Development of Asbestos-free and Environment-Friendly Thermal Protection for Aerospace Application

Abstract

Thermal protection systems (TPS) are components designed to protect the internal and external areas of a rocket motor from high temperatures. There has been studies in Brazil of resin-based polybutadiene hydroxylated (HTPB) loaded with asbestos since the 1970s. Nevertheless, asbestos has been banned in several countries because it is severely harmful to the human health. In this context, the development of asbestos free in flexible thermal protection (FTP) is extremely important. This study evaluates the use of Expanded Perlite (PExp) as an asbestos substitute. Lower densities were observed, which become a very interesting achievement for the aerospace field. Samples with 5 phr of Expanded Perlite showed similar results when comparing with 47 phr of fillers in PTF reference on oxy-acetylene torch test, and a reduction about 20 % of mass loss rate in test with solid propellant, thus showing that Expanded Perlite can replace asbestos in FTP.

Keywords:
asbestos replacement; expanded perlite; polybutadiene hydroxylated; thermal protection

1. Introduction

Rocket structures suffer extreme internal and external heating during operation. The temperature can achieve 3000 ºC in the combustion chamber, near the nozzle region. Thus, it is a critical subject in space programs. To overcome this crucial situation, Thermal Protection Systems (TPS) are designed to reduce the temperature and heat flow by ablation during propellant combustion or reentry^1-9.

In general, there are two groups of TPS: rigid TPS and flexible TPS. Rigid TPS materials are basically phenolic resins, ceramics and metals. Typical flexible TPS are made of polyurethane resins, elastomers, silicon, etc. Rigid protections show higher mechanicals properties in comparison to the flexible protections, nevertheless when considering the protection ability, each one of them has particularities that define its application^6-7,10-13,14.

A typical rocket motor, Figure 1, consists basically of three components: nozzle, igniter, and the motor case. The nozzle is responsible for the expulsion of the combustion gases, and the igniter starts the burning process of the solid propellant in the combustion chamber. The motor rocket is a cylindrical tube that carries the solid propellant.

Figure 1
Components of a rocket motor¹⁵.

As a single material is unable to meet all thermal, physical-chemical and mechanical requirements, a wide variety of materials have been used jointly as TPS, for protection of the internal and external components of a rocket motor ^14,16.

One of this are the polymeric materials, mostly composites, have been widely used as TPS due to their mechanical properties, ablation rate, low density, among others essential characteristics for space application^{2,4-6,8,11,17,18}.

Elastomers such as Acrylonitrile Butadiene Rubber (NBR) and Ethylene Propylene Diene Monomer (EPDM) with reinforcement materials have been employed as matrix in ablative composites. However, they are unable to form char, a protective layer that is very resistant to mechanical erosion. The addition of cork, silica and carbon fiber used as matrix reinforcement can improve significantly the ablative properties^4,19.

The Brazilian Space Program has successfully been developing TPS applied to motor rockets since 1975. These TPS are usually made of a hydroxyl-terminated polybutadiene (HTPB) matrix with asbestos as the main reinforcement. The asbestos has been used due to its excellent thermal properties²⁰.

Over the years, asbestos has been proved very harmful to the human health, and thus has been banned in several countries. Attempts to substitute this material in TPS systems have continuously been made in the aerospace field. A Brazilian study²¹ evaluated by thermal analysis the use of different contents of hydrated alumina silicate (SA) and expandable graphite (GE) in the liner. Thermomechanical analysis (TMA) showed that the thermal expansion coefficients of the liners with SA were lower than the liners with asbestos. Liners containing SA presented the highest tension values in the performed mechanical tests. The thermal stability of liners, evaluated by thermogravimetric analysis (TGA), showed that the filler replacement practically didn’t affect the activation energy (Ea) obtained for the decomposition. The authors concluded that SA can replace asbestos with improvement of properties, although the SA reinforcement resulted in a considerable lower elongation until rupture. At this moment, there is no conclusion related to ablative performance because samples were not tested.

In Brazil, judicial disputes have been taken place over the years about the prohibition of asbestos. There are still debates whether all types are indeed prejudicial. However on November, 29, 2017, asbestos was banned in Brazil²². Even if in a hypothetical scenario, asbestos is liberated in Brazil, the foreign market would force its replacement. Latest tendencies point to the asbestos banning, favoring the human health and preserving the environment²³. According to Jargin²⁴, asbestos replacement studies must be kept aside from the industry interests.

