Deformation modeling of polyamide 6 and the effect of water content using molecular dynamics simulation

Abstract

Polyamide 6 (PA6) shows significant water absorbability and hygroscopicity, which affect its mechanical properties such as Young’s modulus and yield strength, as water content enhances deformability. This study aims to investigate the effect of water molecules on the deformation behavior of PA6 and to elucidate the deformation mechanism at a molecular level. By using excluded volume map sampling method, we explored the possible incursion sites for water molecule absorption in the computational material cell. Using molecular dynamic simulations, we created the computational cell of PA6, and we applied mechanical loadings with and without the water molecule to determine the effect of water molecules on the deformation behavior. To investigate the fundamental reasons why water molecules enhance the deformability of PA6, we calculated the non-bonded potential energy of a pair of amide functional groups with and without the water molecule. The results reveal that water molecules decrease the interaction energy of the amide group, leading to macroscopic deformation. This study clarified the effect of water molecules on the deformation behavior of PA6, and it may be useful for predicting the mechanical deformation of PA6.

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Notes

  1. 1.

    This study creates a semi-crystalline model with the following process. MD simulation was first carried out to obtain appropriate length of bonding stretch for one monomer, so that the total potential energy becomes minimum. Based on the obtained length of bonding stretch, the generation method embedded in J-OCTA [http://www.j-octa.com/] and COGNAC [http://octa.jp/index.html] software was employed to arrange each monomer in the simulation cell in order to create a semi-crystalline structure. For this process, we can determine density and layer thickness of both crystalline and amorphous structures. As described in the text, energy relaxation was carried out repeatedly to obtain actual density of their structures and degree of crystallization.

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Acknowledgments

This work is supported by the JSPS KAKENHI (grant no. 17 K06062) from the Japan Society for the Promotion of Science and by a research grant from The Suga Weathering Technology Foundation (no. 67).

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Correspondence to Akio Yonezu.

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Ikeshima, D., Nishimori, F. & Yonezu, A. Deformation modeling of polyamide 6 and the effect of water content using molecular dynamics simulation. J Polym Res 26, 151 (2019). https://doi.org/10.1007/s10965-019-1815-4

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Keywords

  • Polyamide 6
  • Water
  • Mechanical property
  • Deformation
  • Molecular dynamics simulation