Revisiting the Thermal Transition of β-Form Polyamide-6: Evolution of Structure and Morphology in Uniaxially Stretched Films

Abstract

Structure and morphology evolution of the uniaxially stretched polyamide-6 (PA6) film with the β-form upon heating were investigated mainly by synchrotron twodimensional (2D) wide-angle X-ray diffraction and small-angle X-ray scattering. For comparison, thermal transitions of the oriented PA6 samples with the αand γ-form were also monitored, which undergo "incomplete Brill transition" and direct melting, respectively. Using the results of oriented αand γ-PA6 as the references, we confirm that the stretched β-PA6 is mesomorphic, which can be viewed as a solid mesophase with smectic B-like structure. We identify that upon heating the stretched β-PA6 reorganizes dominantly into γform crystal with the chain orientation unchanged, accompanied by the formation of a little amount of α-PA6 crystallites. Further heating to above the melting temperature of γ-PA6, the α-PA6 crystals grow through a recrystallization process. The lamellae resulting from reorganization exhibit a distribution of orientations, and the α-PA6 lamellae formed at high temperatures have the lamellar basal surface normal parallel to the stretched direction. We consider that the abundant hydrogen bonds in the stretched β-PA6 film construct a network, providing the confinement effect to reduce the chain mobility and thus favor the formation of γform. The lamellae with the basal surface normal tilted relative to the stretched direction can also be attributed to the hydrogenbonded network of oriented chains.

A Novel Synthetic Strategy for Preparing Polyamide 6 (PA6)-Based Polymer with Transesterification

“…The characteristic γ-PA6 diffraction peak is located at 21.3°. The single-diffraction phenomenon of PA6 is attributed to the characteristic diffraction peaks of (200) and (001) superimposed together [29]. Figure 6a shows that the characteristic peak of PEA is exactly the same as that of PA6, indicating that the crystallinity in PEA is completely determined by the polyamide 6 segment.…”

Bioinspired Construction of Artificial Cardiac Muscles Based on Liquid Crystal Elastomer Fibers

“…The authors calculated the order parameter f based on the Hermans-Stein orientation distribution function. [49][50][51] Where I is the intensity and φ is the azimuthal angle as shown in Figure S2c, Supporting Information. The order parameter of aligned LCE fibers was determined to be 0.49.…”

Overview and critical survey of polyamide6 structural habits: Misconceptions and controversies

“…A controversy exists regarding the identification of the β and γ forms of PA6 that exhibit somewhat similar X-ray scattering patterns. Indeed, it has been often reported from wide-angle X-ray scattering experiments (WAXS) that γ crystals prevail in melt spun fibers, blown and cast films, bulk crystallized samples after quick cooling, [23,[37][38][39][40][41][42][43][44][45]48,[55][56][57][58][59][60][61][62] and nanocomposites as well [32,44,[63][64][65][66][67][68][69][70][71][72][73][74] reinforced with various kinds of nanofillers. In most of these studies the γ structure has been associated to the one identified by Arimoto et al [34] on iodine-treated PA6 fibers.…”