Direct investigations of deformation and yield induced structure transitions in polyamide 6 below glass transition temperature with WAXS and SAXS

•By using the combination of the WAXS and SAXS techniques on bulk PA6 during uniaxial drawing, a transient crystalline stage in the course of the γ-α strain-induced phase transformation was observed at 30 °C (below Tg).•The γ-phase slips into incomplete fragments at yield point, and the parts along tensile direction are responsible for the formation of transient phase.•A simplified schematic diagram was provided to illustrate the structure evolution of PA6.

Deformation and yield induced structure transitions of polyamide 6 (PA6) were detected with the combination of the wide- and small-angle X-ray scattering (WAXS and SAXS) at 30 °C below glass transition temperature (Tg) of PA6. During deformation, γ-α phase transition was found at elastic stage. The concentrated stress in crystals at elastic stage provided adequate energy for the direct γ-α phase transition under Tg. The force to promote the γ-phase into α phase directly is insufficient at the yield stage and a transient phase as a compromise was formed. The transient phase was confirmed by DSC measurements and assisted the γ-α phase transition indirectly. The γ-phase slips into incomplete fragments at yield point, and the parts along tensile direction are responsible for the formation of transient phase. The γ-fragments after yield is oriented by shear force following α-phase. The yield of PA6 was intimately related with the γ-transient phase transition and the slippage of γ-fragments. In addition, the increase of long spacing at elastic deformation along tensile direction was mainly contributed by the amorphous region. After yield, the phase transition and crystalline slippage affected the lamellar evolution. A simplified schematic diagram was provided to illustrate the structure evolution of PA6.

Graphical abstractDirect investigations of deformation and yield induced structure transitions in polyamide 6 below glass transition temperature with WAXS and SAXS.Download high-res image (151KB)Download full-size image