Ultraviolet radiation grafting modified hollow glass bead and modified fluororubber

Abstract

According to the ultraviolet radiation grafting modified hollow glass bead and the modified fluororubber, TPO is adopted as a light main initiator for ultraviolet radiation of the hollow glass bead, benzophenone is adopted as a light synergistic initiator for ultraviolet radiation of the glass bead, and rapid and stable grafting of PFDTES is achieved; the prepared ultraviolet radiation graft modified hollow glass beads are used as a filler to be applied to preparation of fluororubber, and the ratio of TPO to benzophenone and the ultraviolet radiation time are optimized, so that the mechanical property and the thermal property of the fluororubber are optimized to the maximum extent.

Description

Technical Field

[0001] This invention relates to the field of fluororubber technology, specifically to a UV-irradiated grafted modified hollow glass microsphere and modified fluororubber. Background Technology

[0002] Fluororubber is widely used in the automotive and aerospace industries due to its excellent solvent resistance and temperature resistance. However, these industries are placing increasingly higher demands on thermal insulation, sound insulation, and cushioning capabilities, requiring improvements in the relevant properties of fluororubber to meet these evolving application requirements.

[0003] Currently, the modification of fluororubber, besides using reinforcement methods such as carbon nanotubes, graphene, and nano-silica, also employs foaming methods. These methods utilize foaming agents and polymeric expanded microspheres to achieve foam modification of fluororubber, reducing its density, lowering its thermal conductivity, and improving its thermal insulation performance, while also enhancing its sound insulation properties. However, while achieving these performance improvements, the mechanical properties of fluororubber, such as tensile strength and elongation at break, will decrease significantly. This results in increased permanent compression set and other adverse effects, negatively impacting the performance of sealing components and limiting its application.

[0004] Hollow glass microspheres (HGM) have a low density, ranging from 0.1 to 0.7 g / cm³. 3 Hollow glass microspheres (HGM) have a low thermal conductivity (0.04-0.11 W / (m·K), are mainly composed of borosilicates, and are resistant to acid and alkali corrosion and possess high compressive strength. While there are reports on the application of HGM in materials such as natural rubber, its application in fluororubber is less common. Although HGM can effectively reduce the density and conductivity of FKM composites and improve their thermal stability, the lack of chemical bonds between HGM and FKM, the differences in their molecular structure and functional groups, and the aggregation of HGM itself reduce the tensile strength and elongation at break of the FKM composite, leading to a decline in mechanical properties. Furthermore, the dispersibility of HGM in the fluororubber composite matrix is ​​generally poor; with increasing concentration, aggregation and breakage of HGM in the FKM composite matrix become more severe. Conventional methods using coupling agents to treat HGM require treatment for 2 hours or longer, plus subsequent drying processes, resulting in a time-consuming and inefficient process.

[0005] By using ultraviolet irradiation to modify hollow glass microspheres, it is possible to quickly graft fluorosilane coupling agent PFDTES onto the surface of the hollow glass microspheres in a short time, while maintaining the structural stability of the glass microspheres themselves. This maximizes the advantages of ultraviolet irradiation modification. When the modified hollow glass microspheres are used to modify fluororubber, the mechanical and thermal properties of fluororubber can be optimized to the maximum extent. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide ultraviolet irradiation grafted modified hollow glass microspheres and modified fluororubber.

[0007] The technical solution adopted by this invention is as follows: The first aspect of this invention provides ultraviolet irradiation grafted modified hollow glass microspheres, the preparation method of which includes the following steps: S1. Prepare a solution by mixing anhydrous ethanol and deionized water, and adjust the pH of the solution to 3-5 using glacial acetic acid; S2. Add the fluorosilane coupling agent PFDTES (1H,1H,2H,2H-perfluorodecyltriethoxysilane) to the solution, and then add the photoinitiator TPO (2,4,6-trimethylbenzoyl-diphenylphosphine oxide) and benzophenone in sequence. S3. After mixing the solution with hollow glass microspheres, transfer the mixture to a petri dish for ultraviolet irradiation to obtain ultraviolet irradiated grafted modified hollow glass microspheres.

[0008] Preferably, in step S2, the mass ratio of the fluorosilane coupling agent to the hollow glass microspheres is 3-7%.

[0009] Preferably, in step S2, the ratio of the photoinitiator TPO to benzophenone is (1-4):1.

[0010] Preferably, in step S2, the proportion of benzophenone in the solution is 0.5-1%.

[0011] Preferably, in step S3, the ratio of the hollow glass microspheres to benzophenone is (5-20):1.

[0012] Preferably, in step S3, the ultraviolet irradiation time is 3-30 minutes and the ultraviolet irradiation power is 700-1000 W.

[0013] Preferably, in step S3, the temperature of ultraviolet irradiation is 25-35℃.

[0014] A second aspect of the present invention provides a modified fluororubber, which is obtained by compounding the above-mentioned ultraviolet-irradiated grafted modified hollow glass microspheres in fluororubber as a filler.

[0015] Preferably, the ratio of the ultraviolet-irradiated grafted modified hollow glass microspheres to fluororubber is (2-4):100.

[0016] Preferably, the preparation method includes the following steps: Fluororubber, magnesium oxide, and calcium oxide are mixed at 60-100℃, and then UV-irradiated grafted modified hollow glass microspheres, octadecylamine, carbon black N990, TAIC, and Luperox 101-XL-45 are added in sequence and mixed evenly to obtain modified fluororubber. The ratio of fluororubber, magnesium oxide, calcium oxide, octadecylamine, UV-irradiated grafted modified hollow glass microspheres, carbon black N990, TAIC, and Luperox 101-XL-45 is 100: (2-4): (4-6): (0.3-0.7): (2-4): (8-12): (2-4): (2-4).

