Nanoparticle-induced radial structural gradients in melt-spun polypropylene/PPgMA fibers

The presence of nanoparticles on the evolution of structural hierarchy in both highly anisotropic clay phase and polymer phase in melt-spun PP/PPgMA (maleic anhydride-modified polypropylene) fibers was investigated. The melt stream that exits the die was found to contain orientation gradient in the radial direction that is preserved even after solidification without application of a takeup. This is due to the influence of shearing in the die that results in a band of oriented outer layers where broad surfaces of the clay particles become parallel to the Surface of the fibers. The polymer phase trapped between these particles exhibits moderate to high preferrential orientation levels. The interior of the fibers was found to exhibit low levels of preferred orientation in both the clay and the polymer phases. Upon application of takeup, the presence of clay particles substantially enhances the orientation of amorphous and crystalline phases in PP/PPgMA fibers. This is due to the substantial decrease in chain relaxation in the proximity of the clay platelets and enhancement of orientation in the polymer phase in the vicinity of particles that create amplified deformation field by their relative motions. Measurements of the clay orientation in the melt-spun fibers as they undergo confined melting in constrained state revealed that these naturally anisotropic nanoplatelets contribute positively to the birefringence of the fibers.