3.1 Morphological Properties
3.1.1 FE-SEM Analysis
Figure 2 shows the FE-SEM images and histograms of nanofiber diameters for (A) Pure PAN, (B) 5% Tipp@ PAN, (C) 8% Tipp@ PAN, (D) 11% Tipp@ PAN, (E) AOPAN, and (F) 5% Tipp@ AOPAN, respectively. The diameter of the nanofibers increases from 244.315 ± 54.721 nm to 1192.76 ± 440.63 nm after the addition of 5, 8, and 11 (w/w) % from a mixing ratio (7:3 Tipp: Ethanol) to PAN. The diameters of the nanofibers increase from 244.315 ± 54.721 nm to 341 ± 69 nm after the modification of PAN to AOPAN by reacting hydroxylamine hydrochloride with a solution of PAN: DMF in the presence of sodium carbonate. On the other hand, increased the nanofiber diameters from 341 ± 69 nm to 463 ± 109 nm after adding (w/w) % from a mixing ratio (7:3 Tipp: Ethanol) to AOPAN. FE-SEM images show that the nanofibers of PAN are regular and that the normal distribution of the fibers is regular and close. In contrast, the regularity of the nanofibers decreases, and its distribution expands with the increase of Tipp content in the composite fibers due to the increase in the solidification rates during electrospinning. These results are consistent with previous studies’ findings 24, 25. On the other hand, the FE-SEM images show that the nanofibers of AOPAN are regular. The fiber distribution is broadened compared to the nanofibers of PAN. The fiber distribution is wider after adding Tipp to AOPAN due to the increase in the electrical conductivity of the solution and the increase in the solidification rate 22.
3.1.2 AFM Analysis
Figure 3 shows the AFM images of electro spun nanofibers for pure PAN, AOPAN, 5 wt.% Tipp@ PAN, and 5 wt.% Tipp@ AOPAN respectively. The surface morphology of the nanofibers is analyzed using atomic force microscopy (AFM), where the surface roughness of the nanofibers represented by root mean square \({(R}_{rms})\) increases by 118.74% when adding 5% Tipp to PAN. At the same time, it increases by 43.95% and 48.85% after developing PAN to AOPAN and adding 5% Tipp to AOPAN, respectively, as a result of increasing the diameters of nanofibers after adding Tipp or after the reaction, the results of this research agree with the results of previous studies 26, 27.
3.3 FT-IR Analysis
Figure 4 shows the FT-IR spectra of pure PAN, Tipp @ PAN, AOPAN, and Tipp@ AOPAN, respectively. Figure 4A presents the FTIR spectra of pure PAN, where peaks 2243, 1740, and 1236 cm− 1 represent (-CN), (C = O), and (C-O) of these peaks and are attributed to PAN, as this copolymer is of methyl acrylate and acrylonitrile, peak 2243 cm− 1 represents the nitrile group, which contributes to the partial conversion to amidoxime groups. On the other hand, for the reinforcement of PAN nanofibers by Tipp, the peak 1625 cm− 1 is attributed to the deformation vibrations of hydroxyl (–OH) and water (H2O) at the surface Tipp corresponding to the Ti-OH group (Fig. 4b) ], also the absorption peaks from 469 corresponding to Ti-O in Tipp 13,28,29.
While the new bands appear at 1229 and 1628 stretching vibration of C–N and C = N groups, which contribute to the success of the conversion of PAN to AOPAN) Fig. 4c (this result is an introduction to amino groups in AOPAN nanofibers (Fig. 1) 22. The FT-IR spectra of Tipp@AOPAN apparent not immersion of new peaks but the reduction in the absorption peaks in AOPAN spectra, such as reducing the peak of a hydroxyl group from 3463 to 3456 cm− 1, the peak of CH stretching in CH, CH2 from 2933 to 2926 cm− 1, peaks corresponding to Ti-O from 442 to 419 cm− 1, while shifting the absorption peaks as C = O stretching from 1736 to 1740 cm− 1, C = O groups in primary amines (NH2) from 1628 to 1631 cm− 1, CH blending from 1446 to 1453 cm− 1, and C-O stretching from 1030 to 1037 cm− 1 respectively (Fig. 4d) 30.
