Abstract
Solid-state 13 C CP/MAS studies of starch cross-linked with urea-formaldehyde prepolymer (St-UF) have been conducted to elucidate its structure and dynamics. 13 C NMR spectra and spin-spin relaxation times (T 2 ,) were obtained for various St-UF samples having different degrees of cross-linking. Line width and T 2 measurements of starch carbons show that a maximum degree of cross-linking it obtained at a urea to starch (w/w) ratio of 0.6. Increasing the urea to starch ratio beyond 0.6 leads to competing self-condensation of dimethylolurea. These results also establish that chemical crosslinking occurs through the primary hydroxyl groups located at the C-6 position of starches.
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