Removing Cured Polyvinylpyrrolidone (PVP) From Nitinol Rods

Hi fortycoats,

I was able to find this:

http://sigma-aldrich.custhelp.com/app/answers/detail/a_id/2768/p/34,885/session/L3NpZC9zX1VWR280aw%3D%3D which states, "This compound is readily soluble in water. It has also been reported in The Merck Index, 12th ed., Entry# 7879 to be soluble in ethanol and chloroform, but practically insoluble in ether."

Keep in mind that this is for 10,000 average molecular weight (AMW) PVP. You didn't state what the AMW of your PVP is, so it may not hold for your specific material.

I would first try ethanol, perhaps with a little heat. The boiling point of ethanol is 78ºC and I would keep well below that unless I had a way of dealing with the vapor generated (flammability hazard). Isopropanol may work as well.

Good luck!

Mike

Hi Mike,

Thanks for replying. Cold Ethanol did not remove it but maybe i could try it when hot as you suggested. I think I will get in trouble if I do this because there is no where for the fumes to go, but its worth a go.

I was going to try a hot air gun to burn it off. Maybe this will work. I am also concerned that I may effect the mechanical properties of the Nitinol rod. There is a black oxide finish on the rod that i dont want to effect either.

Did you try IPA (isopropanol)?

After that, the next solvent to try looks to be chloroform, but maybe dichloromethane (methylene chloride - CH₂Cl₂) could be used. If I could, I would go with the CH₂Cl₂ because it's generally less hazardous. They are both non-flammable, but if heated would still have hazardous vapors.

Depending on the exact composition of the Nitinol, heat could very well affect it's properties in a detrimental way. Do you know why Nitinol was chosen for this application?

Mike. I havent tried IPA but we do have some here so I will give it a go. Another engineer spent quiet some time working on this issue with no sucess so I am thinking he would have tried this. maybe not though. He had a company called 3m in some time ago but they couldnt help. I dont have the compositoin of the solution to hand but i will post it tomorrow when I am back in the office. Off hand I think the PVP makes up 6% of the total volume. There is ethanol in there aswell. I will also look into the the CH2CL2 but to be honest I dont think any of these chemicals will be allowed.

I really appreciate all the advice you have given me so far. I only hope I can contribute in a similiar way.

As far as I am aware Nitinol was chosen because we needed a memery metal. The diameter of the rod is less than 1mm so it was a case of needing the strength and flexibility

I know this will sound sacrilegious, but did you ask the supplier.

Welcome to CR4 BTW.

Hi Lynlynch. Yes They were contacted but not by me. That was my first question aswell. I think they were the ones who recommended the ultrasonic water bath.

I could add IPA to the water bath? maybe that would work

Don't blow yourself up!!!!!!!!!!!

Hi and welcome.

If the problem is inside the catheter tube, then it may be that your solvent is not actually reaching the material to do its work. Merely putting the tubes into a bath may create an air lock.

Have you tried "flushing" the catheter with a stream of solvent/fluid?

The other (and probably more serious question) is what effect will this deviation to manufacturing process have on your medical registration of the device?

I would also suggest to avoid the problem infuture, have a small positive air flow through the catheter while it is being coated so that none of your PVP ever gets inside.

Hi Just an Engineer,

I would also suggest to avoid the problem in the future, have a small positive air flow through the catheter while it is being coated so that none of your PVP ever gets inside.

I think that this is a good idea if processing can be economically done. I just don't know if the air would flow evenly enough around the annular space between the rod and the catheter to prevent ingress at all points. Is your idea something like this?:

Certainly not to scale and some details missing from the catheter (never had to have one, but all I can say is... ouch!).

Mike

I would try NMP (N-Methyl Pyrollidone). Its also bio-compatible, high BP and industrial solvent. It may form Gels so either flush with water or ultrasonication may be needed.

I don't have any data, but you may have something there, according to the general principle, "like dissolves like". I don't know whether the NMP will dissolve the PVP, but I think it's worth a try, especially if the average MW of the PVP is low enough.

Good suggestion!

Hi. I was not specific enough when I described the problem so I am sorry for wasting peoples time.

If you can picture it, this is what happens. The Nitinol rod O.D 1.3mm is inserted into the catheter I.D 2.2mm. 48 of these catheters are placed on a pallet and they are processed through a dip coating machine. There is two eyes 14mm and 25mm from the end of the catheter. The idea of the eyes is to drain waste from the body.

When the catheters are dipped a foam gasket seals the top of the catheter so as not to allow air to escape and therefore prevent solution from rising on the inside of the catheter. The catheter is only required to be coated on the outside. We cannot blow air through it as this will create bubbles in the solution and cause rough spots on the surface of the catheter.

There will always be some solution inside the catheter after being dipped and when the rods are removed from the catheter at the end of the process the solution is smeared over the rod. The Solution then cures on the rods and over time flakes off on the inside of the catheter thus resulting in the issue we currently have. Leaving FM behind. I thought this would be ok because when the catheter is hydrated it would dissolve the FM inside the catheter but it seems after so much UV curing it will not.

That is why I am trying to get a solvent that can break down the dried on solution. The Solution contains the following.

PVP < 6 %
Benzophenon < 1%
Distilled water 45 - 50 %
Methanol 45 - 50%
Polyelectrolyte < 2 %

Glycerol < 1%

I hope now I have given a clearer understanding of the process and issue. If I have time today I am going to try to remove it with ethanol

Sorry a bit more clarification is needed. Is the curing done with the rods inside the catheter or are the rods removed and curing is done in a separate step?

Basically this provides info if the stuff is cured polymer or simply dried PVP..

thanks

Sorry. Yes the rods are inserted into the catheter at the load station and not removed until they reach the unload station. The curing station takes 12mins.

I infer that the rod is removed prior to bake. It's a liquid when rod is removed from device.

BTW, I've used NMP to remove cured epoxy powder coating from screws. Don't know about PVP. Works better if heated.

Hey Guys,

Just to let you know. I soaked the rods in ethanol overnight and then washed them in the hot water ultrasonic bath. It has cleaned them to an acceptable level. Not perfect but much better than they were.

Thanks for all you're help

Telfon coating on mandrels would be a common solution here, also the use of positive pressure would help. Is there a base coat /base layer on the catheter?