Starch was allowed to react thermochemically (oven versus drum drying-
oven) with citric acid to potentially yield biodegradable products pos
sessing high ion exchange capacity. Reaction variables studied were: s
tarch type (amylose content 0-70%), pH (0.5-8.5), sodium level (0-3 mo
les), citric acid level (0.1-0.5 moles), reaction time, temperature (1
10-140 degrees C) and sodium dihydrogen phosphate catalysis. Reaction
efficiencies approaching 100% were achieved, while minimizing crosslin
king and maximizing carboxyl content. Carboxyl content was determined
and copper binding capacity at pH 4.5 was evaluated.