Smith Travis, Feng Jiansheng, Zou Lu, Gao Min, Prévôt Marianne, Wang Shi-Qing
School of Polymer Science and Polymer Engineering, University of Akron, Akron, OH, 44325, USA.
Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH, 44242, USA.
Macromol Rapid Commun. 2023 Jan;44(1):e2200293. doi: 10.1002/marc.202200293. Epub 2022 Jul 3.
The processing-structure-property relationship using poly(lactic acid) (PLA) and poly(ethylene terephthalate) (PET) is explored. Specifically, both pre-extension and preshear of amorphous PLA and PET above their glass transition temperatures T , carried out in the affine deformation limit, can induce a specific type of cold crystallization during annealing, i.e., nanoconfined crystallization (NCC) where crystal sizes are limited to a nanoscopic scale in all dimensions so as to render the processed PLA and PET optically transparent. The new polymer structure after premelt deformation can show considerably enhanced mechanical properties. For example, premelt stretching produces geometric condensation of the chain network. This structural alternation can profoundly change the mechanical characteristics, e.g., turning brittle PLA ductile. In contrast, after preshear of amorphous PLA above T , the NCC containing PLA remains brittle, showing the importance to have geometric condensation from processing. Both AFM imaging and SAXS measurements are performed to verify that premelt deformation of PLA and PET indeed results in NCC from annealing that permits the strain-induced cold crystallization to take place on the length scale of the mesh size of the deformed chain network.
本文探究了聚乳酸（PLA）和聚对苯二甲酸乙二酯（PET）的加工-结构-性能关系。具体而言，在仿射变形极限下，对非晶态PLA和PET在其玻璃化转变温度T以上进行预拉伸和预剪切，均可在退火过程中诱导出一种特定类型的冷结晶，即纳米受限结晶（NCC），其中晶体尺寸在所有维度上均被限制在纳米尺度，从而使加工后的PLA和PET具有光学透明性。预熔融变形后的新型聚合物结构可表现出显著增强的机械性能。例如，预熔融拉伸会使链网络发生几何凝聚。这种结构变化可深刻改变机械特性，如使脆性PLA转变为韧性。相比之下，在T以上对非晶态PLA进行预剪切后，含PLA的NCC仍保持脆性，这表明加工过程中几何凝聚的重要性。通过原子力显微镜（AFM）成像和小角X射线散射（SAXS）测量，证实了PLA和PET的预熔融变形确实会导致退火后的NCC，从而使应变诱导的冷结晶能够在变形链网络的网眼尺寸长度尺度上发生。
