6 Polymer Technology Trends in Aerospace<br />By<br />Assist. Lec. Rand Fadhil Kadhim<br />Plastic materials are seeing increased use in aircraft and spacecraft to reduce weight, <br />improve quality, and lower manufacturing and maintenance costs.<br />1. Using antimicrobial plastics that have enhanced compatibility <br />with disinfectants for aircraft interiors.<br />Due to the COVID-19 pandemic, aircraft interior surfaces are being cleaned and <br />disinfected in ways that can quickly degrade traditional plastic materials. New <br />antimicrobial and disinfectant-resistant plastics initially developed for use in <br />hospitals are now being specified for aircraft interiors. These materials are <br />formulated to meet the stringent flame, smoke, toxicity, and heat-release standards <br />required for commercial aircraft.<br />2. Specifying high-strength thermoplastic composites for weight <br />savings, improved fuel efficiency.<br />Aerospace structures requiring high strength and stiffness have traditionally been <br />made from metals or thermoset composites. However, these materials have some <br />significant limitations. Metals are heavy, limiting their use for aerospace <br />applications where light weight is desired. Thermoset composites tend to be brittle, <br />often having poor chemical resistance. Thermoset manufacturing is laborintensive, with most thermoset composite materials not suitable for temperatures <br />above 100°C.<br />A new class of thermoplastic composites developed by Ensinger has strength and <br />modulus (stiffness) values comparable to metals and thermosets. The technology <br />involves continuous glass fibers or carbon fibers embedded in a thermoplastic <br />polymer matrix, usually consisting of polyetheretherketone (PEEK) or Ultem PEI <br />(polyetherimide). Since the matrix is made from high-performance, thermally <br />stable plastics, these composites can be used at elevated temperatures.<br />Thermoplastic composites offer many advantages associated with thermoplastics <br />including ductility, fatigue resistance, and vibration damping characteristics, as <br />well as resistance to fuels, lubricants, and cleaning chemicals. Sheet stock made <br />from these materials can be quickly formed into finished parts using heated metal <br />tooling, lowering manufacturing costs.<br />3. Choosing plastics that don’t interfere with radio frequency (RF) <br />signals for high-performance communications radomes.<br />The proliferation of unmanned aerial vehicles (UAVs), drones, and satellites that <br />rely on RF signals to control flight operations has increased demand for highly <br />reliable antennas. Optimum antenna function requires plastic radomes that won’t <br />significantly attenuate RF signals at the desired frequency and throughout the <br />device’s operating temperature range. Specialized engineering plastics with low <br />dielectric constants and low dissipation factors as well as enhanced toughness, <br />ultra-violet (UV) resistance, and thermoformability are becoming more widely <br />specified for use as protective antenna radomes.<br />4. Selecting durable, high temperature plastics to separate metal <br />surfaces for improved reliability.<br />Metal-to-metal connections are often points of failure in aircraft assemblies due to <br />inherent problems when mated metal surfaces are subjected to vibration and/or <br />sliding wear. Increasingly, designers are specifying ductile, high-performance <br />polyimide materials for applications such as spline couplings and the anti-rotation <br />elements of locking fasteners to separate metal parts. Introducing the polymer <br />element into the assembly increases service life and extends time between <br />required maintenance cycles.<br />For spline connections that transmit power to various aircraft systems through <br />connected rotating metal shafts, high-temperature couplings made from DuPont <br />Vespel polyimide are installed between mating metal splines for smoother <br />operation and longer life. The approach reduces spline wear when the rotating <br />metal shafts are slightly misaligned. Ductility of the polymer allows for shaft <br />misalignment without creating excessive stress on the metal shafts, bearings, or <br />drive motors.<br />In aerospace locking fasteners, DuPont Vespel polyimide is used as a ductile <br />locking element in a nut or a bolt to prevent unwanted rotation without damaging <br />the mating metal fastener during assembly or disassembly for maintenance. This <br />polymer element prevents the galling associated with all metal locking fastener <br />designs.<br />For both examples, ductility and wear performance of the polymer mitigates problems <br />associated with metal- on-metal contact.<br />5. Opting for low flammability, high dielectric strength plastics for <br />electrical insulation.<br />Plastics have long been the prefered material for applications requiring electrical <br />insulating properties. Electrical systems for modern military and civilian aircraft can <br />be particularly challenging since – in addition to having good dielectric strength <br />and resistance to electrical arcing – polymer insulators must be resistant to aircraft <br />fuels and lubricants; withstand vibration, wear, and fatigue; and have outstanding <br />flammability properties. Plastic insulators in aircraft may also have to operate <br />throughout a broad temperature range – from extremely cold at cruising altitudes <br />to extremely hot near jet engines.<br />Aircraft electrical system designers are now specifying fluoropolymers such as <br />polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), and <br />perfluoroalkoxy alkanes (PFA) as well as high performance thermoplastics <br />including PEEK, Ultem PEI, and DuPont Vespel for demanding aerospace <br />electrical applications including standoff insulators, shrink tubing, and flexible wire <br />wrap insulation.<br />6. Employing innovative polymers to create upscale aircraft <br />interiors.<br />Commercial aircraft are becoming increasingly more upscale, with interiors rivaling <br />luxury hotel lobbies. Printed graphics have traditionally been problematic for <br />aircraft interiors since high-traffic areas are exposed to wear and repeated cleaning <br />that can quickly degrade printing.<br />Newer technologies such as Infused Imaging with KYDEX thermoplastics allow <br />designers to create customized environments using imagery that’s in the material <br />not on it.<br />There have also been significant advances in the plastic lens material used to <br />manage and transmit light on commercial aircraft. New polymer formulations allow <br />for high light transmission, excellent diffusion, and precise color control of LED <br />lamps. Light management using high-performance plastics is positively impacting <br />the aesthetics of aircraft interior spaces.