Effect Of Amylose/Amylopectin Content On Starch-Based Superabsorbent Polymer Through Grafting Acrylamide Monomer

In this work four corn starches with different amylose contents (waxy,4.3%; maize,29.0%; Gelose50,50%; Gelose80,80%) are used as model materials in developing ofstarch-superabsorbents. They are produced by grafting acrylamide onto cornstarch with cericammonium nitrate as an initiator and N.N’-methylene-bisacrylamide (MBA) as a crosslinker.The macroscopic performance (water absorbency capacity, rheological properties) andmicrocosmic characterizations (FTIR, NMR, TGA determination on grafting ratio, graftingefficiency, number/length of branch chain) are observed to explore the correlation betweenamylose/amylopectin ratio of virgin starch and performance of starch-superabsorbents.The copolymerization of grafting acrylamide onto cornstarch only react on hydroxylgroup connected to C6. An increase on amylose ratio results in shorter average length ofbranch chain and higher grafting ratio, grafting efficiency and number of branch chain. Allthese structural diversity can be used to explain the difference of macroscopic performance onwater absorption/releasing, pH sensibility, salt tolerance and rheological properties, which canbe classified as follows:1. SAP based on higher amylose ratio shows better water absorption/retention, inferiorrecycle absorption, more sensitive to pH change and salt tolerance; SAP based onhigher amylopectin ratio shows worse water absorption/retention, better recycleabsorption, less sensitive to pH change and salt tolerance.2. SAP based on highest amylopectin ratio overcomes other3SAP on storage modulus G′,loss modulus G″, and shear viscosity η. This is because high molecular weight andbranched structure of amylopectin reduced the mobility of polymer chains andincreased viscosity after graft copolymerization.