thermoplastic vulcanizate according to claim 1, characterized in that: In step S1, the rotational speed of the torque rheometer is set to 50-150 r / min.

4. The GMA-grafted modified PVDF / FKM thermoplastic vulcanizate according to claim 1, characterized in that: In step S1, the mass ratio of PVDF to BPO is 100:(0.3-1).

5. The GMA-grafted modified PVDF / FKM thermoplastic vulcanizate according to claim 1, characterized in that: In step S1, the mass ratio of PVDF to GMA is 100:(3-7).

6. The GMA-grafted modified PVDF / FKM thermoplastic vulcanizate according to claim 1, characterized in that, In step S2, the preparation method of the fluororubber includes the following steps: Raw rubber, magnesium oxide, calcium oxide, mica, TAIC, and Luperox 101-XL-45 in a mass ratio of 100:(2-4):(2-4):(18-22):(1-3):(0.3-0.7):(2-4) were added to an open mill in sequence and mixed evenly to obtain fluororubber.

7. The GMA-grafted modified PVDF / FKM thermoplastic vulcanizate according to claim 6, characterized in that: Set the roll gap of the open mill to 1-1.4 cm and the roll temperature to 40-60 ℃.

8. A GMA-grafted modified PVDF / FKM thermoplastic vulcanizate according to any one of claims 1-7, characterized in that: In step S3, vulcanization includes the following steps: after the sample heated in step S2 is flattened, it is hot-pressed at 170-210 ℃ for 4-6 min, and then cold-pressed for 2-4 min.

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