| Starch fillers have been added to PE to create low-cost biodegradable plastics for use in yard waste collection bags for municipal composting programs. However, starch-filled plastic films litter composting facilities years after they have been composted along with yard wastes. Based on the need for alternative types of economical biodegradable materials, the aim of this study was to incorporate soybean protein fillers in plastic films, and to compare their biodegradability to unfilled and starch-filled films.; Soybean proteins were denatured with 8M urea, mixed with 50/50 polyethylene (PE)/poly(ethylene-co-acrylic acid)(EAA), and extruded to form films. The mechanical properties and biodegradability of the experimental 11% urea/6% protein/filled 50/50 PE/EAA films were compared to the properties of three conventional films including 100% PE, 50/50 PE/EAA, and 6% starch-filled 50/50 PE/EAA films. The urea/protein fillers decreased the tensile strength and increased the elongation. In particular, the plasticizing action of urea decreased both the strength and elongation of the 11% urea/6% protein-filled 50/50 PE/EAA films.; In the biodegradability experiments, the four film types were mixed into compost media from a municipal composting project, and incubated for 45 days as prescribed in ASTM D 5338-91. During the incubation period, the CO{dollar}sb2{dollar} (g) production was monitored by gas chromatography, and after incubation the changes in the tensile strength and elongation of the films were determined. The changes in both the strength and elongation of the PE, 50/50 PE/EAA, and 6% starch-filled 50/50 PE/EAA films were relatively small. In contrast, there were large strength increases and elongation losses for the 11% urea/6% protein-filled 50/50 PE/EAA films. These changes probably resulted from water in the compost vessels leaching the urea plasticizer out of the films.; In the CO{dollar}sb2{dollar} respiration tests insignificant amounts (g) of CO{dollar}sb2{dollar} were liberated by the biodegradation of PE, 50/50 PE/EAA, and 6% starch-filled 50/50 PE/EAA films. In contrast, a significant amount (g) of CO{dollar}sb2{dollar} was produced during the biodegradation of the 11% urea/6% protein-filled 50/50 PE/EAA films. However, it is unclear whether biodegradation of the urea and/or protein filler fostered the CO{dollar}sb2{dollar} production. |
