Sustainable plastics refer to plastics whose production and use have a benign impact on the environment. This can be either produced from renewable sources, biodegradable, recyclable, or made by recycling used plastics.
Thus far the most effective approach to achieving sustainable plastics is biodegradable plastics produced from renewable sources. PHA is currently the most promising biodegradable plastic with potential as a sustainable alternative to its fossil-derived counterparts like polypropylene and polyethylene.
PHAs are polyesters by structure. The monomers of PHAs have the characteristic carboxylic acid end and the alcohol end. Being thermoplastic bioplastics, PHAs have the most desirable combination of properties for sustainable plastics. This makes them very promising substitutes for widely used fossil-based plastics like polypropylene. P3HB for example has properties similar to PP.
PHAs are essentially produced by nature with a little help from biotechnology. They are naturally produced as storage polymers in bacteria and other microorganisms like algae.
Over 125 different PHA monomers have been identified. These can exist either as homo polymers, co-polymers, or heteropolymers in various combinations within the polymer chain. They can be short medium or long-chain polymers. These properties also vary depending on the type of microorganism that produced the PHA. The properties of PHA such as crystallinity, elasticity, solubility, and viscosity vary with the arrangements of the monomers in the PHA polymer and the molecular weight of the PHA.
The biosynthetic pathways for PHA production vary from organism to organism and with different conditions. Bacillus megaterium for example will form polyhydroxybutyric acid (PHB) under starvation and in the absence of oxygen. Alcaligenes latus bacterium will accumulate around 80% of its weight in PHB under the right conditions. The photosynthesizing bacterium Rhospitillum rubrium synthesizes PHB through the reduction of acetyl-CoA from acetate.
PHAs are generally formed when two acetyl-CoA react by condensation followed by reduction into hydroxyalkanoate which then gets polymerized into PHAs. Many microorganisms have been identified as PHA producers and it is expected that more will be identified in the future. For example, over 15 microorganisms are known to produce PHB.
Properties like molecular weight vary with factors such as production conditions and type of microbes. for example, PHB has a molecular weight ranging between 1kDa to over 300kDa
PHA-based bioplastics can be blended in different ways to obtain specific desired properties. For example, a blend of 44 mol% PHB and 56 mol% PHV will achieve a plastic film with sufficient flexibility for a packaging film application. PHA can also be blended with other bioplastics and conventional plastics.
Figure 1. General structure of PHA Source
Figure 2. Structure of some PHAs. Source
One of the most important attributes of PHA as a sustainable plastic is biodegradability. PHAs are quite resistant to moisture therefore the biodegradation occurs more through enzymatic hydrolysis of the ester bonds rather than by simple hydrolytic biodegradation process. PHA-degrading microorganisms secrete the enzyme PHA depolymerase that breaks down the ester bonds.
The change in the morphology of PHAs during extraction and processing reduces the biodegradation rate. This comes at an advantage since the biodegradation needs to be slow enough to allow the bioplastic product to retain its integrity for a reasonable period.
The degradation rate also depends on the environment within which the bioplastic is placed. A 75-micron thick film of PHB placed in anaerobic conditions will biodegrade within a week. Meanwhile, when the same film is placed in soil, it takes up to 3 months to biodegrade. In the natural environment, PHA generally takes a minimum of 6 months to biodegrade.
Until PHAs the main limitation with most bio-based, biodegradable polymers is that they did not have the thermomechanical properties of being thermoplastics. PHAs are the only known thermoplastic biopolymers.
Another desirable feature of PHAs is that they can be produced from organic waste. Such that their production can be integrated into waste remediation and waste management systems.
PHB for example, is naturally produced in activated sludge alongside other polymers like polysaccharides. VEnvirotech’s primary source of raw material for PHA production is waste from food processing, meat processing, breweries, and agriculture.
Since one of the biggest challenges in widespread application is the cost of production, A lot of research effort has gone into exploring ways to bring down the cost of production. This has included the use of optimized bacteria strains to improve the yield per cell mass.
Downstream processing of bioplastics can also incur significant costs in production. The energy, materials, facilities, and highly skilled labor required to achieve high-quality PHAs make up a huge chunk of the production cost
With any product in the relatively early stage of commercialization, this is expected. As demand for sustainable plastics inevitably increases in coming years, this investment will consequently pay off to the advantage of the early adopters of sustainable plastics technologies.
Since the properties of PHA are linked to the monomer composition and the order of this composition within the polymer chain, there is potential for implementing artificial intelligence (AI) in the facilitation of optimized PHA production by bacteria.
For instance, we know that the glass transition temperature values of PHB homopolymers can be varied between -5 to 20oC when HV is included as a copolymer. The HV content can be controlled through the conditions provided to the PHA-producing bacteria. Using AI a large number of experiments can be performed in a shorter time than it would take humans, to determine the precise condition to achieve a specific glass transition temperature for PHB.
The innovation of using waste as substrate for PHA production has achieved a significant reduction in production cost as well as extended the advantages of PHA to waste management and remediation. Making it even more important as a sustainable plastic.
The main areas of advancement in PHA in recent years are:
While the microorganisms may do the main work of producing the bacteria, it is left to the human expert application of biotechnology to provide the right conditions for optimal yield and quality. There is also the matter of isolating the PHAs most efficiently and sustainably.
VEnvirotech has a team of highly skilled and experienced biotechnologists dedicated to the work production of PHA primarily from organic waste. With an archive of several highly efficient PHA-producing bacteria as well as state-of-the-art technology for the production and extraction of PHA, our team has developed high-quality PHA for diverse applications.
With a drive to make sustainable plastics a scalable reality, VEnvirotech has developed the VEBox, an automated pre-installed technology that facilitates on-site conversion of waste into raw materials for PHA production.
The VEBox is provided as a service to clients who seek a waste management and conversion solution for their establishments. The system is optimized for standardized processing of food waste, sewage sludge, and agri-food waste.
VEnvirotech also has a range of 8 different bioplastics formulations which include PHA-based bioplastics available for purchase. We also develop custom formulations to meet specific client needs.
The products and services VEnvirotech provides are key to moving the industry towards a more diverse implementation of sustainable plastics. We understand that part of the challenges of plastic waste is having alternatives that are well-suited for target applications. VEnvirotech provides consultation to help clients develop sustainable plastic solutions that match their desired specifications.
Contact VEnvirotech for further information on our sustainable plastics products and services.
