Rubber softener for tire prep.

[George4545]

Hey all.
I've been reading up on some old forums. I came across a forum where someone mentioned to use nmp as a tire softener. (N-METHYL-PYRROLIDONE). It works well but I have to apply heat to the tire so the chemical soaks into the rubber. Is there anything j can mix with nmp to help drive it into the tire? What's great about nmp is it doesn't have a smell. Thanks
George.

 

[Compositepro]

Acetone may help swell the rubber so that NMP is absorbed faster. Acetone will evaporate rather quickly, so it needs to be kept from doing so during the soak-in process, and then needs to be given time to evaporate after the soak-in. Be aware that NMP is water soluble so exposing the rubber to water would tend to extract the NMP.

 

[George4545]

So I tried an 8 oz. 75% nmp 25% odorless mineral spirits mix and it's taking a long time (10 hours and counting) to sink in without use of heat. I would think with the relatively small chemical size of nmp compared to other commonly used solvents in tires that it would penetrate easier than it has so far.

 

[Compositepro]

NMP is somewhat high in viscosity at room temp. Its solvent strength is much greater when hot. Molecular mobility increases rapidly near the boiling point and the boiling point of NMP is 400F. But that makes it a good plasticizer.

 

[George4545]

Very interesting. Another quality of nmp from what I've gleaned is that it works well not only as a plasticizer, but it also provides the tire with good external bite, helping to increase the coefficient of friction in addition to softening. Do you know the reason behind this?

 

[Compositepro]

I imagine that effect is due to a softer rubber being able to conform to the roughness of the road surface better, resulting in more mechanical interlocking between the two.

 

[George4545]

So would you say the stickiness always comes as a side effect of the softness? Or are there some chemicals that the two could be separated, say where you could have a a hard sticky tire or vice versa.

 

[George4545]

Or is it more that a chemical that evaporates quickly only has time to soften (and thus make sticky) the very surface of the rubber before it evaporates, while higher boiling point, more viscous, slower evaporating ones drive deeper into the rubber, creating a more "complete" softness.

 

[Compositepro]

For traction you want to only soften the very surface of the tire for increased grab to the road. Stickiness is probably not the best term because there is no real adhesion occurring. Softening rubber significantly reduces its strength and wear resistance, and increases rolling resistance. Use of a volatile solvent for softening will result in rapid change in softness with time, as it evaporates.

 

[George4545]

Thank you. That was put into words better than I ever could. The "stickiness" is just what I feel. It's actually just a more pliable surface that allows more tire into the rough surface of the road, yielding more mechanical grip, correct?