Optical and mechanical properties of pullulan films studied by uniaxial stretching

Optical properties of pullulan films were examined before and after uniaxial stretching to obtain the specific molecular characteristics of pullulan. It was shown that the specific optical rotation for pullulan film was not affected by uniaxial stretching, being the same as that for pullulan in aqueous solution. Combined with the mechanical measurement, the stress-optical coefficient for pullulan was estimated as a material constant on the basis of the modified stress-optical rule. The birefringence was positive and increased with time during the stress relaxation of uniaxially-stretched pullulan film. A set of the stress-optical coefficients CR = 1.9 × 10−9 Pa−1 and CG = −4.6 × 10−12 Pa−1 were obtained, where the subscripts R and G stand for the rubber and the glass components respectively.