課題組章亞瓊博士在CrystEngComm發(fā)表本組第131篇論文 (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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摘要：很少有人關(guān)注過半結(jié)晶性聚合物雙層膜體系環(huán)帶球晶的形成。在此研究中，以偏光顯微鏡（POM）方法探索了聚乙烯醇/聚乳酸(PEO/PLA)雙層膜在PEO膜熔點(diǎn)之上不同溫度下等溫結(jié)晶過程中環(huán)帶球晶的成核和生長。PLA和PEO組分的先后結(jié)晶以兩次淬火結(jié)晶過程來確定。以掃描電子顯微鏡觀察環(huán)帶球晶的表面形貌。實(shí)驗(yàn)結(jié)果和含25 wt% PEO組分的PLA/PEO 共混物的進(jìn)行了比較。有趣的發(fā)現(xiàn)是在PEO/ PLA雙層膜中環(huán)帶球晶的環(huán)間距隨結(jié)晶溫度的變化趨勢比共混物薄膜的更加復(fù)雜。對(duì)前者來說，環(huán)帶球晶在接近65oC的最低溫度形成，在65oC到90oC之間環(huán)間距輕微增加，在90oC到105oC之間，未見環(huán)帶球晶形成，在105oC到115oC之間，環(huán)間距明顯減小，在115oC到135oC之間，環(huán)間距則顯著增加。對(duì)于后者來說，環(huán)間距僅僅在105oC以上隨溫度增加而呈現(xiàn)單調(diào)的增加。文中提出了PEO/PLA雙層膜體系中環(huán)帶球晶的形成機(jī)理。這些實(shí)驗(yàn)結(jié)果可望有助于闡明半結(jié)晶性聚合物的環(huán)帶球晶形成機(jī)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.