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Removing yellowing from plastics - Part 2

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Merlin

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Lorne,

I have used a 60 Watt filament bulb and an 11 Watt energy saving compact fluorescent bulb and I couldn't tell the difference. As far as I am concerned it's a standard blacklight bulb and should be easily available.

I got mine from Maplin in the UK. I reckon Radio Shack or anywhere that sells disco lighting should have them.

Check these Ebay numbers out to see what I mean: 110349346801 and 350162898681

:)
 
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Lorne

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I picked up a cheap blacklight bulb last night.
It works well.
I think it may even be better than the sunshine, as the gel/paste won't dry out as quickly, as is does in the sunshine.

I tried Tezza's gel with the arrowroot, and heated it in the microwave. It foamed like crazy after I added the Oxy, with the foam expanding and almost flowing over the top of the bowl. Tezza's mixture though didn't, in my case, stick to vertical surfaces enough (maybe I didn't get it into enough of a gel). Now I'm trying the hair bleach powder again, but with the blacklight. If that dries out too quickly, I'll give the Xantham gum a shot again but this time with the blacklight.

@ Merlin: As a safety guy, you'll love my thread about plastic packaging in the off topic rants section.
 

tezza

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Hi Lorne,

I've found you have to add a lot of Arrowroot. In fact the more the better,. Two heaped tablespoons is probably best in about 300 mls of peroxide. Stir after heating with a spoon and it makes a lovely gel which sticks nicely.

However, I've found you can overheat it, and when this happens it thickens less and becomes watery. It seems there is a happy medium there somewhere. To little heating and it is too thin. Too much heating it is also too thin (it warns that overheating will cause the Arrowroot to lose consistancy on the packet). I find about 40 seconds in the microwave on high with approx 300 mls is about right but check it at 30 seconds.

I really need to do some trials which different arrowroot measurements and heating times to get the ideal. I don't like wasting peroxide when it's not being used for yellowing though :)

As to the foaming, it was probably because (1) your peroxide was stronger than my 6% lot and (2) the mixture was hot!

All these tests add to the knowledge base.

Tez
 
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Lorne

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@ Tezza

You are right that 1) these tests add to the knowledge base, and 2) that my mixture was foaming because it was probably too hot. I used 30 secs in the microwave, and then another 15 secs, (with one hand) stirring in between :)

I also found out that the hair bleach instead of XGum or Arrowroot, doesn't work as well under blacklight UV. It works fine in the direct sun (maybe the heat?), but it doesn't seem as good with blacklight UV.

I've been reading a few recipes on Epciurious.com (Gourmet magazine) that use Arrowroot, and they all call for mixing with something, and then simmering on a stove (ie: not in the microwave). I've got a small Corningware pan (rather than metal) that I'll try that with tomorrow (my microwave is heavy duty, so it may be heating it too quickly). I can always heat it until it gels, and then let it cool before I add the Oxy.

We'll find out tomorrow.
 

tezza

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@ Tezza

I've been reading a few recipes on Epciurious.com (Gourmet magazine) that use Arrowroot, and they all call for mixing with something, and then simmering on a stove (ie: not in the microwave). I've got a small Corningware pan (rather than metal) that I'll try that with tomorrow (my microwave is heavy duty, so it may be heating it too quickly). I can always heat it until it gels, and then let it cool before I add the Oxy.

We'll find out tomorrow.

Yea, also trying using A LOT of Arrowroot far more than you would use for cooking. As I said, I used about 2 heaped (very heaped) tablespoons (not teaspoons) in the mixture (about 250-300mls). I made a paste with just a small amount of the liquid first, then added more liquid and the rest of the Arrowroot while stiring. Stir with a spoon and break up any lumps. Then microwave for 30-40 secs. (or in the case of YOUR microwave, 20-30 seconds :) ).

Tez
 

cosam

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my microwave is heavy duty, so it may be heating it too quickly.
If timing is critical, you might like to state your respective microwaves' power for reference so that others can better judge the cooking times. I am going to have to try this out sooner or later but we only have a decidedly puny 700W microwave at home. If you boys are nuking this stuff at (say) 1000W, that's a pretty big difference.
 

