[HN Gopher] How plastic can rust, sort of
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How plastic can rust, sort of
Author : giuliomagnifico
Score : 69 points
Date : 2021-09-27 08:01 UTC (1 days ago)
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(TXT) w3m dump (dfarq.homeip.net)
| AlexandrB wrote:
| I suspect a lot of these electronics are intended for indoor use
| and are not made of UV stabilized plastics. I'd rather have
| yellowed electronics than ones made brittle by being left outside
| in the sun.
| VLM wrote:
| Observationally heat seems to make plastics more brittle than
| sunlight. Top of dash car parts seem about as brittle as shaded
| bottom of dash car parts.
|
| Field service people seem to kill laptops in a couple years,
| although we're talking about hours long process not years so
| that shouldn't matter, anyway I don't recall the exposed tops
| of their laptops being worse than the bottoms of their laptops.
|
| The scientific debate about plastic breakdown seems to be over
| centuries vs thousands of years exposures so mere hours will be
| fine.
|
| https://phys.org/news/2019-10-sunlight-degrades-polystyrene-...
| bujak300 wrote:
| A couple of hours will not make a difference. After a couple
| hundred hours you will see uv radiation effects
| timw4mail wrote:
| Most yellowed plastics are likely brittle too.
| titzer wrote:
| I've never heard of setting plastic out in the Sun to reverse
| yellowing. UV light is overall pretty terrible for plastic, as it
| will become brittle and break down. It _will_ eventually turn to
| dust from UV exposure alone. So if you care about the longevity
| of the plastic and not just its cosmetics, don 't do the sunlight
| thing.
| mrspeaker wrote:
| I can't believe the sunlight trick works. My brain always thought
| it was the sun that made it yellow! I saw this first on the Retro
| Recipes channel a while back where he shared some theories on the
| maybe how's and why's.
| (https://www.youtube.com/watch?v=8P1OVj0IcqY)
|
| I was very skeptical, but I tried it out on my very very yellow
| Nintendo Famicon, as well as some smoker-teeth-yellow keyboard
| keys on an old Roland synth... left them out in the sun for a
| couple of days (2x3hours). It worked really well on both my test
| subjects! Certainly not perfect "retrobrite" white - but much
| better than I expected.
| derbOac wrote:
| In the wetshaving community "butterscotch" shaving brushes became
| sort of a sought-after commodity. They're basically plastic
| brushes originally meant to mimic ivory in color that have
| oxidized to a sort of butterscotch color.
|
| Originally there was a lot of interest in restoring them to their
| original ivory-like color. If you search there's lots of advice
| on this, like exposing them to sunlight, or using UV lights
| and/or peroxides.
|
| Eventually though I think there got to be an interest in the aged
| color, and interest in restoring the color declined.
|
| I'm not a dentist, but I have family who are, and they explained
| similar processes are involved in teeth whitening. Basically a
| peroxide gel that gets put on the teeth with a custom fitting,
| and then exposed to UV light.
| drivers99 wrote:
| 8-bit Guy does this frequently in his restorations.[1] He's
| tested a lot of methods in the past. [2] One thing I noticed in
| the old video is that heat worked even better than sunlight in
| the peroxide solution, and the sunlight was also heating the
| water in the Texas sun. But the light makes a difference as seen
| by the rock shadows. He's also built indoor UV setups before. He
| didn't seem to be aware of sous vide immersion heaters as a
| solution for making larger volumes of heated water at a stable
| temperature since he was thinking of inventing his own version of
| one with various parts from the hardware store.
|
| [1] skip to 2:45 https://youtu.be/xhBnyK5lQ2s
|
| [2] https://youtu.be/qZYbchvSUDY
| everdrive wrote:
| I've only heard of retr0bright in this regard. SNES consoles are
| pretty famous for yellowing at different rates. As other
| commenters have stated, sunlight degrades plastic. It may perform
| some whitening, but you're damaging the old electronics.
|
| https://www.retr0bright.com/make.html
| rowanG077 wrote:
| I don't think you are supposed to apply it to the electronics.
| Only the plastics.
| fnord77 wrote:
| several years back there was an article where someone
| methodically tried several compounds to restore yellowed plastics
| (IIRC it was the fire suppressant in the plastic that caused the
| discoloration)
|
| person put a lot of work into finding a solution. Wish I could
| find the article. It was a great read - cleverness, hardwork and
| the scientific method.
| jpm_sd wrote:
| http://www.mountainouswords.com/mountain-air/retr0bright-res...
|
| http://www.retr0bright.com/
| fnord77 wrote:
| yes! thanks
| hok wrote:
| I wonder how hydrogen peroxide (a strong oxidant) can reverse the
| yellowing of plastics, if the yellowing is the result of
| oxidation. I'm not a chemist, but this doesn't seem to make
| sense.
