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United States Department of Agriculture

Agricultural Research Service

Title: A Semi-Empirical Model for Predicting Degradation Profiles of Polymers in Biodegradation of Starch/poly(beta-Hydroxybutyrate-Co-Beta-Hydroxyvalerate)plastic

item Gordon, Sherald
item James, Christopher
item Imam, Syed
item Greene, Richard

Submitted to: National Organization for the Professional Advancement of Black Chemists and Chemical Engineers
Publication Type: Abstract Only
Publication Acceptance Date: February 18, 1999
Publication Date: N/A

Technical Abstract: Plastic prepared from formulations of cornstarch and poly(beta- hydroxybutyrate-co-beta-hydroxyvalerate) (PHBV) biodegraded in tropical coastal waters. The degradation, caused by microbial consumption of starch and PHBV, was monitored for one year. Starch-degraders in the microbial population were 10 to 50 times more prevalent than PHBV- degraders. Accordingly, degradation of plastic, as measured by weight loss, correlated with the amount of starch present. However, the plastic appeared to lose weight in two overlapping phases until both starch and PHBV were entirely consumed. To examine the underlying degradation profiles of starch and PHBV from biphasic weight-loss profiles, a semi-empirical mathematical model was developed from which degradation of each polymer could be predicted individually. Mathematical deconvolution on the model for a 30% starch - 70% PHBV formulation revealed that PHBV degradation was delayed 50 days until more than 80% of the starch was consumed and predicted that starch and PHBV in the plastic had half-lives of 19 days and 158 days, respectively. Computed profiles also predicted that the starch would be completely degraded in 174 days while residual PHBV would persist in the environment for 1009 days. The model was validated by comparison with subsequent experimental data. Deconvoluted weight-loss profiles agreed remarkably well with chemically determined weight-loss profiles for both starch and PHBV.

Last Modified: 5/5/2015
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