Improving ablation properties of liquid silicone rubber composites by in situ construction of rich-porous char layer

In this article, ammonium polyphosphate (APP) and ammonium pentaborate (APB) were introduced to liquid silicone rubber with an aim of building rich-porous char structure in situ, thereby improving thermal insulation properties. Thermogravimetric analyses indicated that the incorporation of APP greatly increased the char residue of the composites. Oxy-acetylene torch tests showed that the addition of either APP or APB powders effectively enhanced the ablation resistance of the composites, whereas Shore A hardness tests revealed that the APP-containing composites exhibited a higher hardness than APB-filled counterparts. The linear ablation rates of composites with 40 phr APP or APB were reduced by 34.16% and 36.19%, respectively, when compared with the control sample. The maximum back-face temperatures of composites with 40 phr APP or APB was reduced to as low as 73°C. The APP-containing composites exhibited superior ablation resistance, considering both the linear ablation rate and the mechanical properties of char layer. In addition to SiO₂, SiC, and C, B₂O₃ was produced in the APB composites, as characterized by XRD and Raman analysis. Combined with SEM, it was proven that the formation of a firm, continuous, rich-porous and thermal insulation char layer was advantageous to improve the ablation and insulation properties.     

Improving the transient thermal response and ablation properties of epoxy-modified silicone rubber composites by adding fluxing agent

In this work, transient thermal response and ablation behavior of liquid silicone rubber composites containing fluxing/ceramic forming fillers were investigated under different heat flows using an oxyacetylene flame. The results indicated that the introduction of zinc borate (ZB) and aluminum oxide (Al₂O₃) effectively reduced the temperature at various depths of the samples, and they improved the thermal insulation properties and lowered pyrolysis rates. The above finding was attributed to the heat absorption arising from water release and melt filling as well as the vitrified reaction of solid melt due to the decomposition of ZB. Besides, the melting and exfoliation of Al₂O₃ and the formation of aluminum silicate (Al₂SiO₅) caused heat absorption effect. Additionally, the mass ablation rates and line ablation rates increased with rising heat flows coupling with a decrease of compressive strength of the char layers. In a nutshell, the effect of adding ZB/Al₂O₃ on the thermal insulation behavior of epoxy-modified vinyl silicone rubber (EMVSR) composites under different heat flows was elucidtaed. This work served as a reference for the design and preparation of flexible ablative materials for thermal protection applications.     

Thermal and mechanical properties of liquid silicone rubber composites filled with functionalized graphene oxide

To improve the thermal and mechanical properties of liquid silicone rubber (LSR) for application, the graphene oxide (GO) was proposed to reinforce the LSR. The GO was functionalized with triethoxyvinylsilane (TEVS) by dehydration reaction to improve the dispersion and compatibility in the matrix. The structure of the functionalized graphene oxide (TEVS‐GO) was evaluated by Thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectra, X‐ray diffraction (XRD), and energy dispersive X‐ray spectroscopy (EDX). It was found that the TEVS was successfully grafted on the surface of GO. The TEVS‐GO/LSR composites were prepared via in situ polymerization. The structure of the composites was verified by FTIR, XRD, and scanning electron microscopy (SEM). The thermal properties of the composites were characterized by TGA and thermal conductivity. The results showed that the 10% weight loss temperature (T₁₀) increased 16.0°C with only 0.3 wt % addition of TEVS‐GO and the thermal conductivity possessed a two‐fold increase, compared to the pure LSR. Furthermore, the mechanical properties were studied and results revealed that the TEVS‐GO/LSR composites with 0.3 wt % TEVS‐GO displayed a 2.3‐fold increase in tensile strength, a 2.79‐fold enhancement in tear strength, and a 1.97‐fold reinforcement in shear strength compared with the neat LSR. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42582.     

Thermal stability and ablation properties study of aluminum silicate ceramic fiber and acicular wollastonite filled silicone rubber composite

The thermal stability and ablation properties of silicone rubber filled with silica (SiO₂), aluminum silicate ceramic fiber (ASF), and acicular wollastonite (AW) were studied in this article. The morphology, composition, and ablation properties of the composite were analyzed after oxyacetylene torch tests. There were three different ceramic layers found in the ablated composite. In the porous ceramic layer, the rubber was decomposed, producing trimers, tetramers, and SiO₂. ASF and part of AW still remained and formed a dense layer. The SiO₂/SiC filaments in the ceramic layer reduced the permeability of oxygen, improving the ablation properties of the composites. The resultant ceramic layer was the densest, which acted as effective oxygen and heat barriers, and the achieved line ablation rate of the silicone composite were optimum at the proportion of 20 phr/40 phr (ASF/AW). Thermogravimetric analysis (TGA) confirmed that thermal stability of the composites was enhanced by the incorporation of ASF and AW. The formation of the ceramic layer was considered to be responsible for the enhancement of thermal stability and ablation properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39700.     

