The objective of this work was to evaluate the discrepancy observed between the fibrillation of Polyamide 6 (PA6) and Polytrimethylene Terephthalate (PTT) formed through a polypropylene (PP) matrix during fiber spinning. Since the aforementioned polymers are widely used in fiber industry, structural changes, along with controlling the final morphology during processing, are of great importance. In this regard, PP was chosen as matrix and two types of polymer blends (PP/PA6, PP/PTT) with varying ratios were prepared by melt blending. Blend preparation was performed on a co-rotating twin screw extruder and the pelletized blends were spun via a Laboratory Mixing Extruder (LME). Scanning electron microscopy revealed a droplet morphology prevalent in as-extruded samples and upon employing fiber spinning, the PA6 and PTT, as dispersed phases, were transformed into fully isolated fibrils throughout the PP matrix. Running the rheological measurements beyond the linear region showed that PA6 and PTT displayed different trends of spinnability. The spinnability was followed by running two different rheological methods. Measuring the startup of steady shear flow revealed that a fibril-fibril coalescence mechanism controlled the dispersed phase viscosity and the fibrillation threshold started at different dispersed phase ratios, which manifested different trends of transient stress responses over the course of the shear measurement. Flexibility, as a representative of fibril size and growth of the physical fibrillar network (PFN), was analysed by monitoring the stress relaxation after cessation of steady shear flow. It was found that PTT has high spinnability and PFN has higher spinnability to form nano-sized fibril network, confirmed by SEM.