Enhancing adhesion of thermosetting urea-formaldehyde resins by preventing the formation of H-bonds with multi-reactive melamine

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 ¹H-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.

KEYWORD:

• Crystallinity
• hydrogen bond
• UF resin
• melamine
• amorphous
• cross-linking
• autocatalytic model

Authorship contribution statement

All authors contributed equally to this manuscript.

Declaration of competing interest

The authors declare no competing financial interest.

Supplementary materials

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Correction Statement

This article has been republished with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by the National Research Foundation of Korea [2020R1A2C1005042].