| In the traditional wood-based manufacturing industry, urea- formaldehyde(UF) and phenol- formaldehyde(PF) and melamine resins, which are based on petrochemical and formaldehyde, are commonly used as adhesives. With increasing concern of environmental pollution from petroleum-based chemicals and the decreased natural resources of oil, a great number of researchers pay their attention to the replacement of petroleum-based materials, such as soy-based adhesives for plywood manufacturing. However, high viscosity, low solid content, and poor water resistance limit the application of soy protein adhesives, and many studies have been carried out to solve these problems. In our research, soy-based plywoods were studied by modifications of soy protein adhesive with polyethylene glycol(PEG) and nanocrystalline cellulose(NCC) and veneer surface with plasma treament. The results can provide theoretical basis and practical experience for soy protein adhesive’s application in the wood-based manufacturing industry.The results are shown as following:1.To reduce the viscosity of NCC modified adhesive, compare PEGs’ effect on the performance of soy protein adhesive. With the increase of molecular weight of PEG, the veener bonding strength was decreased for hard formation of hydrogen interaction. But when the molecular weight was over 2000 da, the veener bonding strength was increased slightly because the high molecular weight PEG can provide orderly self-assembly room for soy protein. By introducing ethylene glycol(EG) into the soy protein adhesive, the viscosity of soy protein adhesive could be reduced by 45% and could make soy protein adhesive hydrophobic due to the strong hydrogen interaction between EG and soy protein.2. By introducing NCC into the soy adhesive, when the addition amount of NCC was smaller than 0.1%, the interface adhesion would be increased because of better wetting, while storage modulus(G’) and loss modulus(G’’) nearly had no change; when the addition amount of NCC was larger than 0.1%, the modulus of the adhesive layer would be increased with the increase of G’ and G’’, but viscosity was also increased. The adhesion strength of soy-based plywood would be increased by 22%, when the addition amount of NCC was 0.1%. When the addition amount of NCC was 0.2%, the adhesion strength decreased because of high viscosity. FTIR showed that weak hydrogen interaction happened between NCC and soy protein. However, DSC results also revealed that the curing temperature of soy protein adhesive increased by introducing NCC.3. Through orthogonal experiment, the effect of hot pressing on bonding strength of soy-based plywood could be concluded as following: hot pressing temperature > pressing time > pressing pressure. The bonding strength increased with hot pressing temperature increased, but when hot pressing temperature reached 160℃, bonding strength remained unchanged. When pressing pressure increasing from 0.8MPa to 1.2MPa, bonding strength increased. But when pressing pressure increased to 1.6MPa,bonding strength did not change. By increasing pressing time from 60s/mm to 80s/mm, bonding strength increased. Optimized hot pressing conditions: hot pressing temperature 160 ℃, pressing time 60s/mm, pressing pressure 1.0MPa.4. With the plasma treatment power increasing, wettability and bonding strength of soy-based plywood increased until 4.5kW; by reducing the plasma treatment rate, wettability and adhesion strength of soy-based plywood also increased. After plasma treatment, etching and nanoscale surface roughness were observed on the surface of poplar, and oxygen based functional groups also increased on the veneer surface, and consequently increased the soy adhesive wetting on veneer surface. When the plasma treatment power was at 4.5kW and 14m/min, the adhesion strength of soy-based plywood had an increase of 21% and resin content could be decreased to 140 g/m2。While wettability and bonding strength of soy-based plywood decreased at 6kW for degradation of poplar wood. |
PDF Full Text Request