Molecular orientation in melt-spun poly(3-hydroxybutyrate) fibers: Effect of additives, drawing and stress-annealing

• We succeeded in spinning robust P3HB fibers applying standard processing techniques.
• With an intermediate godet in the draw-off unit we suppressed secondary crystallization.
• Thus we obtained fibers dominated by oriented lamellae rather than spherulites.
• The fibers produced exhibit long term stability with tensile strengths up to 215 MPa.
• WAXD data suggest that a highly oriented amorphous phase is present in the fibers.

Bacterial poly-3-hydroxybutyrate (P3HB) is a thermoplastic polyester with perfectly isotactic structure; it has the potential of being melt-spun to fibers, and it is thus interesting for textile applications. Aiming at developing an upscalable melt-spinning method to produce high-strength fibers, we have investigated P3HB as native polymer with the additives tri-n-butyl citrate (TBC) as plasticizer, and boron nitride (BN) as nucleating agent, to evaluate their effect on the melt-spinning performance of P3HB. In addition, the draw-off unit has been modified in order to enhance primary crystallization to the extent that secondary crystallization is suppressed. The such drawn fibers are dominated by longitudinally oriented lamellae rather than spherulitic structures. This allows obtaining P3HB fibers which contain domains of highly oriented molecules between crystallites, exhibiting promising tensile strengths up to 215 MPa. The wide-angle X-ray diffraction (WAXD) data suggest that besides the oriented crystalline α-phase, a highly oriented amorphous phase is present.

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