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http://dx.doi.org/10.5658/WOOD.2022.50.5.353

Synchrotron X-Ray Diffraction Studies on Crystalline Domains in Urea-Formaldehyde Resins at Low Molar Ratio  

WIBOWO, Eko Setio (Department of Wood and Paper Science, Kyungpook National University)
PARK, Byung-Dae (Department of Wood and Paper Science, Kyungpook National University)
CAUSIN, Valerio (Dipartimento di Scienze Chimiche, Universita di Padova)
HAHN, Dongyup (School of Food Science and Biotechnology, Kyungpook National University)
Publication Information
Journal of the Korean Wood Science and Technology / v.50, no.5, 2022 , pp. 353-364 More about this Journal
Abstract
The crystalline domain of thermosetting urea-formaldehyde (UF) resins at low formaldehyde-to-urea (F/U) molar ratios (≤ 1.0) is known to be responsible for their poor performance as wood adhesives. Crystallization has been observed in 1.0 F/U UF resins during the addition reaction stage and at the end of the synthesis process (neat UF resins). The crystallinity and X-ray diffraction (XRD) spectra of the uncured neat UF resins, on the other hand, differed significantly from those of the cured neat UF resins, raising the possibility that their crystal structures were also different. This study demonstrates for the first time that the crystalline domains in 1.0 F/U UF resins generated from uncured and cured samples are identical. Despite having a lower crystallinity value, the synchrotron XRD patterns of purified neat UF resins were equivalent to the XRD patterns of cured neat UF resins. Transmission electron microscope images of the cured UF resins showed that the crystals were lamellar structures. This finding suggests that the crystal at low molar ratio UF resins are isotropic polycrystals with random orientation.
Keywords
urea-formaldehyde resins; wood adhesives; crystalline polymer; synchrotron X-ray diffraction; hydrogen bonding;
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Times Cited By KSCI : 11  (Citation Analysis)
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