Elsevier

Polymer

Volume 41, Issue 21, October 2000, Pages 7699-7704
Polymer

Deuterium nuclear magnetic resonance of deuterium oxide in nylon 6 under active uniaxial deformation

https://doi.org/10.1016/S0032-3861(00)00118-XGet rights and content

Abstract

The large strain uniaxial tensile deformation behavior of nylon 6 plasticized by deuterium oxide is investigated by an in situ stretching device built in a deuterium nuclear magnetic resonance (NMR) probe. The D2O molecules probe the environment of the amorphous regions in nylon 6; they do not exist in a “free” state and remain associated with the amide groups by hydrogen bonding during deformation. Deuterium NMR spectra show that the quadrupolar splitting varies linearly with strain throughout the experiment, indicating that the orientation of the D2O molecules in the amorphous regions is simply a function of strain and not of stress. The line width increases rapidly with strain at low to moderate strains but more slowly at large strains (in the strain-hardening regime). From low to moderate strains, larger changes in line width arise from a decrease in the translational motion of the D2O molecules between amide groups in the amorphous chains during elastic deformation and during the transformation of the lamellar structure of nylon 6 to a fibrillar one. At large strains, the existence and deformation of the fibrillar structure cause a slower decrease in the translational motion of the plasticizer.

Introduction

Polyamides are important engineering plastics whose mechanical properties are greatly influenced by its moisture content. Water plasticizes the nylon matrix and causes a reduction in the glass transition temperature (Tg) and Young's modulus [1], [2], [3] but enhances the toughening behavior [4]. It was postulated that such behavior is due to the “softening” of the polymer as water disrupts hydrogen bonds between amide groups [1], but to date there has been no work which is able to shed light upon the motional states of the water molecules or polymer chains during deformation.

Extensive evidence has shown that water only penetrates into the amorphous regions of nylon [5], [6], [7], but there has been some debate regarding its nature. Puffr and Sabenda have suggested the presence of both “loosely” and “tightly” bound water molecules in the matrix [8]. Using deuterium NMR techniques, we have demonstrated that water molecules exist only in one state in wet nylon [9], thus supporting the viewpoint held by le Huy and Rault [10].

We intend to continue to utilize this powerful tool to examine the motion of such absorbed water molecules while the polymer is undergoing active deformation, thereby giving insight into the deformation process and the role of the plasticizer. There have been various NMR studies on plasticizers in polymers [11], [12], [13]. The amount of experimental data available on actively deforming polymers is limited. In an earlier work we studied phenol-d5 in deforming nylon 6, the former being chosen because it does not undergo exchange with the hydrogen atom on the NH group and because of the resulting good signal to noise since it is absorbed in large quantities [14]. Other researchers have also used deuterium NMR to investigate small strain deformation in deuterated polycarbonate [15] and performed time resolved simultaneous X-ray of polyethylene undergoing active cold drawing [16].

Section snippets

Materials and methods

Two millimetre diameter nylon 6 rods were purchased from Goodfellow Corporation and deuterium oxide was obtained from Cambridge Isotope Laboratories. The molecular weight of the polyamide is 60,000 g/mol, determined from viscometry measurements using 2,2,2-trifluoroethanol as a solvent at 23.5±0.5°C. Differential scanning calorimetry (DSC) showed that the crystallinity of the material is about 30%. Without any further modification the rods were dried in vacuum at 100°C for 48 h to remove trace

Results and discussion

Fig. 1ashows plots of engineering stress versus engineering strain (strain, ε, is defined as εL/L0 where ΔL is the increase in length and L0 is the initial length of the sample) of nylon 6 which is fully saturated with D2O (i.e. gained 12 wt% of D2O). Both curves show a yield point and strain hardening. In addition, the curve for the faster elongation rate exhibits a yield drop. The deformation was homogeneous and necking did not occur in either sample. Plasticization of the amorphous regions

Conclusion

During the active large strain tensile deformation of nylon 6 plasticized by D2O, the D2O molecules are found to associate with the amide groups. The quadrupolar splitting varies linearly with strain independent of the rate of elongation. Thus the order parameter of the D2O molecules is simply a function of strain and not of stress. This is similar to the linear dependence of quadrupolar splitting with draw ratio in the work done by Hutchison et al. on D2O in nylon 6 fibers [11]. Furthermore,

Acknowledgements

This work made use of MRSEC Shared Facilities supported by the National Science Foundation under Award Number DMR-9400334. This work was supported primarily by the MRSEC Program of the National Science Foundation under award number DMR 98-08941.

References (26)

  • H.M. Le Huy et al.

    Polymer

    (1994)
  • M.F. Butler et al.

    Polymer

    (1998)
  • A.F. Terzis et al.

    Chem Phy Lett

    (1997)
  • V. Malta et al.

    Euro Pol J

    (1979)
  • J. Rubin et al.

    Pol Engng Sci

    (1968)
  • H.K. Reimschuessel

    J Pol Sci, Pol Chem Ed

    (1978)
  • M. Yokouchi

    J Pol Sci, Pol Phy Ed

    (1984)
  • A. Galeski et al.

    Macromol

    (1988)
  • N.S. Murthy et al.

    Macromol

    (1989)
  • J. Hirschinger et al.

    Macromol

    (1990)
  • H. Miura et al.

    Macromol

    (1990)
  • R. Puffr et al.

    J Pol Sci, Part C

    (1967)
  • L.S. Loo et al.

    Macromol

    (1998)
  • Cited by (11)

    • Direct investigations of deformation and yield induced structure transitions in polyamide 6 below glass transition temperature with WAXS and SAXS

      2015, Polymer
      Citation Excerpt :

      The transition process was intimately related with the existence form of γ-phase, which was affected by the tensile stress and orientation. Deformation induced structural formation and evolution of polymers has a profound impact on polymer science and industry [3,14]. It is generally recognized that macroscopic properties of semicrystalline polymers are governed by their microscopic structural features such as crystalline structure, morphology, and so on [4,15,16].

    • The effect of annealing of linear and branched polyamide 46 on the phase composition, molecular mobility and water absorption as studied by DSC,<sup>1</sup>H and<sup>2</sup>H solid-state NMR

      2015, Polymer
      Citation Excerpt :

      The amount of water absorbed by polyamides varies from a few percent up to about 10–15 wt% depending on the amount of amide groups, crystallinity, the structure of the amorphous phase and the environmental conditions, i.e., temperature and relative humidity. Since water penetrates almost exclusively into the amorphous regions of polyamides, as has been shown by SANS, X-ray scattering, IR spectroscopy [31] and NMR studies [32–34], an increase in crystallinity causes a decrease in water uptake. The equilibrium amount of absorbed water decreases with hydrophobicity of polyamides, as determined by the [CH2]n/[CONH] ratio [35].

    • Physicochemical investigation of chemical paint removers: Interactions of methylene chloride with polyurethane coatings

      2014, Progress in Organic Coatings
      Citation Excerpt :

      However, labeling the solvent with deuterium provides greater selectivity (because of the low natural-abundance of 2H, 0.015%) as well as greater sensitivity to and theoretical interpretability of molecular dynamics and orientation due to the dominance of the large nuclear quadrupole interaction. This is exemplified by 2H NMR studies of D2O in epoxy [20] and in strained and unstrained nylon [21] and of deuterated small organic molecules used to probe stress/strain effects in polymers [22,23] including d5-phenol in nylon [24]. The 2H NMR results provide molecular-level information about the solvent molecule itself, by relying upon isotopic-labeling of the methylene chloride.

    View all citing articles on Scopus
    View full text