Abstract
We have investigated the structural response of melt-spun poly-3-hydroxybutyrate (P3HB) fibers to stress and temperature and its impact on the mechanical properties. Low-stress (≤1.6 MPa, 100–130 °C) annealed P3HB fibers showed a considerable viscoelastic behavior and remained ductile up to at least two months. Stress annealing with high weights (≥32 MPa), however, lead to fibers with a higher tensile strength (182 MPa) and with a lower elongation at break (22%). These significant differences in the tensile properties are closely related to structural changes, which we have studied with in-situ wide-angle x-ray diffraction (WAXD) and small-angle x-ray scattering (SAXS) experiments. A highly oriented non-crystalline mesophase (Pnc), which is located in-between orthorhombic α-crystals is growing during high-stress annealing but disappears during low-stress annealing. However, it is possible to restore the mesophase by post-drawing. The viscoelastic hysteresis behavior of low-stress annealed fibers is explained by a reversible transformation of α-crystals into mesophase and back.
Highlights
Poly-3-hydroxybutyrate (P3HB) is a thermoplastic poly hydroxyalkanoate (PHA), which is biodegradable and of spe cific interest for biomedical applications such as tissue engineering scaffolds, bone and cartilage scaffolds, drug delivery, sutures or wound dressing [1,2,3,4,5,6]
These significant differences in the tensile properties are closely related to structural changes, which we have studied with in-situ wide-angle x-ray diffraction (WAXD) and small-angle xray scattering (SAXS) experiments
In order to better understand the impact of annealing procedures on the structure and its interplay with the mechanical properties, we have explored the structural response of melt-spun P3HB fibers to low-stress annealing ( 16 MPa) and to high-stress annealing ( 32 MPa) with insitu wide-angle x-ray diffraction (WAXD) and small-angle x-ray scat tering (SAXS) experiments
Summary
Poly-3-hydroxybutyrate (P3HB) is a thermoplastic poly hydroxyalkanoate (PHA), which is biodegradable and of spe cific interest for biomedical applications such as tissue engineering scaffolds, bone and cartilage scaffolds, drug delivery, sutures or wound dressing [1,2,3,4,5,6] For such future applications, it is crucial to tailor the mechanical properties of P3HB fibers in order to fulfill specific re quirements regarding tenacity and elasticity. We have obtained stable P3HB monofilaments by an up-scalable meltspinning method, where the take-up godet was installed at an unusually short distance from the spinneret [7] These monofilaments consist of a network of longitudinally oriented lamellae (α-crystals) that are embedded in the amorphous phase. The orthorhombic α-crystals are formed by molecular chains that adopt the 21 helix conformation [8]
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