Welded plastic safe for mouth contact?

[Narzog]

TL;DR Summary

If I were to weld two parts together using a soldering iron or plastic welding tool, would it still be safe for mouth contact?

Hey guys. So I make pennywhistles. And its popular to make the heads out of acetal / delrin. So my question is, if I were to weld two parts together using a soldering iron or plastic welding tool, would it still be safe for mouth contact?

My knowledge of this stuff is very limited. But from the research I've been trying to do, acetal is normally safe, and is a thermoplastic. So it should be safe after melting. But if I'm wrong I don't want to be putting anything that I shouldn't in my mouth haha (like if there could be chemnical leeching or degraded plastic that's not safe for contact after). And other things I need to be aware of, is fumes, and I think it could be worse if I accidentally burn the plastic?

Thanks for any help. I'm too paranoid about my health so things like this I feel like I need a confirmation from people who know what the yare talking about before I do it haha.

 

[jim mcnamara]

Serban C. Moldoveanu, in Pyrolysis of Organic Molecules (Second Edition), 2019
"Acetals are a special type of ether. Many of these compounds are hydrolyzed easily, particularly in a basic medium, and their thermal stability is not very high."

This means they release other compounds on heating.
One of the compounds released at temperatures >250°C is benzofuran.

From the MSDS sheet for 2,3 benzofuran
"This chemical is considered hazardous by the 2012 OSHA Hazard Communication Standard
(29 CFR 1910.1200 )"

So I would say "No it is not safe to put in your mouth".

Short answer - no it is not safe. There clearly are ways to cleanse the acetal objects since finished acetal products are used in medical devices, some of which are implanted in humans. I do not know what that procedure is.

 

[Narzog]

Ooh ok thanks for the solid response. Glad I asked haha.

Is acetal safe as long as I don't melt it? I buy and machine acetal rod stock. Which I always though was one of the safer plastics, and is used by many makers. Edit- and I ask this because its not like its cleansed at the factory or after I machine it. But I'm not sure if it only needs to be cleaned after heating.

 

[BillTre]

I used to work with some guys that did some serious plastic injection work (mostly polycarbonate type thermoplastics).
They produced products for biological and medical research.
Contaminants were a big concern of researchers, because biology is complex and you want to control all possible variables.

From them, I learned some of issues with plastics production:

The plastic was made by a different high quality company (I think in Germany).
It was produced from chemical reactions and delivered in pallet sized crates of plastic pellets (maybe a 2 mm in size). They had large stacks of these (usually of a single lot).
No matter how good the chemical production was (lot to lot differences can be significant), it was expected that there would be impurities in the plastic from the production process (these impurities were presumed to be not good in general, and in some cases clearly demonstrated to be not good).

The pellets were melted before before being injection molded.
These guys would repeatedly draw a vacuum on the melted plastic to remove volatile chemicals.
They claimed this significantly reduced the amount of these volatile contaminants in their final products.
Eventually these contaminants (if present) would leach out of the plastic products and affect the biology being studied. This would be a source of unidentified variability, which should be dealt with by using controls, but it is considered better to just not have it. Controls for relating experiments done at different times would be difficult if they had to deal with lot to lot variability of poorly characterized contaminants.

In addition, some plastics would gradually undergo partial reversal of the chemical processes used in their production, creating more poorly characterized contamination.

When I ran a fish facility, we started bioassying all the plastics and rubbers we had that touched fish or fish water.
About 1/3 of them were very bad for the fish in our very sensitive assay. The effects of each of them was probably pretty low because of the large volumes of water we had (1000's of gallons) and the frequent water changes (about 10% several times/day; which would dilute any contaminants going from plastic to water). However, the periodic histological (tissue slides) examination of our fish showed the certain liver problems decreased after we eliminated the bad plastics.

So to more directly answer you, there is a lot of possibilities for chemical contamination from plastics.
However we found (not to surprisingly) that food grade and biomedical plastics were usually quite good.
Ideally, I would stick with these products or come up with an assay close to whatever use you are intending. Sadly for you, fish are easier to get and experiment on than people, so food grade is a good alternative.

Machining acetal should not produce chemical changes in the plastic.
It could however create new and more surface areas through which any contaminants could be transferred from the plastic to the potentially contaminated surrounding medium (water).
The more surface area, the faster the transfer.
A new surface area may expose parts of the plastic where the contaminants have not leached out as much, since they are farther from a surface.

