Effect of various fibers on the ablation resistance of poly(diaryloxyphosphazene) elastomer

Poly(diaryloxyphosphazene) elastomer (PDPP) is an alternative and promising thermal insulation material to protect the combustion chamber of solid rocket motors. The hybrid inorganic–organic macromolecule with the backbone of alternating nitrogen and phosphorus atoms has good thermal stability and compatibility for inorganic and organic fillers. This article focused on the effect of inorganic and organic fibers on the ablation resistance of PDPP at slow and fast pyrolysis, which was performed by thermogravimetric analysis and oxyacetylene ablation. Two inorganic fibers (alumina and mullite) and two organic fibers (polyimide and phenolic) were introduced into PDPP elastomer. During the process of slow pyrolysis, two inorganic fibers provided higher char yields due to their higher thermal stability. However, SiC in situ formed on the surface of organic fibers effectively improved the ablation resistance of the composites under the process of fast pyrolysis according to the micromorphology and structure analyses of charred layers. In addition, terminal groups of organic fibers affected the in situ formation of SiC. The phenolic/PDPP composite have a better ablation resistance than the other three composites at fast pyrolysis, owing to more in situ formed SiC on its surface and its higher decomposition activation energy. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48534.     

Ablation of the carbon/carbon composite nozzle-throats in a small solid rocket motor

Ablation of needled carbon/carbon (C/C) composite nozzle-throats was studied by hot-fire testing in a small solid rocket motor. The composition of the combustion gases was estimated by principle of free energy minimum. The ablation morphology was investigated by scanning electron microscopy. The ablation mechanism of C/C composites was also studied. The results showed that the ablation performance of C/C composites was determined by mechanical breakage of fibers/matrix together with thermal chemical ablation from the heterogeneous reactions on the throat surface. The mechanical breakage of fibers/matrix dominated the ablation of the composites at high pressure based on the calculated ablation rate. Cone-shaped fibers were formed after ablation in high fiber density area; but in low fiber density area, the fibers were peeled off because of the weakened strength after ablation. Meanwhile, the matrix around the fiber bundles was ablated into a shell shape, while the matrix between the cone-shaped fibers might be blown away by the combustion gases. Oxidation of C/C composites led to the formation of the cone-shaped fibers and shell-shaped matrix, as well as the loss of matrix between the cone-shaped fibers. The fiber/matrix fragments on the ablation surface were caused by the mechanical breakage.     

Mechanochemical fabrication of geopolymer composites based on the reinforcement effect of microfibrillated cellulose

In this study, microfibrillated cellulose-reinforced geopolymer organic/inorganic hybrid materials, were prepared via a simple green mechanochemical method. The interaction between microfibrillated nanocellulose and geopolymer was further investigated by molecular dynamics simulation. The study established that mechanical ball milling could effectively promote the microfibrillation of bamboo pulp fibers to form reinforced geopolymer composites with a uniformly distributed cellulose skeleton network. The compressive strength of geopolymer blended with 2% microfibrillated cellulose was shown to be 85.1% higher than that of the pristine geopolymer after 30 days. In addition, the hybrid system was found to maintain excellent thermal stability due to the effective protection of the biomass components by the inorganic matrix. This one-step mechanochemical process provided an efficient approach for preparing geopolymer composites, which offers significant application potential for use in road repairs, high-temperature-resistant materials, and additive manufacturing via 3D printing.     

Oxidation resistance,ablation resistance and in situ ceramization mechanism of Al-coated carbon fiber/boron phenolic resin ceramizable composites modified with Ti3SiC2

