EPDM based heat shielding materials for Solid Rocket Motors: A comparative study of different fibrous reinforcements

EPDM/aramid ablatives represent the state of the art heat shielding materials for Solid Rocket Motors. Due to their mechanical properties and excellent thermal stability, aramid fibers or pulp constitute the common reinforcement of EPDM based liners. New generation organic fibers were recently tested as a potential replacement of aramid. In this study, Kynol fiber, a phenolic based reinforcement with high mechanical and thermal properties, was evaluated on this class of ablatives: to date, there are no data available on the use of Kynol fibers in EPDM based ablatives. At the same time, silica fibers which are traditionally used on other classes of ablatives, were also tested: in fact, the use of this type of reinforcement is not well documented on EPDM ablatives. It was found that EPDM/Kynol composition produced the char with the smaller dimensional change and the higher adhesion on the virgin material. EPDM/aramid exhibited the higher insulation properties. At the studied fiber percentage, EPDM/silica showed the worst behavior than the other formulations. The obtained data improved the comprehension of the role of the different fibers on the ablation mechanism of this class of ablatives, thus enabling the possibility to exploit their intrinsic properties.     

Studies on the properties of EPDM–CSE blend containing HTPB for case‐bonded solid rocket motor insulation

Elastomeric blends based on ethylene propylene diene (EPDM) rubber as a primary polymer have been investigated for the thermal insulation of case‐bonded solid rocket motors (SRMs) cast with composite propellant containing hydroxy terminated polybutadiene (HTPB) as a polymeric binder. EPDM rubber found as an attractive candidate for the thermal insulation of case‐bonded SRM due to the advantages such as low specific gravity, improved ageing properties, and longer shelf life. In spite of these advantages, EPDM, a non‐polar rubber, lacks sufficient bonding with the propellant matrix. Bonding properties are found to improve when EPDM is blended with other polar rubbers like polychloroprene, chlorosulphonated polyethylene (CSE), etc. This type of polar polymer when blended with EPDM rubber enhances the insulator‐to‐propellant interface bonding. In the present work, an attempt has been made to study the properties of EPDM–CSE based insulator by incorporating HTPB, a polar polymer as well as a polymeric binder, as an additive to the EPDM–CSE blend by varying the HTPB concentration. Blends prepared were cured and characterized for rheological, mechanical, interface, and thermal properties to study the effect of HTPB addition. This paper reports the preliminary investigation of the properties of EPDM–CSE blend containing HTPB, as a novel and futuristic elastomeric insulation for case‐bonded SRM containing HTPB as propellant binder. Copyright © 2007 John Wiley & Sons, Ltd.     

The role of thiophosphoryl disulfide on the co‐cure of CR‐EPDM blends: effect of white fillers

Bis(diisopropyl) thiophosphoryl disulfide (DIPDIS) being a rubber accelerator has a definite role as a coupling agent in the silica filled polychloroprene rubber with ethylene propylene diene rubber (CR‐EPDM) blends. Diethylene glycol can further improve the beneficial effect of DIPDIS in silica filled CR‐EPDM blends. Two‐stage vulcanization technique further improves the physical properties of silica filled CR‐EPDM blends. The results have been compared with non‐reinforcing calcium carbonate filled systems. Scanning electron microscopy (SEM) studies further indicate the coherency and homogeneity in the silica filled CR‐EPDM blend vulcanizates obtained from this two‐stage process. Copyright © 2004 John Wiley & Sons, Ltd.     

Plasma polymerization of acetylene onto silica: an approach to control the distribution of silica in single elastomers and immiscible blends

Surface modification of silica by acetylene plasma polymerization is applied in order to improve the dispersion in and compatibility with single rubbers and their blends. Silica, used as a reinforcing filler for elastomers, is coated with a polyacetylene (PA) film under vacuum conditions. Water penetration measurements show a change in surface energy due to the PA‐film deposition. The weight loss measured by thermo‐gravimetric analysis (TGA) is higher for the PA‐coated silica compared to the untreated filler, confirming the deposition of the PA film on the silica surface. Time of flight‐secondary ion mass spectrometry (ToF‐SIMS) shows the well‐defined PA cluster peaks in the high mass region. Scanning electron microscopy (SEM) measurements show silica aggregates, coalesced by the coating with smooth and uniform surfaces, but without significant change in specific surface area. Elemental analysis by energy dispersive X‐ray spectroscopy (EDX) measurements also confirms the deposition of the polymeric film on the silica surface, as the carbon content is increased. The performance of single polymers and their incompatible blends based on S‐SBR and EPDM, filled with untreated, PA‐ and silane‐treated silica, is investigated by measurements of the bound rubber content, weight loss related to bound rubber, cure kinetics, reinforcement parameter, Payne effect, and mechanical properties. The PA‐ and silane‐modified silica‐filled pure S‐SBR and EPDM samples show a lower filler–filler networking compared to the unmodified silica‐filled elastomers. Decrease in the reinforcement parameter (α_F) for the plasma‐polymerized silica‐filled samples also proves a better dispersion compared to silane‐modified and untreated silica‐filled samples. On the other hand, the PA‐silica‐filled samples show a higher bound rubber content due to stronger filler–polymer interactions. Finally, the PA‐silica‐filled pure EPDM and S‐SBR/EPDM blends show high tensile strength and elongation at break values, considered to be the result of best dispersion and compatibilization with EPDM. Copyright © 2008 John Wiley & Sons, Ltd.     

