Structure Development in Polymers during Fused Filament Fabrication (FFF): An in Situ Small- and Wide-Angle X-ray Scattering Study Using Synchrotron Radiation
Structure Development in Polymers during Fused Filament Fabrication (FFF): An in Situ Small- and Wide-Angle X-ray Scattering Study Using Synchrotron Radiation
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DOI：
10.1021/acs.macromol.9b01620
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发表时间：
2019-12-24
期刊：
影响因子：
5.5
通讯作者：
Bakradze, Georgijs
中科院分区：
文献类型：
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作者：
Nogales, Aurora;Gutierrez-Fernandez, Edgar;Bakradze, Georgijs
采用同步辐射同时测量小角和广角X射线散射(SAXS和WAXS)的方法，研究了PI形多层单壁聚合物熔丝制备过程中各层微结构的形成。我们研究了单层和单层之间的焊接区。作为模型材料，我们使用了等规聚丙烯(IPP)，这是一种商品化的半结晶聚合物，具有很强的作为添加剂制造原料的潜力。这些层是由FFF三维(3D)打印机沉积的，该打印机是为适应同步加速器光束线而定制的。利用WAXS数据确定辐照体积的温度。用结晶度和长间距表征了聚合物的微观结构。Avrami分析表明，iPP在薄层中的结晶行为与块体iPP的静态结晶行为非常相似，表明了类似的成核和生长机制。我们的结果揭示了结晶度在各个层之间的变化，反映了界面(自由面和焊接区)对薄层(厚度h=0.02 cm)最终结晶度的影响：聚合物在层的主体中结晶较多，在界面附近结晶较少。该效果有利于促进层之间的焊接，即，改善3D打印对象的整体机械性能，因为层之间的焊接预计通过聚合物链互扩散发生。沿着薄层，我们观察到由于打印头的减速，在角落附近有更高的结晶度。
Microstructure formation in individual layers during fused filament fabrication (FFF) of Pi-shaped multilayer single-walled polymer sample was studied by simultaneous measurement of small- and wide-angle X-ray scattering (SAXS and WAXS, respectively) methods employing synchrotron radiation. We investigated individual layers and the welding zone between individual layers. As a model material, we used isotactic polypropylene (iPP), which is a commodity semicrystalline polymer and has a strong potential as a feedstock material for additive manufacturing. The layers were deposited by an FFF three-dimensional (3D) printer that was custom-built to fit into the synchrotron beamline. WAXS data were utilized to determine the temperature of the irradiated volume. The polymer microstructure was characterized in terms of crystallinity and long-spacing. Avrami analysis indicates that the crystallization behavior of iPP in thin layers is rather similar to that observed in quiescent crystallization of bulk iPP, suggesting similar nucleation and growth mechanisms. Our results revealed a variation of crystallinity across the individual layers, reflecting the influence of interfaces (free surface and welding zone) on the final crystallinity of the thin layer (thickness h = 0.02 cm): the polymer is more crystalline in the bulk of the layer and less crystalline in the vicinity of the interfaces. This effect can be advantageous to facilitate the welding between the layers, i.e., to improve the overall mechanical performance of the 3D-printed object because welding between layers is expected to occur by polymer chain interdiffusion. Along the thin layer we observed a higher crystallinity near the corners attributed to a deceleration of the print head.