PHA bioplastics
We are surrounded by plastic. Everything we do and every product we consume, from the food we eat to electrical appliances, has somehow dealt with plastic, and at least these materials have been used in its packaging.
In a country like Australia, about one million tons of plastic is produced annually, of which 40% is used for domestic use. About 6 million plastic bags are consumed in this country every year.
Although plastic packaging with a low price provides the possibility of excellent protection of various products, especially food, but unfortunately, the big environmental problem resulting from it has plagued humanity. Most of the common plastics in the market are produced from oil and coal products and cannot be returned to the environment, and it takes thousands of years to decompose them and return to the environment.
In order to solve this problem, biological science researchers are looking for the production of biodegradable plastics from renewable sources such as microorganisms and plants.
The word “biodegradable” means substances that are easily broken down into their constituent subunits by the activity of living organisms and therefore do not remain in the environment.
The word “biodegradable” means substances that are easily broken down into their constituent subunits by the activity of living organisms and therefore do not remain in the environment. This standard is different in different countries.
But the main reason for the non-biodegradability of common plastics is the long length of the polymer molecule and the strong bond between its monomers, which makes it difficult to break it down by decomposing organisms.
But the main reason for the non-biodegradability of common plastics is the long length of the polymer molecule and the strong bond between its monomers, which makes it difficult to break it down by decomposing organisms. For this purpose and with the aim of having an industry in the service of sustainable development and preservation of natural ecosystems, the production of a new generation of raw materials needed by the industry based on natural processes is on the agenda of many advanced countries.
For example, the American government plans to produce biological materials by 2010 using agriculture and solar energy with an approximate income of 15 to 20 billion dollars.
Meanwhile, the production of biopolymers has a special place. The production of these polymers is carried out by a wide range of living organisms such as plants, animals and bacteria. Because these materials have a natural basis, they are also consumed by other organisms, and decomposers are among the most important of these living organisms in our discussion.
For the exploitation of these polymers in the industry, two issues must be considered:
A) environmental view: These materials must break down quickly in the environment, do not disturb the soil texture, and be easily removed from the environment through waste management and recycling programs.
b) Industrial vision: These materials should have the expected characteristics of the industry, including durability and efficiency, and most importantly, after equaling or improving the quality compared to the usual materials, they should have a reasonable cost price.
In both sectors, especially the second sector, it is necessary to use materials production engineering to achieve the expected goals.
As mentioned, the production of renewable polymers using agriculture is one of the sustainable industrial production methods. As mentioned, the production of renewable polymers using agriculture is one of the sustainable industrial production methods.
The first is the direct extraction of polymers from plant biomass. The first is the direct extraction of polymers from plant biomass.
The other category is materials that can be used as monomers for polymers required by the industry after undergoing processes such as fermentation and hydrolysis. Biological monomers can also be converted into polymers by living organisms, the obvious example of which are polyhydroxyalkanoates.
Bacteria are among the organisms that produce this class of substances in the form of granules in their cell bodies. Bacteria are among the organisms that produce this class of substances in the form of granules in their cell bodies.
Another approach is to isolate the genes involved in this process and transfer it to plants. Projects in this field, including the transfer of PHA production bacterial genes to corn, have been carried out.
Another approach is to isolate the genes involved in this process and transfer it to plants. Projects in this field, including the transfer of PHA production bacterial genes to corn, have been carried out.
Another approach is to isolate the genes involved in this process and transfer it to plants. Projects in this field, including the transfer of PHA production bacterial genes to corn, have been carried out.
PHA biodegradable plastics:
Almost all common plastics in the market are obtained from petrochemical products that cannot be returned to the environment. An alternative solution for this purpose is the exploitation of soil bacteria such as Ralstonia eutrophus, which are capable of accumulating non-toxic and degradable polymers of polyhydroxyalkanoate (PHA) up to 80% of their biomass.
PHAs are generally made from beta-hydroxyalkanoate subunit through a simple pathway with 3 enzymes from acetyl-coenzyme A, and the most famous of them is polyhydroxybutyrate (PHB).
During the 1980s, the English company ICI designed and implemented a fermentation process through which PHB and other PHAs were produced by using transgenic E.coli culture that had received PHA production genes from bacteria that produce these polymers. was producing During the 1980s, the English company ICI designed and implemented a fermentation process through which PHB and other PHAs were produced by using transgenic E.coli culture that had received PHA production genes from bacteria that produce these polymers. was producing
Despite the countless environmental benefits of these plastics, such as their complete decomposition in the soil within a few months, the high cost of their production made commercial production on an industrial scale uneconomical.
However, a small and profitable market was created for these products and biodegradable plastics were used to make artificial tissues. By introducing these plastics into the body, they gradually decompose and the body regenerates the natural tissue in the form of the inserted plastic. In this specialized medical application, the price of such biological products is not comparable to the low economic value of plastic in the toy, auto and bag industries.
The production cost of PHAs will be significantly reduced by their production in transgenic plants and extensive cultivation in agricultural lands. This issue caused Monsanto to obtain the license to produce PHA from ICI in the mid-1990s and transfer bacterial genes to the Mandab plant. Preparing the conditions for the accumulation of PHAs in the plastid instead of the cytosol made it possible to harvest the polymeric product from leaves and seeds.
The most important unsolved problem remaining in the technical part of this project is how to extract this polymer from plant tissues with a low-cost and efficient method.
Another problem is in the field of PHB, which is actually the most important group of PHAs, but unfortunately it is fragile and therefore not suitable for many applications. The best biodegradable plastics are copolymers of polyhydroxybutyrate with other PHAs such as polyhydroxyvalerate. The production of such copolymers in transgenic plants is much more difficult than the production of single monomer polymers. In 2001, these problems along with Monsanto’s financial issues caused the company to hand over the privilege of producing transgenic PHA to Metabolix.
In the form of a collaborative project with the US Department of Energy worth approximately 14.8 million dollars, Metabolix is working to produce PHA in transgenic plants by the end of the 2010s.
Other groups are also trying to produce PHA in plants such as oil palm. We should wait until we finally see the economic production of these eco-friendly products in the near future.