Fiber-welded polyionic biocomposites using 1-alkyl-3-vinylimidazolium alkylphosphonate ionic liquids

In this study, imidazolium-based polymerizable ionic liquids (Poly-ILs) were used to prepare novel polyionic biocomposites through Natural Fiber Welding. Two new Poly-ILs containing a 1-alkyl-3-vinylimidazolium cation and an alkylphosphonate anion were synthesized and evaluated for their ability to (i) solubilize a biopolymer (cellulose) matrix and (ii) polymerize with and without dissolved cellulose. Raman spectroscopy and scanning electron microscopy (SEM) were used to characterize the fiber-welded composites. Optimized fiber-welding parameters yielded polyionic biocomposite materials whose physicochemical properties were evaluated using SEM, energy dispersive X-ray spectroscopy (EDS) and water sorption testing in a controlled relative humidity chamber. SEM/EDS revealed polymerized Poly-IL integrated throughout a fiber-welded, polyionic biocomposite matrix; the materials absorbed ca. 38-40 % of their mass in water when exposed to a controlled (70%) relative humidity environment. To reduce the hygroscopic nature of the fiber-welded composites, the methylphosphonate anion was partially exchanged for a more hydrophobic anion (bis-trifluorosufonylimide, TFSI) through a single-pass anion exchange. SEM/EDS of sample cross sections before and after treatment show that this simple anion exchange and rinse procedure delivers up to ca. 5% exchange from methylphosphonate to TFSI. In spite of this low exchange, the water sorption properties of the exchanged polyionic biocomposites were successfully reduced by 14% and could be easily returned to their original dry state at low temperature under vacuum.