Structure development in polymers General concepts

Shaping gives polymer materials a structure that can range from the nanometric to the macroscopic scale, and conditions the final properties of the products. This structure has traditionally been referred to as the "microstructure", because originally, the relevant observations were generally between one micrometer and a few hundred micrometers, i.e. within the range of use of the optical microscope. Today, polymer systems are often complex. In addition to single polymers, polymer blends, filled or reinforced, synthetic or bio-sourced polymers are also processed. In this case, the description of the structures includes the morphology and distribution of phases in the blends, or the distribution or orientation of fillers and reinforcements. These aspects, which have been the subject of abundant literature, are not dealt with here.

This article is limited to the development of structures in semi-crystalline polymers. Crystallization plays a major role in the transition from liquid to solid state. During shaping, crystallization generally occurs under complex, heterogeneous and coupled conditions: mechanical (flow, pressure), thermal (cooling rates, thermal gradients) and geometrical (free surfaces, tool contact). Numerical simulation is an effective tool for interpreting and predicting these coupled phenomena. It involves introducing a crystallization law into a thermomechanical process model.

These general concepts of structure development are illustrated by applications in the following article [AM3121] .