Phase structure of electrospun poly(trimethylene terephthalate) composite nanofibers containing carbon nanotubes

Abstract

Nanofibrous composite mats were prepared by electrospinning of poly(trimethylene terephthalate), PTT, with multi-walled carbon nanotubes (PTT/MWCNT). Tri- fluoroacetic acid (TFA) and methylene chloride (MC) with volume ratio of 50/50 is a good solvent for PTT and was used as the electrospining solution. Scanning electron microscopy was used to investigate the morphology of electrospun (ES) nanofibers with 0, 0.2, 1.0, or 2.0 wt% of MWCNTs. Crystal structure of the ES mats was deter- mined from wide angle X-ray diffraction. Thermal prop- erties were investigated using heat capacity measurements from differential scanning calorimetry (DSC) using the three-runs method for baseline correction, heat flow amplitude calibration, and sample heat capacity determi- nation. A model comprising three phases, a mobile amor- phous fraction (MAF), rigid amorphous fraction (RAF), and crystalline fraction (C), is appropriate for ES PTT/ MWCNT fibers. The phase fractions, Wi (for i = RAF, MAF or C) were determined by DSC. Crystallinity decreases very slightly with the amount of MWCNT. At the same time, a large increase in RAF was observed: WRAF of PTT fiber with 2% MWCNT is twice that of neat PTT fiber. The addition of MWCNTs enhanced the PTT chain alignment and increased RAF as a result. Changes of vibrational band absorbance at 1358 and 1385 cm -1 , cor- responding to characteristic groups, were obtained with infrared spectroscopy. The increased absorbance at 1358 cm -1 and decreased absorbance at 1385 cm -1 , with the addition of MWCNTs, strongly supports the three- phase model for ES PTT/MWCNT nanocomposites.