Araldite - High-Performance Composites for Aerospace Interiors
Huntsman Advanced Materials: High-Performance Composites for Aerospace Interiors

By: Olivier de Verclos, TS Team Manager, Composites and Tooling, and Phillippe Christou, Head of European Technical Support, Huntsman Advanced Materials

With operating costs continuing to rise and the perceived need to improve the revenue potential on each and every new aircraft being commissioned, the OEM, airliners and supply sectors of the aerospace industry are evaluating all aspects of design and weight optimisation.

Over the last few years, international air shows have seen a ubiquitous emphasis on this issue, with an increasing focus on the role of advanced composites. Huntsman Advanced Materials has been a pioneer among the commercial developers of this technology, with composite materials that are valued for reducing weight with the consequential positive impact on fuel consumption and green-house gas emissions.

Most recently, the attention has shifted somewhat from the airframe to aircraft interiors in the continuous drive for weight reduction. For many commercial aircraft, interior use of composites is just as crucial to the cost/revenue equation, as the weight of materials for interiors actually exceeds that of the airframe.

From overhead bins and ceiling panels to cabin dividers, galleys and bulkheads, the use of interior composites in the pursuit of weight reduction vies with lighter textiles and leathers on seating, lighter food carts, the elimination of in-flight magazines and thinner display screens to achieve the desired results.

A unique combination of properties

Huntsman Advanced Materials has developed an entirely new high-performance, inherently flame-resistant and halogen-free solution for RTM and infusion processing which offers greater strength while answering continued demand for weight reduction in interior aerospace designs.

Araldite® FST 40002/40003 is a radically different development that provides a unique combination of fast curing capability, high mechanical, fire, smoke and toxicity (FST) performance alongside high quality and user-friendly composite processing conditions, enabling efficient production of interior carbon and glass composite parts with maximized weight savings.

In addition to weight savings, Araldite® FST 40002/40003, thanks to RTM and infusion process capability, enables highly complex parts production with a high level of function integration significantly reducing the number of parts in many designs.

High-quality versatile processing

The mixed two-component system exhibits a low viscosity at working temperatures above 50°C (Figure 1).

Figure 1: Viscosity versus injection temperature

The atency range from 50°C to 150°C provides the ability to produce complex parts in small and large dimensions (Figure 2).

Figure 2: Viscosity build-up versus temperature

In addition, Araldite® FST 40002/40003 has a low reaction energy of about 220 J/g which eliminates bulk exothermic safety issues as well as exotherm in the composites, enabling both large thickness composite part production and fast production of small to medium parts at high injection temperature.

By comparison with traditional RTM and infusion systems, the new system’s viscosity and reactivity profile shows snap-cure behaviour which allows fast Tg and interlaminar shear strength (ILSS) development.

Large parts requiring low-temperature injection can be demoulded after pre-cure conditions of approximately one hour at 100°C followed by one hour at 120°C, resulting in mould cost optimizations (Table 1).

Table 1: Cure Cycle Examples

The system also allows small to medium part production with very high output as parts can be demoulded after 5 minutes at 150°C.

After both in-mould pre-cure conditions, the system develops 85-90% of its ultimate ILSS -- when measured on carbon fabric reinforcement. In-mould pre-curing is followed by two-hour free-standing post-curing at 180°C, to enable the development of ultimate performance. Post-curing can be optional depending on in-mould cure conditions and composite requirements.

High performance for structural applications

Araldite® FST 40002/40003 develops dry and wet Tg of 260°C and 185°C (measured by DMA) with very high ILSS performance of 97 MPa and 55 MPa at 23°C and 120°C respectively – when measured on unidirectional carbon reinforcement (Table 2).

Table 2: Thermal and Mechanical Performance

Surprisingly for a system with such a high Tg and high crosslinking density, it also exhibits high tensile elongation and appreciable toughness, enabling the substitution of metal in highly structural applications.

Compliance with FAR 25.853 FST requirements

In contrast to other materials used in interiors, Araldite® FST 40002/40003 is an unfilled system. Its inherent FST properties come from the chemical nature of the network and its high cross-link density, and is not based on halogenated chemistry. The nw system meets the FAR 25.853 vertical burn, smoke and toxicity requirements with both carbon and glass fibre in all thickness configurations (Table 3). 

Table 3: FST Performance according to FAR 25.853 / ABD 0031

The heat release performance of the system is dependent on composite thickness, hence it is ideally suited for non-visible structural parts in the interior which do not have direct contact with potential ignition sources as well as cockpit parts that currently do not need to pass heat release.

For applications requiring heat release performance, it is possible to build on the new thermoset platform and formulate in order to meet heat release requirements in any configuration. This is shown in Table 3 comparing a recent development (not yet at commercial stage) to Araldite® 40002/40003, the first member of the Araldite® FST family.

Conclusion

Advanced composite processes and materials are essential for high-performance interior aerospace market. The new thermoset platform, fist illustrated by Araldite® FST 40002/40003, takes RTM and infusion processing into a new dimension, enabling for the first time, the production of structural parts without limitation in part complexity and function integration by comparison with current composite solutions, and with fast curing capability for small to medium RTM part production.

This first innovative high-performance solution creates a radically new and much improved value proposition for aerospace designs, providing a preferred alternative to metal in structural applications. In addition, further developments are planned which will complement and extend the offer.

Aircraft manufacturers are expected to deliver in excess of 17,000 new aircraft in the decade 2012-2022, including dedicated cargo planes. The use of interior composites is expected to increase by some 50 percent over this period with the joint interests of operators and conservationists linked by the relationship between weight reduction and reduced carbon emissions.

With its track record in this sector, Huntsman Advanced Materials expects to consolidate its role as an innovator where product development impacts directly upon operator profiability.