Effects of femtosecond laser micromachining on the surface and substrate properties of poly-lactic acid (PLA).

• Systematic analysis of PLA ablated by femtosecond laser was first explored. • The surface microstructure displayed a dependence on the fs laser parameters. • The photo-thermal oxidation was proved as the dominant reaction on the surface. • The degradation in PLA matrix was also observed during the surface ablation. The effects of femtosecond laser ablation on the surface morphology, surface chemical composition, and matrix properties of poly-lactic acid (PLA) were explored in this paper, since the analysis of the different energy density range is crucial in evaluating to what extent material properties change during the micromachining. Scanning electron microscopy (SEM) analysis found that different surface microstructures, i.e., the convex microstructure and the through hole, were generated by single and multiple pulses femtosecond laser ablations, respectively. The photo-thermal features appeared on the PLA surface displayed a dependence on the femtosecond laser pulse number or fluence. The surface affected by femtosecond laser ablation was also analyzed using Fourier transforms infrared (FTIR) as well as X-ray photoelectron spectroscopy (XPS), which indicated that an oxidation reaction had occurred during the micromachining. The ablation of PLA surface resulted in a decreased molecular weight and an increase of polydispersity, which was consistent with a drop in transition temperature (T m). Therefore, the substrate also degraded although the micromachining process was only performed on the surface. The variation in PLA surface microstructures, chemistry, and matrix performance resulted from different laser parameters were related to the laser-matter interaction effects. [ABSTRACT FROM AUTHOR]