Performance and Compostability of Improved Horticulture Containers Made of Bioplastics and Biocomposites

Horticulture containers made of bioplastics and biocomposites can perform as well as petroleum-plastic containers during crop production, and a few of these novel biocontainers can decompose in soil after use, but little information is available on the compostability of these containers in home composting systems.  In 2015, we evaluated the performance and compostability of seven improved commercial-grade biocontainers (11.4-cm top dia.) that were injection molded on standard manufacturing equipment, and compared their performance and compostability with those of a biopolymer-coated paper-fiber container and a petroleum-plastic control container of the same size.  Material formulations for injection-molded biocontainers were made with base resins of polylactic acid (PLA) or polyhydroxyalkanoate (PHA) and were combined with fillers of soy protein, distillers dry grains with solubles (DDGS), lignin, BioRes, or selected combinations of these fillers.  In our 10-week greenhouse trials with Gerbera daisy (Gerbera jamesonii Bolus ex. Hook f.), plants grown in the injection-molded biocontainers were of equal quality to those grown in petroleum-based control containers.  At the end of the 10-week trial, three of the biocontainer types [PLA-Lignin (90/10), PHA-DDGS (80/20), and Recycled PLA (Resin only)] received appearance ratings that were equal to those of the petroleum-based control, and the appearance of all biocontainers in the trial was acceptable for the plant-container units to be sold commercially.  Instron tests of vertical and horizontal crush strength of containers after their use in the greenhouse for 10 weeks showed that all biocontainers in the trial exceeded the strength of the petroleum-plastic control.  In our experiment evaluating the compostability of container materials in home compost systems, four of the injection-molded container materials [PLA-Soy-BioRes (50/30/20), PLA-Soy (60/40), PHA-DDGS (80/20), and PLA-Soy-BioRes (55/35/10)] decomposed completely during the 12-week compost cycle and another [PLA-BioRes (80/20)] decomposed 96%.  The coated paper-fiber container decomposed the least of the biocontainers (28%), and the petroleum-based control showed no decomposition.  We conclude that decomposition in home compost can be a viable end-of-life option for many of these improved bioplastic container formulations.  All five of the highly compostable biocontainers in our trial were sufficiently durable for production of short- and medium-cycle greenhouse crops, and all five were used to produce gerbera of equal quality to those grown in standard petroleum-plastic containers.  The use of compostable injection-molded biocontainers could provide a substantial improvement in sustainability for growers and consumers who utilize composting in their cultural practices.