Dichroism of poly(ethylene terephthalate)‐disperse dye system

As an approach to the basic study on the orientation behavior of amorphous region, the dichroic orientation factor, D , of poly(ethylene terephthalate), PET, fiber or film dyed with disperse dyes was investigated in relation to Δ n , birefringence of the crystalline and amorphous regions, and Δ n a , birefringence of the amorphous region. It was found that D versus Δ n plot belonged to a linear relationship passing through the origin but breaking slightly toward the D axis at Δ n ≃ 0.14, while D versus Δ n a plot was expressed by a straight line passing similarly through the origin but with no break. D 0 , the value of D at the ideal parallel orientation, was obtained by extrapolating the latter plot of the samples stretched with no relaxation: 1.00 and 0.73 for the PET–C.I. Disperse Yellow 7 and PET–C.I. Disperse Red 17 systems respectively. When the sample had been relaxed, the D versus Δ n a was also linear; however, D 0 's obtained were smaller than the above mentioned respective values. Even in these cases D for Disperse Yellow 7 versus the corresponding D for Disperse Red 17 belonged to a linear relationship with the slop 1:0.73. As the result it was concluded that the transition moment of molecule of C.I. Disperse Yellow 7 coincided with the molecular axis and the dye molecule combined parallel to PET chain, while as to C.I. Disperse Red 17 any definite conclusion could not be determined. However, in the both cases the mode of combination of dye molecules with PET is definite and kept unchanged during stretching and heating.