Study on the influence of hollow glass microspheres structure on the ablation performance of EPDM rubber

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In this study, the effects of different glass microspheres, including solid and hollow HS46 and HS38 microspheres, on the ablation and carbonization behavior of EPDM, PI/EPDM and PPTA/EPDM composites were evaluated using oxyacetylene tests and SEM. The results revealed that the addition of HGM decreased the ablation rates, with reductions of 13% for solid microspheres, HS46 by 3% and HS38 by 16% compared with HGM-free composites. The presence of organic fibers further reduced ablation rates. Solid microspheres exhibited the most pronounced effect due to their superior thermal stability, whereas hollow microspheres with larger diameters tended to increase ablation rates as a result of fragmentation. Notably, the combined addition of HGM and fibers such as PI and PPTA reduced ablation rates by 50%. These findings provide valuable guidance for the design of advanced aerospace insulation materials that are lightweight, thermally stable and exhibit enhanced ablation resistance. hollow glass microspheres EPDM organic fiber ablative performance Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1. Introduction The most commonly used insulation layers for solid rocket engines, both domestically and internationally, are based on nitrile rubber (NBR) and ethylene propylene diene monomer (EPDM). Owing to its lower density and superior resistance to high temperatures and erosion, EPDM insulation has gained widespread application in solid rocket engines worldwide[ 1 – 2 ]. With the development of lightweight solid rocket engine shells, the original metal shell has been transformed into a composite material shell, and the overall weight of the engine has been significantly reduced[ 3 – 4 ]. However, traditional NBR and EPDM insulation layers are still used as thermal protection materials, which serve as negative masses for missile weapon systems[ 5 – 6 ]. Therefore, reducing the density of insulation materials within solid rocket engines and improving the engine mass ratio are effective strategies for enhancing the missile weapon carrying and delivery capabilities for large composite shell engines, where insulation materials are extensively applied. This is an important foundation for the upgrading of the new generation of missile weapons and will be beneficial for promoting and facilitating the update of the new generation of missile weapon systems. To reduce the density of internal insulation materials, methods such as incorporating lightweight materials or foaming are commonly employed[ 7 – 9 ]. Traditional rubber foaming technology requires reserving a certain space for volume expansion based on the foaming size before vulcanization. However, the current winding process for traditional solid rocket motor composite cases tightly combines the fibers with the insulation layer rubber, making it impossible to reserve an expandable space[ 10 – 12 ]. Therefore, foaming technology is not suitable for composite cases. Meanwhile, the introduction of lightweight hollow materials can effectively reduce the density of insulation layers and has no excessive requirements for construction techniques, making it one of the most widely used methods[ 13 – 16 ]. Hollow glass microspheres are inorganic powders with a hollow structure, primarily composed of silicate. Due to their lower density, excellent thermal insulation, and high temperature resistance, they are widely used as lightweight additives in various flame-retardant and ablation-resistant materials, reducing the density of composite materials[ 17 – 19 ]. Rallini et al.[ 20 ] studied the thermal stability and mechanical properties of EPDM-based composites containing different proportions of glass microspheres. Compared to the control group, a significant reduction in density was observed in the composite containing 20 phr of glass microspheres, ranging from 0.9 to 0.95 g/cm 3 , while the overall performance of the material remained good. The introduction of hollow microspheres has a significant effect on reducing the density of the insulation layer. However, the introduction of hollow structure and the fragmentation of microspheres can easily form internal structural defects during the ablation process, which often leads to a decrease in the ablation performance of the insulation layer[ 21 – 24 ]. Tian et al.[ 25 ] introduced different types of hollow microspheres into the SR matrix to investigate their effects on the properties of silicone rubber. The results showed that the addition of GHMS and PHMs both reduced the ablation performance of the SR composite material. This study only provided experimental results, but did not delve into how the structure of hollow microspheres affects the ablation performance of materials. Yang et al.[ 26 ] prepared hollow glass microspheres (HGMs)/silicone rubber composites with excellent thermal insulation properties. The results showed that HGMs fillers introduced large voids in the composite material, reducing its thermal conductivity to 0.11 W/mK and improving the thermal stability of the composite material. However, the effect on the ablation performance of the composite material was not studied. So far, there has been relatively little research and analysis on the ablation performance of hollow microspheres on EPDM internal insulation materials[ 27 – 30 ]. Key scientific issues such as the influencing factors and ablation mechanism of hollow glass microsphere reinforced EPDM internal insulation materials are still unclear. Therefore, based on the above research, it is very important to analyze the mechanism of the influence of hollow glass microspheres on the ablation performance of internal insulation materials. The influence of hollow microspheres on the performance of insulation materials primarily depends on their materials types and the size of the hollow structures. For a given type of hollow microspheres, such as hollow glass microspheres, the influence on the performance of insulation materials is mainly due to their different hollow sizes. At present, there have been no reports on the influence and underlying mechanism of hollow structure of hollow glass microspheres on the ablation performance of insulation materials. This article focused on the above issues and conducted research on the influence of different hollow sizes and structures of hollow glass microspheres on the ablation performance of insulation layers. It also analyzed the effect of different sizes of hollow microspheres combined with fibers on the ablation performance of insulation layers. The study systematically explored the influence of the size and structure of hollow microspheres on the ablation performance of insulation layers, summarized the ablation mechanism of hollow microsphere reinforced internal insulation materials. And the optimal hollow microsphere structure was determined. The results clarified the key influencing factors of ablation performance of hollow microsphere reinforced insulation material, and provided a solid theoretical basis and reference for the design and preparation of lightweight and ablative resistant internal insulation materials. 2. Experiment 2.1 Material Hollow glass microspheres HS46, the particle size D90 is 32 µm, the density is 0.51 g/cm 3 , and the isostatic pressing strength is ≥ 110 MPa, commercially available. Hollow glass microspheres HS38, the particle size D90 is 48 µm, the density is 0.39 g/cm 3 , and the isostatic pressing strength is ≥ 38 MPa, commercially available. Solid microspheres, the particle size of D90 is 16 µm and the density is 2.40 g/cm 3 , commercially available; EPDM rubber, type 4045, commercially available. Curing agent is dicumyl peroxide (DCP), commercially available. Aramid fiber (PPTA), and Polyimide fiber (PI) were purchased from Jiangsu Sinanuo New Materials Technology Co. 2.2 Experiment To effectively avoid damage to the HGM structure during the mixing process, solvent wet mixing technology was used to mix EPDM rubber, fiber, glass microspheres, and curing agent in a weight ratio of 100:8:30:4 to obtain a mixed rubber sample, as shown in Table 1 . The glass microsphere specifications include HS46 hollow glass microspheres, HS38 hollow glass microspheres, and solid microspheres. Simultaneously using the same formula and production process, control group samples were prepared without HGM. The ablated samples were prepared under sulfurization conditions of 160℃*40min*5MPa, and were ablated using oxyacetylene. The microstructure of the