Degradation of poly(l-lactide) under KrF excimer laser treatment

In this paper, the authors present an impact of the KrF excimer laser irradiation above the ablation threshold on physicochemical properties of biodegradable poly(l-lactide). The analysis for the high energy density range is crucial in evaluating to what extent polymer degrades during erosive material removal. This approach was not presented in the available literature. The laser treated samples were analysed by means of Differential Scanning Calorimetry (DSC) and Gel Permeation Chromatography (GPC) which were helpful to characterize the bulk modifications. The surface affected by laser ablation was analysed using infrared spectroscopy (Attenuated Total Reflectance) as well as X-ray Photoelectron Spectroscopy. The techniques used gave a complex image of changes introduced into the material. The ablation of polylactide surface resulted in a decrease of molecular weight within an entire irradiated volume of ∼250 μm thick polymer sheet. The increase of polydispersity was also noted. Both DSC and GPC techniques show that in spite of different laser fluence, the extent of degradation is similar for all laser ablated samples. The XPS analysis revealed no oxidation of the surface. The appearance of vinyl and ketone unsaturated groups as well as carboxyl terminals after laser treatment was revealed by FTIR spectroscopy. The presence of new functional groups is a result of photochemical or/and thermal processes which both yield similar degradation products.