Of all the classic materials applied to polymeric matrices, Expanded Perlite (PExp) has been the reinforcement least applied to TPS. It is commonly used in thermal and acoustic insulation. Perlite is a generic term for siliceous rocks that are usually composed of minerals rich in SiO₂ e Al₂O_3. Perlite is an insulation material of inorganic origin that is light, fire resistance, and present good thermal and acoustic insulation properties^25-29.

The characteristic that differentiates perlite from other rocks is that when heated, usually between 900 and 1100 ºC, its structures undergoes a light softening and the loss of humidity (2 to 5%). Water molecules vaporize leaving a cellular structure, which increases the material in volume by 10 to 30 times. This material is then called PExp and the new expanded structure is responsible for its low mass and excellent thermal and acoustic insulation^25,29.

PExp is very attractive to the insulation industry because, besides its porous insulating configuration, it is fire and chemical resistant^25,30. The hollow spaces inside the PExp structure act as a barrier to conductive and convective heat transfer. Voids reduce energy flow in the conductive heat transfer process. These factors contribute to make PExp a good substitute for asbestos, with the advantage of being a low cost product²⁷.

Thus, there is a need for environmental and health requirements for the replacement of asbestos and a commercial necessity, considering the possibility of Brazil failing to act in the international aerospace market, with the supply of motor rockets, due to the prohibition of these countries in relation to the presence of asbestos. In this context the use of Expanded Perlite can be a suitable solution to the problem, opening new study fronts for this type of material and consequently in the development of new products, not only for the aerospace sector, but for all the sectors in which asbestos had great participation.

The study of asbestos replacement in the composition of Flexible Thermal Protections will serve as a basis for future research on formulations based on polyurethane and epoxy resin, which make up other parts of the motor rockets, such as adhesive coating for solid composite propellant, top inhibitions among others. Thus, this paper proposes the study of asbestos substitutes, with the understanding that the data obtained with these materials will be the starting point for the continuous improvement of thermal protection processes, allowing a multiplier effect, when applied to similar systems.

2. Materials and Methods

2.1 Materials

The most significant materials used in this study are: Hydroxyterminated Polybutadiene resin (HTPB), from Liquiflex, Brazil (Hydroxyl number 0,82 mmol/g); Expanded Perlite (PExp) SF22, from Schumacher Insumos, Brazil; and Toluene Diisocyanate (TDI) type Voranate T80, from Isopol, Brazil.

2.2 Formulations

Samples of TPS without asbestos (PExp-1 to PExp-5) were prepared according to Table 1. TPS binder and TPS Reference refer to the formulation without filler and the usual asbestos TPS, respectively.

Table 1
Compositions of samples used.

Component	TPS Binder(phr)	TPS Reference(phr)	TPSPExp-1(phr)	TPSPExp-2(phr)	TPSPExp-3(phr)	TPS Pexp-4 (phr)	TPSPExp-5(phr)
HTPB	100	100	100	100	100	100	100
TPS reference fillers	-	47.0	-	-	-	-	-
DBP	-	2.11	-	-	-	-	-
Fe(C5H7O2)3	0.016	0.016	0.016	0.016	0.016	0.016	0.016
PExp	-	-	1.0	2.0	3.0	4.0	5.0
TDI	7.50	7.50	7.50	7.50	7.50	7.50	7.50

• phr: Parts per Hundred Rubber, unit of measure used in all components.

2.3 Sample preparation

Initially, fillers were heated to 110 ºC during 2 hours to eliminate the moisture present, according to internal procedure. HTPB resin and plasticizer Dibutyl phthalate (DBP) were also heated to approximately 60 ºC. Thereafter, HTPB resin, plasticizer DBP, catalyzer Iron(III) acetylacetonate Fe(C₅H₇O₂)₃, and respective fillers were weighted according to the formulations, and homogenized by mechanical stirring.

All the samples (mechanical and ablation tests) were cured for 24 hours at 60 ºC and then subjected to additional post curing, at ambient conditions during 7 days, to achieve the ultimate mechanical properties according to internal procedure. For the mechanical tests, the samples were in accordance with ASTM D412 Standard³¹, for the OAT tests, the samples were diameter of 125 mm and 6 mm of thickness. For Propellant Ablation Tests the dimensions of the samples were diameter of 50 mm and height of 40 mm with a square internal piece of solid propellant with 10 mm of side and 40 mm of length.

2.4 Methodology

Morphology of expanded perlite particles: The shape of perlite particles was evaluated in an optical stereomicroscope Carl-Zeiss, model Discovery V12.

