PHA is primarily bio-based. Even better it can be produced from organic waste and implemented within waste management and water treatment systems.
PHA is based on the application of biotechnology in optimizing natural processes that occur in microorganisms. They can be produced with zero to minimal disturbances to the natural environment.
PHAs are produced as storage polymers in the microbes for energy and carbon. Industrial production of PHAs requires the cultivation of the microbes under controlled conditions which optimizes PHA production. The microbes produce PHAs under simulated nutrient starvation and excess carbon. Other factors like temperature, PH, and the presence of macronutrients and trace metals affect the quantity and quality of PHA produced.
PHB is the most widely produced form of PHA. It is also the simplest form of PHA. The production process can be controlled to yield specific types of PHA with desirable properties. For example, steering the process towards the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) over PHB will result in a tougher and more elastic PHA.
On the other hand, PP requires extraction processes that inevitably destroy natural habitats and involve the depletion of fossil resources. There is also the existing risk of disasters such as oil spills and the emission of soot into the atmosphere.
The global production rate of conventional fossil-derived plastics is still far higher than that of bioplastics. Polypropylene has the second highest production rate globally next to polyethylene. In 2022 polypropylene’s global market volume was estimated at 79.01 million metric tonnes. With a gross annual growth rate of 3.6% projected for 2023 to 2030.
Although PHA production volume is much lower with bioplastics making up less than 1% of global plastic production. Government policies and increased efforts to regulate single-use plastics and push for more sustainable plastics have resulted in increased demand for biodegradable plastics with PHA leading.
The global market value of PHA as of 2022 was estimated at 81 million USD. This is projected to rise to 167 million USD by the year 2027. PHA is projected to be the leading commodity bioplastic in the coming years.
Polypropylene has been long favored for its excellent strength, low surface energy, low permeability to gases and liquids, and ease of processing compared to other plastics. For this reason, it has found applications in films, containers, woven and nonwoven bags and sacks, geotextiles, and other applications.
PHA’s appeal is in large part because it combines some of these physical attributes of polypropylene with biodegradability and biocompatibility. This extends its application into areas where polypropylene is not applicable. An example of such is in tissue engineering and scaffolds.
The elongation at break, melting point (Tm), glass transition temperature (Tg), tensile strength, and young modulus of 3 different PHAs and PP are compared in Table 1. Here we see that the properties of PHAs can be varied by varying the composition of the PHA.
Polypropylene is relatively stiffer compared to another commodity plastic; polyethylene. While PHB is much stiffer, other forms of PHAs have higher elasticity that even exceeds that of polypropylene (Table 1).
Table 1 also shows that PHA matches some of the properties of PP such as elasticity, quantified by elongation at break. The melting point of the PHAs can be lower or higher than that of PP. The thermal processing of PHA can be achieved using conventional plastic processing methods.
Table 1. Comparing properties of three PHAs with PP
| Polymer | Tg (oC) | Tm(oC) | Elongation at break (%) | Tensile strength (MPa) | Young’s Modulus (GPa) |
| P(3HB-co-20 mol%3HV) | -1 | 145 | 50 | 20 | 0.8 |
| PHB | 4 | 180 | 5 | 40 | 3.5 |
| P(3HB-co-6 mol$3HA) | -8 | 133 | 680 | 17 | 0.2 |
| PP | -10 | 176 | 400 | 38 | 1.7 |
Assessing the environmental impact of PHA production includes the process of collection and treatment of the raw materials down to the carbon released during the degradation of the bioplastics.
The environmental impact factors that have been considered for PHA production include global warming potential, eutrophication, acidification, and photochemical smog. Direct comparisons of these values for PHA and polypropylene are not made here since these values vary significantly from study to study and the units used also often vary.
PHA produced from corn grain has a global warming potential of 1.6 – 4.1 kg-CO2 eq/ Kg. The fermentation and recovery processes are the main contributors to the environmental impact of PHA production. PHB produced from material recovery facilities had a global warming potential of 3.4 to 5 CO2 Eq/Kg.
The use of waste as feedstock significantly reduces the environmental impact of PHAs since the contribution of the cultivation and processing part of the production of their raw materials is eliminated.
Global warming potential of 1.58 kgCO2eq and fossil fuel depletion of 1.722kg Oil eq have been reported for polypropylene production. However, the environmental assessment depends on other factors such as eutrophication, land use change, water consumption, petrochemical oxidant formation, and fossil resource depletion.
Production of polypropylene pellets exerts a fossil resource depletion of 1.7222 kg oil eq per kg of polypropylene pellets produced while fossil resource depletion for PHA production can be zero if no fossil fuel was used in running the facilities used in the production.
The greenhouse gas emissions during their biodegradation can be mitigated by having the right systems for carbon or methane capture from aerobic or anaerobic biodegradation.
PHA is a bio-based biodegradable plastic. The biodegradation rate depends on the formulation of the PHA and the type of processing it has gone through. For example, if the PHA is in the form of a film, is blended with other polymers and additives.
Where bioplastics like PLA require special industrial composters for their biodegradation, the Biodegradation of neat PHAs typically will occur in natural environments in household composters.
Since PHA is biosynthesized by microorganisms as a storage polymer. These microbes also produce the enzymes required to break down, hence biodegrading PHA. Despite some new findings of the microbe Bacillus flexus being able to degrade t after UV pretreatment, polypropylene is generally non-biodegradable.
Like other fossil-derived non-biodegradable plastics, Polypropylene will, over time, disintegrate into small plastic fragments and eventually microplastics. This has a detrimental impact on the environment.
For high-end applications such as for use in scaffolds and implants, biocompatibility is a key requirement. Several studies have shown that PHAs have high biocompatibility in tissue engineering applications such as sutures, implants, scaffolds, and blood vessel regeneration.
The processibility of PHA combined with its biocompatibility makes it even better suited for biomedical application. PHA can be processed into the diverse and often complex shapes required for biomedical applications using methods such as 3D printing and injection molding.
While polypropylene is not biodegradable, it is however relatively biocompatible. However, some inflammation as a result of host immune response has been observed in several cases where polypropylene has been used in biomedical applications such as implanted meshes for the treatment of pelvic floor conditions. This has put into question the biocompatibility of polypropylene in such applications.
VEnvirotech is dedicated to the production of high-quality bio-based bioplastics with PHA being the primary bioplastic. We also produce blends of PHA and other bioplastics and recyclable plastics.
Prospective clients can select from our existing bioplastics formulation or contact our team of biotechnology experts to customize a formulation to meet your specific needs. Find out more about our products and services including our waste upcycling service at VEnvirotech.
