Authors: Dharmendra kumar
To build our economy on a sustainable basis, we need to find a replacement for fossil carbon as chemical industry feedstock. There are growing concerns about current petroleum based production, accumulation of waste in landfills and in natural habitats including the sea, physical problems for wildlife resulting from ingestion or entanglement in plastic, the leaching of chemicals from plastic products and the potential for plastics to transfer chemicals to wildlife and humans.
About 4% of the world’s oil production is converted into plastics for use in products as varied as shopping bags and the external panels of cars. Another few percent is used in processing industries because oil-based plastics require substantial amounts of energy to manufacture.
Each kilogram of plastic typically requires 20 kilowatt hours of energy in the manufacturing process, more than the amount needed to make steel of the same weight. Almost all this comes from fossil sources
In addition, the use of carbon-based sources of energy for use in plastics manufacturing adds greenhouse gases to the atmosphere, impeding the world’s attempts to cut CO2 emissions.
Disadvantage of plastics :
• Plastics use valuable resources of oil
• The plastics industry uses large amounts of energy, usually from fossil fuel sources which therefore adds to the world’s production of greenhouse gases.
• The durability of plastics means that without effective and ubiquitous recycling we will see continuing pressure on landfill. Although plastics do not represent the largest category of materials entering landfill – a position held by construction waste – they are a highly visible contributor to the problems of waste disposal.
• The manufacturing of conventional plastics uses substantial amounts of toxic chemicals.
• Some plastics leach small amounts of pollutants, including endocrine disruptors, into the environment. These chemicals can have severe effects on animals and humans.
A bioplastic is a plastic that is made partly or wholly from polymers derived from biological sources such as sugar cane, potato starch or the cellulose from trees, straw and cotton. Some bioplastics degrade in the open air, others are made so that they compost in an industrial composting plant, aided by fungi, bacteria and enzymes.
In thinking about the potential role of bioplastics, we need to distinguish between two different types of use:
Items that might eventually become litter – such as shopping bags or food packaging – can be manufactured as bioplastics to degrade either in industrial composting units or in the open air or in water. Strenuous efforts need to be made to continue to reduce the amount plastic employed for single use applications. But if the world wishes to continue using light plastic films for storage, packaging or for carrying goods, then the only way we can avoid serious litter problems is to employ fully biodegradable compounds.
Permanent bioplastics, such as polythene manufactured from sugar cane, can provide a near-perfect substitute for oil-based equivalents in products where durability and robustness is vital. Plastics made from biological materials generally need far smaller amounts of energy to manufacture but are equally recyclable.
They use fewer pollutants during the manufacturing process. Per tonne of finished products, the global warming impact of the manufacture of bioplastics is less, and often very substantially less, than conventional plastics.
Bioplastics, derived from bio-based polymers, may provide a solution. Unlike the chemically synthesized polymers, the bio-based polymers are produced by living organisms, such as plants, fungi or bacteria. Some microorganisms are particularly capable in converting biomass into biopolymers while employing a set of catalytic enzymes.
Attempts to transfer biomass to produce industrially useful polymers by traditional biotechnological approaches have obtained only very limited success, suggesting that an effective biomass-conversion requires the synergistic action of complex networks.
As an interdisciplinary research field which is a unique combination of life science and engineering, synthetic biology can provide new approaches to redesign biosynthesis pathways for the synergistic actions of biomass conversion and may ultimately lead to cheap and effective processes for conversion of biomass into useful products such as biopolymers.
The properties of bio-based polymers for bioplastics equal to or better than their chemical synthetic counter parts will be compared. The subfields of synthetic biology related to polymer biosynthesis will be reviewed synthetic biological approaches to improve the biological system to produce polymers for bioplastics, such as polyhydroxyalkanoates (PHAs).
The fourth section then goes on to evaluate the environmental impacts of the synthetic biology derived bioplastics. Bioplastics are a form of plastics derived from renewable biomass sources, such as vegetable fats and oils , corn starch , peastarch or micro biota ,. Common plastics, such as fossil-fuel plastics , are derived from petroleum . These plastics rely more on scarce fossil fuels and produce more greenhouse gas es.
Bioplastics are more sustainable because they can break down in the environment faster than fossil-fuel plastics, which can take more than 100 years. Some, but not all, bioplastics are designed to biodegrade .
Bioplastics which are designed to biodegrade can break down in either anaerobic or aerobic environments, depending on how they are manufactured.
Uses of bioplastics:
- Biodegradable bioplastics are used for disposable items, such as packaging and catering items (crockery, cutlery, pots, bowls, and straws). Biodegradable bioplastics are also often used for bags, trays, containers for fruit, vegetables, eggs and meat, bottles for soft drinks and dairy products and blister foils for fruit and vegetables.
- Nondisposable applications include mobile phone casings, carpet fibers, and car interiors, fuel line and plastic pipe applications, and new electro active bioplastics are being developed that can be used to carry electrical current. In these areas, the goal is not biodegradability, but to create items from sustainable resources.
