Influence of Nozzle Temperature on Gas Emissions and Mechanical Properties in Material Extrusion-based Additive Manufacturing of Super Engineering Plastics

Abstract

Gas emissions pose significant environmental and health concerns in thermal processes involving thermoplastic polymers. This issue also extends to material extrusion (MEX) additive manufacturing (AM), which is a thermal process. Therefore, it is crucial to examine gas emissions during MEX AM. This study focused on super engineering plastics (SEPs) such as polyetheretherketone, polysulfone, and polyetherimide. A portable emission-measuring device was employed to analyze total volatile organic compounds (TVOCs) and formaldehyde (HCHO) emitted during MEX AM at various nozzle temperatures. Additionally, the anisotropy of tensile strengths in the SEP specimens fabricated in the longitudinal and transverse deposition directions was evaluated. Overall, the SEPs emitted TVOCs and HCHO within the range from not detected (N/D) to 0.595 mg/m³ and from N/D to 0.139 mg/m³, respectively, based on the nozzle temperature during MEX AM. Moreover, the tensile strengths varied from 59.0 to 83.4 MPa in the longitudinal deposition direction and from 19.2 to 55.7 MPa in the transverse deposition direction. Lower nozzle temperatures not only resulted in reduced gas emissions but also led to lower tensile strength in all the SEPs. However, the strategic use of longitudinal deposition can mitigate the reduction in tensile strength. To demonstrate this, a case study involving the fabrication of a Warren truss bridge was presented. This study provides guidelines for the deposition strategy in MEX using SEPs under AM conditions, aiming to minimize gas emissions while maintaining a tensile strength ranging from 81.1% to 88.7% of the bulk specimen strength.