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United States Department of Agriculture

Agricultural Research Service


item Willett, Julious - Jl
item O'brien, Gregory

Submitted to: Annual Meeting of the Bio Environmentally Degradable Polymer Society
Publication Type: Abstract Only
Publication Acceptance Date: 9/26/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: We have recently developed predictive equations for the mechanical properties of starch/PHBV composites. Little is known, however, about the role of additives such as plasticizers and inorganic fillers in biodegradation of these materials. Statistical experimental design was used to formulate a series of composites of PHBV, starch (10% or 25%), CaCO3 (0% or 20%), and plasticizer (7.5% or 15%). Injection molded plaques and extruded ribbons were exposed to soil burial, and weight loss and mechanical properties were monitored over time. Ribbons degraded faster than the thicker plaques, and had essentially no mechanical integrity after 11 weeks in soil. The weight loss was controlled by the starch and CaCO3 content. Formulations with 25% starch showed higher rate of loss of weight and mechanical properties. The presence of CaCO3 significantly increased the rate of weight loss, particularly at the higher starch content. Weight loss was slightly retarded by higher plasticizer levels. Maximum weight loss was approximately 80% for ribbons, and approximately 40% for plaques. Ca analysis of samples after 14 weeks of soil exposure indicated that a portion of the Ca was lost, although the relative Ca content increased due to more rapid loss of organic material. Since the soil pH was slightly alkaline, the loss of Ca was apparently not due to CO2 generation under acid conditions. The CaCO3 may play a role in providing nutrients for the microorganisms colonizing the materials. (Research conducted under Cooperative Research and Development Agreement 58-3K95-M-013 between USDA-ARS and Zeneca Bioproducts).

Last Modified: 10/16/2017
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