38—Sorption of Methacrylic Acid by Nylon II. The Rates of Sorption and Desorption by Drawn Nylon 6.6 Fibres

The rates at which methacrylic acid is sorbed and desorbed from aqueous solution by drawn nylon 6.6 fibres have been measured at 30°, 45°, and 60°C. Desorption is faster than the first sorption, and the second sorption proceeds initially at the same rate as desorption. On first sorption only, there is a very short induction period, and supersorption occurs, the amount sorbed passing through a maximum before falling to the equilibrium value. The rates of change of fibre length on sorption and desorption have been correlated with the sorption and desorption rates themselves. They are roughly proportional for desorption (decrease in length) and for sorptions beyond the second (increase in length) On first sorption, there is a relatively long induction period before the irreversible decrease in length begins. It is considered that the first sorption produces an irreversible relaxation in the fibres, allowing greater diffusion rates subsequently. This process is completed on second sorption. The sorption rates are initially dependent on the square root of the time. Diffusion coefficients have been calculated and are found to increase exponentially with concentration and to have activation energies of 13 and 10 kcal/ mole-1 on first sorption and desorption, respectively.