Weathered plastic table (images added)

[rjlittlefield]

"Why won't this thing come clean, no matter how much I scrub it??"

That was the question I kept asking myself, regarding the top of a weathered plastic table that I've had outside on my deck for, oh, decades.

When I looked close enough, the reason became evident.



Bear in mind, the large blunt cylinder on the left is the bristle of an ordinary cleaning brush. The small clear strand on the right is a fine white hair from my very own head. Obviously not even the hair is fine enough to get down into the cracks of this table and root out the accumulated dust.

Here's the synthetic stereo rendition:



Shot at 10X on an APS-C sensor (Canon T1i), using a Mitutoyo M Plan Apo 10X stopped down with an auxiliary iris to reduce the number of frames needed in this very oblique view. In the end, I opted to process only part of the frames, to give the bristle some separation from background. 78 frames used here, at 20 um step size, with the iris stopped to 5 mm, NA ~ 0.12 .

This particular stack was a lot more challenging than usual to process, because my sensor had gotten quite dirty and I didn't notice it until too late. Nasty dust trails all over the place. I figured it would be a herculean effort to make a presentable stereo, so I switched gears and used Lightroom's healing brush synchronized across the whole stack to kill the dust in the source frames that were presented to Zerene Stacker. That worked pretty well, and turned the episode into a valuable learning experience too.

--Rik

Edit: to add step size and working NA.
Edit: change title for new images

[ChrisR]

Nice.
UV or just ageing damage. Plasticizers evaporate, etc ...More than one mechanism at work.

Designing with Plastics and Composites: A Handbook
By Donald Rosato

[Chris S.]

Very cool, Rik! I love to see macro images that teach me things about the real world. I've myself encountered some plastic surfaces that no amount of scrubbing would clean, and now I know why.

Just yesterday, I cleaned a bicycle chain in a new way (for me). Usually, I clean such chains while they are on the bike, using what is effectively a fancy brush and solvent. This always leaves some intractable grit in the links. But this time, the chain had broken, and before putting it back on the bike and repairing the break, I thought it would be a good idea to clean the chain while it was off the bike. So I dropped the chain into a two-liter Pepsi bottle, poured in a couple inches of kerosene, and shook the bottle. The kerosene rapidly became filthy, so I poured it out and replaced it. After four or five agitation cycles with fresh kerosene, the chain was cleaner than any amount of brushing would have accomplished. Your post is a great illustration of why. Too bad you can't reasonably submerge your table in solvent, and sonicate it.

Brilliant touch, including a brush bristle for relative size. Is that a skin flake on the left end of the hair?

Also, for me, this is one of those cases in which the stereo pair really delivers.

ChrisR, my sense is that crazing isn't what went on here, though I much appreciated the explanation you posted of why stressed plastics sometimes turn white. I'd wondered!

--Chris

[Sumguy01]

Very interesting.
Thanks for sharing.

[elf]

I can see why you were pulling your hair out trying to clean this

p.s Pressure washer would probably work, but you'd have to do it every week.

[ChrisR]

my sense is that crazing isn't what went on here, though I much appreciated the explanation you posted of why stressed plastics sometimes turn white.

It looks crazed to me, so I don't see any doubt that it's crazed
Going white doesn't mean crazed, many materials weather to a powdered surface, etc, which scatters light, making them look white.
"Stress" is perhaps misleading, they're talking about micro-level effects. A dried river bed cracks for somewhat similar reasons - plasticity is inadequate so the material "gives". As mentioned there's a host of failure modes for plastic sufaces in UV, or simply ageing. Evaporation, breakage of polymer cross-links, oxidation, and I daresay more, all mixed up.
uPVC is unplasticised PVC which withstands UV better, and probably not what Rik's table's made of! Almost nothing's pure PVC any more, I believe, so it takes a brave man to be assertive.

