Regulating supramolecular structure to enhance the ductility of regenerated cellulose films from ionic liquid solution

Abstract

Regenerated cellulose films suffer from inherent brittleness, restricting their practical use. Conventional plasticizer-based strategies can enhance ductility; however, plasticizer migration is an issue. Regulating supramolecular structure during processing is an alternative. We investigated the influence of coagulation bath temperature and coagulant types on the microstructure and mechanical properties of regenerated cellulose films using 1-allyl-3-methylimidazolium chloride (AmimCl) ionic liquid. The regeneration bath at 30 °C yielded hydrogels with a fine, dense, uniform network compared to those at 60 °C or 90 °C. Simple drying of the uniform network resulted in films with increased elongation at break (~15 %) while maintaining high tensile strength (~150 MPa). Solvent exchange to ethanol prior to drying preserved the hydrogel network, yielding dry films with elongation at break up to 30 % and a tensile strength above 100 MPa. This property of film is related to the nanoscale structural heterogeneity: (1) a fine, dense and uniform network formed in the hydrogel; (2) lower density and hence looser packing due to the lower surface tension of ethanol. Thus, controlling coagulation conditions can effectively tailor nanoscale structural heterogeneity to significantly enhance ductility.