In this lab a potentiometric titration of a sample of the polymer poly(lactic acid) (PLA) with a known NaOH standard was performed, using a pH meter to track changes in the pH of the acid solution as measured volumes of base was added. PLA was depolymerized into lactic acid in basic solution through a saponification reaction, an organic hydrolysis reaction that is used to make soap. The data was represented in the form of a titration curve and the amount of lactic acid in the final solution was quantitatively measured.
This lab demonstrates important principles of Green Chemistry as PLA is a renewable feedstock that can be derived from corn or potato starches and is biodegradable. Furthermore, the solvent ethanol can be reused, thus minimizing waste.
In addition to the experimental methods, a suggested prelab, a guide to calculating equivalence points from titration data, and a worksheet with data and discussion questions are included in this resource as well.
This design of this laboratory exercise was inspired by Hydrolysis of Post-Consumer Polylactic Acid Waste submitted to GEMs by Rich Gurney (Simmons College) in 2008.\"
Summary prepared March 2012 by Sheba Plamthottam at the UC Berkeley.
Douskey, M. Depolymerization of Poly(lactic acid) Cups to Lactic Acid, College of Chemistry, UC Berkeley, 2012