Ultrathin and nanofibers via room temperature electrospinning from trifluoroacetic acid solutions of untreated lignocellulosic sisal fiber or sisal pulp Bruno V. M. Rodrigues, Elaine C. Ramires, Rachel P. O. Santos, Elisabete Frollini Macromolecular Materials and Lignocellulosic Fibers Group, Center for Research on Science and Technology of BioResources, Institute of Chemistry of S~ ao Carlos, University of S~ ao Paulo, 13560-970 S~ ao Carlos S~ ao Paulo, Brazil Correspondence to: E. Frollini (E - mail: elisabete@iqsc.usp.br) ABSTRACT: Lignocellulosic sisal fiber (LSF) and sisal pulp (SP) were electrospun at room temperature from solutions in trifluoroacetic acid (TFA) prepared at concentrations of 2 3 10 22 g mL 21 and 3 3 10 22 g mL 21 , respectively. Scanning electron microscopy images of the electrospun LSF showed fibers with diameters ranging from 120 to 510 nm. The presence of defects decreased along with increasing the flow rate of the SP solution, which generated nanofibers and ultrathin fibers with diameters in the range of 40–60 (at 5.5 mL min 21 ) up to 90–200 nm (at 65.5 mL min 21 ). Despite the known ability of TFA to esterify the hydroxyl groups present in the starting materials, the Fou- rier transform infrared spectra indicated the absence of trifluoroacetyl groups in the electrospun samples. The thermal stability of the final materials proved suitable for many applications even though some differences were observed relative to the starting materials. This study demonstrated a feasible novel approach for producing nano/ultrathin fibers from lignocellulosic biomass or its main component, which allows for a wide range of applications for these materials. V C 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41826. KEYWORDS: biopolymers & renewable polymers; cellulose and other wood products; electrospinning Received 25 May 2014; accepted 25 November 2014 DOI: 10.1002/app.41826 INTRODUCTION In the last few decades, natural fibers, such as lignocellulosic fibers, have been employed in a wide range of applications and have provided a positive contribution to the environment and to the petroleum supply issue. These fibers are most commonly used in the textile field 1–3 and as a composite reinforcement. 4–7 Among the most known lignocellulosic fibers, lignocellulosic sisal is an excellent candidate for use as reinforcement in composite applica- tions due to its high cellulose content. In addition, Brazil is the largest worldwide producer and exporter of sisal, and many appli- cations of these fibers have been investigated in the last few deca- des to generate final products with high aggregated values. In recent decades, the investigation of nano-sized materials has pro- gressed significantly due to the generation of materials with out- standing properties that typically exhibit superior mechanical performance, 8 large surface area to volume ratio, 9 and a variety of surface functionalities. 10 In this context, many investigations have attempted to extract nanocellulose in its different forms (nanofibrils or nanocrystals) from lignocellulosic fibers and wastes. 11–13 In gen- eral, these nanomaterials are prepared from acid and/or mechanical treatments in the lignocellulosic biomass and exhibit the potential for application as reinforcements in nanocomposites. 11,13 Although the electrospinning technique has gained importance as a versatile technique for preparing fibers at the sub-micro- and nano-scales during the last two decades, 14–17 there has been a notable lack of investigation of lignocellulosic biomass as an alter- native raw material. Few studies have been published regarding the electrospinning of lignocellulosic biomass, and all of these studies were restricted to the utilization of alkali-treated biomass and the 1-ethyl-3-methylimidazolium acetate ionic liquid as sol- vent. 17,18 However, room temperature electrospinning of the native lignocellulosic biomass has not yet been reported. Electrospinning at room temperature requires a solvent that readily volatilizes under this condition. Trifluoroacetic acid (TFA), which is a very strong organofluorine acid, is widely used in organic synthe- sis due to its high acid strength, high volatility, and miscibility with a wide range of organic solvents. Another important advantage offered by TFA is that it can be easily recovered at low operating temperatures due to its low boiling point (72.4  C). 19,20 TFA has been used to disrupt cellulose crystallinity leading to the complete separation and dissolution of cellulose chains due to the nearly exclusive esterification of their hydroxyl groups at C6. 21 The tri- fluoroacetyl groups introduced into the cellulose chains are easily hydrolyzed by exposure to air after regeneration. 21,22 V C 2015 Wiley Periodicals, Inc. WWW.MATERIALSVIEWS.COM J. APPL. POLYM. SCI. 2015, DOI: 10.1002/APP.41826 41826 (1 of 8)