Nicolas Mys

Processing of Polysulfone to Free Flowing Powder by Mechanical Milling and Spray Drying Techniques for Use in Selective Laser Sintering

Polysulfone (PSU) has been processed into powder form by ball milling, rotor milling, and spray drying technique in an attempt to produce new materials for Selective Laser Sintering purposes. Both rotor milling and spray drying were adept to make spherical particles that can be used for this aim. Processing PSU pellets by rotor milling in a three-step process resulted in particles of 51.8 μm mean diameter, whereas spray drying could only manage a mean diameter of 26.1 μm. The resulting powders were characterized using Differential Scanning Calorimetry (DSC), Gel Permeation Chromatography (GPC) and X-ray Diffraction measurements (XRD). DSC measurements revealed an influence of all processing techniques on the thermal behavior of the material. Glass transitions remained unaffected by spray drying and rotor milling, yet a clear shift was observed for ball milling, along with a large endothermic peak in the high temperature region. This was ascribed to the imparting of an orientation into the polymer chains due to the processing method and was confirmed by XRD measurements. Of all processed powder samples, the ball milled sample was unable to dissolve for GPC measurements, suggesting degradation by chain scission and subsequent crosslinking. Spray drying and rotor milling did not cause significant degradation.

Processing of Syndiotactic Polystyrene to Microspheres for Part Manufacturing through Selective Laser Sintering

Syndiotactic polystyrene pellets were processed into powder form using mechanical (ball milling, rotor milling) and physicochemical (spray drying) techniques with the intention of using it as feed material for selective laser sintering. New materials are an important component in broadening the application window for selective laser sintering but must meet strict requirements to be used. Particles obtained were characterized in size and shape using SEM imaging, analyzed by software, and compared to the product obtained by conventional ball milling. Rotor milling and spray drying proved capable of making spherical powders, yet only rotor milling achieved particles with a mean diameter within the desired range of 45–97 µm. Subsequently, the obtained powders were examined for the effect each processing technique imparts on the intrinsic properties of the material. Differential scanning calorimetry analysis revealed amorphization for all methods and a reduction in crystallinity after processing, however, the reduction in crystallinity was acceptably low for the spray-dried and rotor-milled powders. Ball milling displayed an exceptional reduction in crystallinity, suggesting severe degradation. As a final test, the rotor-milled powder was subjected to single-layer test and displayed good coalescence and smooth morphology, albeit with a large amount of warpage.

Processing of polysulfone to free flowing powder for part manufacturing through selective laser sintering

Selective laser sintering (SLS) is a rapidly expanding field of the 3D printing concept. In order to provide new polymeric powder materials with desired properties and morphology the spray drying method has been tested using an ultrasonic nozzle. In this work polysulfone (PSU) has been identified as a promising material. PSU was first dissolved and characterized in order to determine the limiting conditions to process said polymer. A maximum concentration of 12 m% has been found to be atomizable by the VOG nozzle. Initial experiments have shown that the drying conditions play an important role in obtaining the right morphology. The best spray drying conditions were identified at an inlet temperature of 210 °C and feed rate of 21,4 mL/min resulting in particles of 31,8 µm mean diameter. Poor conditions were identified at low feed rates of 7,4 mL/min with inlet temperature of 220 °C leading to inflated or collapsed structures.