[0017] The beneficial effects of this invention are as follows: (1) This invention uses TPO as the primary photoinitiator for ultraviolet irradiation of hollow glass microspheres and benzophenone as the secondary photoinitiator for ultraviolet irradiation of glass microspheres, achieving rapid and stable grafting of PFDTES; directly generating two highly active free radicals through homolytic cleavage. (2) The obtained ultraviolet irradiation grafted modified hollow glass microspheres were used as fillers in the preparation of fluororubber, and the ratio of TPO and benzophenone and the ultraviolet irradiation time were optimized to maximize the mechanical and thermal properties of fluororubber. Attached Figure Description

[0018] 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.

[0019] Figure 1 SEM images of (a) UV-G-0 min HGM, (b) UV-G-5 min HGM, and (c) UV-G-15 min HGM obtained in the embodiments of the present invention; Figure 2 SEM images of (a) M1, (b) M2, and (c) M4 obtained in an embodiment of the present invention; Figure 3 The FTIR images of UV-G-0 min HGM, UV-G-5 min HGM, and UV-G-15 min HGM obtained in the embodiments of the present invention are shown below. Figure 4 (a) tensile strength, (b) elongation at break, and (c) hardness of M0-M6 obtained in the embodiments of the present invention; Figure 5 The densities of M0-M6 obtained in the embodiments of the present invention; Figure 6 (a) thermal conductivity, (b) TG, (c) DTG, and (d) residual carbon content of M0-M6 obtained in the embodiments of the present invention; Figure 7 SEM images of (a) UV-G-2:1 HGM, (b) UV-G-4:1 HGM, and (c) UV-G-5:3 HGM obtained in the embodiments of the present invention; Figure 8 SEM images of (a) M8, (b) M10, and (c) M11 obtained in an embodiment of the present invention; Figure 9 FTIR images of UV-G-2:1 HGM, UV-G-4:1 HGM, and UV-G-5:3 HGM obtained in embodiments of the present invention; Figure 10 (a) tensile strength, (b) elongation at break, and (c) hardness of M0, M2, and M7-11 obtained in the embodiments of the present invention. Figure 11 The densities of M0, M2, and M7-11 obtained in the embodiments of the present invention; Figure 12 (a) thermal conductivity, (b) TG, (c) DTG, and (d) residual carbon content of M0, M2, and M7-11 prepared in the embodiments of the present invention. Detailed Implementation

[0020] 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.

[0021] Example 1 S1. Mix 22.5 mL of anhydrous ethanol and 2.5 mL of deionized water, adjust the pH of the solution to 3.8 using glacial acetic acid, add 5% fluorosilane coupling agent PFDTES to the solution, add 0.45 g of photoinitiator TPO and 0.15 g of benzophenone to the solution in sequence, then mix the solution with 3 g of hollow glass microspheres, and then transfer the mixture into petri dishes. Place the petri dishes on a heating platform, place an ultraviolet irradiation device on top, keep the power of the ultraviolet irradiation device constant at 800 W, the ultraviolet irradiation temperature at 30 ℃, and set the ultraviolet irradiation time to 5 min. This is the modification of hollow glass microspheres to obtain modified hollow glass microspheres HGM@PFDTES-UV.

[0022] S2. Set the roller temperature to 80 ℃ and the roller gap to 8 mm. Feed the fluororubber into the open mill and add the premixed magnesium oxide and calcium oxide evenly. Cut each side 3 times and make triangular wraps 3 times. Then add octadecylamine, HGM@PFDTES-UV, carbon black N990, TAIC and Luperox 101-XL-45 in sequence and make triangular wraps 8 times. Mix until the rubber compound is uniform to obtain the FKM / HGM@PFDTES-UV composite material, which is denoted as M2.

[0023] The ratio of fluororubber, magnesium oxide, calcium oxide, octadecylamine, modified hollow glass microspheres, carbon black N990, TAIC, and Luperox 101-XL-45 is 100:3:5:0.5:3:10:3:3.

[0024] Example 2 The only difference between this embodiment and Embodiment 1 is that in step S1, the ultraviolet irradiation time is set to 8 minutes, and the final composite material is denoted as M2.

[0025] Example 3 The only difference between this embodiment and Embodiment 1 is that in step S1, the ultraviolet irradiation time is set to 15 minutes, and the final composite material is denoted as M4.

[0026] Example 4 The only difference between this embodiment and Embodiment 1 is that in step S1, the ultraviolet irradiation time is set to 20 minutes, and the final composite material is denoted as M5.

[0027] Example 5 The only difference between this embodiment and Embodiment 1 is that in step S1, the ultraviolet irradiation time is set to 30 minutes, and the final composite material is denoted as M6.

[0028] Example 6 The only difference between this embodiment and Embodiment 1 is that in step S1, 0.15g of photoinitiator TPO and 0.15g of benzophenone are added sequentially to the solution, and the resulting composite material is denoted as M7.

[0029] Example 7 The only difference between this embodiment and Example 1 is that in step S1, 0.3g of photoinitiator TPO and 0.15g of benzophenone are added to the solution in sequence, and the ratio of TPO to benzophenone is controlled to be 2:1. The final composite material is denoted as M8.

[0030] Example 8 The only difference between this embodiment and Example 1 is that in step S1, 0.45g of photoinitiator TPO and 0.3g of benzophenone are added to the solution in sequence, and the ratio of TPO to benzophenone is controlled to be 3:2. The final composite material is denoted as M9.

