Modelling flow induced crystallization of IPP: multiple crystal phases and morphologies

Being able to properly model the material structure formation during processing is a fundamental step to predict final product properties, especially for semicrystalline polymers, like isotactic PolyPropylene (iPP), which can develop a multiplicity of different crystalline phases and morphologies. For this reason, in the present work a complete model is presented which can predict the complex structure formation of iPP in conditions comparable to injection moulding. The model includes a full coupling between the non-isothermal flow of a non-linear viscoelastic fluid and its crystallization process, properly capturing the mutual interaction between the two and is implemented in a finite element framework and as such applicable for general processing applications. The model is the result of many years of numerical and experimental research in our group and finally provides a complete simulation tool able to reproduce the complex iPP crystallization behaviour in conditions equivalent to processing. The model can predict not only the local crystalline composition, distinguishing between the multiple phases and morphologies that can develop inside iPP, but also the effect of the structure formation on the rheology. Comparisons with the unique in-situ data of Troisi et al. [1] demonstrate the good performance of the model and encourage further research to adapt the model to simulate other relevant processes and processing conditions. The results presented here are input for future work on structure related mechanical properties, see for example Caelers et al. [2,3]. Notice that the approach as presented here is not specific for iPP. A similar methodology, sometimes with additional modelling, is used for other polymers.