FT-IR Determination of degree of esterification in polycarboxylic acid cross-link finishing of cotton

Cross-linking of cotton with polycarboxylic acids, applied with catalysts based on phosphorus-containing inorganic acids, produces fabrics with excellent smooth-drying properties and which release no formaldehyde at any stage of preparation or on storage. The reaction produces cellulose ester linkages and unreacted carboxylic acid groups. Fourier transform infrared spectroscopy was used to determine the degree of esterification of polycarboxylic acids that occurred on cross-linking of cotton. The height of the carbonyl peak at 1730 cm ^–1 was determined on the same treated fabrics after soaking in dilute acid to convert ionized groups to free acid and then in dilute base to convert free acid to carboxylate ion. The carbonyl peak for the base rinsed fabric (ester only) was ratioed against the same peak for the acid-rinsed fabric (total carbonyl, ester plus acid) to obtain a measure of the degree of esterification. This ratio minimizes the problems of different molar extinction coefficients that are encountered when peaks from different functional groups are used.