The Production of Polyethylene Terephthalate Nanofibers by Electrospinning with Minimum Amount of Trifluoroacetic Acid

Attila The Production of Polyethylene Terephthalate Nanofibers by Electrospinning with Minimum Amount of Trifluoroacetic Acid . Polyethylene terephthalate fiber mats were prepared by solution electrospinning with average fiber diameters ranging from 150 nm to 500 nm depending on the processing conditions. The minimum amount of trifluoracetic acid was determined at which the electrospinning process generates randomly oriented and smooth surfaced fibers. A three factorial Box-Behnken experimental design was used to determine the effect of the processing parameters on the resulting fiber diameter. It was found that the dichloromethane: trifluoroacetic acid 80:20 (wt:wt) solvent system generates a robust electrospinning system, where only the applied voltage shows statistical significance.


Introduction
Polyethylene terephthalate (PET) is a semi crystalline polymer, that is used in a variety of applications due to its resistant to environmental effects and good mechanical properties [1,2]. PET is used in the automotive and packaging industry extensively, however lately PET nanofiber mats were used for filtration [3], protective clothing [4], biomedical applications such as tissue engineering scaffolds [5], electroconductive cardiac patch [6] and others [7]. Electrospinning has become a readily used process to generate polymer fibers with average diameters in the nanometer range [8]. Polymer fiber mats generated by electrospinning offer a high surface-to-volume ratio and high porosity [7]. The solution electrospinning process has been discussed in detail in the literature. Briefly, a polymer solution is placed into a container, typically a syringe, that is connected to a needle. The needle is connected to the positive potential outlet of a high voltage DC power supply and the collector is grounded and placed at a desired distance from the needle. The so-called Taylor cone forms at the end of the needle and the solution becomes positively charged [9]. When the tension due to the repulsion forces of the positive charges exceed the surface tension of the solution a jet forms that travels to the collector. During the travel most of the solvent evaporates and a solid polymer fiber deposits on the collector [7,8].
To generate PET fiber mats trifluoroacetic acid (TFA) alone or its mixture with dichloromethane (DCM) is used [10][11][12]. TFA is a potent acid, pKa = 0.23, thus its use for generating PET fibers has its inherent dangers, and it corrodes the equipment [13,14]. The aim of this work is to determine the minimum amount of TFA needed to dissolve PET and to produce fibers by electrospinning.

Materials
Trifluoroacetic acid (Sigma Aldrich, 99%), dichloromethane (Supelco, ACS grade) and acetone (Supelco, ACS grade) were used as received without any purification. Polyethylene terephthalate (PET) was obtained from a water bottle, that was cleaned with acetone before the solution preparation.  whereas the collector was grounded. A syringe pump was used to supply the desired constant flow rate. The electrospinning process parameters were set as shown in (Table 1).

Scanning Electron Microscopy (SEM)
SEM imaging was performed on a JOEL JSM-5200 scanning electron microscope at 10 kV accelerating potential. The samples were examined as is, without sputter coating. ImageJ software was used to determine the fiber diameter, based on at least 60 measurements for each sample. The measurements were collected from three different x10000 SEM image for each sample.

Results and Discussion
The aim of this work was to minimize the use of TFA when preparing PET fibers via the electrospinning method. In order to do this several solvent ratios were prepared that are presented in ( between the tip of the needle and the collector. This is an undesired phenomenon that is most probably due the high evaporation rate of DCM, since we did not observe this earlier, when only TFA was used as solvent [10]. Using DCM:TFA 80:20 solvent ratio to solubilize PET resulted a stable electrospinning process, and the above-mentioned premature fiber solidification did not occur. In order to investigate the flow rate (F), collector-to-needle distance (D) and the applied voltage (V) electrospinning process parameters on the resulting fiber diameter the Box-Behnken method was utilized. The boundary limits were determined by scoutingexperiments

Conclusions
In conclusion, it can be said that the TFA amount need to produce PET fibers by solution electrospinning was minimized. (wt:wt) solvent ratio is needed. Randomly oriented and smoothsurfaced PET fibers were produced with average diameters ranging from 150 nm to 500 nm. The Box-Behnken experimental design analysis shows statistical significance only in the case of the applied voltage, meaning that the PET electrospinning process using DCM:TFA 80:20 solvent system is robust and only the applied voltage could influence the fiber diameters.