Inherent defect of easy oxidation limited further application of carbon fiber/phenolic resin composites in hostile environments. Herein, a combined strategy of matrix modification and fiber coating was proposed to fabricate a novel ceramizable composite containing Al-coated carbon fibers and Ti₃SiC₂ toward thermal protection materials (TPM), which offered a promising solution to challenge facing long-term thermal protection and load-bearing subject to severe oxidation corrosion and ablation in hypersonic vehicle applications. Oxidation resistance, mechanical strength evolution, phase evolution, microstructure evolution and mechanical strength failure mechanism at elevated temperatures were studied based on thermogravimetric analysis, static ablation test, mechanical test, X-ray diffraction analysis, and scanning electron microscopy coupled with energy dispersive X-ray analysis. The resulting composites exhibited outstanding oxidation resistance, with residue yield at 1600 °C and flexural strength at 1400 °C as high as 87.7% and 31.7 MPa, respectively. It was found that dense multiphase ceramics formed by reactions between Ti₃SiC₂, O₂, pyrolytic carbon (PyC) and N₂, acted as oxygen barriers and self-healing agents during static ablation. Besides, the resulting composites exhibited satisfactory ablation resistance and the linear ablation rate was as low as 0.00853 mm/s. Furthermore, ablation mechanisms were revealed based on phase identification, microstructure characterization and thermodynamic calculation analysis. It was revealed that multiphase ceramics composed of PyC, Al coatings, Ti₃SiC₂, TiC, Al₂OC and AlB₂ contributed great to the ablation resistance during oxyacetylene ablation.     

Preparation and characterization of nanostructured biohybrid

Recently, biohybrid materials have gained considerable interests worldwide. They consist of bioresource based derivative as organic matrix in combination with inorganic components with synergistic properties of both such as environment friendliness, biodegradability, flexibility of the former coupled with hardness, UV radiation stability, thermal stability and solvent resistance of the latter. In the present work, we have prepared DGEBA/Castor oil nanostructured biohybrid with a metal alkoxide as inorganic precursor for reinforcement of the matrix. The structure, morphology, thermal behavior and coating properties of the prepared biohybrid have been studied. Our studies revealed that the said biohybrid can be safely employed up to 180 °C as nanostructured protective coating.     

贝壳的化学成分及其结构特征

以扇贝和珍珠母贝壳为研究对象,对其化学成分、微观结构以及热分解行为进行研究,结果表明,扇贝和珍珠母贝壳都是由95%左右的CaCO₃和5%左右的有机质组成。其中,扇贝的无机相几乎由100%的方解石组成,而珍珠母贝壳的无机相由4.96%的方解石和95.04%的文石组成。且两者所含有机质的成分存在很大的差异。热分析表明,热分解分为两个阶段,第一阶段为有机质的变性和分解,第二阶段为碳酸钙分解为二氧化碳和氧化钙的过程。有所不同的是,珍珠母贝壳在400~500℃出现了由文石转变为方解石的晶型转换,可为生物矿化等提供参考。     

Organic-inorganic composites for novel optical transformation induced by high-energy laser ablation

High-energy continuous-wave (CW) laser has been considered as a significant technology in recent decades. Such laser can destroy conventional materials in an extremely short time, necessitating their protection. In this study, zirconium carbide (ZrC) and silicon carbide (SiC) particle-modified short silicon carbide fiber-reinforced phenolic resin matrix composites (SiC/BPF-ZS) with significant anti-laser performance were designed and prepared. Our results showed that the ceramic particles and SiC fibers rapidly oxidized, leading to the formation of a ceramic coating composed of ZrO₂ and SiO₂. Owing to the formation of the ceramic coating, the reflectivity of the composites improved significantly from 15.8% to 73.2% after ablation at 500 W/cm² for 30 s. Additionally, the SiC fibers played an important role in the formation of a high-reflectivity coating during laser ablation. Contrast experiments indicated that SiC fibers lead to better performance than the carbon fibers. The high reflectivity and low mass ablation rate are demonstrated to be the key factors improving the anti-laser ablation performance of the SiC/BPF-ZS composites.     

用于冲压发动机补燃室热防护的硅橡胶绝热层研究

通过分析影响冲压发动机补燃室热防护层性能的因素,研究了粉状填料和纤维填料对硅橡胶绝热层耐烧蚀性能的影响和填料的组合作用;研究了硅橡胶绝热层与发动机壳体的粘接性能,将几种偶联剂对绝热层与壳体粘接性能的影响进行了对比.结果表明,通过有机填料与无机填料以及纤维的共同作用,可以显著提高硅橡胶绝热层的耐烧蚀性能,降低其烧蚀率;WD-60偶联剂可显著提高硅橡胶与钢的粘接强度.初步探索出适合于冲压发动机补燃室热防护所用的硅橡胶绝热层配方.     