- Medical implants made of PLA, which dissolve in the body, save patients a second operation. Compostable mulch films for agriculture, already often produced from starch polymers, do not have to be collected after use and can be left on the fields.
Constituting about 50 percent of the bioplastics market, thermoplastic starch, currently represents the most widely used bioplastic. Pure starch possesses the characteristic of being able to absorb humidity, and is thus being used for the production of drug capsules in the pharmaceutical sector.
Flexibiliser and plasticizer such as sorbitol and glycerin are added so the starch can also be processed thermo-plastically. By varying the amounts of these additives, the characteristic of the material can be tailored to specific needs (also called "thermo-plastical starch"). Simple starch plastic can be made at home.
Industrially, starch based bioplastics are often blended with biodegradable polyesters. These blends are mainly starch/polycaprolactone or starch/Ecoflex[ (polybutylene adipate-co-terephthalate produced by BASF). These blends remain compostable.
Other producers, such as Roquette, have developed another strategy based on starch/polyeolefine blends. These blends are no longer biodegradables, but display a lower carbon footprint compared to the corresponding petroleum based plastics.
Cellulose bioplastics are mainly the cellulose esters, (including cellulose acetate and nitrocellulose) and their derivatives, including celluloid.
Some aliphatic polyesters:
The aliphatic biopolyesters are mainly polyhydroxyalkanoates (PHAs) like the poly-3-hydroxybutyrate (PHB), polyhydroxyvalerate (PHV) and polyhydroxyhexanoate:
Polylactic acid :
Polylactic acid (PLA) is a transparent plastic produced from cane sugar or glucose. It not only resembles conventional petrochemical mass plastics in its characteristics, but it can also be processed easily, albeit more expensively, on standard equipment that already exists for the production of conventional plastics.
PLA and PLA blends generally come in the form of granulates with various properties, and are used in the plastic processing industry for the production of foil, moulds, cups and bottles.
Poly-3-hydroxybutyrate:The biopolymer poly-3-hydroxybutyrate (PHB) is a polyester produced by certain bacteria processing glucose, corn starch or wastewater. Its characteristics are similar to those of the petroplastic polypropylene .
PHB is distinguished primarily by its physical characteristics. It produces transparent film at a melting point higher than 130 degrees Celsius, and is biodegradable without residue.
Polyhydroxyalkanoates:Polyhydroxyalkanoates are linear polyesters produced in nature by bacterial fermentation of sugar or lipids. They are produced by the bacteria to store carbon and energy.
In industrial production, the polyester is extracted and purified from the bacteria by optimizing the conditions for the fermentation of sugar. PHA is more ductile and less elastic then other plastics, and it is also biodegradable. These plastics are being widely used in the medical industry.
Polyamide 11:PA 11 is a biopolymer derived from natural oil. It is also known under the trade name Rilsan B, commercialized by Arkema. PA 11 belongs to the technical polymers family and is not biodegradable. Its properties are similar to those of PA 12 , although emissions of greenhouse gases and consumption of nonrenewable resources are reduced during its production.
The basic building block ( monomer) of polyethylene is ethylene. This is just one small chemical step from ethanol, which can be produced by fermentation of agricultural feedstocks such as sugar cane or corn. Bio-derived polyethylene is chemically and physically identical to traditional polyethylene - it does not biodegrade but can be recycled. It can also considerably reduce greenhouse gas emissions.
Genetically modified bioplastics:
Genetic modification (GM) is also a challenge for the bioplastics industry. None of the currently available bioplastics - which can be considered first generation products - require the use of GM crops, although GM corn is the standard feedstock.
Looking further ahead, some of the second generation bioplastics manufacturing technologies under development employ the "plant factory" model, using genetically modified crops or genetically modified bacteria to optimise efficiency.
Bioplastics from microorganism :
The term ‘biomaterials’ includes chemically unrelated productsthat are synthesised by microorganisms (or part of them) under different environmental conditions. One important family of biomaterials is bioplastics. These are polyesters that are widely distributed in nature and accumulate intracellularly in microorganisms in the form of storage granules, with physicochemical properties resembling petrochemical plastics.
These polymers are usually built from hydroxy-acyl–CoA derivatives via different metabolic pathways. Depending on their microbial origin, bioplastics differ in their monomer composition, macromolecular structure and physical properties. Most of them are biodegradable and biocompatible, which makes them extremely interesting from the biotechnological point of view.
Biomaterials are natural products that are synthesised and catabolised by different organisms and that have found broad biotechnological applications. They can be assimilated by many species (biodegradable) and do not cause toxic effects in the host (biocompatible) , conferring upon them a considerable advantage with respect to other conventional synthetic products. Bioplastics are a special type of biomaterial. They are polyesters, produced by a range of microbes, cultured under different nutrient and environmental conditions .
These polymers, which are usually lipid in nature, are accumulated as storage materials (in the form of mobile, amorphous, liquid granules), allowing microbial survival under stress conditions .
