左旋聚乳酸/聚(ε-己内酯)共混物在取向聚乙烯基底上的附生结晶行为

Epitaxy of PLLA/PCL Blends on Highly Oriented Polyethylene Substrate

利用电子显微镜结合电子衍射研究了左旋聚乳酸/聚(ε-己内酯)(PLLA/PCL)共混物在取向聚乙烯(PE)基底上的结晶行为.纯PLLA在取向PE基底上能够附生结晶,主要形成分子链相互垂直的片晶结构.PCL在PE基质上也能发生附生结晶,导致两者分子链平行.PLLA/PCL共混物在取向PE基底上结晶的形态结构依赖于共混组成.在PLLA含量大于95 wt%时,PCL不影响PLLA与PE的附生结晶行为.当PCL含量增加至10 wt%时,PLLA在PE上的附生结晶行为受到了一定程度的影响.当PCL含量超过40 wt%时,PLLA在PE上的附生结晶被抑制,取而代之是PCL在PE取向基质上附生结晶,产生两者分子链平行的取向片晶.另外,在PLLA含量在50 wt%~30 wt%之间时,体系产生明显的微相分离,微相分离并不影响PCL与PE的附生结晶,在PCL的富集区仍然发生平行链附生结晶,而PLLA的富集区结构变得模糊.当PLLA含量少于20 wt%时,微相分离不明显,少量PLLA应该分散在PCL片晶间的非晶区.

Highly oriented polyethylene （PE） ultrathin films were prepared by a melt-draw process. The obtainedPE ultrathin films of ca. 50 nm in thickness consist of parallel oriented edge-on lamellae. The electron diffractionexperiment indicates that the prepared PE thin films exhibit high degree of fiber orientation with crystallographicc-axis aligned along the drawing direction, while the a- and b-axes rotate randomly about the c-axis. Theseoriented PE thin films were used to initiate crystallization of poly（L-lactic acid）/poly（e-caprolactone） （PLLA/PCL）blends to check the mutual influence of PLLA and PCL on the related epitaxial crystallization. To this end,double-layered samples of PE and PLLA/PCL blends were prepared by spin-coating a 0.5 wt% PLLA/PCLsolution in choloform on the highly oriented PE thin films. The PLLA/PCL blend ratios are 100/0, 95/5, 90/10,80/20, 50/50, 40/60, 30/70, 20/80, 10/90 and 0/100. After evaporation of the solvent choloform, the samples wereheat-treated at 120 ℃ for 8 h first to ensure the cold-crystallization of PLLA, and then at 40 ℃for isothermalcrystallization of PCL. It was confirmed that pure PLLA cold-crystallized on oriented PE substrate epitaxiallywith its molecular chains arranged mainly in the direction perpendicular to the PE molecular chains. On the otherhand, the epitaxial crystallization of PCL on the PE substrate led to the formation of highly oriented PCL lamellarstructure with moelcular chains aligned along the PE chains. For the blends, when the PCL content was 5 wt%,the epitaxial crystallization of PLLA on PE was not affected at all. A 10 wt% PCL resulted in a more pronouncedperpendicular chain alignment of PLLA and PE. When PCL content reached 20 wt%, both perpendicular chainorientation of PLLA-PE and parallel chain orientation of PCL-PE were observed, indicating the cooccurrence ofboth epitaxial crystallization. For the blends with more than 40 wt% PCL, the epitaxial crystallization of PLLA onPE substrate was inhibited but the existence of PLLA did not influence the epitaxial crystallization of PCL.Epitaxially grown parallel aligned PCL edge-on lamellae were always observed regardles of PLLA content.However, the PLLA/PCL blends at ratio of 50/50 and 30/70 displayed evident phase seperation. In the PCL-richdomains, PCL still crystallized epitaxially on the PE substrate and formed parallel aligned lamellar structure withmolecular chains oriented in the same direction as PE substrate. In contrast, the PLLA-rich regions werestructureless. The phase seperation was not obvious in the blends with PLLA of less than 20 wt%. This indicatesthat a small amount of PLLA can be dispersed into amorphous PCL region between parallel aligned epitaxiallygrown PCL lamellae.