carbonized layer after ablation was observed. Table 1 The formula of cured sample Sample EPDM (g) Fiber (g) HGM (g) DCP (g) EPDM 100 8 30 4 EPDM-HS46 100 8 30 4 EPDM-SW 100 8 30 4 EPDM-HS38 100 8 30 4 2.3 Characterization Microscopic morphology observation: JSM-6360LV scanning electron microscope (SEM) from Japan was used to observe the microscopic morphology of HGM and carbide layer. Linear ablation rate: According to GJB323B, the sample was ablated using oxyacetylene for 10 seconds, with oxygen and acetylene flow rates of 1.512 m 3 /h and 1.116 m 3 /h, and pressures of 0.4 MPa and 0.095 MPa, respectively. Mechanical properties: The tensile strength and elongation at break of the EPDM composites was tested according to the standard QJ916 "solid engine combustion chamber insulation, lining materials tensile test". Density test: The density of the EPDM composites was tested through the standard QJ917A "Density of Insulation and Lining Materials in Solid Engine Combustion Chambers". HGM high temperature crushing test: Using the SDT Q600 thermogravimetric analyzer from TA Company in the United States, the temperature was raised from room temperature to 500 ℃ and 700 ℃ respectively, with a heating rate of 50 ℃/min and a nitrogen atmosphere. The residence time at the highest temperature was 10 minutes; The microstructure of HGM after high-temperature heating was observed using JSM-6360LV SEM from Japan. Thermal conductivity test: The thermal conductivity measurement was performed on a laser flash apparatus (LFA 427, NETZSCH, Germany). Thermogravimetric analysis (TGA): The thermal stability was tested with a thermogravimetric analyzer (TG 209F1 Iris, Netzsch, Germany) in N 2 atmosphere. The temperature ranged from 30 ℃ to 800 ℃ with the heating rate of 10 ℃/min. 3. Results and discussion 3.1 Ablation performance of EPDM/HGM composite materials Study on the influence of different specifications of hollow glass microspheres on the mechanical and ablative properties of EPDM/HGM composites. Figure 1 showed the morphology of different types of hollow microspheres. As shown in Fig. 1 , HS38 possesses a larger particle size, which forms a larger hollow structure in the simple EPDM system, resulting in a lower density of the vulcanized rubber material. According to Table 2 , the lowest density achieved for HS38 filled EPDM prepared via the wet mixing process was 0.687 g/cm 3 . The low shear wet mixing process resulted in a hollow microsphere breakage rate of less than 5%, and the actual density was close to the theoretical density, which is 21.8% lower than that of pure EPDM. Table 2 Mechanical and ablative properties of EPDM simple system filled with hollow glass microspheres of different specifications Sample theoretical density (g/cm 3 ) density (g/cm 3 ) tensile strength (MPa) elongation at break (%) linear ablative rate (mm/s) EPDM 0.876 0.878 1.12 71.1 0.620 EPDM-HS46 0.748 0.755 1.28 66.9 0.605 EPDM-SW 1.020 1.011 1.31 64.3 0.538 EPDM-HS38 0.677 0.687 1.07 59.1 0.720 Figure 2 presented the linear ablation rate of different hollow microsphere modified EPDM materials. As shown in Fig. 2 , the linear ablation rate of HS38 filled EPDM was 0.720mm/s, representing a 16.1% increase compared with pure EPDM material. This deterioration in ablation performance may be attributed to the larger contact area between the hollow structure and heat flow during ablation which accelerated material degradation[ 31 ]. The solid glass microsphere filled EPDM simple system showed a 13.2% reduction in linear ablation rate compared to EPDM pure rubber, indicating that glass material as a filler has the effect of reducing linear ablation rate. The density of EPDM hollow microspheres filled with HS46 was reduced by 9.6% compared to pure EPDM rubber. The hollow structure formed by the broken glass material and unbroken microspheres cancels each other out, resulting in a 2.9% decrease in wire ablation rate compared to pure EPDM. 3.2 The ablation performance of PI fiber-reinforced EPDM/HGM composites Building on previous research, the influence of hollow microspheres on the ablation performance of EPDM materials were investigated in the presence of organic fibers. The first step is to explore the effect of different hollow microspheres on ablation performance in the presence of PI fibers. The ablation performance of HGM/PI/EPDM composites was presented in Fig. 3 . The results indicated that the density of HS38/PI/EPDM material was reduced by 22.42% compared to pure PI/EPDM system, the linear ablation rate was reduced by 30.11%, and the carbonization rate was reduced by 19.38%. For the HS46/PI/EPDM composite, the reductions were 10.65%, 35.79%, and 29.69%, respectively. These findings indicate that, in the presence of PI fibers, HS46 hollow microspheres provided a more pronounced improvement in the ablation performance of EPDM internal insulation materials. Although hollow structures still had a negative impact on ablation performance, the interaction between hollow microspheres and PI short fibers at high temperatures had a positive effect on improving ablation performance. As shown in Fig. 4 a, the thermal stability of the PI fiber reinforced EPDM/HGM composites were analyzed. The PI/EPDM composite exhibited relatively poor thermal stability, with a residual weight at 800 ℃ (R 800 ) of only 4.59%. After adding solid or hollow microspheres, the R 800 of the insulation layer at 800 ℃ was significantly increased. This was due to the high thermal residual weight of hollow or solid microspheres themselves. As shown in Fig. 4 b, compared with the PI/EPDM, the maximum thermal decomposition rate peak of the insulation layer modified with hollow or solid microspheres did not show significant changes. This indicated that the introduction of microspheres did not modify the thermal degradation process of EPDM rubber itself. To further elucidate how the introduction of hollow microspheres improved the linear ablation rate of EPDM materials in the presence of PI fibers, the microstructure of the ablated residual carbon in the HGM/PI/EPDM system were examined. As shown in Fig. 5 a and b, the pure PI/EPDM ablated carbon layer was loose and unformed, with a smooth fiber surface that was directly exposed and lacked corresponding protection, making it difficult to support the carbon layer. As shown in Fig. 5 c and 5 d, in the SW/PI/EPDM system, microspheres and short fibers worked together to form a continuous hard carbonization layer, with a large number of spherical small particles attached to the fiber surface[ 32 ]. These particles played a role in connecting and protecting the fibers, which was beneficial for the fibers to enhance the carbon layer, thereby reducing the linear ablation rate and improving the material's ablation resistance. In Fig. 5 e and 5 f, many large-sized spherical particles can be seen together, with fibers embedded within them and thus difficult to observe directly. The carbon layer was continuous, which may explain the superior ablation resistance imparted by HS46 microspheres. In Fig. 5 g and 5 h, the fibers were enveloped by a dense covering of microspheres, providing good protection, and the stacking of carbon layers was relatively dense. The contour and porosity of the char layer after ablation were characterized using micro-computed tomography (micro-CT). As shown in Fig. 6 a, the central part of the insulation layer exhibited a noticeable depression, and the depression in the HS38/PI/EPDM was even deeper. Figure 6 b presentd the three-dimensional contour maps of two samples, in which the colored area was the selected location for measuring porosity. Figure 6 c and 6 d were top views of the ablated surfaces of HS46/PI/EPDM and HS38/PI/EPDM, and it can be seen that the ablation center had shifted to a certain extent. Figure 6 e and 6 f showed the pore size distribution of the selected areas of samples HS46/PI/EPDM and HS38/PI/EPDM, respectively. The more yellow the area in the picture, the larger the pore size. The porosity rates calculated using the micro-CT software were 22.7% for HS46/PI/EPDM and 26.3% for HS38/PI/EPDM. This indicated that HS38 microspheres with larger hollow sizes were more likely to form larger void structures during the ablation process. The composition analysis of the carbonized layer after ablation was shown in Fig. 7 . There are two distinct characteristic peaks on the carbonization layer curve of PI/EPDM. The peak located near 25° represented the characteristic peak of graphite carbon, and the peak located near 43° represented the characteristic peak of amorphous SiO 2 . After adding solid or hollow microspheres, five characteristic peaks appeared in the curve. The new peak located near 35°, 60° and 70° represented SiC, indicating that the silicate components in solid or hollow microspheres had undergone high-temperature ceramic reaction with EPDM rubber. At this point, the progress of the ceramic reaction was independent of the structure of the microspheres. 