Biodegradable poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHB-HHx) electrospun nanofibers with high molecular orientation were obtained by macroscopically aligning  fibers by  collecting them on an aluminum foil with an air-gap or by collecting them on a rotating mandrel, followed by a cold-drawing process. The molecular orientation of the aligned fibers, with the chains preferentially oriented along the fiber axis, especially after cold-drawing, was confirmed by polarized Fourier Transform Infrared spectra (FTIR) and Wide Angle X-ray Diffraction (WAXD). The degree of orientation for fibers collected using a rotating mandrel is higher than that collected on an aluminum foil with an air-gap, due to the extra mechanical stretch induced by the rotary drum on the fibers. The nano-IR spectra and the Selected Area Electron Diffraction (SAED) patterns via low dose TEM diffraction of a single fiber after cold-drawing revealed an interesting highly ordered core-shell structure where the core region consists of both alpha-form (2/1 helix) and beta-form (planar zigzag) while in the shell region there is only alpha-form. Before cold-drawing, no appearance of beta-form was observed. The real-time development of beta-form during cold-drawing was explored by Planar Array Infrared (PAIR) spectroscopy, which has a time resolution of less than 1 millisecond and allows us to follow chain organization and order on that time scale.Confinement effects on the conformational structure and crystalline morphology was also investigated in this present work. Different solvent systems were used to generate PHB-HHx fibers with various fiber diameters ranging from 200nm to 1300nm. It was observed that the degree of molecular orientation increased with decreasing fiber diameter, and the smaller the fibers are, the easier it is to generate beta-form via cold-drawing.

? Formation of highly-ordered crystalline structure in electrospun poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHB-HHx) nanofibers

247th National Meeting (2014)

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