(306e) Life Cycle Assessment of Polypropylene (PP), Polylactic Acid (PLA), and PLA-Biochar Composite Plant Containers: Evaluating Production and End-of-Life Impact

The horticulture industry relies heavily on plastic plant containers, with over 4 billion used annually in the United States. Unfortunately, 98% of these containers end up in landfills. To address this environmental challenge, biodegradable alternatives like polylactic acid (PLA) containers have been developed. However, PLA’s high production impact and material density present challenges in competing with conventional polymers such as polypropylene (PP).

This study explores the integration of biochar, derived from downed timber, into PLA-based plant containers as a strategy to reduce environmental impact and enhance carbon sequestration. By incorporating biochar as a filler, these containers have the potential to store carbon in soil after disposal, improving their sustainability profile.

A life cycle assessment (LCA) was conducted to compare plant containers made from PP, PLA, and PLA+Biochar across production, and end-of-life stages. The study evaluates the environmental impact of varying biochar content (10–90 wt.%) in PLA composites to determine optimal formulations. The system boundary follows a cradle-to-grave approach, incorporating production, collection, and end-of-life scenarios based on U.S. waste management data. The functional unit is 1,000 plant containers, each with a 3-liter capacity. Life cycle inventory data were sourced from literature, ecoinvent, and USLCI-NREL databases, with environmental impacts assessed using the IMPACT 2002+ method, emphasizing land occupation during end-of-life.

Results indicate that PP containers have the lowest global warming potential (GWP) during production, at 75.54 kg CO₂-eq per functional unit, compared to 160.86 kg CO₂-eq for PLA containers. However, adding biochar to PLA significantly reduces its overall environmental footprint, with GWP decreasing as biochar content increases. End-of-life analysis highlights additional benefits of PLA+Biochar containers, particularly in composting scenarios where biochar contributes to long-term carbon sequestration in soil. The GWP for PP, PLA, and PLA+Biochar containers (based on respective waste management routes) is 16.25, 23.32, and ranges from -0.51 to -27.52 kg CO₂-eq per functional unit, depending on biochar content. The findings suggest that PLA+Biochar containers with 40 wt.% or more biochar could outperform PP containers in terms of overall life cycle impact, presenting a viable and sustainable alternative for horticultural applications.