无机水合盐相变材料过冷度抑制方法的研究进展

无机水合盐相变材料具有较高的相变潜热、原料易得、安全性高等优点,在未来中低温储能领域有巨大的应用潜力,但其在相变过程中易出现“过冷”与“相分离”等现象,严重影响了其热稳定性能,相关问题可通过添加成核剂、增稠剂进行解决。但无机水合盐在液态下会发生泄漏,需要将其限制在一定区域内。通过多孔材料吸附、微胶囊化等方法可以对无机水合盐相变材料进行封装,多孔材料如膨胀石墨、膨润土、泡沫金属等可以吸附无机水合盐,防止其相变过程发生泄漏。微胶囊包覆则是通过将相变材料微胶囊化封装在壳材内,常用壳材包括聚甲基丙烯酸甲酯、三聚氰胺?甲醛树脂或聚脲树脂等,此外,无机SiO2壁材也是常用的材料。通过吸附封装或者微胶囊化,可以将无机水合盐相变材料限制在一定区域内,提高无机水合盐相变材料的分散性能,降低其过冷度、改善相分离现象,进一步提高无机水合盐相变循环的热稳定性,是解决无机水合盐相变材料在相变过程中渗漏问题的有效方法。本工作综述了无机水合盐相变材料过冷、相分离问题的研究现状,总结了采用多孔材料吸附和微胶囊化抑制或解决无机水合盐过冷度的研究进展,并对今后无机水合盐储能应用研究提出了建议与展望。     

Organic–inorganic hybrid copolymer fibers and their use in silicone laminate composites

Nonwoven organic–inorganic fiber mats of poly(methyl methacrylate)‐graft‐poly(dimethyl siloxane) copolymers with various PDMS contents were produced by the electrospinning process. The average fiber diameter increased from 0.7 to 3 μm with increasing PDMS content. The fiber mats were used in the preparation of silicone‐laminated composite materials by distributing them (single, double and triple layer mats) in a silicone matrix prior to thermal curing. The composites showed a remarkably good fiber distribution in the silicone matrix. In general the stiffness and strength increased in the presence of fiber, and surprisingly, so did the toughness/extensibility. An interesting feature was that the most silicon‐rich fibers showed clear signs of yielding after tensile testing and failure. This, together with the greater compatibility of the fibers with the matrix because of the higher PDMS content, most probably favored composite toughness. All composite fracture surfaces were characterized by clear signs of fiber pull‐out. Fracture initiation areas were difficult to locate, and this is accredited to an even distribution of the individual fibers in the matrix. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Preparation and characterization of sol–gel derived UV-curable organo-silica–titania hybrid coatings

In this work, UV-curable organic–inorganic hybrid coatings based on cycloaliphatic epoxyacrylate were prepared by sol–gel technique. Acid catalyzed solutions of tetraethylorthosilane (TEOS) containing Ti:acac complex were used as an inorganic precursors. UV-curable, transparent hybrid coating materials were applied on plexiglass substrates and their coating performance was investigated by the analyses of various tests such as hardness, gloss, cross-cut adhesion tests, stress–strain test and optical transmission. The mechanical measurements showed that, the tensile properties of coatings underwent an abrupt change from a brittle to a tough material when the inorganic part was incorporated into the cycloaliphatic epoxy acrylate based organic network. UV–vis transmission spectroscopy results indicated that the hybrid materials with high titanium content have good transparences. The thermal behaviour of the coatings was also evaluated. It is observed that the thermal stability of the hybrids is enhanced with incorporation of sol–gel precursor.     

