Material extrusion additive manufacturing processes force molten polymer through a printer nozzle at high (> 100 s−1) wall shear rates prior to cooling and crystallization. These high shear rates can lead to flow-induced crystallization in common polymer processing techniques, but the magnitude and importance of this effect 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 combination of infrared thermography and Raman spectroscopy to measure the temperature and percent crystallinity 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, which shows that processing conditions can have a dramatic effect on crystallization kinetics in additive manufacturing.
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机译：材料挤出增材制造工艺在冷却和结晶之前，以高（> 100 s -1 ）壁剪切速率迫使熔融聚合物通过打印机喷嘴。这些高剪切速率可能会导致普通聚合物加工技术中的流动诱导结晶，但是这种影响的大小和重要性对于增材制造而言是未知的。理解该过程的一个重大障碍是缺乏用于量化聚合物长丝挤出后结晶度的原位测量技术。为了解决这个问题，我们结合使用了红外热成像和拉曼光谱技术来测量增材制造过程中挤出的聚己内酯的温度和结晶度。我们根据设备可达到的喷嘴温度和细丝进给速率，将结晶度作为时间的函数进行量化。结果表明，在较高的剪切速率和较低的喷嘴温度下，结晶会更快地发生，这表明加工条件可能对增材制造中的结晶动力学产生重大影响。
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