Electrospinning of cellulose carboxylic esters synthesized under homogeneous conditions: Effects of the ester degree of substitution and acyl group chain length on the morphology of the fabricated mats

Abstract

The increased awareness about environmental issues has resulted in developing novel materials and sustainable solutions to reduce the dependence on fossil-based products. Herein, cellulose from sisal was derivatized into carboxylic esters (acetate, Ac; butyrate, Bu; and hexanoate, Hx); the produced materials were “shaped” into mats composed of nano- and ultrathin fibers. Our objective was to assess the effects of cellulose ester degree of substitution (DS), low- and high DS, ca. 0.2 and 2.6; the length of the acyl group and the electrospinning flow rate, 45.5 and 65.5 μL/min on the morphology of the fibrous material obtained therefrom. Cellulose was converted into its carboxylic esters under homogeneous conditions using LiCl/N,N-dimethylacetamide solvent, and acid anhydrides as acylating agents. The obtained cellulose- acetate, Cel-Ac, butyrate, Cel-Bu, and hexanoate, Cel-Hx were dissolved in trifluoracetic acid. The solutions of esters were subjected to electrospinning, under positive voltage of 25 kV, and needle-collector distance of 4 cm. Scanning Electron Microscopy of the electrospun mats showed the formation of ultrathin- (100 nm > diameter < 1000 nm) and nanofibers (diameter ≤ 100 nm). No fibers were formed from Cel-Ac of low DS. Lower ester solution flow rate favored the formation of nanofibers from Cel-Ac (DS = 2.7), Cel-Bu (DS = 0.2 and 2.6), and Cel-Hx (DS = 0.2), and ultrathin fibers without beads from Cel-Hx (DS = 2.8). Using a flow rate of 65.5 μL/min favored the formation of ultrathin fibers without beads from Cel-Ac (DS = 2.7), Cel-Bu (DS = 0.2 and 2.6), and Cel-Hx (DS = 0.2, and 2.8). That is, the morphology of the fibers formed can be “fine-tuned” by a judicious choice of the length of the acyl group and the conditions of electrospinning. To the best of our knowledge, this is the first study that the effects of these variables on the morphology of the electrospun fibers were studied. The electrospun mats have potential applications in wastewater treatment, filters for air purification, and tissue engineering scaffolds, to be confirmed by future investigations.