Characterization by Fourier Transform Infrared Spectroscopy (FT-IR): FT-IR spectra of PExp samples were collected in a FT-IR Spectrum One PerkinElmer Spectrometer, in the mid-infrared region (4000 to 550 cm^-1). The spectra were obtained by transmission mode and the resolution 4 cm^-1. Samples were prepared as KBr pellets (0.8:400 mg KBr).

Characterization by Thermal Analysis: Thermogravimetric analysis (TGA) was performed to evaluate the PExp thermal stability. Three samples of (4.860 ± 0.432) mg were placed and pressed in a platin sample holder. Analysis were carried in a Simultaneous Thermal Analyzer SDT TA Instruments Q-600, under a nitrogen flow of 50 mL/min, from 30 to 1000 ºC, at a heating rate of 10 ºC/min.

Filler characterization by granulometric analysis: The granulometric analysis was performed in a MASTERSIZER 2000 equipment (MALVERN Instruments), in aqueous (water) medium. Environmental conditions were: temperature from 19.2 to 20.1 ºC, and relative humidity between 36.5 and 37.4 %.

Mechanical tests, hardness, and density determination: Five samples were tested for elongation and ultimate strength in a ZWICK 1474 mechanical tester, according to the ASTM D412 Standard³¹. Hardness tests were carried in an INSTRON S1 tester, according to the ASTM D2240-05 Standard³². Density of three samples was determined by the principle of Archimedes.

Oxy-Acetylene Torch Testing (OAT): Ablation tests were performed with an oxy-acetylene torch, according to the ASTM E285-08 Standard³³. The oxyacetylene burner provides a flow of steady hot gas that simulates the propellant combustion inside the motor rocket chamber. The torch heat flux was approximately (800 ± 20) W/cm².

Propellant Ablation Test: The Figure 2 shows the testing apparatus that allows the investigation of the samples ablative performance in association to the propellant combustion. Subsequently to the combustion in ambient condition, the formed char layer is weighted. Replicates (15 of each sample) were analyzed for the TPS reference formulation e for the TPS PExp-5. TPS PExp-5 was selected because of the superior OAT result. Analysis conditions measured during the test: burn rate (0.94 + 0.02) mm/s and mass flux (0.160 + 0.03) g/s.

Figure 2
Propellant Ablation Test apparatus.

This test, an adaptation of an internal procedure, consists of subjecting the sample to a parallel mass flow and reaction products generated during the combustion of the solid propellant in order to evaluate the wear on the TPS reference and TPS Pexp-5 formulations. During combustion of the propellant, some chemical species such as CO₂, H₂O, OH are generated in addition to Al₂O₃ particles that cause both the surface oxidation of the samples and the mechanical erosion from the mass flow and impact of the alumina particles. The ablation process under the action of the propellant is influenced by the burn area, internal pressure, gas flow and temperature so that the temperature will directly influence the oxidation process and the gas flow will act directly in the mechanical erosion of the surface already weakened by the oxidative process^34,35.

3. Results and Discussions

3.1 Particle morphology

Figure 3 shows optical the stereomicroghaphic image of neat PExp.

Figure 3
Stereomicrography of neat PExp. Magnification: 70x.

The stereomicrography test of neat PExp (Figure 3) shows a porous structure. Such configuration accounts for the material low density and good insulation capacity, and provides good ablation resistance of the TPS PExp. This type of morphology helps to decrease the heat transfer to the lower layers, thereby reducing the pyrolysis process of the HTPB matrix and consequently improving the thermal and ablative resistance of TPS PExp^25,30,36,37.

3.1 Characterization by FT-IR

Neat PExp was characterized by FT-IR, in the medium region (MIR), to characterize its functional groups. Figure 4 shows the obtained FT-IR spectrum.

Figure 4
Transmission FT-IR/MIR Spectrum of neat PExp, prepared as KBr pellets (0.8:400 mg KBr).

The presence of water molecules inside the PExp structure occurs due to its formation process and to the environmental humidity. Water interacts with the perlite structure to promote a chemical reaction that severs many Si-O bonds of the tetrahedral structure of perlite. The result is unstable hydrogen bonds (Scheme 1) which promote the perlite expansion under heating³⁸.

Scheme 1
H₂O molecules reaction with the tetrahedral structure of perlite³⁸

The FT-IR Spectrum of neat PExp showed the presence of absorptions around 3447-2924 cm^-1 that are attributed to the combination of hydroxyl (OH) group, silanol groups (Si-OH), and water adsorbed in the porous structure. These bands are in agreement with the molecules showed in Scheme 1 and in the literature^25,29. An absorption at 1630 cm^-1 shows the presence of water adsorbed as well. It should be noted that all of the above bands can also originate from the material used in the pellets. As well known, KBr salt is highly hygroscopic and it might affect the FT-IR spectrum causing enlargement and increase of bands intensity³⁹ in the region of 3400 and 1650 cm^-1.

