A semiempirical model for predicting biodegradation profiles of individualpolymers in starch-poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) bioplastic

Plastic prepared from formulations of cornstarch and poly(beta-hydroxybutyr ate-co-beta-hydroxyvalerate) (PHBV) biodegraded in tropical coastal waters. Biodegradation was monitored for 1 year. Starch-PHBV bioplastic appeared t o lose weight in two overlapping phases until both biopolymers were entirel y consumed. To examine the underlying degradation of starch and PHBV from b iphasic weight-loss profiles, a semiempirical mathematical model was develo ped from which degradation profiles and lifetimes of the individual biopoly mers could be predicted. The model predicted that starch and PHBV in the bi oplastic had half-lives of 19 days and 158 days, respectively. Computed pro files also predicted that the starch in the composite would be completely d egraded in 174 days, while residual PHBV would persist in the marine enviro nment for 1107 days. The model further revealed that, for a 30% starch : 70 % PHBV composite, PHBV degradation was delayed 46 days until more than 65% of the starch was consumed. This suggested that PHBV degradation was metabo lically repressed by glucose derived from starch. Glucose repression of mic robial PHBV degradation was substantiated in 91 of 100 environmental isolat es. The validity of the elaborated model was proven when its revelations an d predictions were later confirmed by chemical analysis of residual bioplas tic samples. (C) 2000 John Wiley & Sons.