课题组章亚琼博士在CrystEngComm发表本组第131篇论文 (CrystEngComm, 2014, 16, 1026-1037)

Disclosing the formation of ring-banded spherulites for semicrystalline polymers through the double-layer film method

Yaqiong Zhang, Huagao Fang, Zhongkai Wang, Miao Tang and Zhigang Wang*

CrystEngComm, 2014, 16, 1026-1037.

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志刚等在此感谢期刊编辑和审稿人对该研究工作的理解和支持！

摘要：很少有人关注过半结晶性聚合物双层膜体系环带球晶的形成。在此研究中，以偏光显微镜（POM）方法探索了聚乙烯醇/聚乳酸(PEO/PLA)双层膜在PEO膜熔点之上不同温度下等温结晶过程中环带球晶的成核和生长。PLA和PEO组分的先后结晶以两次淬火结晶过程来确定。以扫描电子显微镜观察环带球晶的表面形貌。实验结果和含25 wt% PEO组分的PLA/PEO 共混物的进行了比较。有趣的发现是在PEO/ PLA双层膜中环带球晶的环间距随结晶温度的变化趋势比共混物薄膜的更加复杂。对前者来说，环带球晶在接近65^oC的最低温度形成，在65^oC到90^oC之间环间距轻微增加，在90^oC到105^oC之间，未见环带球晶形成，在105^oC到115^oC之间，环间距明显减小，在115^oC到135^oC之间，环间距则显著增加。对于后者来说，环间距仅仅在105^oC以上随温度增加而呈现单调的增加。文中提出了PEO/PLA双层膜体系中环带球晶的形成机理。这些实验结果可望有助于阐明半结晶性聚合物的环带球晶形成机理。

Abstract: The formation of ring-banded spherulites in double-layer semicrystalline polymer films has seldom been a concern. In this study, the nucleation and growth of ring-banded spherulites in poly(ethylene oxide)/poly(L-lactide) (PEO/PLA) double-layer films during isothermal crystallization at various temperatures above the melting point of the PEO layer have been investigated by using polarized optical microscopy (POM). The sequential crystallization of PLA and PEO components in the double-layer films was confirmed by a double quench crystallization procedure. The surface morphologies of ring-banded spherulites were examined by using scanning electron microscopy. The experimental results are compared with those for PLA/PEO blend films with 25 wt% PEO composition. It is interesting to find that the changing trend of band space in ring-banded spherulites at different isothermal crystallization temperatures in PEO/PLA double-layer films is more complex than that in PLA/PEO blend films. For the former ones, the ring-banded spherulites form at the lowest temperature approaching 65 °C and the band space  slightly increases from 65 to 90 °C, is absent from 90 to 105 °C, obviously decreases from 105 to 115 °C, and significantly increases from 115 to 135 °C. For the  latter ones, the band space only shows a monotonic increase with increasing temperature at above 105 °C.  The mechanism for the formation of ring-banded spherulites in the PEO/PLA double-layer film system is proposed. The experimental results may shed some light on explaining the formation mechanism of ring-banded spherulites in semicrystalline polymers.