GOALI: Tomography and X-ray Interferometry of Flame Retardants and Additive Manufacturing

Louisiana State University, Baton Rouge LA

Investigators

Abstract

With this award, the Chemical Measurement and Imaging Program in the Division of Chemistry and the Grant Opportunities for Academic Liaisons with Industry (GOALI) program in the Division of Industrial Innovation and Partnerships (IIP) are supporting Professor Les Butler at Louisiana State University (LSU) and Dr. Jonathan McCarney at Albemarle Corporation to develop new X-ray imaging methods to assess the performance of flame retardants (FR) in polymers (plastics). Currently, flame retardants are assessed with methods such as the Underwriter Laboratory Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances (UL 94) using a bunsen burner, a stopwatch, and a cotton pad. The UL method is practical, but does not provide a chemical/physical insight into the effectively development of new flame retardants. The approach under development in the labs of Professor Butler and Dr. McCarney evaluates flame retardants by fast recording 2-D x-ray images (i.e. movies) during the burning period. The resulting movie enables direct visualization of chemical and physical processes, such as particle dissolution, gas bubble generation, the flow of the melting plastic, char-layer development, and micro-cracks in the char layer. In addition, the x-ray images provide quantitative information for more in-depth performance evaluations of new flame retardant materials relative to traditional tests. Beyond FR testing, both groups are also applying this new x-ray imaging technique in 3-D printing where new flame retardant materials are incorporated into consumer objects. Professor Butler is actively engaged an outreach effort to science students through the NSF I-Corp program where the combination of non-destructive chemical testing, 3-D printing, and materials development provides many research and educational opportunities to graduate, undergraduate and local high school students. The software under development in the Butler group, in collaboration with the Advanced Photon Source, will be made available to the public through the TomoPy project, an open source tomography software package. The X-ray imaging method under development at LSU uses two new grating-based interferometers recently constructed by the Butler team. The interferometers is operated in two modes: single-shot for speed, and stepped-grating for better image quality. The single-shot interferometry provides absorption, phase, and scattering imaging modalities during the measurements and its fast speed in image collection enables X-ray movie recording of flame retardant in action in a modified UL 94 test and direct observation of the performance of new-generation flame retardants. The same imaging methods is applied to fused deposition modeling (FDM), also known as 3-D polymer printing. The goal is development of procedures for assessing flame retardant impact on the quality of the 3-D print where x-ray movies show in situ fused deposition modeling of filaments composed of flame retardant/polymer blends to assess compatible temperature, flow, and printhead speeds. The knowledge is then to be used in exploring new options for 3-D structure of flame retardants in the printed object.