SAXS studies of lamellar level morphological changes during crystallization and melting in PEEK

Verma, Ravi; Velikov, V.; Kander, Ronald G.; Marand, Herve; Chu, Benjamin; Hsiao, Benjamin S.

doi:10.1016/s0032-3861(96)00387-4

Cited by 76 publications

(74 citation statements)

References 25 publications

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“…In order to do so, the nature of the secondary crystallites must first be established. This discussion is based on the two variances 27,31,40,41,[43][44][45]47,48 of the dual-lamellar population model 35,38 and a recent notion on secondary crystallization in polymers proposed by Marand and Alizadeh. 74 It is well established that overall crystallization in semicrystalline polymers can be divided into two main processes: primary crystallization and secondary crystallization.…”

Section: Dependence Of Subsequent Melting Endotherms On Crystallizatimentioning

confidence: 99%

“…The two extensions of this model 49 are the dual-lamellar stack model 27,31,40,47,48 and the lamellar insertion model. 41,[43][44][45] According to the dual-lamellar stack model, the distribution of the stacks of thick and thin lamellae is such that they exist in different stacks; in the lamellar insertion model they coexist in the same stacks with the thin lamellae distributing between two thick lamellae.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Crystallization and melting behavior in syndiotactic polypropylene: Origin of multiple melting phenomenon

Supaphol

2001

J of Applied Polymer Sci

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ABSTRACT:The melting behavior of syndiotactic polypropylene (s-PP) after isothermal crystallization from the melt state was studied using differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) techniques. Three melting endotherms were observed for isothermal crystallization at high degrees of undercooling. The minor endotherm, located closed to the corresponding crystallization temperature, was postulated to be the melting of the secondary crystallites formed at the crystallization temperature. The low-temperature melting peak was found to be the melting of the primary crystallites formed, and the high-temperature melting peak was a result of the melting of the crystallites recrystallized during a heating scan. The triple-melting behavior observed in subsequent melting endotherms of s-PP was therefore described as contributions from melting of the secondary crystallites and their recrystallization, partial melting of the less stable fraction of the primary crystallites and their recrystallization, melting of the primary crystallites, and remelting of the recrystallized crystallites formed during the heating scan. In addition, determination of the equilibrium melting temperature for this s-PP resin according to the linear and nonlinear Hoffman-Weeks extrapolations provided values of 143.1 and 185.6°C, respectively.

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Section: Dependence Of Subsequent Melting Endotherms On Crystallizatimentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Crystallization and melting behavior in syndiotactic polypropylene: Origin of multiple melting phenomenon

Supaphol

2001

J of Applied Polymer Sci

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“…However, the choice of the Porod region, with such an expression, is extremely sensitive to the signal-to-noise ratio at high angles. For reasons described elsewhere (Verma, Biswas, Hsiao & Marand, 1997), two alternative expressions of Porod's law have been adopted to facilitate the determination of the constants in (3). Two residual terms associated with alternative expressions are defined…”

Section: Saxs Analysis To Determine the Lamellar Dimensionsmentioning

confidence: 99%

Studies of Structure and Morphology Development During the Heat-Draw Process of Nylon 66 Fiber by Synchrotron X-ray Diffraction and Scattering Techniques

Hsiao¹,

Kennedy²,

Leach³

et al. 1997

J Appl Cryst

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Online studies of structure and morphology development during continuous drawing of a nylon 66 fiber at different temperatures were carried out using synchrotron wideangle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) techniques. From the two-dimensional (2D) WAXD measurement, unit-cell parameters were determined. The results confirm that the triclinic cell structure persists above the Brill transition temperature (about 443 K). With increasing temperature, the unit-cell dimension a (dominated by hydrogen bonding) remains almost unchanged, while b increases and c decreases (both show a step-change at 403 K, prior to the Brill transition). The constant value of a agrees with the argument that the hydrogen bonding is relatively immobile at high temperatures prior to melting. The step-changes in b and c suggest that a premelting process of small (or defective) crystals precedes the Brill transition. As a result, the anisotropic thermal expansion of the surviving larger crystals results in a step-change behavior. This hypothesis is consistent with the crystal density data as well as the morphology evaluation by SAXS. Several dimensions were extracted from the 2D SAXS data: lamellar crystal and amorphous thicknesses (along the fiber) determined by the correlation function method, and crystal fibril width (perpendicular to the fiber) determined by the Porod analysis. These results also indicate that drawing annihilates small crystals, but the strain effect is much less than the temperature effect.

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“…Details of the Porod analysis are reported elsewhere. 16,17 From the correlation function, we estimate L (the first maximum), l c and l a using the following equations 17,18 :…”

Section: Methodsmentioning

confidence: 99%

Development of lamellar morphology in poly(ethylene terephthalate)/polycarbonate blends

Lee

2004

Macromol. Res.

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We have studied the lamellar-level morphology of poly(ethylene terephthalate) (PET)/polycarbonate (PC) blends using small-angle X-ray scattering (SAXS). Measurements were made as a function of the holding time in the melt. We determined the morphological parameters at the lamellar level by correlation function analysis of the SAXS data. An increased amorphous layer thickness was identified in the blend, indicating that some PC was incorporated into the interlamellar regions of PET during crystallization. The blend also exhibits a larger lamellar crystalline thickness (l c ) than that of pure PET. A possible reason for the increase in l c is that the inclusion of the PC molecules in the interlamellar regions causes an increase in the surface free energy of folding. At the early stage of isothermal crystallization, we observed a rapid drop in the value of l c in the blend; this finding indicates that a relatively large fraction of secondary crystals form during the primary crystallization. In contrast, the value of l c for the sample that underwent a prolonged holding time increased with time in the secondary crystallization-dominant regime; this observation suggests that the disruption of chain periodicity, which results from transesterification between the two polymers, favors the development of fringed micellar crystals that have larger values of l c , rather than the development of normal chain-folded crystals.

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SAXS studies of lamellar level morphological changes during crystallization and melting in PEEK

Cited by 76 publications

References 25 publications

Crystallization and melting behavior in syndiotactic polypropylene: Origin of multiple melting phenomenon

Crystallization and melting behavior in syndiotactic polypropylene: Origin of multiple melting phenomenon

Studies of Structure and Morphology Development During the Heat-Draw Process of Nylon 66 Fiber by Synchrotron X-ray Diffraction and Scattering Techniques

Development of lamellar morphology in poly(ethylene terephthalate)/polycarbonate blends

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