Tailoring Semicrystalline Polymer Blends for Extrusion-based Additive Manufacturing

Additive manufacturing (AM) of semicrystalline polymers is still largely relegated to rapid prototyping applications. Problems involving shrinkage and warpage of printed parts must be addressed before such polymers can be used for printing functional parts. Moreover, there is a great deal of variation in the morphology and crystallization behavior of the polymer depending upon the processing conditions employed and the inherent material properties. The goal of this work is to provide fundamental understanding of the complex changes that take place during extrusion-based printing of semicrystalline polymer blends and thereby assist in developing tailored compositions for consistent and reliable AM processing. In the present work, we blend polypropylene with polyolefin-based copolymers and evaluate the compatibility of the blends with extrusion-based AM. Differences in crystallization behavior have a profound impact on the interlayer adhesion and residual stress state, which directly controls the mechanical performance and warpage of the printed parts. We investigate the effect of high shear in the printer nozzle on the flow-induced crystallization of the blends. Variations in the crystal structure, degree of orientation, and degree of crystallinity significantly influence the extent of interlayer polymer chain diffusion and interlayer adhesion. The findings from this study can be leveraged in toolpath planning, process parameter optimization, and new feedstock development for AM.