Compatibility and hydrolytic behaviors of polylactide isomer/poly(butylene succinate) mixtures by the Langmuir technique

Abstract

The compatibility and hydrolytic behaviors of the monolayer mixtures of biodegradable stereochemical polylactide (l-PLA or dl-PLA) and poly(butylene succinate) (PBS) were studied by the Langmuir technique at the air/water interface. The π-A behaviors of two binary systems, well mixed and unmixed, were compared with each other to demonstrate their compatibility. From the changes in the occupied area and the transition region, the compatibility of l-PLA/PBS monolayer mixtures decreased with increasing PBS composition while dl-PLA/PBS monolayer mixtures showed better compatibility than l-PLA/PBS monolayer mixtures. Since PBS monolayers at a pH of 6.8 showed a long transition region of approximately 5 mN/m due to the conformation change, the change in the PBS transition in the monolayer mixtures was analyzed. The results were in accordance with the occupied area. The hydrolytic behaviors of the homopolymer and mixed monolayers on an alkaline subphase were monitored at a constant surface pressure as a function of exposure time. The compatible monolayer mixtures showed much slower hydrolytic kinetics than their arithmetic averages. This hydrolytic impedance is mainly due to the interaction between both monolayer chains which prevents the ions from attacking the ester bonds of PBS, resulting in a much faster hydrolytic rate than that of PLA.