Impact of the Synthesis Procedure on Urea-Formaldehyde Resins Prepared by Alkaline–Acid Process
2019
This work studies two synthetic procedures for the preparation of urea-formaldehyde (UF) resins, according to alkaline-acid process, using with final F/U ratios of 1.10 and 1.25 in both cases. The main differences between the two procedures are the number of urea loads and the methylolation temperatures. The aim of the work is to compare two of the most used procedures for UF synthesis, trying to better understand the chemical reactions involved. The molecular weight distribution of the resins was monitored by Gel Permeation Chromatography/Size Exclusion Chromatography (GPC/SEC) and the unreacted oligomers by High-Performance Liquid Chromatography (HPLC), during the synthesis processes. Chemical modifications were investigated using quantitative analysis of carbon-13 Nuclear Magnetic Resonance (13C-NMR). The final resins were also evaluated using X-ray diffraction analysis (XRD). The largest difference identified was related to methylene linkages and methylol groups determined by13C-NMR. The difference in...
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