Composite materials are used in the Department of Defense (DoD) because of their low weight and excellent properties, enabling the production of lighter weight and stronger vehicles, ships, and structures. Programs have been initiated to replace metallic components of high mobility multi-wheeled vehicles (HMMWV) and other Army vehicles and naval ships with composite parts. However, fabrication of composite materials can produce large amounts of volatile organic compound (VOC) and hazardous air pollutant (HAP) emissions.
The Army Research Laboratory (ARL)/Drexel University have developed low HAP fatty acid vinyl ester (FAVE) resin systems that would allow DoD facilities to continue manufacturing vinyl ester (VE) resins using current practices and facilities, while reducing pollution and health risks. These resins reduce HAP content in composite resins by using fatty acid (FA) monomers as styrene replacements and using bimodal molecular weight distributions of VE monomers to maintain high performance while using low styrene/HAP contents.
The objectives of this program were: 1) Demonstrate/validate the processing and performance of low VOC/HAP resins developed by ARL and Drexel as a viable alternative to current VE and unsaturated polyester (UPE) systems used in DoD; 2) Quantify the impact of these resins on facility-wide HAP emissions at selected facilities and DoD contract manufacturing sites, and demonstrate compliance with proposed National Emissions Standard for Hazardous Air Pollutants (NESHAP) standards and existing composites NESHAP standards through monitoring and record-keeping; 3) Demonstrate cost-savings potential for transitioning to low VOC/HAP VE and UPE resins relative to using standard commercial resins or implementing facility modifications.
The FAVE resin technology was demonstrated and validated on a variety of weapons platforms. For the Army, composite materials for tactical vehicles (M35A3 hood, M939 hood, and HMMWV transmission box) were demonstrated. For the Marines Corps, low VOC/HAP FAVE was used to demonstrate a ballistic HMMWV hardtop that currently uses high VOC/HAP VE resins. For the Air Force, these low HAP resins were used to replace current resins used in a composite dorsal cover for the T-38, F-22 canopy cover, and splash molds. This resin was also used to replace VE resins currently used for the composite rudder on mine counter measure (MCM) ships and current and future class of destroyers (DDG and DDX, respectively).
FAVE resin formulations were developed by ARL/Drexel. This was done by blending methacrylated fatty acid (MFA) with various commercial VE resins to produce formulations with properties similar to current resins. A variety of resin formulations were prepared in this manner and were then transitioned to Applied Poleramics, Inc. (API) for production. API of Benicia, CA, was successful in manufacturing the MFA monomers used to partly replace styrene in FAVE. Furthermore, API was successful in manufacturing the FAVE resins. Although initial batches of the MFA and FAVE did not pass all Joint Test Protocol (JTP) testing, after some slight modifications to the manufacture or formulation, all batches subsequently passed all JTP testing.
ARL/Drexel validated composite panels prepared using the resins developed by API and the fibers used in each of the demonstrations. ARL/Drexel did standard mechanical testing as well as accelerated aging and fatigue of these materials. The results indicated that the FAVE performed similarly to commercial resins, but had improved fatigue and weathering properties. Furthermore, each partner group completed panel testing, flow/infusion testing to find that the FAVE resins passed all requirements.
A FAVE resin formulation was demonstrated and validated on three Air Force platforms. The demonstration parts were then validated and showed that the FAVE resin performed similarly to the commercial VE resins used in these applications. A FAVE resin formulation was successfully demonstrated and validated on the MCM rudder. Structural Composites, Inc. (SCI) successfully manufactured two FAVE rudders. One of the rudders was cross-sectioned and was found to have excellent fiber wet-out and few defects. The second rudder will be kept on hand to potentially validate its use on the MCM once approval is granted by the Navy. Ballistic testing of panels for the Marine Corps HMMWV hardtop application showed superior performance of the FAVE resins.
FAVE resin was demonstrated and validated for composite Army applications (M35A3 hood, M939 hood, and HMMWV transmission container). Composite demonstration parts were prepared in the laboratory to prove that the FAVE resin could successfully be used for this application. Composites were then prepared at Sioux Manufacturing Corporation (SMC) to validate the resin processing and to prepare parts for validation testing. SMC was satisfied with the processability of the resins and successfully produced the composite parts alongside parts using commercial resins. These manufactured parts were then validated on a test frame at the Center for Composite Materials (CCM). The results from the test-frame experiments showed identical performance of the FAVE composite versus the commercial resins, and the FAVE composites passed all required specifications. The composite hoods were tested for form, fit, and function at
Red River Army Depot (RRAD) and were shown to pass all requirements. The composite containers were tested at Aberdeen Test Center (ATC) for shock and vibration testing, according to specifications for shipping containers. The results indicated that the FAVE passed all requirements. RRAD validated the FAVE and commercial resin containers by shipping the containers around the depot for a period of 3 months. The results again showed very similar behavior for the FAVE and commercial resins. However, both the RRAD and ATC testing indicated some issues.
Life Cycle Analysis (LCA) analysis of the FAVE resins was performed by two independent groups. The results showed in all cases that the FAVE resins were more expensive per pound of resin than the commercial resins. However, when considering costs associated with emissions capture, FAVE resins become more competitive. In general, production of composites tended to favor the use of FAVE resins, such as in the Army demonstrations. However, smaller scale uses, such as the Navy and Air Force demonstrations, favored the commercial resins.
The FAVE resins are qualified for the Army hoods, HMMWV transmission container, canopy cover, and splash molds. The MCM rudder must undergo field testing, but approvals for that will take 2 to 3 years. The HMMWV hardtop no longer has a market and thus further implementation is unnecessary. The production of FAVE resins is in transition as Dixie Chemicals Inc., has recently licensed the MFA and FAVE technology, precluding API from manufacturing it.