Crystallization of polypropylene near the surface in injection-molded plaques: A comparison of morphology and a numerical analysis
(1236–1244) Polymer  Engineering &  Science 51 #7 (2011)
Kobayashi et al , Japan, studied the skin morphology formation on injection-molded isotactic polypropylene (PP) using micro-beam synchrotron wide-angle X-ray diffraction and numerical simulation.  The 1–20 μm depth range was characterized with an X-ray beam of 0.273 μm χ 0.389 μm in size. From an evaluation of doping nucleating agents (NA) in PP, the NAs did not work at a depth of 1 μm. α-specified NA affected crystallization within a 5-μm depth. β-specified PP showed α-form crystallinity at the 5–20 μm depth.  The mesomorphic crystal near the surface showed extremely high orientation.  From viscoelastic flow simulation, PP molecules near the surface were oriented in the flow direction by extensional flow in the flow front, but freezing occurred faster than flow-induced crystallization. It was estimated that the delay of crystallization occurred during the transient temperature. The deformation rate did not cause a difference in crystal morphology near the surface, but the cooling rate did.  (RDC 6/24/2011)

In-situ analysis of fiber structure development for isotactic polypropylene
(2044-2050) Polymer 52 #9 (2011)
Kang et al Japan and South Korea, analyzed structural development of isotactic polypropylene (iPP) fibers in real time through in-situ WAXD/SAXS and fiber temperature measurements during CO2 laser-heated drawing because the CO2 laser irradiation can nearly fix the necking position on the running fiber.  The in-situ WAXD/SAXS measurements were carried out with a high time-resolution of 0.4 ms. The as-spun iPP fibers of two different initial structures were laser-heat-drawn to a draw ratio of 6.5. For the drawing of PP fiber containing mesophase structure, diffraction from the oriented mesophase remained until an elapsed time of 1.0 ms, when oriented α-phase crystal started to form. Meanwhile, for the drawing of PP fiber containing both an α-phase and a mesophase structure, fragmented microcrystals were reorganized by orientation-induced crystallization before an elapsed time of 1.0 ms. The long period increased drastically with fragmentation, and decreased with reorganization. The long period was about 16 nm for both drawn fibers.  (RDC 6/1/2011)

 Translation and Rotation of Spherulites during the Crystallization of Isotactic Polypropylene with Reduced Chain Entanglements
(2844–2851) Macromolecules 44 #8 (2011)
Wang et al of the University of Science and Technology of China and the Chinese Academy of Sciences, China, studied the isothermal crystallization of isotactic polypropylene (iPP) spherulites under chain entanglements, reduced chain entanglements, and unconfined thick film conditions using polarized optical microscopy (POM).  While spherulite translations and rotations were not observed in entangled iPP samples, the growing spherulites crystallizing the melt with reduced entanglements  conspicuously translated and/or rotated, even when their sizes exceeded the sample film thicknesses. Our entanglements-reduced samples were prepared by first slowly crystallizing a commercial entangled iPP in mineral oil (and then extracting the mineral oil with hexane) and by a direct polymerization method, respectively.  (RDC 5/27/2011)