This study modified urea-formaldehyde (UF) resin with a modifier, and focused on properties of particleboard manufactured with the modified UF resin. The orthogonal design was used to analyze the effects of different levels of hot-pressing temperature, hot-pressing time, glue content, and waterproof agent content on the modulus of rupture (MOR), internal bonding strength (IB), and formaldehyde emission (FE) of the particleboard, and thus determined the optimum technical parameters of hot-pressing. The conclusions were as follows: (1) the modifier used in this study could significantly reduce the free formaldehyde content of UF resin and the formaldehyde emission of particleboard; (2) the optimum hot-pressing technical parameters of particleboard manufactured with the modified UF resin were hot-pressing temperature 180°C, hot-pressing time 50s/mm, glue content 12%, and waterproof agent content 0.6%. The MOR and IB under the optimum technical parameters could reach 20.7 and 0.47 MPa, and the FE was 0.85 mg/L.
In this study, urea-formaldehyde resin was modified and used to bond three-ply plywood. The effect of hot press parameters on properties of plywood bonded by the modified urea-formaldehyde resin adhesive was investigated by an L(43) experimental design. The optimum technical parameters of hot press were obtained. Conclusions were as follows: (1) After modification, the free formaldehyde content of the urea-formaldehyde resin and the formaldehyde emission of resulting plywood were reduced by 74% and 70%, respectively; (2) The optimum technical parameters were 140°C of hot-pressing temperature, 80s/mm of hot-pressing time, 300g/m2 of glue content, and 0.8% of curing agent; (3) Under the optimum technical parameters, the bond strength and the formaldehyde emission of the plywood was 1.17MPa and 0.47mg/L, respectively.
For improving the performance of urea-formaldehyde (UF) resin, modified low molar ratio UF resins were developed to improve water resistance properties and reduce the formaldehyde emission of its bonded products. The effects of modifier feeding amount on the character of the cured resins were characterized by Fourier transform infrared spectroscopy (FTIR) measurement. The viscosity, pH value, solid content, free formaldehyde content, pot time, and curing time of the UF resins were also tested according to Chinese National Standards methods. The results show that the modified 1.00 molar ratio UF resins show lower free formaldehyde content and higher boiling-water-resistance comparing with unmodified ones. The boiling-water-resistant bonding strength of poplar plywood bonded with modified UF resin at 140 °C hot-press temperature can reach type I grade (100 °C water bath 3h) plywood requirement and the formaldehyde emission can meet the E0 grade plywood need.
Jatropha curcas (Jc) was the most favored biomass plant for bio-diesel production. Jc cakes obtained after oil pressed, rich in protein content, were excellent materials for preparing formaldehyde-free wood adhesives, which could provide alternative to formaldehyde-based resins. Sodium hydroxide, used as denaturing agent, modified protein contained in Jc cakes to prepare wood adhesives. Jc adhesives prepared in different pH value and plywood bonded by them were prepared. The curing behavior of these adhesives was conducted by differential scanning calorimetry (DSC) measurement. The gel content and water absorption of the cured Jc adhesives were measured to evaluate their curing content and the water resistant of plywood bonded with these adhesives was also studied. The results showed that pH value influenced the bonding strength of adhesive significantly. The bonding strength of plywood made by modified Jc adhesive significantly increased comparing with that of unmodified one. The curing peak temperature decreased obviously after modified, which was beneficial to achieve complete curing reaction. Modified Jc adhesives provided a potential way to utilize by-product of energy plant, avoided formaldehyde pollution, and reduced dependence on fossil resources.
The effect of melamine content in melamine modified urea formaldehyde (MUF) resin on durable properties of plywood was investigated using ammonium chloride (NH4Cl) with different melamine/urea (M/U) ratios. The plywood specimens were exposed to laboratory accelerated aging and/or cyclic soak-dry (SD). The experiment results indicated that the melamine contents in MUF resin showed an unobservable effect on the durable properties of MUF resin bonded plywood. The mechanical properties of plywood decreased more severely after accelerated aging test in acidic condition. However, the influence of different curing catalyst contents on mechanical properties and formaldehyde emission of UF resin can be minimized by adding melamine to the resin.
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