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This investigation studied the inclusion of various additives to paraffin wax for use in a hybrid rocket motor. Some of the paraffin-based fuels were doped with various percentages of LiAlH4 (up to 10%). Addition of LiAlH4 at 10% was found to increase regression rates between 7 - 10% over baseline paraffin through tests in a gaseous oxygen hybrid rocket motor. Mass burn rates for paraffin grains with 10% LiAlH4 were also higher than those of the baseline paraffin. RDX was also cast into a paraffin sample via a novel casting process which involved dissolving RDX into dimethylformamide (DMF) solvent and then drawing a vacuum on the mixture of paraffin and RDX/DMF in order to evaporate out the DMF. It was found that although all DMF was removed, the process was not conducive to generating small RDX particles. The slow boiling generated an inhomogeneous mixture of paraffin and RDX. It is likely that superheating the DMF to cause rapid boiling would likely reduce RDX particle sizes. In addition to paraffin/LiAlH4 grains, multi-walled carbon nanotubes (MWNT) were cast in paraffin for testing in a hybrid rocket motor, and assorted samples containing a range of MWNT percentages in paraffin were imaged using SEM. The fuel samples showed good distribution of MWNT in the paraffin matrix, but the MWNT were often agglomerated, indicating that a change to the sonication and mixing processes were required to achieve better uniformity and debundled MWNT. Fuel grains with MWNT fuel grains had slightly lower regression rate, likely due to the increased thermal conductivity to the fuel subsurface, reducing the burning surface temperature.

This study focused on the influence of different filler loadings on the elongation at break and flammability properties of the PA11/FR/HNTs nanocomposites. Polyamide 11 (PA11)/flame-retardant (FR) additives/halloysite nanotubes (HNTs) nanocomposites were melt compounded via twin-screw extrusion for all the compositions. Three FR additive loadings (15, 20, and 25 wt%) and three HNTs loadings (2.5, 5, and 10 wt%) were selected. The formula with 25 % FR and 2.5 % HNT had the lowest additives content and the highest elongation at break of 10.22 % among all UL-94 V-0 rated formulas. A homogeneous dispersion of HNTs in PA11 matrix was observed by transmission electron microscopy. Differential scanning calorimeter measurements indicated that HNTs behaved as nucleating agents by accelerating the rate of crystallization, thus increasing crystallization temperature. The young’s modulus of the PA11 nanocomposites was enhanced with the addition of HNTs. Micro-scale combustion calorimeter results demonstrated that the addition of HNTs also decreased the peak heat release rate of the nanocomposites. These results indicate the effectiveness of HNTs on the mechanical, thermal, and flame-retardant performance of PA11/FR/HNTs nanocomposites.

This paper reports a new approach to enhance the through-thickness thermal conductivity of laminated carbon fabric reinforced composites by using nanoscale and microscale silver particles in combination to create heterogeneously structured continuous through-thickness thermal conducting paths. High conductivity of 6.62 W/(m K) with a 5.1 v% silver volume fraction can be achieved by incorporating these nanoscale and microscale silver particles in EWC-300X/Epon862 composite. Silver flakes were distributed within the inter-tow area, while nanoscale silver particles penetrated into the fiber tows. The combination of different sizes of silver fillers is able to effectively form continuous through-thickness conduction paths penetrating fiber tows and bridging the large inter-tow resin rich areas. Positive hybrid effects to thermal conductivity were found in IM7/EWC300X/sliver particle hybrid composites. In addition, microscale fillers in resin rich areas showed less impact on tensile performance than nanoscale particles applied directly on fiber surface.

