Determination of intrinsic physical constants of poly(trimethylene terephthalate) from drawn filament

The intrinsic lateral sonic moduli of the crystalline and amorphous regions of poly(trimethylene terephthalate) (3GT) (about 4.1504 ± 0.8396 GPa and 1.6096 ± 0.0368 GPa, respectively) were obtained from sonic moduli and crystallinities of unoriented 3GT filaments annealed under different conditions. Using the obtained intrinsic lateral sonic moduli of the crystalline and amorphous regions, the degree of orientation of the amorphous region of uniaxially drawn 3GT filaments could also be obtained from the crystallinity, sonic modulus, and the degree of crystalline orientation estimated from X‐ray azimuthal scan data. Thus, the intrinsic birefringences of the perfectly oriented crystalline and amorphous regions of the 3GT fibre (about 0.2057 ± 0.0160 and 0.2175 ± 0.0923, respectively) could be obtained from the appropriate combinations of birefringence, crystallinity, and the degree of orientation of the crystalline and amorphous regions.