Crystallization of polypropylene (PP) droplets produced by thermal break up of multilayered films was investigated. Droplets produced from 12 nm PP layers resulted into exclusive homogeneous nucleation, which is usually viewed as the initial step during polymer crystallization. The structure, thermodynamics and crystallization kinetics of the droplets were analyzed to understand the homogeneous nucleation process. The stability of the homogeneously nucleated droplets was further probed by thermal treatment. Ability to produce homogeneous nucleation provided an opportunity to add various nucleating agents to the droplets and investigate the nature of heterogeneous nucleation. Effect of various nucleating agents on the crystallization of PP droplets is also discussed.
In another approach, confined crystallization of a low crystallinity polymer, syndiotactic PP (sPP), was achieved by “forced assembly” coextrusion process. The crystal orientation was controlled by melt recrystallization of sPP layers under the hard confinement of polycarbonate. A transition from in-plane to on-edge lamellar orientation was observed with decreasing crystallization temperature. Controlled melt recrystallization of sPP layers was successfully used to manipulate the lamellar orientation of sPP and control the gas transport properties over one order of magnitude. Additionally, the effect of confinement on the physical aging and structural relaxation of a glassy polymer, polystyrene (PS), under the hard confinement of polycarbonate (PC) was also investigated in the thermally reset multilayered films.