PERCOLATION EFFECTS IN DEGRADABLE POLYETHYLENE-STARCH BLENDS

The accessibility of starch in polyethylene starch blends was investigated by computer simulation, percolation theory, and acid hydrolysis experiments. The object of this work was to model the bilateral invasion of microbes in polyethylene-starch blends as a function of starch concentration (p), and thickness of the material. It was found that computer simulations in three dimensions were in agreement with both percolation theory and the acid digestion experiments. In computer simulation the accessibility is highly dependent on the percolation threshold concentration (p(c)), which is 31.17%. Similarly, the accessibility of starch is highly dependent on an apparent percolation threshold near 30% by volume or approximately 40% by weight of starch. At p < p(c) a small amount of starch is removed from the surfaces only, but at p > p(c) connected pathways existing throughout the bulk of the material facilitate large amounts of starch extraction. The sharpness of the transition at p(c) increases with the ratio of sample thickness to starch particle size. The results of this work have application to conduction and reacting systems where one component is dispersed in a matrix of the other.