Biodegradable polymers were developed several decades ago, but their full-scale commercial application formed very slowly. Such situations had a place because they were generally more expensive and have less stable physical properties than conventional plastics. In addition, there was little incentive for producers of plastic products in order to include biodegradable materials in their products. However, situation greatly changed and now biodegradable polymers are in area of researchers' interest, because they could be use in medicine, agriculture, packaging and many other areas.
ISO definition of the concept "biodegradable"
According to Narayan and Pettigrew (1999) we see that the American Society for Testing of Materials (ASTM) and the International Standards Organization (ISO) define degradable plastics as material that undergoes an essential change in its chemical structure under the influence of specific environmental conditions. It is necessary to add to this definition that exactly these essential changes result in a loss of not only physical, but also mechanical properties. Naturally occurring microorganism, which are presented by bacteria, algae and fungi greatly influence on biodegradable plastics and change its quality and structure. Gross and Bhanu (2002) stated that "plastics may also be designated as photodegradable, oxidatively degradable, hydrolytically degradable, or those which may be composted." True definition of the term "biodegradable" was the object of great public interest between October 1990 and June 1992, when it was the main topic of debates and lawsuits.
Structure and green chemistry of biodegradable polymers
Natural and synthetic polymers containing links, which are easily hydrolysed, possess a high potential for biodegradation. The presence of constituents in the polymer chain often promotes biological degradation. The last also depends on the degree of substitution and chain length of its sections between the functional groups, the flexibility of macromolecules.
An important factor, which determines the stability of the biodegradable polymer, is the value of its molecules. Simon, Muller, Koch and Muller (1998) proved that while microorganisms may affect monomers or oligomers and serve them a source of carbon, polymers with high molecular mass are resistant to the action of microorganisms. Biodegradation of most technical polymers typically initiate the process of non-biological nature (thermal and photo-oxidation, thermolysis, mechanical degradation, etc.). These degradation processes lead to lower molecular weight polymer. This gives rise to low molecular bio assimilated fragments having at the ends of the chain hydroxyl, carbonyl or carboxyl groups.
We see that polymers chains by the chemical hydrolysis may be broken down and results of such green chemistry presented in the figure 2. Gross and Kalra (2002) explained this process in the next way: "BPs are often derived from plant processing of atmospheric CO2. Biodegradation converts them to CO2, CH4, water, biomass, humic matter, and other natural substances. BPs are thus naturally recycled by biological processes."
Features of biodegradable polymers
Unlike most plastics, biodegradable polymers can break down in the environment with the help of microorganisms such as bacteria or fungi. The polymer is usually considered biodegradable, if all of its mass is decomposed in soil or water for a period of six months. In many cases, the decay products are carbon dioxide and water. Any other decomposition products or residues must be investigated for the presence of toxic substances and safety.
Biodegradable polymers can be produced from renewable sources, such as extracted from corn sugar, or they can be produced from petrochemical raw materials. They can be used alone or in combination with other plastic resins and additives. It is necessary to mention that biodegradable polymers can be processed by most standard technologies for the production of plastics, including thermoforming, extrusion, injection and blow molding.
Innovative technologies and further direction of the biodegradable polymers development
Biodegradable polymers - is an innovative technology that helps to protect the environment from the destructive action of plastic. According to http://bprc.caeds.eng.uml.edu, preferring plastic with biodegradable additives, man cares not only about nature, but also about own purse, significantly saving on waste disposal. Contamination of the environment today - is not a problem of a single country, but it is a problem of the whole world. One of the main sources of garbage is plastic, because the period of its disintegration is over a hundred years. The way out of this situation may be widespread use of oxy-biodegradable polymers (oxy-biodegradable additives) that reduce the term of the expansion of plastic to five - eight years.
Swift (1998) said that a radical solution to the problem of the polymer garbage, according to experts, is the creation and development of a wide ranges of polymers, capable, under appropriate conditions biodegrade into harmless for animate and inanimate nature components. We talk about biodegradable polymers and they will be the priority for development, which would exclude a significant number of problems with "plastic garbage" that arises when using plastic containers and other products made of polymers.
Conclusion
Thus, taking into account all above stated information about biodegradable polymers we see that this question has big perspectives in future and assessment of the situation to develop and produce biodegradable plastics can distinguish three main directions of the development of search and applied research in this area:
- Polyether of hydrocarbon acids;
- Plastics based on natural renewable polymers;
- Give biodegradability to industrial high-molecular synthetic materials.
For example, the company Cargill Dow is the world's first company, which has developed the production of plastics from annually renewable resources. The company manufactures biodegradable polymer, under the brand name "Nature Works" which is made of wort taken from the grains of wheat. This polymer is a material that is taken as manufactured bedding, clothing and packaging products. These plastics can compete with packaging materials and traditional fibres for cost and quality.
Thus, replacing the previous generation of polymeric materials for biodegradable polymers greenhouse evaporation will be reduced by 15-60%. For the production of biodegradable polymers will be used in plant biomass - potatoes, corn, peas, beets, beans and rice and wheat. In addition, American farmers will receive strong support, as able to sell the straw, which they had previously burned, totaling about 20 billion dollars a year.
References:
Bhaskaran, R. US Biodegradable Polymer Market: Greening up for a better tomorrow! February 20, 2004. Retrieved from http://www.frost.com/prod/servlet/market-insight-top.pag?docid=10434867
Center for Biodegradable Polymer Research. Retrieved from http://bprc.caeds.eng.uml.edu/
Gross, R. and Kalra, B. Biodegradable Polymers for the Environment. Science, vol. 297, August 2, 2002. Retrieved from http://162.105.153.170/page/liy/puhua/files/Biodegradable%20Polymers.pdf
Middleton, J. and Tipton, A. Synthetic Biodegradable Polymers as Medical Devices. Medical Plastics and Biomaterials Magazine, March, 1998.
Narayan, R. and Pettigrew, C. ASTM standards help define and grow a new biodegradable plastics industry. ASTM Standardization News. December: 36-42, 1999.
Simon, J., Muller, H., Koch, R., Muller, V. Requirements for biodegradable water soluble polymers. Polymer Degradation and Stability. 59 (1-3): 107-115, 1998.
Swift, G. Prerequisites for biodegradable plastic materials for acceptance in real life composting plants and technical aspects. Polymer Degradation and Stability. 59(1-3): 19-24, 1998.
