Stability of the γ form and the development of the α form in nylon 6

Abstract

The structure of nylon 6 fibers is analyzed by x‐ray diffraction. Our results suggest that only two forms of nylon 6, α and γ, along with lattice distortion and crystallite size, are sufficient to explain the whole range of crystalline structures observed in nylon 6. The γ phase is the preferred initial form in a number of nylon 6 samples. The lattice distortion of the γ form along the chain axis varies from 0.8 to 2.4%, depending on the processing conditions. Upon annealing nylon 6 fibers, the α form is produced primarily by γ‐to‐α conversion in high‐orientation fibers, while additional α form can also crystallize from the amorphous phase in low‐orientation fibers. Finally, we show that α crystallites are favored during conditioning of poorly crystallized fibers in a humid atmosphere, and therefore fibers with α as the major crystalline form are produced upon drawing these conditioned fibers. Fibers drawn without lag time contain primarily the γ phase.

Hydrogen bonding, mobility, and structural transitions in aliphatic polyamides

“…113 Moisture that enables PA-6 to crystallize preferentially in the a-crystalline form at ambient temperatures 39,114 causes it to crystallize completely in the a form at high temperatures and even brings about transformation of the c form into the a form. 28,105,115 Because water (solvent) molecules diffuse preferentially into the amorphous regions, these data show that the interactions between the crystalline stems and amorphous segments are bidirectional; that is, an increase in the mobility of the amorphous chains can affect the motion of the crystalline stems. In fact, it has been shown that amorphous segments interact with the crystalline stems at the interface, preferentially with the bc plane (b being the chain axis).…”

“…In fact, hydration depresses all the temperature-related transitions by about 70 8C: the a process is depressed by 40 8C by 2-3% water; 3 T B is depressed by 70 8C; the temperature at which the crystallization rate is maximum is reduced by as much as 70 8C (unpublished results); and the transformation from c to a occurs at 215 8C in dry PA-6 and at 160 8C in water (accompanied by hydrolysis). 20,28 Likewise, the effects of water are considerably enhanced at elevated temperatures.…”

“…However, the c form obtained by nucleation with nanoclays or by iodine treatments remains c up to melting. 20,28,29 Figure 2 shows the reversible transformation from c to a during stretching. 18,25,26 The features seen for the starting fiber are those of a c fiber, those for the fiber under load are those of an a fiber, and the relaxed fiber shows a partial irreversible conversion of c into a.…”

“…The transformation from c to a can be brought about by heat, strain, or solvents (water) either alone or in combination. 12,18,20,[25][26][27][28] The c form obtained by melt casting, spinning, drawing, and in some instance with nanoclays transforms into a before melting and is most likely a solid-state reorganization. However, the c form obtained by nucleation with nanoclays or by iodine treatments remains c up to melting.…”

Hydration in a new semiaromatic polyamide observed by humidity‐controlled dynamic viscoelastometry and X‐ray diffraction

“…Moreover, there is an indication that the PA9-T crystals have a much higher resistance to moisture in comparison to that of nylon 6 crystals. Although most of the water is considered to penetrate into the amorphous regions, there have been some suggestions that water can also affect the ordering of crystalline regions 17,19,25,26 . To examine this, the structural changes in the crystalline regions of PA9-T and nylon 6 accompanying hydration were investigated further.…”