Characterization of the no-flow temperature of semicrystalline polymers

    Progetto: Research project

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    Layman's description

    ObjectiveChecking the feasibility of a “model” experiment where an “open mould” (slit die) is filled at a constant flow rate, see schematic reported below. Mould walls are conditioned at a temperature below melting point.The mould should be fully equipped in order to determine flow rate (before and at the exit of the mould, checking for compressibility) and pressure profile.Checking whether a feasible steady state condition exists where, for a given mould temperature, one gets a frozen layer with a given thickness (due to the combination of cooling from the mould walls and the heating effect due to convection and viscous dissipation) such that the “channel” where the materials flows is always open (flow rate constant).Action points1) Simulation/Modelling of the experiment (via dedicated software packages) with different levels of complexity:- Starting with isothermal mould wall temperature- Steplike changes of mould wall temperature (from one steady state to another steady state) - imposing a defined mould temperature evolution at the surface (e.g. an exponential decay owing to spray cooling)2) Compare the simulation with the preliminary results (not yet officially reported in a DSM note) of an equipped mould with the following dimensions: 0.2 mm thick, 5 mm wide, 50 mm long.In particular the following problems encountered while running the injection moulding experiments in the aforementioned mould have to be explained/understood, providing suggestions and comments on how to improve/modify the system:- very short filling time, i.e. 20 ms: when determining dP/dx between the initial part of the mould (thick section) and the thin part there is a limitation due to the response time of the sensor. Possible solution: use of dielectric sensors (limited to some materials, problems of frequency?), use of piezoelectric pressure transducers, etc.- difference between the measured flow rate at the screw tip (40 cc/s) and the one estimated via dP/dx (1-2 cc/s): compressibility issue?3) Extensive literature review about “no-flow temperature” and related issues (viscosity vs. temperature, influence of crystallization on viscosity/flow) in order to focus on:- correct “definition” of this parameter and its relevance for crystallization under processing conditions- use of no-flow temperature in software packages for simulation of injection moulding (e.g. MouldFlow): pros and cons, remarks, warnings, constraints- influence of various parameter (cooling rate, pressure, flow) upon crystallization during injection moulding and related “model experiments” so far developed to determine “critical” parameters.4) Experimental campaign based on the Continuous Cooling Transformation (CCT) approach on selected materials (sample preparation, density, WAXD, Micro Hardness, microRaman).To what extent a material behaviour is determined by cooling rate? What is the “additional” effect of superimposed pressure and flow fields?Evaluation of the crystallization kinetics (kinetic parameters) based on the Kolmogoroff-Avrami-Evans (KAE) phenomenological approach. Use of this kinetic information in the software simulation packages for injection moulding: open issues.How and where to develop the projectThe project will represent the topic of a master thesis (about one year time). The master student will work at the university of Palermo. It could be considered the hypothesis to spend a limited amount of time at DSM (up to 1-2 months, starting from June) to carry out selected experiments and/or simulation runs, based on the results already achieved.TimingThe results achieved wil
    Data di inizio/fine effettiva1/1/08 → …