Rheokinetics of graft copolymerization of acrylamide in concentrated starch and rheological behaviors and microstructures of reaction products

A widely recognized challenge in starch chemistry is to manipulate the graft copolymerization onto starch melt by reactive extrusion (REX). To understand the complex in-situ graft copolymerization in highly concentrated systems, we firstly used a mixer to achieve a homogeneous viscous starch melt, and then undertook dynamic rheological measurements to study the rheokinetics of the reaction. The in-situ synthesis also facilitated the characterization of the microstructures of reaction products. The melt mixture could be regarded to be completely micromixed since the rheokinetics was predominated by the reaction kinetics. The rheological characterization revealed that G′of hydrogels followed a linear progression with the crosslinker concentration. Nevertheless, the reaction temperature and initiator content had little influence on the final microstructure of hydrogels, most likely due to the strong chain transfer reaction in the melt. Additionally, high-amylose starches tended to form grafted hydrogels with a high physical crosslinking density.