Study On Morphology And Structure Of A Special Isotactic Polypropylene Spherulite

Isotactic polypropylene(iPP)is a semicrystalline polymer with a variety of crystal structures,the widely studied crystal structures include monoclinic a-form,trigonal P-form,orthorhombic y-form and tetragonal?-form.A great number of odd iPP spherulites can be observed via scanning electron microscopy(SEM)and polarized light microscopy(PLM).At first,it has been established that these odd spherulites differ greatly from the conventional ones in their morphology.The odd iPP spherulites can be identified easily by SEM,and it is composed of a great number of lamellae seen edge-on,without evident radial growth direction,but the spherical symmetry can be kept as a whole.The odd spherulite,however,cannot be distinguished from the conventional a-iPP spherulite easily by PLM.The wide-angle X-ray diffraction(WAXD)can prove the only presence of a-iPP in the odd spherulite.Second,the odd iPP spherulites present different growth kinetics from that of conventional ones.The radial growth rate of odd iPP spherullites exceeds that of the conventional ones at least at high temperature.Moreover,the morphology character of the odd spherulite is approaching that of the conventional ones with growth proceeding,i.e.,evident radial growth direction can be found for the lamellae in the later stage.Meanwhile,the radial growth rate of odd iPP spherulites will decrease,approaching that of conventional ones with time.As a result,one can find that the average radial growth rate of odd spherulites differs with each other even at the same crystallization temperature.The earlier nucleation and lower crystallization temperature favor the quicker transition,resulting in lower average growth rate of the odd spherulites.That is why the odd spherulite nucleated at high temperature can keep it disordered lamellae growth mode when crystallization ends,while lamellae of those nucleated at low temperature show evident radial growth direction,resembling that of conventional a-iPP spherulites.The reason of the special growth kinetics and morphology for these iPP spherulites is,however still unknown.