-------------------------------------------------------------------------- | Add your name to the CLEAN GOA INITIATIVE | | | | by visiting this link and following the instructions therein | | | | http://shire.symonds.net/pipermail/goanet/2005-October/033926.html | -------------------------------------------------------------------------- Savika,
I suspect that there is minimal risk of extended storage of food items in typical plastic containers, unless the containers were not sanitary to begin with. The issue here may be that it is easier to sterilize say, used glass containers than used plastic containers. The other issue with plastic containers is that they may degrade over time (specially if exposed to UV) thus resulting in the possible diffusion of contaminants from the outside environment. In general, plastics are a pretty good barrier to most solvents and are in fact used as barrier materials in landfills to protect contamination of underlying ground water. Banning the use of a material just because people fail to handle the waste properly is not the solution. Regarding the other question raised by Vivian on converting plastics to fuel, yes it is possible to do so. A cursory literature search of a number of engineering databases suggests that this has been studied since the 1960s. A petroleum or perhaps a chemical engineer may be better able to explain this, but basically, most fuels and plastics have the same building blocks (ie. hydro carbons) and very often use the same starting materials (ethylene). Most polymers are very very long chain hydro carbons while most fuels are short chain hydro carbons, with waxes and parafins in between. Conversion of polymers to fuels involves the breaking up of their long chains into the smaller chain molecules using a variety of "cracking" processes. It typically involves a combination of heat and catalysts to enhance the reaction, by lowering the so called activation energy necessary for the cracking reaction to proceed. The contribution of catalysts is very complex, but it typically utilizes a presence of a surface on which the reactants can more easily interact and in this case crack at a lower temperature. One problem with the conversion of plastics to fuels is that one has a constantly changing blend of plastics. What this means is that the cracking reactions will not be consistent, thus leading to a broad spectrum of by product gases having different masses. These gases are then fractionally distilled by taking advantage of their different condensation temperatures (which is a function of their mass). The problem is that, the ratio of these various by products may change drastically based on the type of waste plastic you begin with, which means that control of yield will be difficult. Besides yield control, the other issue would be economic viability. Unlike say crude oil, a lot more energy may be needed to crack the polymers. There may also be issues related to having to more frequently regenerate the catalysts which get "clogged" up with carbon deposits. Marlon Savika Gomes <[EMAIL PROTECTED]> wrote: >Hello Lawrence....... > >Thank your for your email....... > >There are different types of plastics - some suitable to store food grade >items, some suitable to microwave, and others seriously meant for a one time >use!
