Alcohol and Plastic Interactions
Date: Spring 2013
In the archive I found a subject called "Amyl versus Isopropyl Alcohol" and I have a question about the last answer. It says: Neither of these alcohols "dries out" plastic, since there is no water (or any other substance) in plastic to "dry out" in the first place. But on other sites I found that Isopropyl alcohol could extract plasticizers out of plastics, which causes the plastic to craze or stiffen. Is this correct? Please clarify.
Very good question! It is true that alcohols can dissolve out (or extract)
plasticizers in those plastics that contain plasticizers. But of all the
commonly used plastics, the only type that contains plasticizers is
vinyl. All other types including all polyolefins (polyethylene,
polypropylene), polystyrene, ABS, polycarbonate, polyester, melamine,
thermoplastic elastomers, and many more, contain no plasticizers, and
thus are not subject to plasticizer leaching.
So, yes, exposure to solvents like alcohols can eventually case
hardening and cracking of vinyl parts that were once flexible, but none
of the other common plastics suffer this problem.
Plasticizers are usually small molecules such as phthalate esters,
providing softness and flexibility of plastics by separating polymer
chains and lowering interactions between them. They are soluble in
organic solvents such as isopropyl alcohol, and once they are removed
from plastics polymer chains have stronger interactions between them
to be stiff. Or after plasticizers are extracted from plastics, they
leave void spaces and cracks which will become easy to break.
In principle, any solvent that dissolves a plasticizer could extract it from a polymer. That would normally require prolonged contact, because the plasticized would have to diffuse out of the plastic, and diffusion is a slow process.
Richard E. Barrans Jr., Ph.D., M.Ed.
Department of Physics and Astronomy
University of Wyoming
Thanks for the question. The plasticizers in a plastic make the material flexible and reduce the hardness and brittle characteristics of pure plastic. Amyl alcohol and isopropyl alcohol are two of the many liquids which can extract plasticizers out of a plastic. In fact, you will find that cream of broccoli soup (tasty!) will extract plasticizers from a plastic bag (if you store the soup in the bag).
I hope this helps. Please let me know if you have more questions.
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