carbon black measurement in polethylene

carbon black in PE is commonly measured gravimetrically , after burning off polymer either in a muffle furnace or using a TGA instrument. I was wondering if it could be done quicker and more accurately by measuring some electrical property ,like resistance or conductivity, which must change as a function of carbon black level. I am talking about levels of 2.5% , measuring to say the nearest 0.1%. is this feasible - can anyone point me to any references if this has been done? or to any suitable instruments if they are available thanks terry

Reply to
d&tm
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Here are my thoughts, which being just thoughts, can always be trumped by facts:

If it can be done, doing it correctly would be real tricky. In order for the carbon black to be conductive, you would need a continuous network of particles from one probe to the other. There are a number of products that have been made conductive by addition of carbon black, but I think that they are generally at higher loadings in order to have enough particles present that they form the necessary continuous network. However, if you particles are small enough, the number of particles could be acceptably high even if the absolute loading levels are small and you could still have conductivity.

Nonuniform dispersion of the carbon black would be a huge source of error in the electrical measurement that your current technique is oblivious to.

John

Reply to
John Spevacek

Both resistivity and conductivity of PE modified with carbon black will change with addition level. The problem is not all blacks have the same effect. Some are more, some are less conductive. It depends on particle size, shape and how graphitic it is. Typically the smaller the size and the more graphitic, the more conductive. So, this makes it difficult to have a standard test that can measure black level regardless of the type of black used. Hence, the common practice of doing this gravimetrically. Any test that you develop would be specific to the type(s) of black that you use and the method would have to be calibrated against a primary method (e.g. gravimetric). The primary benefits of such a test as you suggest would be speed and perhaps the ability to perform the test in-line with compound or process. As far as speed, how long does it take to weigh, burn and reweigh a sample, 30 minutes? Probably not worth the effort unless you have tons of specimens to crank through.

That said, there are commercial devices to measure the both the resistivity and conductivity of polymers. This is a very standard test in the wire & cable industry, although off the top of my head I can't think of any of the manufacturers of such equipment. You might want to check ASTM for test methods to measure resistivity and conductivity in polymers. Than might lead you to the equipment you'll need if you want to pursue this technique.

Larry Effler

Reply to
Larry Effler

Just a thought - I wonder how the dielectric constant of a sample would be affected by the carbon content?

All the best

Ian Macmillan

Reply to
Ian Macmillan

thanks all for the advice, and many good points raised.

Terry

Reply to
d&tm

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