Structure development in melt spinning syndiotactic polypropylene and comparison to isotactic polypropylene

A basic investigation of the development of crystallization and orientation during the melt spinning of syndiotactic and isotactic polypropylene is described Both polymers were melt spun through ambient air or into ice water at various draw-down ratios and melt temperatures. The melt spun filaments were characterized by wide angle x-ray diffraction (WAXD), birefringence and differential scanning calorimetry (DSC). The polymorphic behavior of isotactic polypropylene during melt spinning is well known. The filaments melt spun through ambient air exhibit the monoclinic alpha -form while the filaments melt spun into ice water form a smectic structure at low draw-down ratios. Syndiotactic polypropylene also exhibited polymorphic behavior during melt spinning. Disordered Form I with (t(2)g(2))(2) helices was found at low spinline stresses and Form III with all trans chain conformation was found at high spinline stress. The criterion of the spinline stress for this transition was found to be about 6-9 MPa for all samples of various molecular weights, melt temperatures and cooling rates. Syndiotactic polypropylene crystallized much more slowly than isotactic polypropylene and did not exhibit a smectic mesomorphism under ice-water quenched conditions. The melt spun filaments of syndiotactic polypropylene exhibited lower birefringences and amorphous orientations but higher crystalline orientations than those of isotactic polypropylene, compared at the same spinline stresses.