Biodegradable plastic refers to a type of plastic material that can be broken down by natural biological processes, primarily through the action of microorganisms such as bacteria and fungi. This decomposition results in simpler substances like water, carbon dioxide, and biomass, without leaving harmful residues. Unlike traditional petroleum-based plastics, which persist in the environment for hundreds of years, biodegradable plastic is designed to degrade under specific environmental conditions, such as exposure to moisture, oxygen, and microbial activity.
The origins of biodegradable plastic trace back to the early days of plastic development in the 19th century. The first plastics were derived from natural materials, including cellulose from plant fibers and shellac from insect secretions, which were inherently biodegradable. For instance, in 1856, Alexander Parkes invented Parkesine, a cellulose-based material that was biodegradable but flammable. By the late 19th century, these bio-based plastics were largely replaced by synthetic polymers like Bakelite, invented in 1907 by Leo Baekeland, which were durable but non-biodegradable.
The modern resurgence of biodegradable plastic began in the mid-20th century amid growing environmental concerns over plastic waste. In the 1970s, researchers explored microbial production methods, leading to the discovery of polyhydroxyalkanoates (PHAs) by scientists like William Haynes in the 1920s, though practical synthesis advanced later. The 1980s saw the commercialization of starch-based biodegradables, and by the 1990s, companies like Novamont in Italy developed Mater-Bi, a starch-derived biodegradable plastic. A pivotal moment came in 2009 when studies highlighted the economic viability of biodegradable plastic only under regulatory mandates, such as Italy's 2011 law requiring biodegradable bags for certain uses.
Throughout the 21st century, innovations accelerated. In 2019, IIT Guwahati in India developed the country's first fully biodegradable plastic from agricultural waste. Recent advancements include barley-based "barley plastic" in 2024, which decomposes in two months, and bamboo-derived variants that biodegrade quickly while maintaining durability.
Biodegradable plastic can be categorized into bio-based and fossil-based types, though the former predominates for environmental benefits. Bio-based options include:
Fossil-based biodegradables, like polybutylene adipate terephthalate (PBAT), incorporate synthetic elements but are engineered to biodegrade. Not all bio-based plastics are biodegradable; for example, bio-polyethylene from sugarcane is durable like conventional plastic.
Production of biodegradable plastic varies by type. For PHAs, bacteria are fermented in bioreactors with carbon sources like glucose or waste oils, accumulating polymers as energy reserves. The cells are harvested, and polymers extracted via solvent or enzymatic methods. Starch-based plastics involve blending thermoplastic starch with additives under heat and pressure. PLA production starts with lactic acid fermentation from biomass, followed by polymerization. These processes generally require less energy than petroleum plastics but can be costlier without scale or subsidies.
Biodegradation of biodegradable plastic occurs through enzymatic hydrolysis by microbes, breaking polymer chains into monomers that are metabolized into CO2, water, and humus. The rate depends on conditions: industrial composting (58-60°C, high humidity) achieves 90% degradation in weeks, while soil or marine environments may take months to years. Standards like ASTM D6400 and EN 13432 certify products for 90% biodegradation within 180 days under controlled conditions. Myths persist; some "biodegradable" plastics, like oxo-degradable ones, fragment into microplastics rather than fully biodegrade.
Advantages include reduced environmental persistence, lower carbon footprints (e.g., PHAs emit 0.5-2 kg CO2/kg vs. 3-4 kg for PET), and compatibility with organic waste streams. They support circular economies by composting into fertilizer. Challenges encompass higher costs (2-10 times conventional plastics), limited scalability, and variable degradation rates. Public scrutiny arose from studies showing some bags intact after three years in soil or sea, emphasizing the need for certified products.
Global regulations promote biodegradable plastic. The European Union's Single-Use Plastics Directive (2019) mandates biodegradability for certain items. In the US, the Biodegradable Products Innovation Act (2018) funds research. Certifications from BPI and TUV Austria ensure compliance. Policies often tie viability to bans on non-biodegradables, as in Italy and parts of India.
Global production of biodegradable plastic reached about 2.1 million tons in 2020, projected to grow to 5.9 million by 2026 amid plastic pollution crises. Innovations like Midori Bio's biorecyclable plastics and hemp-based variants address marine waste. However, experts stress distinguishing true biodegradables from greenwashed products to avoid microplastic proliferation.
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