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Name: Miguel
Status: student
Grade: 9-12
Location: CA
Country: USA
Date: N/A 


Question:
When plastic bottles are being made does the melted plastic release fumes? If so, what happens to the fumes or where does it go?



Replies:
This does not have a "simple" answer. First, "plastic" refers to a whole class of polymers (high molecular weight molecules). There are hundreds of such substances.

Second, these are formulated products containing several (to possibly dozens) of other ingredients, depending upon the application. Some examples: pigments and/or dyes for color, processing aids such, as slip aids, so that the molten plastic does not stick to the bottle-making machinery, plasticizers to make the bottle softer and more flexible. This is just a short list of many variations and combinations. As a general rule, the generation of "fumes" may be a sign that something is decomposing, so that would not be desirable -- but even that is a simplification. The operating temperature of the bottle forming machinery would have an impact. Again, in general, bottle forming equipment is done in a fume hood to capture any volatile effluents from the manufacturing process (for health and safety of the operators). I would like to be more specific, but your question is a large one.

Vince Calder


Hi Miguel,

The vast majority of plastic bottles that contain water, drinks and other liquids, are made of polyethylene terephthalate, or PET for short. Neither this material, nor any of the other myriad of different plastics that are molded into everyday articles, release any significant fumes when melted during molding. The process of injection molding accurately controls the melting temperature to ensure that problems due to excess temperature, such as plastic decomposition and the resulting generation of fumes, cannot occur.

Regards,
Bob Wilson


Miguel,

It really depends on the manufacturing process of the particular plastic.

Some processes involve adding some kind of solvent which will allow the plastic to be processed as a thick solution. This may be done so that the plastic does not have to be processed at high temperatures - there is no need to melt the plastic. In other processing techniques, additives are added somewhere in the processing line. These additives could be for color (dyes), for strength (metals or carbon), for plasticity (plasticizers), for health reasons (antibacterials), etc. Some of these additives may be released during the manufacturing process or even long after the product is in the market. For example, in order to make the packing materials used to package fast-food products, some gases are added to the plastic in order to make it into a foam. Most of these gases are extracted after the processing and what we have are holes were the gases used to be. Or you may have gotten into a new car and smelled that distinctive "new car smell" - that is another one of those gases that are coming off the plastic.

Greg (Roberto Gregorius)
Canisius College



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