the invention provides energy efficient depolymerization of polyesters such as post - consumer polylactic acid . ultrasonic induced implosions can be used to facilitate the depolymerization . the expanding market of polylactic acid - based plastic products , such as water bottles and packaging materials , has raised concerns of contaminating the recycling stream , which is largely filled with petroleum - based plastics . thus the development of an energy efficient and economically viable pla recycling process is urgently needed . post consumer pla was exposed to methanol as the suspension media in the presence of organic or ionic salts of alkali metals such a potassium carbonate and sodium hydroxide as depolymerization catalysts to provide high quality lactic acid monomers in high yield .