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Recycling Plastics
Name: S Sample
Status: Teacher
Age: N/A
Location: N/A
Country: N/A
Date: N/A
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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Update: June 2012
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