Polylactic Acid (PLA) is a bio-based plastic, offering an alternative to traditional petroleum-based materials. Derived from renewable resources, it aims to reduce reliance on fossil fuels and lessen the environmental impact of conventional plastics.
Understanding Polylactic Acid (PLA)
Polylactic acid is a thermoplastic polyester derived from fermented plant starches such as corn, sugarcane, cassava, and sugar beet pulp. Sugars from these plants ferment into lactic acid, which is then polymerized to form PLA.
PLA exhibits properties comparable to traditional plastics like polyethylene terephthalate (PET), polypropylene (PP), or polystyrene (PS). It is typically transparent or translucent and possesses good mechanical properties, including moderate strength and rigidity.
How PLA Biodegrades
PLA’s biodegradability requires specific conditions. It degrades through a two-step mechanism: hydrolysis and subsequent microbial digestion. Hydrolysis involves water breaking down polymer chains into smaller fragments, such as lactic acid monomers. These smaller molecules then become accessible for microorganisms to consume.
Microbial digestion involves specific microorganisms metabolizing these lactic acid products. This process generally occurs under industrial composting conditions, which provide high temperatures, controlled moisture levels, and active microbial populations. Temperatures typically need to be above 50-60°C (122-140°F), with relative humidity above 70%, and a pH between 5.5 and 8.0. Under these optimal conditions, PLA can biodegrade within weeks to a few months, breaking down into water, carbon dioxide, and biomass. In contrast, PLA does not readily biodegrade in typical home composting environments, landfills, or marine settings due to the absence of these specific conditions, with degradation potentially taking decades.
Everyday Uses of PLA
PLA has found a variety of applications across several industries. It is widely used in packaging, including food containers, bottles, and disposable cutlery. Its use extends to compostable bags and loose-fill packaging materials.
PLA is also a popular material for 3D printing filaments, valued for its ease of use and lower melting point compared to other options. In the medical field, PLA’s biocompatibility and ability to degrade safely within the human body make it suitable for applications such as dissolvable stitches, screws, pins, plates, and drug delivery systems. PLA fibers are being explored as alternatives to nonrenewable polyesters in textiles for clothing and home furnishings.
PLA’s Environmental Journey
PLA’s journey from production to disposal presents a nuanced environmental profile. Its origin from renewable plant resources, such as corn or sugarcane, reduces reliance on finite fossil fuels. From a “cradle-to-gate” perspective, which considers production up to the factory gate, PLA typically has a lower carbon footprint compared to many traditional plastics, with a reported reduction of approximately 75% in greenhouse gas emissions in some cases. The conversion stage can be energy-intensive, and optimizing this process can further reduce its carbon footprint.
Despite its renewable origin, the end-of-life management of PLA presents challenges. While it is industrially compostable, the widespread infrastructure for industrial composting facilities is not yet fully developed. If PLA products are not directed to these specialized facilities, they may end up in landfills or general waste streams, where they degrade very slowly, similar to conventional plastics, and can contribute to microplastic formation. Additionally, PLA cannot typically be recycled with traditional plastics as it can contaminate the recycling stream, requiring separate collection and processing. The agricultural practices involved in growing the raw materials for PLA can also have environmental impacts, such as contributing to marine and freshwater eutrophication, mainly due to fertilizer use.