Submitted to: Annual Meeting of the Bio Environmentally Degradable Polymer Society
Publication Type: Abstract Only
Publication Acceptance Date: August 19, 1998
Publication Date: N/A
Technical Abstract: The hygroscopic nature of starch has important implications for its use in biodegradable materials. Water sorption can affect the mechanical properties of starch-based materials, since water is an effective plasticizer for starch; water transport is also essential in the biodegradation of these materials. We have characterized the transient state diffusion coefficients D of granular starch/PHBV materials immersed in water at room temperature. Starch contents up to 0.44 volume fraction and three levels of PHBV plasticizer were used (0, 5, and 10 phr). Sorption data were analyzed assuming Fickian diffusion in a plane sheet. All materials displayed Fickian sorption curves in the early stages of sorption. Values of D were on the order of 10**-9 cm**2/sec. For PHBV resins with no starch, D increased with increasing plasticizer content and was independent of HV content for the two copolymers used (5% and 8% HV). At a fixed plasticizer content, D decreased with starch content to a minimum near 0.2 volume fraction, then increased monotonically with further increases in starch content. Sorption data for starch volume fractions of approximately 0.2 or less could be described by a constant value of D over the entire sorption curve. At higher starch contents, sorption curves deviated from linearity and could not be described by a single value of D. As a consequence of this behavior, materials with higher starch contents required less time to reach equilibrium despite having lower diffusion coefficients in the early stages of sorption. Various approaches to describe the concentration dependence of D will be discussed.