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Protein adhesive spray urea has oxygen atoms and hydrogen atoms.-Shanghai Zhen Niu Chemical Co., Ltd.
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Protein adhesive spray urea has oxygen atoms and hydrogen atoms.
Time:2018-10-30 16:40:46    Page view (383)
The main modification methods of soybean protein include thermal modification, acid-base modification, organic solvent modification, purifier modification, enzymatic modification and urea modification. Cone and Brown used alkali to modify soybean protein in 1934, and Boyer et al. used slow freezing and melting method to produce vegetable protein adhesives for textile, carton packaging and water-based coatings in 1945. Xue Peiyuan, Beijing Agricultural University (1952), made use of soybean meal as raw material. Research and report on the modification of vegetable protein to improve the performance of wood adhesives are rare at home and abroad. Protein sol was prepared by dissolving local protein with sodium hydroxide, and then mixed with water-resistant and dispersive reagents as wood adhesives. . In 1976, Kay L Franzen and John E Kinsella modified soybean protein by succinylation and acetylation [9] Hettiarachchy et al. (Soybean protein was modified by alkali and trypsin in 1995). It was found that soybean protein adhesives bonded strongly with these two modification methods. Degree and water resistance of the adhesives were significantly higher than those of unmodified proteins, especially alkali modified protein adhesives. Sun and Bian (1999) found that urea modified soybean protein adhesives had better water resistance than alkali modified adhesives. Huang and Sun made wood adhesives by modifying soybean protein with different concentrations of urea and guanidine hydrochloride. The results showed that the concentration of urea and guanidine hydrochloride had a significant effect on the structure expansion of the protein, and then affected the properties and functions of the adhesives. Local expansion of protein molecules and maintenance of secondary binding of local molecules were also affected by the concentration of urea and guanidine hydrochloride. It is beneficial to its adhesion.
When wood is hard, Huang and Sun modified soybean protein isolate with different concentrations of sodium dodecyl sulfate SDS and sodium dodecylbenzenesulfonate SDBS to produce wood adhesives. It has great shear strength and water resistance. When the SDS concentration increases, the total enthalpy decreases and the heat energy of the modified protein decreases, which indicates that the protein unfolds more at higher SDS concentration, while maintaining a certain amount of secondary structure is necessary for protein adhesion. When the SDS concentration increases excessively, the shear strength will decrease due to excessive protein unfolding. Compared with urea and guanidine hydrochloride modification, SDS and SDBS have better effect in improving the function of wood adhesives by protein modification. The hydrophobic end of the modified protein will turn outward and interact with the hydrophobic part of the purifier to form micelles, thus increasing hydrophobicity and water resistance. Urea has oxygen atoms and hydrogen atoms, which can interact with hydroxyl groups of proteins and break the hydrogen bonds in proteins, thus enabling the unfolding of protein polymers. When the urea concentration is high, the total enthalpy of protein decreases and the denaturation of protein increases. However, too high urea concentration will reduce the shear strength of the adhesives, which is due to the high level of protein molecular unfolding and the excessive reduction of secondary structures that contribute to bonding. Because at lower urea concentration, there are some unfolded proteins and some protein molecules with secondary structure. The unfolded proteins can increase the contact area with the binder and enhance the adhesion. Moreover, the hydrophobic groups of the modified proteins are mostly outward oriented. The proteins are melting spherical, very unstable and easy to penetrate. In wood, strong bonding strength and hydrophobicity occur, which indicates better shear strength and water resistance. Alkali-modified protein adhesives have high viscosity, which is due to the increase of intermolecular force due to the excessive expansion of protein molecules. The viscosity is too high, and the fluidity of adhesives is poor. Therefore, ways to reduce the viscosity to the appropriate level are needed. An effective way to reduce the viscosity is to reduce the intermolecular interaction force, and the existence of disulfide bonds in natural protein molecules affects its molecular expansion and elongation. Adding reductants such as ionic salts and sulfites can shear the disulfide bonds between or within molecules, thereby improving the hydrophobicity and foaming properties of protein molecules. Foam stability reduces protein viscosity. The bonding strength of protein adhesives depends on the ability to disperse in water and the interaction between polar and non-polar groups and wood.
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