New Insights on Expandability of Precured Epoxy Resin Systems to Form Epoxy Foam Sheet and Bead Foam using CO2 gas versus Carbamate

• Applicant: Professor Dr.-Ing. Holger Ruckdäschel, since 2/2023
• Subject Area: Polymeric and Biogenic Materials and Derived Composites
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 452210919

Polymer foams are nowadays used in many everyday applications, whereby thermoset foams are ideal for high-temperature applications under aggressive environmental conditions due to their high glass transition temperature, excellent mechanical properties and aging resistance. However, the production of thermoset polymer foams is a complex interaction of the foaming process (nucleation, cell growth and stabilization) and the cross-linking behavior (gelation, vitrification). Parameters such as blowing agent concentration and type (gas loading, chemical blowing agent) as well as the cross-linking state (molecular weight between network points, viscosity, modulus) on parameters such as foam density, cell size and compressive strength have for the most part not yet been investigated and are still not understood in detail. The aim of this research project is therefore to investigate the influence of the environmentally friendly blowing agent CO2 and the latent dual-use component carbamate (conversion into amine hardener and release of CO2 as blowing agent at decomposition temperature) on the foaming behaviour of epoxy resins. Resins and hardeners are selected according to their viscosity profile and achievable Tg, whereas values well above 140 °C are targeted.For this purpose, CO2 loading and the structure of the resin system are varied via the degree of cross-linking and the molecular structure of the network in order to influence the gas diffusion and thus the expansion behaviour. This process, the so-called "solid-state foaming", is applied to epoxy particles and epoxy plates. Analogous to the direct CO2 loading of the pre-crosslinked systems in the autoclave, carbamates are to be investigated as an environmentally friendly blowing agent alternative to conventional chemical blowing agents. Due to their latency up to the decomposition temperature they offer the advantage of a better process control. Due to the release of amine and the in-situ generation of CO2, the pre-crosslinking can be specifically adjusted here, with the remaining crosslinking being carried out by the amine. The foam bodies generated from the particle foam as well as the layer-like structure are to be subsequently bonded as sandwich core material with epoxy top layers to generate high-performance sandwich elements. These will be investigated for their joining properties and their mechanical property profile. Here, the applicant sees great potential to present an environmentally friendly alternative to the high-temperature thermosets foams based on melamine or polymethacrylamide. These are currently produced with either little environmentally friendly blowing agents such as pentane or monomers that are hazardous to health. The project aims to provide the basis for understanding the foaming and cross-linking behaviour of epoxy resins with CO2 as blowing agent and to investigate their suitability as sandwich core material.

• DFG Programme: Research Grants
• Ehemaliger Antragsteller: Professor Dr.-Ing. Volker Altstädt, until 2/2023