|St Lawrence, Sterling|
Submitted to: Annual Meeting of the Bio Environmentally Degradable Polymer Society
Publication Type: Abstract Only
Publication Acceptance Date: August 17, 1999
Publication Date: N/A
Technical Abstract: The temperature and strain-rate dependence of yielding has been investigated for two biodegradable poly(hydroxy ester ethers). For these materials, the glass transition temperature, Tg, has been shown to depend on the water content. There is, therefore, a correspondence in terms of the material's tensile behavior between the water content and the testing temperature, T relative to Tg. The equivalent of these variables can be seen if T is expressed in terms of the degree of under cooling, delta T = T -Tg. At high delta T and high strain rates, both materials fail in a brittle manner. At low strain rates the stress drops after yielding to a constant value as a neck propagates through the gauge length. Prior to failure the necked region strain hardens. At small delta T (< 5 deg C) there is a change in the yielding behavior as strain rates increase. There is a more pronounced load drop at the yield stress and at larger strains; the material strain hardens rapidly as the strain rate increases. To predict the yield stress at different conditions an attempt has been made to construct a master curve by superimposing the data from different delta T and strain rates. The failure mechanism in filled samples is also more clearly understood if the yielding behavior of the matrix is well characterized. Since these resins are biodegradable and have good adhesive properties, they can be filled with natural materials such as corn starch. The resulting composites have been shown to have acceptable mechanical properties. This research was conducted under CRADA number 58-3K95-8-633 between ARS and Biotechnology Research Development Consortium (BRDC).