Editing Polyurethane (section)

==Degradation and environmental fate==
===Effects of visible light===
[[Image:UVDistressedFlexMoldedFoam800x600.png|thumb|Polyurethane foam made with an aromatic isocyanate, which has been exposed to UV light. Readily apparent is the discoloration that occurs over time.]]{{Wikinews|Polyurethane plastic substitute can biodegrade in seawater, say scientists}}
Polyurethanes, especially those made using [[aromatic]] isocyanates, contain [[chromophores]] that interact with light. This is of particular interest in the area of polyurethane coatings, where [[light]] stability is a critical factor and is the main reason that [[aliphatic]] isocyanates are used in making polyurethane coatings. When PU foam, which is made using aromatic isocyanates, is exposed to visible light, it discolors, turning from off-white to yellow to reddish brown. It has been generally accepted that apart from yellowing, visible light has little effect on foam properties.<ref>{{cite web| url=http://www.fxi.com/assets/pdf/Discoloration_Info.pdf|title=Discoloration of polyurethane foam|publisher=Foamex Information sheet|access-date=2010-09-26|archive-url=https://web.archive.org/web/20100924224254/http://fxi.com/assets/pdf/Discoloration_Info.pdf|url-status=dead|archive-date=2010-09-24}}</ref><ref>{{cite journal |doi=10.1177/0021955X9302900605 |title=Inhibition of the Discoloration of Polyurethane Foam Caused by Ultraviolet Light |journal=Journal of Cellular Plastics |volume=29 |issue=6 |pages=569–88 |year=1993 |last1=Valentine |first1=C. |last2=Craig |first2=T.A. |last3=Hager |first3=S.L. |s2cid=208363195 }}</ref> This is especially the case if the yellowing happens on the outer portions of a large foam, as the deterioration of properties in the outer portion has little effect on the overall bulk properties of the foam itself.

It has been reported that exposure to visible light can affect the variability of some physical property test results.<ref>{{cite conference |first1=G. Ron |last1=Blair |first2=Bob |last2=Dawe |first3=Jim|last3= McEvoy |first4=Roy|last4= Pask |first5=Marcela Rusan |last5=de Priamus |first6=Carol|last6= Wright  |title=The Effect of Visible Light on the Variability of Flexible Foam Compression Sets |publisher=Center for the Polyurethane Industry |year=2007 |location=Orlando, FL |url=http://www.moldedfoam-ip.com/linkedpdf/Technical%20Info%20-%20The%20Effects%20of%20Visible%20Light%20on%20the%20Variability%20of%20Flexible%20Foam%20Compression%20Sets%20(Final).pdf |access-date=2008-01-26 }}</ref>

Higher-energy [[Ultraviolet|UV]] radiation promotes chemical reactions in foam, some of which are detrimental to the foam structure.<ref>{{cite journal |doi=10.1021/ie0009738 |title=Modeling the Ultraviolet Photodegradation of Rigid Polyurethane Foams |journal=Industrial & Engineering Chemistry Research |volume=40 |issue=15 |pages=3346–52 |year=2001 |last1=Newman |first1=Christopher R. |last2=Forciniti |first2=Daniel }}</ref>

===Hydrolysis and biodegradation===
Polyurethanes may degrade due to [[hydrolysis]]. This is a common problem with shoes left in a closet, and reacting with moisture in the air.<ref>{{cite web |title=Hydrolysis, The Crumbling of Shoe Soles explained {{!}} Safety Shoes and Gloves |url=https://www.safetyjogger.com/en/academy/hydrolysis-crumbling-shoe-soles-explained |website=www.safetyjogger.com}}</ref>

Microbial degradation of polyurethane is believed to be due to the action of [[esterase]], [[urethanase]], [[hydrolase]] and [[protease]] enzymes.<ref>{{cite journal |last1=Toward 
|first1=Gary T. |title=Biodegradation of polyurethane: a review |journal=International Biodeterioration & Biodegradation |date=June 2002 |volume=49 |issue=4 |pages=245–252 |doi=10.1016/S0964-8305(02)00051-3|bibcode=2002IBiBi..49..245H }}</ref> The process is slow as most microbes have difficulty moving beyond the surface of the polymer. Susceptibility to fungi is higher due to their release of [[fungal extracellular enzyme activity|extracellular enzymes]], which are better able to permeate the polymer matrix. Two species of the Ecuadorian fungus ''[[Pestalotiopsis]]'' are capable of biodegrading polyurethane in aerobic and anaerobic conditions such as found at the bottom of [[landfill]]s.<ref>{{cite journal |doi=10.1128/AEM.00521-11 |pmid=21764951 |pmc=3165411 |title=Biodegradation of Polyester Polyurethane by Endophytic Fungi |journal=Applied and Environmental Microbiology |volume=77 |issue=17 |pages=6076–84 |year=2011 |last1=Russell |first1=J. R. |last2=Huang |first2=J. |last3=Anand |first3=P. |last4=Kucera |first4=K. |last5=Sandoval |first5=A. G. |last6=Dantzler |first6=K. W. |last7=Hickman |first7=D. |last8=Jee |first8=J. |last9=Kimovec |first9=F. M. |last10=Koppstein |first10=D. |last11=Marks |first11=D. H. |last12=Mittermiller |first12=P. A. |last13=Nunez |first13=S. J. |last14=Santiago |first14=M. |last15=Townes |first15=M. A. |last16=Vishnevetsky |first16=M. |last17=Williams |first17=N. E. |last18=Vargas |first18=M. P. N. |last19=Boulanger |first19=L.-A. |last20=Bascom-Slack |first20=C. |last21=Strobel |first21=S. A. |bibcode=2011ApEnM..77.6076R }}</ref><ref>{{Cite web|last=|first=|date=2021-04-14|title=Could Plastic-Eating Mushrooms Solve mankind's Plastic Problem?|url=https://sciencemint.com/could-plastic-eating-mushrooms-solve-mankinds-plastic-problem/|access-date=2021-07-02|website=Sciencemint|language=en-US|archive-date=2021-07-09|archive-url=https://web.archive.org/web/20210709182652/https://sciencemint.com/could-plastic-eating-mushrooms-solve-mankinds-plastic-problem/|url-status=dead}}</ref> Degradation of polyurethane items at museums has been reported.<ref>{{cite journal |doi=10.1128/AEM.01768-07 |pmid=18065627 |pmc=2227722 |title=Microorganisms Attack Synthetic Polymers in Items Representing Our Cultural Heritage |journal=Applied and Environmental Microbiology |volume=74 |issue=3 |pages=564–9 |year=2007 |last1=Cappitelli |first1=F. |last2=Sorlini |first2=C. |bibcode=2008ApEnM..74..564C }}</ref> Polyester-type polyurethanes are more easily biodegraded by fungus than polyether-type.<ref>{{cite journal |doi=10.3390/ijms10093722 |pmid=19865515 |pmc=2769161 |title=Biodegradability of Plastics |journal=International Journal of Molecular Sciences |volume=10 |issue=9 |pages=3722–42 |year=2009 |last1=Tokiwa |first1=Yutaka |last2=Calabia |first2=Buenaventurada P. |last3=Ugwu |first3=Charles U. |last4=Aiba |first4=Seiichi |doi-access=free }}</ref>