Conclusion

     After reaching our conclusion, we decided that polylactic acid is an effective alternative to polyethylene and polypropylene. This is because polylactic acid can be created naturally by using the enzyme lactase to produce lactide from which polylactic acid is created through a polymerizing process. Polylactic acid decomposes easily in soil and contrasts with the decomposition of polyethylene since polyethylene takes a long period time to decompose and leaves traces of chemicals in the soil. A negative effect of the production of polylactic acid, however, is that the polymerizing process utilized to create polylactic acid from lactide is rather expensive compared to the processes used to produce polyethylene. As a group, we reasoned that since the burning of fossil fuels contributes to the concentration of greenhouse gases in the atmosphere, it would be better for the US to spend more money producing environmentally friendly bags with expensive green processes rather than produce bags that are difficult to decompose that are economically cheap to produce using the burning of fossil fuels to make.

     As our research stated, the technology utilized to create polylactic acid wasn't available in the 1950s and was suggested by our contact that this was due to the easy and cheap methods available to obtain crude oil. The easy access to oil explains why the US wasn't focused on discovering this technology even though it would have been available through research because they were more focused on producing bags efficiently and easily. If we were to travel back to the 1950's in the US, we would make oil difficult to access, and more expensive. This would force researchers in the 1950's to find more environmentally friendly methods to create plastic bags because they would have to use natural resources and environmental friendly processes in order to create plastic bags. By restricting the use of fossil fuels in the US, we are hoping to encourage the development of bioplastics such as polylactic acid based bags earlier in history so that the build up of plastic bags in the environment wouldn’t be a current issue and also to facilitate the existence of an extremely green bag that is cheap and easy to produce with the technology developed since the 1950s due to our change.  

Structures

 

This is the structure of polyethylene. This is what plastic bags are made of today.

 

This is a structure of polylactic acid. This is what we would substitute for polyethylene in the production of plastic bags.

Interview with Dr. Craig S. Criddle from Stanford University

Here is a recording of the interview we held with Dr. Criddle from Stanford University. 

Link to Interview with Dr. Craig S. Criddle 

Special Thanks:

 - Dr. Craig S. Criddle

 - Stanford University 

International Contact from Stanford University

Craig S. Criddle
Professor, Environmental Engineering & Science (EES)
Senior Fellow, Woods Institute for the Environment

Craig Criddle is interested in the environmental engineering, science, and science literacy needed for clean water, clean energy, and healthy ecosystems. His research focus is environmental biotechnology.  He is best known for large interdisciplinary field projects, studies of microbial ecology in bioreactors, and work on microbial transformations of persistent contaminants. Some current projects include a field-scale evaluation of uranium remediation; DNA-monitoring of microbial community structure at full-scale biological wastewater treatment plants; development of membrane bioreactors for energy recovery and nutrient removal; and studies to elucidate the mechanisms and kinetics of microbial transformation of halogenated solvents. To promote science literacy, he worked with award-winning San Francisco cartoonist, Larry Gonick to write "The Cartoon Guide to Chemistry".  "Cartoons can give us an intuitive feeling for the why, and deeper understanding can grow from that intuition".

http://cee.stanford.edu/faculty/layout.php?sunetid=ccriddle
http://www.stanford.edu/group/evpilot/

Possibility of Making Plastic Bags without Fossil Fuels

CNN reports that the Korea Advanced Institute of Science and Technology (KAIST) have developed a new method in 2009 of producing polylactic acid (PLA) without the use of fossil fuels. The Korean scientists have been able to produce polymers for our everyday plastic bags with the help of bioengineering. PLA is a polymer of interest, especially today because of our concern for the environment in its current state and the limiting nature of non renewable resources. According to Professor Sang Yup Lee, "PLA is considered a good alternative to petroleum-based plastics, as it is both biodegradable and has a low toxicity to humans." Before the new method of producing PLA was discovered, a two-step fermentation and chemical process of polymerization was used. This process was both costly and complex. Lee states, "By developing a strategy which combines metabolic engineering and enzyme engineering, we've developed an efficient bio-based one-step production process for PLA and its copolymers,This means that a developed E. coli strain is now capable of efficiently producing unnatural polymers, through a one-step fermentation process." KAIST hopes to propose new, efficient methods to producing unnatural polymers that are safe for the environment using the direct fermentation of renewable resources by developing this new method to produce PLA. 


http://edition.cnn.com/2009/TECH/science/11/23/eco.korea.plastic/index.html

The Three Basic Types of Plastic Bags and Alternative Production Method

This source summarizes two main points. When and how the plastic bag was created and the chemicals involved as well as the method used. Plastic shopping bags were made from one of three basic types: high-density polyethylene (HDPE), low-density polyethylene (LDPE), or linear low-density polyethylene (LLDPE). These materials and methods were first discovered and used by Karl Ziegler and Giulio Natta. They discovered a method that uses a transition-metal catalyst, in which polymerization would initiate. They won a Nobel prize for this in 1963. As William Carroll, a polymer chemist said, ""With the possible exception of a little lubricant to help in extrusion, plastic bags are pretty much just the native polymer."" The only other things you add to plastic bags are pigments, to change the color of the bags. They suggest that we can make plastic bags out of starch, which can be found in potatoes and corn. This makes bags biodegradable, although it does make the production of plastic bags much more expensive.  


http://pubs.acs.org/cen/whatstuff/stuff/8238plasticbags.html

Negative Effects of Plastic Bags to the Planet

As plastic bags are being used daily, most plastic bags go into landfill, or rubbish tips. Each year more and more plastic bags are ending up littering the environment. Once they become litter, plastic bags find their way into our waterways, parks, beaches, and streets. And, if they are burned, they infuse the air with toxic fumes. About 100,000 animals such as dolphins, turtles whales, penguins are killed every year due to plastic bags. Many animals ingest plastic bags, mistaking them for food, and therefore die. And worse, the ingested plastic bag remains intact even after the death and decomposition of the animal. Thus, it lies around in the landscape where another victim may ingest it. 

http://www.buzzle.com/articles/environmental-pollution-the-harmful-effects-of-plastic-bags.html