Merlin

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I am using the glycerine to slightly change the surface tension and to act as a kind of surfactant. The OH groups in the Glycerine have an affinity for water (obviously), however, the remainder of the molecule is slightly hydrophobic and would prefer to cling to more insoluble materials.

I am exploiting this property, by using the hydrophobic part of the Glycerine to coat the particles of Xanthan Gum by sticking to the hydrocarbon part of the gum molecules, to prevent it from agglomerating into lumps. This is why I said to let the mixture rest after mixing, as the glycerine then goes to work to assist the gum in taking up the water and swelling up to make the gel structure. Easy when you know how, eh?

It's a similar principle to that used when people add soap liquid to concrete or plaster, to make it more workable. You are changing the surface tension of the water to make it "wetter". I used to use alcohol to help to disperse hydroxy ethyl cellulose in the same way in some products I worked on years ago.

There's some very elegant chemistry going on behind this deceptively simple front end to the process... Harpo at Atari Age called it as a "surgical strike" on the bromine molecules in the plastic instead of "Carpet bombing the polymer" and it's a fantastic description, in my opinion.

I'll write more up on this at the weekend as I update the Wiki.
 

Lorne

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@Tezza:

Ok, something's screwed up with your conversions or your recipe.

I got the recipe for the Arrowroot paste from your blog titled "Removing the yellowing from a Vic-20 case". There you say to use 1/2 cup (= 118 ml) of peroxide and 1 heaping tablespoon, then 1 or 2 teaspoons more of the Arrowroot.

In a previous post, you say to use 2 heaped tablespoons in 250-300 ml (= 1-1 1/4 cups).

Are you trying to keep the "real" secret formula all to yourself? :)



I just made up a batch using the following:
1/3 cup (78 ml) H2O2
I mixed 1 heaped tablespoon of Arrowroot into the H202. I then added another heaped tablespoon of Arrowroot and mixed again. The mix at this point is like a white liquid.
I zapped it in a 1000 watt microwave at full power for 15 seconds. I took it out and stirred it. I zapped it for another 15 seconds at the same setting. I took it out and stirred it again. It was still a whitish liquid, but there were some strings of gooey stuff forming on the bottom. I zapped it for another 15 seconds. It was now quite warm and the mixture had changed from a whitish liquid to a translucent goo, with the consistancy (almost) of chewed bubble gum. I added 1/8 teaspoon of Oxy and stirred. It started foaming. I then applied it (using a spoon, because it was indeed thick and gooey enough to stick to anything) to the part to be de-yellowed.

I think that anyone else trying this, might want to use a lower power setting on a 1000 watt microwave. 45 seconds at full power is almost too sticky.

I've got loads of Xantham Gum left, but I'm out of Arrowroot, so I'm going to get some glycerin and try Merlin's recipe. The glycerine should fix the lumping problem I previously had using the XG.
 

tezza

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Lorne,

Your experiences with Arrowroot reflect mine. Sorry about the imprecision. Peroxide is expensive and none was wasted hence I didn't "experiment" as such. The VIC-20 recipie in the blog wasn't refined. It's just what I did and it seemed to work. It wasn't necessarily the BEST way to do it. In other de-yellowings I tried slightly different amounts but I've done no trials where I've tried to alter one variable (say heating time or amount of arrowroot) keeping other variables constant.

Firstly to clear up some confusion. My microwave is 750 or 800 Watts. I couldn't find any values on the case itself but it's a small microwave, and I'm SURE it's either of those two.

Second, the quantities. I haven't measured the liquid in mm, just estimated but it's been about 1/2 to 2/3 of a cup each time. If 250-300ml is 1-1 1/4 cup then I've estimated the mm incorrectly.

Another thing, where I've found the mixture seems too thick on heating, vigourous stirring with a spoon seems to thin it a bit. On the packet it says NOT to stir it too vigourously or it will thin. Of course those instructions are for cooking where you might not want to thin it. In some cases, we might want to.

