Structure evolution and orientation mechanism of long-chain-branched poly (lactic acid) in the process of solid die drawing
Structure evolution and orientation mechanism of long-chain-branched poly (lactic acid) in the process of solid die drawing
复制标题
DOI：
10.1016/j.eurpolymj.2017.03.005
复制
发表时间：
2017-05-01
影响因子：
6
通讯作者：
Martyn, Michasel
中科院分区：
文献类型：
--
作者：
Li, Jiafeng;Li, Zhengqiu;Martyn, Michasel
制备了高取向长支链聚乳酸（LCB-PLA），并与聚乳酸（PLA）进行了比较，研究了LCB-PLA在固态模拉伸过程中的结构演变。在拉伸过程中，样品不仅经历了模具拉伸过程，而且还经历了自由拉伸过程。拉深速度对自由拉深过程的影响最为显著，而模具厚度对模具拉深过程的影响更为明显。对于PLA而言，自由拉伸工艺主要影响其最终取向度和结晶度，因此拉伸速度对PLA的力学性能影响很大。而对于LCB-PLA，口模拉伸工艺对最终取向度和结晶度的贡献较大，其力学性能主要受口模厚度的影响。在相同拉伸条件下，LCB-PLA的拉伸强度和拉伸模量始终高于PLA，分别达到228 MPa和7.2 GPa，基本满足了生物固定材料的要求。仅进行模具拉伸的样品显示出明显的“三明治”结构，并且LCB-PLA的取向皮层厚度比PLA的厚，这表明由于长支链之间的缠结增强，剪切诱导的取向更容易保持。拉伸后，LCB-PLA样品的L-lateral尺寸比PLA小，L-ac周期比PLA大，说明LCB-PLA的低链运动限制了链滑移运动，从而导致相邻的晶体片层被拉伸断裂。
Highly oriented long-chain-branched poly (lactic acid) (LCB-PLA) was prepared and the structure evolution was studied in the process of solid die drawing by compared with poly (lactic acid) (PLA). During drawing, samples underwent not only die drawing process but also free drawing process. Drawing speed presented a prominent effect on the free drawing process, while die thickness showed a more obvious influence on the die drawing process. For PLA, free drawing process mainly contributed to its final orientation degree and crystallinity, and thus the mechanical properties of PLA were greatly influenced by drawing speed. However, for LCB-PLA, die drawing process made a greater contribution to the final orientation degree and crystallinity, and its mechanical properties were mainly affected by die thickness. Under the same drawing condition, the tensile strength and modulus of LCB-PLA were always higher than those of PLA, and reached up to 228 MPa and 7.2 GPa, respectively, which basically met the requirement for born fixation materials. Samples which only underwent die drawing showed obvious "sandwich" structure, and the thickness of the oriented skin layer for LCB-PLA was thicker than that for PLA, suggesting that shear-induced orientation can be easily retained due to the enhanced entanglement between long branched chains. After drawing, LCB-PLA samples showed smaller lamellae size (L-lateral) but larger long period (L-ac) compared with PLA, suggesting that the low chain mobility restricted the motion of chain slipping of LCB-PLA and thus resulted in the fragmentation of neighboring crystal lamella by chain stretched-out.