Microstructure evolution in polyamide PA11 under small uniaxial extension

Polyamide 11 (PA11) is a linear semicrystalline polymer. Bulk samples of PA11 were compression moulded from the melt. The aim of this study is to describe the deformation of the structure during an uniaxial drawing (up to a true strain of 0.4) at room temperature. The structure of the studied samples is described on two scales by two different X-ray scattering techniques. The small angle X-ray scattering (SAXS) method investigates the structure on the scale of lamellae, whereas the wide-angle X-ray scattering (WAXS) method investigates the macromolecular structure. The studied samples are constituted of three macromolecular structures: an amorphous phase (approximately 60 vol%), a crystalline phase called α (≈20 vol%), and a smectic phase called δ′ (≈20 vol%). The study of the descriptive parameters of the diffusion peaks shows that lamellae orient themselves weakly towards the drawing direction. The same tendency is observed for the chain segments of the smectic and amorphous phases. On the other hand, the chain segments of the crystalline phase, that constitutes the lamellae, orient themselves strongly perpendicularly to the drawing direction. The comparison between the results from the two investigated scales allows us to propose the activation of a twinning mechanism in the lamellae parallel to the drawing direction.