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Removing Yellowing from Plastics - Part 3

Somewhere around page 15 of this thread we will have MILspec designes for deyellowing plastic in a $100,000 computer controlled precision chemical dispensing chamber. ;)
 
Covering everything at once

Covering everything at once

Surely two lamps above opposite corners of a cuboid piece would give you the same coverage(?)
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Well, two things.
First of all, a surface at 45 degrees to the UV source is only going to get one half of the strength as a surface at right angles to the UV source. (Think of the strength of the sun at a lower angle in Winter).
Second, the parts that are farthest away from the UV source will get less exposure. Remember the "square of the distance" rule.
Looks like I'm going to have to deal with "one surface at a time" and go through five treatments per piece.

Rich
 
Rich113 said:
Well, two things.
First of all, a surface at 45 degrees to the UV source is only going to get one half of the strength as a surface at right angles to the UV source. (Think of the strength of the sun at a lower angle in Winter).
Second, the parts that are farthest away from the UV source will get less exposure. Remember the "square of the distance" rule.
Looks like I'm going to have to deal with "one surface at a time" and go through five treatments per piece.
Click to expand...
While I understand the physics, I'm not sure completely even exposure is all that critical. Folk seem to have been getting good results with a single UV lamp above the piece(s) being treated. YMMV and all that ;-)
 
Mixed up my first batch this evening just to give it a quick go. I think I may have overdone it with the Xanthan gum though, as the stuff ended up looking like a big bowl of thick, white snot. I'll be adding it more gradually next time...

Anyway, I spread it out on the old C64 case I had waiting for it and it's sunning itself away on top of the washing machine as we speak. I have a half-metre UV tube hanging above the cling-film-covered de-yellowing chambers, which are glowing like something out of a sci-fi movie. I'll rinse the lot down before turning in for the night and see if anything's happened...
 
snq said:
Does any of the swedes here have a shopping list for swedish equivalents of the retr0bright ingredients? I have no idea what Xanthan Gum is, or Oxy laundry booster for that matter. My laundry skills go about as far as using a different powder for color/white laundry and I usually throw in some softener as well...
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OK....

Xanthan Gum is a food thickener that can be found in some supermarkets and health food shops; it is sold as a replacement for gluten in bread for people with gluten intolerance or coliac disease. You can also get it via Ebay.

Oxy Laundry booster; This goes under loads of names. the most popular seem to be Oxi-Clean and Vanish. It's usually sold in 1/2 kilo pots to be used as one scoop to your laundry - it's in the laundry aisle (meh) at the supermarket.

Glycerine (or Glycerol - same thing) can be obtained from a pharmacy, usually in 100ml bottles.

I presume you have read the Wiki article, which has pictures of the ingredients...??
 
cosam said:
Mixed up my first batch this evening just to give it a quick go. I think I may have overdone it with the Xanthan gum though, as the stuff ended up looking like a big bowl of thick, white snot. I'll be adding it more gradually next time...

Anyway, I spread it out on the old C64 case I had waiting for it and it's sunning itself away on top of the washing machine as we speak. I have a half-metre UV tube hanging above the cling-film-covered de-yellowing chambers, which are glowing like something out of a sci-fi movie. I'll rinse the lot down before turning in for the night and see if anything's happened...
Click to expand...

Yup, XG is good stuff, isn't it? You don't need much! :D

The glowing you are seeing is partly due to UV optical brighteners that the manufacturers add to the Oxy, so that your whites look super bright (and your shirts glow at the disco). it looks like really mad science though, eh?

I went to college with a guy that worked for Ciba-Geigy, who make these optical brighteners; his lab coat was giving off so much UV, we reckoned he was getting radiation poisoning!!

LOL
 
Merlin said:
Yup, XG is good stuff, isn't it? You don't need much! :D
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Certainly not seen anything quite like it before. Now that the oxy's been in there a while, the snot's transformed into whipped cream. Don't fancy tasting it though!

Merlin said:
The glowing you are seeing is partly due to UV optical brighteners that the manufacturers add to the Oxy, so that your whites look super bright (and your shirts glow at the disco). it looks like really mad science though, eh?
Click to expand...
I don't see an awful lot of glowing in the goo itself, but the plastic tubs look like some kind of alien hatchery. There must be something in there that reacts the same way. Cool effect though, yeah ;-)
 
Merlin said:
OK....

Xanthan Gum is a food thickener that can be found in some supermarkets and health food shops; it is sold as a replacement for gluten in bread for people with gluten intolerance or coliac disease. You can also get it via Ebay.

Oxy Laundry booster; This goes under loads of names. the most popular seem to be Oxi-Clean and Vanish. It's usually sold in 1/2 kilo pots to be used as one scoop to your laundry - it's in the laundry aisle (meh) at the supermarket.

