Morphology And Crystallization Kinetics Of PP/EPR In-reactor Alloys

In this dissertation, morphology and crystallization kinetics of two polypropylene /poly(ethylene-co-propylene) (PP/EPR) in-reactor alloys prepared by multi-stage sequential polymerization (MSSP) and two-stage polymerization (TSP) processes, respectively, were investigated. Two thermal treatments were applied to the samples: (1) The samples were directly quenched from homogeneous melt state to isothermal crystallization temperature; (2) The samples were held at a temperature for phase separation before crystallization and then cooled to crystallization temperature. The effects of structure and thermal treatment on the morphology of the alloys were examined. Moreover, the effects of crystallization temperature, phase separation temperature and phase separation time were studied to reveal the interplay of crystallization and phase separation. Finally, the PP/EPR in-reactor alloys were fractionated into two fractions (soluble part and insoluble part in n-octane) and these two fractions were blended with polypropylene (PP) at a certain proportion respectively. The morphology of the blends was primarily studied.It is found that the alloy prepared by MSSP (EP2.5P7.5) exhibits lower phase separation temperature than the alloy prepared by TSP (EP20P60). For EP2.5P7.5 and for the samples subjected to phase separation prior to crystallization, the EPR-rich phase contains more PP and thus is more viscous, which leads to more inclusion of the EPR-rich phase into the spherulites. The included EPR-rich phase with higher PP content also has stronger crystallizability, leading to a coarse spherulitic structure. More included dilute phase and its stronger crystallizability further leads to the narrower boundaries and connections among the spherulites. The structure inside the spherulites becomes coarser with the increase of crystallization temperature, phase separation temperature, and phase separation time. Phase separation reduces the linear spherulitic growth rate G while increases the fold surface free energyσ_e. The value ofσ_e also increases with phase separation temperature since the PP content in thePP-rich phase is lower at a shallow quench depth. The parameters for the overall crystallization kinetics including Avrami exponents (n), crystallization rate constant (K) and half-crystallization time (t_1/2) were discussed. It is observed that, at a relatively low phase separation temperature or within a relatively short phase separation time, crystallization is retarded by phase separation, while acceleration of crystallization can be observed at longer the phase separation time. A multi-layered morphology in the PP binary blends is observed. It is found the insoI-EP2.5P7.5 has better compatibility with PP than the other fractions while the compatibility between sol-EP20P60 and PP is poor.