The question is very relevant. I know from experience that a sufficiently long UV exposure of such materials will cause cross-linking, please bear in mind the depth of penetration for UV radiation in your material, you will probably obtain only surface effect.

Thanks Andrzej, the surface effect (a most rigid skin) can be produced, but if a solution at constantly stirring is submitted to UV irradiation and only after this are dryed. However, a photoinitiator should be used to start the free radicals?

Could be but the efficiency will be low mainly for solid materials. The better way to induce crosslink in rubber or polymers is irradiated them with an electron beam between 5 and 10 Mev during some seconds (radiotherapy machines in hospitals can do this)

Theoretically, it should be possible to vulcanize natural rubber using UV irradiation. However, as rubber may undergo autoxidation under UV conditions, there may be degradation and the mechanical properties may decrease. But one may select conditions whereby the free radicals are to enhance vulcanization and cross linking over degradation. For example, a photoinitiator and a poly-functional thiol if added to NR latex, bond cleavage of the photoinitiator takes place on UV irradiation and cross-linking of the latex particles is then achieved by a thiol-ene addition reaction.

Thanks Cks Pillai, I will try using a thiol-ene under UV in an inert atmosphere.

Go back to Chemistry and review your idea. If the crosslinking reaction will happen. then any kind stimulation (UV, Heat...., ) could induce the reaction. So, you can success. otherwise, it will not happen.

Thanks Dr. Feng, I'm physical and and sometimes fail me the basic knowledge of chemistry . Yet even that is chemically possible (in theory) is not always easy or possible experimentally. I will try find out if it is possible and the best conditions to do.

Generally, high energy radiation leads to cross-linking. But on Industrial point of view, it is not economical and efficient. Sufur vulcanisation is cheaper and effective.

besides what have been said, also important to bear in mind the oxidation of the polymeric matrix by radiation, so in fact the two processes are in competition, i.e., crosslinking (increasing in MW) and degradation (decreasing MW). Another aspect that was mentionned before is the possible occurrence of a crosslink gradient since the radiation is exposed to a damping process while going through the matrix.

In all situations a compromise should be established and taken between the irradiation dose and exposure time.

UV penetration is too poor to be of any practical applications for bulk processing, unless of course it is for coating purposes