I. Simkovic et al., PREPARATION OF A WEAKLY BASIC ION-EXCHANGER BY CROSS-LINKING STARCH WITH EPICHLOROHYDRIN IN THE PRESENCE OF NH4OH, Carbohydrate polymers, 30(1), 1996, pp. 25-30
Crosslinking of starch with epichlorohydrin in the presence of NH4OH,
NaOH and water was studied. The reaction was optimized and the product
s analysed by solid-state C-13-NMR in the presence of water, acid-base
titration and dye-binding measurements. The presence of different typ
es of hydroxypropyl groups was confirmed by NMR, but their linkage to
polysaccharide could not be confirmed because of their minor abundance
relative to all other CH2 groups, and because the motion of the sidec
hains is much greater than the starch component, which remains fairly
constant despite the presence of water. Yield of crosslinked, water-in
soluble product is increased as a greater amount of NH4OH and a lower
amount of water is used in the reaction. Product yield using water-ins
oluble starch is higher than with a water-soluble starch. Closed-vesse
l (pressurized) reaction conditions increases product exchange capacit
y. Potentiometric titration of products in Cl--form or in non-ionized
form indicated smaller exchange capacity values than expected from pro
duct nitrogen contents, reflecting the difficulty in fully protonating
the products. Dye binding by the crosslinked-starch exchangers is pH-
dependent, with an increased quantity of dye bound at lower pH, which
is consistent with the weak-amine nature of the products. Hydrolyzed R
emazol Brilliant Red F3B, a trivalent reactive dye, binds less effecti
vely under acidic conditions, on a molar basis, to the starch-based ex
changers than does Alizarin Red S, a monovalent mordant dye. Dye-bindi
ng capacities are somewhat lower than the total ion-exchange capacitie
s determined by potentiometric titration, suggesting that a portion of
the exchange sites are unavailable to the dyes.