This research encompasses the study of testing protocols and the design of sensors for evaluating the compressive strength of the char layer of ablative material used in solid rocket motors (SRMs). The testing protocol that has been developed is the continuation of previous work for determining the compressive strengths between different SRM insulation materials. A crushing test method was further developed, and a sensor platform was assembled to perform the tests. The test procedure consists of measuring the amount of force required to crush a given area of the charred sample for a specified depth. The test was repeated for the industry standard Kevlar®-filled ethylene propylene diene monomer rubber and thermoplastic polyurethane elastomer nanocomposite with different weight loading of multi-walled carbon nanotubes, montmorillonite nanoclay, and carbon nanofibers. The energy of destruction or energy dissipated was quantified to determine which ablative exhibited the best performance. Maximum force was also recorded as a secondary quantity to determine char strength. The proposed test method is fully automated to ensure repeatability of each measurement and to remove the potential for human-induced error. Because char layer thickness varies depending on the material, a method of differentiating neat material from char was proposed and explored. The introduced procedure also represents a novel and unique approach to solve the problem of the determination of the char strength. Copyright © 2014 John Wiley & Sons, Ltd.

A foamed polymer nanocomposite system is developed as an ablative for thermal protection applications. Polymer nanocomposite foams exhibit better thermal properties with the inherent benefit of being lightweight. In this study, Polyetherimide (PEI) was compounded with nanoclay to enhance the flame retardant property. A thermoplastic elastomer, Kraton, was added to improve the mechanical strain. Samples with various compositions of nanoclay and Kraton were foamed using a batch solid-state foaming process. The thermal protection performance of the material system was characterized with an oxy-acetylene flame ablation test. It is shown that foaming helped reduce the mass loss of the samples during the ablation test. The loadings of nanoclay and Kraton and the foam density can be used to optimize the thermal protection performance. The foams obtained in this study had a graded structure with an overall porosity of 20–60%.

Flame retardant polyamide 6 (nylon 6) nanocomposite nanofibers containing montmorillonite clay (MMT) platelets and intumescent non-halogenated flame retardant (FR) additives were processed by electrospinning. Different methods of mixing nano fillers before electrospinning were explored and compared. It was found that high loadings of nanoclay particles affected the electrospinnability of the nanocomposite material. Good dispersion and exfoliation of nanoclay platelets within individual nanofibers was verified by transmission electron microscopy. The degradation temperature of nanocomposite samples was lower than pristine nylon 6 samples. However the degradation of all nanocomposite formulations was overall slower. Moreover, the difference in residual char weight after decomposition was significant. Microscale combustion calorimeter results show that FR particles played a major role in reducing flammability of the material in both solution- and melt-compounded samples, while MMT nanoclay was effective in improving char residue and in reducing flammability in high-shear melt premixed samples.

Multi-wall carbon nanotubes (MWNTs) with different loadings (0, 1, 3, 5, 7 and 9 wt%) were incorporated into polyamide 11 using a powder–powder mixing technique to form nanocomposites. The density and specific heat of each nanocomposite were measured. Thermal conductivities of these polymer nanocomposite powders were measured in a nitrogen atmosphere using a commercial transient plane-source device. Results indicate the thermal conductivity of preheated powder was larger than the fresh powder and similar to that at the melting temperature. The powder formulations were also pressed into films using a heat press and room temperature electrical conductivity measurements were performed. Substantial improvements in electrical conductivity were observed with increasing loading of MWNT. Microstructures of the nanocomposite specimens were examined using scanning electron microscopy.

Summary In this work, the effect of 6 different fillers as a nanomodifier of phenolic matrix was evaluated in thermal stability and reaction to fire. The chosen nanoparticles were montmorillonite, silica, carbon black, and 3 carbides—boron, silicon, and zirconium carbides. The nanofillers were mechanically dispersed in the matrix, and the dispersion and distribution of the nanosized particles in the matrix was evaluated by transmission electron microscopy. The thermal stability of nanocomposites was investigated by thermogravimetric analysis both in nitrogen and in air while the thermal combustion properties were measured using a microscale combustion calorimeter. The experimental data highlighted the remarkable effects of nanoboron carbide on the thermal properties it can confer to the phenolic matrix. Rheological behavior of the blends was also investigated to evaluate the effect of the different fillers on the viscosity of the nanostructured matrices.

