Window of Pressure and Flow to Produce β-Crystals in Isotactic Polypropylene Mixed with β-Nucleating Agent

Using a pressuring and shearing device (PSD), we explored the simultaneous effects of pressure and flow on β-crystal formation. Interestingly, pressure plays a versatile role in β-crystal formation in isotactic polypropylene (iPP) mixed with β-nucleating agent (β-NA) when a flow field exists simultaneously. At a low pressure (5 MPa), a mass of β-crystals can be obtained over the entire range of applied shear rates (0.0-24.0 s^-1). As the pressure increases (50-100 MPa), a weak shear flow (3.2 s^-1) can profoundly suppress the β-crystal formation. When elevating the pressure to 150 MPa, β-crystals cannot be generated. The pressure and flow window to produce β-crystals in iPP mixed with β-NA were successfully summarized for the first time. The diversified β-crystal formation behaviors in iPP mixed with β-NA under the simultaneous effects of pressure and shear flow were well elucidated by combining classical nucleation theory and the growth of different crystalline phases. Our current work lays a solid foundation to tailor β-crystals in iPP mixed with β-NA in practical processing and thus to optimize the mechanical properties of iPP products.