Enhancing adhesion of thermosetting urea-formaldehyde resins by preventing the formation of H-bonds with multi-reactive melamine. Issue 3 (17th February 2022)

• Record Type: Journal Article
• Authors: Wibowo, Eko Setio; Park, Byung-Dae
• Is Part Of: Journal of adhesion. Volume 98:Issue 3(2022)
• Page Start: 257
• Page End: 285
• Publication Date: 2022-02-17
• Subjects: Crystallinity -- hydrogen bond -- UF resin -- melamine -- amorphous -- cross-linking -- autocatalytic model; Adhesion -- Periodicals; 541.33
• DOI: 10.1080/00218464.2020.1830069
• Languages: English
• ISSNs: 0021-8464

Abstract

ABSTRACT: Contemporary urea-formaldehyde (UF) resins with low-molar-ratio contain highly crystalline domains induced by the hydrogen (H) bonds between their linear molecules, which inhibits cross-linking, and results in poor adhesion. In this study, a novel way of controlling the crystallinity of such resins by preventing the formation of H-bonds using multi-reactive melamine during synthesis was reported. FTIR and 1 H-NMR spectroscopy confirmed the shifting of the carbonyl (C = O) peak, and N-H signal. XRD patterns revealed the conversion of crystalline to amorphous domains by adding 20% melamine, resulting in a decrease in crystallinity from 52 to 22%. The amorphous UF resins cured faster, have higher molecular weight and cross-linking density, and also followed the autocatalytic reaction model with excellent theoretical fitting. In addition, a 33% increase in adhesion strength, and a 62% reduction in formaldehyde emission was recorded. Hence, the addition of 20% melamine into the UF resins leads to better adhesion and less formaldehyde emission.