Several other bands were detected as well: 1055 cm^-1 and 786 cm^-1, assigned to the Si-O vibrational stretching of the Si-O-Si groups and of the Si-O-Al groups, respectively; and a band at 459 cm^-1 from the Si-O-Si bonds, assigned to bending vibrations³⁹.

3.2 Characterization by thermal analysis

Figure 5 shows the TGA analyzes of neat PExp. TGA profile shows a mass loss of (4.637 + 0.424) mg or (4.6 ± 0.6) %, from 50 ºC to 980 ºC. This mass loss relates to the evaporation of water molecules present at the surface of neat PExp^29,40 and confirms that neat PExp is basically perlite. According to Celik⁴¹, the water loss mechanism happens in three distinct steps due to the porous structure of the PExp. Initially, at 250 ºC occurs the first water loss from the surface and from the more superficial porous. The second dehydration step occurs between 250 and 550 ºC, which are related to the water from the internal porous. Third step happens between 550 e 950 ºC, and is related to the dissociation of the OH groups bonded to the oxygen atoms.

Figure 5
PExp TGA Thermal profile.

3.3 Filler characterization by granulometric analysis

Table 2 presents results from the granulometric analysis of the PExp.

The value that best represent the PExp granulometric results is average d(0.5), because the d(0.9) e D[4.3] values may contain errors that suggests higher levels due to possible agglomerations. Thus, granulometric analysis indicates that PExp present the average d(0.5) of (53 ± 1) µm.

Table 2
Granulometric distribution of the PExp sample.

Sample	Distribution (µm)			Diameter médio (µm)
	d (0.1)	d(0.5)	d(0.9)	D[4.3]
PExp	15 ± 1	53 ± 1	158 ± 1	76 ± 1

• d(0.1) = 10% in volume present values lower than indicated.
• d(0.5) = 50% in volume present values lower than indicated.
• d(0.9) = 90% in volume present values lower than indicated.
• D[4.3] = mediam particle diameter.

3.4 Mechanical properties and density

   Figure 6 shows optical stereomicroghaphs of neat PExp disperse in HTPB matrix and Table 3 shows results from the mechanical tests and density determination for all the formulations.

Figure 6
Stereomicrographs of PExp disperse in HTPB matrix. Magnification: A) 40x and B) 100x.

Table 3
Results from mechanical tests and density determination.

Sample	σ (MPa)	ε (%)	E (MPa)	H (Sh.A)	ρ (g/cm3)
TPS Binder	1.23 ± 0.10	116 ± 15	2.15 ± 0.05	47 ± 1	0.930 ± 0.001
TPS Reference	1.98 ± 0.17	157 ± 11	3.57 ± 0.44	58 ± 1	1.151 ± 0.001
TPS PExp-1	1.25 ± 0.07	131 ± 9	2.16 ± 0.15	50 ± 1	0.932 ± 0.004
TPS PExp-2	1.26 ± 0.04	141 ± 6	2.18 ± 0.06	48 ± 1	0.934 ± 0.004
TPS PExp-3	1.49 ± 0.04	145 ± 4	2.54 ± 0.11	48 ± 1	0.941 ± 0.003
TPS PExp-4	1.39 ± 0.03	120 ± 8	2.85 ± 0.07	51 ± 1	0.947± 0.001
TPS PExp-5	1.22 ± 0.06	130 ± 6	2.56 ± 0.09	50 ± 1	0.951± 0.001

Figure 6 displays particles of PExp in the HTPB matrix. Darker regions suggest that some particles did not disperse properly in the matrix. Such areas cause variations in ablative and mechanical properties because these properties depend on good particles dispersion, according to Kallergis⁴².

Figure 7 presents the tensile strength versus elongation profile for the TPS binder, TPS reference and TPS PExp samples.

Figure 7
Tensile strength versus elongation profile for the TPS PExp samples.

The examination of Table 3 and Figure 7 indicates differences between the mechanical properties of the formulations. TPS reference shows higher values that can be attributed to the filler content. Fillers reinforce the HTPB matrix, however they can affect negatively the density as it increases its values⁴². For aerospace application, this is definitely undesirable.

Kallergis⁴² in your research explain that perlite possibly forms a second phase with the matrix due to clusters, decreasing the mechanical properties as can be seen in Table 3.

