Rheological Properties Of Modified Soy-based Adhesive

Soybean protein is an ideal raw material for adhesives due to their high protein contend and renewability. The native soy-based adhesive has poor moisture resistance performance, which has stimulated many researchers focus on the modification of the soy-based adhesives. However, modified soy-based adhesives had high viscosity, which has prevented the application of the adhesive. The rheological characterization of adhesive is essential for the design of unit operations, process optimization, controlled delivery of adhesive.In this paper, on the basis of domestic and foreign research on soy-based adhesive for its modification process rheology issues, conducted the following studies:(1) Using the High pressure homogenization prepare soy-based adhesive, the rheological characterization of different homogenization pressure, homogenization time, reaction temperature, reaction time was studied by single factor experiment.(2) Effect of different chemical modification methods (acid, alkali, salt) on the rheological properties of soy-based adhesive was studied.(3) The change of the modified soy-based adhesive Micro-morphology, particle size, protein aggregation state were characterized by Mastersizer, SDS-PAGE, SEM, revealing the mechanism of the modified soy-based adhesives rheological properties. And according to the modified adhesive rheological parameters, the relationship between viscosity and the each factor were analyzed, and the corresponding regression equations were established, providing a theoretical basis for the preparation and application of the soy-based adhesive.The main conclusions of this paper are as follows:(1) The soy-based adhesive with high pressure homogeneous treatment showed a shear-thinning non-Newtonian liquid characteristic. As the homogenization pressure increased, the viscosity of soy-based adhesive first decreased, and then increased. When the pressure was5MPa, the viscosity reached lowest value. As the homogeneous time extension, the viscosity decrease in the1～3min, then relatively slowly over time reaching a plateau in the3～5min. When reaction time was60min, the viscosity reached lowest value, then with the reaction proceeds, the viscosity increases. The viscosity showed a tendency to decrease with increasing temperature at the range of0℃to45℃, while at the range of45℃to65℃, its viscosity rised sharply. The regression equation model between homogenization pressure and viscosity was established (R2=0.9975). The significant decay in parameters of G’and G" was also found under high pressure homogeneous treatment.(2) The soy-based adhesive modified with acid showed a shear-thinning non-Newtonian liquid characteristic. When HCl at the range of2to4g, shear stress and shear rate was negatively correlated, while at the range of6to10g, shear stress and shear rate is positively correlated. As the addition of HCl and reaction time increased, the viscosity of soy-based adhesive first decreased, and then increased. With the temperature increased, the viscosity of soy-based adhesive decreased. The regression equation model between the amount of HCl and viscosity was established (R2=0.9875). The significant increase in parameters of G’and G" was also found under modified with acid.(3) The soy-based adhesive modified with alkali showed a shear-thinning non-Newtonian liquid characteristic. As the addition of NaOH increased, the viscosity showed a tendency to first increased, and then decreased. With6g NaOH does, the viscosity was3.64Pa-s (shear rate at13.80γ/s-1), reached maximum value. As the reaction time increased, the viscosity first decreased, and then increased. There was no significant difference is found at the range of25℃to55℃, while at65℃, the viscosity rised sharply. The regression equation model between the amount of NaOH and viscosity was established (R2=0.9752). The significant increase in parameters of G’and G" was also found under modified with alkali.(4) The soy-based adhesive modified with salt was non-Newtonian liquid. The viscosity of soy-based adhesive modified with CaSO4reached a maximum of3.57Pa·s (shear rate at13.80γ/s-1), then followed by CaCl2, CaF2, Ca (OH)2. As the addition of CaSO4increased, the viscosity decreased. The regression equation model between the amount of CaSO4and viscosity was established (R2=0.9632). The decrease in parameters of G’and G" was also found under modified with salt.(5) Results of the Mastersizer, DSC, SEM showed that particle size was reduced and cross-linked structure was destroyed under high pressure homogeneous acid and alkali treatment. The calcium salt causes aggregation of protein molecules, the surface roughness, the droplets aggregate and particle size increase.