Rheological and crystallisation behaviour of high melt strength polypropylene under gas-loading

The understanding of the rheology and crystallisation under processing conditions like high pressure and gas-loading is crucial in foam-processing. A new method to measure both the rheology and crystallisation is introduced. A pressure cell for a conventional rheometer is firstly used to study the crystallisation process under saturation pressure up to 400 bar.With this new method, the effect of pressure and CO2-concentration on the rheology as well as cooling-rate, pressure and gas-concentration on the crystallisation of a high melt strength polypropylene is studied. The viscosity of the melt is reduced by one order of magnitude in the non-linear region. The combined gas-concentration and pressure shift factor is calculated and separated into both components. For crystallisation, it shows that higher cooling rate and gas-loading decrease the crystallisation temperature by a great deal. Crystallisation temperature also exhibits an exponential correlation to the shift factor for pressure and gas-concentration.

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