Dyeing to Degrade: A Bioplastics Experiment for College and High School Classrooms

A versatile experiment is described for the high school and college laboratory setting based on the synthesis of biobased polymers prepared from inexpensive, renewable, and nonhazardous chemicals. Combinations of readily available citric acid, glycerol, and tapioca root starch are used to prepare three polymeric materials with different observable physical properties. Simple qualitative comparisons of aqueous degradation rates can be made or a dye can be added for quantitative assessment. Food and Drug Administration (FDA) approved Yellow Dye No. 5 is selected as a dye stable to basic conditions and is added to each sample in the form of commercial food coloring. The dyed polymer samples are observed to degrade in an aqueous sodium hydroxide solution, releasing the dye. Both ultraviolet-visible spectroscopy and smartphone colorimetry are used to follow the increasing dye concentration, which is inversely correlated to polymer degradation. The collected data is suitable for analysis and graphing by students. Potential learning outcomes of the experiment include Le Chatelier's principle, types of intermolecular forces, hydrolysis, absorption spectroscopy, Beer's Law, rate determinations, and graphing. The experiment models green chemistry principles of design for safer chemicals, degradation, and use of renewable feedstocks. Paramount to the educational objectives of the curriculum are the societal connections to plastics that are accumulating in the environment and causing harm, as well as examples of successful advances in commercial bioplastics such as poly(lactide) (PLA).