XRD-analysis
Figure 5 and Table 2 show the X-ray diffraction patterns of Pure PAN, 5% Tipp @PAN and AOPAN, and 5% Tipp @AOPAN with ranges of 2 \(\theta\) (10°–80°) at room temperature. The composite nanofibers showed two strong peaks at 2 \(\theta =\) 16.89° and 49.88° compared with the X-ray diffraction pattern of Pure PAN at the weaker peak at 2 \(\theta =\) 24.75° depending on the d- spacing and planes hexagonal crystals 5.25 Å (100), 1.83 Å (220) for 5% Tipp @PAN sample and 3.59 Å (100) for pure PAN at Fig. 5a,d. The increment of average crystalline size and crystallinity % was about 222.8% and 38.56% after adding 5% Tipp to PAN compared with the average crystalline size and crystallinity % at pure PAN, respectively; this result is consistent with a previous study 31. On the other hand, the chemical reaction between the hydroxylamine hydrochloride and PAN: DMF solution by the presence of sodium carbonate at 70°C produces the amidoxime polyacrylonitrile (AOPAN). Reaction product lead to the emersion of new peaks, such as stretch vibration of C–N and C = N groups, which contribute to the success of the conversion of PAN to AOPAN. The XRD spectra of Fig. 5b (AOPAN) show the strong peaks at 2 \(\theta =\) 16.70°, 28.05°, and 52.49° according to the d-spacing and planes hexagonal crystals 5.31 Å (100), 3.10 Å (111), and 1.77 Å(221) and the composite of nanofibers at Fig. 5c ( 5% Tipp @AOPAN ) shows peaks 2 \(\theta =\) 17.375°, 24.425°, and 48.475° according to the d-spacing and planes hexagonal crystals 5.13 Å (100), 3.36 Å (200), and 1.82 Å (220) by increment in average crystalline size and crystallinity % after modifying the PAN to AOPAN and adding 5% Tipp to AOPAN about 488.235% and 61.38% compared with the average crystalline size and crystallinity % at pure PAN 15.
Table 2
shows the crystalline properties of Pure PAN, 5% Tipp @PAN and AOPAN, and 5% Tipp @AOPAN. respectively
Samples | Position [°2Th.] | d-spacing [Å] | Crystalline Size [nm] | Crystallinity [%] |
Pure PAN | 24.75 | 3.59 | 6.8 | 18.80 |
5% Tipp@PAN | 16.89 49.88 | 5.25 1.83 | 21.95 | 26.05 |
AOPAN | 16.70 28.05 52.49 | 5.31 3.10 1.77 | 44.75 | 30.92 |
5% Tipp@AOPAN | 17.375 24.425 48.475 | 5.13 3.36 1.82 | 40.00 | 30.34 |
Thermal Properties
The pure nanofibers (PAN, AOPAN) and composites nanofibers as (5% Tipp@PAN, 5% Tipp@AOPAN) were subjected to DSC-TGA analysis by SDT Q600 V20.9 Build 20 with a range of heating temperature (0-1000°C) as shown in Fig. 6. The results of the TGA analysis proved that the addition of Tipp to PAN increases the thermal stability of the composite nanofibers due to the presence of a good interaction between them, represented by the presence of the hydroxyl group and the nitrile group, where the rate of weight loss decreased as a result of exposing the nanofibers to thermal stress by 16%. In comparison, the melting point increased from 328.32°C to 366.31°C and the heat required for fusion increased by 11.6%; these results agree with the previous study 30. On the other hand, the chemical reaction between the PAN: DMF solution and the hydroxylamine hydrochloride produced new bands led to stretch vibration of C–N and C = N groups because the surface of AOPAN fibers contains medoxime groups (–C (NH2) = NOH), which lead to high thermal stability 16. Therefore, the weight loss percentage decreased by 32.53% after the chemical reaction and produced the AOPAN; it also increased the melting temperature from 328.32°C to 367.96°C and the heat required for fusion increased by 12.1%. In contrast, an increase in the weight loss by 9 .13% and a decrease in the melting temperature from 366.31°C to 348.37°C and the heat required for fusion by 4.89% after the addition of the 5 wt.% of Tipp to AOPAN compared with the addition of a same amount of Tipp to PAN. Referring to FE-SEM, FT-IR and XRD analysis, the effect of adding Tipp to Pure PAN is better. In contrast, adding Tipp to AOPAN has negative results because it increases the stiffness of the nanofibers and decreases their flexibility.