Molecular structure and rheological properties of common microcapsule wall materials

The molecular structure and rheological properties of five common materials, namely modified starch, gum arabic, gelatin, soybean protein isolate (SPI), and carboxymethyl cellulose (CMC), which are used to prepare microcapsule walls by spray drying were studied. The molecular weight distributions of the materials were determined by gel permeation chromatography (GPC), the functional groups and secondary structures were determined by Fourier transform infrared spectroscopy, while the apparent viscosity, dynamic modulus, and creep compliance were measured by a rotational rheometer. The results showed shear-thinning behavior in all five wall material pastes. The apparent viscosity of wall material pastes gradually decreased with temperature. The elastic modulus G' and viscous modulus G″ increased with increasing oscillation frequency. With constant time, creep compliances J(t) values were in the following order: modified starch>gum arabic>gelatin>CMC>SPI. The higher the molecular weight, the greater the apparent viscosity. For the wall materials with molecular weight in the same order of magnitude, the non-Newtonian shear-thinning phenomenon was more obvious with a wider molecular weight distribution. Additionally, the apparent viscosity was higher when the molecular structure was more rigid and molecules had a higher polarity. ©, 2015, South China University of Technology. All right reserved.