3.3 Ablation performance of PPTA fiber-reinforced EPDM/HGM composites Based on the above research, the influence of different hollow microspheres on the ablation performance of EPDM in the presence of PPTA fibers were continued to explore. As shown in Fig. 8 , the influence of different hollow microspheres on the ablation resistance of EPDM in the presence of PPTA fibers was consistent with that of PI fibers. The introduction of solid and hollow microspheres had an improvement effect on the ablation performance of the system. Among them, the solid microsphere modified material had the lowest linear ablation rate, while increasing the size of the hollow microspheres led to higher linear ablation rates. The density of HS38/PPTA/EPDM system was reduced by 21.37% compared to pure PPTA/EPDM system, the linear ablation rate was reduced by 17.83%, and the carbonization rate was reduced by 7.61%. The density of HS46/PPTA/EPDM system was reduced by 10.19% compared to pure PPTA/EPDM system, the linear ablation rate was reduced by 25.06%, and the carbonization rate was reduced by 26.14%. This indicated that the interaction between hollow microspheres and PPTA short fibers at elevated temperatures contributed positively to the ablation resistance of the composites. Furthermore, the surface and back microstructures of ablated residual carbon from different systems were observed. As shown in Fig. 9 a and 9 b, the carbon layer of the PPTA/EPDM system was loose and unformed, with organic fibers directly exposed and no sediment protection on the fiber surface. In Fig. 9 c and 9 d, the fiber surface was covered with a large number of spherical small particles, which protect the fiber from direct erosion by heat flow. Figure 9 e and 9 f showed that almost no short fibers were observed on the surface of the ablated residual carbon. The fibers were embedded in the matrix, and the short fibers worked together with low-density fillers to form a continuous hard carbonization layer. A relatively dense carbon layer was observed in Fig. 9 g and 9 h, and the interaction between surface hollow microspheres and organic short fibers at high temperatures was beneficial for improving the quality of the carbon layer and enhancing its ablation performance[ 33 ]. As shown in Fig. 9 , microspheres or smaller ball structures were observed in various regions of the carbonized layer of hollow glass microsphere-reinforced EPDM composites. Notably, almost no intact hollow glass microspheres were present at the front of the carbonized layer directly exposed to the oxyacetylene flame, but a large number of small-sized small ball structures appeared. On the back of the carbonized layer, there were a large number of hollow glass microspheres with intact or atrophied structures preserved. This was because the flame temperature of oxyacetylene was about 2000 ℃ and had a high flushing speed, which caused most hollow glass microspheres to break directly in high-temperature and high-speed airflow. At the same time, some fragments further transformed into small droplets, which form small particle balls after the carbonization layer cooled down. The hollow glass microspheres on the back of the carbonization layer experience a significant decrease in temperature due to the dual effects of efficient insulation and blocking of high-speed airflow by the carbonization layer. They mainly undergo high-temperature melting, and the complete spherical structure collapses, forming a shrinking structure after the carbonization layer cools down. As shown in Fig. 10 , the oxyacetylene ablation rate exhibited a consistent trend across HGM/EPDM, HGM/PI/EPDM, and HGM/PPTA/EPDM systems. The ablation rate significantly decreased after adding solid glass microspheres, but increased after replacing with hollow glass microspheres, and the ablation rate continued to increase with the increase of hollow degree. The main component of solid or hollow glass microspheres was silicate. The EDS spectrum of HS38 was shown in Fig. 11 , which had excellent thermal stability. The silicate compound melted and absorbed heat during the ablation process, while covering the surface of the rubber composite material to resist the erosion of high-temperature and high-speed airflow and prevent the oxidation of the base material by gas. Therefore, the addition of solid glass microspheres significantly improved its ablation resistance. As shown in Table 3 , transforming solid microsphere into hollow ones slightly reduced the thermal conductivity of the composite. Under high-speed and high-temperature oxyacetylene flames, the hollow glass microsphere structure at the surface rapidly collapsed, providing limited thermal insulation. At the same time, the breakage of hollow glass microspheres led to a significant increase in the porosity and ablation surface area of the rubber matrix. The accelerated heat transfer led to an increase in ablation rate, and the larger the diameter of the hollow microspheres, the more pronounced this effect became. Table 3 Thermal conductivity of HGM reinforced composite materials Thermal conductivity(W·m⁻¹·K⁻¹) HGM/EPDM PI/HGM/EPDM PPTA/HGM/EPDM EPDM 0.194 0.192 0.239 EPDM-SW 0.208 0.201 0.239 EPDM-HS46 0.191 0.189 0.224 EPDM-HS38 0.176 0.160 0.171 To further examine the crushing behavior of hollow glass microspheres at elevated temperatures, tests were conducted at 500°C and 700°C with varying insulation times. As shown in Fig. 12 , the results indicated that due to the significant increase in its hollow degree, HS38 was more prone to stress fracture caused by internal and external temperature differences at high temperatures, with only a portion of products with smaller diameters remaining. This was consistent with the previous analysis and judgment. To gain deeper insight into the ablation conditions, a schematic model illustrating the pre and post-ablation states was established, as shown in Fig. 13 . In Fig. 13 a and 13 b, the structure of HS38 was intact prior to ablation. After ablation, the hollow beads were broken and the hollow volume was lager. Therefore, the contact area with the gas flow was increased, which led to the decline of the ablation performance. As shown in Fig. 13 c and 13 d, the solid microsphere was smaller in size than hollow glass microspheres. After ablation, the crushing area of the solid microsphere was smaller and the contact area with the gas flow was smaller. Therefore, EPDM composites filled with solid microspheres exhibited superior ablation resistance and a lower linear ablation rate. 4. Conclusion This study systematically investigated the effects of different types of hollow microspheres (HS38, HS46) on the ablation performance of EPDM rubber simple systems, as well as the influence and mechanism of the combination of hollow microspheres and organic fibers (PI, PPTA fibers) on the ablation performance of EPDM rubber composite systems. The results indicated that the introduction of hollow microspheres alone was difficult to improve the ablation resistance of EPDM rubber materials. In the presence of organic fibers, the introduction of hollow microspheres can significantly improve the ablation resistance of EPDM while reducing the density of the material. The ablation rates of HS38/PPTA/EPDM and HS38/PI/EPDM were reduced by 17.83% and 30.11% for pure PPTA/EPDM and PI/EPDM systems, respectively. The ablation rates of HS46/PPTA/EPDM and HS46/PI/EPDM were reduced by 25.06% and 35.79% for PPTA/EPDM and PI/EPDM systems, respectively. Under the same conditions, the smaller the hollow structure of hollow glass microspheres, the better the effect on improving the ablation performance of EPDM, and the interaction between hollow microspheres and PI organic short fibers at high temperatures had a greater positive effect on improving the ablation performance. The research results of this article will provide theoretical guidance and support for the design and preparation of lightweight and ablation resistant internal insulation materials. Declarations Conflicts of interests ：We certify that this is an original work and all coauthors have seen and agree with all contents of this review and have no fnancial interest to report. Funding Declaration: there was no Funding in this work. Author Contribution declaration: Conceptualization: [Mingchao Wang]. Methodology: [Xin Chen], [Yuan Wang]. Formal analysis and investigation: [Lei Wu], [Jun Zhou], [Li Liu]. Writing - original draft preparation: [Zibin Lin], [Wenjun Ren], [Chen Liu]. Writing - review and editing: [Mingchao Wang], [Yuan Wang]. All authors read and approved the final manuscript. References Xu Y H, Hu C B, Zeng Z X, YX Yang (2012) Research on mechanical model of EPDM insulation charring layer. Applied Mechanics and Materials, 152: 57-63. 