Production of PHA and PP
PHA has a primarily biological basis. Even better, it can be produced from organic waste and applied in waste management and water treatment systems.
PHAs are based on the application of biotechnology to optimize the natural processes that take place in microorganisms. They can be produced without altering the natural environment, or with minimal alterations.
PHAs are produced as energy and carbon storage polymers in microbes. The industrial production of PHAs requires cultivating microbes under controlled conditions that optimize PHA production. Microbes produce PHAs under simulated conditions of nutrient starvation and excess carbon. Other factors, such as temperature, pH, and the presence of macronutrients and trace metals, affect the quantity and quality of the PHAs 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 obtain specific types of PHA with the desired properties. For example, if the process is directed toward the production of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) instead of PHB, a tougher and more elastic PHA will be obtained.
PP, on the other hand, requires extraction processes that inevitably destroy natural habitats and involve the depletion of fossil resources. In addition, there is a risk of disasters such as oil spills and the emission of soot into the atmosphere.
The global production rate of conventional fossil-based plastics remains far higher than that of bioplastics. Polypropylene has the second-highest global production rate, alongside polyethylene. In 2022, the global polypropylene market volume was estimated at 79.01 million metric tons, with a gross annual growth rate of 3.6% forecast for 2023 to 2030.
Although PHA production volume is much lower and bioplastics account for less than 1% of global plastic production, government policies and growing efforts to regulate single-use plastics and promote more sustainable plastics have led to increased demand for biodegradable plastics, with PHA at the forefront.
The global PHA market value in 2022 was estimated at 81 million dollars. It is expected to rise to 167 million dollars by 2027. PHA is expected to become the leading commodity bioplastic in the coming years.
Physical properties
Polypropylene has long been 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 non-woven bags and sacks, geotextiles, and other applications.
PHA’s appeal is largely due to the fact that it combines some of these physical attributes of polypropylene with biodegradability and biocompatibility. This expands its application to areas where polypropylene is not applicable. One example is tissue engineering and scaffolds.
Table 1 compares elongation at break, melting point (Tm), glass transition temperature (Tg), tensile strength, and Young’s modulus of three different PHAs and PP. Here we can see that the properties of PHAs can vary by changing the composition of the PHA.
Polypropylene is relatively more rigid than another commodity plastic, polyethylene. While PHB is much more rigid, other forms of PHA have greater elasticity that even exceeds that of polypropylene (Table 1).
Table 1 also shows that PHAs match some of the properties of PP, such as elasticity, quantified by elongation at break. The melting point of PHAs can be lower or higher than that of PP. Thermal processing of PHAs can be carried out using conventional plastic processing methods.
Table 1. Comparison of the properties of three PHAs with those of PP
| Polymer | Tg (°C) | Tm (°C) | 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 |
Environmental impact
The assessment of the environmental impact of PHA production includes everything from the collection and treatment of raw materials to the carbon released during the degradation of bioplastics. The environmental impact factors 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, as these values vary significantly from one study to another 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. Fermentation and recovery processes contribute the most to the environmental impact of PHA production. PHB produced in material recovery facilities had a global warming potential of 3.4 to 5 kg CO2 eq/kg.
The use of waste as raw material significantly reduces the environmental impact of PHAs, as it eliminates the contribution from the cultivation and processing stage in the production of their raw materials.
A global warming potential of 1.58 kg CO2 eq and fossil fuel depletion of 1.722 kg oil eq have been reported for polypropylene production. However, environmental assessment depends on other factors such as eutrophication, land-use change, water consumption, petrochemical oxidant formation, and fossil resource depletion.
The production of polypropylene granules entails fossil resource depletion of 1.7222 kg oil eq per kg of polypropylene granules produced, while fossil resource depletion for PHA production can be zero if no fossil fuel is used in the operation of the facilities involved in production.
Greenhouse gas emissions during biodegradation can be mitigated by having appropriate systems in place to capture carbon or methane from aerobic or anaerobic biodegradation.
Biodegradability
PHA is a bio-based biodegradable plastic. The biodegradation rate depends on the PHA formulation and the type of processing it has undergone. For example, if the PHA is in film form, it may be mixed with other polymers and additives.
While bioplastics such as PLA require special industrial composters for biodegradation, pure PHAs generally biodegrade in natural environments and in home composters.
Since PHA is biosynthesized by microorganisms as a storage polymer, these microbes also produce the enzymes needed to break down, and therefore biodegrade, PHA. Despite some new findings that the microbe Bacillus flexus is capable of degrading t after UV pretreatment, polypropylene is generally non-biodegradable.
Like other non-biodegradable fossil-based plastics, polypropylene will eventually disintegrate into small plastic fragments and, ultimately, into microplastics. This has a harmful impact on the environment.
Biocompatibility
For high-level applications, such as use in scaffolds and implants, biocompatibility is a key requirement. Several studies have shown that PHAs exhibit high biocompatibility in tissue engineering applications such as sutures, implants, scaffolds, and blood vessel regeneration.
PHA’s processability, combined with its biocompatibility, makes it even more suitable for biomedical applications. PHA can be transformed into the diverse and often complex shapes required by biomedical applications through methods such as 3D printing and injection molding.
Although polypropylene is not biodegradable, it is relatively biocompatible. However, some inflammation has been observed as a result of the host immune response in several cases where polypropylene has been used in biomedical applications, such as implanted meshes for the treatment of pelvic floor conditions. This has called into question the biocompatibility of polypropylene in such applications.
Where to source PHA
VEnvirotech is dedicated to the production of high-quality bio-based bioplastics, with PHA as its main bioplastic. We also produce blends of PHA and other bioplastics and recyclable plastics.