From: "semi hemi" 
To: atm{at}shore.net
Reply-To: "semi hemi" 


>Next:  Organic chemistry help please.  I am looking for a solvent that >can
>soften and dissolve polycarbonate soda bottles.   This might enable >us to
>make many kinds of small plastic parts while recycling evil >plastic.  A
>similar solvent for plastic grocery bags could also be >useful.

The company where I work has a very well equipped plastics lab.  They will
do just about anything with plastic except - dissolve it.  The reason is
that the solvents in question are just too harmful.  Most are carcinogenic,
need to be registered, etc.  This is true of solvents for  polycarbonate
(PC) which has relatively poor chemical resistance.  It is a hundred times
more true of anything that will dissolve grocery bags, which are typically
made from polyethylene (PE). If it will dissolve PE, stay far far away.

Incidentally, I am not aware of any polycarbonate soda bottles.  Most are
made from polyethylene terephthalate (PET or PETE).  PET is also amazingly
impervious to chemical attack so anything that will dissolve it shouldn't
be handled by us ATM's.

>Melting with heat does not seem to work well.

These polymers belong to the phylum Thermoplastics.  As we may infer from
the name, melting with heat is in fact the only viable way to soften them,
but it is difficult to control for amateurs. PE, depending on the grade,
will melt process at roughly 320F up to 550F.  PC would be at the high end
with processing temps often above 500F but below 600F.

As mentioned in  another response, injection molding is a fabulous way to
recycle these materials.  One need only mechanically grind the scrap down
to a size of 1/4 of an inch and then just shovel it into the molding
machine. Voila - out the other end come brand new parts!  No solvents or
other messiness.  However, injection molds are horrendously expensive,
ranging from $20,000 to $400,000 US.  Thus, recycling is usually done on a
massive, rather than an individual, scale.

Thus, individual processing of plastics is usually limited to small casting
and/or machining projects.  Particularly casting will liberate some
undesirable volatiles, but the danger pales in comparison to attempting to
dissolve most thermoplastics in the home workshop.

Hope this provides a little perspective.  If not, feel free to give me hell!

John

PS: Anyone who has seen a family member on a crash cart or in the ICU might
not so freely characterize plastics as evil!!
                                                 \/

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