Evaluation of the Dependence of Tensile Strength and Fracture Strain of PLA Film on Machining Method

Abstract

Some machining methods were used for making prototype of biodegradable stent made from poly lactic acid(PLA) film. Decrease of the tensile strength and fracture strain after machining was frequently observed. Therefore, in this paper, the tensile strengths of the films after machining were evaluated. The tensile strengths had maximum average value of 127.2MPa by the cutting plotter, and the minimum average value of 89.4MPa by the excimer laser. The machined surfaces were observed by scanning electron microscope. The machined surfaces by the cutting plotter and FHG -YAG laser were relative smooth. Those by the excimer laser and oxygen RIE, however, were rough. That by turret punch press was relative smooth and had flake-like burr. The surface roughness was related to the tensile strength, but not always related to fracture strain. It is supposed that surface irregularity caused the stress concentration and it reduced the tensile strength. On the other hand, it is supposed that the fracture strain was affected by the changes of property of surface and inner material, and they was caused by the shear deformation and the resolidification, crystallization and degradation induced by the processing heat.