According to Verbeek⁴³ and Li⁴⁴ the properties of composites are extremely dependent of presence of filler and their characteristics such as particle size, distributions, shape, interactions matrix filler and nature of filler. The evaluation of tensile strength in Table 3 for TPS PExp-1 to 5, is possible to observe the percolation phenomenon, because of significant change in physical properties after TPS PExp-3^45,46.

The percolation phenomenon can be used to explanation the particle-particle of expanded perlite in HTPB matrix and is the responsible for the decliner of the tensile strength according the quantity of perlite is increase, i.e the excessive amount of particle causes resin-poor area around the perlite that leads to weak stress transfer between the HTPB matrix and perlite that causes a decrease of tensile strength^43,45,47.

Furthermore, increasing the PExp concentration affects significantly the density due to its content, porosity and to the low granulometry of the perlite^41,42,48. Even so, the density of the TPS PExp samples showed lower results than the TPS reference.

3.5 Ablative properties

Figure 8 shows photographs of TPS PExp-5 sample before and after oxy-acetylene torch ablation test.

Figure 8
Photographs of TPS PExp-5 sample: A) before; and B) after oxy-acetylene torch ablation test³³.

Figure 8-B illustrates the TPS PExp-5 sample with a central orifice after oxy-acetylene torch ablation test. It occurs during the pyrolysis under certain conditions of mass flux and heat from the torch. Thereby, the burn time and ablation rate parameters can be estimated to determine the final thickness of the TPS³³.

Table 4 and Figure 9 show the ablation test results, burn time and ablation rate for some formulations. The choice of TPS PExp-1, 3 and 5 was according to percolation phenomenon, how is the result with minimum, medium and maximum amount of perlite in HTPB matrix. According to the ASTM E285-08 Standard³³ burn time refers to the time taken to burn-through the sample while the ablation rate represents the burning distance as a function of time (mm/s). Results were evaluated statistically by using the Chauvenet Criterion^49,50.

Table 4
Results for burn time and ablation rate for the different samples.

Sample	Filler content (phr)	Burn time (s)	Ablation rate (mm/s)
TPS Binder	0	6.8 ± 0.1	0.94 ±0.02
TPS Reference	47.0	9.5 ± 0.5	0.68 ± 0.02
TPS PExp-1	1.0	8.0 ± 0.4	0.80 ± 0.03
TPS PExp-3	3.0	8.5 ± 0.2	0.75 ± 0.01
TPS PExp-5	5.0	9.2 ± 0.4	0.70 ± 0.04

Figure 9
Burn time and Ablation rate with an oxyacetylene torch for the formulation studied

Materials with good ablative properties present high burn time and low ablation rate¹⁴. In this context, TPS reference and TPS PExp-5 are the ones with the best results. Considering the results and in view of the filler content of each formulation, the efficiency of the expanded perlite is evident as the addition of 5.0 phr in the HTPB matrix was enough to improve the ablative properties, practically at the same level as the TPS reference.

Table 5 shows TPS Reference and TPS PExp-5 rates of mass loss in propellant ablation test. Only these formulations were tested considering the preliminary good results of TPS PExp-5, and due to samples costs and availability. This test evaluates char layer resistance during propellant combustion. It simulates what actually happens inside real combustions chambers, unlike what occurs with the OAT test¹⁴.

Table 5
TPS Reference and TPS PExp-5 rates of mass loss in propellant ablation test.

Sample	Rate of Mass Loss(g/s)
TPS Reference	0.041 ± 0.001
TPS PExp-5	0.033 ± 0.001

Table 5 results agree with Kallergis⁴²studies as they confirm the pyrolysis characteristics of expanded perlite particles. TPS composition with expanded perlite as the filler provides a char layer more resistant to the heat and the mass flux generated by the propellant combustion.

Results of the PExp samples, Figure 9 and Tables 4 and 5, are in agreement with the literature¹⁴, to diminish the ablation rate and thus increase the burn time it is a requirement to create a stable char layer. This layer in the surface reduces the heat flow, the oxygen diffusion, and consequently the thermal degradation of the material more internal layers^42,48. According to Sheu⁵¹, the use of asbestos fibers in the reference material helps the anchoring of the char layer during the pyrolysis process of the organic matter. Thus, it difficults the heat flow and the oxygen diffusion to the internal layers. Moreover, the presence of SiO₂ assists in the generation of an uniform inorganic layer that acts as a momentary barrier to the ablation process. Nevertheless, these fillers tend to increase the material thermal conductivity allowing for faster heating of the lower layers, thereby causing an increase in degradation rate^7,52.

