Can plastic "rot" or "rust"?

The Craftsman humidifier I'd installed on the air handler of our home's heat pump HVAC system started dripping water. I assumed that the float valve which controls the water level in the plastic tray which wets the motor driven rotating sponge drum had gotten leaky and wasn't shutting off properly.
Much to my surprise, the float valve was fine, but the bottom of that tray was "rotting through", and with a slight push my fingertip went right through it.
The tray is molded from a hard gray plastic and the bottom which rotted is about 3/32" thick. The rest of the tray is still hard as a rock.
The water in it was a dirty brown color and there was a fair amount of brown "mud" in there too.
Might be my fault for not taking it apart and cleaning it more often, but I'm still amazed that the plastic gave out that way.
BTW, I installed that humidifier about 23 years ago, so I'm not complaining about "short life", just surprised to see "rotting" of plastic. I hope some of the plumbing pipes in our home don't suffer the same fate.(G)
Jeff
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Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
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On 6/3/2013 12:56 PM, jeff_wisnia wrote:

Depends on the type of plastic and exposure to light and chemicals. Plastic degrades in many ways but usually it is scission of the polymer chains and loss of properties. Since the surface gets attacked first it may form a degraded coating. Rest assured that your plumbing pipes are different plastic, not that it makes them have any longer lifetime.
I had one of those Craftsman humidifiers in my old house and am surprised yours lasted that long. I remember having to constantly clean out the residue. My current house has an Aprilaire which only needs a pad changed every year or so but needs overflow to go to a drain or French drain in my case.
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On 6/3/2013 10:16 AM, Frank wrote:

that is not natural color contains a separate resin with color. They are mixed prior to molding and then when melted for injection, they are stirred together by the molding machine. Either or both may be breaking down. Or the color may not be compatible with the pan resin. If exposed to ozone or UV, both color and the pan resin must have protection for the polymers.
Paul
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The color concentrates are usually pigments dispersed in the same resin. Lots of other materials like toughening agents, stabilizers and fillers can be added to the mix. What is important is that the producer subjects the final part to end use conditions. You can run accelerated aging tests. Unfortunately defects may not show up until years of end use.
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Jeff: I would take the plastic tray back to Sears. There are some plastics that do deteriorate in water. Inexpensive latex paints, for example will soften up and lose their adhesion if they get wet. However, part of any designer's job is to ensure that the materials they're using for their humidifier are appropriate to the job, and if your plastic water tray has "rotted" out, then it wasn't an appropriate material right from the get go.
Paul Drahn;3073055 Wrote:

With utmost respect for Paul's knowledge and experience, some plastics are dyed (like fabrics) and some are pigmented (like paints) and still other plastics are the colour they are because they have printing ink on them.
Nylon or polyester carpet fiber, for example, is most often dyed to it's final colour. That's why when you spill bleach on a carpet like that, you take the colour out of it. If the plastic had the colour all the way through it, as was suggested, then bleach wouldn't affect the colour of the plastic because it couldn't penetrate into the plastic. The bleach could only affect plastics that are dyed to their final colour after they're drawn or molded into their final shape, where the colour is entirely at the surface of the plastic.
Top quality latex paints, for example are made of the same plastic that Plexiglas is made of. But, instead of being dyed, those latex paints are pigmented, meaning it has tiny solid particle suspended in it. Since bleach can't penetrate into the plastic paint film, putting bleach on latex paint won't affect the paint colour because the bleach won't penetrate into the plastic film.
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nestork

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Jeff-
Nestork may be right. It would be worth checking with Sears to see if they will do anything for you. Success might depend on finding a Sears manager who believes in customer satisfaction.
Before you do, check with Sears Parts to see if the tray is still available. <http://www.searspartsdirect.com/partsdirect/index.jsp You will need the model number, which should be in the form of 123.456789. The first part identifies the source, which might be 119 (Frigidaire) or 110 (Whirlpool) for example.
Fred
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Fred McKenzie wrote:

Thanks, I'll give it a try sust for S's and G's.
About ten years ago I took a failed Craftsman lawn sprinkler back to the local Sears store and they did give me a free replacement. The replacement didn't have the Craftsman name on it, so I asked the nice guy I was dealing with if it still came with a "lifetime warranty" and was told it didn't and that they no longer made sprinklers bearing the Craftsman name. Can't complain, I never thought I'd live this long anyway. (G)
Jeff
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Jeffry Wisnia
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On 6/3/2013 11:56 AM, jeff_wisnia wrote:

Johnstone Supply sells an aerosol spray can of "Pan Spray" it's a sealer for leaking plastic or metal drain pans in AC evaporators and I've found many other uses for it. It applies as a layer much like the undercoat on cars and will seal any sort of unpressurized container for water. If you cant find a replacement pan, it may be some help. ^_^
http://www.johnstonesupply.com/storefront/search.ep?keyWords=pan+spray
http://tinyurl.com/m82ekty
TDD
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