As part of the research project "ExSaZell - Efficiency and Performance Enhancement of Thermoplastic

Honeycomb Cores through Innovative, Extrusion-Based, Foamed Cellular Wall Systems with Sandwich

Structure," an innovative three-layer cellular wall was developed in collaboration with the Kunststoff-

Zentrum in Leipzig and HTWK Leipzig. This development is based on the extrusion of thermoplastic

polymer polypropylene into a multi-layer flat film followed by a process of thermoforming into

honeycomb cores. The structured cellular wall comprises of two solid outer layers and a lower density

inner layer, as shown in Fig. 1. The application of this method has resulted in significant improvements

in stiffness and mechanical strength under compressive loads, making it particularly advantageous for

lightweight construction applications.

The foamed inner layer plays a crucial role by contributing to the overall density reduction of the cellular

wall, thus enabling cellular walls with an increased cross-sectional area at a constant weight. This

increase in wall thickness results in a simultaneous rise in buckling stiffness, delaying the onset of

buckling failure as the primary failure mechanism of honeycomb cores under shear and compressive

loads. Initial industrial trials demonstrated that the flatwise compressive strength, a critical performance

metric for honeycomb cores, was increased by 21.8 % compared to a mono-layer structure at

comparable honeycomb core density [1]. The internal cellular structuring was achieved by adding a

chemical blowing agent and nucleation to the base granulate of the inner layer. The concept creation

and production trials conducted by ThermHex were supported by FEM simulations in collaboration with

project partner HTWK Leipzig as well as morphological and mechanical investigations by KUZ Leipzig.

The results obtained thus far indicate that the optimized sandwich structure has the potential to replace

conventional materials in various industrial applications, particularly in the automotive and aerospace

industries. The improved energy efficiency during honeycomb core production and the resulting

reduction in manufacturing costs underscore the economic and ecological benefits of this innovative

material solution as well as the potential for optimal resource-efficiency in use phase of parts based on

this innovative technology.