Changes in the morphology of bulk spherulitic nylon 6 due to plastic deformation

Abstract

The change in spherulitic morphology of bulk nylon 6 due to plastic deformation was studied by means of transmission electron microscopy of ultrathin sections. Fixation of morphology was achieved by using quick cooling and infiltration with 0s04 before sectioning. Transmission electron microscopy of ultrathin sections cut from the neck regions of specimens deformed to draw ratios from 2 to 3 reveals spherulitic structures, although no regular lamellar structure could be detected within spherulites. The impression of the presence of spherulites is created by radial orientation of dark spots and radially arranged strips of stained material. The dark spots are small regions of nylon 6, in which the microstructure is damaged during deformation and reacts and cross-links with 0s04. For the same strain, the number of dark spots decreases with increasing water content in the material and with decreasing crystalline fraction. Density decreases of deformed samples, as well as DSC data, indicate that the dark spots are regions of very low density, suggesting that the dark spots are cavities formed to relieve stresses due to material misfit developed between domains of lamellae and between different spherulites during the course of plastic deformation.

Microfocus X‐Ray Scattering Scanning Microscopy for Polymer Applications

“…Figure 3 infers that the inhomogeneities are radially spread around a range of orientations, with different thicknesses across the different directions. This finding is in agreement with the results reported in the literature by Galeski et al [15] for PA6, and would correspond to a radial arrangement of inhomogeneities with respect to spherulitic radii. In their study, Galeski et al investigated deformation mechanisms in PA6 specimens with the use of TEM and showed that cavities develop between the crystalline lamellae of spherulites.…”

“…In addition, Galeski et al measured the dimensions of the cavities, which they described as rod-like particles, with a length of the order of 60 nm and a diameter of the order of 8-10 nm. In our study these rodlike particles are found to be better described as plate-like particles, but the calculated thickness from the SAXS experiments of the present study is in excellent agreement with the reported diameter/thickness of the study of Galeski et al [15] A second interesting feature in Figure 3 is the apparent maximum in cavity thickness oriented to 758/2558. Furthermore, the pattern is slightly asymmetrical as the calculated thickness in the hemisphere between 180 and 3608 is somewhat less than the hemisphere between 0 and 1808.…”

“…As also discussed in the study of Galeski et al, [15] the largest cavity thickness is usually observed on an axis perpendicular to the applied stress direction. However, in the present study, this direction corresponds to 808 in inverse space (or À108 in real space).…”

“…Thus, the plane of maximum stress is almost parallel to the crack direction in this case. This discrepancy may be due to a different mechanism operating here than the one in the study of Galeski et al [15] Along with the development of nanocracks inside the spherulites, the material is also drawn to form microfibrils parallel to the stress. Hence, the high thickness of voids almost parallel to the stress probably comes from the matrix fibrillation, while the voids in the other directions are due to nanocracks inside single spherulites.…”

Structural mechanics of semicrystalline polymers prior to the yield point: a review

“…However, continuous separation of lamellae in equatorial domain is restricted by their lateral rigidity. It may cause violation of continuity of amorphous phase resulting in the formation of the interlamellar nanovoids [29][30][31][32][33][34]. The main question arising from these observations concerns the onset of cavitation.…”