| Melamine formaldehyde resin and urea resin are widely used as wet strength agent and wood adhesives because of its high performance. But MF and UF resin could release free formaldehyde during the process of use which can endanger people’s life and environment. Therefore, much attention have been put to the study of lower formaldehyde or new type of non-formaldehyde adhesive.In this paper, glyoxal,a sort of aldehyde with low volatile and nontoxic, was chosen to substitute for formaldehyde to react with melamine and urea in order to prepare environmental protection glyoxal-melamine-urea resin(GMU). The synthesis, characterization and properties of the glyoxal/melamine/urea resin that was used as wet strength agent and wood adhesive have been investigated in detail. The main parts of the paper are as followed:First, the optimal synthesis conditions, including the molar ratios of raw material, reaction p H, reaction time and reaction temperature was determined after investigating the effects of various kinds of synthesis conditions based on the resins’ properties. The study on the synthetic process of GMU co-condensation shows that the basic properties of GMU resins made by one-step method and multiple-step method are almost the same. But, the basic properties of resin made by two-step are much different from those made by the other two methods.Compared with glyoxal-melamine resin, the addition of a certain amount of urea to the GMU resin result in improvement of flexibility of impregnated paper. Also, the water resistance property of GMU resin will decrease with the addition of too much urea.Second, the structures of GMU resin were characterized by FT-IR and LC-MS. Compared with FT-IR spectra of melamine, urea and glyoxal, the disappearance of the infrared peak of primary amine and the appearance of ether bond suggested that some reactions happened in GMU resin. The analysis of LC-MS results of the GMU resin indicated that the reactions of synthesized process of GMU resin are multiple reactions, which lead to the different products contained in the solution of GMU resin, i.e., MG, UG binary reaction product and GMU ternary reaction product. The curing temperature and the heat-resistance were studied by DSC and TG. The decomposition process of GMU resin was explored using TG-IR technology. The results showed that water was released at the temperature of 170℃ around,corresponding to the dehydration process of the resin curing. When the temperature is above 200℃,the main released composition of decomposition products of MGU resin is CO2. The accurate enthalpies of resins curing process were obtained using the method of equivalent non-latent heat baseline; in the meanwhile, the curing kinetics formula is also solved based on the data got above.Third, the GMU resin was used as chipboard adhesive.The optimal curing conditions of GMU is determined on the basis of the experimental data of chipboard properties that tested on the different curing conditions, including the amount of MGU, curing time and curing temperature. A new type of emulsified wax(EW) possessing optimal comprehensive properties with compound emulsifier has been developed by investigating some influences,such as emulsification temperature, emulsification time and amount of emulsifier, on the properties of emulsified wax. We added various amount of emulsified wax to MGU resins in order to improve the water resistance of MGU resins. The experimental data compared with those of poly(vinyl alcohol)(PVA) showed the water resistance of EW/MGU is much better than that of PVA/MGU. |
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