How Polylactic Acid Helps Combat Microplastic Pollution

Summary

Sources

packaging-gateway.combioplasticsmagazine.com

Polylactic Acid, commonly known as PLA, stands out in the realm of biopolymers due to its origin from fermented plant sugars and its wide application in packaging products. As a biobased polymer, PLA presents a unique property that makes it inherently different from many traditional plastics—it is hydrophilic. This characteristic implies that PLA has an affinity for water, which plays a crucial role in its environmental impact concerning the formation of microplastics. Hydrolysis, an abiotic process that occurs in the presence of moisture, affects PLA significantly. This process targets the ester bonds within the PLA polymer, leading to the gradual breakdown of its polymer chains. Over time, and with continuous exposure to moisture, the molecular weight and size of PLA fragments decrease progressively. This transition moves them from the micrometer range down to the nanometer scale, and eventually, the polymer chains become so short that the material transforms into soluble substances. These substances, which include oligomers and lactic acid monomers, are non-toxic and can be biodegraded by microorganisms into biomass, carbon dioxide, and water. The inherent properties of PLA and the hydrolysis process it undergoes ensure that if PLA enters the environment, it does not contribute to the long-term microplastic pollution problem. This is in stark contrast to non-biodegradable polymers such as High-Density Polyethylene (HDPE), which persist and accumulate in the environment as nano or microplastics. The hydrolyzable and biodegradable nature of PLA means that degradation continues as long as moisture is present, preventing the long-term environmental accumulation. Furthermore, PLA is recognized for its safety in various applications. It is classified as Generally Recognized as Safe by the US Food and Drug Administration and the European Union for food contact, and certain grades of PLA have been used in medical applications such as sutures and drug administration substrates. After their use, these PLA materials are absorbed and degraded by the human body, showcasing their compatibility and safety. The degradation rate of PLA, however, is dependent on several factors including the crystallinity of the polymer, environmental conditions like temperature and water availability, and the presence of microorganisms. In industrial composting facilities, conditions such as temperature and moisture are optimized to accelerate the hydrolysis and subsequent biodegradation of PLA. In natural environments, complete degradation times can vary widely, generally depending on climatic conditions and the presence of water. In summary, PLA offers a promising alternative to conventional plastics with its ability to degrade fully in the environment through hydrolysis, preventing the formation of persistent microplastics. This attribute, coupled with its non-toxic nature and compliance with global safety standards for food contact and medical use, positions PLA as an environmentally friendly material with diverse applications. As previously mentioned, the hydrophilic nature of PLA plays a pivotal role in its environmental degradation process, specifically through hydrolysis. This process initiates when PLA is exposed to moisture, leading to the cleavage of its ester bonds. This interaction with water is crucial as it triggers the systematic breakdown of PLAs polymer chains. During hydrolysis, the long polymer chains of PLA are broken down into smaller and smaller fragments. These fragments transition from larger molecular structures through the micrometer scale and further into the nanometer range. As the process progresses, these chains become so short that they transform into oligomers and eventually into monomers like lactic acid, which are completely soluble in water. The solubility of these substances is significant because it marks the phase where PLA ceases to exist as a plastic material and instead becomes a part of the natural biochemical cycles. These soluble forms are then readily metabolized by microorganisms in the environment, converting them into biomass, carbon dioxide, and water through the process of biodegradation. This complete breakdown is possible due to the inherent properties of PLA and the environmental conditions that facilitate these reactions. Contrasting sharply with PLAs hydrolyzable nature are non-biodegradable polymers such as High-Density Polyethylene (HDPE). HDPE and similar plastics do not possess bonds that are susceptible to hydrolysis. As a result, they are resistant to breaking down in the presence of moisture. Without the ability to hydrolyze, these plastics do not degrade into smaller molecules that can be easily assimilated by microorganisms. Instead, they break down physically into smaller pieces through processes such as photodegradation or mechanical wear, eventually turning into microplastics and nanoplastics. These particles persist in the environment, accumulating over time and contributing to the growing problem of plastic pollution in terrestrial and aquatic ecosystems. The stark difference in how PLA and non-biodegradable plastics like HDPE interact with the environment highlights the importance of choosing materials that are not only effective in their application but also sustainable in their life cycle. The ability of PLA to undergo complete hydrolysis and biodegradation addresses the critical environmental issue of plastic pollution, offering a pathway to reduce the accumulation of persistent microplastics and supporting overall ecosystem health. This contrast underlines the need for continued research and adoption of biodegradable materials like PLA, which align with environmental conservation goals while still providing the functional benefits required in various industries. Building upon its environmental benefits, PLA also demonstrates significant advantages in terms of safety and regulatory compliance, particularly in applications that involve direct contact with humans. Polylactic Acid is classified by the US Food and Drug Administration and the European Union as Generally Recognized as Safe for use in food contact materials. This designation underscores its non-toxicity, making it a preferred material for food packaging solutions. These global standards ensure that products made from or with PLA are safe for widespread use, adhering to rigorous health and safety regulations. In addition to its use in food packaging, PLAs biocompatibility extends to the medical field. It has been successfully employed in various medical applications, including sutures, tissue scaffolds, and substrates for drug administration. These applications take advantage of PLAs ability to safely degrade within the body. After fulfilling their function, PLA-based materials are absorbed and broken down by the human body, converting them into harmless substances. This bioresorbable characteristic of PLA is particularly valuable in medical treatments, reducing the need for surgical removal of implants and minimizing long-term foreign body risks. The safety profile of PLA is complemented by its compliance with longstanding legislation concerning food contact materials. Many grades of PLA have been extensively tested and approved for contact with food items, ensuring that they do not leach harmful substances into food products during their intended use. This compliance is crucial for consumer safety and has facilitated the adoption of PLA in various food-related applications, from disposable cutlery and plates to packaging films and containers. Furthermore, the specific grades of PLA used in medical applications are subjected to additional scrutiny to ensure they meet the stringent sterility and purity requirements necessary for medical use. These standards are in place to protect patients and ensure that the materials perform as expected without causing adverse effects. Overall, the non-toxic nature of PLA, combined with its compliance with international safety standards for both food packaging and medical applications, highlights its suitability as a material that meets the critical needs of these industries while also supporting environmental sustainability goals. This dual benefit of safety and eco-friendliness makes PLA an exemplary material in the ongoing effort to balance human health, product functionality, and environmental conservation.