Ablation properties of zinc borate and aluminum hypophosphite filled silicone rubber composites

The ablative properties of epoxy modified silicone rubber composites filled with zinc borate (ZB) and aluminum hypophosphite (AHP) were studied. The decomposition of the added fillers and covering connection of residual on the substrate contribute to the improvement of heat insulation. The ablation test shows that the formation of a dense char layer with certain strength is key to improving the ablative properties. The optimal ablative performance is achieved when the concentration of ZB and AHP is 10 and 5 phr, respectively. Under such circumstances, the linear ablation rate is as low as 0.032 mm/s, which is about 61% lower than the pure silicone rubber. Furthermore, the structure and composition of the formed char layer were analyzed using X-ray diffraction analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy.     

A comparison of ablative resistance properties of liquid silicone rubber composites filled with different fibers

Flexible ablative materials play a key role in thermal protection systems to protect space vehicles during hypersonic flight missions. In this work, epoxy resin modified liquid silicone rubber was adopted as elastomeric matrix. Two inorganic fibers (carbon fibers (CF) and quartz fibers (QF)) and two organic fibers (aramid fibers (AF) and poly (p-phenylene benzobisoxazole) fibers (PBO)) were chosen as functional fillers. The ablation resistance and thermal insulation properties were evaluated using oxyacetylene torch test. Microstructure and phase composition of the char layer was fully characterized to investigate the ablation mechanism. SEM observations revealed that the fibers are well dispersed and integrated in the matrix. TGA analysis indicated that the inorganic fibers possess significantly higher thermal stability than organic fibers. In addition, a molten silica film can be formed on the material surface, which can exert a better thermal protection effect on the matrix. Furthermore, the ablation test shows that the linear ablation rate decreases first and then increases with an increase of fiber content. This work provides basic data to guide optimal selection of fibrous ablatives to enhance ablation performance.     

Processibility and mechanical properties of micronized polytetrafluoroethylene reinforced silicone rubber composites

Various micronized polytetrafluoroethylene (PTFE) powders were compounded with silicone rubber (MQ) and mechanical properties of the MQ/PTFE composites were evaluated. The fracture surface morphologies of prepared composites were also investigated using scanning electron microscopy (SEM). At a level of only 5 wt %, the fractured surface of MQ/PTFE composites show layered structure morphology. This structure effectively improves the tear strength of MQ but it also led to lower the tensile properties of the composites. The addition of fluorosilicone rubber (FMQ) as compatibilizer, tensile and tear strength of the composites improved considerably. However, tensile properties of the MQ/solution of sodium in liquid ammonia treated PTFE composite decreased compared with those of the untreated one. To investigate the production potential of extrusion process, an electric wire was extruded with MQ/PTFE/FMQ composites. During the curing process, volatile molecules lead to bubble and void formation of extruded layer depending on the filler shapes. The spherical PTFE powder was suitable for extrusion process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Ablation properties of aluminum silicate ceramic fibers and calcium carbonate filled silicone rubber composites

The ablative performance of aluminum silicate ceramic fiber (ASF) and calcium carbonate (CaCO₃) filled silicone rubber composites prepared through a two‐roll mill was examined. The properties of the composites were investigated by thermogravimetry, thermal conductivity measurements, and oxyacetylene torch testing. After the material was burnt, the structure and composition of the char were analyzed by Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy (SEM). The results of the ablation test showed that the ablation resistance improved greatly in an appropriate filler scope. Combined with SEM, it was proven that a firm, dense, and thermal insulation layer, which formed on the composites surface during the oxyacetylene torch test, was a critical factor in determining the ablation properties. Thermogravimetric analysis revealed that the thermal stability of the composites was enhanced by the incorporation of ASF and CaCO₃. The thermal conductivity measurements showed that the silicone rubber composites had a very low thermal conductivity ranging from 0.206 to 0.442 W m^?1 K^?1; this significantly prevented heat from transferring into the inner matrix at the beginning of the burning process. The proportion of 20/40 phr (ASF/CaCO₃) was optimum for improving the ablation resistance of the silicone rubber composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41619.     

