New Resin Systems for Thermal Protection Materials
materials and coatings
New Resin Systems for Thermal Protection Materials (TOP2-260)
A unique approach to making a carbon reinforced ablator.
Overview
This innovation focuses on an improved low density ablator with improved structural performance and high temperature capability. A new polymer system consisting of cyanate ester and phthalonitrile resins were used to create this carbon reinforced ablator. Cyanate ester resin is a thermoset resin which has high char stability, high decomposition temperature, low oxygen content, low moisture absorption and high glass transition temperature (400 degrees Celsius). Phthalonitrile resin is another type of thermoset resin which has very high char stability, and high decomposition temperature (480 degrees Celsius).
The Technology
This method produces a low density ablator similar to Phenolic Impregnated Carbon Ablator (PICA) using a cyanate ester and phthalonitrile resin system, rather than the heritage phenolic resin. Cyanate ester resin systems can be cured in a carbon matrix and generate high surface area structure within the carbon fibers. This helps to reduce the thermal conductivity of the material which is one of the key requirements of thermal protection system (TPS) materials. The material has densities ranging from 0.2 to .35 grams per cubic centimeter. NASA has successfully processed the cyanate ester and phthalonitrile resins with a morphology similar to that of the phenolic phase in PICA, but with more advanced properties such as high char stability, high char yield, and high thermal stability. This new generation of TPS materials has the same microstructure as heritage PICA, but improved characteristics of PICA such as increased char yield, increased char stability, increased thermal stability and increased glass transition temperature.


Benefits
- Increase in the char yield
- Enhanced char stability
- Increased thermal stability
- Increased glass transition temperature
Applications
- Space exploration
- Systems engineering
- Thermal Protection Systems
- Materials engineering
- Mechanical engineering
Similar Results

A New Family of Low-Density, Flexible Ablators
The invention provides a family of low density, flexible ablators comprising of a flexible fibrous substrate and a polymer resin. The flexible ablators can withstand a wide range of heating rates (40-540 Watts/cm2) with the upper limit of survivable heat flux being comparable to the survivable heat flux for rigid ablators, such as PICA and Avcoat. The amount and composition of polymer resin can be readily tailored to specific mission requirements. The material can be manufactured via a monolithic approach using versatile manufacturing methods to produce large area heat shields, which provides a material with fewer seams or gaps. The goals of the work are primarily twofold: (i) to develop flexible, ablative Thermal Protection System (TPS) material on a large, blunt shape body which provides aerodynamic drag during hypervelocity atmospheric entry or re-entry, without perishing from heating by the bow shock wave that envelopes the body; and (ii) to provide a relatively inexpensive TPS material that can be bonded to a substrate, that is unaffected by deflections, by differences in thermal expansion or by contraction of a TPS shield, and that is suitable for windward and leeward surfaces of conventional robotic and human entry vehicles that would otherwise employ a rigid TPS shield. This technology produces large areas of heat shields that can be relatively easily attached on the exterior of spacecraft.

Creating Low Density Flexible Ablative Materials
The low density flexible ablator can be deployed by mechanical mechanisms or by inflation and is comparable in performance to its rigid counterparts of the same density and composition. Recent testing in excess of 400W/cm2 demonstrated that the TPS char has good structural integrity and retains similar flexibility to the virgin material, there by eliminating potential failure due to fluttering and internal stress buildup as a result of pyrolysis and shrinkage of the system. These flexible ablators can operate at heating regimes where state of the art flexible TPS (non-ablative) will not survive. Flexible ablators enable and improve many missions including (1) hypersonic inflatable aerodynamic decelerators or other deployed concepts delivering large payload to Mars and (2) replacing rigid TPS materials there by reducing design complexity associated with rigid TPS materials resulting in reduced TPS costs.

A New Class of Strong and Flexible Carbon Fiber Reinforced Phenolic Composites
This unique approach modifies the phenolic polymer network by adding thermoplastic molecules with flexible segments such as aliphatic carbon and siloxane. The thermoplastic molecules are terminated with bifunctional groups that can directly react with the phenolic under the curing condition to form chemical bonds. Further incorporation of these segments can be facilitated by a relay reaction of a second molecular component which can bond with both the first flexible segments and the phenolic network. The selections of flexible, thermoplastic segments are based on desired properties, which include flexibility, ablative, an charring ability, heat resistance, and low catalycity.
The modified phenolic is a truly molecular composite in which flexible segments are connected with the phenolic network through strong chemical bonds and are uniformly distributed among the networks. This feature renders a uniform toughening/strengthening effect without compromising the lightweight nature of the materials. The process is also feasible to scale up and amenable for manufacturing.

Surface Densification Of Phenolic Impregnated Carbon Ablator (PICA)
The graded Thermal Protection System (TPS) offers a lower density than comparable state-of-the-art TPS systems operating at similar maximum heating conditions. This approach is straight forward in terms of processing and surface-treatment application and can be applied to machine PICA materials without having an effect on the final tolerance. The process results in increased usability and handling since standard uncoated PICA is relatively weak. Surface-densified PICA provides an approach for improvements in the robustness for the baseline CEV heat shield. A graded approach eliminates the need for joints and/or bonding agents between material plies. PICA surface densification offers robust mechanical protection against transit damage, handling damage, and in-flight object damage.

Advanced Isothermally Produced Next-Gen Composites
Next generation aircraft are anticipated to be largely made with composite components, requiring significant increases in manufacturing rates of composites to meet the demand for a new fleet of aircraft. The higher rate manufacturing will require multiple advances, including rapid curing and lower processing temperatures. These requirements can be enabled by new processing methods such as isothermal rapidly cured composite parts.
NASA has developed materials and methods that meet those stringent requirements for high-rate manufacturing. The innovators have demonstrated at least two families of new resin formulations that meet the expected high-rate manufacturing needs. These new formulations have been engineered to be infused and cured at the same (i.e., isothermal) temperature, below that of commercially available materials. The materials can then be removed from the mold while still hot without distorting the shape, thereby reducing the processing times by eliminating the need for cooling to occur in the mold. After a post-cure process - which takes 4 hours or less and can be performed in batches - the mechanical properties of NASA's next-gen composites.
The related patent is now available to license. Please note that NASA does not manufacturer products itself for commercial sale.