Effects of the Addition of Amino-Terminated Highly Branched Polyurea on Curing Properties of Phenol-Formaldehyde Resin

Abstract

In this work, a highly branched polyurea (HBP-NH2) similar to urea structure was introduced to phenol-formaldehyde (PF) resin to accelerate itscuring speed The results of gel time and bonding strength were combined to obtain a good modified additional stage and amount of HBP-NH2. The relative molar mass changes of HBP-NH2-modified PF resin were investigated by gel permeation chromatography (GPC). The effects of HBP-NH2 on the curing of PF resin were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The effect of HBP-NH2 on the structure of PF resin was also investigated by nuclear magnetic resonance carbon spectroscopy (13C-NMR). The test results show that the gel time of the modified PF resin was reduced by 32% and 51% at 110 °C and 130 °C, respectively. Meanwhile, the addition of HBP-NH2 increased the relative molar mass of PF resin. The bonding strength test showed that the bonding strength of modified PF resin increased by 22% after soaking in boiling water (93 °C ± 2) for 3 h. The DSC and DMA analysis indicated that the curing peak temperature decreased from 137 °C to 102 °C, and the curing rate of the modified PF resin was also faster than that of the pure PF resin. The 13C-NMR results showed that HBP-NH2 in the PF resin reacted to produce a co-condensation structure. Finally, the possible reaction mechanism of HBP-NH2 for the modification of PF resin was given.

Crosslinking Mechanism of Tannin-Based Adhesives Based on Model Compounds: Copolycondensation of Resorcinol with Dimethylol Urea

“…As for the structural analysis method, 13 C-NMR, which has been widely used at present, calibrates different carbons by different chemical shifts in the carbon nucleus in the strong magnetic field according to the electron cloud density around the carbon nucleus. This method, which is of a relatively high identification degree, is more accurate for structural analysis [48][49][50] and more feasible for the quantitative analysis of the content of chemical structures and can provide effective data support for the reaction mechanism study. Figure 2 shows the 13 C-NMR graphs of the reaction products of formaldehyde and resorcinol under pH = 2~2.5, 3~4, 5~6, 7~8, and 9~10, and the attribution of the corresponding chemical structures is listed in Table 4.…”

“…The phenolic hydroxyl groups on resorcinol are o-p-positioning groups, and the two phenolic hydroxyl groups are located at meta-positions, so resorcinol has three active reaction sites: 1 o-position and 2 o-p-positions, respectively. Similar to phenol, the resorcinol-formaldehyde system can undergo hydroxymethylation and polycondensation; ether bond polycondensation and bridge 66-67 0 0 4.17 0 method, which is of a relatively high identification degree, is more accurate for structural analysis [48][49][50] and more feasible for the quantitative analysis of the content of chemical structures and can provide effective data support for the reaction mechanism study. Figure 2 shows the 13 C-NMR graphs of the reaction products of formaldehyde and resorcinol under pH = 2~2.5, 3~4, 5~6, 7~8, and 9~10, and the attribution of the corresponding chemical structures is listed in Table 4.…”