Structure Development during Shear Flow Induced Crystallization of i-PP: In Situ Wide-Angle X-ray Diffraction Study

Citations Over TimeTop 10% of 2001 papers

Abstract

In situ synchrotron wide-angle X-ray diffraction (WAXD) was used to monitor crystallization of isotactic polypropylene (i-PP) in the subcooled melt at 140 °C after step shear. The melt was subjected to a shear strain of 1430% at three different shear rates (10, 57, and 102 s-1) using a parallel-plate shear apparatus. WAXD results were used to determine the type (α- and β-crystals), orientation, and corresponding mass fractions of i-PP crystals. It was found that formation of oriented α-crystals occurred immediately after application of the shear field. Subsequently, growth of primarily unoriented β-crystals was observed. WAXD patterns clearly showed that β-crystals grew only after the formation of oriented α-crystals in the sheared i-PP melt. The contribution of β-crystals to the total crystalline phase was as high as 65−70% at high shear rates (57 and 102 s-1) and low (20%) at low shear rates (10 s-1), which was attributed to the different amount of surface area of oriented α-crystal cylindrites generated at different shear rates. The growth of β-crystals which is related to the surface area of the oriented α-form crystalline assembly has been proposed earlier. Also, the unoriented nature and fast growth of the β-crystals determined from WAXD experiments provide an explanation for the 2 orders of magnitude increase in the kinetics of crystallization of the unoriented structures, which was previously observed (but not explained) in our crystallization study by small-angle X-ray scattering (SAXS).

Related Papers

• → Light Scattering Experiments on Shear Induced Structures of Micellar Solutions(1997)25 cited
• → Morphological and rheological responses to the transient and steady shear flow for a phase-separated polybutadiene/polyisoprene blend(2012)18 cited
• → Lamellar Orientation and Corresponding Rheological Properties of Symmetric Diblock Copolymers under Steady Shear Flow(2002)25 cited
• → Crossover between equilibrium and shear-controlled dynamics in sheared liquids(2002)12 cited
• → Structure development under transient shear flow in semidilute polystyrene solution(1996)6 cited