Morphology and deformation behavior of samples of iPP homopolymer containing exclusively γ-modification with only minor traces of R-crystals, obtained by isothermal crystallization at high pressure of 200 MPa, were investigated. It was found that the growth of γ-lamellae is initiated on "seeds" consisting of a spine of single R-lamella and several shorter R-lamellae branching at the angle of 80°. Epitaxial growth of γ-lamellae on (010) faces of R-parent and daughter lamellae of the seed leads to the formation of immature spherulites, which eventually fill completely the sample volume. The plane-strain and uniaxial compression tests demonstrated higher modulus, higher yield stress and flow stress, yet slightly lower ultimate strain of γ-iPP as compared to R-iPP. During plastic deformation numerous fine shear bands, initiated by the interlamellar shear of the amorphous layers start to develop already at the yield point. Their propagation across the sample causes a limited destruction of γ-lamellae oriented perpendicularly to the direction of the band. Destroyed fragments of crystallites transform partially into a smectic phase. No γ-R phase transformation was detected. With increasing strain the shear bands multiply and tilt gradually toward the flow direction. Lamellae, already fragmented within shear bands, undergo kinking and rotation, resulting in the formation of a chevron-like lamellar morphology. Simultaneously, a relatively weak one-component crystalline texture is developed. This texture is described by the orientation of c crystallographic axis along the constrained direction, b axis 10-30°away from the loading direction toward the flow direction, and a axis 10-30°away from FD. Both crystalline texture and lamellae orientation are developed due to the activity of the same deformation mechanismsthe interlamellar slip produced by the shear within interlamellar amorphous layers. Activity of any crystallographic deformation mechanism within crystalline component was not detected. The interlamellar amorphous shear appears the primary deformation mechanism of γ-iPP. The other identified mechanism, γ-smectic phase transformation, plays a minor, supplementary role in the deformation sequence.
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