Manufacture, Characterization, and Structure Analysis of Melt-Spun Fibers Derived from Paramylon Esters

Paramylon—a β-1,3-glucan photoproduced by Euglena—is a promising raw material for bio-based plastics. Three kinds of paramylon ester derivatives—paramylon propionate (PaPr), paramylon butyrate (PaBu), and paramylon valerate (PaVa)—were synthesized to manufacture melt-spun fibers. The melt processing temperatures were determined by combining differential scanning calorimetry (DSC) and a melt flow test. The molecular orientation, crystallinity, and tensile properties of the melt-spun fibers were investigated using a polarized optical microscope (POM), wide-angle X-ray diffraction (WAXD), and tensile testing, respectively. The POM revealed that the PaPr molecular chains were aligned along the spinning direction, despite variation in the take-up rate. However, WAXD confirmed that crystallization only occurred in PaPr fibers spun at a higher take-up rate of over 108 m/min, suggesting that crystallization is induced by high shearing force. This phenomenon seems to be due to the rigid mainchain structure consisting of pyranose rings. With further annealing of the PaPr fibers, the tensile strength increased with an increase in crystallinity. These tendencies were also observed in the PaBu and PaVa melt-spun fibers. The melt-spun fibers of paramylon ester derivatives were manufactured from powders without any additives.