Investigation of Novel Thermosetting Copolymer-Based Monomethylolurea–Glyoxal for Wood Manufacturing

Abstract

The purpose of this investigation was to design novel alternating copolymers (monomethylolurea–glyoxal, MMU–G) as adhesives for wood manufacturing. MMU–G were synthesized under acid (pH = 5) conditions. After the 120-day storage period, the MMU–G resins were used for plywood production, which exhibited a wet shear strength of about 2.15 MPa, similar to the freshly prepared MMU–G resin. The excellent water resistance and long storage stability showed that MMU–G has particular characteristics and properties all of their own, which, in certain respects, are very different from those of urea-formaldehyde (UF) adhesives. The X-ray diffraction results showed that only a few crystallinities occurred in MMU–G resins, indicating the presence of long side chains in the MMU–G polymer structures, leading to better adhesion strength than UF resins. The structure characteristics of the MMU–G resin were studied by Fourier transform infrared and electrospray ionization mass spectrometry, and a possible molecular structure has been inferred, which is consistent with spectroscopic results.

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

“…The assigned structures (Figure 4b) 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, 15 the new peak appearing at 29.50 ppm in the 13 C NMR spectrum (Figure 4c) 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 4d 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 15 and MH-3.0, 21 owing to the refined molar ratio and extended reaction time.…”

“…Comprehensive Characterization of MHG Adhesive. To understand the structure of MHG adhesives, the synthesized MH polymers were separately characterized using ESI-MS, 13 C NMR, and GPC. The results are listed in Figure 4.…”

“…Nuclear Magnetic Resonance (NMR) Examination. The liquid-state 13 C NMR examination of the MH-2.5 sample was for examination. After being completely dissolved, the sample was transferred into an NMR tube and processed for the NMR spectra.…”

“…Nuclear Magnetic Resonance (NMR) Examination. The liquid-state 13 C NMR examination of the MH-2.5 sample was performed on a Bruker AVANCE III 500 spectrometer (Bruker Corporation, Billerica, MA, USA) with a 6 s relaxation delay using the inverse-gated proton decoupling method. Approximately 10 mg of sample was dissolved in 500 μL of dimethyl sulfoxide-d 6 (DMSO-d 6 ) for examination.…”

“…It was speculated that glyoxal is less reactive than formaldehyde . Thus, in later studies, , formaldehyde was introduced back to the UG system, leading to UGF or UFG resins. Besides UG and MG resins, biomass materials like lignin, , tannin, and protein were also used to obtain glyoxal-based adhesives.…”