— PHA, or polyhydroxyalkanoates, not only represent an advanced class of biopolymers but also the future of sustainability in the polymer world. These extraordinary polymers are synthesized by bacterial microorganisms that use organic carbon sources (sugars, CO2, and even various types of waste!) to transform them into a vital source of energy and carbon. Just as animals store fat to survive during periods of hibernation, these non-pathogenic microorganisms accumulate PHA in their cells as an energy source for potential periods of carbon scarcity. This capability turns them into a vital and renewable source of biodegradable materials, with enormous potential in numerous industrial sectors.
– Polyhydroxyalkanoates (PHA) are produced through a biological synthesis process, not an industrial one, significantly differentiating them from traditional petroleum-based polymers. For this reason, when discussing this group, we can use the definition of "biopolymer" because PHAs are entirely derived from a natural and biological source, rather than from fossil sources.
– The production of PHA begins with fermentation. Microorganisms, under conditions of nutritional stress where carbon is abundant but other essential elements like nitrogen are limited, begin to synthesize PHA. They accumulate these polymers within their cells as an energy source. This process not only helps microorganisms manage metabolic imbalances but also provides an easily available energy source when external conditions become unfavorable.
– The secret of PHA lies in its completely natural and renewable origin. Unlike many synthetic materials derived from fossil sources, PHAs are a perfect example of a "biopolymer": they come entirely from biological sources. Polyhydroxyalkanoates (PHA) are a family of polymers synthesized by various bacterial microorganisms as an energy and carbon reserve.
– There are different types of PHA, all with similar chemical structures, and all produced by bacteria capable of absorbing and utilizing organic carbon sources (sugars, CO2, and even various types of waste!) and using them as energy to grow and accumulate this biopolymer, which then becomes a valuable resource for the bacteria. All these polymers are accumulated in the form of long carbon chains within specific cellular structures, ready to be used.
– Think of an animal storing fat for hibernation: similarly, non-pathogenic microorganisms capable of producing PHA use carbon sources to accumulate it within the bacterial cell as an energy source for potential periods of carbon scarcity.
Materials like PE and PLA tend to fragment rapidly, leading to the accumulation of micro- and nanoplastics. In contrast, PHAs follow a di erent path: they undergo biotically accelerated hydrolysis, transitioning from macro and mesoplastics to soluble products through depolymerization, eventually becoming nal products. Unlike PE and PLA, PHAs degrade gradually due to microorganisms, which break them down until they disappear.
Biodegradation rates depend on complex factors at each site.
External factors such as weather, aging, sunlight, soil burial, water, and temperature can significantly speed up the degradation of polymers. These conditions lead to thermal, chemical, mechanical, and photodegradation processes, which interact to accelerate biodegradation.
Chemical degradation often results from atmospheric pollutants, agrochemicals in the soil, oxygen, and water. Oxygen, in particular, plays a key role in abiotic chemical degradation by attacking covalent bonds and generating free radicals. The specific structure of a polymer influences this process—features like unsaturated bonds or branched chains can either hinder or promote degradation, leading to reactions like crosslinking or chain scission.
Photodegradation, triggered by light exposure, is another crucial abiotic factor in the biodegradation process, often proceeding through mechanisms like Norrish reactions. Additionally, if the polymer backbone contains hydrolyzable bonds such as esters, ethers, anhydrides, or amides, hydrolysis becomes another important abiotic degradation pathway.
Oxidative and hydrolytic degradation are further influenced by the polymer's amorphous and crystalline regions. Amorphous areas tend to facilitate degradation by allowing better oxygen and water diffusion, while crystalline domains can restrict this diffusion, thereby slowing down chemical degradation.
Environmental conditions, including water activity, pH, temperature, and time, need to be managed to optimize hydrolytic degradation. For example, polymers like PLA, PCL, and PPC degrade very slowly in neutral conditions but break down much faster in acidic or basic environments. This process often involves the hydrolysis of ester groups, resulting in the release of low molecular weight molecules and consequent polymer degradation.
Thus, biodegradability claims are approximate and must be validated by lab testing. Real-world biodegradation may vary with factors such as plastic size and polymer grade. Testing is often done after milling, which demonstrates the material's biodegradability, though actual rates may differ in natural settings. (source Nova-Institut GmbH).
Unlike traditional plastics and the leading bioplastics on the market, PHAs biodegrade without releasing microplastics in all environments, including soil, freshwater, saltwater, and both organic and industrial compost. The ability to fully biodegrade eliminates the environmental persistence of plastics, reducing pollution and improving ecosystem health.
Test conditions, certification schemes, and standards are essential for evaluating the biodegradability of materials. These parameters define requirements across various environments, such as marine and freshwater, soil, and compost. Certifications like those from TÜV Austria and DIN CERTCO verify that materials meet international standards such as ASTM, ISO, and EN.
Marine Environment
Fresh Water
Soil
Home Composting
Landfill
Anaerobic Digestion
Industrial Composting