| richrichardsson wrote:
| If you follow some links in the OP you can end up at a source
| article[1] that has some comments on the actual chemical
| processes occurring for both the discolouration and reversal
| (Ctrl-F "bromine").
|
| TL;DR: Over time the bromine based flame retardants in retro-
| era plastics degrade (hence the yellow/brown colour) and H2O2
| plus some energy (UV light/heat) can be used to reverse the
| process.
|
| [1] http://www.vintagecomputing.com/index.php/archives/189
| xattt wrote:
| I am not sure either. I have some quirky white plastic
| Matroshka measuring cups that I left out on the sill as a
| decoration for several years. They were exposed to sunlight,
| and have yellowed. Interestingly, if I run them through the
| dishwasher they become even more yellow, and fade with a bit of
| time.
|
| I wonder if it has anything to do with sodium perchlorate in
| the dishwasher tabs, the heat of the dishwasher or both.
| delinom wrote:
| I am not a chemist, but the following comment from a
| retr0bright video[1] claims that retr0bright works not by
| reversing the process, but by speeding it up.
|
| _Interestingly, The idea that the yellowing is from the
| Brominated Flame Retardants in the plastic is actually itself a
| myth. It 's a sort of believable just-so story because people
| look up bromine, see it is brown, and go "ah, makes sense". The
| interaction doesn't actually involve the brominated Fame
| Retardants, and is a breakdown of the butadiene chain of the
| plastic polymer which is effectively an oxidization which is
| catalyzed by energy (whether light (UV being the most
| energetic), or Heat). This happens with All ABS plastics,
| including those that don't have any Tetrobromobisphenol-A. This
| is why UV Stabilisers and absorbers tend to be a common
| inclusion in the formula of ABS plastic. (And why when they are
| forgotten/omitted you see things like car recalls due to
| seatbelt fasteners degrading). The yellowing is effectively the
| molecular debris from that breakdown, which gives a colour to
| the plastic. Hydrogen Peroxide is a strong oxidizer- it works
| in retrobrite not by reversing the process, but actually
| speeding it up. It reverses the colour change because while it
| significantly speeds up the butadiene being broken down, it
| also breaks down the molecular debris that results from it, to
| smaller, colorless compounds. It will also interact with other
| compounds in the plastic- for example, those that might have
| been added for the factory colouring.The result is that the
| colour of the original plastic returns- possibly without any
| factory set colouring compounds as well. Another downside is
| that because the butadiene chain is still compromised,
| retrobrite can never restore the structure of the plastic, so
| it will remain brittle. I've seen suggestions that an acid
| might be able to chemically recompose the butadiene polymer. I
| was able to successfully test a paste of Oxalic Acid, without
| any sunlight exposure for example- though it took a week and
| the colour change was very small._
|
| This might explain why direct sunlight can brighten plastic
| instead of yellowing it even more.
|
| [1] https://www.youtube.com/watch?v=xBS_UEV35W4
| eutectic wrote:
| Hydrogen peroxide is a very aggressive oxidizer compared to
| molecular oxygen and will break down molecules instead of just
| adding to them.
| jstanley wrote:
| I'd guess it strips away a thin layer of plastic to reveal the
| non-yellowed plastic underneath.
| VLM wrote:
| Unfortunately retrobriting doesn't take off surface dirt or
| ink or similar. Painting-like surface preparation is required
| beforehand. Just dumping sort-of-casually clean parts in the
| solution will lead to splotchiness and areas that don't get
| cleaned. The official site recommends a gentle dishwasher
| cycle, I've had luck with that.
|
| In a way, its good it works that way. It doesn't strip off
| the apple logo or "mac" lettering or whatever.
|
| Your theory is reasonable but it seems its actually breaking
| down a bromine based fire retardant. Bromine itself is kinda
| gross brown color and some oxides like dibromine pentoxide
| are clearish-white so its quite realistic that hitting it
| with an oxidizer clears things up.
| bena wrote:
| This is done with Lego bricks as well. It may weaken the plastic
| to some degree. For larger pieces of plastic it shouldn't be a
| problem though.
| hyperman1 wrote:
| Maybe someone here can explain me something.
|
| I dug up my old duplo blocks from around 1980. Most colors are
| ok. The blue ones, however, have all gone brittle.
|
| Is this normal? Why only blue?
| kloch wrote:
| I remember reading about using Brasso to de-yellow LEGO but
| I've never tried it myself.
| snvzz wrote:
| I see the retrobright community as pure OCD.
|
| Just leave it as it is. Yellow is cooler. It shows vintage class.
| buescher wrote:
| Agreed. Most antiques, you want to keep the patina, right?
| tantalor wrote:
| I think the reason for "keep the patina" is actually because
| if you try to remove it then you will inevitably damage the
| underlying material.
|
| e.g., a very skilled art restorer can remove discolored
| varnish
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