Two poly(arylene ether phosphine oxide)s (PAEPOs) have been found to be suitable as matrix and coating materials for composite-material (matrix/fiber) tanks and pipes that contain liquid oxygen (LOX). One of these PAEPOs is denoted by the trade name "Triton Oxygen Resistant" (TOR); this is a clear, yellowish material with the structural formula shown in the figure. The other PAEPO is a clear, colorless material called "colorless oxygen resistant" (COR).
These polymers exhibit properties that make them attractive for incorporation into composite-material LOX containers:
- They are physically and chemically compatible with LOX.
- They are compatible with the other component materials (toughened epoxies and graphite fibers) of composite-material LOX containers.
- They are amenable to processing by techniques used commonly in the fabrication of composite-material structures.
Some other commercially available polymers are compatible with liquid oxygen, but the use of them is inhibited, variously, by poor adhesion to other component materials, difficulties in processing, and/or the need to process them at temperatures high enough to damage other component materials.
These PAEPOs in film form have been shown to be highly compatible with LOX. The films have passed the Marshall Space Flight Center LOX mechanical-impact-sensitivity test at the maximum required energy level of 72 ft-lb (98 J). The PAEPOs are soluble in a number of polar solvents and can therefore be applied from solution onto complexly shaped surfaces with relative ease; for example, by dip coating or brushing. The PAEPO films can be made very thin if necessary, and they adhere well to composites made of other component materials.
These PAEPOs can also be used as matrix materials, along with graphite-fiber reinforcements, in prepregs and in composites made from prepregs by standard thermoplastic-matrix-composite consolidation techniques: A composite panel can be laid up by stacking multiple prepreg plies; the layup is then vacuum bagged and consolidated in a hot press or autoclave. However, like composites made with other matrix materials, composites made with these polymers fall shy of the neat polymer films in LOX testing. The reason for this behavior and what (if anything) can be done about it will be addressed in subsequent development work.
Although a PAEPO film can be applied to a previously cured epoxy-matrix/graphite fiber structure, the most unique and promising way of coating such a structure with a PAEPO film is to make the film become intimately bonded with the underlying composite by use of the composite cocure process. In this approach, a thin film of the PAEPO is applied on one side of a epoxy/graphite prepreg layup prior to curing. Then as the layup is cured to the finished composite, the film forms a strong bond with the epoxy matrix. This process offers two advantages: (1) it is solventless and (2) it results in an excellent bond.
This work was done by Marvin A. Guiles and Ross Haghighat of Triton Systems, Inc., for Marshall Space Flight Center. MFS-26541