Editing Polyurethane (section)

===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>