In the Vic-20 trial I talk about adding a tablespoon, then a couple of teaspoons. I've found two heaped tablespoons are fine for 1/2 - 2/3 cup. Best to make a paste with a small amount of arrowroot and solution then slowly add the rest of liquid and arrowroot while stirring with a spoon to avoid lumps.

Good idea to check it during heating. This is what I did when I did my first one, and I stopped heating once it was obviously thickened. I found it was about 45 seconds in my microwave so for subsequent de-yellowings I didn't bother to check before that time. Doing it first time, it's worth checking every 15 seconds though as microwaves vary.

Me feeling is that the H2O2 concentration should be no MORE than 6% otherwise you might get too much foaming AND it's more dangerous if it gets on the skin or in the eyes. It certainly works at 6% so my recommendation would be to dilute it to that.

I'll replace the receipe on the blog with the refined one below, showing where we are at. I think there is a lot of scope still for experimentation with qualities and heating times but from your experiences would you agree on the below..

RetroBrite paste receipe (Arrowroot varient).

Ingredients are:

  • A weak solution of H2O2 at 6% concentration (dilute if necessary. Six to 12% solutions can be found at pharmacies and hairdressers)
  • Arrowroot thickener (found in most large supermarkets)
  • A laundry activator like Oxy or Oxi-magic (also found in supermarkets)
Wear gloves. Even a low concentration of Peroxide can burn, especially when heated.

1. Make up a 1/2 to 2/3 cup of arrowroot/H2O2 solution by gradually adding small quantities of both ingredients one at a time while stirring.

2. Heat in a microwave until the solution thickens (about 45 seconds for a 750 Watt microwave. Less for higher powered units). Do not overheat. If doing for the first time, check after every 15 seconds and stir between checks to ascertain progress.

3. Add a very small amount of Oxy (1/5 of a teaspoon). Stir into mixture. If the mixture seems too thick stir it vigourously, which will thin the mixture a little. It will foam a little but it is not explosive.

The mixture is now ready for use.

Tez
 
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tezza

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Guys,

I've written a blog entry JUST on the Arrowroot recipe, rather than having it hidden in the Vic-20 blog. I'll be amending the Vic-20 blog to point to this page for the present "state of the recipe" so to speak.

Merlin you could link this page from the wiki.

It's at http://www.classic-computers.org.nz/blog/2009-02-12-de-yellowing recipe.htm

I haven't linked it to the blog index yet. Any comments before I do?

Tez
 

Lorne

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@Tezza:

Revised recipe looks good.
I can't comment on the quantities, as I used a different amount of H2O2 and arrowroot, but you're right on with the checking every 15 secs. I did notice that stirring vigorously thinned the mixture somewhat. Good thing too, because it was pretty thick after 45 secs in the micro.

I was pleased with the results of the thicker/stickier mixture. I just have to try Merlin's recipe now, and see which one "tastes" better.

We're getting there - it's definitely an on-going process.
 

Merlin

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@ Lorne

My mixture wasn't 100% precise when I came up with it, as people may have got different results in relation to viscosity than I did.

The glycerine does make a difference, and is a trick I used years ago to disperse starchy viscosity modifiers before they had a time to form lumps.

Feel free to play around with my recipe it in terms of XG content and let me know what works best for you.
 

Merlin

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OK,

I've updated the Wiki article with some of the science behind what we are doing; I've tried to keep it readable and interesting (not easy to do, believe me). Comments are welcomed, as long as they are nit-picky ones from Lorne... :lol:
 

Lorne

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OK,

I've updated the Wiki article with some of the science behind what we are doing; I've tried to keep it readable and interesting (not easy to do, believe me). Comments are welcomed, as long as they are nit-picky ones from Lorne... :lol:

Whoooo. Was that an invitation or "another" typo?
"as long as they are nit-picky ones from Lorne".
You can bet they will be.
I can't wait to read that Wiki !
 
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