Plasticity of semi-crystalline polymers: crystal slip versus melting-recrystallization

Abstract

Semi-crystalline polymers can be drawn up to very high draw ratios that involve a complete molecular rearrangement of the chain-folded lamellar morphology into a more or less chain-unfolded fibrillar microstructure. This metamorphosis is likely to take place through an intermediate state of high molecular disorder at a local scale. This is the reason why some authors talk of a strain-induced melting-recrystallization process. In contrast, several structural features occurring at moderate plastic strains are relevant to strictly crystallographic processes. A critical discussion of experimental findings and theoretical approaches is made for pointing out the strength or the deficiency of the different author argumentations. No doubt that both phenomena can occur: crystallographic processes are active at all strain levels whereas meltingrecrystallization is restricted to the post-yield stage accompanied with chain unfolding. Melting-recrystallization is rather a corollary of chain unfolding than a basic mechanism of the plastic deformation. Besides, it may concern only a part of the crystalline phase and can be inhibited under adequate deformation conditions.

Effective viscoplastic behavior of polycrystalline aggregates lacking four independent slip systems inferred from homogenization methods; application to olivine

“…21 Similarly, many synthesized materials, such as semi-crystalline polymers (see,e.g. Bow-22 den and Young, 1974; Argon, 1997;Seguela, 2007), do not exhibit four independent slip 23 strain field, as illustrated in Castelnau et al (2006) for the case of strain-hardening. 1 For nonlinear polycrystals, a linearization of the local constitutive behavior is nec-2 essary, leading to the definition of a N-Phase Linear Comparison Polycrystal (NPLCP).…”

On the strain-induced fibrillar microstructure of polyethylene: Influence of chemical structure, initial morphology and draw temperature

“…the higher the temperature the greater the long period [7][8][9][10]. Considering this complete reconstruction of the stacking long period, many authors claimed that fibrillar transformation necessarily involves a strain-induced melting-recrystallization process [11,12]. Several phenomena have been proposed for providing physical support to this hypothesis: the chainunfolding mechanism that necessarily goes through a transitory state of disordered chain segments analogous to the amorphous state, the conversion of plastic work into heat that may generate significant temperature increase at high strain rates, the stressinduced depression of the melting point, etc.…”

Cyclic viscoplasticity of semicrystalline polymers with finite deformations

“…For a detailed discussion of these phenomena, the reader is referred to recent reviews (Seguela, 2007;Bartczak and Galeski, 2010;Patlazhan and Remond, 2012) and the references therein. Plastic deformations in the crystalline phase reflect (i) inter-lamellar separation, (ii) rigid rotation and twist of lamellae in stacks, (iii) fine slip of lamellar blocks (homogenous shear of layer-like crystalline structures), (iv) coarse slip of lamellar blocks (heterogeneous interlamellar sliding), (v) transformation of folded-chain lamellae into oriented mesomorphic phase, (vi) martensitic transformation of orthorhombic into monoclinic crystal phases, (vii) crazing and cavitation in large spherulites, (viii) fragmentation of lamellae into blocks linked by tie chains and formation of a mosaic structure, and (ix) alignment of lamellar blocks along the direction of maximal stress and formation of a fibrillar texture.…”