PMR-15 is a polyimide resin used to make composite materials for high-temperature applications such as aircraft engine components, rocket casings, engine bypass ducts, nozzle flaps, bushings, bearings, missile fins, structural wing components, and radar domes. PMR-15 is widely regarded as the most-versatile of polyimides, having a balance of processing, mechanical, and thermal properties that meet the widest array of applications. However, 4,4’-methylenedianiline (MDA), a monomer used in this resin system, is a known carcinogen and liver toxin. Despite the drawbacks to this polyimide, previously identified alternatives had not gained traction because of expectations of reduced lifecycles and robustness/confidence of material components, with only a potentially small reduction in toxicity risk.
Novel chemistries have recently been discovered that meet performance requirements and improved environmental impact in comparison with PMR-15 resins using MDA. Under its Weapons Systems and Platforms Program Area, SERDP is nearing the conclusion of a 4-year project (WP-2402) to develop an understanding into the relationships between structure, physical properties, and toxicity for alternatives to MDA. Led by Dr. John La Scala, the research team from Army Research Laboratory has developed several alternative compounds with significantly lower toxicity when compared to MDA.
Some of the alternate compounds identified through this project have also shown promising performance properties as compared to MDA. MDA-free alternates with the best resin properties were formed into composites for extensive material testing. In particular, p-cymene dianiline (CDA) has been successfully scaled-up and evaluated. Performance testing of these composites has shown promising results in the areas of strength and modulus. 2,6-dimethyl MDA (TMMDA) has also been evaluated and has shown promising thermal properties. Additional scale up and composite evaluations of CDA and TMMDA are planned for the remainder of the project.
The introduction of these alternatives will offer the engineering and system design communities equivalent performance and improved environmental safety and occupational health for our warfighters and civilian workforce.
EPA Presidential Green Chemistry Award
Web Articles: Bisphenol alternatives
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