Obtaining and Microstructural Study of a Multifunctional Highly Phosphorylated Starch

Abstract This study reports the phosphorylation of starch by a method used for kraft fibers. Energy dispersive X‐ray (EDX) analysis shows that this product contains 20% phosphorus and 9% nitrogen. The corresponding degrees of substitution (DS), on the anhydroglucose repeating unit (AGU), by phosphorus‐containing (DS P ) and nitrogen‐containing (DS N ) groups are 2.32 and 1.38, respectively. The microstructural characterization techniques ( 13 C and 31 P NMR, ATR‐FTIR), indicate the existence of several functional groups simply linked or acting as bridges between the chains. The degree of charge (4446 mmol kg −1 ), determined by potentiometry, is lower than that calculated theoretically (6617 mmol kg −1 ). This is due to a transformation of the phosphate groups (─O─PO 3 H 2 ) into (─O─PO 3 H─) forming inter‐chain bridges. The viscosimetric increment varies very little with concentration, indicating that the study is dealing with particles made up of highly cross‐linked polysaccharide chains, whose hydrodynamic volume expansion is strongly restricted. The thermogravimetric study, mass loss as a function of temperature, generates levoglucosan as the majority product. It indicates the persistence of AGU despite modification reactions. By pooling all the data, the study is able to propose an approximate microstructure. Application tests for fertilizer, adsorbent, flame retardant, water retainer, and gelling agent are conclusive.