Fig. 5: Oriented PCL materials.
a Hot-pressed sheets of mPCL/A (5 wt%), PCL/A (5 wt%), and PCL melt drawn at 70 °C and a nominal strain rate of 2 s−1. mPCL/A (5 wt%) forms films with a uniform thickness, while PCL and PCL/A show viscous necking, resulting in inhomogeneous filaments. b In addition to the meridional scattering corresponding to the lamellar long period, 2D synchrotron SAXS patterns of melt-drawn films of mPCL/A (5 wt%), show a pronounced equatorial streak, which is particularly marked at high draw ratios and in films drawn under non-isothermal conditions. This combination of features is attributed to the formation of shish-kebab structures, that is, extended-chain polymer crystals oriented along the fiber axis and epitaxially nucleated lamellar polymer crystals oriented perpendicularly to the fiber axis. Accordingly, c DSC scans of the deformed specimens show a significantly higher melting transition in the first than in the second heating or than non-deformed PCL specimens. d AFM phase images of mPCL/A (5 wt%) non-isothermally melt-drawn to a nominal strain, εm, of 2000% together with selected grey-level profiles confirm the existence of a highly oriented morphology composed of nanofibrils (identified with finely spaced features observed locally, profile A–B), extended-chain PCL crystals (coarser fibrillar features with a spacing of about 25 nm, profile C–D), and lamellar PCL crystals growing epitaxially from the extended-chain crystal cores and stacked perpendicularly to the draw direction (average spacing of Lp = 18 ± 2 nm, profile E–F), as is schematically shown in (e). f Representative room temperature nominal stress-strain curves of melt-drawn mPCL/A (5 wt%) films show a strong increase in yield stress with increasing εm accompanied by a decrease in strain-at-break, which is particularly marked for non-isothermal drawing. g Young’s modulus vs. ultimate tensile strength for common packaging films (cf. Table S2) compared with the present results for PCL (orange) and mPCL/A (5 wt%) films at different εm after isothermal (blue) and non-isothermal (red) drawing. Error bars indicate the standard deviations.
