The Complex Story of Biobased Plastics in LCA

Author: Nowell Stoddard, Junior Sustainability Analyst

Biobased plastics are often promoted as a promising solution for reducing greenhouse gas (GHG) emissions – especially in packaging, which accounted for over half of global plastic waste in 2015. These materials do offer real environmental advantages, but as with most things in life cycle assessment (LCA), the reality is more nuanced. For practitioners, the challenge lies in capturing that full complexity when modeling biobased systems.

Carbon Benefits and Their Limits

Biobased plastics such as polylactide (PLA) can outperform fossil-based polymers like PET or polypropylene (PP) in global warming potential (GWP). The key factor is biogenic carbon – the carbon stored in biomass feedstocks (like corn, sugarcane, or other plants) that absorb CO? during growth. In most LCAs, this carbon uptake is treated as “burden-free,” as the carbon released at end-of-life is compensated for by the carbon uptake during the plant's growth. This mechanism alone can make a bioplastic appear significantly lower in GWP than its fossil counterpart.

Moreover, focusing only on carbon can be misleading. A full life cycle view reveals additional impacts that may counterbalance those climate benefits.

Beyond Carbon: Water, Land, and Nutrients

Producing biomass for biobased plastics often requires fertilizer, irrigation, and land conversion – each carrying its own environmental burden. These agricultural inputs can increase eutrophication, acidification, and water use impacts compared to conventional plastics. In some cases, converting natural ecosystems to cropland for feedstock cultivation can even release more carbon than the bioplastic saves.

That’s why it’s critical to avoid burden shifting – reducing one impact (like carbon) at the expense of others. A well-rounded LCA should include multiple impact categories to reveal trade-offs, not conceal them.

Energy and Manufacturing

The production process for bioplastics also matters. Fermentation and pretreatment steps required to produce PLA and similar materials can be more energy-intensive than the polymerization of fossil-based plastics. The energy mix – renewable vs. fossil-based – can determine whether the climate advantage of a bioplastic holds up or disappears.

End-of-Life Pathways

End-of-life (EoL) scenarios for bioplastics vary widely. Some can be recycled, composted, or digested anaerobically, but in reality, many still end up landfilled or incinerated –similar to traditional plastics. Even so, due to their biogenic carbon content, bioplastics often retain a lower GWP than fossil-based materials in these scenarios. Still, accurate modeling requires regionally specific assumptions about actual disposal practices.

Improving the Sustainability Profile

There are ways to mitigate many of these trade-offs. Using agricultural residues or waste feedstocks avoids land use change impacts, and sourcing renewable electricity for fermentation and polymerization can significantly improve results. Integrating heat recovery or circular production systems further strengthens the environmental performance of bioplastics.

What About Microplastics?

One area still underexplored in LCA is the microplastic impact of plastics. Their generation and persistence affect human and ecosystem health, yet these effects are rarely quantified. As methods evolve, incorporating such impacts will be key to a more holistic assessment of both fossil and biobased materials.

Key Takeaways for Practitioners

“Biobased” does not automatically mean “sustainable.”

Robust LCAs of biobased plastics should:

• Include multiple impact categories beyond carbon.
• Clearly document allocation choices and data assumptions.
• Reflect realistic end-of-life scenarios.
• Consider energy sources and feedstock types.

Only by capturing the full environmental profile can we ensure that biobased materials genuinely advance a more sustainable future – rather than simply shifting burdens elsewhere.

Sources:

Bioplastic production in terms of life cycle assessment: A state-of-the-art review. (2023). In Environmental Science and Ecotechnology [Journal-article]. https://doi.org/10.1016/j.ese.2023.100254

Rikhter, P., Dinc, I., Zhang, Y., Jiang, T., Miyashiro, B., Walsh, S., Wang, R., Dinh, Y., Suh, S., & VitalMetrics. (2022b). Life Cycle Environmental Impacts of Plastics: A review. In NIST GCR 22-032. U.S. Department of Commerce. https://doi.org/10.6028/NIST.GCR.22-032

Senila, L., Kovacs, E., Resz, M., Senila, M., Becze, A., & Roman, C. (2024). Life Cycle Assessment (LCA) of Bioplastics Production from Lignocellulosic Waste (Study Case: PLA and PHB). Polymers, 16(23), 3330. https://doi.org/10.3390/polym16233330