Life Cycle Assessment of Sweet Potato Waste-Derived Biopolymer Film

Introduction: Petroleum-based packaging contributes to greenhouse gas emissions and persistent plastic pollution, motivating circular alternatives from agricultural residues. Sweet potato processing waste, including peels, pulp, and trimmings, is rich in starch and fiber but remains underutilized. Based on USDA production data and literature-based processing loss/yield assumptions, the U.S. waste stream is estimated at ~0.5 × 10⁶ t/year, corresponding to an indicative production potential of ~6 × 10⁸ m²/year (~3 × 10⁴ t/year) of bio-based film at the modeled reference flow. However, the environmental implications of this valorization pathway remain insufficiently quantified.

Methods: An attributional cradle-to-gate life cycle assessment was developed in openLCA 2.6 using ecoinvent 3.10 and the TRACI v2.1 midpoint method. The functional unit was 1 m² of bio-based film (~0.050 kg). The system included feedstock collection and transport, washing, starch extraction and drying, cellulose nanocrystal production, film formulation, casting, and residue/wastewater treatment. Sweet potato waste was modeled using a zero-burden cutoff approach. Inventory data were compiled from the literature, preliminary process assumptions and lab measurements; therefore, the results are interpreted as screening-level estimates. Uncertainty was addressed through scenario-based sensitivity analysis of foreground electricity use and transport distance.

Results: The baseline climate change impact was 0.423 kg CO₂-eq/m². Starch extraction (29.4%), cellulose nanocrystal production (20.1%), and washing/slurry preparation (20.0%) were the dominant foreground hotspots. Increasing foreground electricity by 50% increased climate change impacts by 40.2%, whereas increasing feedstock transport from 20 to 100 km increased impacts by 4.5%.

Conclusions: Results suggest that sweet potato waste-derived film is a promising circular packaging pathway, but energy-intensive extraction and nanocellulose processing must be improved. Ongoing work will refine primary inventory data, quantify uncertainty, validate functional equivalence, and benchmark results against conventional LDPE/LLDPE packaging films.