Polyamide 11 (PA11) is widely used in selective laser sintering (SLS), but it has poor thermal, electrical, and flame-retardant properties. This research introduces two types of SLS PA11 nanocomposites: one possesses enhanced thermal and electrical properties and one possesses enhanced thermal and flammability properties. PA11 was twin-screw extruded with multiwall carbon nanotubes and nanographene platelets and was cryogenically ground into SLS powders. SLS processing parameters were optimized to obtain overall material properties. The multiwall carbon nanotubes were effective at increasing the material's electrical conductivity, with minimal losses of mechanical properties. This approach was extended to study an FR SLS polymer. The results indicate that although modified PA11 shows an effectively reduced flammability, it suffers a significant loss in elongation at the break. PA11 with intumescent FR additives toughened by a maleic anhydride-modified elastomer were melt-compounded and injection molded into specimens for property characterizations. The best candidate will be used to fabricate SLS test specimens.

Antimicrobial polyamide 11 (PA-11) films containing low-cost, thermally stable and water resistant polymeric biocide polyhexamethylene guanidine dodecylbenzenesulfonate (PHMG-DBS) have been obtained by compression moulding. The structure of the modified PA-11 films containing from 3 to 10 wt% of PHMG-DBS was characterized using Raman and FTIR spectroscopy and atomic force microscopy (AFM). The surface properties were evaluated both by contact angle and contactless inductive method. The introduction of PHMG-DBS into PA-11 films was found to increase positive surface charge density to 5.5·10−11 C/cm2 for 10 wt% of PHMG-DBS. Antibacterial activity of PA-11/PHMG-DBS films against both Gram-positive (Escherichia coli) and Gram-negative (Bacillus subtilis) bacteria was demonstrated for films containing from 5 to 7 wt% of polymeric biocide. According to thermal investigations data, PA-11/PHMG-DBS composite has excellent thermal stability to at least 390 °C both in air and in argon atmosphere which indicates on its availability for the melt processing by common methods. It has also been found that polymeric biocide is highly resistant to leaching from PA-11 film.

The broader goal of this research is to develop a commercially viable material system and manufacturing method to mass produce functional parts using selective laser sintering, a rapid manufacturing method, for electrostatic charge dissipation applications. The specific objective of this research is to produce and characterize polyamide 11/ nanographene platelets nanocomposites that have improved electrical conductivity for electrostatic charge dissipation applications and better thermal stability to be used in selective laser sintering manufacturing. Polyamide 11 and nanographene platelets were blended using industry size co-rotating twin-screw extrusion. Four batches were prepared containing 1 wt%, 3 wt%, 5 wt% and 7 wt% of nanographene platelets. Microsctrucre of nanocompoistes was studied using scanning electron microscopy. Thermal characterization of nanocomposites was conducted using thermogravimetric analysis at three heating rates 5, 20, 40℃/min. Electrical resistivity was measured using the Hioki Megaohmmeter Instrument four probe method. Mechanical characterization includes tensile, flexure, and Izod-impact properties. Flammability property was measured using UL94 test.

The objective of this study is to evaluate thermal properties of polyamide 11 (PA11)/nanographene platelet (NGP) nanocomposites. Samples were prepared using 1 wt%, 3 wt%, and 5 wt% of NGPs. Isopropyl alcohol (IPA) was used as a solvent to assist in dispersion of the NGPs within the PA11 powder. The NGPs were hand mixed evenly into the PA11 powder using a wooden dowel. Morphological characterization of the PA11/NGP nanocomposite was conducted using scanning electron microscopy. Thermal characterization of nanocomposites includes thermogravimetric analysis, differential scanning calorimetry and thermomechanical analysis. Results indicate that the addition of NGPs shows an initial increase in thermal stability and crystallization temperature (T(c)) along with a decrease in glass transition temperature (T(g)) and no improvement in coefficient of thermal expansion (alpha). These results are attributed to improved interfacial adhesion between NGPs and PA11, restricting polymer chain mobility.

