Not only is it possible to make rubber out of urine, it's already being done. Researchers have developed a new rubber-like substance from a complex combination of fatty acids and urea, a key component of processed urine. The rest of the ingredients generally found in urine are mercifully not used, although the finished product does leave a strong urine smell after handling.
The process required to make rubber out of urine is still very labor-intensive as of this writing, but researchers have been able to produce several kilograms at a time in test batches. The resulting urine rubber has a distinctive dark amber color, and a soft consistency somewhere between Silly Putty and rubber cement.
One of the advantages of rubber made of urine is the ecological green effect. Natural rubber products require significant resources to produce, and synthetic rubber products may exude harmful gases over time. If a tire or adhesive company could make rubber out of urine and fatty acids, the impact on the natural world would be minimal.
Urine rubber may sound distasteful, but it has amazing self-healing qualities which would make it an ideal material for many future products. A toy truck made from this material, for example, would eventually reclaim its original shape and elasticity even if a part were completely torn in half. A car tire made from urine rubber would eventually reseal after suffering a puncture or even a slash. Cutting boards made from this rubber would eventually heal from damage caused by blades.
The reason rubber made from a component of urine works so well is the nature of the chemical bonds between the urea and fatty acids. When a normal rubber band snaps, the ends cannot reform the strong covalent chemical bonds necessary to self-heal.
When the researchers decided to make rubber out of urine, however, they discovered the snapped ends still contained millions of tiny "hands" which wanted to reform strong bonds with other "hands." Once these two ends were mated back together and given some time to heal, the new bond was just as strong as if the rubber had never snapped at all.
While research on urine rubber is still in the early stages, it is hoped that the material will eventually be mass produced and used in a number of industries which would benefit from the advantage of self-healing adhesives and rubber products.