Thermogravimetric Analysis and Tensile Testing of PEEK structures Fabricated via Extrusion and 3D Printing

Polyether ether Ketone (PEEK) is a thermoplastic polymer with superior chemical resistance, thermal stability, flame retardancy and mechanical properties. It is also known for its biocompatibility. The mechanical properties of PEEK are in the similar range as that of human bone making it preferable over metals for orthopaedic implant fabrication. PEEK is also FDA-approved material for orthopaedic applications. Additive manufacturing has emerged as a efficient method to fabricate complex and customizable structures. The process of extrusion of PEEK into a filament aids in additive manufacturing and hence extrusion of PEEK and 3D printing has to optimized for obtaining desired properties. This work reports the extrusion of PEEK filament from pellets and fabrication by 3D printing. The thermal and mechanical properties of extruded filament and 3D-printed dog bone samples were evaluated respectively. The filament of 1.75 mm diameter was produced by extruding PEEK pellets in an extruder with 4-zone heaters at temperatures above the melting point of PEEK. The extruded filament in a spool was immediately used to 3D print the dog bone geometry (as per ASTM D638 Type 1) using the fused filament fabrication (FFF) using appropriate printing parameters. Tensile testing of dog bone samples showed Ultimate Tensile Strength of $44.93 \pm 0.41$ MPa and Young’s Modulus of $1.50 \pm 0.07 \text{GPa}$. Thermogravimetric Analysis (TGA) was also performed (as per ASTM E 1131) on the extruded filament, evaluating the thermal decomposition of PEEK. TGA characterization aids in understanding the mechanism of decomposition of the substance based on mass loss as a function of temperature for a given heating rate. TGA showed that extruded filament was thermally stable up to $600^{\circ} \text{C}$ above which the mass started to decompose rapidly till $800^{\circ} \text{C}$. To summarize, PEEK was successfully extruded and 3D printed. The tensile and thermal properties were evaluated and reported. The applications of these 3D-printed PEEK parts can be found in biomedical, aerospace, marine, and energy fields given their superior mechanical and thermal properties. PEEK also has been used extensively in composites for various applications.