Improving properties of silicone rubber composites using macromolecular silane coupling agent (MMSCA)

Two types of vinyl silicone oil (VSO), allyl‐capped hyperbranched polycarbosilane (HBP), and triethoxysilane (TES) were employed to synthesize macromolecular silane coupling agent (MMSCA) by hydrosilylation. VSOs, HBP, and the hydrosilylated products were used as crosslinker, respectively, to improve weak mechanical properties of silicone rubber (SR). Structures of the crosslinkers were studied by gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). Crosslinking density test and scanning electron microscope (SEM) observation showed an increased interaction between silicone rubber and fumed silica by the use of MMSCA. Mechanical properties of the resulted composites using MMSCAs were increased to varying degrees compared with those possessing crosslinkers without ethoxy group. MMSCAs were effective for further property enhancements of composites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43415.     

硅灰石对陶瓷化硅橡胶性能的影响

研究硅灰石长径比和用量对硅橡胶性能的影响。结果表明:加入硅灰石,硅橡胶能够在高温烧蚀下形成坚硬、致密的陶瓷状壳体;随着硅灰石用量的增大,硅橡胶烧结体的弯曲强度增大,硅橡胶的阻燃性能和热稳定性提高;硅灰石用量相同时,添加普通硅灰石的硅橡胶烧结体的弯曲强度较大,添加针状硅灰石的硅橡胶的阻燃性能和热稳定性更好;针状硅灰石用量为60份时,硅橡胶的综合性能最佳。     

硅橡胶的耐热稳定性

综述了硅橡胶的热老化机理,分析了主链及侧基、端基、添加剂等硅橡胶结构与组成以及水、酸和碱、氧和臭氧等环境条件对其耐热性的影响,指出改变主链结构和侧基结构、消除硅羟基、加入耐热添加剂和少量硅树脂是提高硅橡胶耐热性的方法。     

过氧化物高温硫化硅橡胶的热稳定性机理

研究了铁锡氧化物的复合物作为耐热添加剂的过氧化物高温硫化硅橡胶的热空气老化性能及其热稳定机理。热重法－差热分析说明铁锡氧化物的复合物可以提高硅橡胶的抗热氧化温度,Ｘ射线光电子能谱分析证明锡元素在硫化过程和热空气老化过程中被从Ｓｎ＾＋４还原到了Ｓｎ＾０,发生了多个电子转移的氧化－还原反应。     

Improving properties of ceramic silicone rubber composites using high vinyl silicone oil

Reactive high vinyl silicone oil (HVSO) was selected to prepare the ceramic silicone rubber composites. The effects of HVSO on the mechanical properties and thermal stabilities of ceramic silicone rubber composites were investigated. The structures of the cross‐linked network of silicone rubber with or without HVSO were studied. The intermolecular space of silicone rubber was enlarged, and the cross‐linked point was concentrated by addition of HVSO, which was demonstrated by cross‐linking densities, scanning electron microscope (SEM) images, and dynamic mechanical analysis (DMA). The cross‐linked network model was formed with the slipping of the cross‐linked points along with the silicone rubber chain. Mechanical properties of composites were enhanced by the formation of this cross‐linked network. The tear strength, tensile strength, and elongation at break of the composites were increased by 18.5%, 13.2%, and 37.4% by the adding of 2 phr HVSO, respectively. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41864.     

硅橡胶／纳米铜复合材料的结构与性能研究

采用机械混炼法制备了一种新型的宫内节育器材料——硅橡胶／纳米铜（SiR／nano-Cu）复合材料。利用扫描电子显微镜（SEM）和X射线衍射仪（XRD）观察了复合材料的组织结构,系统研究了nano-Cu含量对复合材料的力学性能、热稳定性能和吸水性能的影响。结果表明,纳米铜在复合材料的分散比较均匀,呈纳米级分布,只有极少数发生团聚。nano-Cu能提高复合材料的硬度,在高添加量时,材料的拉伸强度稍稍下降,但撕裂强度得到了很好的保持。随着纳米铜含量的增大,复合材料的热稳定性和吸水性能大大提高。     

4种网格结构模具用硅橡胶性能研究

分析了网格结构模具用4种不同的室温硫化硅橡胶的性能结果表明,该4种硅橡胶均具有较小的线收缩率及较长的凝胶时间,但加成型室温硫化硅橡胶较缩合型硅橡胶具有突出的室温力学性能、热稳定性及热线胀性能,完全满足用于制作网格模具的硅橡胶要求.     