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Supplementary Files Response.docx Cite Share Download PDF Status: Published Journal Publication published 25 Apr, 2026 Read the published version in Journal of Polymer Research → Version 1 posted Editor assigned by journal 14 Nov, 2025 Reviewers agreed at journal 06 Oct, 2025 Reviewers invited by journal 06 Oct, 2025 Editor invited by journal 24 Aug, 2025 First submitted to journal 22 Aug, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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3","display":"","copyAsset":false,"role":"figure","size":124539,"visible":true,"origin":"","legend":"\u003cp\u003eAblation performance of HGM/EPDM composite materials\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/bde45f1b9bd0ac6bf9dff442.png"},{"id":93714218,"identity":"f3e3ca98-32db-493c-803d-a64657f6d067","added_by":"auto","created_at":"2025-10-16 18:58:57","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":211908,"visible":true,"origin":"","legend":"\u003cp\u003eablation performance of HGM/PI/EPDM composite materials\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/9572b476bf4880d03cb62db5.png"},{"id":93714219,"identity":"a53b0c64-ae9b-43fe-b5c0-8c7293f222e0","added_by":"auto","created_at":"2025-10-16 18:58:57","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":579368,"visible":true,"origin":"","legend":"\u003cp\u003e(a) TG curves and (b) DTG curves of cured samples in N\u003csub\u003e2\u003c/sub\u003e atmosphere.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/c406d10b567eecc937cf72aa.png"},{"id":93714513,"identity":"cec59717-cb27-45f6-8a34-f506c0821a28","added_by":"auto","created_at":"2025-10-16 19:06:58","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":343710,"visible":true,"origin":"","legend":"\u003cp\u003eMicroscopic morphology of EPDM composite system based on PI fiber, back (a)and front (b) of PI/EPDM; back (c) and front (d) of SW/PI/EPDM; back (e) and front (f) of HS46/PI/EPDM; back (g) and front (h) of HS38/PI/EPDM\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/791170cfc6766214927ca521.png"},{"id":93713502,"identity":"a2f66586-b768-42ba-a173-56944bdad583","added_by":"auto","created_at":"2025-10-16 18:50:57","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":113642,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Front view of HS46/PI/EPDM (up) and HS38/PI/EPDM (downward), (b) three-dimensional map of the sample, (c) surface topography image of HS46/PI/EPDM, (d) surface topography image of HS38/PI/EPDM, (e) pore distribution diagram of HS46/PI/EPDM, (f) pore distribution diagram of HS38/PI/EPDM\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/94dd345affe5a6c91dc4ce74.png"},{"id":93713504,"identity":"c2ddf50b-1a76-426d-8eb9-d18655eb4395","added_by":"auto","created_at":"2025-10-16 18:50:57","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":94239,"visible":true,"origin":"","legend":"\u003cp\u003eXRD curves of the carbonized layer of the cured samples\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/f979ef41913c4d6bec274acd.png"},{"id":93713510,"identity":"b35bb748-eff5-4408-930a-9ffca4e29149","added_by":"auto","created_at":"2025-10-16 18:50:58","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":522347,"visible":true,"origin":"","legend":"\u003cp\u003eAblation Performance of HGM/PPTA/EPDM Composite Materials\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/ebadbfeab899cde9df6c8d44.png"},{"id":93715106,"identity":"45fa27e8-e978-4978-a487-f12c36600593","added_by":"auto","created_at":"2025-10-16 19:22:58","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":64164,"visible":true,"origin":"","legend":"\u003cp\u003eMicroscopic morphology of EPDM composite system based on PPTA fiber, back (a) and front (b) of PPTA/EPDM; back (c) and front (d) of SW/PPTA/EPDM; back (e) and front (f) of HS46/PPTA/EPDM; back (g) and front (h) of HS38/PPTA/EPDM\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/db5820ab6ccf7602ff0591c1.png"},{"id":93714915,"identity":"7bad9ae8-1823-4bf0-833a-2dc130f6214a","added_by":"auto","created_at":"2025-10-16 19:14:57","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":45719,"visible":true,"origin":"","legend":"\u003cp\u003eLine ablation rate of EPDM composites\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/2a4aa31d46cc32def1953155.png"},{"id":93714509,"identity":"d6ec34a9-be4d-48b2-91a7-27dec9ed15dd","added_by":"auto","created_at":"2025-10-16 19:06:58","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":335544,"visible":true,"origin":"","legend":"\u003cp\u003eEDS spectrum of hollow glass microspheres (HS38)\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/a28e3df7c8f296e5d7ad25ce.png"},{"id":93713514,"identity":"74832e2b-6885-43a0-a8f3-f2b8d97a14ef","added_by":"auto","created_at":"2025-10-16 18:50:58","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":190144,"visible":true,"origin":"","legend":"\u003cp\u003eMicroscopic morphology after pyrolysis, (a) HS46 at 500 ℃, (b) HS38 at 500 ℃, (c) HS46 at 700 ℃, (d) HS38 at 700 ℃\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/ba84af9a046a49940002aed5.png"},{"id":107928081,"identity":"ff8e1797-3f5e-4f2e-9d7b-afeb4d0843ae","added_by":"auto","created_at":"2026-04-27 16:07:30","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3407595,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/a44d3d95-9289-4567-9049-255134ee8f0a.pdf"},{"id":93714916,"identity":"b54a163c-26d7-4314-95a3-1c4ba554e4ab","added_by":"auto","created_at":"2025-10-16 19:14:57","extension":"docx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":1115866,"visible":true,"origin":"","legend":"","description":"","filename":"Response.docx","url":"https://assets-eu.researchsquare.com/files/rs-5834611/v1/d4d9ab6da5f045f50d537bcc.docx"}],"financialInterests":"","formattedTitle":"Study on the influence of hollow glass microspheres structure on the ablation performance of EPDM rubber","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe most commonly used insulation layers for solid rocket engines, both domestically and internationally, are based on nitrile rubber (NBR) and ethylene propylene diene monomer (EPDM). Owing to its lower density and superior resistance to high temperatures and erosion, EPDM insulation has gained widespread application in solid rocket engines worldwide[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. With the development of lightweight solid rocket engine shells, the original metal shell has been transformed into a composite material shell, and the overall weight of the engine has been significantly reduced[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. However, traditional NBR and EPDM insulation layers are still used as thermal protection materials, which serve as negative masses for missile weapon systems[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Therefore, reducing the density of insulation materials within solid rocket engines and improving the engine mass ratio are effective strategies for enhancing the missile weapon carrying and delivery capabilities for large composite shell engines, where insulation materials are extensively applied. This is an important foundation for the upgrading of the new generation of missile weapons and will be beneficial for promoting and facilitating the update of the new generation of missile weapon systems.\u003c/p\u003e\u003cp\u003eTo reduce the density of internal insulation materials, methods such as incorporating lightweight materials or foaming are commonly employed[\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Traditional rubber foaming technology requires reserving a certain space for volume expansion based on the foaming size before vulcanization. However, the current winding process for traditional solid rocket motor composite cases tightly combines the fibers with the insulation layer rubber, making it impossible to reserve an expandable space[\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Therefore, foaming technology is not suitable for composite cases. Meanwhile, the introduction of lightweight hollow materials can effectively reduce the density of insulation layers and has no excessive requirements for construction techniques, making it one of the most widely used methods[\u003cspan additionalcitationids=\"CR14 CR15\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Hollow glass microspheres are inorganic powders with a hollow structure, primarily composed of silicate. Due to their lower density, excellent thermal insulation, and high temperature resistance, they are widely used as lightweight additives in various flame-retardant and ablation-resistant materials, reducing the density of composite materials[\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Rallini et al.