[0031] Example 9 The only difference between this embodiment and Example 1 is that in step S1, 0.60 g of photoinitiator TPO and 0.15 g of benzophenone are added to the solution in sequence, and the ratio of TPO to benzophenone is controlled to be 4:1. The final composite material is denoted as M10.

[0032] Example 10 The only difference between this embodiment and Example 1 is that in step S1, 0.75g of photoinitiator TPO and 0.45g of benzophenone are added to the solution in sequence, and the ratio of TPO to benzophenone is controlled to be 5:3. The final composite material is denoted as M11.

[0033] Comparative Example 1 S1. Mix 22.5 mL of anhydrous ethanol and 2.5 mL of deionized water, adjust the pH of the solution to 3.8 with glacial acetic acid, add 5% fluorosilane coupling agent PFDTES to the solution, mix with 3 g of hollow glass microspheres, and then transfer them sequentially to petri dishes. After standing for 8 hours, dry the solution, i.e., without ultraviolet irradiation treatment (UV irradiation time is 0 min), to obtain HGM@PFDTES.

[0034] S2. Set the roller temperature to 80 ℃ and the roller gap to 8 mm. Feed the fluororubber into the open mill and add the premixed magnesium oxide and calcium oxide evenly. Cut each side 3 times and make triangular wraps 3 times. Then add octadecylamine, HGM@PFDTES, carbon black N990, TAIC and Luperox 101-XL-45 in sequence and make triangular wraps 8 times. Mix until the rubber compound is uniform to obtain the FKM / HGM@PFDTES-UV composite material, which is denoted as M1.

[0035] The ratio of fluororubber, magnesium oxide, calcium oxide, octadecylamine, HGM@PFDTES, carbon black N990, TAIC, and Luperox 101-XL-45 is 100:3:5:0.5:3:10:3:3.

[0036] Comparative Example 2 The difference between this embodiment and Comparative Example 1 is that no coupling agent is used and no ultraviolet irradiation treatment is adopted. That is, the hollow glass microspheres are added directly in the open milling process in step S2 without going through step S1. The final composite material is denoted as M0.

[0037] 1. Morphology and performance test results of the composite materials obtained in Examples 2-5 and Comparative Examples 1-2 (1) Morphology analysis of FKM / HGM@PFDTES-UV composite material like Figure 1 The images show SEM images of hollow glass microspheres (HGM) modified with a photoinitiator TPO:benzophenone ratio of 3:1 and UV irradiation for 0 min, 5 min, and 15 min at 30 °C. The images show that the HGM without UV irradiation modification has fewer PFDTES grafted onto its surface, while the addition of TPO and benzophenone, followed by UV irradiation for 5 min and 10 min, results in a significantly increased PFDTES coating on the HGM surface, indicating a substantial increase in grafting rate. The modified HGM structure remains intact without any breakage.

[0038] like Figure 2 The figures show cross-sectional views of FKM / HGM@PFDTES-UV composites M1, M2, and M4 prepared by modifying HGM with a photoinitiator TPO:benzophenone ratio of 3:1 at 30 °C and UV irradiation times of 0 min, 5 min, and 15 min. As can be seen from the figures, when the UV irradiation time is 0 min, the modified HGM in the fluororubber matrix shows partial breakage, which is related to the small amount of PFDTES grafted onto the HGM surface. However, when the UV irradiation time is 5 min and 15 min, the HGM in the FKM / HGM@PFDTES-UV composites is uniformly dispersed, the structure is intact, and the composites are tightly bonded to the fluororubber, and the cross-sectional layers of the composites are relatively regular.

[0039] (2) Infrared analysis of modified hollow glass microspheres like Figure 3 The image shows the FTIR spectra of hollow glass microspheres (HGM) prepared using a photoinitiator TPO:benzophenone ratio of 3:1 at 30 °C and modified with UV irradiation for 0 min, 5 min, and 15 min. The image shows that the three types of HGM exhibit similar wavelengths at 802 cm⁻¹. -1 1030 cm -1 Corresponding infrared characteristic peaks appeared near the location, and the HGM shift was more pronounced after ultraviolet irradiation. Among them, 802 cm⁻¹ -1 The peak at 1039 cm⁻¹ represents the Si-O asymmetric stretching vibration of SiO₂, reflecting the vibrational characteristics of the silicon-oxygen bond; while the peak at 1039 cm⁻¹... -1 The peak at this point represents the Si-O symmetric stretching vibration of SiO2. In contrast, the characteristic peak of the unmodified HGM appears at 792 cm⁻¹. -1 1007 cm -1As can be seen, after adding the photoinitiator, with the increase of UV irradiation time, the photoinitiator decomposes to generate free radicals, triggering the chemical bonding of the coupling agent, and the Si-O-Si network is gradually modified by fluorosilane. With the extension of irradiation time, the surface grafting rate increases, and the movement of Si-O bonds is affected, resulting in a gradually obvious peak shift. Its characteristic peak shows a significant shift, indirectly proving the success of UV irradiation modification of HGM.

