Dependence of the mechanical properties of a pullulan film on the preparation temperature

The mechanical properties of pullulan films prepared at various temperatures were investigated. The films prepared at high temperatures (40degreesC and 60degreesC; H-films) did not show any clear plastic deformation in tensile test, indicating that they were brittle. In contrast, those prepared at low temperatures (4degreesC, 13degreesC, and 25degreesC; L-films) showed such deformation. The latter films had higher values for both tensile strength and elastic modulus than the former, indicating that the L-films were stiffer and more flexible than the H-films. Stretching the L-films clearly showed a shear deformation band inclined at 45degrees to the stretching direction, indicating that they were amorphous.