Polyhydroxyalkanoates (PHAs) are linear polyesters made naturally through fermentation by bacteria of sugars, fats and oils. Bacteria use them to reserve energy and carbon. They are ecological plastics that one can use to manufacture environmentally-friendly plastics. They become modifiable at temperatures between 40 to 180 degrees Celsius and have weak forces joining the molecules. Transformation of physical properties of these polymers is done by fusing, modifying surface molecules or mixing (Randall, 18) PHAs with other polymers, enzymes and substances that are synthetic. The modification of the polymers is enabling application of PHAs in many industries and areas.
Production of polyhydroxyalkanoates
There are three possible means of production of PHAs namely, fermentation by bacteria, manufacturing in plants that are undergoing genetic modification and catalysis by enzymes in systems that are cell free. Of the three methods, the most common industrial method is fermentation in bacteria.In this method, put a suitable bacteria in a favourable growth medium containing the required nutrients and adequate oxygen (Endres, Hans, and Andrea,2)for optimum growth and rapid cell division.
Maintain the suitable conditions until the bacterial colony reaches a satisfactory level after which you substitute the growth medium and oxygen supplies. This change will force the bacteria to manufacture PHAs as the energy reserves. Highly refractive granules as the form of the polyesters will deposit in the cells. The above is the discontinuous production process which occurs in bacteria like “alcaligenes eutrophus“. In another type of bacteria, example being “alcaligenes latus” production of the polymer will occur (Endres, Hans, and Andrea,3) continually despite the conditions.maximising the conditions of sugar fermentation enable extraction and purification of the formed polyesters in the industrial production.
Components of PHAs
The raw materials for the fermentation will include sugars, oils from vegetables and glycerin extracted from petroleum in the bacterial cells. Other possible sources of PHA under research include expression of the PHA synthesis route in genetically modified plants and enzyme catalysis in waste water. The major (Koller, Martin, et al., 2) single subunits are hydroxyl alkanoic acids will join by weak intermolecular attractions to form the PHA polymer.
Chemical and physical properties
The PHA molecules have different properties depending on their composition chemically.In general, these molecules become plastic on heating and will harden on repeatedly cooling, making them thermostatic. On the concept of resistance, the molecules are resistant to humidity, breakdown by hydrolysis, ultra violet light but have poor resistance to acidity and alkalinity. They will not dissolve in water but will be highly soluble in chlorinated compounds and chloroform. These compounds will be (Bugnicourt, Elodie, et al., 4) compatible with biological compounds thus suitable for medical uses and are not toxic. They will also sink in water because of high density where biodegradation of sediments will occur by anaerobically. Lastly, on melting, they tend to be less sticky.
Application of PHAs
PHAs are proving to be very useful in the modern medical field because of its biocompatibility.It is efficient for use in the manufacturing of antibiotics such as macrolides and carbapenem as the starting building block; therefore they act as carriers for the drugs. Because they are degradable, they are useful in manufacturing sutures, implants and cardiac valves, which degrade naturally in the body without causing harm. Another use is as( Keshavarz, Tajalli, and Ipsita,7) a drug itself in many medical conditions such hemorrhagic shock, major traumatic injuries by elevating the level of ketones in the blood, diseases of neurones degeneration such as Alzheimer’s and osteoporosis.
There are also numerous other uses in other industries such as the chemical, energy and textile industries. Because they are plastics, factories use them in the production of packaging materials for short period’s storage, and plastic films in disposable materials. Another possible use is in the print and photography firms as they will stain (Keshavarz, Tajalli, and Ipsita, 8) very fast. They are also proving to be very useful as fuels. Through the process of hydrolysis, the by-products will have some heating power.
Social importance of PHAs
Socially, PHAs production is costly, which means that they need extra funds at the expense of other economic development industries. As this industry expands, it will take up resources meant for other development projects which will affect the economy of concerned states. Because of the increased cost of production, they will be scarce( Averous, Luc, Eric,12) to the public as most low-income earners cannot afford them.Also; it will take a lot of efforts and inducement to justify the use of these polymers as an alternative source of energy to other low-cost fuels. Another negative impact is that PHAs require setting aside of land and resources to grow the bioengineered food crops at a time of increasing food insecurity globally or from the protection of the delicate environment at a period of disappearing biodiversity.
However looking at the positive aspects of PHAs, living in an environmentally friendly setting has become very important in the modern society. PHAs go a great length to reduce the levels of fossil oil consumption for producing plastics. Use of biodegradable plastics is important in reducing dumpsites which are not appealing (Averous, Luc, Eric, 12) to the public socially. A clean country will attract many tourists and visitors improving social diversity.
PHAs are promising in reducing the levels of pollution. Because they will be broken down to natural gases which are harmless to the environment, they reduce air, land and water pollution. Decomposition of these polymers produces low levels of carbon dioxide thus less air pollution. However, they play no significant role in reducing littering as the concept of biodegradability increases the possibility of inappropriate dumping of garbage; this will increase soil pollution as some of the PHAs take time( Averous, Luc, Eric,13) to decompose depending on the environmental conditions. They are of use in protection of marine life as they are less dangerous to the organisms due to their biocompatibility.
The industrial method of production of PHAs is still dangerous to the surroundings because there is still the output of waste materials which they release to the environment. These polymers are harmful to the health of (Averous, Luc, Eric, 14) human beings if not handled properly because thePHAy react differently on recycling. Their standard will deteriorate with time and thus are not good for long term food packaging as they expose the food to microbial growth. Also during anaerobic decomposition, these polymers release methane gas which is a good source of bio-energy under proper harnessing. However, if this gas escapes to the surroundings, it contributes to air pollution and global warming.
Comparison with other polymers
- Poly (3-hydroxybutryrate) a type of PHA shares some properties with petroleum products polymers such as extreme melting point and high inelasticity .this makes it very fragile therefore it is rarely used.
- PHAs are very environment-friendly and decompose quickly when they come into contact with the humidity, soil and manure as compared with other fossil fuel polymers such as polyethene.
- In comparison with other biopolymers, PHAs prices are much higher. Therefore, they are less affordable
- Upon degradation, PHAs will not produce any biohazardous products as compared to other polymers an example of which is Polycaprolactone (PCL).
- During the production of PHA, it undergoes a natural biosynthesis method in contrast to polylactic acid which requires an artificial (Bugnicourt, Elodie, et al., 11) polymerization process to obtain the final product.
Bugnicourt, Elodie, et al. “Polyhydroxyalkanoate (PHA): Review of synthesis, characteristics, processing and potential applications in packaging.” (2014). http://www.iris-eng.com/wp-content/uploads/2016/03/EPL-0005219_article.pdf
Endres, Hans-Josef, and Andrea Siebert-Raths. “Basics of PHA.” future 2.3 (2011): 4. f2.hs-hannover.de/…/Bioplastics_Magazine__03_11__Vol._6_S._43-45.