Plastic polish
Nail polish comes in many different forms. The most basic paint and draw polishes are made predominantly with an ingredient called nitrocellulose, which is made from mixing cotton fibres and nitric acid. However, over the years cosmetic chemists have created stronger nail gels for a more robust manicure with the help of compounds called photoinitiators. Most gel polishes require the wearer to place their hand underneath a UV lamp to cure their manicure. The gel polish goes into the lamp fluid, and after a couple of minutes is completely hard. This is because the photoinitiators in the polish absorb the UV light, releasing a free radical – an unbonded molecule. Free radicals then attach to small chains of plastic molecules called monomers, forcing them to combine with other monomers to form polymers. This causes a chain reaction, building polymers until the molecules are all stitched together, hardening the polish.
Polymerisation in action
1 Freeing the radical
The bonds between monomer molecules are broken – by UV radiation in the case of polish curing – and a free radical is released.
2 Chain reaction
Free radicals then act like sewing needles, threading molecular beads together to form elongated molecular chains called polymers.
3 All together
Once all the monomers have been used up or the free radical has found another free radical to join with, the process of polymerisation stops.