A new class of thermal protection materials based on a novel organic silicone polymer system, referred to generically as SM8000, was investigated. The composite material undergoes “ceramitization” on exposure to elevated temperatures under solid rocket exhaust plumes. SM8000 converts in situ to an oxidative resistant ceramic material at elevated temperatures. The remaining char forms a tough, abrasion-resistant surface. This paper summarizes the four year research anddevelopment program in refining, testing, anddeveloping this class of silicone polymer matrix composites as thermal protection materials. Composite design, specifically resin and reinforcement selection, composite geometry, ablation testing method development, as well as both prepreg and laminate manufacturing scale-up issues, were considered as an integral part of this research program. Thermal performance of this new class of silicone-based matrix composites exceeds the performance of the conventional phenolic-based matrix composites. A silicone quartz composite and process were developed that could provide a high-quality, flat, uniformpanelmeasuring 2.44 by 1.22mby9.53mm.SM8000 offers one of the best alternative polymer systems to the phenolic system that has been in use for the last 40 years.

Polyamide (nylon) 11 (PA11) were melt-blended by dispersing low concentrations of nanoparticles (NPs), namely nanoclays (NCs) and carbon nanofibers (CNFs) via twin-screw extrusion. To enhance their thermal and flame retardant (FR) properties, an intumescent FR additive was added to the mechanically superior NC and CNF PA11 formulations. For neat and NP-reinforced PA11 as well as for PA11 reinforced by both intumescent FR and select NPs (NC or CNF), decomposition temperatures by TGA, flammability properties by UL 94, and cone calorimetry values were measured. All PA11 polymer systems infused with both NPs and FR additive had higher decomposition temperatures than those infused with solely FR additive. For the PA11/FR/NC polymer blends, Exolit® OP 1312 (FR2) is the preferred FR additive to pass the UL 94 V-0 requirement with 20 wt%. For the PA11/FR/CNF formulations, all Exolit® OP 1311 (FR1), OP 1312 (FR2), and OP 1230 (FR3) FR additives passed the UL 94 V-0 requirement with 20 wt%.

Phenolic resin was modified using nanoclay to improve flammability/thermal properties. High-shear and planetary centrifugal (PC) mixing techniques were used to blend nanoclay into phenolic. This was followed by vacuum-assisted resin transfer molding to manufacture glass-reinforced nanocomposites. Loadings of 2.5, 5.0, and 7.5 wt% of nanoclay were processed using both techniques. The degree of dispersion was analyzed using scanning electron microscope and transmission electron microscope. Flammability/thermal property was evaluated using mass loss calorimeter. Mechanical properties such as flexural strength and modulus, compressive strength, interlaminar shear strength, and tensile strength and modulus were evaluated. It is concluded that the cost-effective PC mixing technique can be used in manufacturing nanocomposites to enhance flammability/thermal property without sacrificing mechanical properties.

This study summarizes our current research in using different types of nanographene platelets (NGPs) to create polymer–graphene nanocomposites for selective laser sintering manufacturing application. This article describes five NGPs that were available to our research group. Morphological characterization of their microstructures was examined using scanning electron microscopy. Thermal characterization of these NGPs was conducted using thermogravimetric analysis. Kinetics of these NGPs was calculated using the isoconversion technique. Similarities and differences of these NGPs were drawn from the above measurements and calculations. Two NGPs were selected for further studies.

A new class of silicone polymer matrix composites was evaluated using a simulated solid rocket motor test apparatus. Conversion of this organic silicone polymer to a ceramic (i.e. silica) structure on exposure to flame impingement or high temperature, accounts for its outstanding thermal stability. A research program was aimed to develop and evaluate this new class of thermal protection materials for military applications. This article presents the effects of the type and form of reinforcements on the thermal performance of a novel class of silicone polymer matrix composites. Reinforcement types such as glass, silica, quartz, NextelTM, and NicalonTM were used. Reinforcement forms such as random continuous-fiber mat, chopped-fiber mat, 2-D fabric, 3-D fabric, chopped roving, and broadgood tapes with different ply angles were tested. Detailed microstructural, mass loss, and peak erosion analyses were conducted on the phenolic-based matrix composite (control) and silicone-based matrix composites to understand their protective mechanisms.