[0040] (3) Mechanical properties of FKM / HGM@PFDTES-UV composite material like Figure 4 (a) shows the tensile strength of FKM / HGM@PFDTES-UV composites prepared by modifying hollow glass microspheres (HGM) with different UV irradiation times at 30 °C using a photoinitiator TPO:benzophenone ratio of 3:1. Compared with the unirradiated M1, the tensile strength is 16.8 MPa. The FKM / HGM@PFDTES-UV composite reaches its maximum at a UV irradiation time of 5 min, with a tensile strength of 18.6 MPa. Compared with M1, the tensile strength is increased by 10.7%, and compared with M0, it is increased by 52.7%. Subsequently, the tensile strength slowly decreases with the increase of UV irradiation time, dropping to 16.1 MPa at a UV irradiation time of 30 min. It is evident that when the UV irradiation time is 5 min, the processes of TPO photoinitiator cracking and benzophenone absorbing light energy to generate free radicals are relatively complete. These free radicals can effectively initiate the condensation reaction between the fluorosilane coupling agent PFDTES and HGM, forming a strong Si–O–Si bond, while simultaneously grafting fluorocarbons onto the HGM surface. This can also be confirmed by the SEM images of the modified HGM and the cross-sectional SEM image of M2. However, when the UV irradiation time is extended to 5 min, the tensile strength slowly decreases. This may be because as the UV irradiation time increases, excessive energy damages the internal structure of HGM, causing the HGM wall to thin. Although successful grafting occurs on its surface, the thinning of the HGM wall is not easily observed in the SEM image. This phenomenon weakens the reinforcing effect of HGM, thereby reducing the tensile strength of the FKM / HGM@PFDTES-UV composite material.

[0041] like Figure 4(b) Elongation at break of FKM / HGM@PFDTES-UV composite material prepared by UV irradiation modification of HGM with photoinitiator. It can be seen that without photoinitiator and without UV irradiation, the elongation at break of M0 is 209.27%, and the elongation at break of M1 is 185.2%. However, with the increase of UV irradiation time, the elongation at break of FKM / HGM@PFDTES-UV composite material slowly decreases. At an irradiation time of 30 min, the elongation at break of M6 is 167.8%, a decrease of 9.4%. The reason for this change may be that with the extension of UV irradiation time, the photoinitiator continues to act, causing the reaction of PFDTES on the HGM surface to continue. PFDTES itself forms a silanol interface, which reduces the sites for effective connection between HGM and fluororubber molecular chains, weakening the interfacial bonding. Under external force, slippage easily occurs at the interface, leading to a gradual decrease in elongation at break.

[0042] like Figure 4 (c) shows the hardness of the FKM / HGM@PFDTES-UV composite material prepared by modifying HGM with a photoinitiator through UV irradiation. It can be seen that the hardness of the FKM / HGM@PFDTES-UV composite material gradually increases with the UV irradiation time. The hardness of M6 increases by 7.1% compared to M1, and by 7.9% compared to M0. This is because the main photoinitiator TPO can efficiently generate free radicals under UV irradiation. Benzophenone, as a co-initiator, works synergistically with TPO to prolong the free radical lifetime and increase the number of free radicals. Some of these free radicals can assist PFDTES in grafting onto the HGM surface, while excess free radicals are grafted onto the HGM surface along with PFDTES, promoting crosslinking between the modified HGM and fluororubber. Figure 4 (c) also reflects that the increased cross-linking degree between HGM and the fluororubber matrix leads to a tighter fluororubber molecular chain, which restricts the movement of the molecular chain. Macroscopically, this is manifested as an increase in the hardness of the FKM / HGM@PFDTES-UV composite material.

[0043] (4) Density of FKM / HGM@PFDTES-UV composite material like Figure 5 The figure shows the density of the FKM / HGM@PFDTES-UV composite material. As can be seen from the figure, the density of the FKM / HGM@PFDTES-UV composite material initially decreases and then slowly increases with UV irradiation time. Without the addition of a UV photoinitiator and without UV irradiation, the M0 density is 1.798 g / cm³. 3 When the UV irradiation time was 5 min, the density of M2 decreased to the lowest level, 1.773 g / cm3, compared to 1.786 g / cm3 for M1. 3The decrease was relatively small; after 30 min of UV irradiation, the M6 ​​density increased to 1.791 g / cm³. 3 Overall, the introduction of photoinitiators to modify hollow glass microspheres (HGM) under UV irradiation had little effect on the density of the prepared FKM / HGM@PFDTES-UV composite material. This phenomenon may be because, in the initial stage of UV irradiation, the cross-linking reaction initiated by the photoinitiator free radicals remaining on the HGM surface in the fluororubber system has just begun. The degree of cross-linking between HGM and fluororubber is low, and the bonding between molecular chains is not tight enough, resulting in some relatively large voids inside the fluororubber, thus causing a decrease in density. However, as the UV irradiation time increases, the photoinitiator continues to generate free radicals, promoting a tighter cross-linking between HGM and fluororubber, reducing the internal voids and increasing the density. The stable overall density trend of the FKM / HGM@PFDTES-UV composite material is related to the constant amount of HGM added after modification.

[0044] (5) Thermal properties of FKM / HGM@PFDTES-UV composite material like Figure 6 (a) shows the thermal conductivity of FKM / HGM@PFDTES-UV composites prepared by modifying HGM with a photoinitiator TPO:benzophenone ratio of 3:1 at 30 °C for different UV irradiation times. As shown in the figure, the thermal conductivity of M0 is 0.2100 W / (m·K). The thermal conductivity of the FKM / HGM@PFDTES-UV composite decreases from 0.2125 W / (m·K) before UV irradiation to 0.1945 W / (m·K) after 5 min of UV irradiation, and then increases to 0.2034 W / (m·K) after 30 min of UV irradiation, showing an overall trend of first decreasing and then increasing. The reason for this trend may be that when the UV irradiation time is 5 min, PFDTES is grafted through UV-induced free radical reaction, the amount of coupling agent grafted is moderate, HGM has the best dispersion in fluororubber, forming a uniform isolation network. The air in the hollow structure effectively blocks the heat conduction path, resulting in the thermal conductivity of the FKM / HGM@PFDTES-UV composite material reaching its lowest value at this time. However, if the UV irradiation time is too long, PFDTES will be over-grafted, causing filler agglomeration. Agglomerated HGM will destroy the uniformly dispersed isolation network, the hollow structure will be compressed or filled, the proportion of solid area will increase, and the thermal conductivity will be improved, thereby increasing the thermal conductivity of the FKM / HGM@PFDTES-UV composite material.

