The feasibility of thermally-induced phase separation and crystallization for the production of semi-crystalline polyetherimide (PEI) microparticles from an amorphous feedstock has been reported recently. Here, we investigate process parameter dependencies for designing and control of particle properties. A stirred autoclave was used to extend the process controllability, as the applied process parameters, e.g., stirring speed and cooling rate, were adjusted. By increasing the stirring speed, the particle size distribution was shifted to larger values (correlation factor ρ = 0.77). Although, the enhanced droplet breakup, induced by the higher stirring speed, led to the formation of smaller particles (ρ = -0.68), broadening the particle size distribution. The cooling rate showed a significant influence on the melting temperature, reducing it with a correlation factor of ρ = -0.77, as confirmed by differential scanning calorimetry. Lower cooling rates led to larger crystalline structures and enhanced the degree of crystallinity. The polymer concentration mainly affected the resulting enthalpy of fusion, as an increased polymer fraction enhanced the latter (correlation factor ρ = 0.96). In addition, the circularity of the particles was positively correlated to the polymer fraction (ρ = 0.88). The structure assessed via X-ray diffraction, was not affected.
Keywords: high-performance thermoplast; liquid–liquid phase separation; microparticles; precipitation; process control.