Additive manufacturing of stimulus-responsive materials is an area of four-dimensional (4D) printing that is continuing to gain interest. Cellulose nanocrystal (CNC) thermoplastic nanocomposites have been demonstrated as a water-responsive, mechanically adaptive material that shows promise in generating 4D-printed structures. In this study, a 10 wt% CNC thermoplastic polyurethane (TPU) nanocomposite was produced through a masterbatching process and printed using fused filament fabrication. A design of experiments was implemented to establish a processing window to highlight the effects of thermal energy input on the mechanical adaptivity of the printed parts. The combination of high temperatures and low speeds resulted in thermal energies that induced degradation of the CNC/TPU network and reduced the absolute values of storage moduli, but the mechanical adaptation persisted for all the printed samples. However, for slower speeds and increasing temperatures, the nanocomposites experienced a 15% decrease in adaptability. Further, a folded box structure was printed to establish the reversibility of the mechanical response and corresponding ability to generate a structure that can serve as a deployable shape-memory material based on response to water. The printed structure demonstrated fixity and recovery values of 76 and 42%, respectively. These results show significant promise for CNC/TPU nanocomposites in 4D-printed adaptable structures for academic and industrial applications.

中文翻译：

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使用纤维素纳米晶体实现机械自适应 4D 打印

刺激响应材料的增材制造是四维 (4D) 打印领域，它继续引起人们的兴趣。纤维素纳米晶体 (CNC) 热塑性纳米复合材料已被证明是一种水响应性、机械适应性材料，在生成 4D 打印结构方面显示出前景。在这项研究中，10 wt% CNC 热塑性聚氨酯 (TPU) 纳米复合材料是通过母料工艺生产的，并使用熔融长丝制造进行印刷。实施实验设计以建立处理窗口，以突出热能输入对打印部件机械适应性的影响。高温和低速的结合导致热能导致 CNC/TPU 网络退化并降低存储模量的绝对值，但是对于所有印刷样品，机械适应性仍然存在。然而，对于较慢的速度和升高的温度，纳米复合材料的适应性下降了 15%。此外，还打印了一个折叠的盒子结构，以建立机械响应的可逆性和相应的能力，以产生一种结构，该结构可用作基于对水的响应的可展开形状记忆材料。印刷结构的固定性和恢复值分别为 76% 和 42%。这些结果表明，CNC/TPU 纳米复合材料在 4D 打印的适应性结构中具有重要意义，可用于学术和工业应用。打印了一个折叠的盒子结构，以建立机械响应的可逆性和相应的生成结构的能力，该结构可以作为基于对水的响应的可展开形状记忆材料。印刷结构的固定性和恢复值分别为 76% 和 42%。这些结果表明，CNC/TPU 纳米复合材料在 4D 打印的适应性结构中具有重要意义，可用于学术和工业应用。打印了一个折叠的盒子结构，以建立机械响应的可逆性和相应的生成结构的能力，该结构可以作为基于对水的响应的可展开形状记忆材料。印刷结构的固定性和恢复值分别为 76% 和 42%。这些结果表明，CNC/TPU 纳米复合材料在 4D 打印的适应性结构中具有重要意义，可用于学术和工业应用。