Why does rubber "dry"?

[f95toli]

Everyone knows that rubber "dries" after a few years and that this can cause problems.
On your average hifi-forum you will find lots of "tricks" that supposedly can help you preserve the rubber around the speaker cone.
After reading one such thread (with recommendations ranging from silicone to isopropanol and glycerin) I started wondering what is REALLY happening?
What kind of chemical reaction is causing the rubber to "dry"? Oxidation?

 

[ZeroNine8]

it's a combination of ozone attacking & deteriorating the molecular bonds and the oils and VOC's evaporating off and leaving it less flexible.

the best way to preserve rubber is to seal it somehow, to both prevent ozone from reaching the rubber and prevent any oils and such from evaporating.

 

[quentinterintino]

It's due to cross-linking in the monomers. The effect is known as plasticizing... products like Armor All for you car are "plasticizers" that "lubricate" and keep the polymer chains from deteriorating. I have heard of many people using a pure white petroleum (aka vasaline) on rubber o-rings to preserve them.

 

[imported_StormGod]

quentinterintino is exactly right. In fact "new car smell" is actually plasticizers evaporating from all the brand new PVC in your car. And that greasy haze that can form on the inside bottom of new windsheilds on very hots days....you guessed it, plasticizers from the dash board condensing on the "cold" windshield (colder than the super hot car interior). The PVC plant that I was a chemical engineer at made PVC dust and pellets. The dust was sold to the plastic pipe and siding industries (rigid). The pellets that we made were sold to industries that needed flexible plastic, and these pellets were half plasticizers by volume. So you can image why rubber would become rigid as these plasticizers evaporate.

 

[wseyller]

Exactly right Plasticizers. It is possible if you have a way to apply some sort of coating over it you could help slow the process of evaporation. I'm not an expert on this stuff but, I am one dealing with laser cartridge engineering. There is a roller inside a laser cartridge called a PCR (Primary charge roller) that is made of rubber. Problems exist in high heat and humidity area where the plasticizers will evaporate causing the pcr the crack all over. I have a coating that is applied to the PCR originally used to protect the roller from wear, but to also create a barrier from the plasticizers from evaporating.

 

[dkozloski]

I have seen aircraft rubber tires and tubes that were packaged in wax saturated paper boxes during WWII that are in good ondition to this day. It seems to me that the solution to your problem is to dip your speakers in molten wax.

 

[f95toli]

So this means that there is no way to reverse the process? Only slow it down?

Fortunately I do not have a problem with my speakers, I was just curious.

 

[wseyller]

I my situation:

The coating doesn't make the PCR bullet proof. It does give it a better level of protection. Different levels of temp. and humidity change the speed of the evaporation majorly. I'm just guessing but it probably also depends on what material the object is made of (ex., rubber, polyurothane, silicon). One problem also that could happen in my situation is that in high temp and low humidity of course will cause evaporation much faster. PCRs rest against the OPC drum in a laser cartridge. When the plasticizers start to evaporate to the surface they tend to contaminate the drum. Some of the test during developement was to try and speed up the evaporation process by place the waste hopper section of a toner cartridge with the drum and pcr in place and place the waster hopper in a convection oven at a high temp for 24 hrs. If the drum was ruined in one spot where the pcr rest against it did not have enough protection. With my coating applied to the pcr and then run the same test we found it was protected. In extreme temp and humidity for long periods of time nothing that I know of is going to protect it from cracking.

 

[Smilin]

Possibly related question:

Plastic lawn chairs. You know the old aluminum ones with weaved plastic bands on them. They get really frail after sitting out for a few years. I've heard we add something to the plastic to make them more resistent to this and that it's caused by UV rays. I also read somewhere (I think, or heard, hell I dunno) that to make photodegradeable plastic bags we simply leave this substance out.

Someone with some brizains know anything about this? I'm curious as always.


Also, I never did get the whole photodegradeable plastic bags thing. Seems kinda stupid to make something photodegradeable that's going to be sitting in a landfill away from the sun. At least it's not taking a tree to make it I suppose.

 

[dkozloski]

The idea is not to have the object degrade in the landfill but after some dipstick pitches it out the car window.