 

[Narzog]

Thanks for the info Bill. So while we are talking about chemical contamination- Isnt it true that pretty much everything is contaminated, at least to a point, and that the goal is for exposure to be in small amounts? Where the normal things we use on a daily basis arent some medical grade plastics. A 10$ amazon pennywhistle straight from china is probably no better, or even worse quality plastic (ABS not acetal, but I'm assuming the same concept works for other plastics) than what I'm using. And other example,s water bottles that the water tastes like plastic. So even if I'm using not the highest end medical grade acetal, shouldn't that be safe overall (not counting any welding). And then in the case of welding, that could throw it off to be more contamination than ideal if I was to overheat it and make it be worse?

 

[BillTre]

Isnt it true that pretty much everything is contaminated, at least to a point,

Yes.

the goal is for exposure to be in small amounts?

i would think that you would want a contamination level appropriate for your use.
Thus, there are for example different purity levels for chemicals made for different intended uses.

Where the normal things we use on a daily basis arent some medical grade plastics. A 10$ amazon pennywhistle straight from china is probably no better, or even worse quality plastic (ABS not acetal, but I'm assuming the same concept works for other plastics) than what I'm using. And other example,s water bottles that the water tastes like plastic.

The nets we used to use in our fish facility (made in China) required testing because there was a high level of variability in the plastic coating of the wire used for the handle. Some of the lots of nets killed fish in our assay, some were OK.
Not all apparently similar plastics are the same.

I would not want to drink out of something that gave the water a plastic taste.

And then in the case of welding, that could throw it off to be more contamination than ideal if I was to overheat it and make it be worse?

I think @jim mcnamara's comment is relevant here.
If the plastic gets overheated during the welding, it could make more toxic materials.
It may be difficult to control the temperature during plastic welding.

 

[Baluncore]

So my question is, if I were to weld two parts together using a soldering iron or plastic welding tool, would it still be safe for mouth contact?

If you are turning plastics in a lath you might consider “friction welding”. Rotate one while holding the other against it. When sufficient heat builds up they weld together and you let the weldment rotate. That will avoid excessive heat or burning since the weld takes place while it is still plastic, before it actually melts.

 

[chemisttree]

...or you could design it to just snap together.

 

[Narzog]

Thanks for all the info guys. I at least feel good again about the safety of using acetal. The welding idea is too fishy though so I probably won't try it. My idea if I did was to use my adjustable soldering iron and turn the heat down and test to see if it melts, and slowly turn it up until I can find the minimum melting temp. But That might work poorly and if I somehow overheated the plastic sounds bad so I probably won't risk it.

On friction welding, that is a good idea but sadly the part I'm trying to attach is a flat cut off the top, so it can't be rotated on the lathe to attach.

On redesigning it to snap on, that is a really good idea, but I don't think it will work for my case. My goal of this method was that I save a lot of time on making the windway by cutting the top off, cutting a windway into one or both of the parts, and sticking it back together. So I don't have the tooling or ability to make a part that would perfectly snap in. If I was still trying to 3d print though I'd totally try it. But 3d printing had a ton of issues with material safety so I dropped it (FDM printers are almost impossible to get a good finish without using chemicals or fishy coatings, and resin printers are unsafe materials to begin with for mouth contact).

While we are talking about leeching. Could it be possible to let an object soak in water or somethign and have it do some of its leeching there and then leech less with actual use, or would that somehow make it worse, or do nothing? Its just an interesting idea I just thought of, that probably wouldn't work for one reason or another haha.

 

[BillTre]

While we are talking about leeching. Could it be possible to let an object soak in water or somethign and have it do some of its leeching there and then leech less with actual use, or would that somehow make it worse, or do nothing? Its just an interesting idea I just thought of, that probably wouldn't work for one reason or another haha.

Unlikely that it would makes things worse.
If the contaminant concentrations are not so high, it might help.

On the other hand, we had a rubbery item made of a bad material and tried to leach the bad stuff out because we really liked the part.
We did long soaks (for a month), washes with detergents, and several boilings in water, but it did not get better (however, it was very toxic).
Without a bioassay, you would not be able to tell if the contaminant was removed.

 

[jim mcnamara]

If you have to proceed: Go to the mouthpiece manufacturer. They can give you the grade of plastic (e.g. medical or food, etc.) and any material safety data regarding their products. We cannot help you. You want the engineering or manufacturing side of the house -- most definitely not customer service or sales.

GO TO the people who make the mouthpieces - it is simple. Not another musician who makes penny whistles either...
Alternative:
Cyanoacrylate glues are used in wound closures. They are vary safe, fast, and not expensive. Get one with an extended "open time". Then you can then attach the mouthpiece without heat and have some time to insert the tube and wiggle it to perfect pitch, before the glue hardens.

The downside is if you use faster glue and get it on your fingers, the fingers can become stuck together unpleasantly and more or less forever. So it seems, anyway. Nothing but a special solvent will un-stick them. I know this first hand...