可瓷化硅橡胶的制备与性能

以硅橡胶为基材、低软化点玻璃粉为成瓷填料,采用双辊开炼的方法制备一种可瓷化硅橡胶复合材料。研究玻璃粉用量对复合材料拉伸性能及瓷化性能的影响。结果表明:玻璃粉用量对复合体系的拉伸强度影响较小,在6~7 MPa间波动,对体系的断裂伸长率有显著影响,从约180%下降到110%;玻璃粉用量较大时,瓷化温度从750℃迅速下降到600℃;玻璃粉用量增加可提高低温瓷化物的抗热冲击性。扫描电镜观察结果表明:瓷化物内部存在大量气孔,导致试样的致密性均较差。     

Magnetically aligning multilayer graphene to enhance thermal conductivity of silicone rubber composites

The increasing demand for packaging materials calls for new technologies to achieve excellent thermal conductivity of polymer composites with low content of thermal conductive filler. This article prepared a kind of magnetically functionalized multilayer graphene (Fe₃O₄@MG) via electrostatic interactions, which efficiently enhanced the thermal conductivity of silicone rubber (SR) composites by the alignment of Fe₃O₄@MG in an external magnetic field. The morphology and structure of the Fe₃O₄@MG together with the thermal conductivity of corresponding Fe₃O₄@MG/SR composites were systematically investigated by SEM, TEM, XRD, elemental mapping, and thermal conductivity tester. The obtained results showed that Fe₃O₄@MG was induced to form chain-like bundles in silicone rubber matrix under the applied magnetic field, which enhanced the MG–MG interaction, and formed effective thermal pathways in the alignment direction. Furthermore, as coating mass ratio of Fe₃O₄@MG increased, the thermal conductivity of randomly oriented Fe₃O₄@MG/silicone rubber composites (R-Fe₃O₄@MG/SR) decreased gradually, whereas the through-plane thermal conductivity of vertically aligned Fe₃O₄@MG/silicone rubber composites (V-Fe₃O₄@MG/SR) increased even filled with same contents of thermal conductive filler. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47951.     

Electrically insulating ZnOs/ZnOw/silicone rubber nanocomposites with enhanced thermal conductivity and mechanical properties

In this work, hybrids of surface modified zinc oxide spherical (ZnOs) nanoparticles and tetrapod‐shaped whiskers (ZnOw) were incorporated into the silicon rubber (SR) to prepare the ZnOs/ZnOw/SR nanocomposites. The incorporation of the ZnOs/ZnOw facilitated the formation of three‐dimensional thermally conducting network. It was found that the thermal conductivity of the ZnOs/ZnOw/SR reached up to 1.309 W m^?1 K^?1 when the ZnOs/ZnOw content was 20 vol % (V_m‐ZnOs:V_ZnOw = 7:3), which was nearly 6.5 times that of the pristine SR. The dielectric and resistivity measurements showed that the incorporation of the ZnOs/ZnOw hybrids did not cause much change in the electrical properties. In addition, the results show that the tensile strength of ZnOs/ZnOw/SR nanocomposites is higher than that of pristine SR. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46454.     

Maxam推出用于苛刻工况的新优质实心防滑轮胎

采用了四甲基四乙烯基环四硅氧烷和四甲基四氢环四硅氧烷在铂金催化剂的作用下发生硅氢加成反应得到了高交联密度的硬质硅橡胶,制备过程中采用了“液面悬浮”和“阶梯升温”的工艺。利用差示扫描量热仪、傅里叶红外光谱仪、原子力显微镜、邵氏硬度计和热重分析仪分别对其固化过程、表面性能、硬度和热稳定性进行研究,并利用了平衡溶胀法计算了其交联密度。实验结果表明：阶梯升温能有效控制交联反应;硅橡胶具有极低的粗糙度,均方根粗糙度Rq为1.74 nm,平均粗糙度Ra为1.39 nm;邵氏D硬度为78.3;交联密度为2.87′10-3 mol/cm-3;硅橡胶在质量损失为5%时,对应温度为602.1 o C,最终的残余量为83.57%。     

硅油和白炭黑比表面积对硅橡胶性能的影响

气相法白炭黑是硅橡胶补强的最佳填料,羟基硅油是硅橡胶补强中常用的1种结构控制剂。本文研究了羟基硅油的用量以及气相法白炭黑比表面积对硅橡胶力学性能的影响。结果表明:随着羟基硅油用量的增加,硅橡胶的硬度、拉伸强度均逐渐降低,而断裂伸长率却随羟基硅油用量的增加而逐渐增大;随着气相法白炭黑比表面积的增大,硅橡胶的硬度、拉伸强度逐渐增大,而断裂伸长率逐渐减小。