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Question
What would you guess is the usual longevity of the high density polyurethane? foam typically used for the soles of sneakers?

The reason I'm asking is I am in the sports memorabilia business and I have a pair of Nike basketball shoes whose foam soles are disintegrating.

I was somewhat familiar with vinyl deterioration due to plasticizer instability but wondering if this is typical of polyurethane foam, and if there's anything that can be done to slow or stop the deterioration.

Answer
Hello Theo:

Residual reactivity/loss of plasticizer is not usually the cause of polyurethane (PU) degradation as most PUs can get by with little or no small molecule additives.  My strong suspicion is that you are looking at biodegradation of the soles - urethanes, unlike vinyl composites, are pretty tough against mechanical wear but very susceptible to fungal and bacterial degradation over time.  This will not necessarily manifest as discoloration of any sort (eg it need not be black or green or have any color at all) for this to be occurring.

Below is a link to a pdf of a book chapter that is available for free (book edited by Singh, book chapter by Howard at Southeastern Louisiana University) that does a great job on talking about PU biodegradation.  It's a very well researched area, as the scientific community is always interested in the biodegradability and environmental impact of plastics/rubbers.  

http://www.selu.edu/acad_research/depts/biol/faculty/publications/pdf/2012/howar

The things you are interested in start in section 14.4.  My suggestion would be to 1. isolate your collection if possible to prevent increased exposure to new fungi and bacteria and 2. test a small, not-so-obvious region with an anti fungal or anti-microbial spray or ointment.  If it appears that the antimicrobial is not reacting (ie further degrading) the PU, then treating the soles might be an option.  

Please feel free to send a follow up if you have any other questions about the book chapter or if you need to discuss other possible options.

Take care!

Careers: Chemistry

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Dr. Jeffery Raymond

Expertise

Materials chemistry. Materials science. Spectroscopy. Polymer science. Physical Chemistry. General Physics. Technical writing. General Applied Mathematics. Nanomaterials. Optoelectronic Behavior. Science Policy.

Experience

Teaching: General Inorganic Chemistry I & II, Organic Chemistry I & II, Physical Chemistry I, Polymeric Materials, General Physics I, Calculus I & II
My prior experience includes the United States Army and three years as a development chemist in industry. Currently I am the Assistant Director of the Laboratory for Synthetic Biological Interactions. All told, 13 years of experience in research, development and science education.

Organizations
Texas A&M University, American Chemical Society, POLY-ACS, SPIE

Publications
Journal of the American Chemical Society, Nanoletters, Journal of Physical Chemistry C, Journal of Physical Chemistry Letters, Ultramicroscopy Proceedings of SPIE, Proceedings of MRS, Polymer News, Chemical and Engineering News, Nano Letters, Small, Chemistry.org, Angewandte

Education/Credentials
PhD Macromolecular Science and Engineering (Photophysics/Nanomaterials Concentration), MS Materials Science, BS Chemistry and Physics, Graduate Certificate in Science Policy, AAS Chemical Technology, AAS Engineering Technology

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