[rjlittlefield]

ChrisR, thanks for the snippet about crazing. I've heard that term used in a variety of ways since I was a kid, including to describe what happens when things go wrong with ceramic glazing and tiny cracks develop in the surface layer. I'm pretty sure those cracks in the glazing layer would not contain fibrils capable of carrying stress, so I can only conclude that the word "crazing" means different things to different people.

The situation with this plastic tabletop is even more complicated than just age. It was several years ago when the tabletop first started to become annoyingly difficult to clean. At that time I did finally get it clean by scrubbing and bleaching, and then I immediately applied several coats of "Pledge With Future Shine Floor Finish", which I gather is an acrylic product.

Since then the table has withstood several summers of blazing sun plus periodic rain and sometimes frost, augmented by fallen leaves, mold, bird poop, and the occasional batch of mayfly eggs deposited by divebombing females.

So, the table certainly consists of a white base material, possibly PVC, perhaps with a clear or age-whitened layer of acrylic stuff stuck on top. If I had to guess, I'd go with the frankly cracked stuff as being acrylic.

Too bad you can't reasonably submerge your table in solvent, and sonicate it.

Indeed. If I could get it clean that way, then perhaps I could again coat it with shiny clear stuff and get a few more years of use out of it that way.

As it is, I've discovered that the surface can be cleaned quite effectively with 00-grade steel wool, applied with a bit of water and a lot of scrubbing. The sensation is interesting. For a while the steel wool is obviously catching on rough stuff, and then suddenly it starts to feel like it's gliding on smooth plastic. At the same stage that the tactile feeling changes to gliding, the visual appearance goes white.

I have not yet examined the cleaned surface at high magnification. Through a 10X loupe, the surface appears to be dominated by a fine pebbly texture, instead of the primarily scraped or scratched surface that I would naively expect from rubbing with steel wool. Perhaps the steel wool is mostly grabbing hardened lumps, and pulling them away from an underlying layer of more intact plastic?

Brilliant touch, including a brush bristle for relative size.

To be honest, this is a case of perspiration, not inspiration. At first I shot just the plastic. That was interesting to me personally, but it told no story. Then I added the hair and shot again. That gave a better impression of scale, illustrating how small and inaccessible those cracks are, but still (I realized too late) did not tell the story. Only then, on the third try, did it occur to me (well, duh!) to include one of the bristles that I had been trying to work with in the first place. All in all, quite a humbling experience.

Is that a skin flake on the left end of the hair?

Beats me. I plucked the hair, placed the hair, took a few shots, noticed crud on the end, removed the hair, stroked it between my fingers thinking that would clean it, and put it back. It still had crud, albeit with some changes in appearance, so I decided to accept the crud as a visually interesting mystery, and left it at that.

--Rik

[rjlittlefield]

Here is a follow-up showing what the surface looks like after cleaning with steel wool. This is not exactly the same place as shown earlier, but it's within a few inches, on the same tile of the table.

First, the overview shot. I hope it's obvious that I've cleaned only one tile of this section.



Then, photographed at 2X. This is pretty much the perception that I get when looking through a 10X loupe. As I wrote earlier, the surface appears to be dominated by a fine pebbly texture, instead of the primarily scraped or scratched surface that I would naively expect from rubbing with steel wool. Perhaps the steel wool is mostly grabbing hardened lumps, and pulling them away from an underlying layer of more intact plastic?



Shot again at 10X, the expected scratches become evident. (By the way, I have deliberately not done any removal of sensor dust when processing this stack. You can see what I meant earlier when I said that my sensor had gotten quite dirty. Bear in mind, this is processed using the DMap method; PMax was a lot worse. )



It's clear that while the surface is now clean, if dirt does accumulate in those scratches and pits, none of the usual scrubbing devices will be able to reach into them to get it out. Perhaps I would be well advised to put on another sacrificial surface coating, while this underlying part still looks good.

