Polyester Manufacturing and Modification Involving Crosslinking: Characterization (Limits) and Challenges

ABSTRACT Polyester polymer materials play a key role in our daily and future lives, as they are used in a broad range of applications and have great potential for sustainable and renewable production and recycling. Nevertheless, application challenges arise regarding the melt strength, crystallization kinetics, thermal stability, and mechanical properties. To address these challenges, polyesters can be crosslinked, enhancing their material properties. Crosslinking is typically conducted via a reactive extrusion (REX) process, which is known to be highly complex, with many factors from different length scales interacting to govern reaction progress and final material properties. Furthermore, the one‐to‐one correlation between the REX parameters and polymer microstructure is hard to establish, as cross‐linked materials are challenging to characterize with typical solution‐based laboratory methods. This has resulted in the need for better characterization tools for crosslinked polymers to understand the molecular level and to optimize the reactive process efficiently. In the present contribution, the effect of crosslinking on several material properties is explained. First, we provide an overview of different crosslinking methods, including radiation initiated and chemical techniques, using radicals and end‐groups in their reaction chemistry. Next, typical methods for microstructure characterization are discussed with a particular focus on the limitations introduced by partial insolubility. Finally, a characterization pipeline is proposed that allows for a full understanding of the molecular‐ and meso‐scale properties, focusing on combining experimental and modeling techniques.