The objective of this study is to develop improved polyamide (nylon) 11 (PA11) and 12 (PA12) polymers with enhanced flame retardancy, thermal, and mechanical properties for selective laser sintering rapid manufacturing. PA11 and PA12 were melt-blended, dispersing low concentrations of nanoparticles, namely nanoclays (NCs), carbon nanofibers (CNFs), and nanosilicas (NSs) via twin-screw extrusion. To enhance their thermal and flammability properties, an intumescent flame retardant (FR) was added to the mechanically superior NC and CNF PA11 formulations. NC or CNF additions to either PA11 or PA12 generally increased its tensile strength and modulus, but sharply reduced its elongation at rupture. FR additives reduced PA11’s properties considerably. This substitution, however, only exacerbated the already steep drop in elongation at rupture due to FR additives alone; while elongation dropped 58% with the addition of 30 wt% FR, it dropped 98% with the addition of 25 wt% FR/5 wt% CNF.

The thermal insulation properties of thermoplastic polyurethane elastomer nanocomposites were characterized at different heat fluxes. Thermoplastic polyurethane elastomer was modified with different loadings of montmorillonite nanoclays and carbon nanofibers (CNFs) via twin screw extrusion processing. The addition of nanoparticle into thermoplastic polyurethane elastomer resulted in the formation of a char layer and modified the thermal insulative properties of the material. It was found that thermoplastic polyurethane elastomer with 10 wt% CNFs and with 5 wt% nanoclays gave the best thermal performance with respect to protecting a substrate. The surface temperature of the thermoplastic polyurethane elastomer-clay nanocomposites did not vary much with addition of clay particles while the surface temperature of the thermoplastic polyurethane elastomer-CNF nanocomposites varied more substantially. Some of the trends in surface and substrate temperature measurements with nanomodification can be described using a simple energy balance model that takes into account the basic heat transfer mechanisms.

Polyamide (nylon) 11 (PA11) and 12 (PA12) were melt-blended, dispersing low concentrations of nanoparticles, namely nanoclays (NCs), carbon nanofibers (CNFs), and nanosilicas (NSs) via twin-screw extrusion. To enhance their thermal and flame-retardant (FR) properties, an intumescent FR additive was added to the mechanically superior NC and CNF PA11 formulations. For neat and nanoparticle-reinforced PA11 and PA12, as well as for PA11 reinforced by both intumescent FR and select nanoparticles (NC or CNF), decomposition and heat deflection temperatures were measured, as were the peak heat release rates while burning the composites. All PA11 polymer systems infused with both nanoparticles and FR additive had higher decomposition temperatures than those infused with solely FR additive. For the PA11/FR/NC polymer blends, only the 20 wt% FR and 7.5 wt% clay formulation passed the UL 94 V-0 requirement, while all PA11/FR/ CNF formulations passed UL 94 V-0 requirement.

A comparison of different model forms for non-oxidative thermoplastic degradation rate is presented. A physically meaningful model is derived from a three-step radical depolymerization mechanism. A moment-based approximation to the population balance equations is derived and implemented to predict the thermal degradation of polyethylene (PE) and poly(methyl methacrylate) (PMMA). In the absence of accurate molecular dynamical calculations to predict the controlling model parameters, it is necessary to use experimental data to find the best fit parameter values. A sequential quadratic programming algorithm (SQP) was used to find the set of parameters that minimized the error between the model and sets of non-isothermal thermogravimetric (TG) data at different heating rates for PE and PMMA.