[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] studied the thermal stability and mechanical properties of EPDM-based composites containing different proportions of glass microspheres. Compared to the control group, a significant reduction in density was observed in the composite containing 20 phr of glass microspheres, ranging from 0.9 to 0.95 g/cm\u003csup\u003e3\u003c/sup\u003e, while the overall performance of the material remained good.\u003c/p\u003e\u003cp\u003eThe introduction of hollow microspheres has a significant effect on reducing the density of the insulation layer. However, the introduction of hollow structure and the fragmentation of microspheres can easily form internal structural defects during the ablation process, which often leads to a decrease in the ablation performance of the insulation layer[\u003cspan additionalcitationids=\"CR22 CR23\" citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. Tian et al.[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e] introduced different types of hollow microspheres into the SR matrix to investigate their effects on the properties of silicone rubber. The results showed that the addition of GHMS and PHMs both reduced the ablation performance of the SR composite material. This study only provided experimental results, but did not delve into how the structure of hollow microspheres affects the ablation performance of materials. Yang et al.[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] prepared hollow glass microspheres (HGMs)/silicone rubber composites with excellent thermal insulation properties. The results showed that HGMs fillers introduced large voids in the composite material, reducing its thermal conductivity to 0.11 W/mK and improving the thermal stability of the composite material. However, the effect on the ablation performance of the composite material was not studied. So far, there has been relatively little research and analysis on the ablation performance of hollow microspheres on EPDM internal insulation materials[\u003cspan additionalcitationids=\"CR28 CR29\" citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Key scientific issues such as the influencing factors and ablation mechanism of hollow glass microsphere reinforced EPDM internal insulation materials are still unclear. Therefore, based on the above research, it is very important to analyze the mechanism of the influence of hollow glass microspheres on the ablation performance of internal insulation materials.\u003c/p\u003e\u003cp\u003eThe influence of hollow microspheres on the performance of insulation materials primarily depends on their materials types and the size of the hollow structures. For a given type of hollow microspheres, such as hollow glass microspheres, the influence on the performance of insulation materials is mainly due to their different hollow sizes. At present, there have been no reports on the influence and underlying mechanism of hollow structure of hollow glass microspheres on the ablation performance of insulation materials. This article focused on the above issues and conducted research on the influence of different hollow sizes and structures of hollow glass microspheres on the ablation performance of insulation layers. It also analyzed the effect of different sizes of hollow microspheres combined with fibers on the ablation performance of insulation layers. The study systematically explored the influence of the size and structure of hollow microspheres on the ablation performance of insulation layers, summarized the ablation mechanism of hollow microsphere reinforced internal insulation materials. And the optimal hollow microsphere structure was determined. The results clarified the key influencing factors of ablation performance of hollow microsphere reinforced insulation material, and provided a solid theoretical basis and reference for the design and preparation of lightweight and ablative resistant internal insulation materials.\u003c/p\u003e"},{"header":"2. Experiment","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Material\u003c/h2\u003e\u003cp\u003eHollow glass microspheres HS46, the particle size D90 is 32 \u0026micro;m, the density is 0.51 g/cm\u003csup\u003e3\u003c/sup\u003e, and the isostatic pressing strength is \u0026ge;\u0026thinsp;110 MPa, commercially available. Hollow glass microspheres HS38, the particle size D90 is 48 \u0026micro;m, the density is 0.39 g/cm\u003csup\u003e3\u003c/sup\u003e, and the isostatic pressing strength is \u0026ge;\u0026thinsp;38 MPa, commercially available. Solid microspheres, the particle size of D90 is 16 \u0026micro;m and the density is 2.40 g/cm\u003csup\u003e3\u003c/sup\u003e, commercially available; EPDM rubber, type 4045, commercially available. Curing agent is dicumyl peroxide (DCP), commercially available. Aramid fiber (PPTA), and Polyimide fiber (PI) were purchased from Jiangsu Sinanuo New Materials Technology Co.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Experiment\u003c/h2\u003e\u003cp\u003eTo effectively avoid damage to the HGM structure during the mixing process, solvent wet mixing technology was used to mix EPDM rubber, fiber, glass microspheres, and curing agent in a weight ratio of 100:8:30:4 to obtain a mixed rubber sample, as shown in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The glass microsphere specifications include HS46 hollow glass microspheres, HS38 hollow glass microspheres, and solid microspheres. Simultaneously using the same formula and production process, control group samples were prepared without HGM. The ablated samples were prepared under sulfurization conditions of 160℃*40min*5MPa, and were ablated using oxyacetylene. The microstructure of the carbonized layer after ablation was observed.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe formula of cured sample\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"5\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eEPDM (g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eFiber (g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eHGM (g)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eDCP (g)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM-HS46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM-SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM-HS38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e100\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e8\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e4\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Characterization\u003c/h2\u003e\u003cp\u003eMicroscopic morphology observation: JSM-6360LV scanning electron microscope (SEM) from Japan was used to observe the microscopic morphology of HGM and carbide layer.\u003c/p\u003e\u003cp\u003eLinear ablation rate: According to GJB323B, the sample was ablated using oxyacetylene for 10 seconds, with oxygen and acetylene flow rates of 1.512 m\u003csup\u003e3\u003c/sup\u003e/h and 1.116 m\u003csup\u003e3\u003c/sup\u003e/h, and pressures of 0.4 MPa and 0.095 MPa, respectively.\u003c/p\u003e\u003cp\u003eMechanical properties: The tensile strength and elongation at break of the EPDM composites was tested according to the standard QJ916 \"solid engine combustion chamber insulation, lining materials tensile test\".\u003c/p\u003e\u003cp\u003eDensity test: The density of the EPDM composites was tested through the standard QJ917A \"Density of Insulation and Lining Materials in Solid Engine Combustion Chambers\".\u003c/p\u003e\u003cp\u003eHGM high temperature crushing test: Using the SDT Q600 thermogravimetric analyzer from TA Company in the United States, the temperature was raised from room temperature to 500 ℃ and 700 ℃ respectively, with a heating rate of 50 ℃/min and a nitrogen atmosphere. The residence time at the highest temperature was 10 minutes; The microstructure of HGM after high-temperature heating was observed using JSM-6360LV SEM from Japan.