Depolymerization of Poly(lactic acid) Cups to Lactic Acid

Laboratory Procedures (PDF)

Author Contact: douskey@berkeley.edu

Summary

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.

Category Descriptors

Chemistry Concepts

• Aldehydes/Ketones
• Aqueous Solution Chemistry
• Carbonyl Chemistry
• Lewis Acids/Bases
• Natural Products
• Polymerization
• Reactions of Alcohols
• Solutions/Solvents
• Stoichiometry

Laboratory Techniques

• pH
• Titration/Volumetric Analysis

Green Chemistry Principles

• Analyze in Real-Time to Prevent Pollution
• Avoid Chemical Derivatives
• Design for Degradation
• Design Less Hazardous Chemical Syntheses
• Design Safer Chemicals and Products
• Increase Energy Efficiency
• Maximize Atom Economy
• Minimize the Potential for Accidents
• Prevent Waste
• Use Renewable Feedstocks
• Use Safer Solvents/Reaction Conditions

Chemistry Subdiscipline

• Analytical Chemistry
• Interdisciplinary/Multidisciplinary
• Materials Science
• Polymer Chemistry

Target Audience

• Colleges/Universities
• Secondary Schools

Source

• Original Contributions - unpublished