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Old 20-06-2016, 19:07   #1
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Flame Treating Polyethyene and Starboad Before Bonding with Sealant

I've been doing some testing of sealants, determining shear strength with various substrates. Polyethylene is always one of the poorest, since nothing really to sticks. That's why the tube nozzles are always PE!

I'd read that flame treating the surface could dramatically improve bonding, by damaging the surface layer just enough to allow the sealant to get a grip. It is simple enough; play a propane flame back and forth across the surface just enough to color the surface and knock off the gloss. Do not hold it still and melt the PE--that is NOT the goal.

Early testing is showing all shear failures and no adhesive failures, though I have only tested a few sealants (3M 4200, Sudbury, and Sika 291). the sealant is impossible to peal. Without the treatment, failure was always by adhesive failure, at 3-5 times lower load.

----

Has anyone tried this, and does anyone have long-term experience? I have tried this on foam bulkheads on a PE kayak, and it seemed to make a real difference, though it has only been 1 year and I did not pull-test those joints.
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Old 20-06-2016, 19:15   #2
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

Sure on whitewater kayaks. Rough up the surface so the rough things get crispy under a propane torch. Then go for it
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Old 20-06-2016, 19:26   #3
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

Works with G-Flex

But they showed slightly better strength with alcohol wipe followed by flame treating rather than sanding and flame treating.

WEST SYSTEM | Gluing plastic with G/flex Epoxy

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Old 20-06-2016, 19:28   #4
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

Well... not exactly the same PE compound, but I've done flame treating of "Coroplast" (corrogated plastic signboard) and it does improve bonding with CyanoAcrylate glues.

I've had similar results from just lightly sanding.

The flame treatment vaporizes oil left over from the extrusion process.

Long term the glue still fails. It depends on what stresses you put on the joint as to how long it lasts.

My application was building cheap radio controlled aircraft for contests with high probability of mid-air collision and seeking cheap, easily repairable models. Glue joints surviving one year's competition season (appx 4 months) was doing good. (usually the planes were beyond repair sooner due to collisions)

For similar construction and wanting it to survive years... I drill and bolt the plane together in addition to the glue. The glue still fails, but the screws hold well enough to land then I redo the joint.

***********

E-6000 craft glue sticks well to the plastics also (if its a plastic the glue doesn't attack...)

But for PE based plastics not much is permanent other than "plastic welding" where you use a special high temp version of a hot melt glue gun and melt a bead of plastic into the joint very similar to welding steel.
https://www.interstateplastics.com/L...WELDINGKIT.php
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Old 20-06-2016, 19:59   #5
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

Flame scouring of PE will improve bond strength markedly. Fatigue failure will still be poor.

Welding with filler or hot plate welding is the preferred method of pipe welding for PE.

What is your application?

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Old 20-06-2016, 21:28   #6
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

I am thinking about non-structural bonding, specifically bedding PE to decks. My go-to for anything structural would always be mechanical fastenings or welding.
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Old 21-06-2016, 08:35   #7
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

Quote:
Originally Posted by TurninTurtle View Post
-----My application was building cheap radio controlled aircraft for contests with high probability of mid-air collision and seeking cheap, easily repairable models. Glue joints surviving one year's competition season (appx 4 months) was doing good. (usually the planes were beyond repair sooner due to collisions)
-----
Those "contests" sound interesting. Got a video or website?
Thanks
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Old 21-06-2016, 08:41   #8
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

I used starboard to make platforms for air conditioner installation under berths, etc. Used gflex to affix to hull. Didn't flame scour or anything else. Holding firm for eight years, so far.
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Old 21-06-2016, 10:27   #9
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

West System told me to use a propane torch to heat, not burn, the high density polyethylene before applying the G-Flex.

My application was making a deck aperture a bit smaller to fit the frame of a new hatch. Nine years later, no separation, no leaks.

I have noticed that G-Flex does stick to my mixing cups that regular West System doesn't.

