Gel in oil extended rubber 1

[joysop]

Hi there,

Could you tell me about the effects of the gel on cured-rubber's physical properties when the rubber is an oil extended one and have many gels in it?
I guess it will make inconsistancy especially in the physical properties? Am I wright?

 

[tom1953]

The gel would almost certainly reduce the strength properties of the compound, both from the standpoint of the inhomogeneity of the compound and from the standpoint of the gelled rubber doesn't have any of the reinforcing fillers, or other ingredients, that are in the compound. You will get some migration of curatives into the gel particles, so it will (partially) cure into the rubber matrix.

Depending on the amount of gel and the geometry of the finished parts, the effect can be very or minimally significant. If the cured part is relatively thick, the presence of the gel particles may not be a big factor in the bulk strength of the part.

Hope this helps.

Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[joysop]

tom, thank you for delivering helpful information to me. Do you know how to detect the existence of the gel?

 

[tom1953]

If you're trying to detect gel in a polymer, you can try dissolving the polymer in a solvent, as gel particles will normally swell but won't dissolve, but the non-gel materials will dissolve. The type of solvent to use will depend on the rubber you're working with. For millable urethanes, we use methylene chloride to dissolve the polymer.

You can also press some of the polymer in a heated press, putting the polymer between Mylar sheets. The non-gel polymer will smooth out nicely, while any gel particles will usually not flow out, and may look like a smooth or rough lump. We typically use press temperatures of about 150C, with max pressure (on our 12"x12" lab press).

Lastly, you may be able to extrude the polymer in a small extruder and extrude a thin strip which will show gel particles as lumps in the (hopefully) smooth extrudate. The raw polymers I work with don't extrude very smoothly without compounding with fillers and plasticizers, so this may or may not work with the polymers you're working with.

Hope this helps!

Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[GrahamBennett]

Use toluene to dissolve NR, SBR, BR and CR.

 

[joysop]

Thanks Tom, it hepls me a lot.
As I know, most of SBR adopted the cold polymerization method to prevent it from having gel. But in case of oil extended SBR, there is possibly a lot of gels in it, because its molecular weight is very high compared to non-extended SBRs.
But there is no problem in tire-application.
The only case gel will effect on the physical properties would be one the end product is thin relatively.
Am I right?

 

[tom1953]

It's tough to give you a definitive answer on this, as there are many factors involved, but I'd think the effect of gel will be less in a thick part than a thin part. In tires, there are many other factors than the effect of gel on tensile strength, for example; heat build-up or other properties may be affected. So, you should do whatever evaluations are necessary to assure that the quality of the finished product is not compromised.

Regarding gel in oil extended polymers, I used to work for a company that produced EPDM rubber, and light (UV) can cause gel in oil-extended EPDM, moreso when the oils had significant aromatic content. I'd assume the same effect happens in SBR, so protecting these rubbers from light (even flourescent light) may be highly desirable to prevent gel formation on the surface. FWIW.


Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com

 

[joysop]

If physical properties of the rubber compounds of oil extended SBR are up and down through the lot numbers from the typical values that the supplier qurantees , what things would be the most considerable causes to give that problems to it you think? Gel?
Thanks for your quick and valuable reply.

 

[tom1953]

Assuming your process gives consistent properties with batches made from the same lot of oil extended SBR (OESBR), variablility in the OESBR would seem to be the cause. I've never worked much with SBR, but from experience with other polymers, I'd think possible areas of variablity that might affect properties would include:

polymer (SBR) compositional variability in:
molecular weight
molecular weight distribution
styrene/butadiene ratio
other compositional variations (emulsifier?)
oil
oil amount
oil type/composition
gel

If you mix test batches in your lab, maybe with just curative added to the OESBR, you should be able to get some information as to what the variability might be (for example, Mooney viscosity would probably give an indication of molecular weight/distribution; specific gravity would give an indication of oil content.

What does your OESBR supplier say about the variability you're seeing? If you have an alternate supplier, you may want to evaluate their material for consistency.



Tom Jablonowski, TSE Industries, Inc.

http://www.tse-industries.com