Designing Polymer Materials for Improved Additive Manufacturing

Currently, two of the most used additive manufacturing methods for polymers are selective laser sintering (SLS) and fused filament fabrication (FFF). Although at high market size, they both have imperfections. The materials for SLS are limited and the objects manufactured by FFF existing anisotropic behavior. Targeting on these drawbacks, this thesis has proposed a novel method to prepare polypropylene (PP) microsphere which is suitable for SLS with low cost and scalable potential; and a novel material with polycarbonate as matrix that has shown a decrease in anisotropy after FFF printing.

The PP microsphere in this thesis was prepared via liquid-liquid phase separation, by changing the processing condition such as temperature, solution concentration and molecular wight, we have the capability to control the size of microsphere. The size of resulting particles was characterized by scanning electron microscopy and analyzed by ImageJ. The relationship between processing condition and particle size has been correlated to phase diagram, in which a higher equilibrium polymer-rich phase concentration will result in a larger particle size. We have also shown the versatility of this method by successfully prepared SLS suitable PP powders from a recycled pill bottle.

The polycarbonate matrix has been blended with photoinitiator and crosslinker by a single screw extruder. We have applied a customized UV-LED functionalized 3D printer to print our blend. Tensile strength has been used as an indicator of anisotropy. Although decrease in anisotropy for some samples, the result indicates a competition between interlayer crosslink and in-bulk crosslink. For interlayer crosslink, it will decrease anisotropy by the crosslink on the interface with adjacent layers of the oxidation product of polycarbonate. The in-bulk crosslink, on the other hand, will increase anisotropy by crosslink in the filament and constraint the flow of polymer melts during FFF.