Feel at home foam

With the future of aircraft interior materials migrating to more advanced, hi-tech solutions, David Stirling, group chief executive officer of leading cellular materials technology provider, Zotefoams explains how the company’s ZOTEK F product offers versatility for a whole host of applications to replace traditional materials.

While aircraft interiors might be viewed as the understudy to the structural design of an aircraft, behind the scenes revolutionary technology is emerging to meet ever more demanding regulatory standards for aviation.

As technology evolves, traditional – and even some newer – materials, including silicone, PU and composites, are being superseded by alternatives that offer greater functional benefits and flexibility to the meet complex technical, regulatory and aesthetic requirements for aircraft interior design.

Two of the prime factors here are weight – with reducing carbon emissions through reduced fuel consumption a priority – and safety, particularly the need to reduce the risk of flammability. Aviation material standards are central when evaluating components used for aircraft as they encompass various mechanical requirements including thermal, chemical and, most notably, Fire, Smoke and Toxicity (FST) credentials.

Zotefoams, a British manufacturer of closed-cell polyethylene (PE), polyvinylidene difluoride (PVDF) and nylon foams for demanding industrial applications, has recognised the unique properties of PVDF foams that can provide a sophisticated, lightweight, fire resistant solution for aviation, eliminating the aforementioned problems and complying with and exceeding demanding industry standards.

Originally founded as a manufacturer of expanded rubber products in the 1920s, the forerunners of Zotefoams supplied aviation-grade foamed rubber through the 30s and 40s, before switching to a polyolefin-based portfolio during the 1970s, believing the future lay in the more specialised and sophisticated properties afforded by plastics. During the 1990s, Zotefoams investigated other materials that could be used for foaming; the result was a range of high-performance foams produced from engineering polymers.

Key to the performance of these materials and ultimately the success of the company is a unique manufacturing process which uses only pure nitrogen to expand foams. The air we breathe is 78% nitrogen, so the process is inherently environmentally-friendly; far more so than the more widespread method of expanding foams chemically. Nitrogen is also chemically inert, which is an important factor where flame retardance is a critical requirement.

This is a three-stage process, with the first stage seeing base resin and additive ingredients extruded to produce solid polymeric sheets. Depending on the material, these are crosslinked either during the extrusion process or offline subsequently; crosslinking is essential to the strength and performance of the finished product.

In the second stage foams are loaded into a high-pressure autoclave and heated above their softening temperature while being subjected to a high-pressure dose of pure nitrogen. Finally, the nitrogen-charged slabs are loaded into a low-pressure autoclave, again heated above their softening temperature to allow controlled expansion of the nitrogen and thereby uniform physical foaming.

Fit, form and function

Most foams today are chemically blown, with the plastic heated and mixed with a blowing agent to produce expansion. This process is more difficult to control reliably than physical expansion and can result in and end product with variable densities and different properties in different directions. The chemical blowing agent is released over time, producing odour and potential fogging.

One of the most successful products of the Zotefoams manufacturing process is a PVDF foam known as ZOTEK F, an inherently flame-retardant material releasing very little heat and small quantities of smoke during combustion, offering a host of beneficial characteristics for aviation interior technology. The nitrogen expanded foam provides a uniform cell structure, offering the same properties in all directions.

Its physical performance means that it is compatible with a wide range of forming methods, allowing the production of complex shapes for applications including soft-touch trims, aircraft seating and Environmental Control Systems (ECS) ducting. It is also the only foam compatible with bake moulding, an increasingly popular manufacturing method for components requiring high durability, such as armrests.

Compared with other foam materials, PVDF has excellent chemical resistance, even to aviation fluids and chemicals, and it is biologically inert, making it resistant to mould and bacteria. As a closed-cell foam, it does not absorb water and so where it is used as an underlay, water is unable to collect and cause corrosion.

With no flammability agents added during manufacture, the fluoro-polymer foam is inherently non-flammable, so it meets the requirements of aviation flammability standards, including standards set up by major OEMs meeting BMS 8-371D and AIMS04-14-009 thanks to its low Heat Release performance and Fire, Smoke and Toxicity properties, and adding little to the overall combustibility of soft-touch interior fittings.

Aerospace manufacturers such as leading supplier of premium aircraft seating, Thompson Aero Seating, have recognised the need for lightweight, flexible materials with low flammability at the forefront of its designs; complying with and exceeding demanding industry standards is central to all Thompson’s products and designs.

Are you sitting comfortably?

Thompson’s latest concepts require soft touch trims around the rear of the business class seating to negate the need for a composite panel to give structural support; reducing the overall weight of the seat and, in turn, lowering flammability and saving on fuel costs.

Zotefoams was approached by Thompson Aero Seating to maintain its sophisticated, hi-tech seating with a lightweight, fire resistant solution. ZOTEK F was selected to complement the aluminium frame around the seating due to its distinctive range of characteristics. With densities starting at just 33kg/m³ the lightweight material offers impressive weight savings – up to 50% compared to traditional materials – as well as significant cost savings.

Thompson Aero Seating has adopted the PVDF material in all ranges of its product portfolio and has since benefited from an estimated 1.6kg reduction in weight per seat; subsequently saving on fuel costs and, most importantly, surpassing rigorous flammability criteria.

To put this into perspective, Zotefoams’ data suggests that a 100kg weight reduction is the equivalent of $25million in fuel costs over the life of an aircraft. Furthermore, as a result of overall mass reduction, Thompson now has the flexibility to add more technology to their seats without compromising weight limitations.

The future of aircraft interior materials is, without doubt, shifting to more advanced, hi-tech solutions that offer applications and functionality beyond the obvious. ZOTEK F is a unique material produced by a unique processing method, it offers a great deal to the aviation industry, not least in terms of versatility for a whole host of applications to replace traditional materials.

www.zotefoams.com