Evaluation and Classification of Bioplastic Plant Containers

More than 750,000 metric tons of petroleum-based plastics are consumed annually by the greenhouse and nursery industries in the United States for single-use plant containers.  This extensive use of petroleum-based materials is an obstacle to sustainability because they are non-renewable, non-biodegradable, and about 98% of used containers are disposed in landfills.  Bioplastics have potential for use in plant containers that fulfill the functional advantages of conventional plastic but are made of renewable materials that have much lower environmental footprints.  In 2012 and 2013, we created 46 novel biocontainers (35 injection-molded bioplastics or biocomposites and 11 bioplastic-coated fiber containers).  We evaluated container materials for cost, processability, and biodegradability in soil, and evaluated the prototype containers, along with other commercially available biocontainers, in greenhouse, nursery, and landscape trials.  Greenhouse and nursery evaluations demonstrated that many of the injection-molded bioplastics function as well or better than petroleum plastics for crop containers.  Soy-based bioplastic containers released plant-available nutrients and improved root-system morphology during crop production.  Adding bio-based fibers to form injection-molded biocomposite containers reduced the cost of containers and improved the processability, function, and degradation of the bioplastic materials.  Coating fiber containers with bioplastics improved water-use efficiency during crop production and resulted in containers similar to those made from petroleum-based plastics in durability and function.  Many of the bioplastics and biocomposites degraded over 50% during two years in the landscape, suggesting that containers made of these materials could end their life cycles as degraded organic matter in soil, instead of entering the solid waste stream.  Based on results of these trials, we classified the biocontainers into three categories: 1) containers biodegradable in soil within one to two years; 2) containers not degradable in soil, but degradable by composting; and 3) exceptional or durable containers that can be recycled, or will be carbon-negative if landfilled.  Biocontainers from any of these categories constitute an improvement in sustainability with regard to the container material.  Containers from category 1 have potential to reduce or eliminate the problems related to disposal of used containers, and containers from category 3 could provide an improvement in sustainability while providing nearly identical function to that of petroleum-based plastic and requiring little or no change in cultural practices.  Soy-based containers from categories 1 and 2 provide additional functions beyond those of petroleum plastic by supplying intrinsic fertilizer and improving root systems.