|MadSci Network: Chemistry|
I am not sure what can kind of substance you are looking for, but there is a patended film by 3M that can block 99.9% of the UV.
Click here to get to that page
In the previous case all (or most) of the UV is reflected by the coating on the film. Now about absorbing all of the UV rays, the object is going to get very hot, unless it will be radiated in some fashion. If there is no cooling system in place, the object will heat up until it deforms, or changes form.
Hope this helps, or give me a specific situation and I'll try to help you as much as I can.
Try the links in the MadSci Library for more information on Chemistry.