笼型倍半硅氧烷改性树脂的性能分析

笼型倍半硅氧烷是一类具有特殊分子结构的有机硅化合物。其分子的无机硅氧骨架核心为材料提供良好的耐热性,外围有机基团可增强与聚合物基体间的相容性,以它为前驱体可以得到硅氧骨架为核心的分子级有机/无机纳米杂化材料。笼型倍半硅氧烷通过共价键或共混接入聚合物中会限制分子链的运动,使高分子链的柔性降低,导致了聚合物玻璃化转变温度升高。笼型倍半硅氧烷最显著的特性是提高聚合物的热性能及阻燃性。     

Thermal ablation behavior of SiBCN-Zr composites prepared by reactive spark plasma sintering

To meet the ultrahigh temperature requirements of a thermal protection system, an ultrahigh temperature phase of ZrB₂ was introduced into a SiBCN matrix that was fabricated using a reactive spark plasma sintering method. The thermal ablation behavior of SiBCN-Zr composites was investigated using an oxyacetylene flame test. The test results indicated that the ablation behavior of the modified ceramic composites was significantly improved over that of a monolithic SiBCN ceramic. The linear and mass ablation rates of the SiBCN-Zr material were found to be 0.004 mm/s and 4.75×10⁻⁴ g/s, which was indicative of excellent ablation resistance. Analysis of the material after thermal ablation testing showed that ablation products mainly consisted of the ZrSiO₄, SiO₂ and ZrO₂ phases. A reaction occurred between the SiO₂ and ZrO₂ phases in the central region of the ceramic forming ZrSiO₄ that protected the material from further thermal damage. A loose and porous oxidation layer was found from the matrix based on analysis of a cross-section image.     

High temperature ablation of highly filled polymer‐layered silicate nanocomposites

At instantaneous thermal shocks and high temperature conditions, using the charring ablative heat shields is more effective than the other heat protection methods. In recent years, low‐filled layered silicate polymeric nanocomposites were introduced as new class of ablative materials. In this work, highly filled ablative polymeric nanocomposite is prepared and its thermal stability and ablation mechanism is studied under high external heat flux. The thermal degradation kinetics during pyrolysis, the variation of thermophysical properties as a result of ablation process and mathematical modeling of ablation process are performed for highly filled ablative polymeric nanocomposite samples compared with those of their composite counterparts under oxyacetylene flame test. The results show that the ablation performance of highly filled polymeric nanocomposite is higher than that of the composite, and the mathematical model is adequately confirmed by the experimental data of the thermophysical and ablation properties of highly filled nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Performances of novel poly(diaryloxyphosphazene) based heat shielding materials with various fibrous reinforcements

Elastomeric heat shielding materials (EHSMs) are necessary to protect combustion chambers of solid rocket motors during their working. Poly(diaryloxyphosphazene) (PDPP) elastomers own inherent thermal stability and flame retardancy because the backbone of alternating phosphorus and nitrogen atoms can be a novel promising polymer matrix toward EHSMs. The present study deals with the development of a novel PDPP based EHSMs with several different fibrous reinforcements, including Kevlar, polyimide, and carbon short fibers. It is found that PDPP/Kevlar composites show outstanding tensile strength and ablation resistance because of their strong interfacial bonding between matrix and fibers which benefits from the possible network of intermolecular hydrogen bonds. PDPP/carbon composites produce a compact charred layer due to their high char yields of carbon fibers. These results improve the understanding of the role of polyphosphazenes with different kinds of fibers on ablation mechanisms, which enable the possibility to exploit intrinsic properties of polyphosphazenes.     

Effect of Organic Gas Plasmas on the Adhesion of Matrix Resins to Carbon Fibers

IM7 carbon fibers were surface treated in methane, ethylene, trifluoromethane and tetrafluoromethane plasmas. The surface chemical composition of the fibers was determined by X-ray photoelectron spectroscopy (XPS). The adhesion between as-received and plasma-treated carbon fibers and polyethersulfone (PES) and an epoxy resin was measured by the microbond pull-out test. XPS showed that the methane and ethylene plasmas deposited a thin layer of hydrocarbon on the fiber surface. The trifluoromethane plasma deposited a layer of fluorocarbon on the surface of the fibers. The tetrafluoromethane plasma etched the fibers and introduced a significant amount of fluorine on the surface. The microbond pull-out test results indicated that an etching plasma, such as the tetrafluoromethane plasma, improved the adhesion between carbon fibers and PES. These results are consistent with earlier work performed with ammonia plasma. The adhesion is believed to be due primarily to the differential thermal shrinkage between the fiber and the matrix. It was shown that in the case of a reactive matrix such as an epoxy resin, the fiber chemical composition plays a role in the fiber-matrix adhesion. However, this chemical effect is secondary to the cleaning effect of the surface treatment.     

