Tuning the hydrolytic degradation rate of poly-lactic acid (PLA) to more durable applications

The disposal of polymeric waste is increasingly becoming an issue of international concern. The use of biodegradable polymers is a possible strategy to face most of the problems related to the disposal of the durable (non-biodegradable) polymers. Among biodegradable polymers, PLA (obtained from renewable sources) is a very attractive one, due to its good processability, biocompatibility, interesting physical properties. Hydrolysis is the major depolymerisation mechanism and the rate-controlling step of PLA biodegradation in compost. The propensity to degradation in the presence of water significantly limits specific industrial applications such as automobile, biomedical, electronic and electrical appliances, agriculture. Therefore the control of biodegradation rate is somewhat even more important than the characteristic of biodegradability itself. This is the reason why it is critical to find additives able to modulate the biodegradation rate of biodegradable polymers in relationship to the expected lifetime. Since the kinetics of hydrolysis strongly depend on the pH of the hydrolyzing medium, in this work some fillers able to control the pH of water when it diffuses inside the polymer were added to PLA. In particular, fumaric acid, a bio- and eco-friendly additive, was used. In order to control the dispersion of this molecule inside the polymer, it was intercalated in a biocompatible nanofiller: layered double hydroxides (LDH). These fillers were added to the material using melt-compounding technique, suitable for industrial application. The preliminary results obtained are encouraging toward the possibility of effectively controlling the degradation rate.