1 research outputs found
Core–Shell Fibers Electrospun from Phase-Separated Blend Solutions: Fiber Formation Mechanism and Unique Energy Dissipation for Synergistic Fiber Toughness
Through single-tube
electrospinning, the biodegradable core–shell
fibers of polyÂ(3-hydroxybutyrate) (PHB) and polyÂ(d,l-lactic acid) (PDLLA) were obtained from blend solutions with different
compositions at a total polymer concentration of 7 wt %. Regardless
whether PHB is the major or minor component (PHB/PDLLA = 90/10, 75/25,
50/50, and 25/75 wt. ratio), these phase-separated solutions all yielded
core–shell fibers with PHB as core and PDLLA as shell. A new
scenario of core–shell fiber formation was proposed on the
basis of the relative magnitude of the intrinsic relaxation rate of
fluids and external extension rate during electrospinning. The effects
of blend compositions on the morphologies of the Taylor cone, whipping
jet, and as-spun fibers were investigated. The diameters of core–shell
fibers can be tailored by simply varying the PHB/PDLLA ratios. Two
scaling laws describing the apparent viscosity (η<sub>o</sub>) dependence of the outer fiber diameter (<i>d</i><sub>fo</sub>) and core fiber diameter (<i>d</i><sub>fc</sub>) were derived. That is, <i>d</i><sub>fo</sub> ∼
η<sub>o</sub><sup>0.38</sup> and <i>d</i><sub>fc</sub> ∼ η<sub>o</sub><sup>0.86</sup>. The microstructures
of the as-spun fibers were determined by differential scanning calorimetry,
Fourier transform infrared spectroscopy, and synchrotron wide-angle
and small-angle X-ray scatterings. Results showed that the PDLLA component
was in the amorphous state, and the crystallizability of PHB component
remained unchanged, except the amorphous 10/90 fibers electrospun
from a miscible solution state. The synergistic mechanical properties
of the core–shell fibers were obtained, along with the ductile
PDLLA shell enclosing the brittle PHB core. The enhanced toughness
was attributed to the fragmentation of the brittle PHB core and necking
fracture of the ductile PDLLA shell, which served as an effective
route for energy dissipation. Compared with the neat PHB fiber, the
90/10 and 75/25 core–shell fibers possessed larger elastic
moduli, which was attributed to the high PHB crystal orientation in
their core sections despite the reduced PHB crystallinity. By contrast,
the crystal <i>c</i>-axis of PHB in the 25/75 core–shell
fibers was preferentially perpendicular to the fiber axis, suggesting
the significant stretching of developing PHB crystals during electrospinning