Melting and Crystallization of Ultra-High Molecular Weight Polyethylene with Appearance of Hexagonal Phase I. Melting Processes of Fibers under Constrained State
Melting and Crystallization of Ultra-High Molecular Weight Polyethylene with Appearance of Hexagonal Phase I. Melting Processes of Fibers under Constrained State
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DOI：
10.1295/polymj.28.489
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发表时间：
1996-06
期刊：
影响因子：
2.8
通讯作者：
Shinsuke Tsubakihara;A. Nakamura;M. Yasuniwa
中科院分区：
文献类型：
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作者：
Shinsuke Tsubakihara;A. Nakamura;M. Yasuniwa
采用差示扫描量热法（DSC）和X射线衍射法研究了两种不同分子量的商品超高分子量聚乙烯（PE）纤维在约束状态下的熔融行为。DSC熔融曲线的约束样品进行了比较，与那些无约束的。结果表明，约束样品主要通过两个吸热峰2和3熔化，而非约束样品主要通过单个吸热峰1熔化，其峰温度低于峰2和3的峰温度。对于每个样品，这些峰值温度是非常可再现的。峰1的不受约束的样品归因于所谓的延伸链晶体组成的正交相的熔融。另一方面，基于X-射线数据，峰2和3的约束样品被分配到一个过渡正交相到六方相和熔融的六方相，分别。基于视觉观察，峰3还显示伴随着样品的断裂和快速热收缩。根据自由能图讨论了聚乙烯在约束状态下的这些特殊的转变和熔化机制，并成功地解释了实验结果。
Melting behavior under constrained state was studied for two kinds of commercial ultra-high molecular weight polyethylene (PE) fibers with different molecular weights by means of differential scanning calorimetry (DSC) and X-ray measurement. DSC melting curves of constrained samples were compared with those of unconstrained ones. It was shown that the constrained sample mainly melts through two endothermic peaks 2 and 3, while the unconstrained sample mainly melts through single endothermic peak 1 whose peak temperature is lower than those of peaks 2 and 3. These peak temperatures were very reproducible for each sample. Peak 1 of the unconstrained sample was attributed to the melting of orthorhombic phase composed of so-called extended-chain crystals. On the other hand, based on the X-ray data, peaks 2 and 3 of the constrained sample were assigned to a transition orthorhombic to hexagonal phase and a melting of the hexagonal phase, respectively. Based on the visual observation, peak 3 was also shown to be accompanied by the break and rapid thermal-contraction of the sample. These peculiar transition and melting mechanisms of PE under the constrained state were discussed on the basis of a free energy diagram that can explain the experimental results successfully.