Advancing In-Nozzle C-FRTP Printing
Experimental Insights into Melt Impregnation Dynamics and Interface Adhesion through Meso-Level FDM printing
D. de Grijff (TU Delft - Mechanical Engineering)
J. F L Goosen – Mentor (TU Delft - Computational Design and Mechanics)
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Abstract
The ever-growing demand for high-performance materials and more functional 3D printing has raised tremendous interest in advancing Multi-Material Additive Manufacturing (MMAM). Developing C-FRTP 3D printing through FDM Technology opens new scalable FRP solutions. These components possess exceptional properties such as specific strength, recyclability, impact/chemical resistance, and geometrical complexity. Researchers have successfully exploited FDM technology to print C-FRTP composites but lack high interface bonding between the reinforcing fibers and thermoplastic polymer matrix. Moreover, C-FRTP is limited to weak frictional forces and mechanical interlocking. Besides, porosities are observed at the interface, which results in overall mechanical weakness.
Various Meso-level C-FRTP 3D printing methods and print heads have been developed and standardized, but more knowledge is needed of essential 'In-Nozzle' C-FRTP impregnation dynamics. During In-Nozzle impregnation, solid-dry fiber and molten Thermoplastic polymer matrix bond inside the print head before extrusion. This master thesis explores the challenges and potential solutions by conceptualizing a functional ’In-Nozzle’ impregnation extruder capable of extruding proper C-FRTP composites using FDM printing.
Initially, a theoretical framework is presented on melt impregnation dynamics and Interface adhesion, followed by experiments as validation. Based on the melt impregnation analysis observations, a limited permeability of Thermoplastic polymer melt is observed. These are primarily from the high viscosity of the thermoplastic materials (PLA) and the dense fibers. Applying an overflow of melt with extensive external pressure achieves a smoother and faster melt flow around the interface. Tensile strength experiments underscored the dependency on the exposure time and encapsulation of fibers by matrix and showed an increase in IFSS compared to the neat thermoplastic polymer. Further research is recommended to augment contact surfaces between fibers and the matrix. This research highlights the current challenges and lays the foundation for future advancements in C-FRTP 3D printing through in-nozzle impregnation, offering insights into improving material compatibility, impregnation quality, and interfacial bonding.