Dynamic mechanical behavior of vinylester matrix composites reinforced by Luffa cylindrica modified fibers

Currently, there is a demand for new engineering materials presenting a combination of strength, low density, processing easiness, and reduced costs. In this context, polymer matrix composites reinforced by natural fibers have been studied in recent years due to their ecological and economic advantages. Some fibers are still little explored in literature despite presenting a great potential as reinforcement like Luffa cylindrica. The present work aims at the preparation and characterization of a vinylester thermoset matrix composite material reinforced by fibers of the natural L. cylindrica fruit after modification treatments. In this study, extraction treatments in organic solvents, mercerization, and a quite new esterification with BTDA dianhydrides were used and the results showed that in all cases, the composite materials reinforced by Luffa fibers have showed improvements in mechanical and thermal properties compared to the vinylester matrix. As an example, 50% tensile increase was obtained for the composite reinforced by fibers esterified with benzophenone tetracarboxylic dianhydride when compared with thermoset matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Optimized ablation resistance behavior and mechanism of C/SiC composites with high thermal conductive channels

Aimed to enhance the high-temperature service performance of C/SiC composites in high-speed aircraft thermal protection system, in this article, pitch-based carbon fibers were used to construct high thermal conductive channels to improve the heat transfer capability of C/SiC composites. The results revealed that the as-prepared composites equipped with 4.7 times higher thermal conductivity than that of conventional C/SiC composites. The oxyacetylene flame ablation test confirmed that the constructed high thermal conductive channels, which quickly conducted the heat flow from the ablation center area to other areas is the main reason of as-prepared composites exhibiting a very impressive ablation resistance property. Briefly, the ablation temperature of the as-prepared composite surfaces considerably dropped by about 300°C compared with conventional C/SiC composites, while the linear ablation rate and mass ablation rate of the composites are 1.27 μm/s and 0.61 mg/s respectively, which is superior to many recent reports, demonstrating that this article provides a simple but highly effective measure to improve the ablation resistance property of C/SiC composites.     

Processing and mechanical properties of organic filler–polypropylene composites

The addition of organic fillers into thermoplastic polymers is an interesting issue, which has had growing consideration and experimentation during the last years. It can give rise to several advantages. First, the cost of these fillers is usually very low. Also, the organic fillers are biodegradable (thus contributing to an improved environmental impact), and finally, some mechanical and thermomechanical properties can be enhanced. In this study, the effect of the addition of different organic fillers on the mechanical properties and processability of an extrusion‐grade polypropylene were investigated. The organic fillers came from natural sources (wood, kenaf, and sago) and were compared to short glass fibers, a widely used inorganic filler. The organic fillers caused enhancements in the rigidity and thermomechanical resistance of the matrix in a way that was rather similar to the one observed for the inorganic filler. A reduction in impact strength was observed for both types of fillers. The use of an adhesion promoter could improve their behavior. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1906–1913, 2005     

耐高温隔热保温涂料的研究

采用有机硅树脂、空心玻璃微珠和无机纤维为主要原料制备隔热保温涂料。讨论了空心玻璃微珠的用量与种类、涂料生产工艺,以及涂料中加入无机纤维后对涂料隔热性能的影响。使用扫描电子显微镜观察保温涂料的微观形态。实验结果表明,空心玻璃微珠的适宜用量为33-36g;从保温效果及生产工艺综合考虑,型号为7032的空心玻璃微珠最佳;搅拌速度300r／min、反应时间20min时制得的涂料导热系数最小;加入硅酸铝纤维的涂料冲击强度最好。