Studies On The Effect Of Nanomaterials On Adhesive Properties Of Soybean Proteins As Bioingredients

In this paper, soy protein isolates(SPI)were modified by nano-particle SiO₂ and CaCO₃,the influences of nano-SiO₂ addition,reaction temperature and time on adhesive properties of SPI were investigated, and followed by a combined urea chemical modification to improve the shear strength and water resistance of SPI, to investigate the adhesive properties after freeze-drying. Meanwhile, the change of enthalpy and the protein secondary structure of modified and unmodified SPI was measured by DSC and FT-IR,storage research was also did; Soy 7S and 11S globulins extracted from defatted soybean meal were modified by nano-particle SiO₂ and followed by a combined urea modification by adding urea solution to investigate the influences of nano-SiO₂ addition on adhesive properties; The nano-particle SiO₂ and CaCO₃ surface was treated with the silane coupling agent and titanate coupling agent respectively to optimize the reaction conditions.The mechanism of improvement of the enhanced adhesive strength of SPI was also interpreted.Testing results indicated that the adhesive strength of SPI were improved significantly after adding nano-SiO₂ or CaCO₃ , and that the effect of nano-SiO₂ was better than nano-CaCO₃'s, the response surface showed that specimens glued with SPI modified with nano-SiO₂ at concentrations of 1%, nano-CaCO₃ at concentrations of 3% ,reaction temperature and time was 66℃,70℃and 1h respectively had the highest shear strengths, then decrease in shear strength happens when continue to add nano-particles.SPI adhesives exhibited the highest shear strength and viscosity when modified by 1% nano-SiO₂ and 3 mol/L urea; SPI adhesives have the worst water resistance on pine wood; all methods did not improved the water resistance significantly.There is almost no influence on soy protein structure, the shear strength and water resistance of SPI after freeze-drying.FTIR spectral analysis showed that nano- SiO₂ modifications or freeze-drying did not change the secondary structure of protein, but the urea did significantly, it was also found thatβ-Sheet structure tended to convert toβ-Turn and random coil structure after being modified with 3mol/L urea.Testing results of 7S and 11S indicated that the adhesive strength of globulins were improved significantly after adding nano-SiO₂, and that the optimum addition was 1%. The urea modification at 1mol/L concentration combined with nano-SiO₂ modification at 1% level gave protein adhesive the highest shearing strength. The shear strength of 7S and 11S globulins adhesives applied in cherry plywood was better than others. Nano-SiO₂ modification almost never denature SPI; The soy proteins modified by urea at relatively low concentration(1mol/L) might have been partly unfolded and had a certain amount of secondary structure, resulting in higher shear strengths.The surface modification of nano-particle by coupling agents did not continue to improve the shear strength of SPI adhesives, and the optimum contents of the silane coupling agent and titanate coupling agent for nano-SiO₂ and nano-CaCO₃ was about 1% and 2.5% respectively, reaction temperature and time was 70℃and 1h.