Materials used in the production of current aircraft interiors, with some exceptions, tend to have better tire resistance than materials used in other transportation systems. Regulatory requirements have been significant driving forces in the optimization of fire-resistant polymers and the development of required product forms for aircraft interior applications. Independent programs pursued by industry have also resulted in essentially a new generation of materials that found application in the 747, DC-10, and L-1011, and then a second generation of materials used for the 767, 757, and A300-600/A310. The FAA's heat and smoke release regulations drove improvements to the second-generation materials and to the application of new materials such as more fire-resistant thermoplastics to satisfy specific application needs.
The committee has identified three approaches to provide further improvements in tire-resistant materials:
Modification of specialty polymers including thermoplastics such as polyetheretherketone, polyetherimide, polyphenylene sulfide, and polysulfone and thermosets such as cyanate ester, bismaleimide, polyimide, and polybenzimidizole. This approach may provide the best performance in the near term (< 10 years).
Development of new, high-performance, thermally stable materials including organic/inorganic polymer systems, copolymers, polymer blends and alloys, and glasses and ceramics. These materials have the potential for the best performance in the long term (> 10 years).
Modification of existing engineering polymers including thermoplastics such as polycarbonates, nylons, and polyethyleneterephthalate and thermosets such as phenolics and polyesters. While it is not clear that this approach would lead to the significant improvement in performance sought, this approach may result in significant cost reductions.
A basic scientific understanding of char and intumescence (swelling, foaming) is crucial to the development of improved materials. Research in char formation should include structural characterization and mechanical behavior (durability) and its relationships to ambient environment, heating rate, chemical derivatization, additives, and coatings.
The two general technical directions identified by the committee for polymeric materials development to improve fire and smoke resistance are incorporation of additives in polymers and synthesis of thermally stable, fire-resistant polymers. Particularly promising approaches are discussed in detail in Chapter 4. These include thin laminated or co-extruded films and blends, coatings and additives (including intumescents), phase-change or temperature sensitive materials, organic/inorganic polymer blends, polymer blends utilizing a high char-forming polymer as an additive, and polymer modifications. Additive approaches include volatile-phase active flame retardants that inhibit the combustion process, condensed-phase active flame retardant that lead to char or intumescence, flame retardants that endothermically lose volatile components, heat-sink additives, toxicant suppressants, and combinations of additives that take advantage of synergistic effects (i.e., multiple additives with differing but cooperative modes of activity in optimized combinations).
Perform research to improve the fundamental understanding of polymer combustion, including thermal degradation, char formation, intumescence, toxic gas production, and heat effects. Place special emphasis on the characterization of char and intumescence processes.
Investigate new additive approaches that allow for significant improvements in fire resistance and reduced toxic gas production in current materials.
Facilitate the development of new or modified polymers with significantly improved resistance to ignition and flame spread. Emphasize the modification of existing specialty polymers to obtain desired properties and the development of new thermally stable polymers or blends.
Evaluate and prioritize research and technological development efforts to ensure that the new materials will meet end-use requirements. Issues to be considered include costs; the contemporaneous processing and production capabilities of the materials and aircraft industries; ability to meet the design, performance, comfort, and aesthetic demands of aircraft interior applications; and compliance with environmental and health and safety regulations and practices.
New fire-resistant materials are of little practical value for aircraft interior use if the industrial processing technologies required to manufacture parts are not fully developed and broad-based. Short-and long-term strategies should be developed to characterize new material opportunities for compatibility with existing processes, as well as determining needs for future designs and manufacturing technologies. Short-to mid-range strategies should focus on researching materials that can be produced with existing tooling and manufacturing processes. Long-term strategies should evaluate both materials that can be processed with today's technologies as well as with future technologies. Where improved tire performance can only be achieved with materials requiring new manufacturing processes, materials research and manufacturing process development should be conducted concurrently to ensure smooth implementation.