Biodegradation characteristics of starch-polystyrene loose-fill foams in a composting medium

The structures and biodegradabilities of loose-fill foams, containing starch and polystyrene at ratios of 70:30 and 80:20, were evaluated using a laboratory composting system. Each formulation was foamed (extrusion expanded) using either 0.2% azodicarbonamide or 0.25% citric acid as the chemical blowing agent. Biodegradability, a measure of the quantity of material mineralized, was expressed as the percentage of CO2 in the exhaust gas eluted from the individual chambers. The CO2 generation peaked after about 15 days of composting, and then decreased. The rate and amount of CO2 eluted depended on the starch content in the foams. Similarly, there were significant differences in the rates and quantities of CO2 emissions for the foams blown with azodicarbonamide versus citric acid. At the end of the composting tests, the remaining foam material had fibrous and crumbly textures, presumably consisting primarily of polystyrene. FTIR and NMR spectra of the foams, taken after 39 days of composting, did not reveal the spectral features of starch, thereby confirming the decomposition of the starch.