Direct fluorination of para-aramid fibers 1: Fluorination reaction process of PPTA fiber

• The PPTA fiber was fluorinated with different partial pressure of F2.
• The reaction of F2 with the amide bonds is easier at low Fp (Fp ≤10 kPa) while the reaction of F2 with benzene rings is more favorable at high Fp.
• The results of FTIR prove that the reaction of F2 with benzene rings is mainly an addition reaction, rather than a substitution reaction.

Fluorination reaction process of PPTA fiber is studied in detail by means of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) spectra. We prove that the reaction of F2 with the amide groups is easier than that with benzene rings at the low partial pressure of F2 (Fp ≤10 kPa) due to higher charge density of N atom. With the further increase of Fp, the increase of reaction degree of F2 with the amide group gradually decreases, which may be due to the decrease of the concentration of amide groups. On the contrary, the reaction of F2 with benzene rings gradually becomes more favorable when Fp is higher than 10 kPa resulting from the saving high concentration of benzene rings. The results of FTIR prove that the reaction of F2 with benzene rings is mainly an addition reaction, rather than a substitution reaction. As the value of Fp is lower than 10 kPa, fiber surface morphology is smooth with few grooves. However, more and more lengthwise furrows and grooves are observed on the surface of fluorinated fiber with the further increase of Fp. Moreover, the mechanical properties of fluorinated PPTA fibers almost keep constant at the low Fp (Fp ≤10 kPa). However, when the Fp is higher than 10 kPa, the tensile strength of fluorinated PPTA fibers gradually decreases while the initial modulus and crystallinity have a little change.

The PPTA fiber was fluorinated with different partial pressure of F2. The reaction of F2 with the amide bonds is easier at low Fp (Fp ≤10 kPa) while the reaction of F2 with benzene rings is more favorable at high Fp. The results of FTIR prove that the reaction of F2 with benzene rings is mainly an addition reaction, rather than a substitution reaction.Figure optionsDownload as PowerPoint slide