--Rik

[ChrisR]

So, the table certainly consists of a white base material, possibly PVC, perhaps with a clear or age-whitened layer of acrylic stuff stuck on top. If I had to guess, I'd go with the frankly cracked stuff as being acrylic.

Perhaps it's just an added, textured coating to impart some perception of quality, that you just don't need.
If the table is one of the myriad uPVC grades, which would be reasonable to hope, then it shouldn't be affected much by weathering.
I don't know anything about anything you can coat PVC with post-manuafacture, that wouldn't flake off and look awful.

Remonds me of the "Zen" finish on Sigma lenses. My 400mm aged horribly, so I sat down with nail varnish remover. Now the lens is just black plastic, very ordinary and OK.

[rjlittlefield]

Perhaps it's just an added, textured coating to impart some perception of quality, that you just don't need.

Remember the chronology. When new, the table was smooth, shiny, and easy to clean. Over the years it became progressively less smooth and harder to clean. Several years ago I cleaned it as best I could. I don't remember exactly how I did that, but I'm pretty sure that it did not involve steel wool. Then I added a coat of that "Pledge With Future Shine Floor Finish" stuff, which I was pleasantly surprised to see did stick well to the plastic of the table. It's that Pledge layer that I suspect as being the frankly cracked stuff, now removed by steel wool.

--Rik

[ChrisR]

Ah, sorry I'd misunderstood the Pledge product. The only ones I've heard of are cleaners whch leave a very slight film of wax or silicone.

I don't know whether we have the one at Walmart - we don't have Walmart either.

Yours does say it adds "acrylic" (a rather imprecise/overused term).
One of the one-star reviews complained that the product "alligatored". I'm not sure I've seen a definition of that one, but it might fit what has happened to your table.
I note they do produce a "Cleaner" with a similar label which annoyed some of the reviewers because they didn't read the label. Isn't it terrible when people can't read what's in front of them .
Perhaps the cleaner would help.

[rjlittlefield]

Perhaps the steel wool is mostly grabbing hardened lumps, and pulling them away from an underlying layer of more intact plastic?

After much more study, this appears to be exactly what's going on.

Here's a photo of the margin between original and cleaned surfaces, showing the evolution.



At upper right is the original fractured surface. In the diagonal band near image center, I see the underlying plastic surface with the "big" chunks of fractured surface having been recently pulled away. Then near the left margin I see more polished new surface, where the steel wool has scratched away the high spots, leaving small high regions of essentially flat and lightly scratched surface, surrounded by deeper pits.

It's not shown in this same image, but I presume that as I continue to rub with steel wool, the flat areas get worn down su that they become bigger, while the pits get smaller and shallower as seen several posts back.

It's interesting to me that in the photo I posted earlier, my perception of raised versus lowered is quite simply reversed. Here is another copy of that image:



The light source here is positioned at upper right, as can be clearly seen from the shadows of the bristle and hair. So, applying my best cognitive analysis, it must be the case that those long linear features of the texture are raised ridges, with the light bouncing off their right sides.

Nonetheless, my immediate perception stubbornly insists on seeing them as depressed valleys, reflecting light that is coming from the left, not the right. I have no idea why this is. Maybe I've spent too much time looking at landforms, and not enough at dimpled plastic!

The new image is uncropped, 5X on an APS-C sensor, so about 4.4 mm across the frame. Stacked from 53 frames at 100 microns, shot using an auxiliary iris to reduce the frame count needed to cover this depth.

--Rik

[rjlittlefield]

Here is a stereo version of the new stack. It may give a more vivid impression of how the surface is structured, for those who can see stereo!



--Rik

[ChrisR]

From 2 posts ago:

my immediate perception stubbornly insists on seeing them as depressed valleys

I previously even, couldn't force myself to see them that way.
Perhaps we need a poll!

[KurtM]

rjlittlefield, have you got a thread somewhere that tells about your macro rig, how you get those shots?

And love the stereo pairs too, gotta learn how to do them someday!