The presence of PExp creates a stable and resistant char layer, with the advantage of being light and insulating due to the natural porous structure. Furthermore, its particle sizes allow a better accommodation of the filler in the HTPB matrix, reducing the sites that the matrix would occupy and, thus, creating a more effective inorganic layer against the heat flow and oxygen diffusion. Consequently, it minimizes the pyrolysis of internal layers and, this way, the thermal protection consumption. These results demonstrate that PExp has potential to substitute asbestos in insulating materials^42,48.

4. Conclusions

The ablation tests results of oxy-acetylene torch and under the action of the gases generated by the combustion of the solid propellant show that the Expanded Perlite performance as ablative filler in the HTPB matrix is adequate to replace asbestos as a component of thermal protections. It also has the additional advantage of reducing the material density, which is also of great value for the aerospace industry.

This replacement also solves the severe problem of having to use asbestos, a product known to be carcinogenic, allowing Brazil to remain in the international space market.

However, regarding the mechanical properties of the PExp formulations, the performance was not as good as the reference TPS with asbestos. This can be credited to the fact that this material does not present reinforcing characteristics for the HTPB matrix. However, the use of PExp in TPS formulations is still considered feasible because its flap configuration allows the mechanical properties presented.

In an attempt to resolve the problem of low mechanical properties, other studies are being developed by this group to make the use of perlite more attractive, by the addition of compatibilizing agent to improve the interaction of PExp in the HTPB matrix. This will be the goal of a new publication.

5. Acknowledgments

This study was supported partially by the National Senior Visiting Professor Program (PVNS) from the Coordenação de Aperfeiçoamento Pessoal de Nível Superior (CAPES).