Use of the TMA film tension technique for differentiating polymeric materials in the Space Shuttle program

During the recent processing of a forward segment of the Reusable Solid Rocket Motor (RSRM) for the Space Shuttle, the topcoat white paint turned light brown after autoclave cure of the case insulation. Thermomechanical analysis (TMA) in the film tension mode produced modulusvs. temperature data that helped to explain why a certain insulation vacuum bagging material contributed to the brown paint color. TMA film tension data was also obtained on lab-created white and brown topcoat paint samples (with and without primer). The brown/white ratios of moduli were about 2/1 and 4/1 for topcoat/primer and topcoat only samples, respectively, from 25 to 55C.     

硅藻土增强橡胶复合材料的研究进展

硅藻土是单细胞硅藻的遗骸经自然条件形成的硅质沉积岩,因其具有质轻、大的比表面积、超强的吸附性、隔音、耐磨、耐热以及耐腐蚀等特点而被广泛应用于化工、石油、建材、生物医药卫生以及环保等众多领域。然而由于硅藻土与白炭黑的结构成分相似,白炭黑通常用作橡胶的补强填料,目前硅藻土用于橡胶补强填料的研究鲜少报道。本文综述了硅藻土的性能、硅藻土的国内外研究现状、硅藻土的改性以及硅藻土增强橡胶复合材料的制备过程,并对硅藻土增强橡胶复合材料的发展趋势做了展望。     

Preparation of nanoalumina/EPDM composites with good performance in thermal conductivity and mechanical properties

In this paper, nanoalumina (Al₂O₃) highly filled ethylene propylene diene monomer (EPDM) composites are prepared, and the mechanical (static and dynamic) properties and thermal conductivity are investigated systemically through various characterization methods. Furthermore, influences of in situ modification (mixing operation assisted by silane at high temperature for a certain time) with the silane‐coupling agent bis‐(3‐triethoxy silylpropyl)‐tetrasulfide (Si69) and stearic acid (SA) pretreatment on the nano‐Al₂O₃ filled composites are as well investigated. The results indicate that nano‐Al₂O₃ particles can not only perform well in reinforcing EPDM, but also improve the thermal conductivity significantly. Assisted by in situ modification with Si69, the mechanical properties (especially dynamic mechanical properties) of the nano‐Al₂O₃ filled composites are improved obviously, without influencing the thermal conductivity. By comparing to the traditional reinforcing fillers, such as carbon black (grade N330) and silica, in situ modified nano‐Al₂O₃ filled composites exhibit excellent performance in mechanical (static and dynamic) properties as well as better thermal conductivity, especially lower compression heat build‐up and better fatigue resistance. In general, our work indicates that nano‐Al₂O₃, as the novel thermal conductive reinforcing filler, is suitable to prepare rubber products serving in dynamic conditions, with the longer expected service life. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of the placement of aerogel insulation in the heat transfer properties

Nowadays, the thermal insulation both of existing and new buildings is one of the most important actions for reducing the energy loss of buildings and to reduce the emission of green house gases. In the European Union, buildings account for about 20–40% of the total final energy consumption. Examination of the thermal properties (e.g., effective thermal conductivity) of building materials and structures are very important both for the manufacturers and for the consumers. Several possibilities are available for measuring this parameter of materials. The mainly used thermal insulating materials are the plastic foamy and mineral wool materials; moreover, the nanotechnological insulators (e.g., aerogel, hollow nanospheres) are requiring spaces for themselves also. One promising them for the future is the silica aerogel-based slabs. Aerogels are nanoporous lightweight materials that were discovered more than 70 years ago. Nowadays, their applications are truly widespread. Firstly, in this article thermal transmittance measurements of wall structures will be presented with calibrated chamber method. These measurements were accomplished through an inbuilt plaster/brick/plaster wall construction individually. After that, it was covered with a 0.013-m-thick aerogel layer at first in a cold and then in the warm side. Comparison of the heat fluxes, insulation capabilities and effective thermal conductivities measured by the above-mentioned method will be presented. The change in the retardation time and in the surface temperatures will be also discussed. Secondly, in order to investigate the conductive effect, thermal conductivity measurements with Holometrix lambda 2000 apparatus were accomplished too.

