Section 4.9 - Plasticity of Polymers

Abstract

This chapter deals with the explanation of plasticity of polymers. In crystalline materials, plasticity is interpreted in terms of the motion of linear defects or dislocations. Plasticity of polymers refers to large deformations of amorphous polymers in a temperature range below and near the glass transition temperature, and of semicrystalline polymers below their melting temperature. Semicrystalline polymers are very often deformed when the amorphous phase is in the rubberlike state. This mobility of the amorphous component allows, at the beginning of deformation, relative displacements of the crystalline lamellae. Then, plastic deformation of polymer crystals takes place, essentially by crystallographic slip. At large strains, the lamellar crystals are broken into smaller crystalline blocks connected by amorphous fragments of molecules. This lamellar-to-microfibrillar transformation occurs in the macroscopic neck. The ultimate step is the extension of the amorphous network. Consequently, the deformation of the crystalline phase can be modeled using micromacro approaches based on slip mechanisms, whereas strain-hardening at high strain can be treated with a rubber elasticity formalism. When the amorphous phase is in the glassy state, deformation combines the specific mechanisms of the amorphous and crystalline phases.