[0045] like Figure 6(bc) and Table 1 show the TG, DTG, and thermal decomposition temperatures at each stage of the FKM / HGM@PFDTES-UV composite material prepared by modifying HGM with different UV irradiation times after the introduction of a photoinitiator, measured within a temperature range of 40 ℃ to 700 ℃. The initial decomposition temperature increased from 417.3 ℃ at M0 to 436.2 ℃ at M2 after 5 min of UV irradiation, an increase of 18.9 ℃, at which point the decomposition temperature was highest. With the gradual increase in UV irradiation time, the initial decomposition temperature gradually decreased to 419.2 ℃, showing a trend of first increasing and then slowly decreasing. The reason for this phenomenon may be that when the irradiation time is 5 min, PFDTES forms a uniform and dense molecular layer through UV-induced free radical reaction, covering the HGM surface, and HGM obtains the optimal grafting density; however, as the UV irradiation time increases, the coupling agent layer becomes too thick, resulting in excessively high crosslinking density of fluororubber and enhanced rigidity of the interface layer. At the same time, the coupling agent layer is prone to microcracks under thermal stress, becoming the initiation point of thermal decomposition, which in turn leads to a decrease in the initial decomposition of FKM / HGM@PFDTES-UV composite material.

[0046] Figure 6 (d) shows the residual carbon content of the FKM / HGM@PFDTES-UV composite material. As can be seen from the figure, the variation pattern of the residual carbon content of the composite material is roughly consistent with the variation pattern of the initial decomposition temperature. At 0 min of UV irradiation, the residual carbon content is 21.35%, while after 5 min of UV irradiation, the residual carbon content is 32.14%, an increase of 50.5%, compared to a 20.85% increase compared to M0. However, after 30 min of UV irradiation, the residual carbon content decreases to 21.92%. This variation is due to the synergistic protective effect of the PFDTES interface layer and the HGM structure. At 5 min of UV irradiation, a moderate grafting density and a complete hollow structure are generated, both of which jointly promote the formation of a stable carbon layer, effectively blocking the diffusion of heat and decomposition products. However, as the UV irradiation time increases, the photoinitiator generates excessive free radicals after irradiation. Furthermore, the HGM structure may be damaged, the wall thickness may decrease, and the interface of the fluororubber is easily degraded, leading to the destruction of the hollow structure, reduced heat insulation effect, and accelerated decomposition, thus causing a decrease in the residual carbon content.

[0047] Table 1 Thermogravimetric data of FKM / HGM@PFDTES-UV composite material 2. Morphology and performance test results of the composite materials prepared in Examples 1, 6-10 and Comparative Example 2 (1) Morphology analysis of FKM / HGM@PFDTES-UV composite material like Figure 7The images show SEM images of hollow glass microspheres (HGM) modified by UV irradiation for 5 min, with TPO:benzophenone ratios of 2:1, 4:1, and 5:3. As can be seen from the images, HGM surfaces were grafted with fluorosilane coupling agent PFDTES when modified with different ratios of photoinitiator. The number of grafts was higher when the TPO:benzophenone ratio was 2:1. Under all three ratios, the modified HGM structure remained intact.

[0048] like Figure 8 The figures show cross-sectional views of FKM / HGM@PFDTES-UV composites M8, M10, and M11 prepared by modifying HGM with a photoinitiator TPO:benzophenone ratio of 2:1, 4:1, and 5:3 at 30 °C and irradiated with UV light for 5 min. It can be seen that when the TPO:benzophenone ratio is 2:1, HGM is uniformly dispersed in the composite cross-section, HGM is tightly bonded to the fluororubber, and the composite cross-section is relatively smooth. When the photoinitiator ratio is 4:1 and 5:3, the HGM dispersion decreases slightly, and the bonding with the fluororubber matrix decreases somewhat; most HGM exists in a free state within the fluororubber matrix.

[0049] (2) Infrared analysis of modified hollow glass microspheres like Figure 9 The figures shown are the FTIR spectra of HGM modified hollow glass microspheres (HGM) under the following conditions: TPO:benzophenone ratio of 2:1, 4:1, and 5:3, respectively, after 5 min of UV irradiation. The three HGM spectra are at 802 cm⁻¹. -1 1024 cm -1 1046 cm -1 Corresponding infrared characteristic peaks appeared near the location, and the HGM shift was more pronounced after ultraviolet irradiation when the photoinitiator ratio was 2:1. Among them, 802 cm⁻¹ -1 The peak at 1024 cm⁻¹ represents the Si-O asymmetric stretching vibration of SiO₂, reflecting the vibrational characteristics of the silicon-oxygen bond; while the peak at 1024 cm⁻¹... -1 The peak of the Si-O symmetric stretching vibration of SiO2 is located at 1046 cm⁻¹. -1The peak at this point represents the vibrational peak of CF in PFDTES. The reason for this phenomenon may be that when the ratio is 2:1, the synergistic effect of the two photoinitiators reaches an optimal balance, resulting in a moderate free radical generation rate that promotes the hydrolysis and condensation reactions of PFDTES, leading to more thorough grafting onto the HGM surface. However, at a ratio of 4:1, the photoinitiator ratio is too high, potentially causing excessively rapid free radical generation, premature consumption of the photoinitiator, or increased side reactions. At a ratio of 5:3, there are insufficient free radicals, resulting in incomplete reactions. Comparing the infrared characteristic peaks of HGM modified with a TPO:benzophenone ratio of 3:1 after 5 minutes of UV irradiation, the results are similar to those with a 2:1 ratio, further confirming the important role of an appropriate photoinitiator ratio in HGM modification.

