Translucent and flame-retardant SMC semi-finished products for interior applications in aircraft (TraNa)

Innovative SMC semi-finished products open up new application possibilities

Given the high number of air passengers, the development of environmentally friendly solutions for achieving sustainable aviation is becoming increasingly important. In the cabin area, the use of ecologically and economically efficient lightweight materials is particularly highlighted.

Sheet Molding Compounds (SMC) offer great potential in this regard thanks to their high design freedom and economically attractive manufacturing costs. This is achieved by avoiding environmentally harmful phenolic resins and employing efficient manufacturing processes. Currently, most polyester- or vinyl ester-based SMC semi-finished products used in the cabin area are modified with particulate flame retardants, such as aluminum hydroxide (ATH) or ammonium polyphosphate (APP) to meet stringent fire, smoke, and toxicity (FST) requirements. However, the particle structure of these flame retardants necessitates high filler loadings, which negatively impact the optical quality of the components (resulting in streaking and poor colorability), while also leading to reduced mechanical properties and increased material density. As a result, the application possibilities of current SMC semi-finished products in the aircraft cabin are limited.

Most applications involving visible components require an expensive and environmentally harmful additional coating due to the inadequate optical quality. These aspects present significant obstacles to the widespread use of SMC in the cabin.

Within "TraNa" research project, (Aviation Research Program), SMC semi-finished products are being developed using novel flame retardants based on Layered Double Hydroxides (LDH) nanoparticles. LDH acts as a flame retardant due to an endothermic decomposition reaction, releasing both H₂O and CO₂. Additionally, LDH forms an inorganic O₂ barrier layer. Due to their nanoparticle nature, LDH does not scatter or reflect light, allowing very high filler loadings and the production of translucent resin pastes when perfectly dispersed in a specially adapted epoxy resin matrix. Furthermore, it enables homogeneous coloring, which, combined with the high surface quality of the manufactured components, can replace environmentally harmful coatings. The production and processing of such resin pastes into translucent or homogeneously colored SMC semi-finished products open up completely new application areas in the aviation interior sector while meeting lightweight and fire protection requirements thus offering high innovation potential.

In the course of the project's work so far, SMC semi-finished products based on epoxy resins with 40 wt. % flame retardant particles, 25 wt. % glass fiber content and resulting density of 1.65 g/cm³ have been developed. They are comparable to conventional flame-retardant semi-finished products in terms of manufacturing and processing but exhibit a translucent appearance after processing as shown in Figure 1. The mechanical properties already meet the level of conventional semi-finished products at the current stage of development, considering the same fiber mass content as shown in Figure 2. Further project progress will focus on improving the dispersion quality of LDH particles, as shown in Figure 3, to further optimize the material and flame retardant properties.

Project partner:          

• CompriseTec GmbH
• Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. (Institut für Angewandte Polymerforschung IAP und Silicatforschung ISC)
• Schmidt & Heinzmann GmbH & Co. KG

Associated partners:

• jetlite GmbH
• Nabaltec AG
• Polynt Composites Germany GmbH
• Recaro Aircraft Seating GmbH & Co. KG
• Schill + Seilacher “Struktol” GmbH

Contact:

Dr.-Ing. Florian Gortner
Postdoc Press & Joining Technologies
E-Mail: florian.gortner@ivw.uni-kl.de
Telephone: +49 631 2017 439