The effect of a small amount of Polymethylmethacrylate (PMMA) additive on the fiber structure formation of poly(ethylene terephthalate) (PET) has been studied by means of birefringence, tensile properties, wide-angle-X-ray scattering, and DSC profiles. The investigations have been carried out under various spinning speeds (1000-5000m/min) and temperatures (275-295°C). A small amount of PMMA, which is immiscible with PET, suppressed the structure formation of PET at spinning speeds higher than 3000m/min, in that the birefringence and the melting point became lower and the wide angle X-ray scattering pattern was not clear compared with those of pure PET. Higher spinning temperature led to higher tenacity, the smaller elongation at break, and higher birefringence in PET/PMMA blend fiber. These tendencies were quite opposite to those in pure PET. To understand the cause of the suppression of structure formation of PET and the opposite tendencies with respect to the increase in spinning temperature by the presence of a small amount of PMMA, the melt viscosity of PET/PMMA blend, the deformation of PMMA particles after spinning were examined. Also the effect of solidification temperature of blend polymer on the orientation was investigated by using some PMMAs having different Tgs. These results suggested that PMMA does not work as plasticizer, and that the dispersed PMMA particles at higher spinning temperature had larger aspect ratio (L/D) compared with those of spun at low temperature. The molecular orientation decreased with increasing Tg(80-116°C) of PMMA. Taking these facts into consideration, the major cause for the less oriented PET(Tg=65°C) structure was considered that the formation of PET fiber structure should be finished before the solidification of PMMA due to its higher solidification temperature compared with those of PET itself, and the elongation flow of PET on the spinning line was restricted by the PMMA which deformed in parallel with PET.
