Synchrotron X-ray scattering study on amorphous poly(ethylene furanoate) under uniaxial deformation

Abstract

Uniaxial deformation of amorphous poly(ethylene furanoate) (PEF) was studied using synchrotron-based simultaneous wide- and small-angle X-ray scattering (WAXS/SAXS) techniques, at four temperatures, namely, 90 °C, 100 °C, 110 °C, and 120 °C. Local ordering of the chains with a preferred orientation occurred before onset of strain-induced crystallization. The ordered domain in the amorphous phase displayed two characteristic length scales (∼4 Å and ∼2 Å), associated with the lateral inter-chain distance and staggering along the polymer chain direction, respectively. Fibrillar crystal morphology was induced, containing ∼2–3 unit cells on average in the direction of each lattice primitive basis, due to crystallization from highly-oriented polymer chains in amorphous phase. Time-resolved in situ scattering studies have allowed direct correlations between structure and stress-strain behavior. In the early stage of deformation, stress increased slowly with strain, leading to a degree of orientation in the amorphous phase reaching ≈0.3 before strain-induced crystallization was first observed. The onset of strain-hardening occurred immediately after crystallization occurred, which could be explained by the reinforcement of material due to small amounts of crystals serving as physical cross-linking points.