131. Disclosing the formation of ring-banded spherulites for semicrystalline polymers through the double-layer film method
作者：Yaqiong Zhang, Huagao Fang, Zhongkai Wang, Miao Tang and Zhigang Wang*
關鍵字：環帶球晶，雙層膜法，聚乳酸
論文來源：期刊
具體來源：CrystEngComm, 2014, 16, 1026-1037
發表時間：2014年
摘要：很少有人關注過半結晶性聚合物雙層膜體系環帶球晶的形成。在此研究中，以偏光顯微鏡（POM）方法探索了聚氧化乙烯/聚乳酸(PEO/PLA)雙層膜在PEO膜熔點之上不同溫度下等溫結晶過程中環帶球晶的成核和生長。PLA和PEO組分的先后結晶以兩次淬火結晶過程來確定。以掃描電子顯微鏡觀察環帶球晶的表面形貌。實驗結果和含25 wt% PEO組分的PLA/PEO 共混物的進行了比較。有趣的發現是在PEO/ PLA雙層膜中環帶球晶的環間距隨結晶溫度的變化趨勢比共混物薄膜的更加復雜。對前者來說，環帶球晶在接近65 oC的最低溫度形成，在65 oC到90 oC之間環間距輕微增加，在 90 oC到105 oC之間，未見環帶球晶形成，在105 oC到115 oC之間，環間距明顯減小，在115 oC到135 oC之間，環間距則顯著增加。對于后者來說，環間距僅僅在105 oC以上隨溫度增加而呈現單調的增加。文中提出了PEO/PLA雙層膜體系中環帶球晶的形成機理。這些實驗結果可望有助于闡明半結晶性聚合物的環帶球晶形成機理。
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.