Development of New Evaluation Method for Biodegradation Behavior of Biodegradable Polymers by Multiple Analytical Measurements

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The enzymatic degradability of poly (lactic acid) [PLA]/ polycaprolactone [PCL] blend was evaluated focusing on the changes in the chemical compositions during its biodegradation. The almost equimolar blended samples were biodegraded in a phosphate buffer solution added with Pseudomonas sp. cholesterol esterase for 1-5 days. After this biodegradation procedure, the residual blend samples were subjected to Py-GC measurements in the presence of tetramethylammonium hydroxide (TMAH). Various methylesters and cyclic esters originating from each constituent polymer were sensitively observed on the pyrograms of the blend samples. The observed composition of the original blend estimated on the basis of their peak intensities was in good agreement with the feed composition. Moreover, the relative amounts of PCL constituent in the blend determined by reactive Py-GC slightly decreased with the time for the enzymatic degradation test, corresponding to the increase in the TOC in the buffer solution. This fact suggested that the biodegradation rate of PCL in the blend was faster than that of PLA.Furthermore, it is interesting to note that the degradation rate of PLA constituents in the blend, which was estimated from the weighed recovery and the observed composition by Py-GC,was much faster than that of pure PLA whereas the biodegradation of PCL constituent in the blend was significantly depressed as compared with that of pure PCL.This specific biodegradation behavior of the blended polyester can be correlated to its molphological "sea-island" structures.