[0050] (3) Mechanical properties of FKM / HGM@PFDTES-UV composite material like Figure 10(a) shows the tensile strengths of FKM / HGM@PFDTES-UV composites M7, M8, M2, M9, M10, and M11 prepared from modified hollow glass microspheres (HGM) with photoinitiator ratios of 1:1, 2:1, 3:1, 3:2, 4:1, and 5:3, respectively, after 5 min of UV irradiation. It can be seen that M0 has the lowest tensile strength (12.18 MPa) without photoinitiator addition or UV irradiation. When the photoinitiator ratio is 1:1, the tensile strength is 14.95 MPa. The composite has the highest tensile strength (19.90 MPa) when the photoinitiator ratio is 2:1. The tensile strength of M8 is 33.11% higher than that of M7 and 63.38% higher than that of M0. The tensile strength of the composite material generally decreased slowly when the photoinitiator ratio increased from 2:1 to 3:2, increased slightly when the ratio was 4:1, reaching 19.53 MPa, and decreased again when the ratio was 5:3, at which point the tensile strength of the composite material was 17.27 MPa, which is 15.5% higher than when the ratio of photoinitiator was 1:1. The reason for this variation may be that TPO mainly relies on long-wave ultraviolet absorption, while benzophenone requires synergy with amines or depends on the energy transfer of TPO. At a 1:1 ratio, the synergistic effect between the two has not yet been established, and the photoinitiator free radical generation rates are mismatched. This leads to insufficient hydrolysis and condensation reaction of PFDTES, low grafting rate on the HGM surface, and a large number of ungrafted HGM surface hydroxyl (-OH) residues, resulting in poor compatibility with fluororubber and low interfacial stress transfer efficiency, thus causing low tensile strength of the composite material. However, when the photoinitiator ratio is 2:1, the TPO to benzophenone ratio may reach a dynamic equilibrium, which can significantly improve the free radical generation efficiency, promote rapid hydrolysis of PFDTES and its reaction with the -OH on the HGM surface, and the higher grafting rate allows the HGM surface to be covered with fluorocarbon chains, significantly improving compatibility with fluororubber, enhancing interfacial bonding, and effectively transferring stress, thereby increasing tensile strength. When the photoinitiator ratio is 3:1 and 3:2, excessive TPO may lead to an excessively rapid free radical generation rate, causing PFDTES to rapidly condense locally on the HGM surface, forming an uneven graft layer and reducing the uniformity of interfacial bonding. When the ratio is 4:1, the high TPO content weakens the effect of benzophenone, and TPO rapidly generates a large number of free radicals in the early stages of UV irradiation, which may temporarily increase the grafting rate of PFDTES, forming a thicker graft layer. This roughens the HGM surface, enhancing the local bonding force with fluororubber and partially offsetting the negative impact of uneven grafting. However, when the photoinitiator ratio is 5:3, the free radical generation rate and reaction rate are mismatched, and the reaction between PFDTES and the HGM surface may become uncontrolled due to changes in the free radical generation rate. Incomplete grafting on the HGM surface weakens the interfacial bonding strength between HGM and fluororubber, thereby reducing the tensile strength of the composite material.

[0051] like Figure 10 (b) Elongation at break of several FKM / HGM@PFDTES-UV composites. It can be seen that M0 has the highest elongation at break at 209.27%. When the TPO:benzophenone ratio is 1:1, composite M7 has the lowest elongation at break at 153.27%. When the photoinitiator ratio is 4:1, the elongation at break of composite M10 is 185.12%, which is 20.7% higher. The overall trend is that the elongation at break gradually increases and then tends to stabilize. The reason for this change may be that when the photoinitiator ratio is 1:1, the synergistic effect of TPO and benzophenone is not activated, the PFDTES grafting rate is low, the interfacial compatibility between HGM and fluororubber is poor, and local stress concentration points are easily formed at weak interfaces, resulting in brittle fracture of fluororubber under external force. However, as the proportion of TPO in the photoinitiator increases, the free radical generation rate accelerates, the PFDTES graft layer gradually thickens and maintains uniformity, the thicker graft layer can buffer stress, and enhance the interfacial toughness through the flexibility of fluorocarbon chains, delaying crack propagation, which is manifested as a gradual increase in the elongation at break of the composite material. When the photoinitiator ratio is 5:3, the grafting amount of PFDTES on the HGM surface reaches the upper limit of physical adsorption and chemical bonding, and further increasing the TPO ratio cannot significantly change the interfacial structure. At this time, the influence of interfacial properties on the elongation at break of the composite material weakens, which is manifested as the elongation at break gradually stabilizing in a certain region.

