Functionally graded polymers and polymer composites based on solid resin systems

• Applicants: Dr. Katharina Koschek; Professor Dr.-Ing. David May
• Subject Area: Plastics Engineering ; Lightweight Construction, Textile Technology ; Polymeric and Biogenic Materials and Derived Composites
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 537556366

Functionally Graded Materials (FGMs) is a group of materials with a gradient in properties, i.e. a continuous change of one or more material properties over a given unit of length or volume. Functionally grading polymers does not only allow for tailoring to specific applications. Modifications often improve a certain property while others get worse. By grading, the properties can be adapted only where this is really required. In fiber-reinforced plastic composites (FRP) the internal fiber structure is the dominating influence on the mechanical performance and could be used for grading of these properties. However, the matrix also plays a crucial role e. g. for toughness (impact behavior) and fatigue. For 2D- (in-plane) or even 3D-grading (all directions) of parts single layers with in-plane graded properties would be required. In this context solid resins (SR) bear great potential because of their unique processing characteristics. SR are completely mixed resin systems, but they are solid at room temperature and stable in storage until a limit temperature is reached. Above this temperature they liquefy, becoming low viscous (< 1 Pa*s) at further elevated temperatures, with the crosslinking reaction still remaining negligible. Only at even higher temperatures relevant crosslinking activities take place. SR can therefore be melted, shaped and re-solidified, thus enabling long-term stable, partially impregnated semi-finished fiber products. This is an option that otherwise requires thermoplastics, but their high melt viscosity (often >> 10,000 Pa*s) does not allow large flow distances. Hence, SR seem an ideal material concept for 3D functional graded FRPs. Pre-studies at IFAM with benzoxazine-based systems showed high potential for property grading combined with vitrimer-like properties. However, similar to epoxy-SRs they are highly brittle in their uncured state which is a severe challenge for their processing to composites. Pre-studies at IVW showed that textiles with printed patterns of SR on their surface allow for the drapeability needed for part manufacturing. The overall target of the project is to develop the fundamental material know-how and technologies required for 3D functionally graded SR composites. Considering benzoxazine- and epoxy-based SRs the target material property of grading will be the toughness, whereas possible negative influences on temperature stability and processing behavior (viscosity, wetting) are to be minimized. Aside the targeted material properties, printable SR and 3D printing technology and the related processing parameters will be developed aiming at the understanding of structure/property and processing relationships. Stability, handling, and drapeability of the pre-impregnated textiles and fibers will be studied and correlated with the resulting graded fiber/polymer-composites.

• DFG Programme: Research Grants