Colorant leaching out of Nylon in Autoclave

[PatrickSebast]

We have recently had a customer seeing color leaching out of our Nylon parts into surrounding plastics during autoclaving.

The nylon parts they have noted seem to have a colorant with some oil based components, our colorant supplier says that the colorant SHOULD be inert once mixed during injection molding but obviously they don't have much experience with autoclaving. Also the colors with oil mixed in tend to be a bit darker so it may simply be that the leaching is more noticeable and it is not directly related to the oil.

We don't have an autoclave on site, but I have boiled the parts and found that there is no color leach.

I also boiled the (nylon based) colorant pellets and found that the colors leached very prominently in the colorants that contained oil and very slightly in the colorants that did not.

Wondering if anyone else has ever encountered this as I can't find anything about it online and none of our colorant contacts seem to have any idea what is going on.

 

[Ronen E]

We have recently had a customer seeing color leaching out of our Nylon parts into surrounding plastics during autoclaving.

The nylon parts they have noted seem to have a colorant with some oil based components, our colorant supplier says that the colorant SHOULD be inert once mixed during injection molding but obviously they don't have much experience with autoclaving. Also the colors with oil mixed in tend to be a bit darker so it may simply be that the leaching is more noticeable and it is not directly related to the oil.

We don't have an autoclave on site, but I have boiled the parts and found that there is no color leach.

I also boiled the (nylon based) colorant pellets and found that the colors leached very prominently in the colorants that contained oil and very slightly in the colorants that did not.

Wondering if anyone else has ever encountered this as I can't find anything about it online and none of our colorant contacts seem to have any idea what is going on.

Hello Patrick and welcome to the Cove

Please note that autoclave may go up to 134C (minimum 121C) so open boiling in water is not a very good simulation.

Are these parts / clients / uses / processes well established, or is something new? Was any change implemented?

First step in finding a root cause is being able to reproduce the failure. If you don’t have access to an autoclave and wish to avoid buying one (a small / simple one might suffice and maybe isn’t too costly in comparison with the cost impact of the issue, but pay attention to the complaining customer autoclave’s spec), you might be able to “outsource” the autoclaveing from a nearby healthcare provider or a lab.

Please also consider the potential effects of vacuum inside the autoclave.

Cheers,
Ronen.

 

[PatrickSebast]

It is a brand new product that they are sampling for the first time. This is a universal failure and they are doing testing on all the products so they will let us know if other colorants start to leak with more time.

The autoclave will be set to 121C, multiple cycles may occur, and it will be 13psia.

Investigations should get us to a reasonable root cause eventually, but it would be much faster to have someone confirm a similar experience if one is available.

 

[Ronen E]

Is your product intended for autoclaving (ie was it part of the design input)? If yes, wasn’t it verified and validated before being offered to customers?

If it wasn’t intended, I guess a design change will be required for accommodating it.

 

[NikkiQSM]

Is your product intended for autoclaving (ie was it part of the design input)? If yes, wasn’t it verified and validated before being offered to customers?

If it wasn’t intended, I guess a design change will be required for accommodating it.

I agree. Why not look into other colorants which are certified to hold up against autoclaving in nylon? Suggest these new colorants to the customer - they may be willing to make the change and save the hassle.

 

[rob73]

Patrick
Is there a reason nylon was chosen as a material? Nylon is hygroscopic i.e. it will absorb water, if as you suggest some of the colourant is suspended in oil then migration is quite possible. Nylon would not be my first choice of material for autoclave use, polypropylene or polysulfone's are better known for their thermal stability during autoclaving.

https://www.industrialspec.com/imag...ility-with-Sterilization-Methods-from-ISM.pdf

 

[PatrickSebast]

Just wanted to update this thread for anyone who might run into this problem in the future:

After extensive testing in conjunction with the customer and our colorant supplier we did isolate the color leaching specifically to the oil component in the colorant. Only colorants with an oil component leaked out, and removing the oil component from the colorant removed the problem.

We did discuss the idea that Nylon was a not ideal for autoclaves, but the customer only had a limited set of 'approved' material via their own regulations for the product and said it would take too long to add in a new material so they preferred to stay with Nylon.