Conductive plastic 4

How conductive? Comparable to??

Electrical and thermal conductivity can be added to any plastic by blending in appropriate fillers. Such compounds are available from many suppliers, look at the RTP site for some examples.

Chris DeArmitt

"Knowledge has no value except that which can be gained from its application toward some worthwhile end."
Think and Grow Rich - Napoleon Hill

That is an anti-static grade. Almost all plastics can made conductive enough to be anti-static. Looks like carbon black additive.

I am aware of the fact that plastic can be made conductive by doping in carbon black or even metal particles, but I have no interest in pursuing this avenue myself.

I am looking for a kind of conductive plastic can be used to handle flammable liquids safely? For eg. I presume that gasoline jerry cans are made of conductive plastic (it would make sense) - what type of plastic would that be?

I have no idea how conductive (number?) such a plastic should be. Flammable non-conductive liquids accumulate static charge when being transferred from A to B. The faster the flow, the more charge is accumulated. Additives are usually added to make these type of liquids more conductive, like jet fuel or gasoline. However, if the container receiving charged liquid is non-conductive, then the charge has nowhere to dissipate to and thus might spark and ignite. I hope this explains a bit better where I am coming from...

Jerry cans are normaly made of HDPE with a fluoride treatment to improve barrier properties.

When required, permanant antistatic is normally obtained by incorperation of SS fibres, aluminium flakes or high surface area ratio carbon black. I have heard that Bassel did some work on naturally conductive polymers, but have seen no commercial aplication.

Is this simply speculation or daydreaming or do you have a serious work related application in mind. If you can be more forthright we might be prepared to do some real research for you

Regards
Pat
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I don't think any of my HDPE 5-gal. gas "cans" are anti-static to any degree. Typically, the hose at the fuel pump is anti-static and grounded to reduce any charge transfer from the flowing liquid, and placing the can on the ground is sufficient to discharge its surface to a safe level. Tens of thousands of gas cans filled every day, but the incidence of fiery deaths is quite low.

"a kind of conductive plastic can be used to handle flammable liquids safely?"

WHAT flammable liquid(s) exactly? The right plastic for your tank depends more on knowing what the liquid to be contained than anything else. As Demon, Pud, and Pat have pointed out, once you've found a polymer that works as a container, you can then think of ways to reduce its potential to cause static spark discharges.

bttrueblood, thanks for your comment and interesting thoughts.

Further on the jerry can discussion, that is relevant to my original post. The reason why jerry cans do not catch fire when filled up at the gas station, in my opnion, is because: i) the atmosphere inside the can is too rich with fuel and ii) there is (usually) no spark around. Sparks could come from anywhere though, this is why people are not supposed to leave the hose and get in and out of the car during fueling since this usually results in those annoying sparks...

Unless the jerry can is made of conductive plastic it does not matter if you hold it in your hand or place it on the ground, it still cannot be grounded!

I think there is lots of opportinuty for conductive plastic (and fibers/textiles) in a variety of applications, from conductive jerry cans, anti-static car seats, to petrochemical industry.

Static and tribocharge seems like fascinating subject that's closely related to material science, fluid flow and conductivity measurement of liquids and solids. I am in the process of scouting literature on the subject - this is why this post.

Patprimmer, thanks for your insightful comments and the offering, I'll keep it in mind.

Actually, it makes a great difference whether a plastic container is on the ground or not when filling. A plastic container is a large electrical capacitor for storing charge. Voltage of a capacitor is equal to charge divided by capacitance. Charge build-up in the container depends on the fluid and the filling process (i.e., high velocity not good). A plastic container on the ground has a much higher electrical capacitance than one that is held off the ground. So the same charge will result in a much higher voltage if the container is not on the ground.

There are documented cases of people filling buckets with solvent which catch fire when the bucket is lifted off the ground after filling due to a spark to the person.

I've not seen anti static plastic containers used for flammable liquids, although it is desirable for the container to be conductive. I think this is because of the detrimental effect these additives have on permeability of the plastic. Humectant anistats would probably quickly leach out of the plastic.

