Sticky Tubes

[Jeffzee]

Hello everyone, I have a chance to purchase a Walker Bay Rib really really really cheap. The problem is the tops of the tubes have become sticky and discolored. Has anyone heard of this happening before? The tubes are PVC. MEK seems to clean it up fairly well, but not sure if it will just re-occur.

Thanks for your input!

Jeff

[Dave Cowell]

We see it on a few inflatables. I haven't seen it reappear in the short term.
MEK is too aggressive to clean PVC, that is why it is used to prep the surface before glueing. You risk damaging the material and would be better using a less aggressive cleaner.

[Pikey Dave]

Either it's been parked under a "Sappy" tree or the PVC is starting to degrade (perhaps that's why it's "really really really cheap" ) If the PVC is failing, walk away, it ain't cheap.

[office888]

Sticky PVC is caused by plasticizer migration. UV radiation from the sun breaks down the material overtime. Lighter colors are more susceptible to it than darker colors, since they contain less pigment that acts as an attenuator to neutralize UV radiation in to heat.

Carbon black is a wonderful thing. Titanium dioxide, not so much.

[Jeffzee]

It is basically free, i would be using it as a tender to my sailboat. It is a lighter color. Is there a cleaner anyone would recommend I try?

Thanks!

[Patch]

Originally Posted by office888

Sticky PVC is caused by plasticizer migration. UV radiation from the sun breaks down the material overtime. Lighter colors are more susceptible to it than darker colors, since they contain less pigment that acts as an attenuator to neutralize UV radiation in to heat.

Carbon black is a wonderful thing. Titanium dioxide, not so much.

Spot on! We see it a lot in Australia through the UV and heat we have but also an unfortunate popularity of cheap PVC boats. Walker Bay are some of the worst for it especially the logos on the side.

Nothing will keep it away long term and then gradually the PVC becomes brown, stiff and crispy which you can not patch repair if necessary.

If it's free and you don't care what it looks like or if it will actually function when you need it to, go ahead.

[Jeffzee]

If i get it cleaned to where it looks good, and i keep it covered from the sun when not in use do you think it will stay good, or will it just keep coming back regardless?

[whisper]

Personally, I'd leave them sticky. they're ideal for keeping the kids in the boat, for reading newspapers on a breezy day and for using old post it notes that have lost their stickiness...

But be warned, DO NOT sunbathe on your tubes if you are boating alone, unless you can reach your VHF...

Safe boating dude

[Patch]

It will come back. Slower if you keep good care of it but it will come back.

[Poly]

Originally Posted by Jeffzee

If i get it cleaned to where it looks good, and i keep it covered from the sun when not in use do you think it will stay good, or will it just keep coming back regardless?

If it is plasticiser migration and/or depolymerisation (which is what it sounds like) then a wee chemistry lesson might help you understand the long term problem you face.

Pvc is actually a rigid material (they make sewage waste pipes, and window frames from It). It is made up from very long chains of atoms that pack neatly together which gives it rigidity. In its pure form it would not be suitable for making boat tubes from as it is too brittle when thin and not flexible enough. So during manufacturing they add small molecules (plasticisers) in to disrupt the regularity of the pvc chains which makes it flexible, this works well for a reasonably long time - flexible pvc was ubiquitous in the 70s and 80s but eventually it ages, how long that takes depends on how it is treated. UV, heat and age have two effects. first those plasticiser can start to work their way out from between the pvc chains. Generally heat will speed that up, especially if the temp is different inside/outside the material. That will leave the pvc chains more rigid, and the area where the excess plasticiser migrates to (the surface) gets softer, and eventually sticky. washing the surface with strong solvents can remove the plasticiser but you won't be able to control the process so you get just the excess plasticiser and risk making the material even stiffer (if you try it with a very thin beach toy you'll see you can make flexible material go stiff just by washing it!).

It is NOT possible to put the plasticiser back where it "belongs" or reverse the process, and so it is inevitable that you will eventually get tubes that fail and can only be replaced. It's impossible to predict with any accuracy how long that will take...

The second effect is depolymerisation, this is when those long chains of atoms start to break down into shorter chains (which like the spaghetti in a tin doesn't tend to organise itself as neatly as the long stuff you make bolegnase from). Shorter chains are more flexible but also weaker (hence why they don't make the fabric that way in the first place!). Again this process is irreversible. It might be confined to just the surface layer (as it will most likely by UV driven, and as office888 suggests TiO2 which gives it the white colour makes matters worse (actually it absorbs UV very well, but in doing so it generates free radicals which are bad!). If it was "just" depolymerisation I wouldn't expect the tubes to go brittle, but what you would see is that patches wouldn't stick as the material underneath is "gooey".



Hopefully that gives you some idea of the cause, and helps you see why cleaning it off might only be a temporary fix, and why a boat with those symptoms might be particularly hard to patch now or in the future.

Retubing isn't cheap but if the boat is nearly free and is only a tender for short hops then it might be a risk you are willing to take.