Why does UV light (i.e. sunlight) degrade PVC?
438723
UV light causes a homolytic cleavage of the carbon-chlorine bond, generating free radicals that initiate a chain reaction of degradation.\n\nC-Cl goes to  C. + Cl.  The Cl. goes on to further react with PVC at different sites along the chain, splicing it
505387
Ozone (O3) reflects/scatters ultraviolet radiation back into space.  However, if it is depeleted, this radiation makes it past the atmosphere and down to the surface.  The amount of shorter wavelength (higher energy) radiation passing through the atmosphere would increase, causing higher mortality rates from skin related ailments and can also destroy plant tissue.  Also, this radiation would heat the earth more since it carries more energy with it.  This is not usually a problem, since this thermal radiation currently passes back into space.  However, with pollution clouds/dust being more prominent, it would reflect the thermal radiation back down to earth's surface, driving the temperature up even more.
695121
UV light directly causes DNA damage.  Causes formation of thymine dimers.
170850
I just spilled something rude on my black leather sofa & it went lighter not darker!\n\nSeriously though, very good question. \n\nIt obviously has something today with absorbency - a pair of blue jeans gets much darker, a blue plastic sheet hardly changes.\n\nAt a guess, I would say the surface tension of the water bonds it to surrounding molecules, creating a smaller surface area, thus reflecting less light.\n\nIt's just a guess, but feel free to spank me with a wet fish if I'm wrong, lol.
553010
The manufacturer may be able to supply you with the spectral analysis for a particular light source.  For example flourescent bulbs use UV to cause phosphors to emit light and may absorb most or all the UV in the process.
512383
Vinyl chloride is polymerized to make polyvinyl chloride, also called PVC.\n\nPVC can be molded or extruded into just about any shape, including pipe.  It is a rigid plastic itself, but can be made flexible by the addition of plasticizers.  Plasticized PVC is often called simply: vinyl.\n\nPVC is a very durable plastic, although pure PVC can be degraded by UV exposure.  PVC for outdoor use (vinyl siding, vinyl windows) often contains other chemicals that prevent that degradation, either by absorbing the UV light or by preventing the subsequent chemical reaction.
1185470
I've wondered this myself. I think that in the case of an illuminated sign, the landlord wants to continue to protect the lighting tubes from vandals so its quick & cheap to reverse the plastic panel.
1141579
A number of colours are sensitive to UV - usually when you don't want them to be. They will fade or degrade under UV light. Many organic pigments are like this - particularly some of the organic red pigments.\n\nA few compounds fluoresce under UV - the "dayglow" type dyes and pigment, some stilbenes (compounds like Tinopal which are used as optical brighteners), fluoroscene, some of the rhodamines. They all look impresssive under UV.
1010815
First, you can't change the bonds unless you replace one or both of the atoms involved in the bond.  Second, it's the halogen radicals (Cl and F) that are (supposedly) the problem.  If you start replacing the halogens with other kinds of elements, you will lose the molecular properties that made CFCs so useful to begin with.  \n\nI wonder what, if any, effect a higher UV flux would have on the mutation rate here on the surface of the Earth.  What kinds of changes do you think might occur?  This might be a good topic for your project.  And the best part is that no one can prove you wrong...
166888
pvc pipe does not corode or oxydize. copper does. the salt in the system acelerates the rate of corotion. i think that the pvc would last longer anyways because plastic takes like 10000 years to break down. i dont know what bsk stands for(its probably obvious but im just not making the connection)
1047935
UVA:\nCan pass through window glass.\nIs not affected by a change in altitude or weather.\nIs present all day and every day of the year.\nPenetrates deep into skin layers.\nIs 5% of the sun's rays.\nIs 20 times more abundant than UVB rays.\nAffects long-term skin damage.\n\nUVB:\nCannot pass through window glass.\nCauses sunburn.\nCauses tanning.\nHelps the body with normal vitamin D production.\nVaries with the season. It is more intense in the summer than in the winter.\nVaries with weather conditions.\nIs more intense at midday than in the morning or late afternoon.\nIs more intense at high altitudes and near the equator.\nIs 0.5% of the sun's rays.\nIs protected against by the sun protection factor (SPF) in sunscreens.\nIs related to more than 90% of nonmelanoma skin cancer.\nIs related to cataracts.\n\nMore:\n\nHow Sunlight Works\n\nSunlight arrives on earth in three forms: infrared (heat), visible light and ultraviolet. Ultraviolet light is classified into three categories: \nUVA (315 to 400 nm), also known as black light, which causes tanning \nUVB (280 to 315 nm), which causes damage in the form of sunburn \nUVC (100 to 280 nm), which is filtered out by the atmosphere and never reaches us. \n99% of the sun's UV radiation at sea level is UVA. It is the UVB that causes most of the problems related to sun exposure: things like aging, wrinkles, cancer and so on, although research is increasingly implicating UVA as well. \nOne of the interesting things about UV radiation is that it is reflected by different surfaces. These reflections can amplify the effects of UV exposure. For example, snow reflects 90% of UV light. That is why you can get snow blindness and severe sunburns from skiing on a sunny day. Sand can reflect up to 20% of UVB that hits it, meaning that you can get extra UV exposure at the beach. \n\nOn the other hand, certain things absorb almost all UV radiation partially or completely. Glass is one of these substances - many glasses are very good absorbers of UV (which is why you may have heard that you cannot get sunburn in a greenhouse - just make sure it is glass and not plastic covering the greenhouse!). Most sunscreens use chemicals that have the same UV-absorbing properties.
166740
I guess u need a UV light
970333
UV rays are just a "color" of light that cannot be seen by humans. It has too short of a wavelength. UV is typically broken down into UVA and UVB. \nAmongst other things, UV light can be used for gettnig a nice tan, curing some adhesives, damaging most kinds of plastics (take a look at the dashboard of an old car - that cracking is due to UV damage)
432601
the UV waves cause heterolytic fission of chemical bonds creating "radicals" which are very reactive species.  They will react with pretty much anything.  The UV radiation is therefore breaking down the skin and the colour molecules in paint and clothes, making them look like they are losing their colour.  The purpose of sun-tan lotion is not only to stop the UV radiation getting to your skin, but also to mop up all the free-radicals formed before they do any damage.  Skin cancer is caused by this process.  You are essentially changing the structure of the skin.
571942
Photocatalytic degradation is any process that decomposes a compound that is catalyzed by the presence of electromagnetic radiation.  For example, certain plastics will naturally oxidize over time, and become brittle.  this reaction is accelerated by the presence of sunlight.
556005
no\n\nyou're skin only gets darker when exposed to ultraviolet light.
235390
because of the ultraviolet rays.