Biodegradation describes a process wherein a material decomposes over time as a result of the biological activity of microorganisms. Biodegradable materials are capable of being broken down (decomposed) by the action of microorganisms (bacteria, fungi, protozoans, etc.) Biodegradable substances can include organic and natural materials as well as manufactured products based on natural materials, such as paper, wood, starch, PHA and other natural polymers.
Biodegradable materials are generally organic, natural or bio-based, and that when broken down, provides nutrient for microorganisms. These materials can be degraded aerobically (with oxygen) or anaerobically (without oxygen). During the process of biodegradation, microorganisms (primarily fungi and bacteria) decompose organic materials by converting them into metabolic energy needed by the microorganisms. Carbon dioxide and water are the two primary products that result from biodegradation, and the amounts and ratios of water and carbon dioxide generated during biodegradation is specific to the microorganism and degradation environment and not by the biomass consumed.
PHA, like other biological polymers such as cellulose and starch, is readily biodegradable. During biodegradation, PHA is consumed by the microorganisms, converted to carbon dioxide, water and other components used by the microorganism.
Although often used synonymously, biodegradable and compostable are distinct in meaning. While biodegradable essentially means that materials can be consumed by microorganisms, the term compostable indicates that the material will only break down under specific composting conditions including temperature, moisture, oxygen and time. Although essentially any biodegradable material can be composted not all compostable materials are biodegradable. It is important to discriminate between these two processes and the materials that can be degraded by each. Biodegradable materials can be degraded in the environment including fresh water and marine environments. Compostable materials may only be able to degrade in specific soil-based composting conditions.
Although bioplastics are made from renewable resources, not all bioplastics are biodegradable. While there has been a few definitions of a bioplastic over the last few decades, the currently most widely accepted definition is that bioplastics are plastics derived from renewable resources.
Bioplastics are further categorized into biodegradable and non-biodegradable plastics.
Some non-biodegradable bioplastics can be degraded by heat, exposure to UV light, and/or by mechanical stress.
Degradable Plastic: a plastic designed to undergo a significant change in its chemical structure under specific environmental conditions resulting in a loss of some properties that may vary as measured by standard test methods appropriate to the plastic and the application in a period of time that determines its classification.
Some non-biodegradable bioplastics are only compostable in special facilities.
Most compostable cups are made from PLA (Polylactic Acid) plastic. For PLA to biodegrade, you must break up the polymer by adding water to it (a process known as hydrolyzing). Heat and moisture are required for hydrolyzing to occur.
If a PLA cup or fork is thrown in the trash, where it will not be exposed to the heat and moisture required to trigger biodegradation, it will sit there for decades, much like an ordinary plastic cup or fork.
PHA (Polyhydroxyalkanoates) is the only biodegradable plastic today; it can be made into different plastics with multifaceted physical properties and many applications.
Polyhydroxyalkanoates are natural aliphatic polyesters, synthesized through the fermentation of sugar and lipids (glucose, sucrose, vegetable oils) by a wide variety of bacteria, as an intercellular carbon and energy reserve, when the cells grow in stressful conditions.
They can combine more than 150 monomers, thus obtaining materials with various characteristics. PHAs are biodegradable, and biodegradation usually takes place with enzymes.
They can change mechanical and biological compatibility by mixing, altering the surface or combining PHAs with other polymers, enzymes or inorganic materials, which allows them a wider range of uses.
PHA polymers are thermoplastics and can be cultivated/treated with equipment for processing conventional plastics thereby enhancing the physical properties of these plastics. One such application is as hardener in cosmetic, hygiene, and packaging products.