The number and size of the granules, the monomer composition, macromolecular structure and physico-chemical properties vary, depending on the producer organism . They can be observed intracellularly as light-refracting granules or as electronlucent bodies that, in overproducing mutants, cause a striking alteration of the bacterial shape .
Currently, the main limitations for the bulk production of bioplastics are its high production and recovery costs. However, genetic and metabolic engineering has allowed their biosynthesis in several recombinant organisms (other bacteria, yeasts or transgenic plants, by improving the yields of production and reducing overall costs .
Bioplastic from al gae:
Algae serve as an excellent feedstock for plastic production owing to its many advantages such as high yield and the ability to grow in a range of environments. Algae bioplastics mainly evolved as a byproduct of algae biofuel production, where companies were exploring alternative sources of revenues along with those from biofuels. In addition, the use of algae opens up the possibility of utilizing carbon, neutralizing greenhouse gas emissions from factories or power plants.
Algae based plastics have been a recent trend in the era of bioplastics compared to traditional methods of utilizing feedstocks of corn and potatoes as plastics. While algae-based plastics are in their infancy, once they are into commercialization they are likely to find applications in awide range of industries.
Nanotechnology for bioplastics:
Recent years have witnessed a tremendous expansion of research and technology developments in the nanotechnology field resulting in significant application developments in the food and agricultural areas. This is particularly the case of the food packaging field, where significant advances in the nanoreinforcement of biobased materials provide a more solid ground towards increasing the technical and economical competitiveness of renewable polymers for different applications.
However, there is still a long way to go, not only in the materials development and energy consumption minimization parcels, but also regarding the widespread commercialization of these novel nanostructured biopolymers and the full characterization of any particular potential toxicological and environmental impacts.
Nanotechnology, by definition, is the creation and subsequent utilization of structures with at least one dimension in the nanometre length scale (i.e. less than 100 nm) that creates novel properties and phenomena otherwise not displayed by either isolated molecules or bulk materials .
The term nanocomposite refers to composite materials containing typically low additions of some kind of nanoparticles. Specifically in the food biopackaging sector, nanocomposites usually refer to materials containing, typically, 17 wt.% of modified nanoclays .
For reinforcing purposes, a good interaction between matrix and filler is highly desired, which is often one of the major challenges faced when developing new nanocomposite materials. It has been observed that the interactions matrixefiller significantly improve when reducing the size of the reinforcing agent, always considering that both phases are compatible and that the filler is properly dispersed .
Challenges and strategies:
In the bioplastics field the two main challenges are associated with functionality, specifically generating reproducible performance of bioplastics as petroleum-based counterparts, and achieving truly positive life-cycle analysis, i.e. achieving the goal of carbon neutral materials or minimizing fossil energy consumption.
In these issues, as the physicist Richard P. anticipated, “there is plenty of room at the bottom”, i.e. there is no doubt that nanotechnology will play a significant role, due to the potential property enhancements that can be achieved incorporating nanoparticles.
Since more recently, there is also the debate of potential competition between the use of crops for foods and to obtain biobased products, in what has been claimed as the cause for recent increases in the price of foods. The latter issue is perhaps not so relevant when it comes to bioplastics, since consumption of food competing resources to make biobased plastics is currently very small.
Regarding nanoparticles, it is reckoned that to achieve the level of performance associated to the use of nanotechs a high dispersion should be achieved in the bioplastic matrix. Hence, nanoparticles dispersion still remains a challenge for the full delivery of the expected properties as announced by the early modelling work.
There are several technologies to achieve nanodispersion in biopackaging materials being the most common, in situ polymerization, dispersion in solution and dispersion via melt-blending. Despite the two formers being more efficient in achieving nanodispersion in most cases, the latter route, less efficient in achieving dispersion, is without doubt the most demanded technology from an applied viewpoint, because it makes use of industry available machinery and processes to convert plastics into final articles.
Therefore, it is a very important concern that most of the nanocomposite formulations (first generation nanocomposites, i.e. containing standard or general purpose organicmodified nanoclays) in the market are currently making use of ammonium salts as organophilic chemical modifiers, which have been devised to enhance the properties of engineering polymers in structural applications.
Bioplastics, defined as plastics derived from renewable carbon sources that are also biodegradeable, have been considered as good candidates for sustainable development as well as eco-friendly environment. The R&D on SB approaches is highly expected to deliver feasible approaches to bulk production of bioplastics. There are many aspects where SB can contribute to obtain this goal . Both SB and bioplastics are in their early stage of development. Most of the SB related research on bioplastics is focused on improving production of PHAs.
More matured processes for large-scale conversion of biomass to polymer by SB design approaches could significantly influence the bulk production of bioplastics. However, adoption by industry on a new biological processing is expected to be slow, even though there are clear benefits on environmental perspectives over the longterm.
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About Author / Additional Info:
Currently doing Ph.D from IARI, New Delhi