Tech Facts Volume 4
Only a small portion of solar radiation consists of invisible ultraviolet (UV) light. But the light in this spectral range is responsible for photo degradation. Photo degradation results in discoloration, fading, embrittlement, cracking, chalking and/or loss of mechanical properties. Chalking gelcoat fiberglass, yellowing plastics, fading and weakening fabrics and sunburned skin are all familiar problems caused by UV light. Before UV light can cause harm, it must first be absorbed. If it is not turned into heat or transferred to a nearby stabilizer molecule called a quencher, it breaks weak chemical bonds. This is the beginning of UV damage.
Some materials absorb UV light more readily than other materials. Materials that readily absorb UV light are quickly damaged...rubber, vinyls, gelcoat fiberglass, and many other plastics. Acrylic is slow to absorb UV light and accordingly very resistant to photo degradation.
UV stabilizers are a group of chemical agents with the ability to counteract or neutralize the harmful effects of UV light. Competitive absorbers provide protection by converting UV light to heat so it can dissipate harmlessly (See Vol. I). Other UV stabilizers work differently. All UV stabilizers are consumed as they do their job. In a way, they serve as sacrificial molecules, taking the abuse from the UV light instead of the material they are protecting.
This brief overview greatly simplifies this very complex subject. Discoloring due to absorbers that have absorbility into the visible light range is a problem. And there are many others.
Two important points: UV stabilizers have to be periodically renewed or replenished if continuing UV protection is to be achieved. Second, there is no such thing as a permanent UV stabilizer. a matter of physics, not chemistry.
A FEW MORE FACTS. . .
When UV light is absorbed, it starts to break (cleave) weak chemical bonds which leads to bleaching (fading), discoloration, chalking, brittleness and cracking, all indications of UV deterioration.
The bond cleavages resulting from UV absorption cause the formation of "radicals." Each free radical can trigger a chain of reactions (in the presence of air), leading to more bond cleavages and destruction. These oxidating chain reactions require no further UV exposure, just the presence of air.
Thus, it is important to provide UV protection with agents that use competitive absorption to convert the light wave energy into harmless heat (like carbon black does in tires - refer to Vol. I). It is equally important to protect with quenching agents that have radical scavenging ability.
Summary: No matter what it's called UV protection, UV screening, sunblock - to provide true UV protection in a maintenance product form, it is necessary to utilize effective, active chemical agents called UV stabilizers.
|Untreated rubber, vinyl and other plastics readily absorb, and are degraded by, UV light.||The best UV protection money can buy. 303® restores, beautifies and lasts longer. Guaranteed!|