Water-induced crystalline transition of polyamide 66: a combined x-ray and molecular modeling approach

Vergelati, Caroll; Pérez, Sonia

doi:10.1021/ma00069a005

Cited by 24 publications

(22 citation statements)

References 6 publications

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“…In fact, it has been shown that amorphous segments interact with the crystalline stems at the interface, preferentially with the bc plane (b being the chain axis). 113 Such a mechanism is consistent with the observation that the Brill transition occurs by point-by-point motion involving a small group of adjacent PA chains. This does not involve long-range cooperative motion of the entire crystal.…”

Section: Interaction Between Amorphous and Crystalline Domainssupporting

confidence: 87%

“…Water transforms the pseudohexagonal crystalline phase in PA-66 (not the high-temperature Brill phase) to a triclinic a phase. 113 Moisture that enables PA-6 to crystallize preferentially in the a-crystalline form at ambient temperatures 39,114 causes it to crystallize completely in the a form at high temperatures and even brings about transformation of the c form into the a form. 28,105,115 Because water (solvent) molecules diffuse preferentially into the amorphous regions, these data show that the interactions between the crystalline stems and amorphous segments are bidirectional; that is, an increase in the mobility of the amorphous chains can affect the motion of the crystalline stems.…”

Section: Interaction Between Amorphous and Crystalline Domainsmentioning

confidence: 99%

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Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

Murthy

2006

J Polym Sci B Polym Phys

215

197

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Some salient results in nylon research are reviewed to identify the fundamental principles that are applicable to other strongly interacting or hydrogenbonded polymers, including proteins. The effects of hydrogen bonds on stress-, heat-, and solvent-induced changes in macroscopic properties are discussed. These data provide a window into the chain mobility and linkages between the crystalline and amorphous domains, both of which are important for any predictive model. The changes in the characteristics of the amorphous phase with the crystallinity and orientation require that it be modeled with at least two components: a rigid/immobile/ anisotropic component and a soft/ mobile/isotropic component. The deformation and shrinkage behavior of these polymers are discussed in terms of the relative contributions of the amorphous and crystalline domains and of the interactions between them. The premelting crystalline transition is accompanied by the merging of intersheet and intrasheet diffraction peaks in some nylons, as observed by Brill, and not in others even though the underlying mechanism that gives rise to these transitions, the onset of volume-increasing librational motion of the crystalline stems, is the same. Because the effects of the temperature, deformation, and solvent have a common origin associated with mobility, a fictive temperature can be associated with a given solvent activity or stress level. The magnitude of this fictive temperature is the amount by which the glass or Brill transition temperature is reduced in the presence of solvents ($50 8C) or stress or by which the annealing temperature can be reduced in the presence of a solvent (or active stress) to achieve the same structural state as that of a dry (or static) polymer.

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Section: Interaction Between Amorphous and Crystalline Domainssupporting

confidence: 87%

Section: Interaction Between Amorphous and Crystalline Domainsmentioning

confidence: 99%

Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

Murthy

2006

J Polym Sci B Polym Phys

215

197

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“…3 By dilatometric technique Kettle noted the glass-transition temperature Tg of nylon 6 as a function of water content decreased first sharply, then slowly with an increase in water content with plateau region (water content region 3-5 wt%). 4 The transition of ct2 to ct 1 crystal for nylon 66 by water has been reported by Vergelati et al 5 and the relaxation times (T 2 ) of water which penetrated into nylon 66 has been found to be shorter by three order of magnitude than that of bulk water by Fyfe et al 6 However, all the literature has ignored the effect of the balance of terminal groups which might facilitate the ionization of water penetrated in polyamide. Thus, in order to explain the phenomenological facts described above the hydrogen bonding in polyamide should be discussed in view of fN and the existing state of water in the polymer with different fN·…”

Section: Introductionmentioning

confidence: 90%

Relation between the Behavior of Water and Hydrogen Bonding in Poly(hexamethylene adipamide) Films with Different End Group Balance

Koizumi¹,

Ono²,

Tomokiyo

et al. 1996

Polym J

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ABSTRACT:As an extension of the previous studies [M. Tomokiyo et al., submitted to Sen-i Gakkaishz], an attempt was made to elucidate the intrinsic role of terminal groups in the hydrogen bonding formation and the existing state of water in poly(hexamethylene adipamide) (nylon 66) with different molar fraction of amino end group fN· (fN = [NH2]1([NH2] +[COOH])) For this purpose, the heat-pressed nylon 66 films were subject to infrared (IR) and tanfJ-t analyses and at the same time the films which absorbed !Owt% of water were subject to 1 H NMR measurements to determine relaxation time T 1 of water. Analyses on the change in the wave numbers of NH and CO stretching vibrations (K,NH• K,c0 ), the activation energy evaluated from the temperature dependence of K,NH and K,co and the activation enthalpy and entropy for C£. and C£b relaxations indicated that the stronger hydrogen bond is formed for nylon 66 with larger fN, which corresponds to the higher molecular packing density and higher activation energy for flow of the melt for these polymers. 1 H NMR revealed that water which penetrated into nylon 66 is composed of two electro-magnetically different species, one of which might be the ionized water by end groups, and those species are also composed of at least two components with shorter T1 (Tt,8 ) and with longer T1(T1.A). The existence of ionized water was supported by the pH measurement of water containing nylon 66. The both T1 were shorter for nylon 66 with lower fN, denoting that the nylon interacts more strongly with water, which is quite comparative to the facts that nylon 66 with low fN exhibits the lower resistance to the penetration of water for this polymer. These facts leaded to an idea that water in polyamide is ionized by the polar terminal end groups and based on this idea a tentative hydrogen bonding for nylon 66 with high and low fN ( Authors have already pointed out the importance of the balance of terminal groups of poly(hexamethylene adipamide) (nylon 66) in the water adsorption behavior, the rheological and thermal properties and the crystallization kinetics of the polymers 1 and the fiber structure formation during its melt-spinning process. 2 All these data have revealed that 1) nylon 66 with higher molar fraction of amino end group fN is more resistant to the water adsorption, lowers the crystallization rate but exhibits the lower molecular mobility brought about by an increase in the activation energy for flow of the polymer melt and 2) the nylon 66 with larger fN is fabricated into the fiber having amorphous region characterized by stronger cohesive nature of molecular chains. All result seems to support the idea that nylon 66 with highfN has inherently stronger molecular interaction in the amorphous region to hinder the structural change induced by heat and humidity to some extent. However, the essential reason for the above phenomena has not been fully understood yet. Since polyamide has a potential ability to form hydrogen bond between amide groups (amino hydrogen and carboxyl groups) ...

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“…First, some recent advances in the understanding of the Brill transition will be discussed. It is almost certain now that crystallization of nylon 66 at the quiescent state or during processing (such as extrusion and spinning) in the melt always first produces the pseudohexagonal structure (Vergelati, Imberty & Prez, 1993;Ramesh, Keller & Eltink, 1994;Hsiao et al, 1995). The transformation to the conventional triclinic structure not only depends on the previous crystallization conditions but is also kinetically limited.…”

Section: Draw Ratio (A)mentioning

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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Water-induced crystalline transition of polyamide 66: a combined x-ray and molecular modeling approach

Cited by 24 publications

References 6 publications

Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

Relation between the Behavior of Water and Hydrogen Bonding in Poly(hexamethylene adipamide) Films with Different End Group Balance

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

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