Manufacture of strong melt-spun fibers derived from α-1,3-glucan esters and determination of their crystal structures and crystalline elastic moduli

Melt-spun fibers derived from α-1,3-glucan esters were successfully manufactured without a plasticizer. Fibers derived from α-1,3-glucan butyrate had a tensile strength of over 1000 MPa. The crystalline structures of the α-1,3-glucan esters were determined as monoclinic systems by X-ray diffraction. The linear esters comprised threefold helices and the branched esters comprised five- or eightfold helices. The crystalline elastic moduli (El) parallel to the fiber axes were determined by time-resolved X-ray diffraction with tensile tests. Specifically, α-1,3-glucan propionate, α-1,3-glucan butyrate, and α-1,3-glucan valerate—which had threefold helices—had El values of 24.0, 12.4, and 4.2 GPa, respectively. In contrast, α-1,3-glucan 2-methyl valerate—which had a fivefold helix—had an El of 1.0 GPa. Therefore, the El decreased as the length of the side chain and the helix inclination increased. We concluded that El values of polysaccharide esters are not dependent on the glycosidic linkages, but rather on helix structures.