Effect of viscosity ratio on structure of polypropylene polyamide 6 blend fiber

Blend fibers of polypropylene (hereafter ''PP'') and polyamide 6 (hereafter ''PA6'') having various molecular weights were prepared by the melt spinning and drawing processes. Effect of the viscosity ratio of the polymers on the structure of the blend fibers were examined. For the undrawn PP fibers,the crystal orientation was very low even at a draft ratio of about 6.0. On the contrary, the undrawn blend fibers having a viscosity ratio (eta(PP)/eta(PA6)) of 1 and lower was found to have the oriented PP crystals even at a draft ratio of 2.0 to 4.0. The drawn blend fibers having a viscosity ratio of 1 and higher exhibited stronger and more distinct Xray diffraction peaks of the PA6 crystals as compared with the blend fibers having a viscosity ratio of 1 and lower. An unusual phenomenon was observed in the DSC measurement of the drawn blend fibers :two melting endothermic peaks of the PA6 component appeared for the fibers with a viscosity ratio of 1 and lower. It was speculated that the imperfect and small PA6 crystallites were formed because of the inflluence of the PP component. The significant changes observed in the crystal orientation and the melting endothermic behavior in the blend fibers was considered to depend largely on the dispersion state of the PP and PA6 phases : when the viscosity ratio was lower than 1, the two phases are finely dispersed. On the ohter hand, when the viscosity ratio is high than 1, the phases are coarsely dispersed and the interaction between two phases are relatively low.