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.

摘要

现代低摩尔比的脲醛 (UF) 树脂含有由其线性分子之间的氢 (H) 键诱导的高结晶域，这会抑制交联，并导致粘附力差。在这项研究中，报道了一种通过在合成过程中使用多反应性三聚氰胺防止形成 H 键来控制此类树脂结晶度的新方法。FTIR 和¹H-NMR 光谱证实了羰基 (C = O) 峰和 NH 信号的移动。XRD 图案显示通过添加 20% 三聚氰胺将结晶域转化为无定形域，导致结晶度从 52% 降低到 22%。无定形UF树脂固化速度更快，具有更高的分子量和交联密度，并且遵循具有良好理论拟合的自催化反应模型。此外，粘合强度增加了 33%，甲醛释放量减少了 62%。因此，在 UF 树脂中添加 20% 三聚氰胺会导致更好的附着力和更少的甲醛释放量。