Determination of Crystallinity of Thermosetting Urea-Formaldehyde Resins Using Deconvolution Method

Current low formaldehyde/urea (F/U) molar ratio urea-formaldehyde (UF) resins are quite different from high molar ratio UF resins used 20 years ago in terms of their crystallinity. For the first time, this paper reports a method of determining the crystallinity of thermosetting urea-formaldehyde (UF) resins of different molar ratios with the deconvolution method, using Voigt, Lorentzian, and Gaussian function. The Gaussian deconvolution of X-ray diffraction (XRD) patterns was the most suitable and reliable curve-fitting method, which gave the crystallinity value from 31.8% to 56.1% as the molar ratio decreased from 1.6 to 1.0. These results also indicated that low-molar-ratio (1.2 and 1.0) UF resins were semi-crystalline, whereas high molar-ratio (1.6 and 1.4) resins were amorphous. The Gaussian function was also employed to determine the crystallinity of the low-molar-ratio (1.0) UF resins cured at different curing and hardener conditions. Hardener level had greater influence on the crystallinity than hardener type even though the curing temperature and time affected the crystallinity.