Preparation Of The Soy Protein Isolate Adhesives And Its Application In The Plywood

The adhesives made by formaldehyde have a fatal flaw, with the use of this adhesive, it inevitably releases the free formaldehyde and other harmful gases, which will be harmful to the producers and the consumers, long-term living in the polluted environment of high concentrations of formaldehyde will produce a variety of chronic diseases,serious carcinogenic. The synthetic polymer adhesives are biologically non-degradable, these adhesives will have a certain pollution to the environment. Therefore, it will become a development trend of using renewable, biodegradable and the natural resources with wide source such as soy protein isolate (SPI) to produce wood adhesives.In the experiments of SPI adhesives modified by sodium dodecyl sulfate (SDS), the orthogonal experimental method is used to explore the effect of the mass concentrations of SPI and SDS, the reaction temperature and the reaction time on the adhesive strengths of the modified SPI adhesives. And the adhesive mechanism of the modified SPI adhesives is discussed too. The results have shown that the optimum formula conditions are 14% SPI,1% SDS,0.2% hexamethylenetetramine, the reaction temperature 35℃ and the reaction time 3h. And under the optimum conditions, the dry adhesive strength of the modified SPI adhesives is 1.82MPa, the wet adhesive strength is 0.69MPa, the viscosity is 3300mPa.s, the solid content is 13.06%. After the SDS is added into SPI, the composites of SDS-SPI are formed, the internal hydrophobic groups among the SPI molecule structure are turned out and the water resistance of the modified SPI adhesives is enhanced with an increase of the modification time. When the concentration of SDS is over a define value, the disulfide bond is broken and the modification effect of SDS goes bad.In the experiments of SPI adhesives modified by urea, the orthogonal experimental design method is used to investigate the effect of the mass concentrations of SPI and urea, the reaction temperature and the reaction time on the adhesive strengths of the modified SPI adhesives. And the adhesive mechanism of the modified SPI adhesives is discussed. The results have shown that the optimum formula conditions are 12%SPI, 8%urea,0.2% hexamethylenetetramine, the reaction temperature is 35℃ and the reaction time 60min, And under the optimum conditions, the dry adhesive strength of the modified SPI adhesives is 0.96MPa, the wet adhesive strength is 0.70MPa, the viscosity is 43000mPa.s, the solid content is 13.04%. When the polar urea molecule is added to the protein solution, and it can rapidly form intermolecular hydrogen bonds with water, which destructs the molecular structure of water, affects the surrounding environment of the protein molecule, change the hydrophobic interactions among the protein molecules, spreads the protein molecules, escapes the non-polar groups, so that the content of the ordered structural protein decreased, the content of the disordered structural protein increased, the water resistance of modified SPI adhesives is improved.In the experiment of SPI adhesive modified by both SDS and urea, the orthogonal experimental design method is used to explore the effect of the mass concentrations of SPI, SDS, urea and hexamethylenetetramine, the reaction temperature on the adhesive strengths of the modified SPI adhesives. And the adhesive mechanism of the modified SPI adhesives is discussed. The results have shown that the optimum formula conditions are 15%SPI,0.8% SDS,6.0%urea,1.2% hexamethylenetetramine, the reaction temperature is 50℃, the reaction time 3h, And under the optimum conditions, the dry adhesive strength of the modified SPI adhesives is 1.87MPa, the wet adhesive strength is 0.83MPa, the viscosity is 84600mPa.s, the solid content is 29.03%.The results have shown that, compared to the SPI, SDS modified SPI, urea modified SPI, the thermal decomposition temperature and water resistance of SPI modify by both SDS and urea has been improved to some extent, because the tertiary structure and the quaternary structure of protein molecules are extended by the surfactant SDS, the hydrophobic groups are turned out,the polar molecule of urea can further open the secondary structure of the protein molecules, the oxygen and hydrogen atoms of urea molecules can react with the hydroxyl groups of SPI, disconnecting the hydrogen bonds in the protein system and extending the composite structure within the SPI molecules. Therefore that further increases the water resistance.In this experiment of SPI adhesives grafted onto by ethanol and urea, the orthogonal experimental method is used to discuss the effect of the mass concentrations of SPI, ethanol, urea and hexamethylenetetramine, the reaction temperature on the adhesive strengths of the modified SPI adhesives. And the adhesive mechanism of the modified SPI adhesives is discussed. The results have shown that the optimum formula conditions are 11% SPI,35% ethanol,6.0% urea and 0.3% hexamethylenetetramine, the reaction temperature is 60℃, the reaction time 1h. And under the optimum conditions, the dry adhesive strength of the modified SPI adhesives is 1.75MPa, the wet adhesive strength is 0.77MPa, the viscosity is 44600mPa.s, the solid content is 13.23%. Because the main component of soy protein isolate globulin in aqueous solution is a ball, the hydrophobic group is surrounded by hydrophilic groups inside the ball molecules, so many active groups is invalid, which is not conducive for the grafting reaction. Oxygen atoms and nitrogen atoms surrounded by urea can act with the hydroxyl groups of the protein SPI, breaking the hydrogen bonds within the protein molecules, unfolding the structure of the protein dimmers, so increasing both the viscosity and the water resistance. The infrared spectrum shows that there is some reactions between the-COOH on the SPI molecular chains and-OH on the ethanol, so increasing the chain length. The long molecular chain cross-linked to form a network structure under the cross linking agent, improving the adhesive strength and the water resistance of the modified SPI adhesives.In this experiment of SPI adhesives blend-modified by polyvinyl alcohol (PVA) and urea, the orthogonal experimental method is used to explore the effect of the mass concentrations of SPI, urea, PVA and 2,4-diisocyanatotoluene(TDI), the reaction temperature on the adhesive strengths of the modified SPI adhesives. The results have shown that the optimum formula conditions are 9.0% SPI,15.0% PVA,4.0% urea, 0.8% TDI, the reaction temperature is 80℃,the reaction time 40min. And under the optimum conditions, the dry adhesive strength of the modified SPI adhesives is 1.11MPa, the wet adhesive strengths is 0.60MPa, the viscosity is 90000mPa.s, the solid content is 18.23%. PVA is a biodegradable nature of the polymer materials, which can not only improve the adhesive tack force, the sizing of industrialization, but also improve the adhesive solid content, greatly decreased the adhesive strength. Its hydrophobic groups can be immersed into the inside of the protein molecule, there by undermining the molecular structure of protein molecules, resulting in protein denaturation, exposing the hydrophobic aminoacid residues of protein molecules, improving the adhesive strength and the water resistance of soy protein.In the plate process, the orthogonal experimental method is used to discuss on the effect of the hot-pressing pressure, temperature and time, mass of the spreading adhesive, the glue drying time on the hot-pressing process. The used adhesive was SPI adhesive modified by both SDS and urea, the optimal formula was the hot-pressing temperature of 140℃, the hot-pressing pressure of 2.0MPa, the hot-pressing time 3min/mm, mass of the spreading adhesive 200g/m2, the glue drying time of 4min, And under the optimum conditions, the dry adhesive strength of the modified SPI adhesives by both SDS and urea is 2.45MPa, the wet adhesive strength is 1.06MPa.