Novel melamine-based engineering thermosets: Facile synthesis, extraordinary thermostability, high strength and toughness

Long-Chain Polyamine-Glyoxal Wood Adhesive: Formaldehyde-Free, Green Synthesis, and Ultra-Performances

“…The assigned structures (Figure b) according to the ESI-MS spectrum suggest that expected MH polymers with H terminals have been formed. Similar to MH-2.0, which was characterized before, the new peak appearing at 29.50 ppm in the 13 C NMR spectrum (Figure c) can confirm the formation of M–H linkages via deamination reaction. The single peak at 165.61 ppm for the triazine ring indicates almost all melamine units have been blocked by H. The GPC result in Figure d shows the successful formation of large MH polymers as they have a number-averaged molecular weight ( M n ) above 70 000 and weight-averaged molecular weight ( M w ) above 130 000, which are about 10 and 16 times higher than that of the previously reported MH-2.0 and MH-3.0, owing to the refined molar ratio and extended reaction time.…”

“…At a temperature higher than 400 °C, the internal cross-linking network began to collapse, and the maximum decomposition temperature (T max ) was observed at 461 °C. Although a previous study demonstrated that the T max of MH was observed at 500 °C, 15 the high thermal stability of MHG resin should not be simply ascribed to MH resin as such superior heat-resistance can only be achieved by curing MH at high temperatures of 240−270 °C for several hours. Therefore, such extraordinary thermal stability of the MHG-C adhesive cured at 120 °C for 2 h could be attributed to the formation of highly stable conjugated imine linkages.…”

“…Synthesis of Melamine-1,6-hexanediamine (MH) Polymer. The MH polymer was synthesized via the polymerization between M and H according to the previously reported method, 15 except that a higher H to M molar ratio (H/M = 2.5) and longer reaction time were applied in this study. Typically, at room temperature, M, melted H (preheated at 50 °C), and a catalyst (NH 4 Cl, 6% weight percentage of M) were mixed in a three-necked flask equipped with a reflux condenser and a thermometer.…”

“…We have revealed in a recent study that the MH polymer can be a thermosetting resin with excellent properties if a relatively low H/M molar ratio is used (≈ 2.0). 15 However, the curing of MH resin requires continuous heating for several hours at temperatures of 250−270 °C. Therefore, such resin is not suitable for application as wood adhesive, but different resins will be obtained by combining MH polymer with glyoxal.…”

“…Based on this hypothesis, in this study, the melamine-1,6-hexanediamine (MH) polymer was chosen as a candidate. We have revealed in a recent study that the MH polymer can be a thermosetting resin with excellent properties if a relatively low H/M molar ratio is used (≈ 2.0) . However, the curing of MH resin requires continuous heating for several hours at temperatures of 250–270 °C.…”