Polymer-based additive manufacturing (AM) processes have drawn great interest because of their potential to transform production of customizable low-volume parts and to reduce cost in the development of complex prototypes. However, the lack of understanding between processing conditions and final part quality severely limits the widespread implementation of this technology. There is a critical need for process line measurements of physical and material properties that are relevant to AM processes. This talk will address the effect of shear flow at various temperatures on the resulting structural and mechanical properties of polycaprolactone, a semicrystalline polymer often used in AM for biomaterials and medical implants. The first part of the talk will focus on process line measurements of IR thermography and Raman spectroscopy of polycaprolactone extruded from a printer nozzle in a simplified setup. Thermography allows for measurement of the temperature at short distances from the nozzle, and Raman spectroscopy probes vibrational modes sensitive to chain conformation in the crystallizing polymer. Separate correlation of the Raman peak intensities with differential scanning calorimetry measurements allows a quantitative measure of crystallinity as a function of time following extrusion. These measurements reveal the enhancement of crystallization kinetics at lower temperatures and faster shear rates (of order 100 s^-1) inherent in extrusion AM processes. To address the effect of crystallinity on mechanical properties, the second part of the talk will describe simultaneous measurements of Raman spectroscopy and rheology to develop a model relating crystallinity to the viscoelastic shear modulus during polycaprolactone crystallization from the melt. The model allows us to characterize the structural and mechanical evolution of the crystallizing polymer melt after a period of shear at a rates ~1 s^-1 at temperatures near the equilibrium melt temperature (~70 °C). The resulting relationship between crystallinity and rheology after controlled deformation provide a critical assessment of flow-induced crystallization concepts.

Effects of material extrusion parameters on the properties of crystallizing polycaprolactones for additive manufacturing

255th National Meeting (2018)

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