\u003c/p\u003e\u003cp\u003eThermal conductivity test: The thermal conductivity measurement was performed on a laser flash apparatus (LFA 427, NETZSCH, Germany).\u003c/p\u003e\u003cp\u003eThermogravimetric analysis (TGA): The thermal stability was tested with a thermogravimetric analyzer (TG 209F1 Iris, Netzsch, Germany) in N\u003csub\u003e2\u003c/sub\u003e atmosphere. The temperature ranged from 30 ℃ to 800 ℃ with the heating rate of 10 ℃/min.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Ablation performance of EPDM/HGM composite materials\u003c/h2\u003e\u003cp\u003eStudy on the influence of different specifications of hollow glass microspheres on the mechanical and ablative properties of EPDM/HGM composites. Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e showed the morphology of different types of hollow microspheres. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, HS38 possesses a larger particle size, which forms a larger hollow structure in the simple EPDM system, resulting in a lower density of the vulcanized rubber material. According to Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the lowest density achieved for HS38 filled EPDM prepared via the wet mixing process was 0.687 g/cm\u003csup\u003e3\u003c/sup\u003e. The low shear wet mixing process resulted in a hollow microsphere breakage rate of less than 5%, and the actual density was close to the theoretical density, which is 21.8% lower than that of pure EPDM.\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eMechanical and ablative properties of EPDM simple system filled with hollow glass microspheres of different specifications\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eSample\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003etheoretical density (g/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003edensity (g/cm\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003etensile strength (MPa)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eelongation at break (%)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003elinear ablative rate (mm/s)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.876\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.878\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.12\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e71.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.620\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM-HS46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.748\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.755\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e66.9\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.605\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM-SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e1.020\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e1.011\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.31\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e64.3\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.538\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM-HS38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.677\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.687\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e1.07\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e\u003cp\u003e59.1\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e\u003cp\u003e0.720\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e presented the linear ablation rate of different hollow microsphere modified EPDM materials. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the linear ablation rate of HS38 filled EPDM was 0.720mm/s, representing a 16.1% increase compared with pure EPDM material. This deterioration in ablation performance may be attributed to the larger contact area between the hollow structure and heat flow during ablation which accelerated material degradation[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. The solid glass microsphere filled EPDM simple system showed a 13.2% reduction in linear ablation rate compared to EPDM pure rubber, indicating that glass material as a filler has the effect of reducing linear ablation rate. The density of EPDM hollow microspheres filled with HS46 was reduced by 9.6% compared to pure EPDM rubber. The hollow structure formed by the broken glass material and unbroken microspheres cancels each other out, resulting in a 2.9% decrease in wire ablation rate compared to pure EPDM.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e3.2 The ablation performance of PI fiber-reinforced EPDM/HGM composites\u003c/h2\u003e\u003cp\u003eBuilding on previous research, the influence of hollow microspheres on the ablation performance of EPDM materials were investigated in the presence of organic fibers. The first step is to explore the effect of different hollow microspheres on ablation performance in the presence of PI fibers. The ablation performance of HGM/PI/EPDM composites was presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The results indicated that the density of HS38/PI/EPDM material was reduced by 22.42% compared to pure PI/EPDM system, the linear ablation rate was reduced by 30.11%, and the carbonization rate was reduced by 19.38%. For the HS46/PI/EPDM composite, the reductions were 10.65%, 35.79%, and 29.69%, respectively. These findings indicate that, in the presence of PI fibers, HS46 hollow microspheres provided a more pronounced improvement in the ablation performance of EPDM internal insulation materials. Although hollow structures still had a negative impact on ablation performance, the interaction between hollow microspheres and PI short fibers at high temperatures had a positive effect on improving ablation performance.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea, the thermal stability of the PI fiber reinforced EPDM/HGM composites were analyzed. The PI/EPDM composite exhibited relatively poor thermal stability, with a residual weight at 800 ℃ (R\u003csub\u003e800\u003c/sub\u003e) of only 4.59%. After adding solid or hollow microspheres, the R\u003csub\u003e800\u003c/sub\u003e of the insulation layer at 800 ℃ was significantly increased. This was due to the high thermal residual weight of hollow or solid microspheres themselves. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, compared with the PI/EPDM, the maximum thermal decomposition rate peak of the insulation layer modified with hollow or solid microspheres did not show significant changes. This indicated that the introduction of microspheres did not modify the thermal degradation process of EPDM rubber itself.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTo further elucidate how the introduction of hollow microspheres improved the linear ablation rate of EPDM materials in the presence of PI fibers, the microstructure of the ablated residual carbon in the HGM/PI/EPDM system were examined. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea and b, the pure PI/EPDM ablated carbon layer was loose and unformed, with a smooth fiber surface that was directly exposed and lacked corresponding protection, making it difficult to support the carbon layer. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ed, in the SW/PI/EPDM system, microspheres and short fibers worked together to form a continuous hard carbonization layer, with a large number of spherical small particles attached to the fiber surface[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. These particles played a role in connecting and protecting the fibers, which was beneficial for the fibers to enhance the carbon layer, thereby reducing the linear ablation rate and improving the material's ablation resistance. In Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ee and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ef, many large-sized spherical particles can be seen together, with fibers embedded within them and thus difficult to observe directly. The carbon layer was continuous, which may explain the superior ablation resistance imparted by HS46 microspheres. In Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eg and \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eh, the fibers were enveloped by a dense covering of microspheres, providing good protection, and the stacking of carbon layers was relatively dense.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe contour and porosity of the char layer after ablation were characterized using micro-computed tomography (micro-CT). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ea, the central part of the insulation layer exhibited a noticeable depression, and the depression in the HS38/PI/EPDM was even deeper. