Polycarbonate (PC / Lexan) chemical tolerance question

[Mumblecrust]

Hi there,
This is my first post here. I've just found your forum, such a great place!

I'm solvent welding some PC tubes closed at one end, using methylene chloride, so they can hold water. The join won't be on show, so I will be using an appropriate silicone sealant as a nonstructural bond, to prevent leaks in case my butt joint isn't 100%.

This tube will be filled with water. The water needs to be a milky white colour, so that coloured light can be diffused through it. It doesn't matter what ingredient I add to the water so long as it's non-toxic. It won't be consumed or anything. It just needs to have the optical quality of watered-down milk and not go mouldy!

I watched a youtube video by a doll maker who makes a milk substitute out of moisturizing lotion mixed into water. I was going to use this, however, having read through this forum, I find PC/Lexan isn't tolerant of aromatic hydrocarbons or chlorinated hydrocarbons, and trace amounts of these can be present in petroleum-based products.

Quantity of lotion would likely be one or two tablespoons to about 3 litres of water. So not much, but of course I want to make sure my PC tubes don't craze or go brittle and stress-fracture!

If this lotion idea isn't a good one, can anyone help suggest a viable and safe alternative ingredient?
Thank you very much,
Tony

 

[Mumblecrust]

Well, of course, i could use a bit of white poster paint, the stuff kids use in kindergarten/nursery school. Or cornstarch, talc, calcium carbonate or magnesium hydroxide, although these tend be alkaline, except corn starch.

I know these are very mild substances, and I don't want to get silly. In the forum here people are generally talking quite extreme industrial environments, like cryogenics laboratories and motor oil factories etc. However, I would be really interested to know how sensitive PC can be, and since the aesthetics and strength of the PC is important, if there's any cause for concern with the above domestic substances/chemicals.

Thanks.

 

[MikeHalloran]

Cut some coupons of PC sheet.
Bend them in your fingers; they won't break.
Dip them once, quickly, in whatever mixture you want to use.
Wash and dry if you wish.
Then bend test again; chances are that most will fail easily, as if made of some brittle material,
unless your soup if really innocuous.



Mike Halloran
Stratford, CT, USA

 

[jari001]

If it's critical, it's worth doing the coupon tests that MikeHalloran recommends. You may also want to include some way to test temperature and material stress effects if those factor into the application. Alkalinity can be detrimental to PC because it can start etching it; the actual base and time of exposure will determine how fast the PC will get etched. There's solvents and such in traditional paint, so that may not work out with all kinds of paint.

I think if you are going to make something that will have to last a long time without attention/maintenance, that's when trace amounts starts being a concern (because material compatibility can be about both acute and chronic exposure effects). Also, you can look at material compatibility charts from various vendors or manufacturers of PC to get a better feeling of what PC is generally acceptable with.

Example material compatibility chart

 

[Mumblecrust]

Thank you both very much for your thoughts. My research has turned up a common whitening additive, which might well be an ingredient in both lotion and paint: Titanium dioxide.

They actually add this to PC as a pigment.

https://onlinelibrary.wiley.com/doi/abs/10.1002/app.26807

I will do a coupon test as you say, but I'm hopeful that a small amount of it suspended in some water will be fine, and will have some nice optics too.

If you have any words of warning please do let me know. Best wishes and thanks again,
Tony