Phase transitions during heating of melt-drawn ultrahigh molecular weight polyethylenes having different molecular characteristics.
Phase transitions during heating of melt-drawn ultrahigh molecular weight polyethylenes having different molecular characteristics.
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DOI：
10.1021/jp709782g
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发表时间：
2008-04
期刊：
影响因子：
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通讯作者：
Masaki Kakiage;M. Sekiya;T. Yamanobe;T. Kōmoto;S. Sasaki;Syozo Murakami;H. Uehara
中科院分区：
文献类型：
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作者：
Masaki Kakiage;M. Sekiya;T. Yamanobe;T. Kōmoto;S. Sasaki;Syozo Murakami;H. Uehara
采用原位广角x射线衍射分析了不同分子特性的熔融拉伸超高分子量聚乙烯（UHMW-PEs）在加热过程中晶体结构的变化。所有样品都观察到从正交相到六边形相的相变，但对于只含有较高分子量组分的样品，六边形相的可能温度窗口更大。相比之下，对于含有较低分子量组分的样品，加热过程中收缩应力增加，反映了折叠链晶体（FCC）的熔化。差示扫描量热法和透射电子显微镜揭示了样品的分子特征对所得形态的依赖性。结果表明，FCC的存在决定了熔融拉伸超高分子量聚乙烯加热过程中六方相温度窗的质量和宽度。
Changes in the crystalline structure during heating of melt-drawn ultrahigh molecular weight polyethylenes (UHMW-PEs) having different molecular characteristics were analyzed by in situ wide-angle X-ray diffraction measurements. A phase transition from the orthorhombic into the hexagonal phase was observed for all samples, but the perfection was enhanced and the possible temperature window for the hexagonal phase was greater for the sample containing only a higher molecular weight component. In contrast, an increase in retractive stress during heating was confirmed for the sample containing a lower molecular weight component, reflecting melting of the folded-chain crystal (FCC). Differential scanning calorimetry and transmission electron microscopy revealed the dependency of the molecular characteristics of the sample on the resultant morphologies. These results demonstrate that the existence of FCC determines both the quality and the width of the temperature window for the hexagonal phase during heating of melt-drawn UHMW-PEs.