Thermal protection materials are required to protect structural components of space vehicles during the reentry stage, missile launching systems, and solid rocket motors. Novel materials based on nanotechnology creating nontraditional ablators are rapidly changing the technology base for thermal protection systems. In this study, different polymer nanocomposite compositions were created by melt-compounded montmorillonite nanoclays or carbon nanofibers in a neat thermoplastic polyurethane elastomer polymer using twin-screw extrusion. The kinetic and thermophysical properties that are required to analyze the ablation characteristics were measured for selective thermoplastic polyurethane materials. Properties of the nanomodified systems were then compared against those of the current state-of-the-art insulation material, Kevlar®-filled ethylene-propylene-diene monomer and the neat thermoplastic polyurethane elastomer, for the investigation of kinetic parameters using the isoconversion technique. Based on temperatures at peak weight-loss rate, Kevlar-filled ethylene-propylene-diene monomer outranked the proposed formulations at all heating rates. Recognizing that ablation performance is a complex function of kinetic and thermophysical/transport properties, a surrogate test for ablation performance was investigated. Samples of neat and nanomodified thermoplastic elastomer were run in an oxygen-consumption (cone) calorimeter. The peak heat release rates of the nanomodified samples were substantially less than that of the neat thermoplastic elastomer.

As the performance of polymer layered silicate nanocomposites strongly depends on their interior layer dispersion, quantification of the layer dispersion degree is needed. In this work, a new methodology was developed to determine the dispersion parameter D0.1, based on the measurement of the free-path spacing distance between the single clay sheets from the transmission electron microscopy (TEM) images. Several examples of exfoliated, intercalated, and immiscible composites were studied. It was found that the exfoliated composites had D0.1 over 8%, while that of intercalated composites were between 4 and 8%. In the case of intercalation, a high frequency peak appeared at a short spacing distance in the histogram, which was a characteristic of the intercalation, distinct from the exfoliation. The main utility of this TEM methodology is for the quantification of exfoliated or intercalated samples with small number of layers with stacks. The dispersion parameter D0.1 below 4% was suggested to classify as immiscible. A unique advantage of the TEM measurement is that the dispersion degree of different fillers can be counted individually.

Ablatives are a compelling class of materials for thermal protection systems (TPS) in aerospace and defense applications because they demonstrate unique resilience in hyperthermal environments. An Oxy-acetylene Test Bed (OTB) was used to burn ablative samples under application of controlled heat flux. During the application of up to 1000 W/cm heat flux, high-definition (HD) optical video and infrared (IR) video were captured simultaneously to observe surface changes in morphology and temperature, respectively. In these conditions, videos were recorded of heat shielding materials PICA and Avcoat, provided by NASA. Digitally rendered videos were analyzed in post-processing to obtain meaningful measurements of material properties. In previous experiments, video-based techniques for measuring ablation recession rates of these materials were attempted. In this paper, a controlled comparison of data obtained from optical high-definition video and in-situ thermocouple data is presented. In addition, the limitations and sources of error for measuring recession with infrared video capabilities are discussed and calibrations are proposed.

The introduction of inorganic nanomaterials as additives into polymer systems has resulted in polymer nanostructured materials exhibiting a multiplicity of high performance characteristics beyond what traditional polymer composites possess. These “multifunctional” features attributable to polymer nanocomposites consist of improved thermal resistance and flame resistance, moisture and chemical resistance, decreased permeability, charge dissipation and conductivity. Through control/alteration of the additive at the nanoscale level, one is able to maximize property enhancement of selected polymer systems to meet or exceed the requirements of current commercial, military, and aerospace applications. The technical approach involves the introduction of nanoparticles into selected polymer matrix systems whereby nanoparticles may be surface-treated to provide hydrophobic characteristics and enhanced inclusion into the hydrophobic polymer matrix. The objectives of this paper are to summarize our current research efforts in the use of polymer nanostructured materials for high temperature applications such as rocket nozzle ablative materials, carbon/carbon composites, and damage tolerant high performance epoxy carbon fiber reinforced composite systems.