Wang Meng, Ding Weiwei, Xie Yeping, Zhang Lifan, Chen Yinghong
The State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu 610065, China.
Polymers (Basel). 2021 Mar 13;13(6):887. doi: 10.3390/polym13060887.
Microinjection molding is a novel frontier polymer processing strategy different from conventional ones. In this paper, three different cavity-sizes of micro-mold tools were firstly fabricated, and the influences of micro-mold cavity dimension on the phase morphology structure, crystallization and orientation, and mechanical performance of the microinjection molded polylactic acid (PLA)/polycaprolactone (PCL) blend microparts were carefully investigated accordingly. The results show that the reduction of the cavity size would result in much higher shear stress field and cooling temperature gradient, which is advantageous to the fibrillation and orientation of PCL-dispersed phase. Consequently, with decreasing the micro-mold cavity dimension from length 26 mm to 15 mm, the interfacial compatibility is improved, significantly increasing number of PCL fibers with smaller diameter are in situ formed in PLA matrix and their orientation degree also obviously increases, which is verified by SEM and 2D-WAXD measurements. The Differential Scanning Calorimetry (DSC) analysis shows that the decrease in cavity dimension causes the enhancement of PLA crystallization property due to shear-induced crystallization, which is reflected by the decreasing PLA cold crystallization temperature and increasing PLA crystallinity (almost doubling that of conventional macropart). As a result, the dynamic/static mechanical property measurements exhibit that with decreasing the cavity size, the storage modulus, and the loss modulus of PLA/PCL blend micropart increase, and the corresponding tensile strength, elongation at break, and Young's modulus also present an obviously increasing tendency. The related investigations would provide some new spaces and insights for realization of high-performance of PLA/PCL blend micropart.
微注塑成型是一种不同于传统方法的新型前沿聚合物加工策略。本文首先制造了三种不同型腔尺寸的微模具，并据此仔细研究了微模具型腔尺寸对微注塑成型聚乳酸（PLA）/聚己内酯（PCL）共混微部件的相形态结构、结晶与取向以及力学性能的影响。结果表明，型腔尺寸的减小会导致更高的剪切应力场和冷却温度梯度，这有利于PCL分散相的原纤化和取向。因此，随着微模具型腔尺寸从长度26mm减小到15mm，界面相容性得到改善，PLA基体中原位形成的直径更小的PCL纤维数量显著增加，且其取向度也明显提高，这通过扫描电子显微镜（SEM）和二维广角X射线衍射（2D-WAXD）测量得到了验证。差示扫描量热法（DSC）分析表明，由于剪切诱导结晶，型腔尺寸的减小导致PLA结晶性能增强，这表现为PLA冷结晶温度降低和PLA结晶度增加（几乎是传统大尺寸部件的两倍）。结果，动态/静态力学性能测量表明，随着型腔尺寸减小，PLA/PCL共混微部件的储能模量和损耗模量增加，相应的拉伸强度、断裂伸长率和杨氏模量也呈现明显增加的趋势。相关研究将为实现PLA/PCL共混微部件的高性能提供一些新的空间和见解。
