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Properties of starch–polyglutamic acid (PGA) graft copolymer prepared by microwave irradiation − Fourier transform infrared spectroscopy (FTIR) and rheology studies

Xu, Jingyuan, Solaiman, Daniel, Ashby, Richard D., Garcia, Rafael A., Gordon, Sherald H., Harry‐O'kuru, Rogers E.
Die Stärke = 2017 v.69 no.3-4
Fourier transform infrared spectroscopy, agricultural products, composite polymers, crosslinking, equations, gels, microwave radiation, rheology, stress relaxation, viscoelasticity
The rheological properties of waxy starch‐γ‐polygutamic acid (PGA) graft copolymers were investigated. Grafting was confirmed by FTIR spectroscopy. The starch–PGA copolymers absorbed water and formed gels, which exhibited concentration‐dependent viscoelastic solid properties. Higher starch–PGA concentrations resulted in stronger viscoelastic properties. The analysis for moduli of different concentrations indicated that the starch–PGA graft copolymer gels were physical gels, meaning the cross‐links between the molecules were physical junctions. However, stress relaxation measurements showed that the starch–PGA graft copolymer gels had long relaxation times, which result from the presence of the chemical cross‐links that were evident in the FTIR spectra. The non‐linear steady shearing rheological properties studies indicated that starch–PGA gels exhibited shear thinning behavior, which can be well fitted with the power law constitutive equation. The function and behavior of the starch–PGA graft copolymer gels suggest that this kind of starch‐based biomaterial could be a potential candidate for applications in cosmetic gels, skin wound care materials, and agricultural products.