Reactive extrusion of cellulose esters in ionic liquid: exploring properties and performance across different cellulose types and degrees of polymerization

Abstract

This study compares the efficacy of reactive extrusion and traditional reactor methods in altering cellulose structure to produce cellulose esters (CEs) with targeted properties. Ionic liquids (ILs) afford high cellulose solubility and recyclability, while chemical reactors enable complete cellulose dissolution and homogeneous transesterification. However, prolonged reaction times and potential oxidation issues necessitate further optimization. Conversely, reactive extrusion allows shorter reaction times, reduced solvent usage, and scalability. The current study aims to investigate how the type of cellulose (microcrystalline and fibrous) and its degree of polymerization (DP) affect the transesterification process and properties of CEs produced by reactive extrusion, as opposed to traditional methods. It was obtained that it is possible to produce cellulose laurates (CLs) with a degree of substitution (DS) of up to 2.5 via reactive extrusion. Examination of CLs obtained from the reactor (R-CLs) and reactive extrusion (REX-CLs) reveals structural properties diverging, with REX-CLs maintaining residual crystallinity despite esterification. Additionally, reactive extrusion produces CLs with lower molar mass due to a reduced DS, and in the case of fibrous celluloses, shear-induced degradation may occur. Cellulose DP emerges as pivotal for attaining desired thermal stability, with higher DP compounds displaying enhanced resistance to thermal degradation. Furthermore, reactive extrusion enhances the thermal stability of CLs more than traditional methods. However, comparative rheological analysis reveals that REX-CLs exhibit higher complex viscosity and G-moduli values than R-CLs. This phenomenon suggests that the structural arrangement of REX-CLs promotes intermolecular interactions, contributing to increased viscosity and stiffness. Reactive extrusion in an IL environment shows promise for scaled-up production of CEs with tailored properties. This indicates its potential as a sustainable and efficient manufacturing method for cellulose-based materials.

Graphical abstract