Preparation of starch–poly–glutamic acid graft copolymers by microwave irradiation and the characterization of their properties

• Poly-γ-glutamic acid was grafted onto waxy starch using microwave irradiation.
• The reaction conditions were optimized to temperature and pH.
• The starch–g–PGA gel absorbed more than 20 times of its own weight amount of water.
• The starch–g–PGA gel exhibited viscoelastic solid behavior.

Graft copolymers of waxy maize starch and poly-γ-glutamic acid (PGA) were produced in an aqueous solution using microwave irradiation. The microwave reaction conditions were optimized with regard to temperature and pH. The temperature of 180 °C and pH7.0 were the best reaction conditions resulting in a PGA graft of 0.45% based on nitrogen analysis. The average graft content and graft efficiency for the starch–PGA graft copolymer prepared at 180 °C and pH7.0 were 4.20% and 2.73%, respectively. The starch–PGA graft copolymer produced at 180 °C and pH7.0 could absorb more than 20 times its own weight amount of water and form a gel. The preliminary rheology study revealed that the starch–PGA graft copolymer gel exhibited viscoelastic solid behavior while the control sample of waxy starch showed viscoelastic liquid behavior.