Modeling Crystallization Kinetics and Resulting Properties of Polyamide 6

Yaghini, Nazila; Peters, Gwm Gerrit

doi:10.1021/acs.macromol.0c02588

Cited by 18 publications

(22 citation statements)

References 20 publications

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“…Semicrystalline polymer materials are widely used in various fields owing to their excellent properties directly related to the processing process. − As the applied flow field is inevitable in polymer processing, flow-induced crystallization (FIC) is of critical importance for polymer physical and designing high-performance products. − Under uniaxial stretch or shear flow, molecular chains are straightened and arranged in parallel simultaneously to promote crystal nucleation and growth. − However, the individual roles of flow-induced chain straightening and orientation in FIC have not been fully understood yet. − …”

Section: Introductionmentioning

confidence: 99%

Biaxial Stretch-Induced Crystallization of Polymers: A Molecular Dynamics Simulation Study

Nie

Fan

et al. 2021

Macromolecules

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Molecular dynamics (MD) simulations are employed to study biaxial stretch-induced crystallization of polymers, during which the individual roles of chain conformation and orientation on crystal nucleation and growth are clarified. Systems with different stiffness and orientations are constructed by changing the stretch ratios of the x-and y-axis, which allow us to figure out the individual contributions of chain conformation and orientation to flowenhanced nucleation. The results show that nucleation occurs in areas with high segment orientation, and the higher orientation corresponds to the shorter nucleation induction period. The relationship between the nucleation induction period and orientation is quantitatively expressed, which indicates that orientation plays a dominant role in flow-enhanced nucleation. On the other hand, the results show that chain stiffness exhibits a negative correlation with nucleation in biaxial stretch, supporting that conformational entropy reduction is not the main driving force in flow-induced crystallization of polymers. With the secondary nucleation model, the crystal growth rates in different directions correlate well with the orientation at the growth front of the clusters, further confirming the decisive role of orientation in crystal nucleation and growth. Finally, crystal cluster merging is proposed to be a way to form shish structures in highly oriented melts.

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Section: Introductionmentioning

confidence: 99%

Biaxial Stretch-Induced Crystallization of Polymers: A Molecular Dynamics Simulation Study

Nie

Fan

et al. 2021

Macromolecules

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“…Dotted lines are added to emphasize the abrupt changes and are not from data fitting. PA6 heterogeneous nucleation density data from Yaghini and Peters is added for comparison. Nuclei density of crystal with a size of 550 nm is added.…”

Section: Resultsmentioning

confidence: 99%

“…An abrupt break of nucleation density is found near the kinetics break temperature in both polyamides. PA6 heterogeneous nucleation data from Yaghini and Peters is added for comparison . A drastic change of nucleation density follows the explanation of polymorphism transition since different polymorphs can have different nucleation energy barriers, determined in some polymers .…”

Section: Resultsmentioning

confidence: 99%

Key Insights into the Differences between Bimodal Crystallization Kinetics of Polyamide 66 and Polyamide 6

et al. 2022

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Polyamide 66 (PA66) and polyamide 6 (PA6) share many comparable properties due to their similar chemical structures. However, their crystallization kinetics and morphological differences are not as well understood as other properties. This work establishes the crystallization kinetics and morphology of additive-free PA66 and PA6 at high undercooling conditions using a modified fast scanning calorimetry technique. Two polyamides show similar kinetics profile and morphology, but the transitions associated with polymorphs occur at different temperatures. Regarding kinetics, PA66 always crystallizes faster than PA6 regardless of the polymorphs formed, supported by the temperature-dependent Avrami kinetics coefficients k. Both PA66 and PA6 show a bimodal kinetics profile with a local crystallization rate minimum at 135 and 110 °C, respectively. Apart from the crystallization rate, a sudden broadening of the exothermic crystallization peak is found near the rate minimum. The broadening is described by a drastic change of the Avrami index n from 3 to 2. The morphology at the micro- and nanoscales of polyamides was followed by a polarized optical microscope (POM) and atomic force microscopy (AFM). The POM reveals that both polyamides turn translucent from transparent near the rate minimum. The temperature-dependent AFM micrographs show multistep transitions from amorphous-like morphology, cauliflower-like crystal, crystal aggregates, and lamellar structure after T c changes from near T g to above the kinetics break temperature. Although two polyamides have similar molecular weight and the same content of amide groups, the morphological transition in PA66 is found to always be 20 °C higher than in PA6, suggesting a difference in their thermodynamic drive to nucleate. The conclusions drawn from the Avrami analysis in the final part of this study provide a universal explanation of the drastic peak broadening observed in many previously studied thermoplastics.

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“…Polyamide (PA) is a thermoplastics polymer containing amide repeat units on the main chain, which serves as an important lightweight material due to its light weight, good mechanical properties, excellent chemical resistance, and low cost. [1][2][3][4][5][6] In order to further improve its mechanical properties and replace currently used metals, a large amount of glass fiber (GF) must be added into polyamide matrix. [7][8][9][10] Nevertheless, traditional polyamide resin is a linear polymer and possesses high viscosity, and the addition of a large amount of GF into this resin would significantly increase the viscosity of composite and lead to poor dispersion, inferior appearance quality and even material rupture, which limit its application.…”

Section: Introductionmentioning

confidence: 99%

Thermal, morphological and mechanical properties of glass fiber reinforced star‐branched polyamide 6

Wang

Zhang

et al. 2022

Polymer Composites

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Using star‐branched polyamide 6 (SPA6) with hexafunctional cyclotriphosphazene core as a matrix resin and glass fiber (GF) as a reinforcing material, star‐branched polyamide 6/glass fiber (SPA6/GF) composites with different GF content were prepared by melt‐compounding method. The star‐branched structure of SPA6 and GF content have great effects on the properties of SPA6/GF composites. Compared with linear polyamide 6 (LPA6), SPA6 with star‐branched structure has low viscosity, high melt flowability and good impregnation and adhesion to GF, which endow SPA6/GF composites outstanding processability, good surface qualities and excellent mechanical properties even when the content of GF reaches 60 wt%. The use of SPA6 resin with star‐branched structure fundamentally solves the industry problem of traditional LPA6 resin in high‐filled modification. Such high‐performance SPA6/GF composites will provide great promise for large‐scale applications.

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Modeling Crystallization Kinetics and Resulting Properties of Polyamide 6

Cited by 18 publications

References 20 publications

Biaxial Stretch-Induced Crystallization of Polymers: A Molecular Dynamics Simulation Study

Biaxial Stretch-Induced Crystallization of Polymers: A Molecular Dynamics Simulation Study

Key Insights into the Differences between Bimodal Crystallization Kinetics of Polyamide 66 and Polyamide 6

Thermal, morphological and mechanical properties of glass fiber reinforced star‐branched polyamide 6

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