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

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 , 100 , 110 , and 120 . 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 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.