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb presentd the three-dimensional contour maps of two samples, in which the colored area was the selected location for measuring porosity. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ec and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ed were top views of the ablated surfaces of HS46/PI/EPDM and HS38/PI/EPDM, and it can be seen that the ablation center had shifted to a certain extent. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ee and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003ef showed the pore size distribution of the selected areas of samples HS46/PI/EPDM and HS38/PI/EPDM, respectively. The more yellow the area in the picture, the larger the pore size. The porosity rates calculated using the micro-CT software were 22.7% for HS46/PI/EPDM and 26.3% for HS38/PI/EPDM. This indicated that HS38 microspheres with larger hollow sizes were more likely to form larger void structures during the ablation process.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe composition analysis of the carbonized layer after ablation was shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. There are two distinct characteristic peaks on the carbonization layer curve of PI/EPDM. The peak located near 25\u0026deg; represented the characteristic peak of graphite carbon, and the peak located near 43\u0026deg; represented the characteristic peak of amorphous SiO\u003csub\u003e2\u003c/sub\u003e. After adding solid or hollow microspheres, five characteristic peaks appeared in the curve. The new peak located near 35\u0026deg;, 60\u0026deg; and 70\u0026deg; represented SiC, indicating that the silicate components in solid or hollow microspheres had undergone high-temperature ceramic reaction with EPDM rubber. At this point, the progress of the ceramic reaction was independent of the structure of the microspheres.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Ablation performance of PPTA fiber-reinforced EPDM/HGM composites\u003c/h2\u003e\u003cp\u003eBased on the above research, the influence of different hollow microspheres on the ablation performance of EPDM in the presence of PPTA fibers were continued to explore. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, the influence of different hollow microspheres on the ablation resistance of EPDM in the presence of PPTA fibers was consistent with that of PI fibers. The introduction of solid and hollow microspheres had an improvement effect on the ablation performance of the system. Among them, the solid microsphere modified material had the lowest linear ablation rate, while increasing the size of the hollow microspheres led to higher linear ablation rates. The density of HS38/PPTA/EPDM system was reduced by 21.37% compared to pure PPTA/EPDM system, the linear ablation rate was reduced by 17.83%, and the carbonization rate was reduced by 7.61%. The density of HS46/PPTA/EPDM system was reduced by 10.19% compared to pure PPTA/EPDM system, the linear ablation rate was reduced by 25.06%, and the carbonization rate was reduced by 26.14%. This indicated that the interaction between hollow microspheres and PPTA short fibers at elevated temperatures contributed positively to the ablation resistance of the composites.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFurthermore, the surface and back microstructures of ablated residual carbon from different systems were observed. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ea and \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eb, the carbon layer of the PPTA/EPDM system was loose and unformed, with organic fibers directly exposed and no sediment protection on the fiber surface. In Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ec and \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ed, the fiber surface was covered with a large number of spherical small particles, which protect the fiber from direct erosion by heat flow. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ee and \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ef showed that almost no short fibers were observed on the surface of the ablated residual carbon. The fibers were embedded in the matrix, and the short fibers worked together with low-density fillers to form a continuous hard carbonization layer. A relatively dense carbon layer was observed in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eg and \u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003eh, and the interaction between surface hollow microspheres and organic short fibers at high temperatures was beneficial for improving the quality of the carbon layer and enhancing its ablation performance[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, microspheres or smaller ball structures were observed in various regions of the carbonized layer of hollow glass microsphere-reinforced EPDM composites. Notably, almost no intact hollow glass microspheres were present at the front of the carbonized layer directly exposed to the oxyacetylene flame, but a large number of small-sized small ball structures appeared. On the back of the carbonized layer, there were a large number of hollow glass microspheres with intact or atrophied structures preserved. This was because the flame temperature of oxyacetylene was about 2000 ℃ and had a high flushing speed, which caused most hollow glass microspheres to break directly in high-temperature and high-speed airflow. At the same time, some fragments further transformed into small droplets, which form small particle balls after the carbonization layer cooled down. The hollow glass microspheres on the back of the carbonization layer experience a significant decrease in temperature due to the dual effects of efficient insulation and blocking of high-speed airflow by the carbonization layer. They mainly undergo high-temperature melting, and the complete spherical structure collapses, forming a shrinking structure after the carbonization layer cools down.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, the oxyacetylene ablation rate exhibited a consistent trend across HGM/EPDM, HGM/PI/EPDM, and HGM/PPTA/EPDM systems. The ablation rate significantly decreased after adding solid glass microspheres, but increased after replacing with hollow glass microspheres, and the ablation rate continued to increase with the increase of hollow degree. The main component of solid or hollow glass microspheres was silicate. The EDS spectrum of HS38 was shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, which had excellent thermal stability. The silicate compound melted and absorbed heat during the ablation process, while covering the surface of the rubber composite material to resist the erosion of high-temperature and high-speed airflow and prevent the oxidation of the base material by gas. Therefore, the addition of solid glass microspheres significantly improved its ablation resistance. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, transforming solid microsphere into hollow ones slightly reduced the thermal conductivity of the composite. Under high-speed and high-temperature oxyacetylene flames, the hollow glass microsphere structure at the surface rapidly collapsed, providing limited thermal insulation. At the same time, the breakage of hollow glass microspheres led to a significant increase in the porosity and ablation surface area of the rubber matrix. The accelerated heat transfer led to an increase in ablation rate, and the larger the diameter of the hollow microspheres, the more pronounced this effect became.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThermal conductivity of HGM reinforced composite materials\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"4\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eThermal conductivity(W\u0026middot;m⁻\u0026sup1;\u0026middot;K⁻\u0026sup1;)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eHGM/EPDM\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003ePI/HGM/EPDM\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ePPTA/HGM/EPDM\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.194\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.192\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.239\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM-SW\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.208\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.201\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.239\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM-HS46\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.191\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.189\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.224\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eEPDM-HS38\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e\u003cp\u003e0.176\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e\u003cp\u003e0.160\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e\u003cp\u003e0.171\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eTo further examine the crushing behavior of hollow glass microspheres at elevated temperatures, tests were conducted at 500\u0026deg;C and 700\u0026deg;C with varying insulation times. