Surface analysis of biodegradable polymer blends of poly(sebacic anhydride) and poly(DL-lactic acid)

The erosion behavior of blends of biodegradable polymers is determined by the chemical composition and the molecular organization of the surface of the material. Providing a comprehensive characterization of polymer blend surfaces requires a multi-instrumental approach, as no individual surface analysis technique can ascertain both the chemical and morphological nature of surfaces. In this study we have characterized the surfaces of immiscible and miscible blends of the biodegradable polymers poly(sebacic anhydride) (PSA) and poly(DL-lactic acid) (PLA) using the surface techniques of static secondary ion mass spectrometry (SSIMS), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). SSIMS and XPS have recorded the surface enrichment of all of the blends with the PLA component. For the immiscible blends, differential charging within the XPS spectra also provides evidence of phase separation. AFM data have contrasted the surface morphologies of the immiscible and miscible blends, and the use of in situ AFM techniques has enabled the effect of blend morphology on surface erosion to be visualized. For the immiscible systems, clear phase separation morphologies can be observed and at certain blend compositions the rapid loss of the PSA from the films results in the exposure of the PLA morphology. However, as the PLA content is increased, the surface enrichment effect results in the degradation behavior of the blend being dominated by the slow degrading PLA surface layer. For the miscible systems, the in situ AFM studies visualized a disintegration of the whole blend film without the exposure of a PLA morphology, indicating that the hydrolysis of the PSA component rendered the whole film unstable. The use of SIMS, XPS, and AFM, while highlighting the complexity of polymer blend surfaces, can provide a rapid analysis of the physicochemical phenomena underlying the organization of these systems and therefore should facilitate the application of such systems as biomaterials.