Study of Transformations among α, γ and γ' Forms in Nylon 12 by X-Ray and DSC

Abstract

The transformation behaviors of nylon 12 were investigated using wide-angle X-ray diffraction (WAXD), X-ray fiber patterns and differential scanning calorimetry. The γ' form could be distinguished from the γ form in spite of their very similar WAXD patterns, because the γ form cannot be transformed into the α form, while the γ form can be so transformed under high pressure. The γ' to γ transformation occurs on annealing above 110°C at atmospheric pressure. The γ to γ' and α to γ' transformations occur on drawing at atmospheric pressure above 50°C and above 70°C, respectively. The transformation behaviors presented in this paper and in a previous paper [N. Hiramatsu, S. Hashida and S. Hirakawa: Jpn. J. Appl. Phys. 21 (1982) 651] are summarized.

Transparent hydrophobic and superhydrophobic coatings fabricated using polyamide 12–SiO2 nanocomposite

“…On the contrary, if the samples are crystallized by slow cooling or by rapid quenching from the melt, then it shows γ or hexagonal phase at room temperature . If the polyamide 12 is crystallized at high temperature and pressure, then it exhibits both α and γ phase at room temperature …”

“…It has been demonstrated that polyamide 12 shows two strong characteristic diffraction peaks around 2θ = 20.3° and 21.0° which are designated as α′ and α phases of polyamide, and the crystal structure is mostly monoclinic and is believed to be a less stable phase . On the contrary, if the samples are crystallized by slow cooling or by rapid quenching from the melt, then it shows γ or hexagonal phase at room temperature . If the polyamide 12 is crystallized at high temperature and pressure, then it exhibits both α and γ phase at room temperature …”

Microporous Organic Materials from Hydrophobic Dipeptides

“…We suggest that this exotherm might arise from the solid state transformation into the α form of a few unstable defective γ crystals that can be suspected from the WAXS pattern of Figure 1(c). As a matter of fact, the occurrence of a small exotherm just before the main melting peak has been clearly shown to result from the reorganization of unstable crystals into a more stable form before melting, in the case of PA638, 39 and PA1240 as well. Similar exotherms have been also reported for several severely deformed semicrystalline polymers as a result of structural reorganization of the material into a more stable crystalline state following a strain‐induced phase change 41.…”

Crystalline structure of polyamide 12 as revealed by solid‐state 13C NMR and synchrotron WAXS and SAXS

“…Crystalline structure and polymorphism of polyamides obtained by ring‐opening polymerization have been studied by many researchers 1–14. It is generally accepted that these polymers possess layer‐like structure formed by hydrogen‐bonded sheets.…”

“…As regards the transitions between the four PA12 polymorphs, it was reported that thermal treatment under pressure gives rise to a γ′‐ to α‐form transition, whereas the same treatment does not change the γ‐crystalline form 6, 13. The γ′‐structure can be transformed into α‐form also by annealing above 110 °C at atmospheric pressure 13. In their early WAXS study, Northolt et al14 investigated the effect of drawing on the structure of PA12.…”