Traditional polymer powder and micropellet-based processes, such as powder bed fusion and rotational molding, have shown an increased demand in modern processing industries, where polymer powders are required to have a size between 50 to 1000 micrometers. A new technique developed at the PEC yields micropellets with a controlled morphology and narrow particle size distribution for sizes within this range.
Powders and micropellets are produced by subjecting a polymer melt strand to compressed air, causing surface disturbances on the polymer melt. At the exit of the nozzle, the polymer melt is surrounded by an air stream of controlled temperature and airflow rate. Figure 1 shows the micropelletization setup. Different types of breakup mechanisms occur, including cohesive-brittle fracture, elongation, and break-up due to Rayleigh disturbances. Processing primarily depends on the following parameters: extrusion rate, polymer and airflow temperatures, airflow rate, and material properties. Particle size distribution and aspect ratio are shown for a PA12 material are shown below.
The current tasks for this project include the investigation of different materials to determine their micropelletization capability. These materials include PP, PA12, PA6, and PC. In addition, selective laser sintering (SLS) will be used to determine the feasibility of SLS printing using micropellets, with a goal of improving the quantity of particles produced under 100 micrometers.
Schematic of the micropelletization die.
Particle size and aspect ratio measurements using PA12 resin.