Uniaxial deformation of nylon-6 and nylon-11: changes in orientation and crystal phase

Abstract

The effect of uniaxial drawing on orientation of the crystalline fraction of two polymers forming hydrogen bonds, nylon-6 and nylon-11, has been investigated using X-ray diffraction. These two polymers have similar crystal phases, although their hydrogen bond density differs. For both polymers, the deformation occurs in two steps, the first being a plastic deformation of the α-phase spherulites. This leads to two populations of crystals, one with the chain axis oriented parallel to the draw direction, the second with the a axis (hydrogen bond direction) aligned along the draw direction. In the second step, the a-axis aligned population gradually tilts, leading to a uniaxial orientation of the samples with chain axis aligned along the draw direction. For nylon-11, the onset of this step corresponds to the emergence of crystals of the γ phase, which rapidly becomes the major phase. It reaches a higher orientation than the α phase, and stems from crystallization upon tension of the polymer. For nylon-6, although the γ phase also appears during drawing, at the maximum draw ratio only a small fraction is present. This difference is attributed to the relative stability of the two phases, which is different for nylon-6 than for nylon-11.Résumé : L'effet d'un étirement uniaxial sur l'orientation des cristaux de deux polymères formant des liaisons hydrogène, soit le nylon-6 et le nylon-11, a été étudié par diffraction des rayons X. Ces deux polymères possèdent des phases cristallines semblables, bien que la densité de liaisons hydrogène diffère. Pour les deux polymères, la déformation se produit en deux étapes, la première étant une déformation plastique des sphérolites de la forme α. Ceci conduit à l'existence de deux populations de cristaux, un orientée avec l'axe de chaîne parallèle à la direction d'étirement, l'autre avec l'axe a (direction des liaisons hydrogène) parallèle à cette même direction. Dans le second stade, il y a bascul des cristaux ayant l'axe a orienté avec l'axe d'étirement, résultant en une orientation uniaxe où l'axe de chaîne est orienté avec la direction d'étirement. Pour le nylon-11, ce stade correspond à l'apparition de la phase γ, qui devient rapidement majoritaire. Celle-ci est plus orientée que la phase α, et son apparition est attribuée principalement à la cristallisation sous tension du polymère. Pour le nylon-6, la phase γ apparaît aussi en cours d'étirement, mais elle reste minoritaire. Cette différence est attribuée à la stabilité relative de ces deux phases, qui est différente pour le nylon-6 et pour le nylon-11.

Crystallization of Nylon 11 under compressive high strain rates

“…The sample strains at the end of the tests carried out in this work were in the region of 20–100%. This observation is similar to the strain‐induced α–γ transition observed by Moffatt et al9 However, unlike in Moffatt's work which was carried out at low strain rates and at a temperature of 80°C, the transformation in this work was observed in tests carried out at room temperature and only at a strain rate of ∼10 3 s −1 and not at low rates. The explanation for this is probably due to the adiabatic nature of the high‐rate tests.…”

“…The low‐rate tests will be essentially isothermal with only a modest temperature increase. Based on experiments where Nylon 11 samples were annealed at temperatures in the range 80–170°C followed by quench cooling but no γ phase was observed, Moffatt et al9 suggested that strain alone is responsible for the α–γ transition. However, this work suggests that both strain and an elevated temperature are required; the discrepancy between the results can be resolved when the fact that Moffatt et al's experiments were carried out at 80°C is considered.…”

“…However, the first set of Miller indexes seem to be more widely accepted. More recently, Moffatt et al9 carried out a series of experiments uniaxially deforming Nylon 11 at a low strain rate and at a temperature of 80°C. They found a transition from the α to the γ form, commencing at a draw ratio of ∼2 with an increasing fraction of the γ phase as the draw ratio further increased.…”

Nanocomposites of polyamide‐11 and carbon nanostructures: Development of microstructure and ultimate properties following solution processing

“…It is also known that the microstructure and ultimate properties of PA‐11 can be further influenced by the presence of nanoparticles,4, 6–12 consistent with the effects of the incorporation of nanoparticles on the final microstructure and ultimate properties of other polymers 13–17. Here carbon nanotubes and nanofibers have attracted notable interest due to their excellent mechanical, electrical, and physical properties 18–21.…”

In-Situ Reaction Influenced Polyamide 11 Crystallization in Polymer Blends

“…They also reported that PA11 crystallized at atmospheric pressure contained both a form and one of the pseudohexagonal crystal d 0 forms, different from the variation d observed when annealed at high pressures. Moffatt et al [11] carried out a series of experiments of uniaxially deformed PA11 at a low strain rate and at a temperature of 80 C. They found a transition from a to c form, commencing at a draw ratio of $ 2 with an increasing fraction of the c phase as the draw ratio further increased. Fernandez et al [8] studied the effect of a high-rate compressive deformation on crystallographic and thermal properties of PA11.…”