Ask A Scientist Chemistry Archive

name         Lovelyn Faith L. C.
status       student
age          15

Question -   What is the safest and most effective way of melting plastic sheets at home? This process is 
actually part of our research project. We tried melting cut sheets of HDPE over a gas stove, but then 
everything, including the container, darkened and, in fact, almost completely charred.
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I would not recommend melting any plastic at home.  Some plastics give off toxic fumes when 
heated/melted/burned.  I do not know if HDPE does.  I do not know of a way to guarantee safety in this 
endeavor.

Pat Rowe
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A kitchen is NOT an appropriate place to do what you are trying to do. There are too many potential 
hazards, and the conditions cannot be controlled (e.g. temperature and fumes generated by decomposition). 
You and your teacher need to re-think the research project. As explained by you, the project is potentially 
hazardous, and not likely to be successful in a kitchen environment.
Softening (rather than melting) polymeric plastics depends upon what the plastic is. Do not try heating the 
plastic over an open flame or electric stove. Two dangerous things can happen, depending upon the material. 
1. It may catch fire. 2. It may give off toxic fumes. In particular polyvinyl chloride (the stuff water 
pipes are made with) decomposes to produce HCl and other nasty fumes.
Some plastics (for example Bakelite, the black plastic on pots and pans) will not soften at all it will 
just char, giving off noxious fumes.
HDPE is partially crystalline. This raises the softening point so high that in the presence of air (oxygen) 
it burns before it melts.
Polystyrene, when heated to high enough temperature to soften it "unzips" and produces styrene monomer 
which is toxic and flammable. Polystyrene burns with a very smokey flame and will set off your smoke 
detector in an instant.
Polymethylmethacrylate (Plexiglas is the trade name) softens at about 100 C but it does not really "flow" 
very much. It too tends to "unzip" to give off methyl methacrylate monomer.

Vince Calder
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