Saturday, September 1, 2007

Product Contamination

Skippy – ran into someone who was asking about how to deal with Product Contamination:

“I have just been given a project to resolve the problem of separation of Ammonium Nitrate from Polystyrene Beads, this contamination takes place a service truck so my project consist of vacuuming the product out of these trucks , then separating the AN from the Poly , and then lean phase conveying the products to their different silo’s. If anyone out there has had to solve this problem please email any ideas.”

Buzz – the problem sounds like a simple one we in the plastic business deal with frequently; one of using a magnetic flux field to disrupt the electrostatic charge between contaminants and pellets, and a air wash deck to separate and remove the contaminants.

There are several products that can do this, and I would search on the phrase above to find companies that have them on the shelf who would provide a sampling to prove that their product will do the job for you.

Specifically, you could find more info on a product that could do that job at sites similar to


Buzz – Here was an interesting question - "Why does PVC react with polystyrene? It also reacts with several other plastics. The result can be dangerous. Or just messy. Any one know about this"? We had a subsequent discussion where a buddies son had a small plastic toy firetruck with a flexible ‘hose’ that was shot. They had found some similar looking PVC material at the hardware store to replace it with. A couple weeks later, the new hose basically ‘melted off’ the rigid protrusion it had been pushed on to – What’s Up?

Skippy - it is likely that some residual 'aromatic' plasticizer is leaching out of the FPVC and is reacting with the Polystyrene. If you are trying to construct items where it is important to have these two products in contact with each other, you need to work with material vendors who are familiar with using 'non-migrating' PVC compounds - these are special formulations designed to overcome the difficulties you are experiencing. While being extremely compatible with PVC these special plasticizers have very low affinity for ABS and Polystyrene resins and therefore can be used in applications where plasticized PVC comes in contact with these other resins.

Oh, and by the way – watch out what you ‘clean’ PVC with as well - MEK will attack PVC and ABS - if you don't believe it, take a scrap piece of material you don't care about and observe the gloss level (the glossier at the start the better). Apply a little MEK to it with a rag using the appropriate personal protective equipment and watch the material surface move towards 'dull' - you are attacking the material. Acetone is even more aggressive.

In the surface repair process of ABS and PVC fabrications, it is a common practice to take shavings and slowly disolve them in MEK building up an adhesive paste that can can be spread on and into to repair a surface crack. Once the MEK vapor dissipates, the repair area can be machined.

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