[0052] like Figure 10 (c) The hardness of several FKM / HGM@PFDTES-UV composites. Comparison revealed that the hardness variation of the composites was similar to that of the elongation at break. When the photoinitiator ratio was 1:1, composite M7 exhibited the lowest hardness, while when the photoinitiator ratio was 4:1, composite M10 achieved the highest hardness, increasing by 7%. This indicates that increasing the TPO ratio to 4:1, by controlling the graft layer thickness and chemical environment, achieved the optimal balance of filler-matrix synergistic rigidity; beyond 4:1, the system's hardness tended to stabilize due to physical adsorption saturation and the intrinsic properties of the matrix.

[0053] (4) Density of FKM / HGM@PFDTES-UV composite material like Figure 11 The figure shows the density of FKM / HGM@PFDTES-UV composites prepared by modifying HGM with different photoinitiator TPO:benzophenone ratios after 5 min of UV irradiation. As can be seen from the figure, the overall density of the composite material does not change significantly, with M0 density being 1.798 g / cm³. 3 When the TPO:benzophenone ratio is 1:1, the density of composite material M7 is 1.796 g / cm³. 3At this point, the density is highest, while when the TPO:benzophenone ratio is 2:1, the density of composite material M8 is 1.754 g / cm³. 3 The density of the composite material is reduced to its lowest value. The reason for this change, corresponding to the aforementioned changes in the mechanical properties of the composite material, can be summarized as follows: When the TPO:benzophenone ratio is 1:1, the synergistic effect between TPO and benzophenone is poor, the PFDTES grafting rate is low, resulting in insufficient shielding of the hydroxyl groups on the HGM surface. The large polarity difference between unmodified HGM and fluororubber leads to collision and breakage during dispersion due to uneven interfacial tension, causing the hollow structure to collapse and failing to effectively reduce the composite material density. However, when the TPO:benzophenone ratio is 2:1, PFDTES forms a uniform and dense grafted layer, resulting in… Figure 8 The SEM images of the modified composite material also show that the compatibility between the modified microspheres and fluororubber is improved, which leads to a decrease in the density of the composite material. As the proportion of TPO increases, the free radical generation rate accelerates and the PFDTES graft layer thickens, further protecting the HGM structure. However, excessive TPO may cause local thermal effects, resulting in softening or even cracking of a small amount of HGM surface, which partially offsets the protective effect of the graft layer. This is also one of the reasons why the overall density of the composite material does not change significantly.

[0054] (5) Thermal properties of FKM / HGM@PFDTES-UV composite material like Figure 12(a) shows the thermal conductivity of FKM / HGM@PFDTES-UV composite materials prepared after 5 min of UV irradiation at 30 °C with different ratios of photoinitiator TPO:benzophenone. As shown in the figure, when the photoinitiator ratio is 1:1, the thermal conductivity of composite material M7 is 0.2321 W / (m·K). When the photoinitiator ratio is 3:1, the thermal conductivity of composite material M2 is 0.1945 W / (m·K), which is the lowest, a decrease of 16.2% compared to the previous value. Compared to the previous value, the thermal conductivity of M0 is 0.21 W / (m·K), a decrease of 7.3%. When the photoinitiator ratio is 3:2, the thermal conductivity of composite material M9 rises again to 0.2268 W / (m·K), and then slowly decreases again with the increase of the TPO ratio in the photoinitiator. The reason for this variation may be that when the photoinitiator ratio is 1:1, the PFDTES grafting rate is low, and the hydroxyl groups on the HGM surface are not effectively shielded, leading to collision and breakage of HGM during processing and dispersion, collapse of the hollow structure, and escape of internal gas. After being added to fluororubber, it forms a continuous thermally conductive path inside, improving the thermal conductivity of the composite material, manifested as an increase in thermal conductivity coefficient. At a 2:1 ratio, PFDTES forms a uniform grafted layer, the hollow structure of HGM is intact and uniformly dispersed, blocking the heat conduction path. At a 3:1 ratio, the TPO ratio increases, the grafted layer thickens but does not damage the HGM. In the GM structure, the hydrophobicity and low polarity of the fluorocarbon chain further enhance the interfacial thermal resistance, thus reducing the thermal conductivity of the composite material. However, at a 4:1 ratio, excess TPO may trigger the explosive generation of free radicals, and local photothermal release may cause the HGM surface to soften or even partially collapse, damaging the integrity of the hollow structure and causing the thermal conductivity to rebound, resulting in a further increase in the thermal conductivity of the composite material. When the ratio of the two photoinitiators is 5:3, the grafting amount of PFDTES is close to saturation, and excess TPO triggers a self-quenching effect, leading to microcracks or pores in the grafted layer, causing the interfacial thermal resistance to rise again, and the thermal conductivity of the composite material to decrease once more.

[0055] like Figure 12Tables (b) and (c) show the TG, DTG, and thermal decomposition temperatures at each stage of the FKM / HGM@PFDTES-UV composite materials prepared by modifying HGM at 30 ℃ for 5 min, after introducing different photoinitiator ratios, measured in the temperature range of 40 ℃ to 700 ℃. As shown in the figure, when the photoinitiator ratio is 2:1, the initial decomposition temperature of composite material M8 is 402.3 ℃, which is the lowest. Conversely, when the ratio is 4:1, the initial decomposition temperature of composite material M10 is the highest, at 441.3 ℃. This variation may be due to insufficient synergy between TPO and benzophenone at a 1:1 photoinitiator ratio, resulting in a low PFDTES grafting rate. The residual TPO, containing phosphine oxide groups, may decompose at high temperatures to generate acidic substances (such as phosphoric acid derivatives). Its catalytic effect on the breakage of the fluororubber backbone (CF bond) reduces thermal stability. At a 2:1 ratio, the photoinitiator synergistic effect is optimal, with PFDTES forming a dense grafted layer and no residue after complete reaction of the initiator. However, the excessively strong Si-O-Si bonding of the modified HGM leads to inconsistent interfacial thermal expansion coefficients, making it prone to microcracks during heating, which in turn reduces the thermal conductivity of the composite material. As the photoinitiator ratio increases from 3:1 to 4:1, the proportion of TPO gradually increases, the PFDTES grafted layer thickens, and a denser and more stable Si-O-Si network forms on the HGM surface, which can effectively delay the heat transfer to the HGM-matrix interface and inhibit the thermal degradation chain reaction. At a 5:3 ratio, the amount of PFDTES grafting exceeds the adsorption limit of the HGM surface, forming stress-induced microcracks, which become thermal oxygen permeation channels, and the initial decomposition temperature of the composite material decreases again.