     

Polyurea based aerogel for a high performance thermal insulation material

Less fragile lightweight nanostructured polyurea based organic aerogels were prepared via a simple sol–gel processing and supercritical drying method. The uniform polyurea wet gels were first prepared at room temperature and atmospheric pressure by reacting different isocyanates with polyamines using a tertiary amine (triethylamine) catalyst. Gelation kinetics, uniformity of wet gel, and properties of aerogel products were significantly affected by both target density (i.e., solid content) and equivalent weight (EW) ratio of the isocyanate resin and polyamine hardener. A supercritical carbon dioxide (CO₂) drying method was used to extract solvent from wet polyurea gels to afford nanoporous aerogels. The thermal conductivity values of polyurea based aerogel were measured at pressures from ambient to 0.075 torr and at temperatures from room temperature to −120 °C under a pressure of 8 torr. The polyurea based aerogel samples demonstrated high porosities, low thermal conductivity values, hydrophobicity properties, relatively high thermal decomposition temperature (~270 °C) and low degassing property and were less dusty than silica aerogels. We found that the low thermal conductivities of polyurea based aerogels were associated with their small pore sizes. These polyurea based aerogels are very promising candidates for cryogenic insulation applications and as a thermal insulation component of spacesuits.     

Ethylene propylene diene monomer rubber‐based heat shielding materials for solid rocket motor: Impact of Kevlar fiber reinforcement on the thermal and mechanical properties

This work scrutinizes the utilization of ethylene propylene diene monomer rubber matrix (EPDM) with an embodiment of aramid fiber for the heat shielding applications in solid rocket motor (SRM). Aramid fibers are aromatic poly‐paraphenylene terephthalamide, here deployed are Kevlar fibers (KF). However, the literature that encompasses the thermal and mechanical behavior with the fiber loading is reported nowhere else. The effect of fiber addition on the surface morphology and density was thoroughly studied, and it revealed that the EHSMs were of lower density to act as an efficient payload for the SRM. In this regard, the thermal conductivity, heat capacity, thermal diffusivity, fire behavior, and mechanical properties of the EPDM/KF‐based EHSMs were explored. The results revealed that the EHSMs are thermally insulating and thermally stable material with balanced mechanical properties that can engender the thermal and mechanical strains of the rocket motor. Furthermore, other analytical techniques such as scanning electron microscopy and energy dispersive X‐ray spectroscopy have been exploited to monitor the performance of the char residues of the EHSM to delineate its performance in the fire atmosphere.     

Comparative study on the effect of partial replacement of silica or calcium carbonate by bentonite on the properties of EPDM composites

The effects of the partial replacement of silica or calcium carbonate (CaCO₃) by bentonite (Bt) on the curing behaviour, tensile and dynamic mechanical properties and morphological characteristics of ethylene propylene diene monomer (EPDM) composites were studied. EPDM/silica/Bt and EPDM/CaCO₃/Bt composites containing five different EPDM/filler/Bt loadings (i.e., 100/30/0, 100/25/5, 100/15/15, 100/5/25 and 100/0/30 parts per hundred rubber (phr)) were prepared using a laboratory scale two-roll mill. Results show that the optimum cure (t₉₀) and scorch (t_S2) time decreased, while the cure rate index (CRI) increased for both composites with increasing Bt loading. The tensile properties of EPDM/CaCO₃/Bt composites increased with the replacement of CaCO₃ by Bt from 0 to 30 phr of Bt. For EPDM/silica/Bt composites, the maximum tensile strength and E_b were obtained at a Bt loading of 15 phr, with enhanced tensile modulus on further increase of Bt loading. The dynamic mechanical studies revealed a strong rubber-filler interaction with increasing Bt loading in both composites, which is manifested by the lowering of tan δ at the glass transition temperature (Tg) for EPDM/CaCO₃/Bt composites and tan δ at 40 °C for EPDM/silica/Bt composites. Scanning electron microscopy (SEM) micrographs proved that incorporation of 15 phr Bt improves the dispersion of silica and enhances the interaction between silica and the EPDM matrix.     

