Preparation and Crystal Structure Analysis of High-Strength Film Derived from Nigeran Ester Derivatives

Nigeran (α-1,3-alt-α-1,4-glucan) is a linear glucan with alternating α-1,3- and α-1,4-glycosidic linkages. It is extracted from the cell walls of certain species in the genera Aspergillus and Penicillium. Nigeran can be esterified and used as a film, but its strength is only approximately 4–25 MPa. However, in the present study, high-strength nigeran ester films with tensile strengths of 100 MPa were successfully prepared by thermally stretching and annealing the melt-quenched films. Two-dimensional wide-angle X-ray diffraction (2D-WAXD) analysis revealed that the highly oriented films of nigeran butyrate (NGBu), nigeran valerate (NGVa), and nigeran hexanoate (NGHx) studied herein had two-fold helix symmetry along the molecular axis. Assuming the crystal systems to be orthorhombic, the unit lattice of each ester was calculated as NGBu (a=28.6Å, b=9.07Å, c=16.5Å), NGVa (a=31.5Å, b=9.07Å, c=16.2Å), and NGHx (a=36.7Å, b=9.07Å, c=16.2Å). In the calculated unit lattice parameters, only the a-axis was extended as the number of ester carbons increased.