Shear-induced precursors in polyethylene: An in-situ synchrotron radiation scanning X-ray microdiffraction study

Localized shear flow was imposed by pulling glass fiber in polyethylene (PE) melt below and above its equilibrium melting point (141.6 degrees C). Immediately after the cessation of shear, the structure around the fiber was investigated with in-situ synchrotron radiation scanning X-ray microdiffraction (SR-mu SXRD), which had spot area of 4.2 x 4.5 mu m2 and step size of 6 mu m. Results indicate that crystalline precursors are induced below equilibrium melting point, as evidenced by the occurrence of crystalline diffractions. Whilst at temperature above equilibrium melting point, no crystalline diffraction is observed. SR-mu SXRD measurements on the crystallization behaviors at 127 degrees C after shearing at 145 degrees C suggest that noncrystalline precursors are induced, which is supported by three evidences. (i) The occurrence of crystallization near the fiber surface implies shear-induced formation of precursors at 145 degrees C since the fiber has no ability to induce crystallization at quiescent condition; (ii) No crystalline diffraction is detected immediately after cessation of shear at 145 degrees C; (iii) The necessity of induction time for the precursors to transform into crystalline nuclei further demonstrates the non-crystalline nature of precursors. The concentration of precursors is observed to reduce with increasing shearing temperature, as evidenced by twisting degree of lamellar crystals after isothermally crystallized at 127 degrees C. (C) 2017 Elsevier Ltd. All rights reserved.