Hydrolytic degradation of polyester blend monolayers at the air/water interface: Effects of a slowly degrading component

The hydrolytic behavior of monolayers of biodegradable [poly(l-lactide)/poly(∈-caprolactone)] (l-PLA/PCL) blends spread at the air/water interface is studied to identify the relative rate of hydrolytic degradation of each component when exposed to a basic subphase. As the hydrolysis time increases, the isotherm recorded from (l-PLA/PCL) blend monolayers was found to be similar to that of PCL homopolymer; this is likely due to the preferred hydrolysis of l-PLA. The rate of hydrolysis was recorded by a change of occupied area when the monolayer is maintained at a constant surface pressure. The hydrolysis of the blend in a basic condition was much faster than that of each homopolymer, regardless of the composition, arising from a dilution effect on the concentration of l-PLA monolayers. From the deviation behavior (D) between the arithmetic average and experimental values, blends with compositions less than 50 mol % l-PLA showed the maximum dilution effect (D_t = 0.11t, where t is hydrolysis time) whereas high l-PLA compositions (≥ 75 mol % l-PLA) showed a smaller effect.