Effect of unidirectional drawing process on fracture behavior of poly(L-lactide)

Drawing process is known to be an effective way to improve the mechanical properties of thermoplastics, and effects of drawing on tensile and fracture properties of thermoplastics have been studied. PLLA is usually draw-processed when it is used for bone fixation devices, and therefore, fundamental effect of drawing on its fracture behavior needs to be characterized. In the present study, plate samples of amorphous PLLA were prepared, and draw-processed unidirectionally at different draw ratios. Critical J-integral at crack initiation, was evaluated as a mode I fracture property in the directions perpendicular and parallel to the drawing direction, i.e. the direction of molecular orientation. Scanning electron microscopy (SEM) of fracture surfaces was also performed to characterize the effects of drawing on the fracture micromechanism. The roughness of these fracture surfaces were also measured using a laser microscope to assess the relationship between the surface roughness and the fracture properties, and tried to be correlated with the fracture micromechanism.