Regrinding Material - Verify whether a product contains any regrinding material

vivkrish

Involved In Discussions
#1
Hello All,

I have some clarification. We are purchasing plastic parts from suppliers.

I need to verify whether the product contains any regrinding material or not. If yes how much they mixed with virgin material (Mixing ratio).

How can I qualify my products as above condition.

At what test can we conclude.


Thanks,
Vivkrish.
 
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kuyakut

Involved In Discussions
#4
If it is molded components , its a bit tough to determine how much regrind they use.
It always boils down to your supplier honesty and integrity.
One way is to test mechanical properties of the molded plastic but you need a very sophisticated equipment to be able to determine if they use regrind on the molded parts.
 

locutus

Involved In Discussions
#5
It always boils down to your supplier honesty and integrity.
+1 basically they have to certify that it is virgin material. As mentioned you can find out if mixed by doing chemical analysis like NMR, but costly and will probably have to test much material to determine. Does you own specification require virgin materials or mix is allowed? Working in the medical device industry, usually only virgin material is allowed, but other industries I know will allow mix with a ratio sometimes not specified. The issue arises that once plastic is heated up, then ground down, and heated up again, it loses some of its properties. I am not a materials expert, but had a really, really smart materials guy spend 4 hours telling me about plastics ... then at the end, said, "do you want to go get a whiskey? i need one after that." lol.
 

Ronen E

Problem Solver
Staff member
Moderator
#6
OK, time to clarify some things.

The presence of any significant percentage of regrind can be detected quite simply because every moulding cycle will manifest in some degradation (polymer chain scision), which in turn will manifest in lower MFI (Melt Flow Index).

To check a sample’s MFI you don’t need large samples, the method is not complicated, the equipment is not that sophisticated, not that expensive and not that rare. If it’s a recurring situation you can simply buy a basic MFI analyser; otherwise contact a lab that provides this (basic) service. This will tell you with reasonable confidence whether the article was made from pure virgin material or includes a significant percentage of regrind (please remember that some degradation should be expected in any but an ideal moulding process, so the MFI of a moulded sample will almost never be exactly the same as that of a 100% virgin raw material).

What’s complicated is determining the exact percentage of regrind. That would need calibrating first, ie moulding samples at different known regrind percentages and finding out their respective MFIs. Of course, in order to be a valid test method a whole host of issues would need to be accounted for (as per usual when developing a test method) and some statistical rigor would be required. Another complication is material having gone through more than one regrind cycle (a natural result in a process that uses in-line regrinding).

Basic MFI is a crude tool; it’s not that accurate and the resolution is limited. I’d normally recommend it only for saying whether regrind has been used or not. It’s good because it’s simple, quick and not too expensive. However, there are additional, more sophisticated methods such as DSC and DMA, that can tell you much more about the polymer’s molecular weight (which will tell you about degradation), and are more accurate. Those methods do require more expensive equipment and some expertise in running the tests and interpreting the results; however, they are normally available from any large lab dealing with polymer testing. I didn’t check with UL (no affiliation here) but I guess they offer such testing.
 
Last edited:

vivkrish

Involved In Discussions
#7
Best bet is to ask them. You would need a pretty sophisticated lab and testing to determine. Not sure.
What are the testing equipments we need to know the regrinding material presence and the percentage of the regrinding material.

Thanks,
Vivkrish.
 

vivkrish

Involved In Discussions
#8
OK, time to clarify some things.

The presence of any significant percentage of regrind can be detected quite simply because every moulding cycle will manifest in some degradation (polymer chain scision), which in turn will manifest in lower MFI (Melt Flow Index).

To check a sample’s MFI you don’t need large samples, the method is not complicated, the equipment is not that sophisticated, not that expensive and not that rare. If it’s a recurring situation you can simply buy a basic MFI analyser; otherwise contact a lab that provides this (basic) service. This will tell you with reasonable confidence whether the article was made from pure virgin material or includes a significant percentage of regrind (please remember that some degradation should be expected in any but an ideal moulding process, so the MFI of a moulded sample will almost never be exactly the same as that of a 100% virgin raw material).

What’s complicated is determining the exact percentage of regrind. That would need calibrating first, ie moulding samples at different known regrind percentages and finding out their respective MFIs. Of course, in order to be a valid test method a whole host of issues would need to be accounted for (as per usual when developing a test method) and some statistical rigor would be required. Another complication is material having gone through more than one regrind cycle (a natural result in a process that uses in-line regrinding).

Basic MFI is a crude tool; it’s not that accurate and the resolution is limited. I’d normally recommend it only for saying whether regrind has been used or not. It’s good because it’s simple, quick and not too expensive. However, there are additional, more sophisticated methods such as DSC and DMA, that can tell you much more about the polymer’s molecular weight (which will tell you about degradation), and are more accurate. Those methods do require more expensive equipment and some expertise in running the tests and interpreting the results; however, they are normally available from any large lab dealing with polymer testing. I didn’t check with UL (no affiliation here) but I guess they offer such testing.
Hello,

We Have DSC and MFI instrument in our factory. We do the test with both method, but we can't able to identify. If I purposely prepare and test the regrinding material also, we get the tolerable results in DSC. MFI concern I found some deviations in results.

Thanks,
Vivkrish.
 

Golfman25

Trusted Information Resource
#9
What are the testing equipments we need to know the regrinding material presence and the percentage of the regrinding material.

Thanks,
Vivkrish.
No clue. Like someone said every reuse degrades the material. You would need someone who could pick up that degradation.
 

vivkrish

Involved In Discussions
#10
+1 basically they have to certify that it is virgin material. As mentioned you can find out if mixed by doing chemical analysis like NMR, but costly and will probably have to test much material to determine. Does you own specification require virgin materials or mix is allowed? Working in the medical device industry, usually only virgin material is allowed, but other industries I know will allow mix with a ratio sometimes not specified. The issue arises that once plastic is heated up, then ground down, and heated up again, it loses some of its properties. I am not a materials expert, but had a really, really smart materials guy spend 4 hours telling me about plastics ... then at the end, said, "do you want to go get a whiskey? i need one after that." lol.
Hello Locutus,

I have gone through NMR technique and as well as visited a research body who is doing NMR test. They also not much confident that by NMR we can find regrinding material presence in our product.

Please explain how can we identify the regrinding material presence in our product by NMR?

I am waiting for your valuable support.

Thanks,
Vivkrish.
 
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