Thermogravimetric study of starch derivatives with amine/ammonium ion-exchanging groups in oxidative environment

Abstract

The amine/ammonium materials were prepared by cross-linking of starch (S) with epichlorohydrin (E→SE) in the presence of ammonia (A→SEA) or choline (C→SEC–HO −) or with 1,3-bis-(3-chloro-2-hydroxypropyl)imidazolium hydrogensulphate (BCHIHS→SHI–HO −) and transfered into the acid/salt forms with HCl (SEA–HCl, SEC–Cl −, or SHI–Cl −), H 2SO 4 (SEA–H 2SO 4, SEC–HSO 4 −, or SHI–HSO 4 −), and H 3PO 4 (SEA–H 3PO 4, SEC–H 2PO 4 −, or SHI–H 2PO 4 −) and analyzed with thermogravimetry (TG) under dynamic and isothermal conditions in nitrogen or oxygen environment. According to the values of thermooxidation maxima (TM) calculated from the maximal difference of measured residues on the dynamic TG curves run in nitrogen and oxygen environments the order of decreasing thermooxidation resistance is: S>SEA–H 3PO 4>SHI–H 2PO 4 −>SHI–HSO 4 −>SEA–H 2SO 4>SEC–HSO 4 −>SEC–HO −>SEA–HCl>HCl–Cl −> SEC–Cl −>SHI–HO −>SEA>SEC–H 2PO 4 −>SE. The first-order rate constants calculated by the linear regression method (regression coefficient R>0.95) represented the initial rate constants for residue formation ( k r's) and gasification ( k g's). All the derivatives had greater values of rate constants than S and the k g's were about 1000 times greater than k r's. The values obtained in nitrogen were smaller than those calculated from runs in oxygen environment with the exception of S. Most of the salt forms had greater values of k g's in oxygen environment. The activation energies ( E's) were usually greater in nitrogen than in oxygen as well as for residue formation than for gasification. The SHI–HO − sample had high k g's and low E g's in oxygen environment while for SHI–H 2SO 4 − the opposite was true. This we consider as two extremes for labile and resistant samples for gasification.