1a. Objectives (from AD-416):
Characterize the amounts and rate of compostability and biodegradation of poultry feather keratin-based polymer composite formulations in soils, potting soils, composts, and composting processes using ASTM 6400, ASTM 5338, ASTM D790 protocols and particle-size reduction along with spectroscopy/microscopy protocols developed by ARS for this project; determine the short and long-term growth response of selected horticultural plants grown in biodegradable pots; and provide USDA with data generated from controlled environment and field studies, including at least quarterly, a status report and completed milestones.
1b. Approach (from AD-416):
Determine the biodegradation of the subject keratin-based thermoplastic formulations under natural soil, soil with compost amendment, and during thermophilic and backyard composting conditions over short (1-3 months) and long (6-12 month) periods using ASTM 6400, ASTM 5338, ASTM D790, particle size reduction, and advanced microscopy and Raman spectroscopy; determine the short and long-term growth response of selected horticultural plants grown in biodegradable pots; the biopolymeric items to be tested will be provided by the Horticultural Research Institute, Washington, D.C.
3. Progress Report:
A biodegradable alternative to plastic horticultural pots is being sought to reduce the landfilling of 1.8 trillion individual horticultural nursery pots that are discarded after use. Eight keratin-based polymers derived from chicken feathers were tested to determine their biodegradability. The keratin-based polymer resin formulated materials were produced and molded by the extrusion process. They were tested and compared to polyethylene, polyhydroxyalkanoate, and wood for rate of biodegradation in soil and compost-amended soil in greenhouse tests. Two formulations were identified with potential for biodegradation in 120 days in moist soils. Based on these results, formulations were modified and new standard coupons were prepared of keratin-based polymer resin, produced and molded by the extrusion process, for use in ASTM biodegradation tests with composting. A gas pressure monitoring system for conducting the ASTM standard method for up to 180 days at 58 C, as required by the ASTM protocol for determining compost biodegradability for the formulations, was developed and constructed to allow for continuous respiratory measurement. Conversion of the biopolymers to plant available nutrients is being evaluated by Raman spectroscopy. Decomposition of the keratin-based formulations that were provided by a contractor and included polyethylene and polypropylene are so slow that they are not significantly different from the background compost in the 180 day incubations. Microscopically the test materials reveal a limited evidence of microbial degradation of the polymers, in comparison to the wood-based controls. A horticultural sod-mesh was also prepared using a keratin-based biopolymer formulation by a collaborating contractor. The mass loss of multiple replicates of equivalent size samples of this mesh was determined at 45, 90, 180, and 240 days after exposure to field soils amended with compost and with a grass cover crop. The particular formulation provided did not lose mass or show signs of degradation during this period. Results will also be obtained at 365 days of exposure. Results from all these studies show that formulations incorporating polyethylene and polypropylene have limited biodegradability in short-term exposures to soil and compost-amended soil. Formulations with polyhydroxyalkanoate show evidence of very slow biological decomposition. Additional formulations with wood-fiber, other biodegradable polymers, or modified polyhydroyalkanoates and keratin polymer will need to be prepared and tested to develop horticultural pots and containers with a range of ‘fit-for-purpose’ properties customized to specific horticultural conditions and applications. This project will be extended to do testing on longer incubations of these materials.