Rheological properties of reactive extrusion modified waxy starch and waxy starch-polyacrylamide copolymer gels

Abstract

The rheological properties of modified waxy starch and waxy starch–polyacrylamide graft copolymers prepared by reactive extrusion were investigated. Both materials can absorb huge amount of water and form gels. The modified waxy starch and waxy starch–polyacrylamide graft copolymer gels all exhibited viscoelastic solid properties. The waxy starch–polyacrylamide graft copolymer gels with the concentration ≤10% showed weaker viscoelastic behaviors than those of the same concentrations of modified waxy starch gels. However, at concentration ≥11.25%, the waxy starch–polyacrylamide graft copolymer gels displayed much stronger viscoelastic properties than those of the same concentrations of modified waxy starch gels. The analysis of modulus and concentration dependence and stress relaxation measurements indicated that both modified waxy starch and waxy starch–polyacrylamide graft copolymer gels were physical gels meaning the cross-linkers between the molecules were physical junctions. The nonlinear steady shearing rheological properties studies indicated that both modified waxy starch and waxy starch–polyacrylamide graft copolymer gels exhibited shear thinning behavior, which can be well fitted with the power law constitutive equation. The function and behavior of the modified waxy starch and waxy starch–polyacrylamide graft copolymer gels suggest that these starch-based biomaterials should be potential candidates for applications in cosmetic gels, wound skin care materials, and agricultural products.