Glycerine (or Glycerol - same thing) can be obtained from a pharmacy, usually in 100ml bottles.

I presume you have read the Wiki article, which has pictures of the ingredients...??
Click to expand...
Thanks!

Yes, I've seen the pictures.. But to be honest the last time I was in the laundry isle was at least a year ago (I buy the biggest boxes), and I have no idea if Vanish or Oxi-Clean are available here. And I have no idea what's available in the bread baking isle either ;)

Anyway, thanks for the explanation, I think/hope I'll manage to find the stuff now.
 
cosam said:
Folk seem to have been getting good results with a single UV lamp above the piece(s) being treated.
Click to expand...

After loads of trials, I found that one UV lamp just didn't cut it.
I've been using four spaced about 4" apart, and doing one side of a piece at a time.
Here's my setup:

UV Lights.jpg

UV light is a required ingredient, and it's seems the more the better (or quicker).

Just be careful opening those UV light packages !

.
 
cosam said:
Mixed up my first batch this evening just to give it a quick go. I think I may have overdone it with the Xanthan gum though, as the stuff ended up looking like a big bowl of thick, white snot. I'll be adding it more gradually next time...
Click to expand...

@ Cosam: there's some good instructions in the Wiki about just how to mix the stuff. If you are talking about having overdone it with the Xanthan Gum, and adding it more gradually, I think you may be trying to reinvent the wheel. We've already been through that stuff. You could save yourself the pain and expense.

The stuff may get nice and foamy like whipped cream, but I don't think I've ever seen my XG mix get like that. Early mixes did get foamy, but not the newer recipe.

Having said all that - this all experimentation - if you come up with something better by not following the "rules", then Great ! Merlin will give you a pat on the back because that's what he did - ie: not follow the rules. We'll perfect it somehow.

.
 
Lorne said:
@ Cosam: there's some good instructions in the Wiki about just how to mix the stuff. If you are talking about having overdone it with the Xanthan Gum, and adding it more gradually, I think you may be trying to reinvent the wheel. We've already been through that stuff. You could save yourself the pain and expense.
Click to expand...
Yeah, I was following those very instructions. I was however making a small test batch as a pint is quite a lot, and I didn't have a jar at hand to store the non-activated gel. So there was a bit of guestimation involved when it came to the quantities and I reckon I have a non-standard table spoon ;-) I'm using one of those hand-held blenders, so I think next time I'll just sprinkle the stuff in whilst mixing so I can keep an eye on the consistency.

Lorne said:
The stuff may get nice and foamy like whipped cream, but I don't think I've ever seen my XG mix get like that. Early mixes did get foamy, but not the newer recipe.
Click to expand...
The stuff I applied didn't seem to foam at all but the leftover paste in the mixing pot did get significantly larger.
 
@ Lorne

You are starting to get into SERIOUS obsession, bordering on OCD about this mate...........:mrgreen:
 
I finally figured out what OCD was.
Just bordering?
Phew, I thought I was already there.
And geezz Merlin: the way you throw out the acronyms, you could be an American.

I'm just trying to duplicate the outdoor UV conditions in an indoor environment.
If it takes a Gig, I'll just have to call in the electrician for a new electrical panel.

I've been busy lately, but I have the next suspects all lined up for the Retr0brite treatment.
 
After giving my C64 case another couple of sessions, it's not getting any whiter. I think the dishwasher episode must've bleached spots of it past its original colour. Looks like a dog's dinner but, well... it's clean, and that's why we have test pieces.

I did have more luck with the bezel on the front of one of my PDP-11s though:

before.jpg
after.jpg


Not quite as white as the rest of the machine, but after a good 4-5 hours today (on top of the original 6) it didn't appear to be getting any less yellow. Is there anything special about that last smidgen of yellow that needs more effort or is this just as good as it's going to get?
 
cosam said:
I did have more luck with the bezel on the front of one of my PDP-11s though:

Is there anything special about that last smidgen of yellow that needs more effort or is this just as good as it's going to get?
Click to expand...


To follow up on what Terry Yager is asking, have you tried taking a screwdriver to the inside of the bezel, and scraping off some old plastic to see what color the plastic is supposed to be, under the yellowing?
If it's whiter than what you see on the inside, I'd just keep processing it, and see what happens. (don't be blaming me though, if it screws up :) )
 
The only really white ones I've seen are on the covers of DEC manuals. I guess that suggests it was at some time the same colour as the rest of the machine. It is however a different sort of plastic, so I expect there may be a small difference.

I'll have a dig with something sharp and see if it's any whiter underneath. If so, I'll perhaps try mixing up an extra strong batch to get that last bit of yellow off...
 
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