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Name: S Sample
Status: Teacher
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Question:
I am a junior high school science teacher and I have a question about recycling of plastics. I know there are seven plastic categories, but I do not know anything about the process involved to recycle plastics. Do you reheat them up until melting point is reached or do you have to add chemistry before they are reusable liquid? In other words, can a junior high school teacher actually take a #2 milk container and reform it in school or develop an activity whereby my kids can do this?



Replies:
About 86% of the plastic in use today falls into the category of thermosetting plastic. This total consists of about 55% polyethylene and polypropylene, 20% polystyrene, and 11% PVC. Your #2 milk jug, high density polyethylene, is a thermosetting plastic. Unfortunately, thermosetting plastics have cross linked polymers and cannot be remelted. If heated until it melts, the plastic will decompose. This is a problem from two points of view. First, if you melt thermosetting plastic and then attempt to reset it, you will have a non-cohesive blob of goo to contend with. Second, if heated to the point that the cross links of the polymer degrade, some actual degradation of the plastic and (if present) plasticizer release will occur. PVC, for example, contains a polyethalate ester to keep the final product from being hard and brittle. Polyethalate ester vapors are not pleasant compounds that I would like to introduce to a junior high classroom. Also, the point at which plastic melts and that which it decomposes (burns) are very close. Melting plastic would result in a release of a host of unpleasant compounds (as anyone who every burned a polystyrene foam cup will attest to). Re-softened and remolded under very controlled conditions with appropriate environmental controls. It probably is not a good idea to attempt this in a classroom setting. I am however involved in a sort of a community awareness type presentation for local school districts. Right now we (USDOE) are only speaking at grade schools (topics include waste reduction, recycling, pollution prevention, composting, etc.) I would be very much interested in hearing from you on any ideas you have, and perhaps we can come up with some type of recycling experiment that does not involve releasing hazardous compound.

Eric Dallman



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