Two Distinct Morphologies for Semicrystalline Isotactic Polypropylene Crystallized after Shear Flow

摘要: Application of shear flow to molten, highly isotactic polypropylene (iPP) results in two different morphology transitions: (1) above a certain rate but below critical stress σ*, flow-induced precursors nucleate many small crystallites; (2) for shish oriented shish-kebab morphology. Herein we study crystallization (FIC) iPP with molecular weights, using rotational and capillary rheometry. Since created by are quite stable, can also use differential scanning calorimetry (DSC) polarized optical microscopy (POM) crystallization, melting, samples histories. Above (inverse long-chain relaxation time 1/τ), the onset on cooling shifts higher temperatures compared unsheared samples. POM micrographs see clear border between regions affected FIC (with γ > 1/τ) crystallizing as thoug...