6. References:

• ¹
  Bahramian AR, Kokabi M, Famili MHN, Beheshty MH. High temperature ablation of kaolinite layered silicate/phenolic resin/asbestos cloth nanocomposite. Journal Hazardous Materials 2008;150(1):136-145.
• ²
  Bahramian AR, Kokabi M, Famili MHN, Beheshty MH. Ablation and thermal degradation behaviour of a composite based on resol type phenolic resin: process modeling and experimental. Polymer 2006;47(10):3661-3673.
• ³
  Cheng GC, Venkatachari BS, Cozmuta I. Multi-scale simulations of in-deph pyrolysis of charring ablative thermal protection material. Computers & Fluids 2011;45(1):191-196.
• ⁴
  Vaia RA, Price G, Ruth PN, Nguyen HT, Lichtenhan J. Polymer/layered silicate nanocomposite as high performance ablative materials. Applied Clay Science 1999;15(1-2):67-92.
• ⁵
  Pulci G, Tirillò J, Marra F, Fossati F, Bartuli C, Valente T. Carbon-phenolic ablative materials for re-entry space vehicles: Manufacturing and properties. Composites Part A: Applied Science and Manufacturing 2010;41(10):1483-1490.
• ⁶
  Gori F, Corasaniti S, Worek WM, Minkowycz WJ. Theoretical prediction of thermal conductivity for thermal protection systems. Applied Thermal Engineering 2012;49:124-130.
• ⁷
  Natali M, Monti M, Puglia D, Kenny JM, Torre L. Ablative properties of carbon black and MWNT/phenolic composites: A comparative study. Composites Part A: Applied Science and Manufacturing 2012;43(1):174-182.
• ⁸
  Firouzmanesh MR, Azar AA. Study of thermal stability and ablation behavior of carbon/epoxy-novolac composites. Journal of Applied Polymer Science 2003;88(10):2455-2461.
• ⁹
  Yin J, Xiong X, Zhang H, Huang B. Microstructure and ablation performance of dual-matrix carbon/carbon composites. Carbon 2006;44(9):1690-1694.
• ¹⁰
  Davenas A, ed. Solid Rocket Propulsion Technology Oxford: Pergamon Press; 1993.
• ¹¹
  Yang D, Zhang W, Jiang B, Guo Y. Silicone rubber ablative composite improved with zirconium carbide or zirconia. Composites Part A: Applied Science and Manufacturing 2013;44:70-77.
• ¹²
  Rossman GA, Dec JA, Braun RD. Flexible Thermal Protection System Physics-Based Modeling for Temperature Profile Predictions In: AIAA SciTech. 52^nd Aerospace Sciences Meeting; 2014 Jan 13-17; National Harbor, MD, USA. 20 p.
• ¹³
  Owens W, Meyers J, Fletcher DG. Surface Catalyzed Recombination Efficiencies for Flexible Thermal Protection Materials in Air Plasma Fluid Dynamics and Co-located Conferences. 44^th AIAA Thermophysics Conference; 2013 Jun 24-27; San Diego, CA, USA. 18 p.
• ¹⁴
  Natali M, Kenny JM, Torre L. Science and technology of polymeric ablative materials for thermal protection systems and propulsion devices: A review. Progress in Materials Science 2016;84:192-275.
• ¹⁵
  Paterlini WC, Botelho EC, Rezende LC, Lourenço VL, Rezende MC. Efeito da concentração do catalisador acetilacetonato férrico na cura de poliuretano à base de polibutadieno líquido hidroxilado (PBLH) e diisocianato de isoforona (IPDI). Química Nova 2002;25(2):221-225.
• ¹⁶
  Zhang G, Wang F, Huang Z, Dai J, Shi M. Improved Ablation Resistance of Silicone Rubber Composites by Introducing Montmorillonite and Silicon Carbide Whisker. Materials (Basel) 2016;9(9). pii: E723.
• ¹⁷
  Park JK, Kang TJ. Thermal and ablative properties of low temperature carbon fiber-phenol formaldehyde resin composite. Carbon 2002;40(12):2125-2134.
• ¹⁸
  Torre L, Kenny JM, Maffezzoli AM. Degradation behavior of a composite material for thermal protection systems. Part I - Experimental characterization. Journal of Material Science 1998;33(12):3137-3143.
• ¹⁹
  Deuri AS, Bhowmick AK, Ghosh R, John B, Siriram T, De SK. Thermal and ablative properties of rocket insulator compound based on EPDM. Polymer Degradation and Stability 1998;21(1):21-28.
• ²⁰
  Palmerio AF. Introdução à Tecnologia de Foguetes 2^a ed. São José dos Campos: SindCT; 2017.
• ²¹
  Crespim H, Azevedo MFP, David LH, Cassu SN, Lourenço VL. Substituição de amianto por silicato de alumínio e grafite expansível em compósito de poliuretano utilizado em motor-foguete. Polímeros 2007;17(3):228-233.
• ²²
  Moura RM. STF proíbe extração e venda do amianto crisotila no País. O Estado de S. Paulo 2017 Nov 20. Available from: <http://saude.estadao.com.br/noticias/geral,stf-proibe-extracao-e-comercializacao-de-amianto-crisotila-no-pais,70002102051>. Access in: 16/01/2018.
  » http://saude.estadao.com.br/noticias/geral,stf-proibe-extracao-e-comercializacao-de-amianto-crisotila-no-pais,70002102051
• ²³
  Souza AP. Usos e abusos do amianto no Brasil, o diálogo impossível entre o capitalismo e a saúde pública [Dissertation]. Araraquara: Centro Universitário de Araraquara; 2015.
• ²⁴
  Jargin SV. Asbestos and its substitutes: International coordination and independent research needed. Journal of Environmental and Occupational Science 2015;4(1):1-4.
• ²⁵
  Topçu IB, Isikdag B. Manufacture of high heat conductivity resistant clay bricks containing perlite. Build and Environment 2007;42(10):3540-3546.