A numerical analysis of heat transfer in an evacuated flexible multilayer insulation material

In this article, the theoretical heat transfer of flexible multilayer insulation material which can be used in high (<433 K) and low temperature (>123 K) environments has been analyzed. A mathematical model has been developed to describe the heat flux through flexible multilayer insulation material, where the heat transfer consists of thermal radiation, solid spacers and gas heat transfer. The equations for heat transfer model have been solved by iterative method combining with dichotomy method using Matlab. Comparison between the experimental results and the calculated values which are obtained from the model shows that the model is feasible to be applied in practical estimation. The investigation on the flexible multilayer thermal insulation material will present active instruction to improve the performance and accomplish optimum design of the material.     

Optimization of electron beam crosslinking of wire and cable insulation

The computer simulations based on Monte Carlo (MC) method and the ModeCEB software were carried out in connection with electron beam (EB) radiation set-up for crosslinking of electric wire and cable insulation. The theoretical predictions for absorbed dose distribution in irradiated electric insulation induced by scanned EB were compared to the experimental results of irradiation that was carried out in the experimental set-up based on ILU 6 electron accelerator with electron energy 0.5–2.0 MeV.The computer simulation of the dose distributions in two-sided irradiation system by a scanned electron beam in multilayer circular objects was performed for various process parameters, namely electric wire and cable geometry (thickness of insulation layers and copper wire diameter), type of polymer insulation, electron energy, energy spread and geometry of electron beam, electric wire and cable layout in irradiation zone. The geometry of electron beam distribution in the irradiation zone was measured using CTA and PVC foil dosimeters for available electron energy range. The temperature rise of the irradiated electric wire and irradiation homogeneity were evaluated for different experimental conditions to optimize technological process parameters. The results of computer simulation are consistent with the experimental data of dose distribution evaluated by gel-fraction measurements. Such conformity indicates that ModeCEB computer simulation is reliable and sufficient for optimization absorbed dose distribution in the multi-layer circular objects irradiated with scanned electron beams.     

Lightweight lignocellulosic foams for thermal insulation

Foams are mainly composed of dispersed gas trapped in a liquid or solid phase making them lightweight and thermally insulating materials. Additionally, they are applicable for large surfaces, which makes them attractive for thermal insulation. State-of-the-art thermally insulating foams are made of synthetic polymeric materials such as polystyrene. This work focuses on generating foam from surfactants and renewable lignocellulosic materials for thermally insulating stealth material. The effect of two surfactants (sodium dodecyl sulphate (SDS) and polysorbate (T80)), two cellulosic materials (bleached pulp and nanocellulose), and lignin on the foaming and stability of foam was investigated using experimental design and response surface methodology. The volume-optimized foams determined using experimental design were further studied with optical microscopy and infrared imaging. The results of experimental design, bubble structure of foams, and observations of their thermal conductivity showed that bleached pulp foam made using SDS as surfactant produced the highest foam volume, best stability, and good thermal insulation. Lignin did not improve the foaming or thermal insulation properties of the foam, but it was found to improve the structural stability of foam and brought natural brown color to the foam. Both wet and dry lignocellulosic foams provided thermal insulation comparable to dry polystyrene foam.

Graphical abstract

     

Fabrication of silk fibroin film with properties of thermal insulation and temperature monitoring

Silk fibroin exhibits excellent mechanical properties, good biocompatibility, and biodegradability combined with benign processing conditions, attracting considerable research interest for the application as biomedical materials. Among the diverse forms of sponges, hydrogels, films, and mats manufactured from silk fibroin, films are especially appealing due to the high water and oxygen permeability, good cell attachment, and low immunogenicity. Fabrication of silk fibroin films with novel properties has been successfully developed simply by incorporating various functional components into it. In the present study, the properties of thermal insulation and temperature monitoring for the silk fibroin film are demonstrated for the first time through the incorporation of thermochromic microcapsules within it. Moreover, the silk fibroin film is also endowed with improved mechanical properties in terms of tension strength and elongation at break because of the reinforcing effect of thermochromic microcapsules. The silk fibroin film fabricated with novel features in this study can be a good candidate for the application of wound dressings, tissue engineering scaffolds, and bio‐related devices in the future. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1846–1852     

Electrical insulation performance of flame retardant fillers filled with polypropylene/ethylene propylene diene monomer composites

