Production of Biodegradable Organic Plastics

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[edit] Introduction and Motivation

In light of the massive surge for environmental accountability in this day and age, one of the major sources of pollution is that of plastics. Since the 1950's it can be estimated that over 1 Billion tons of plastic have been placed into landfills, and current estimates state that it will take hundreds or thousands of years to completely degrade [1]. There has been a great response in people recycling much of their plastic waste, but if the plastic could simply be composted, or designed to degrade in a quick, environmentally friendly way much of the waste could be eliminated from the landfills, and the hassle of recycling would become moot. This page will therefore look at the production of biodegradable plastics, how widespread the implementation is and can be, and attempt to find ways to make the process more energy or materials efficient. As well,the actual process will be evaluated to see if it is actually better for the environment in the long run. Such breakthroughs will hopefully further drive the plastics industry to develop the processes needed to produce this plastic, and help the environment.

[edit] Definition of Biodegradability

In order to understand the processes of creating biodegrradable plasticsW one must first have a working understanding of what is meant by "biodegradation." In 1992, a conference was held for many of the most prominent biodegradability researchers, and one of the outcomes of this meeting was a list of postulates that have since governed the basic definition, classification and measurement of biodegradability. The postulates are as follows:[2]

- For all practical purposes of applying a definition, material manufactured to be biodegradable must relate to a specific disposal pathway such as composting, sewage treatment, denitrification, and anaerobic sludge treatment.
- The rate of degradation of a material manufactured to be biodegradable has to be consistent with the disposal method and other components of the pathway into which it is introduced, such that accumulation is controlled.
- The ultimate end products of aerobic biodegradation of a material manufactured to be biodegradable are CO2, water and minerals and that the intermediate products include biomass and humic materials. (Anaerobic biodegradation was discussed in less detail by the participants).
- Materials must biodegrade safely and not negatively impact the disposal process or the use of the end product of the disposal.

[edit] Overview of Plastic Production

PlasticsW are the basic building blocks of today's society. Over the last 60 years[3], the development of plastics has been developed and perfected to such a degree that almost anything can be made of plastic and it's many compositesW. For much of this time, the primary source of the plastic monomer chains, such as ethyleneW and propyleneW, has always been from the processing of crude oil and petroleum. This also has the effects of producing other organic compounds such as benzeneW and xyleneW which can then be used to produce off-shoots from the initial monomer chains, ie. side-groups or chains[4]. These basic building blocks are then chemically processed to join into long chains called polymers. This can be performed through various methods, and these are often required due to specific side-groups that have attached. However, often this process will involve a dehydratingW process where the hydrogen atoms (and possibly oxygen atoms) are removed from the ends of the monomer chains and combined to produce water as a byproduct. From this, numerous chemical processing techniques can be used to produce the particular lengths of chains, compositions of the plastics, and will in general determine the final form and properties of the products.

The production of these plastics has provided a wide range of properties, however, in almost every case the final product is made of polymer chains with properties such that they are highly resistive to degredation. The final result is a material that is highly resistive to natural forces and is not recognized by living organisms as food. Therefore, in order to produce similar products with the capacity to biodegrade, a completely separate set of monomer chains and production techniques must be implemented.

[edit] Bioplastic Production/Processing Methods Used today

Throughout the human history, the production of bio-friendly processes and materials has been closely monitored and used to great effect in the medical sciences.[3] The production of plastics that can be readily absorbed by the body without harmful effects has been a large focus ever since plastics have been discovered. This has widespread

[edit] Thermoplastic Starches: manipulation of starches with other agents

The actual form of starch is often granular. A crystalline complex-carbohydrate chain outer coating often encapsulates an amorphous inside of the same chains.[5] When placed in the presence of water, the hydrophobic aldehyde bonds within the starch will attempt to drive away the water. However, once a low enough temperature is reached, the starch will in fact become plasticized by the water undergoing many crystal phase tranisitions and having a generally complicated relationship with the water in it's structure[5] . This can lead to basic thermoplastic properties depending on the concentration of the water in the plasticized mixture.

[edit] PHA production: production of plastic directly within bacterial and plant cells

Produced within living cells, PHA, specifically PHB polyhydroxy butyrate can be produced inside of organisms ranging from bacterial to alfalfa plants [6]

[edit] PLA production: Manipulation of sugars and starch into polylactides

Produced from the polymerizationW of lactic acid, the PLA plastics exhibit different characteristics depending on the concentration of the lactic acid in the initial mix. This can be modified easily depending on the desired application. [5].

[edit] Developements in Bioplastic processing

[edit] Energy,Cost and Waste comparison

Incomplete

[edit] References

  1. Alan Weisman, "The World Without Us," St. Martin's Press, NY, 2007.
  2. Maarten Van der Zee,"Biodegradation of Polymeric Materials An Overview of Available Testing Methods." Biomedical polymers: sustainable polymer science and technology, eds. Chiellini, Emo.Kluwer Academic / Plenum Publishers, New York:2001. pp.265
  3. 3.0 3.1 Michel Vert, "Biopolymers and Artificial Biopolymers in Biomedical Applications, an Overview", Biomedical polymers: sustainable polymer science and technology, eds. Chiellini, Emo.Kluwer Academic / Plenum Publishers, New York:2001. pp.63
  4. "How is plastic made?" American Chemistry Council, Inc. 2007. Available: http://www.americanchemistry.com/s_plastics/doc.asp?CID=1571&DID=5974
  5. 5.0 5.1 5.2 Richard P. Wool, Xiuzhi Susan Sun, Bio-Based Polymers and Composites.Elsevier Academic Press, San Diego:2005.pp.369
  6. Purev Saruul, Friedrich Srienc, David A. Somers, and Deborah A. Samac, "Production of a Biodegradable Plastic Polymer, Poly-�-Hydroxybutyrate in Transgenic Alfalfa".
Mat.png This page was developed as part of a project for MECH370, a Queen's University class on materials processing. It is now open edit.