High surface area carbon black does give PE permanent AS without to much degradation of physical properties, but it has a very substantial increase in cost and limits colour choice to black or very dark grey. I have seen it used for caps and nozzles on plastic fuel drums. I have no data as to whether or not fluorine gas treatment increases conductivity but I strongly suspect I would know if it did as someone would be shouting it from the rooftops and I would hear them.

You still have not stated a valid reason for asking the question, so I must presume the OP is a students homework.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules

One of the best sites that I have found for informative articles about static is:


I've developed products to eliminate static that use carbon fiber, so I've been studying the subject for some years.

I can see three ways to increase the electrical conductivity.

1. Add fillers (carbon black, metal, carbon nanotubes), in order to conduct well the particles must touch each other to create a conductive path. The minimum amount needed to create that path is called the percolation threshold. At that point the conductivity suddenly leaps by several orders of magnitude.

2. Dissolve a conducting polymer (polyanilines, polythiophenes, polypyrroles) in the matric polymer. Because the conductive polymer is soluble, there is no percolation threshold, instead, the conductivity increases steadily as you add more conducting polymer. This approach is known but not used much commercially.

3. Increase the conductivity of the surface layer by adding polar additives (stearamides, PEGs etc.) that migrate to the surface, or by oxidizing the surface, e.g. with plasma treatment, flame treatment or corona treatment. The level of conductivity achievable is lower than for methods 1 and 2 but enough for anti-static purposes.

Chris DeArmitt

"Knowledge has no value except that which can be gained from its application toward some worthwhile end."
Think and Grow Rich - Napoleon Hill

Dear all, these are all great suggestions - thanks to all who contributed so far.

I like Demon3 suggestions specially the 1st one: apparently there is a company in Belgium offering masterbatches filled with carbon nano tubes (CNT): as well as antistatic coatings
They claim that CNT-filled polymers work at much lower conc compared to carbon black... It would be interesting to get some user feedback on their product line, pricing, durability, materials (eg. solvents) compatibility etc. As well as benchmarking vs. high surface area CB masterbatches.

I am told that pharma industry does not like to use CB-filled composites because of potential contamination problems - any comment on materials compatibility and durability of CB-composites? It seems like Compositepro might have some experience in this area?

The inherently conductive polymers (such as polythiophenes, polyanilines, etc) are very appealing approach but I am not aware of any commerical suppliers outside university and R&D labs (not yet?). I'd appreciate any links to commercial suppliers of such polymers.

Finally, I see this venue as a discussion forum not as a way to solve my technical work-related problems; so far seems to be working well.

Not to beat this to death, but I'd want to know that the liquid being contained won't attack the anti-static additives. Polyethylene is pretty much inert to a lot of exotic chemicals, the additives are likely not as inert (dunno, but I know some polyaniline salts are dissolved by toluene, and some gasoline blends have small amounts of such solvents added, or more likely "left"). Wouldn't do to fill my little chainsaw with a bunch of dissolved goo from the 5-gallon jerry can, now would it?

These are the UK's specialist compounder of conductive plastics (resins)


H

I would make some enquiries re cost, performance, availability and impact on other qualities before I made any decisions

The other properties most likely impacted are:-
Colour.
Transparency.
Toxicity.
Flammability.
Impact strength.
Elongation at yield.
Flexural modulus.
Tensile strength.
Melt flow index.
Mould shrinkage.
Isotropy.
Surface fiction
Abrasion.
Surface hardness.
Oily or scum or powder deposits on surface.

There is also a very remote possibility of a reaction with other additives.



Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &
for site rules

Antistatic grades of plastic are used in automotive fuel systems.

Does all this imply that the old metal gas cans are better than the plastic ones?

compositepro is CE mag still in publication?

It appears that the magazine stopped in 2005 but the website is still up and has a new subscription application. As I recall I found it through another site for a consultant on static. Perhaps he is keeping this site up. Better download the articles while you can.

Interesting point about automotive fuel system plastic being anti-static. They are also almost always black. So why aren't plastic jerry cans black? Simply aesthetics? Does this compromise safety?

The DOT may require that the cans for gas are red. Diesel cans appear to be yellow.

The car parts are that way for aesthetic reasons.