Using multimodal blends to elucidate the mechanism of flow‐induced crystallization in polymers

Okura, Masayuki; Chambon, Pierre; Mykhaylyk, Oleksandr O.; Fairclough, J. Patrick A.; Ryan, Anthony J.

doi:10.1002/polb.22234

Cited by 9 publications

(23 citation statements)

References 27 publications

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“…Nonetheless, Kimata et al. found using their SANS experiments ,, that long chains are not overrepresented in flow-induced precursors . Instead, the concentration of deuterated long chains in shish structure is the same as the remaining material.…”

Section: Introductionmentioning

confidence: 95%

“…Shearing semicrystalline polymers forms flow-induced precursors that increase the nuclei number density and transform the crystalline morphology. − When a fast deformation is applied for a period of time, chains get stretched and bundled together to create flow-induced precursors, ,− forming structures variously called shish-kebabs, fibril structures, row-nucleated structures, or cylindrite structures. ,,,− The change in crystalline morphology speeds up crystallization, ,,− increases the crystallization temperature, and increases the persistence time of anisotropic nuclei (i.e., flow-induced precursors) ,,− at elevated temperatures.…”

Section: Introductionmentioning

confidence: 99%

“…Specific work is an important process parameter, which controls the strength of flow-induced crystallization (FIC). ,,,,, Specific work is defined as stress σ times strain γ: Here η is the shear viscosity at the applied constant shear rate γ̇, and t is the duration of the applied shear; hereafter specific work W (J/m 3 or Pa) is simply referred to as work.…”

Section: Introductionmentioning

confidence: 99%

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Transition in Crystal Morphology for Flow-Induced Crystallization of Isotactic Polypropylene

2016

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Deformation applied to a semicrystalline polymer melt prior to quenching can dramatically increase the concentration of nuclei and even transform the final crystalline morphology, phenomena collectively known as flow-induced crystallization (FIC). Using polarized optical microscopy and atomic force microscopy, we image the changes in morphology of an isotactic polypropylene (iPP) sample previously sheared in a rotational rheometer. Sufficiently large deformations promote the formation of "rice grain" shaped crystalline domains. These anisotropic structures are randomly oriented and are about 1.5− 3.0 μm long (depending on applied work), with an aspect ratio of about 2:1. Well below the critical specific work threshold W c , the crystalline morphology of our iPP sample is predominately composed of spherulites, with a fraction of rice grains that increases as the applied work increases. Above W c , rice grains predominate, with no visible spherulites. The size of spherulites appears to be independent of applied work. In contrast, the size of rice grains decreases with increasing applied work, up to a saturation specific work W sat , remaining constant thereafter. Similarly, the isothermal crystallization time decreases with increasing applied work up to W sat and is constant thereafter. The effects of flow-induced precursors persist after repeated melting and recrystallizations, observable by elevated freezing temperatures in DSC experiments. Here, we probe directly the robustness of these precursors in optical microscopy, in which we repeatedly melt, anneal, and recrystallize a thin slice of an FIC sample. We observe rice grain domains appearing over and over, with the first domains to crystallize tending to reappear near the same locations.

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Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Transition in Crystal Morphology for Flow-Induced Crystallization of Isotactic Polypropylene

2016

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“…While several variables contribute to FIC, a single working term combines the effects of shearing time ( t s ), shearing rate (γ̇), and temperature of the melt during shear ( T s ) into “specific work” ( W ). During flow, the deformations caused by W drive the FIC process. − The equation for specific work ( W ) is shown in eq , where σ is the applied stress and η the shear viscosity at the applied shear rate (γ̇). At low levels of W , there is no influence on ensuing crystallization processes. However, there are defined flow regimes that result from increasing the amount of specific work W in the melt, as evidenced by changes in the solidified polymer microstructure .…”

Section: Introductionmentioning

confidence: 99%

Sensitivity of Polymer Crystallization to Shear at Low and High Supercooling of the Melt

et al. 2018

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Flow-induced crystallization (FIC) is a dominant mechanism of polymer self-assembly, but the process is poorly understood at high supercooling and under fast cooling conditions because of structural rearrangements that occur during slow heating and cooling conditions typically used for investigation. Incorporating fast-scanning chip calorimetry techniques, the influence that specific amounts of shear flow have on the subsequent crystallization of polyamide 66 over a wide range of temperatures, 85–240 °C, is determined. At high temperatures, heterogeneous nucleation dominates and crystallization rate increases with increasing shear. Low-temperature crystallization, driven by homogeneous nucleation, is not influenced by previous shear flow, but sheared samples are able to crystallize via the heterogeneous nucleation route at temperatures 15 K lower than unsheared materials. The magnitude of previous shear flow also dictates α-/γ-crystalline phase development and crystallization during cooling at rates below 200 K/s. This approach provides a route to develop important thermodynamic and kinetic insights that describe the crystallization behavior of many important polymers to enable the advanced engineering of polymer processing and injection molding applications, where practical cooling rates typically range between 10 K/s and 1000 K/s.

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“…The highest shear rate of 10 s –1 was only slightly higher than the inverse of the Rouse time of the very small fraction of chains (less than 1 wt %) at the high M end, which might be stretched to form the precursors to facilitate the subsequent crystallization. We found that the shear effect is saturated when the specific work defined as W = η(γ̇)γ̇ 2 t s is above a critical value W crit , − where η(γ̇) is the viscosity as a function of shear rate γ̇ and t s is the shearing time.…”

Section: Introductionmentioning

confidence: 88%

Shear-Induced Oriented Crystallization for Isotactic Poly(1-butene) and Its Copolymer with Ethylene

Liu

Zhang

et al. 2020

Macromolecules

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Shear-induced crystallization was examined for poly(1-butene) (PB) and its random copolymer with 1.5 mol % ethylene (PBE) upon shearing at a temperature slightly above the nominal melting temperature. When the shear rate approached the reciprocal of the Rouse time of a small fraction of the longest chains (∼7%), shear thickening was observed in both shear stress and normal stress after the temporary steady state had been achieved. The thickening appeared to arise from gel-like percolation of precursors of the fibrillar crystals, yielding a birefringent region seen in polarized optical microscopy after the crystallization. Critical work W crit was evaluated as (1) the applied work before the onset of thickening and (2) the localized work at the boundary of the birefringent region (shown in the figure at right). For both cases, W crit decreases as the shear rate is increased, while saturation of W crit is only seen for the onset of thickening. W crit of PBE is consistently ∼twice higher than that of PB, possibly owing to the fewer stereoregular chains that need more applied work to form the fibrillar bundles. The precursors lead to a slow relaxation process detected in the storage modulus, further lending support to its gel-like structure.

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Using multimodal blends to elucidate the mechanism of flow‐induced crystallization in polymers

Cited by 9 publications

References 27 publications

Transition in Crystal Morphology for Flow-Induced Crystallization of Isotactic Polypropylene

Transition in Crystal Morphology for Flow-Induced Crystallization of Isotactic Polypropylene

Sensitivity of Polymer Crystallization to Shear at Low and High Supercooling of the Melt

Shear-Induced Oriented Crystallization for Isotactic Poly(1-butene) and Its Copolymer with Ethylene

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