The Effect of Printing Parameters on Composites with Continuous Liquid-Crystal Fibrils

It is well known that the strength and stiffness of parts made by Fused Filament Fabrication (FFF) are highly dependent on printing parameters. This is especially true for Z-direction and interlaminar properties. While in-plane strength and stiffness for parts made from unreinforced amorphous polymer are not strongly affected by printing parameters, the strength and stiffness are somewhat affected for parts made from semi-crystalline polymer, and strongly affected for parts made from chopped carbon or glass fiber reinforced polymer.

Various forms of Thermoplastic-Liquid Crystal-Polymer (TLCP) filament have been studied in the research literature and have recently become available in the 3D printing market. One form of these new TLCP based filaments involves continuous TLCP fibrils reinforcing a matrix polymer. These new high performance filament materials have been used to 3D print FFF parts with strengths upwards of 200MPa and modulus upwards of 20GPa using open system desktop 3D printers. However, the effect of printing parameters on the strength and stiffness of these new TLCP is not well understood.

This presentation will share the results of a systematic study of strength and stiffness as a function of printing parameters including layer height, print speed, and print temperature. In-plane (X & Y direction) tension properties as well as Z-direction or interlaminar properties will be presented and compared for three different filament materials; unreinforced polymer, chopped-fiber-reinforced polymer, and continuous-TLCP-fibril-reinforced polymer. Both the strength and stiffness of parts printed from the TLCP based filament were seen to vary by up to 10x with simple modification of acceptable printer parameters. A theoretical explanation for this wide range of performance from one filament input will be discussed. These new materials with exceptional and tailorable properties can be used with distributed compliant design for innovative applications such as morphing wings and other aerostructures in unmanned drones.