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The effect of two colorant particles with different surface geometries on the stability of shear-induced precursors in isotactic polypropylene was studied after the cessation of shear flow at 140 °C. In the absence of particles, the shear-induced precursors survived for at least 100 s after the shear flow ended. The presence of particles was found to stabilize lower molecular weight chains assisting in the formation of additional shear-induced precursors. The precursors thus formed in the samples containing particles contained two oriented clusters with different molecular weights. Incorporation of lower molecular weight chains in the precursors led to increased dissolution rates of the shear-induced precursors. Particle surface geometry was found to influence precursor dissolution, with planar particles stabilizing the shear-induced precursors to a much greater extent than curved particles. The particles investigated thus act like structural probes to follow quantitatively the dissolution process of precursors after shear and importantly to infer the formation of precursors during shear. [ABSTRACT FROM AUTHOR]

Abstract: The present study presents a method to predict the flow distribution imposed on an injection moulded melt crystallised isotactic polypropylene (iPP) from its experimentally determined morphological distribution. A microrheological model, based on the Doi–Edwards model, was used to calculate the flow-induced free energy for the flow-induced crystallisation. The low limit flow field required to generate the final structures was then obtained. The effect of Cu-phthalocyanine (CuPc), a nucleating agent, on the flow history was also studied. Instead of geometric positions, structural parameters such as molecular orientation and crystallinity were correlated to the flow history of the injection-moulded iPP. The work provides a simple approach to predict flow–structure relationships for complex thermo-mechanical processing treatments, which can then guide the realistic design and control of the flow-induced crystallisation of polymers. [Copyright &y& Elsevier]

Abstract: The morphology of isotactic polystyrene (iPS) particles which had been compounded into an isotactic polypropylene (iPP) matrix was varied in-situ by selective heat treatment to be either amorphous (iPSamorphous) or semicrystalline (iPScrystalline). The influence of iPS morphology on the quiescent and shear-induced isothermal crystallisation of iPP was then studied using differential scanning calorimetry (DSC), in-situ simultaneous small and wide angle X-ray scattering (SAXS/WAXS) and polarised optical microscopy (POM). In the quiescent condition iPScrystalline was found to selectively nucleate the β phase while iPSamorphous nucleated the α phase of iPP. Compared to the control sample (iPPcontrol), the presence of both morphologies of iPS increased the number of shear-induced oriented crystal precursors that form as a result of the step shear. During isothermal crystallisation the shear-induced nuclei promote oriented α form crystal growth, accelerate the crystallisation kinetics and ultimately swamp the effect of the nucleating particles present. [Copyright &y& Elsevier]