## 4 Results and Discussion
During the cross-linking process, hydroxyl groups of polyvinyl alcohol formed acetal bonds (PVA-O-C-O-PVA) with the carbonyl group of GTA. This shows that the formation of intermolecular interaction can limit the diffusion of water into fiber mats and blocked hydroxyl groups can reduce the hydrophilicity of nanofibers and lower drug release time. Figure 5: Viscosity versus the shear rate of electrospinning solutions. The FT-IR spectrum (Figure 7) of PVA electrospun nanofibers showed the characteristic absorption bands of PVA: Broad C-H alkyl stretching band (2926 cm\({}^{-1}\)) and the strong hydroxyl bands at 3423 cm\({}^{-1}\),1045 cm\({}^{-1}\) (C-C), 1234 cm\({}^{-1}\)(C-O), 1350 cm\({}^{-1}\)(C-H), 1535 cm\({}^{-1}\) (CH-OAc) and 1645 cm\({}^{-1}\) (C=O), (Figure 8). The FT-IR spectra of the PVP electrospun fibers are depicted in Figure 8. The absorption bands at 3433, 2955, 1662, 1423, 1284 cm\({}^{-1}\) related to OH stretching aliphatic CH, amide C=O and C-N respectively, are the characteristic peaks of PVP. The FT-IR spectrum of PVA/PVP nanofibers is shown in Figure 2:0 The peaks at1043, 1193, 1365, 1491, 1597, 1641, 2405 and 3404 cm\({}^{-1}\) were assigned to the vibrations of C-N, C-O, C-O-C, CH, CH2, amide C=O, acetate C=O, N=CHO and OH, respectively. By comparison, the FT-IR spectrum of PVA/PVP nanofibers with PVA and PVP nanofibers, the presence of both PVA and PVP structure in blend nanofibers was analyzed. This agrees well with the stability of polymer structure during the blending or electrospinning process. The FT-IR spectra of Bup and electrospunBup/PVP/PVA clearly revealed the characteristic absorption bands of buprenorphine at 1462 and 947 cm\({}^{-1}\) which indicates that the structural integrity of buprenorphine was maintained after loading into the electrospun nanofiber mats. The overlap of other characteristic bands of Bup in drug-loaded PVP/PVA mats can be attributed to a high percentage of PVP than the drug in drug-loaded mats. The comparison of the FT-IR spectra of GTA cross-linked and non-crosslinked Bup/PVP/PVA nanofiber mats demonstrated minor absorption bands at 1473, 1464, 1429 cm\({}^{-1}\) assigned to the C-H stretching of Bup, PVA and PVP polymers. Figure 2:1 (**a**) SEM images, (**b**) fiber diameter distribution of cross-linked Bup/PVP/PVA nanofiber mats. Absorption bands at 1658, 1645 and 1639 cm\({}^{-1}\) confirmed the incorporation of drug, PVP and PVA in the nanofiber structure. According to the FT-IR spectrum of cross-linked mats, diminished intensities and C-O band broadening at around 1300-1000 cm\({}^{-1}\) in contrast to non-cross-linked mats were assigned to cross-linking. The appearance of vibrational bands characterizing PVP polymer and disappearance of PVA peaks in the fingerprint region indicated that PVA can become cross-linked with GTA. Absorption peaks at 2740, 1026, 976 and 947 cm\({}^{-1}\) are characteristic of Bup and indicated that the electrospinning process did not affect the chemical structure of the drug. Figure 2:2 Fourier transform infrared (FT-IR) spectra of PVA nanofibers, PVP nanofibers, PVA/PVP nanofibers, Bup, Pup/PVP/PVA nanofibers and cross-linked Bup/PVP/PVA nanofibers. The AFM image of cross-linked Bup/PVA/PVP nanofiber mats demonstrated the3D structure of GTA cross-linked mats and the preservation of porous nanofibrous structure after crosslinking (Figure 8). The 3D AFM image exhibited that two coordinates had an amometric scale while the third was longer. BET surface area analysis and BjH pore size and volume analysis were done on Bup/PVP/PVA nanofibers and cross-linked Bup/PVP/PVA nanofibers. The BET and BjH analysis provides precise specific surface area and pore area and specific pore volume yielding important information in studying the effects of surface porosity and particle size in many applications. The BET analysis of the Bup/PVP/PVA nanofibers showed the BET surface area and langmuir surface area in the amount of \(-0.0610\) m\({}^{2}\)/g and \(-3.2186\) m\({}^{2}\)/g, respectively.