No abstract

No abstract

In this study, a further investigation was carried out on the synthesis mechanism, optimal manufacturing conditions, and curing behavior of a sucrose-ammonium dihydrogen phosphate (SADP) adhesive. The results of 13C nuclear magnetic resonance (NMR) spectroscopy confirmed that SADP was composed of 5-hydroxymethylfurfural (5-HMF), deoxyfructosazine (DOF), amino compounds, Schiff base, monosaccharides, and oligosaccharide. The optimal hot-pressing conditions were a hot-pressing temperature of 170 °C, a hot-pressing time of 7 min, and a spread rate of 120 g/m2. The wet shear strength of plywood bonded at optimal manufacturing conditions met the requirements of China National Standard (GB/T 9846-2015). Thermal analysis and insoluble mass proportion measurements showed that the main curing behavior of the SADP adhesive occurred at curing temperatures higher than 145 °C, and more than 50% insoluble mass was formed when the heating time was longer than 5 min. Fourier-transform infrared spectroscopy (FT-IR) indicated that cross-linking of the cured adhesive was promoted by prolonging the heating time. In addition, pyrolysis gas chromatography and mass spectrometry (Py-GC/MS) confirmed that the cured SADP adhesive was composed of furan and nitrogen-containing compounds.

The most commonly used curing agents for soybased adhesives are polyamines, which have the problem of low solid content and/or high viscosity. To overcome this problem, a new type of polyamidoamine (PADA) resin was synthesized and applied to soy flour-based adhesives to improve their water resistance. The PADA solution obtained had a high solid content of 50 wt% and low viscosity of 270 cP. The optimum weight ratio of soy flour/ PADA/maleic anhydride to prepare adhesive was 40/7/1.68. The wet strength of plywood prepared at the optimum weight ratio was 0.82 MPa, which meant the plywood could be used as type II plywood according to the Chinese National Standard GB/T 9846.7-2004. The results of waterinsoluble solid content measurement and SEM observation demonstrated that cured soy flour-PADA-maleic anhydride adhesive had a 16 % greater water-insoluble solid content than soy flour-NaOH adhesive. The cross-linking network formed by the reactions of PADA and MA would increase the water-insoluble solid contents and improve water resistance of cured soy flour-based adhesives.