Regrinding Material - Thermal properties

V

vivkrish

#1
Hi All,


I have a question, Does the regrinding material changes the melting point / Glass transition temperature by lowering it.

Pls clarify.

If yes what will be the lowering temperature range.

Thanks,
Vivkrish.
 
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Ronen E

Problem Solver
Staff member
Moderator
#2
Does the regrinding material changes the melting point / Glass transition temperature by lowering it.
Regrinding itself probably doesn’t. However, regrind indicates a previous moulding cycle. Each such cycle causes some degradation in the polymer which means lower average molecular weight, which can manifest in lowered characteristic temperatures.

If yes what will be the lowering temperature range.
This is very hard to predict theoretically because many variables affect this phenomenon.
 
V

vivkrish

#3
Regrinding itself probably doesn’t. However, regrind indicates a previous moulding cycle. Each such cycle causes some degradation in the polymer which means lower average molecular weight, which can manifest in lowered characteristic temperatures.



This is very hard to predict theoretically because many variables affect this phenomenon.
Hello Mr. Ronen E,

If we use 20-30% regrinding material also reduces the molecular weight of the polymer.?

I have discussed with laboratory where they are doing molecular weight by GPC method, they declared by 20-30% regrinding mixing we cannot conclude the regrinding material mix up.

Thanks,
Vivkrish.
 

Ronen E

Problem Solver
Staff member
Moderator
#4
If we use 20-30% regrinding material also reduces the molecular weight of the polymer.?
Theoretically, yes.
Anyway, the figure you stated is probably only theoretical too. Because once you’ve used that regrind it goes into articles that will go through regrind again, and so on and so forth. A smaller and smaller fraction will go through more and more moulding cycles, thus undergoing further degradation (reduction in average molecular weight). This generally needs to be factored in, but it’s very difficult to determine the exact resulting percentage / effect theoretically.

I have discussed with laboratory where they are doing molecular weight by GPC method, they declared by 20-30% regrinding mixing we cannot conclude the regrinding material mix up.
A good lab would use a combination of methods and should be able to tell you accurately the molecular weight distribution, level of degradation etc. However, as explained above it would be difficult to state the exact regrind use percentage. To do that you’d have to run a controlled experiment in which you make samples with known (certain) regrind percentage, over a number of cycles representative of real production, and compare with the test results from the unknown-content sample.

One more thing to note:
The degradation in each moulding cycle is not something fixed. It depends on several factors, such as barrel and melt temperature profile, residence time, purity / additives, mould gate design, part design, injection speed profile, in-mould flow path etc. So you can have anything from negligible to prominent degradation in a single cycle, further complicating any theoretical analysis. This is why I recommend a more empirical approach if you absolutely have to know, with medium to high accuracy, the actual regrind content. It would basically be a mini-project.
 
Last edited:
V

vivkrish

#5
Theoretically, yes.
Anyway, the figure you stated is probably only theoretical too. Because once you’ve used that regrind it goes into articles that will go through regrind again, and so on and so forth. A smaller and smaller fraction will go through more and more moulding cycles, thus undergoing further degradation (reduction in average molecular weight). This generally needs to be factored in, but it’s very difficult to determine the exact resulting percentage / effect theoretically.



A good lab would use a combination of methods and should be able to tell you accurately the molecular weight distribution, level of degradation etc. However, as explained above it would be difficult to state the exact regrind use percentage. To do that you’d have to run a controlled experiment in which you make samples with known (certain) regrind percentage, over a number of cycles representative of real production, and compare with the test results from the unknown-content sample.

One more thing to note:
The degradation in each moulding cycle is not something fixed. It depends on several factors, such as barrel and melt temperature profile, residence time, purity / additives, mould gate design, part design, injection speed profile, in-mould flow path etc. So you can have anything from negligible to prominent degradation in a single cycle, further complicating any theoretical analysis. This is why I recommend a more empirical approach if you absolutely have to know, with medium to high accuracy, the actual regrind content. It would basically be a mini-project.
Thank you Mr.Ronen E.

I will go with testing and let you know the results.


Thanks,
Vivkrish.
 
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