Phase Transition during Heating of Nanostructured Ultrahigh Molecular Weight Polyethylene Membranes

• Published in: The journal of physical chemistry. B Vol. 119; no. 52; pp. 15909 - 15918
• Main Authors: Uehara, Hiroki, Tamura, Takuya, Yamashita, Hideyuki, Yamanobe, Takeshi, Masunaga, Hiroyasu
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 31.12.2015
• Subjects: crystals; differential scanning calorimetry; electron microscopy; endothermy; melting; molecular weight; polyethylene; temperature; X-radiation; X-ray diffraction
• ISSN: 1520-6106; 1520-5207; 1520-5207
• DOI: 10.1021/acs.jpcb.5b07086

Ultrahigh molecular weight polyethylene (UHMW-PE) membranes were prepared using biaxial melt-drawing and subsequent melt-shrinking. Electron microscopy observations indicate that the former membrane has more extended-chain crystals (ECCs), whereas the latter is mainly composed of folded-chain crystals (FCCs). Corresponding double-melting endotherms are recorded on differential scanning calorimetry (DSC) measurements. Detailed assignments of such double-melting components are performed using in situ X-ray measurements during heating. Wide- and small-angle X-ray diffraction and scattering (WAXD/SAXS) images were simultaneously recorded at SPring-8. Changes in WAXD images indicate that the orthorhombic reflection peak begins to decrease at 130 °C, followed by the appearance of the hexagonal reflection peak beyond 145 °C for both membranes, but the latter melt-shrunk membrane exhibits weaker hexagonal reflection intensity. Simultaneous SAXS results indicate that FCCs rapidly disappear at 135 °C for the melt-shrunk membrane, resulting in a sharper endotherm. In contrast, residual ECCs restrict the melting of FCCs for the melt-drawn membrane, resulting in a broader endotherm of FCC melting spread to a slightly higher temperature position.