Efficient Cellulose Dissolution and Film Formation Enabled by Superbase Amino Acid Ionic Liquids

Cellulose is a promising feedstock for the production of sustainable materials. To fully utilize its potential, exploring efficient cellulose solvents is a paramount prerequisite. In this study, ten superbase amino acid ionic liquids (SAAILs) are synthesized using 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) with different amino acid anions via a simple neutralization method. The properties of these SAAILs, such as viscosity and glass transition temperature, varied with their cation and anion structures. The ability of the SAAILs to dissolve cellulose is related to their Kamlet-Taft parameters, particularly hydrogen bond basicity (beta). The main driving force for cellulose dissolution in SAAILs is thought to be hydrogen bonding interactions between SAAILs and cellulose hydroxyl groups. Four SAAILs composed of DBN or DBU cations and proline, or aspartic acid anions are identified as promising solvents for preparing regenerated cellulose films (RCFs). The RCF prepared from [DBN]Proline(Pro) showed a favorable combination of high tensile strength (76.9 MPa), high Young's modulus (5201.2 MPa), good transparency (approximate to 70% at 550 nm), and smooth surface morphology. These halogen- and metal-free SAAILs show the potential to provide a new avenue for cellulose processing.

Automated summary

Cellulose is a promising feedstock for sustainable materials, and efficient cellulose solvents are essential for its full utilization. Ten superbase amino acid ionic liquids (SAAILs) were synthesized in this study and their properties varied with their cation and anion structures. The ability of the SAAILs to dissolve cellulose is related to their Kamlet-Taft parameters, especially hydrogen bond basicity (beta). Four SAAILs composed of specific cations and anions were identified as promising solvents for preparing regenerated cellulose films (RCFs) with high tensile strength, high Young's modulus, good transparency, and a smooth surface morphology. These halogen- and metal-free SAAILs offer a new avenue for cellulose processing.