Quantifying crystalline fraction within polymer spherulites

The crystallinity profile in the interior of a single isotactic (iPP) spherulite crystallized from the melt was analyzed by using laser Raman spectroscopy (LRS). The Raman spectra recorded along the diameter of an iPP spherulite between points A and B. Moving along the diameter of the spherulite, the crystallinity values increased to a maximum 45% as the beam approached the core of the spherulite. The dense packing of the chain-folded lamellae away from the fronts of the spherulite was attributed to the fibril branching at small noncrystallographic angles of the main fibril growth. The spherulite growth was completed ~6 min, whereas the sampling of one-half of the spherulite took no more than 3 min, therefore, it can be assumed that no secondary crystallization took place. A polarized transmission optical microscopy and an atomic force microscopy (AFM) were used to take images from the vicinity of the spherulite center.