The mechanical behavior of poly(lactic acid) unreinforced and nanocomposite films subjected to monotonic and fatigue loading conditions

The mechanical and fatigue behavior of neat poly(lactic acid) (PLA) films and PLA films reinforced with 5 wt% nanoclay particles has been examined using various analytical procedures. The results showed that for the films tested in this study, PLA-5 wt% samples were more susceptible to crazing at the same maximum fatigue stress as the neat PLA samples, as evidenced by results from light transmission experiments. Optical microscopy results confirmed this observation. In addition, under fatigue loading conditions, the neat PLA samples displayed almost the same fatigue resistance (number of cycles to failure) at 3 and 30 Hz, while the PLA-5 wt% samples showed a shift in the number of cycles to failure to higher values at a frequency of 30 Hz. Using the linear regression curves from the S-N data (stress vs. number of cycles to failure), time-to-failure curves were generated to show the difference between the neat PLA and PLA-5 wt% samples when tested at frequencies of 3 and 30 Hz. Based on these results, it is known that the nanoclay particles served to increase the fatigue resistance at the higher frequency of 30 Hz, when compared to the neat PLA sample.