• ²⁶
  Vaou V, Panias D. Thermal insulating foamy from perlite. Minerals Engineering 2010;23(14):1146-1151.
• ²⁷
  Pilkington Insulation Ltd.; Willoughby J. Insulation. In: Snow D. Plant Engineer's Reference Book Oxford: Butterworth-Heinemann; 2003. 18 p.
• ²⁸
  Virta RL. Asbestos substitutes. In: Kogel JE, Trivedi NC, Barker JM, Krukowski ST, eds. Industrial Minerals & Rocks: Commodities, Markets, and Uses Littleton: Society for Mining, Metallurgy, and Exploration; 2006. p. 3-5.
• ²⁹
  Sodeyama K, Sakka Y, Kamino Y, Seki H. Preparation of fine expanded perlite. Journal of Materials Science 1999:34(10):2461-2468.
• ³⁰
  Tian H, Tagaya H. Preparation, characterization and mechanical properties of the polylactide/perlite and the polylactide/montmorillonite composites. Journal of Materials Science 2007;42(9):3244-3250.
• ³¹
  ASTM International. D-412-06 - Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers-Tension West Conshohocken: ASTM International; 2006.
• ³²
  ASTM International. ASTM D2240-05 - Standard Test Method for Rubber Property- Durometer Hardness West Conshohocken: ASTM International; 2005.
• ³³
  ASTM International. ASTM E-285-08 - Standard Test Method for Oxyacetylene Ablation Testing of Thermal Insulation Materials West Conshohocken: ASTM International; 2008.
• ³⁴
  Li K, Shen XT, Li HJ, Zhang SY, Feng T, Zhang LL. Ablation of the carbon/carbon composite nozzle-throats in small solid rocket motor. Carbon 2011;49(4):1208-1215.
• ³⁵
  Peng L, He G, Li J, Wang L, Qin F. Effect of combustion gas mass flow rate on carbon/carbon composite nozzle ablation in a solid rocket motor. Carbon 2012;50(4):1554-1562.
• ³⁶
  Oktay H, Yumrutas R, Akpolat A. Mechanical and thermophysical properties of lightweight aggregate concretes. Construction and Building Materials 2015;96:217-225.
• ³⁷
  Abidi S, Nait-Ali B, Joliff Y, Favotto C. Impact of perlite, vermiculite and cement on the thermal conductivity of a plaster composite material: Experimental and numerical approaches. Composites Part B: Engineering 2015;68:392-400.
• ³⁸
  Varuzhanyan AA, Varuzhanyan AA, Varuzhanyan HA. A mechanism of perlite expansion. Inorganic Materials 2006:42(9):1039-1045.
• ³⁹
  Smith AL, ed. Applied Infrared Spectroscopy: Fundamentals Techniques and Analytical Problem-Solving New York: John Wiley & Sons; 1979.
• ⁴⁰
  Kabra S, Katara S, Rani A. Characterization and study of Turkish perlite. International Journal of Innovative Research in Science, Engineering and Technology 2013;2(9):4319-4326.
• ⁴¹
  Celik AG, Kilic AM, Çakal GO. Expanded perlite aggregate characterization for use as a lightweight construction raw material. Physicochemical Problems of Mineral Processing 2013;49(2):689-700.
• ⁴²
  Kallergis G, Pisania M, Simitzis J. Manufacture and Characterization of Heat Resistant and Insulating New Composite Based on Novolac Resin - Carbon Fibers - Perlite. Macromolecular Symposium 2013;331-332(1):137-143.
• ⁴³
  Verbeek CJR. Effect of Percolation on the Mechanical Properties of Sand-filled Polyethylene Composites. Journal of Thermoplastic Composite Materials 2007;20(2):137-149.
• ⁴⁴
  Li C, Chou TW. Continuum percolation of nanocomposites with fillers of arbitrary shapes. Applied Physics Letters 2007;90(17)174108.
• ⁴⁵
  Chodak I, Krupa I. "Percolation effect" and mechanical behavior of carbon black filled polyethylene. Journal of Materials Science Letters 1999;18(18):1457-1459.
• ⁴⁶
  Nan CW, Shen Y, Ma J. Physical Properties of Composites Near Percolation. Annual Review of Materials Research 2010;40:131-151.
• ⁴⁷
  Hassanabadi HM, Wilhelm M, Rodrigue D. A rheological criterion to determine the percolation threshold in polymer nano-composites. Rheologica Acta 2014;53(10-11):869-882.
• ⁴⁸
  Sahraeian R, Esfandeh M, Hashemi SA. Rheological, Thermal and Dynamic Mechanical Studies of the LDPE/Perlite Nanocomposites. Polymer & Polymer Composites 2013;21(4):243-249.
• ⁴⁹
  Fatchur AF. Chauvenet´s Criterion, Peirce´s Criterion and Thompson´s Criterion (Literatures Review).2^nd Quantitative and Qualitative Analysis Course Homework Jakarta: University of Indonesia; 2016.
• ⁵⁰
  Mostarac P, Malarić R, Hegeduš H. Comparison of outliers elimination algorithms. In: Proceedings of the 7^th International Conference Measurement; 2009 May 20-23; Smolenice, Slovakia. p. 49-52.
• ⁵¹
  Chu HT, Sheu SM, Chou JH. Experimental Study of Ablative Materials by Oxyacetylene Flame Flow System. Journal of Propulsion and Power 2011;27(5):1108-1113.
• ⁵²
  Koo JH, Miller MJ, Weispfenning J, Blackmon C. Silicone polymer composites for thermal protection system: fiber reinforcements and microstructures. Journal of Composite Materials 2010;45(13):1363-1680.

Publication Dates

• Publication in this collection
  20 Aug 2018
• Date of issue
  2018

History

• Received
  25 Sept 2017
• Reviewed
  18 May 2018
• Accepted
  30 July 2018