Kinetics of hydrolysis, acetylation, and deamination reactions on polyamide fibers in heterogeneous medium

Abstract

The kinetics of reactions, namely, hydrolysis, acetylation, and deamination, on polyamide fibers has been studied at different temperatures. Rate constants and apparent activation energies of these reactions were determined. All the three reactions studied show two rates, the initial fast rate, followed by the slow one. The existence of two rates has been explained on the basis of two-phase structure of the polyamide fibers, the fast rate corresponding to the weakly hydrogen-bonded regions and the slow rate corresponding to the regions which are strongly hydrogen bonded in the regular fashion. For hydrolysis, the fast rate was 38 times faster than the slow one, while the fast rate of acetylation reaction was about 162 times that of the slow rate. The ratio between the fast and slow rates was constant at all the temperatures studied in case of the hydrolysis and acetylation reactions. This ratio, however, was found to be extremely temperature sensitive for the deamination reaction. The hydrolysis and acetylation reactions were found to be strongly temperature dependent leading to the increase in the extent of modification with increase in temperature. Deamination, on the other hand, showed negative temperature dependence giving progressive decrease in the modification with increase in temperature. All the three modifications studied observed first-order kinetics. The apparent activation energy for hydrolysis was 1.38 and 1.05 kcal/mole corresponding to the fast and slow rates, respectively. The apparent activation energy values for acetylation were 2.53 and 3.29 kcal/mole, while those for deamination reaction were −8.28 and −46.0 kcal/mole, respectively. The apparent activation energy values for the deamination reaction bore negative signs possibly because of the negative temperature dependence of this reaction. The apparent activation energy for slow reactions in case of acetylation and deamination was found to be higher than that of the fast rate, while the reverse was true in case of hydrolysis, showing that the acetylation and deamination reactions, being the chemical modification of polyamide fibers at the NH2 groups, proceed by altogether different mechanisms than the hydrolytic breakdown of the polyamide linkage.