Resin Transfer Molding (RTM) 370 Resin for High-Temperature Applications
materials and coatings
Resin Transfer Molding (RTM) 370 Resin for High-Temperature Applications (LEW-TOPS-115)
A solvent-free, low-melt process for creating a high-performance resin with zero emissions
Overview
Innovators at NASA's Glenn Research Center have developed a Resin Transfer Molding (RTM) imide resin known as RTM370 that is generated using a revolutionary, solvent-free process. Its many desirable properties earned it a prestigious R&D 100 Award in 2017. RTM370 has a high glass transition temperature (Tg = 370°C), low-melt viscosity (20 to 30 poise), and long shelf life (up to 2 hours). It can perform at temperatures exceeding 300°C. It melts at 260 to 280°C and can be cured at 340 to 370°C without releasing any harmful or volatile compounds. It is suitable for composite fabrication by injection molding, RTM, resin film infusion (RFI), or vacuum-assisted resin transfer molding (VARTM). Furthermore, carbon fiber filled RTM370 is adaptable to additive manufacturing and can be printed into composite parts by laser sintering - a major breakthrough in high-temperature composite fabrication. These cutting-edge carbon fiber composites can replace any metallic part, providing high-quality, lightweight materials to a variety of industries at low-cost.
The Technology
RTM370 imide resin was developed to address the limitations of conventional imide resins, which are generated from commercially available symmetrical biphenyl dianhydride and oxydianiline (ODA). These resins form symmetrical dianhydride or diamine compounds that result in a substance with much higher viscosity than is viable for RTM, RFI, and VARTM. RTM370 harnesses the unique properties of asymmetric biphenyl dianhydride (a-BPDA) used in combination with a kinked ODA and a 4-(Phenylethynyl) phthalic anhydride endcap to form a mixture that can be melted without the use of solvents, and achieve the desired low-melt viscosity. RTM370 displays a high softening temperature (Tg = 370°C) and can be melted at 260-280°C. It can then be injected into fiber preforms under pressure (200 psi) or through a vacuum (VARTM) to form composites with excellent toughness. The resin can also be made into powder prepregs by melting the resin powders so that they fuse onto fibers. Recently, carbon fiber filled RTM370 imide resins have been fabricated into composites by laser sintering. This exciting advancement in additive manufacturing represents a new frontier for high-temperature composites.
Not only are RTM370 composites lightweight, durable, and impact-resistant, they also possess outstanding abrasion resistance and significant thermo-oxidative stability (as demonstrated in long-term isothermal aging at 288°C for 1,000 hours). In summary, this groundbreaking approach yields a vastly superior resin for fabricating high-quality composites with improved performance, durability, and adaptability. RTM370's unique, solvent-free melt process is simpler, more environmentally friendly, and more cost-effective than competing systems, lending it broad appeal for a variety of Earth-based applications.
Benefits
- High-temperature capability: Retains mechanical properties at extremely high temperatures (up to 315°C)
- Long pot-life: Maintains suitable viscosity for RTM and RFI (20 to 30 poise) for 1 to 2 hours
- Lightweight: Components made from RTM370 are 30 percent lighter than metallic parts
- Clean and green: This solvent-free production process does not produce any harmful, volatile compounds
- Excellent impact-resistance and char yield: RTM370 composites demonstrate high impact resistance and outstanding abrasion resistance at ambient and high temperatures
Applications
- Mechanical systems
- Oil and gas
- Construction
- Electronics
- Aerospace
- Automotive
- Marine
- Commercial space
Similar Results
3D-Printed Composites for High Temperature Uses
NASA's technology is the first successful 3D-printing of high temperature carbon fiber filled thermoset polyimide composites. Selective Laser Sintering (SLS) of carbon-filled RTM370 is followed by post-curing to achieve higher temperature capability, resulting in a composite part with a glass transition temperature of 370 °C.
SLS typically uses thermoplastic polymeric powders and the resultant parts have a useful temperature range of 150-185 °C, while often being weaker compared to traditionally processed materials. Recently, higher temperature thermoplastics have been manufactured into 3D parts by high temperature SLS that requires a melting temperature of 380 °C, but the usable temperature range for these parts is still under 200 °C.
NASA's thermoset polyimide composites are melt-processable between 150-240 °C, allowing the use of regular SLS machines. The resultant parts are subsequently post-cured using multi-step cycles that slowly heat the material to slightly below its glass transition temperature, while avoiding dimensional change during the process. This invention will greatly benefit aerospace companies in the production of parts with complex geometry for engine components requiring over 300 °C applications, while having a wealth of other potential applications including, but not limited to, printing legacy parts for military aircraft and producing components for high performance electric cars.
Blocking/Deblocking Resin Systems
This technology enables the fabrication of co-cured structures without the need for an autoclave or oven large enough to contain the full-scale structure. Instead, sub-components can be prepared in a less expensive, smaller autoclave or oven with co-cure plys applied to the faying surfaces. A continuous, assembled structure can be prepared using a subsequent curing process in a heated press. The co-cured structures can be designed to meet FAA certification criteria for composite structures because no adhesive bond or mechanical fasteners are needed. The structure can be treated as a single, joint-free component.
Mechanoresponsive Healing Polymers
The method chemically introduces mechanically sensitive chemical groups into the structure of a resin. By introducing mechanoresponsive functional groups to a polymer, it is possible to induce self-healing through the transformation of such chemical groups to where mechanical properties of a structure are almost completely restored. The forces imparted by a damage event can therefore be used to enable healing or repair of the structure.
AERoBOND+ for Manufacturing Composite Structures
The AERoBOND and AERoBOND+ technologies are composite resin materials design innovations that enable new methods for composites joining and manufacturing. The resins are formulated with carefully selected off-set stoichiometries to delay/control the cure such that initial curing of individual components can be followed separately by joining/curing of components together. The ability to delay and control the co-cure joining step provides ease of manufacturing of multi-part composite structures, without compromising joint integrity. There are significant cost savings associated with eliminating fasteners and joint surface preparation steps. To date, the focus of the NASA development effort has been on novel epoxy-based prepreg formulations though other types of thermosets could be considered as well.
The AERoBOND+ innovation provides an added adhesive layer to the AERoBOND joint design to improve the ability to join composite surfaces when these surfaces are less tightly matched. Conventional adhesives, e.g., film, paste, etc., are employed. By including an adhesive between the offset stoichiometric prepreg plies, the adhesive can fill the gaps between the bonding surfaces while maintaining reflowable AERoBOND layer interfaces. Since all interfaces are reflowable, they are much more tolerant of surface contamination, thereby mitigating a primary challenge for conventional adhesive bonding.
New Resin Systems for Thermal Protection Materials
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.
