| Summary: | 碩士 === 元智大學 === 化學工程學系 === 92 === The polyester-based polyurethane (PU) was prepared by using prepolymer synthesis method. The materials of polyesterpolyols and diisocyanate were reacted with a chain prolong dosage of 1.4 Butanediol in order to produce the PU resin. By the gel permeation chromatography (GPC) technique, the molecular weight of the PU resin was around 50,000 g/mol characteristically. The silica nanoparticles were embedded and well dispersed into PU resins measured by transmission electron microscopy (TEM) and field emission- scanning electron microscopy (FE-SEM). The optimal mixing ratio of 50 nm/4 μm for SiO2 particles was 3/7. Therefore, the modulus of elasticity, tensile strength or weatherability of the PU resin of this optimal formula was significantly enhanced for comparing with the one of all-nanosized SiO2. The chemical structures and morphology of TiO2-SiO2-PU nanocomposites were also characterized by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffractometer (XRPD). The results showed that silica nanoparticles were amorphous and evenly dispersed in the PU coatings and intensively bonded with PU interstructures. Measurements of modulus of elasticity or tensile strength of the polyurethane by Instron tester indicated the PU coatings increased after adding silica nanoparticles. The optimal addition of 4 and 8 % of SiO2 into PU resins showed the C=O peaks shifted from 1735 cm-1 to 1729 cm-1 and 1723 cm-1, respectively. Thus, the bonding of C=O with OH might form the COOH group, a conjugation of OH and NCO in silica nanoparticle was observed.
In order to more thoroughly examine the nature of the TiO2-SiO2-PU nanocomposites, the extended X-ray absorption fine structure (EXAFS) or X-ray absorption near edge structure (XANES) spectroscopy was conducted. The Ti EXAFS spectra indicated that the weight ratio of TiO2/SiO2 of 0, 1/1, and 2/1 possesses the bond distances of 1.09, 1.96, and 1.97 ± 0.05 Å, respectively and the coordination numbers (CN) were of 5, 4, and 4, respectively. It also showed that the silica and titania nanoparticles were reacted and formed into Ti-O-Si bonding. In addition, the increasing of UV tensile properties of the PU resin films by the mixing of silica and titania nanoparticles were found. The XRPD patterns represented that the TiO2/SiO2 peaks of 2θ = 26、38、48、55 might undulate. The FTIR spectra also showed that the peak of 980 cm-1 might indicate the SiO2 and TiO2 nanoparticles bond to form the into Ti-O-Si. Electron paramagnetic resonance spectrometry (EPR) showed the adsorptive peaks at 2050 Gauss of Ti species increased with the increasing concentration of Ti. Moreover, Instron tester showed the PU coatings of UV tensile strength increased after mixing TiO2/SiO2 nanoparticles. The PU coating possessed an 8-hr cracking-resistance indicated the performance of PU resins increased by the mixing of embedded TiO2/SiO2 nanoparticles.
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