Fast Flow Induced Non-equilibrium Phase Transition Of Isotactic Polypropylene

Flow induced crystallization(FIC)is an important subject in both industrial processing and polymer physics science.Due to chains structure of polymer,relaxation time of molecular chains can be so long that macroscopical flow can effectively influence the microscope behavior.In lots of processing and service condition,polymer is under fast flow whose time scale is beneath the terminal relaxation time of molecular chains,which means it’s under an typical non-equilibrium situation.The coupling of chain deformation and relaxation during phase transition making thermal and dynamical competition more complicated.In this thesis,formation mechanism and thermal/dynamical competition in fast flow induced crystallization is investigated via discussion of the crystal morphology and phase transition kinetic.High speed devices for in-situ optical measurement are designed and fabricated to perform the experiments.Crystallization of isotactic polypropylene(iPP)and other different sample systems are characterized with the combination of the home-made devices and different characterization methods.Main results are provided as follows:1)Varies of devices are designed and fabricated to provide different fast external field and fit the high time resolution measurement requirement.They are:segmented acceleration extensional rheometer,operando quenching modules(matching rheometer),high speed creep rheometer and ultrafast conformation characterization system based on Quantum Cascade Laser(QCL).In-situ wide-and small-angle X-ray scattering(SAXS/WAXS)is combined with the devices for structural characterization.2)FIC of iPP under different temperature and strain rate is studied.β and αcrystal can be simultaneously generated under high strain rate even over melting temperature of both modifications.β crystal is relatively favored under higher temperature and higher strain rate.Based on the results,a phase diagram is constructed to describe the competition and transition mechanism between 0 crystal,a crystal,shish and melting phase.3)Cross-linked iPP is applied as a dynamical asymmetric system to investigate the role of asymmetric relaxation in FIC.The different relaxation time scale results in the squeezing out,relaxation and disentanglement of shorter free and dangling chains.Crystallization kinetic is slowed down,while orientation increases continuously attributed to extension of cross-linked network.Unusual condensed structure is generated due to the multi-scale response of cross-linked network and shorter chains.Main innovations in the thesis:1)Different in-situ devices are designed and fabricated to fit the requirement for fast external field and in-situ characterization.2)The phase diagram of FIC in wide Temperature-Strain rate space is constructed to discuss dynamical phase transition under non-equilibrium condition.3)Cross-linked iPP is prepared by y-irrigation to be applied as an extreme demo for FIC in polydisperse polymer.Structural dynamics and morphology are measured and discussed...