Modelling flow-enhanced crystallisation during fused filament fabrication of semi-crystalline polymer melts
Modelling flow-enhanced crystallisation during fused filament fabrication of semi-crystalline polymer melts
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DOI：
10.1016/j.addma.2018.10.018
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发表时间：
2018-12-01
影响因子：
11
通讯作者：
Graham, R. S.
中科院分区：
文献类型：
--
作者：
McIlroy, C.;Graham, R. S.
实现更好的熔丝制造（FFF）控制依赖于对热塑性打印材料在打印过程中如何表现的分子理解。对于半结晶聚合物来说，最终的晶体形态及其在冷却过程中的发展方式对于确定部件性能至关重要。在这里，结晶动力学添加到以前开发的模型，其中包含一个分子意识的本构方程来描述聚合物的拉伸和取向在典型的非等温FFF流，和条件下，流动增强的成核发生由于残余拉伸揭示。流动增强的成核导致在沉积的长丝的表面处的加速的结晶时间，而长丝的主体由较慢的静态动力学支配。预测的10%结晶度的时间t（10）与聚己内酯（PCL）的原位拉曼光谱测量定量一致。该模型突出了tn的单一测量无法捕获的重要特征。特别是，晶体形态不同的横截面，与较小的球晶形成的外皮层，解释在全瞬态结晶测量中观察到的功能。最后，开发流动增强结晶提出了一种机制，以增加焊接强度之间的界面沉积丝。
Achieving better control in fused filament fabrication (FFF) relies on a molecular understanding of how thermoplastic printing materials behave during the printing process. For semi-crystalline polymers, the ultimate crystal morphology and how it develops during cooling is crucial to determining part properties. Here crystallisation kinetics are added to a previously-developed model, which contains a molecularly-aware constitutive equation to describe polymer stretch and orientation during typical non-isothermal FFF flow, and conditions under which flow-enhanced nucleation occurs due to residual stretch are revealed. Flow-enhanced nucleation leads to accelerated crystallisation times at the surface of a deposited filament, whilst the bulk of the filament is governed by slower quiescent kinetics. The predicted time to 10% crystallinity, t(10), is in quantitative agreement with in-situ Raman spectroscopy measurements of polycaprolactone (PCL). The model highlights important features not captured by a single measurement of tn. In particular, the crystal morphology varies cross-sectionally, with smaller spherulites forming in an outer skin layer, explaining features observed in full transient crystallisation measurements. Finally, exploitation of flow-enhanced crystallisation is proposed as a mechanism to increase weld strength at the interface between deposited filaments.