Crystallization kinetics of polypropylene under high pressure and steady shear flow

Watanabe, Kaori; Suzuki, Toshihiko; Masubuchi, Yuichi; Taniguchi, Takashi; Takimoto, Jun–ichi; Koyama, Kiyohito

doi:10.1016/s0032-3861(03)00604-9

Cited by 50 publications

(33 citation statements)

References 21 publications

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“…In a different study, Pantani et al [13] investigated the effect of varying the packing pressure on the morphology of injection molded samples. The effect of pressure on crystallization kinetics was also assessed in a study by Watanabe et al, [14] in which the authors measured the half time, t 1/2 , for crystallization (defined as the time at which the volume fraction of crystallized material reaches 50%) and verified that pressure indeed simply acts as to increase undercooling. Van der Beek [15,16] experimentally studied the combined effect of pressure, cooling rate, and shear deformation on the specific volume of iPP, in a new PVT (pressure-volumetemperature) apparatus which allows PVT measurements at high cooling rates (100 8C Á s…”

Section: Introductionmentioning

confidence: 99%

Model Development and Validation of Crystallization Behavior in Injection Molding Prototype Flows

Custódio

Steenbakkers

Anderson

et al. 2009

Macro Theory & Simulations

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To control the final properties of semi‐crystalline polymer products, an accurate prediction of the material microstructure developed upon processing is required. For that purpose a model for flow‐enhanced nucleation of semi‐crystalline polymers is proposed, which relates molecular deformation with the enhancement of crystallization. Flow kinematics, computed in a decoupled fashion, are used to solve a coupled viscoelastic stress—crystallization problem. Morphological features concerning the number, size, and shape of crystalline structures are predicted and a comparison is made with experimental results reported by Housmans et al.1,2 in which the morphology development of an isotactic polypropylene (iPP) resin was studied.magnified image

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Section: Introductionmentioning

confidence: 99%

Model Development and Validation of Crystallization Behavior in Injection Molding Prototype Flows

Custódio

Steenbakkers

Anderson

et al. 2009

Macro Theory & Simulations

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“…1 The structure and morphology of the resulting crystals are strongly influenced by the applied flow conditions. [2][3][4][5][6] It is possible to control and predict the final morphologies and properties of semicrystalline polymers by controlling different shear flow parameters. [7][8][9][10][11][12][13][14][15] It is well known that isotactic polypropylene (iPP) exhibits pronounced polymorphic crystalline modifications, which are designated as a-form (a-iPP), b-form (b-iPP), and c-form (c-iPP).…”

Section: Introductionmentioning

confidence: 99%

Crystal morphology and structure of the β‐form of isotactic polypropylene under supercooled extrusion

Zhang

Shen

2011

J of Applied Polymer Sci

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A supercooled melt of isotactic polypropylene (iPP) was extruded through a capillary die. Polarized light microscopy (PLM), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC) were used to investigate the effects of the relatively weak wall shear stress (r w ), extrusion temperature (T e ), and crystallization temperature (T c ) on the structure and morphology of b-form isotactic polypropylene (b-iPP). b-cylindrites crystals could be observed by PLM in the extruded specimen even at a lower r w 's (0.020 MPa), and the b-iPP content increased with decreasing T e . Under a given T e of 150 C, the increase in r w positively influenced the b-iPP content. The DSC and WAXD results indicate that the total crystallinity and b-iPP content increased when T c was set from 105 to 125 C; the other experimental parameters were kept on the same level. Although T c was above 125 C, the b-iPP content obviously decreased, and the total crystallinity continued to increase. On the basis of the influences of r w , T e , and T c on the b-iPP crystal morphology and structure, a modified model is proposed to explain the growing of shearinduced b-iPP nucleation.

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“…In most processing operations, such as fiber spinning, film blowing, extrusion, injection molding, etc., it takes place in the presence of or just after flow, which is referred to as flow-induced crystallization. [14][15][16][17][18][19][20][21][22][23][24] The imposed flow field conditions (i.e., elongational, shear, or mixed), temperature, and mechanical strain all affect the molecular conformations of polymer chains. The deformed melt becomes an ensemble of random, fully, and partly extended/oriented entangled chains.…”

Section: Introductionmentioning

confidence: 99%

“…Consequently, the crystallization kinetics can increase by several orders of magnitude and the final solid-state morphologies are usually an overlap of spherulities and flow-induced oriented crystalline structures, such as cylindrites, shish-kebabs. [14][15][16][17][18][19][20][21][22][23][24] Clearly, the size, shape or form, orientation, and perfection of the crystals, as well as the fraction (i.e., crystallinity) of the polymer bulk they constitute will affect the polymer solid-state properties. For example, it is well-established that the inhomogeneous and anisotropic structures of skin and core of injection-molded samples [25][26][27][28][29][30][31][32] can significantly influence the physical properties such as dimension stability, 33 Young's modulus, and tensile strength.…”

Section: Introductionmentioning

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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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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Crystallization kinetics of polypropylene under high pressure and steady shear flow

Cited by 50 publications

References 21 publications

Model Development and Validation of Crystallization Behavior in Injection Molding Prototype Flows

Model Development and Validation of Crystallization Behavior in Injection Molding Prototype Flows

Crystal morphology and structure of the β‐form of isotactic polypropylene under supercooled extrusion

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

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