[0056] like Figure 12(d) Residual carbon content of FKM / HGM@PFDTES-UV composite material. It can be seen that the residual carbon content of the composite material gradually increases as the photoinitiator ratio changes from 1:1 to 3:1. When the photoinitiator ratio is 3:1, the residual carbon content of composite material M2 is the highest, reaching 32.14%, an increase of 65.4% compared to 19.434% at the 1:1 ratio. At a ratio of 3:2, it decreases to 19.07%, then gradually increases to 30.24% before decreasing again to 22.93%. This shows that as the photoinitiator ratio increases from 1:1 to 3:1, the photoinitiator efficiency improves, and a uniform and dense Si-O-Si grafted layer forms on the HGM surface. The Si-O network can be transformed into a SiO2 framework at high temperatures, which synergistically forms a "Si-OC" composite carbon layer with the carbon produced by the decomposition of fluororubber, thereby significantly improving the residual carbon rate of the composite material. However, the sharp drop in residual carbon rate at a ratio of 3:2 may be due to the increased proportion of benzophenone interfering with the energy transfer efficiency of TPO, resulting in local weak points in the PFDTES graft layer. During pyrolysis, these weak points preferentially crack, and the unreacted benzophenone decomposes at high temperatures to generate benzoic acid, which catalyzes the breakage of the fluororubber backbone (CF) and disrupts the continuity of the carbon layer. At a ratio of 4:1, the residual carbon rate may increase again, possibly because excessive TPO promotes the thickening of the PFDTES graft layer on the HGM surface, and the outer fluorocarbon chain decomposes to generate fluorinated carbon, thus forming a dense barrier layer. At a ratio of 5:3, the amount of PFDTES grafting may exceed the limit of chemisorption sites, and the physical adsorption layer volatilizes rapidly during pyrolysis, destroying the integrity of the carbon layer and causing the residual carbon rate of the composite material to decrease again.

[0057] Table 2 Thermogravimetric data of FKM / HGM@PFDTES-UV composite materials 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 type of ultraviolet-irradiated grafted modified hollow glass microspheres, characterized in that, Its preparation method includes the following steps: S1. Prepare a solution by mixing anhydrous ethanol and deionized water, and adjust the pH of the solution to 3-5 using glacial acetic acid; S2. Add the fluorosilane coupling agent PFDTES to the solution, and then add the photoinitiator TPO and the photoco-initiator benzophenone in sequence. S3. After mixing the solution with hollow glass microspheres, transfer the mixture to a petri dish for ultraviolet irradiation to obtain ultraviolet irradiated grafted modified hollow glass microspheres.

2. The ultraviolet-irradiated grafted modified hollow glass microspheres according to claim 1, characterized in that: In step S2, the mass ratio of the fluorosilane coupling agent to the hollow glass microspheres is 3-7%.

3. The ultraviolet-irradiated grafted modified hollow glass microspheres according to claim 1, characterized in that: In step S2, the ratio of the photoinitiator TPO to benzophenone is (1-4):

1.

4. The ultraviolet-irradiated grafted modified hollow glass microspheres according to claim 1, characterized in that: In step S2, benzophenone accounts for 0.5-1% of the solution.

5. The ultraviolet-irradiated grafted modified hollow glass microspheres according to claim 1, characterized in that: In step S3, the ratio of hollow glass microspheres to benzophenone is (5-20):

1.

6. The ultraviolet-irradiated grafted modified hollow glass microspheres according to claim 1, characterized in that: In step S3, the ultraviolet irradiation time is 3-30 minutes and the ultraviolet irradiation power is 700-1000 W.

7. The ultraviolet-irradiated grafted modified hollow glass microspheres according to claim 1, characterized in that: In step S3, the temperature of ultraviolet irradiation is 25-35℃.

8. A modified fluororubber, characterized in that: It is obtained by using ultraviolet irradiation grafted modified hollow glass microspheres as described in any one of claims 1-7 as fillers and compounding them in fluororubber.

9. A modified fluororubber according to claim 8, characterized in that: The ratio of the ultraviolet-irradiated grafted modified hollow glass microspheres to fluororubber is (2-4):

100.

10. A modified fluororubber according to claim 8, characterized in that, Its preparation method includes the following steps: Fluororubber, magnesium oxide, and calcium oxide are mixed at 60-100℃, and then UV-irradiated grafted modified hollow glass microspheres, octadecylamine, carbon black N990, TAIC, and Luperox 101-XL-45 are added in sequence and mixed evenly to obtain modified fluororubber. The ratio of fluororubber, magnesium oxide, calcium oxide, octadecylamine, UV-irradiated grafted modified hollow glass microspheres, carbon black N990, TAIC, and Luperox 101-XL-45 is 100: (2-4): (4-6): (0.3-0.7): (2-4): (8-12): (2-4): (2-4).

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