Degradation and Nitrogen Release of Zein-based Bioplastic Containers

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Abstract Environmental problems caused by petroleum-based plastics have led to interest in alternatives made from biodegradable polymers (bioplastics), but little effort has been made to evaluate horticultural containers made from these materials. We hypothesized the stability and longevity of containers made from polymers of the hydrophobic corn (Zea mays L.) protein, zein, is sufficient to make commercial use of zein-based containers feasible. Our objectives were to fabricate containers from zein, to determine longevity under conditions typical of horticultural production, and to identify limitations of the containers that might be overcome by further research. Zein-based, bioplastic containers of two wall thicknesses were filled with either a peat-based, soilless potting substrate or with coarse perlite and irrigated every 2 or 4 days. After 10 weeks, weight loss of containers was determined as a measure of their degradation. Containers filled previously with soilless substrate lost nearly twice as much weight as containers filled with perlite, and irrigation every 4 days led to greater weight loss than irrigation every 2 days. The containers released nitrogen (N) as they degraded; as much as 208 mg N·kg−1 was present in leachate after irrigation with water. In a second experiment, to simulate the potential practice of installing plants in the landscape without container removal, bioplastic containers of two sidewall thicknesses were filled with the soilless potting substrate and planted in either drained or saturated field soil, and the two substrates were either sterilized (autoclaved) or nonsterilized. After 12 weeks, containers in drained soils had greater weight loss than containers in saturated soils regardless of substrate sterilization treatment. Zein-based, bioplastic containers appear suitable for crops having production cycles of ≤ 3 months, and the containers will decompose and release N if installed with plants in the landscape. Further research is needed to increase the longevity of zein-based containers for crops with longer production cycles. In addition, the influence of containers made from zein on plant growth needs to be determined, and potential effects of degrading containers installed in the landscape on the establishment of transplants warrant investigation.