Flame retardant fillers composed of zinc hydroxy stannate (ZHS), calcium borates (CaB), and NP‐100 were embedded separately in 50% polypropylene (PP) and 50% ethylene propylene diene monomer (EPDM) blends. Several formulations containing flame retardant fillers, PP, and EPDM were prepared using an internal mixer and were molded in a compression mold to form test samples. The effects of filler loading (15, 30, 45, and 60 vol%) on the dielectric breakdown strength and contact angle were determined. It was found that PP/EPDM/NP‐100 has higher breakdown strength than PP/EPDM/ZHS and PP/EPDM/CaB. The contact angle of PP/EPDM/NP‐100 and PP/EPDM/ZHS showed an ascending order with filler loading, implying an increase in hydrophobicity. With regard to the PP/EPDM/CaB system, the contact angle showed an ascending order up to 30 vol% followed by a descending order at 45–60 vol%. Water absorption studies indicated that PP/EPDM/NP‐100 has lower water absorption compared with PP/EPDM/ZHS and PP/EPDM/CaB. PP/EPDM filled with 15 vol% NP‐100 was found to exhibit interesting insulating properties in comparison with other composite systems, thanks to high breakdown voltage, good hydrophobicity, and low water absorption. Copyright © 2014 John Wiley & Sons, Ltd.     

Aerogel: Space exploration applications

The unique physical properties of aerogel have proven to be enabling to a variety of both flight and proposed space exploration missions. The extremely low density and highly porous nature of aerogel makes it suitable for stopping high velocity particles, as a highly efficient thermal barrier, and as a porous medium for the containment of cryogenic fluids. The use of silica aerogel as a hypervelocity particle capture and return media for the Stardust Mission has drawn the attention of many in the space exploration community. Aerogel is currently being used as the thermal insulation material in the 2003 Mars Exploration Rovers. The SCIM (Sample Collection for the Investigation of Mars) and the STEP (Satellite Test of the Equivalence Principle) Missions are both proposed space exploration missions, in which, the use of aerogel is critical to their overall design and success. Composite materials comprised of silica aerogel and oxide powders are under development for use in a new generation of thermoelectric devices that are planned for use in many future space exploration mission designs. Work is currently ongoing in the development and production of non-silicate and composite aerogels to extend the range of useful applications envisioned for aerogel in future space exploration projects.     

Sorption of cesium on composite sorbents based on nickel ferrocyanide

Composite sorbents based on potassium nickel ferrocyanide embedded in silica gel matrix were prepared and characterised by powdered X-ray diffraction analysis, IR spectra, Mössbauer spectra and electron microscopy. The sorbent exhibits very good efficiency for cesium uptake and radiation resistance. The sorption capacity for cesium ions is comparable with the capacity for the pure ferrocyanides.     

Understanding rice hull ash as fillers in polymers: A review

The polymer industry has a newfound interest in fillers from industrial by-products and other waste materials having potential recyclability. This new class of fillers includes fillers from natural sources (e.g., natural fibers), industrial by-products (e.g., saw dust, rice husks) and a recent entry in the form of silica ash – an industrial waste material –obtained by burning rice husks. Rice hulls possess an unusually high percentage of `opaline silica'. Its annual worldwide output is more than 80 million tons, which corresponds to 3.2 million tons of silica. Silanol groups present on the surface of rice hull ash can positively influence its reinforcing character ash as a filler, however, being hydrophilic, it suffers fromfiller-aggregation and moisture absorption. Present article reviews the performance of rice husk ash, or silica ash, in polymeric composites. This paper emphasizes the need for better characterization of silica ash to obtain an in-depth understanding of its behaviour with the view to identifying suitable modifications to improve its performance as a filler. It is emphasized that poor understanding of silica ash as a filler is linked to the lack of surface characterization, since its behaviour is significantly linked to its surface properties. Based on this analysis, a new approach to silica ash modification is proposed.     

Ablation characteristics of silicone insulation

Ablation characteristics of silicone insulation were examined in an induced air combustion chamber and by thermogravimetric analysis. The rate of ablation increased with the combustion pressure. Although the flame temperature was less effective in increasing the ablation rate, the ablation rate below 1160 K was much smaller than expected. The decomposition kinetics of the silicone insulation was significantly altered at this temperature range. The stability of the char layer was much higher below approximately 1000 K. Since the lower ablation rate was obtained in higher mass flow rate condition, the heat input from the boundary layer to the insulation surface was decreased at this condition. The expended insulation consisted of a virgin zone, reaction zone, and char layer. These degraded materials were generated at relatively narrow temperature ranges. The char layer maintained a silicone backbone structure even though it experienced severe conditions. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 233–239, 1998