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

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