Process line measurements of polycaprolactone crystallization in additive manufacturing

Polycaprolactone is a semicrystalline polyester used in additive manufacturing processes for biomaterials. Filament-based additive manufacturing processes often force molten polymer through a printer nozzle at high (> 100 s^-1) wall shear rates prior to cooling and crystallization. Although the phenomenon of flow-induced crystallization is well-known, the effect of flow on the crystallization kinetics of polymers is unknown for additive manufacturing. A significant barrier to understanding this process is the lack of in situ measurement techniques to quantify crystallinity after polymer filament extrusion. To address this issue, we use a fiber optic probe to measure the Raman spectrum of extruded polycaprolactone during additive manufacturing. We quantify crystallinity as a function of time for the nozzle temperatures and filament feed rates accessible to the apparatus. Crystallization is shown to occur faster at higher shear rates and lower nozzle temperatures. Our measurements provide experimental evidence of the effect of shear flow on polymer crystallization in additive manufacturing.