Rheology and structure of isotactic polypropylene near the gel point: quiescent and shear-induced crystallization

Pogodina, N.V.; Lavrenko, Victor; Srinivas, Srivatsan; Winter, H. Henning

doi:10.1016/s0032-3861(01)00402-5

Cited by 190 publications

(186 citation statements)

References 42 publications

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“…) corroborated the earlier observations, not only in PE but also in a variety of other polymers, such as iPP, 43,44,50,[52][53][54][55][56][57][70][71][72][73][75][76][77][78] isotactic poly-1-butene (iPB), 90 polyethylene terephthalate (PET), 91 polydiethylsiloxane (PEDS), 91 etc. In some report, the quasicrystallographic flowinduced structures are referred to as ''mesophase.''…”

supporting

confidence: 85%

“…It was shown that a fraction of PE molecules adopted all-trans sequence configurations upon shearing, which remained stable for several hours even after cessation of shear. The recent results of the techniques that couple flow (parallel plate, [42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57]66,68,[74][75][76][77][78] fiber pullout, 14,79,80 die extrusion 15,[70][71][72][73][81][82][83] ) with a physical probe of the structure development (transmitted light, [70][71][72][73][81][82][83] optical microscopy, 14,[75][76][77][78]79,80 X-ray diffraction, 42-57 atomic force microscopy, …”

mentioning

confidence: 99%

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Thermal stability of shear‐induced precursor structures in isotactic polypropylene by rheo‐X‐ray techniques with couette flow geometry

Somani

Šics

Hsiao

2006

J Polym Sci B Polym Phys

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Combined in situ rheo-SAXS (small-angle X-ray scattering) and -WAXD (wide-angle X-ray diffraction) studies using couette flow geometry were carried out to probe thermal stabilty of shear-induced oriented precursor structure in isotactic polypropylene (iPP) at around its normal melting point (162 8C). Although SAXS results corroborated the emerging consensus about the formation of ''long-living'' metastable mesomorphic precursor structures in sheared iPP melts, these are the first quantitative measures of the limiting temperature at which no oriented structures survive. At the applied shear, rate ¼ 60 s À1 and duration t s ¼ 5 s, the oriented iPP structures survived a temperature of 185 8C for 1 h after shear, while no stable structures were detected at and above 195 8C. Following Keller's concepts of chain orientation in flow, it is proposed that the chains with highly oriented high molecular weight fraction are primarily responsible for their stability at high temperatures. Furthermore, the effects of flow condition, specifically the shear temperature, on the distributions of oriented and unoriented crystals were determined from rheo-WAXD results. As expected, at a constant flow intensity (i.e., rate ¼ 30 s À1 and duration, t s ¼ 5 s), the oriented crystal fraction decreased with the increase in temperature above 155 8C, below which the oriented fraction decreased with the decrease in temperature. As a result, a crystallinty ''phase'' diagram, i.e., temperature versus crystal fraction ratio, exhibited a peculiar ''hourglass'' shape, similar to that found in many two-phase polymer-polymer blends. This can be explained by the competition between the oriented and unoriented crystals in the available crystallizable species. Below the shear temperature (155 8C), the unoriented crystals crystallized so rapidly that they overwhelmed the crystallization of the oriented crystals, thus depleting a major portion of the crystallizable species and increasing their contribution in the final total crystalline phase.

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supporting

confidence: 85%

mentioning

confidence: 99%

Thermal stability of shear‐induced precursor structures in isotactic polypropylene by rheo‐X‐ray techniques with couette flow geometry

Somani

Šics

Hsiao

2006

J Polym Sci B Polym Phys

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“…Such limitations can be overcome by a variety of real space imaging techniques. 22,27,28 More recently, for samples with structures larger than the wavelength of light, confocal microscopy has been used to measure a material's microstructure under shear. Using this technique, individual structures of interest can be followed in real time or, by scanning through the sample, the full three-dimensional (3D) structure can be mapped out, allowing for accurate reconstruction of flow profiles using particle velocimetry and detailed measurements of a material's dynamic microstructure.…”

Section: Introductionmentioning

confidence: 99%

A multi-axis confocal rheoscope for studying shear flow of structured fluids

Lin

McCoy

Cheng

et al. 2014

Review of Scientific Instruments

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We present a new design for a confocal rheoscope that enables uniform uniaxial or biaxial shear. The design consists of two precisely positioned parallel plates with a gap that can be adjusted down to 2 ±0.1 μm, allowing for the exploration of confinement effects. By using our shear cell in conjunction with a biaxial force measurement device and a high-speed confocal microscope, we are able to measure the real-time biaxial stress while simultaneously imaging the material three-dimensional structure. We illustrate the importance of the instrument capabilities by discussing the applications of this instrument in current and future research topics in colloidal suspensions. © 2014 AIP Publishing LLC.[http://dx

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“…Because timescales for flow and crystallization are separated, this protocol isolates flow-induced structure formation. Using this protocol, flow-induced point-like nucleation (appearing for low to mild flow rates) has been thoroughly characterized, using a shear cell combined with optical microscopy, for iPP [19][20][21][22][23][24][25][26][27][28], isotactic poly(1-butene) [29][30][31], and poly(lactic acid) [32]. Alternatively, a rheometer can be used to apply flow and monitor subsequent crystallization in terms of rheology [32][33][34][35][36][37][38].…”

Section: State Of the Artmentioning

confidence: 99%

Modeling Flow-Induced Crystallization

Roozemond

Drongelen

Peters

2016

Polymer Crystallization II

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A numerical model is presented that describes all aspects of flow-induced crystallization of isotactic polypropylene at high shear rates and elevated pressures. It incorporates nonlinear viscoelasticity, including viscosity change as a result of formation of oriented fibrillar crystals (shish), compressibility, and nonisothermal process conditions caused by shear heating and heat release as a result of crystallization. In the first part of this chapter, the model is validated with experimental data obtained in a channel flow geometry. Quantitative agreement between experimental results and the numerical model is observed in terms of pressure drop, apparent crystallinity, parent/daughter ratio, Hermans' orientation, and shear layer thickness. In the second part, the focus is on flow-induced crystallization of isotactic polypropylene at elevated pressures, resulting in multiple crystal phases and morphologies. All parameters but one are fixed a priori from the first part of the chapter. One additional parameter, determining the portion of β-crystal spherulites nucleated by flow, is introduced. By doing so, an accurate description of the fraction of β-phase crystals is obtained. The model accurately captures experimental data for fractions of all crystal phases over a wide range of flow conditions (shear rates from 0 to 200 s À1 , pressures from 100 to 1,200 bar, shear temperatures from 130 C to 180 C). Moreover, it is shown that, for high shear rates and pressures, the measured γ-phase fractions can only be matched if γ-crystals can nucleate directly on shish.

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Rheology and structure of isotactic polypropylene near the gel point: quiescent and shear-induced crystallization

Cited by 190 publications

References 42 publications

Thermal stability of shear‐induced precursor structures in isotactic polypropylene by rheo‐X‐ray techniques with couette flow geometry

Thermal stability of shear‐induced precursor structures in isotactic polypropylene by rheo‐X‐ray techniques with couette flow geometry

A multi-axis confocal rheoscope for studying shear flow of structured fluids

Modeling Flow-Induced Crystallization

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