Last spring, I closed the Pearson "smile" with G-Flex premixed with collodial silica. I will see how it holds when I haul the boat next winter.
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Old 21-06-2016, 10:29   #10
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

Have experience welding HDPE
No experience gluing it,but you might check this product.
https://www.tapplastics.com/product/...d_adhesive/435
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Old 21-06-2016, 10:57   #11
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

Quote:
Originally Posted by sailjumanji View Post
I used starboard to make platforms for air conditioner installation under berths, etc. Used gflex to affix to hull. Didn't flame scour or anything else. Holding firm for eight years, so far.
I will have to look into epoxies as well.

I'm not sure I understand why you wouldn't use precast FRP for such a project, the same as the rest of the hull. The same material cost and it becomes, without question, a permanent part of the hull.

The problem with anecdotes is that they tell us nothing about the actual stresses involved. I appreciate the story, but assuming the HDPE is resting on stringers or something and the bond area is large, chewing gum might still be holding. Not a criticism, sounds like you must have a good design, but it's hard to know what to make of the information. I've tested G-flex that looked well-adhered to plastics only to find that it was very weak. For example, it may not be binding to the cups much better than 105/205, but it is flexing with the cup rather than popping off.

Unfortunately, there is little data out there, probably because it is hard to make reproducible, and because the vendors would not be proud of the numbers.
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Old 21-06-2016, 12:25   #12
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

Thinwater, are you doing another Practical Sailor test?

You need to look at Sudbury's Sealant. It will stick to Starboard without any special prep.

They are careful to not claim it as a structural adhesive but the little samples they gave me are certainly stuck strong enough to act as bedding.

Send me a PM with your address and I'll send you some to play with.
Sudbury Elastomeric Sealant

I've used it to bed some hardware that I normally would have used 5200. It skins over much faster and doesn't seem to have the ability to jump through the air and get all over you like 5200. I can't walk within six feet of 5200 without getting it on me.
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Old 21-06-2016, 12:37   #13
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

Quote:
Originally Posted by HopCar View Post
Thinwater, are you doing another Practical Sailor test?

You need to look at Sudbury's Sealant. It will stick to Starboard without any special prep.

They are careful to not claim it as a structural adhesive but the little samples they gave me are certainly stuck strong enough to act as bedding.

Send me a PM with your address and I'll send you some to play with.
Sudbury Elastomeric Sealant

I've used it to bed some hardware that I normally would have used 5200. It skins over much faster and doesn't seem to have the ability to jump through the air and get all over you like 5200. I can't walk within six feet of 5200 without getting it on me.
I think for now I will just say that Sudbury is one of the products I am testing.

As for skin-over time, I am finding that for actual strength testing, the curing time of slow products like Sudbury (most sealants, really) are measure in months, not hours or days when the application covers a large area. Typically 1 week per 10mm from the edge, slowing the greater the distance. A typical bedding can take months to really cure, depending on the weather.
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Old 21-06-2016, 13:21   #14
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

Since you're playing with it already, how about testing the Sudbury both with and without flame testing? It would be interesting to see if that improves the bond.

When I speak of skin time, I'm just talking about the exposed surface. Yes the bonding time is a lot longer. Still it's faster than 5200.

I look forward to your report.
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Old 21-06-2016, 13:43   #15
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Re: Flame Treating Polyethyene and Starboad Before Bonding with Sealant

Quote:
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Since you're playing with it already, how about testing the Sudbury both with and without flame testing? It would be interesting to see if that improves the bond.

When I speak of skin time, I'm just talking about the exposed surface. Yes the bonding time is a lot longer. Still it's faster than 5200.

I look forward to your report.
Done, and yes, there was a big improvement. I have mentioned this to Sudbury. Also tested 3M4200 and saw a big improvement. Huge. In both cases they went from adhesive failure at very low strain to cohesive failure, which is as good as it gets for the product. That said, while tat is good enough for a sealant (the sealant fails before the bond), that might not be nearly good enough for an epoxy or any real purpose, since the cohesive strength of epoxy is MUCH higher.

But it is a pretty darn good thing if you are just trying to bed a Starboard spacer. 25psi in shear vs 100 psi on a 30 square inch winch pad is the difference between 750 pounds (not enough) and 3000 pounds (plenty).

My real question is whether the improvement is long-term.
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