Studies On Adhesive Properties Of Soy Proteins With Chemical Modifications

This study was based on the soy protein isolates(SPI) as raw materials. Chemical modification( acetylation,succinylation ,phosphorylation and urea modification) of SPI were used to improve adhesive strength and water resistance of SPI-based plywood adhesives. Then two modified ways combined were applied to SPI and their adhesive properties were studied. This research also characterized the thermal and adhesive properties of two major soy protein components 7S conglycinin and 11S glycinin after urea modification. Finally, the mechanism of improving SPI's adhesive properties was preliminarily discussed.Experimental results showed that acetylation, succinylation, phosphorylation, and urea modification could increase adhesive strength, but that acetylation and succinylation did not enhance water resistance. Compared to other modification ways, phosphorylation was the best method to improve adhesive properties. When the Sodium Tripolyphosphate(STP) concentration was 8%, SPI showed the highest shear strength and water resistance. The Circular Dichroism (CD) spectrum of SPI indicated that the secondary structures of globule proteins changed from order to disorder. The modified SPI with 8% STP had 35.3% random content, and unmodified SPI had only 28.6%.Using two methods combined(urea and phosphation modification, urea and pH modification) to modify SPI, when urea concentration was 3mol/L, at pH 10, it had the largest adhesive strength, and good water resistance ability.For unmodified proteins, 7S and 11S had higher shear strength and water resistance than SPI, and 11S had the highest adhesive properties. Urea could improve shear strength(adhesive strength) and water resistance of 7S conglycinin and 11S glycinin, and 11S glycinin had a maximum value at 1mol/L urea. DSC data showed that the urea modified 7S and 11S have lower enthalpy values than the unmodified, and higher concentration of urea, lower the enthalpy values of 11S. The enthalpy of 7S and 11S with 5mol/L urea modification was zero.Finally, the 11S glycinin was modified by 1mol/L urea and then phosphorylated to various degrees by varying solutions of STP(0～10%), but this could not improve its adhesive properties.