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e, the results indicated that due to the significant increase in its hollow degree, HS38 was more prone to stress fracture caused by internal and external temperature differences at high temperatures, with only a portion of products with smaller diameters remaining. This was consistent with the previous analysis and judgment.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eTo gain deeper insight into the ablation conditions, a schematic model illustrating the pre and post-ablation states was established, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e. In Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003ea and \u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003eb, the structure of HS38 was intact prior to ablation. After ablation, the hollow beads were broken and the hollow volume was lager. Therefore, the contact area with the gas flow was increased, which led to the decline of the ablation performance. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003ec and \u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003ed, the solid microsphere was smaller in size than hollow glass microspheres. After ablation, the crushing area of the solid microsphere was smaller and the contact area with the gas flow was smaller. Therefore, EPDM composites filled with solid microspheres exhibited superior ablation resistance and a lower linear ablation rate.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis study systematically investigated the effects of different types of hollow microspheres (HS38, HS46) on the ablation performance of EPDM rubber simple systems, as well as the influence and mechanism of the combination of hollow microspheres and organic fibers (PI, PPTA fibers) on the ablation performance of EPDM rubber composite systems. The results indicated that the introduction of hollow microspheres alone was difficult to improve the ablation resistance of EPDM rubber materials. In the presence of organic fibers, the introduction of hollow microspheres can significantly improve the ablation resistance of EPDM while reducing the density of the material. The ablation rates of HS38/PPTA/EPDM and HS38/PI/EPDM were reduced by 17.83% and 30.11% for pure PPTA/EPDM and PI/EPDM systems, respectively. The ablation rates of HS46/PPTA/EPDM and HS46/PI/EPDM were reduced by 25.06% and 35.79% for PPTA/EPDM and PI/EPDM systems, respectively. Under the same conditions, the smaller the hollow structure of hollow glass microspheres, the better the effect on improving the ablation performance of EPDM, and the interaction between hollow microspheres and PI organic short fibers at high temperatures had a greater positive effect on improving the ablation performance. The research results of this article will provide theoretical guidance and support for the design and preparation of lightweight and ablation resistant internal insulation materials.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflicts of interests\u003c/strong\u003e：We certify that this is an original work and all coauthors have seen and agree with all contents of this review and have no fnancial interest to report.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding Declaration:\u003c/strong\u003e there was no Funding in this work.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contribution declaration:\u003c/strong\u003e Conceptualization: [Mingchao Wang]. Methodology: [Xin Chen], [Yuan Wang]. Formal analysis and investigation: [Lei Wu], [Jun Zhou], [Li Liu]. Writing - original draft preparation: [Zibin Lin], [Wenjun Ren], [Chen Liu]. Writing - review and editing: [Mingchao Wang], [Yuan Wang]. All authors read and approved the final manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eXu Y H, Hu C B, Zeng Z X, YX Yang (2012) Research on mechanical model of EPDM insulation charring layer. Applied Mechanics and Materials, 152: 57-63.\u003c/li\u003e\n\u003cli\u003eRybiński P, Janowska G, Ślusarski L (2020) Influence of cryogenic modification of silica on thermal properties and flammability of cross-linked nitrile rubber. Journal of Thermal Analysis and Calorimetry, 101(2): 665-670.\u003c/li\u003e\n\u003cli\u003eWang Y, Li J, Wan L, L Wang, K Li (2023) A lightweight rubber foaming insulation reinforced by carbon nanotubes and carbon fibers for solid rocket motors. Acta Astronautica, 208: 270-280.\u003c/li\u003e\n\u003cli\u003eYoshida M, Kimura T, Hashimoto T, S Moriya, S Takada (2017) Overview of research and development status of reusable rocket engine. 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Polymer Degradation and Stability, 225: 110781.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"hollow glass microspheres, EPDM, organic fiber, ablative performance","lastPublishedDoi":"10.21203/rs.3.rs-5834611/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5834611/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe increasing demand for lightweight, ablation-resistant materials in solid rocket engines has promoted the application of hollow glass microspheres (HGM) owing to their low density and high thermal stability. In this study, the effects of different glass microspheres, including solid and hollow HS46 and HS38 microspheres, on the ablation and carbonization behavior of EPDM, PI/EPDM and PPTA/EPDM composites were evaluated using oxyacetylene tests and SEM. The results revealed that the addition of HGM decreased the ablation rates, with reductions of 13% for solid microspheres, HS46 by 3% and HS38 by 16% compared with HGM-free composites. The presence of organic fibers further reduced ablation rates. Solid microspheres exhibited the most pronounced effect due to their superior thermal stability, whereas hollow microspheres with larger diameters tended to increase ablation rates as a result of fragmentation. Notably, the combined addition of HGM and fibers such as PI and PPTA reduced ablation rates by 50%. These findings provide valuable guidance for the design of advanced aerospace insulation materials that are lightweight, thermally stable and exhibit enhanced ablation resistance.\u003c/p\u003e","manuscriptTitle":"Study on the influence of hollow glass microspheres structure on the ablation performance of EPDM rubber","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-16 18:50:53","doi":"10.21203/rs.3.rs-5834611/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorAssigned","content":"","date":"2025-11-14T09:22:15+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2025-10-06T08:43:29+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-06T08:30:18+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Journal of Polymer Research","date":"2025-08-25T02:54:27+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Polymer Research","date":"2025-08-22T07:53:43+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-polymer-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jpol","sideBox":"Learn more about [Journal of Polymer Research](https://www.springer.com/journal/10965)","snPcode":"10965","submissionUrl":"https://www.editorialmanager.com/jpol/","title":"Journal of Polymer Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"1a9d847b-e8f4-46fa-9568-4db62031ec38","owner":[],"postedDate":"October 16th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-04-27T16:05:17+00:00","versionOfRecord":{"articleIdentity":"rs-5834611","link":"https://doi.org/10.1007/s10965-026-04858-x","journal":{"identity":"journal-of-polymer-research","isVorOnly":false,"title":"Journal of Polymer Research"},"publishedOn":"2026-04-25 15:59:18","publishedOnDateReadable":"April 25th, 2026"},"versionCreatedAt":"2025-10-16 18:50:53","video":"","vorDoi":"10.1007/s10965-026-04858-x","vorDoiUrl":"https://doi.org/10.1007/s10965-026-04858-x","workflowStages":[]},"version":"v1","identity":"rs-5834611","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5834611","identity":"rs-5834611","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}