This problem of not being able to wet the surface can be seen when dripping water on a recently waxed car. The water forms beads and quickly rolls off the surface. If the car's surface has not been waxed in a long time, the water droplet may stick to the surface and form a sheet or stream of water flowing on the surface. The difference is that the wax provides a much lower energy surface to the water, which has a difficult time sticking to the wax and forms a bead and rolls away.
Plastics with low surface energy (polypropylene, polyethylene, etc) are used for food containers and other vessels because of their mechanical properties and also their inert surface that allows liquids to easily roll off. So, how to glue them? I searched the web and found this product:
3M Scotch-Weld DP8005. It has some magical composition that allows it to wet very low energy surfaces.
It's pretty expensive -- a little over $20 at McMaster, plus the special plunger (another $8). The tube of adhesive and plunger are intended to be used in a dispenser that works like a caulk gun. They also sell a mixing tip that swirls the two parts of the adhesive before dispensing. That's all fine, but I prefer to just mix with a nail on a piece of paper. I bought only the tube and plunger and had no difficulty dispensing, mixing then applying with a nail.The adhesive itself is pretty weird. It's gritty, like it contains tiny glass beads or sand. I applied the adhesive to my project (polypropylene bottle and flat slab of polypropylene), and put the pieces with very light clamping pressure in an oven at about 80*F for about six hours. I shut off the oven and went to bed. The overnight temperature in my shop was probably 50*F.
The next day, I took the parts out of the oven and was glad to see the adhesive worked very well. It made a very strong bond -- strong enough for me to drill and tap two holes with 1/8" pipe threads in the 1/4" thick slab that I glued to the bottle. The plastic showed no signs of coming loose. I made six bottles like this, but didn't have a spare bottle for destructive testing.
Amazing GOOP 3.7 oz Interior/Exterior Plumbing Glue
ReplyDeleteYou can get it at Lowes or Home Depot... their motto is "Glues whatever. Lasts forever." I use it all the time to glue just about every type of surface, including poly-plastics. I glued a makeshift nozzle into one outlet of my garden sprinkler (cut from a WD-40 straw) with Goop and it's holding under pressure.
I had a similar problem to solve with HDPE (high density polyethylene); I tried this same adhesive without success. However, I was surprised how easy it was to just melt the two parts together - they solidify and intermix forming a strong bond. I didn't try it but you might look into plastic welding using hot air - from your other posts I think you might like it!
ReplyDeleteThe gritty mixture can be explained by the datasheet "The joint design of the substrates should facilitate a .005" to .008" adhesive thickness at the bondline. Adhesive contains .008" micropheres for this purpose". I first suspected my adhesive had been contaminated when I used it.
ReplyDeleteLoctite makes a primer which I believe contains hexane. It is a clear liquid. You brush it on, wait a few seconds for it to flash dry and the plastic will accept their cyanoacrylate (crazy glue). I use their 401. It is also sold in the usual retail stores in a tiny combi pack, good for one or two small jobs. The solvent treats the surface of PP, PE, teflon, delrin, etc. To accept the adhesive. Works oretty good. I have forgotten the number if the primer but it aint cheap, either
ReplyDeleteLoctite makes a primer which I believe contains hexane. It is a clear liquid. You brush it on, wait a few seconds for it to flash dry and the plastic will accept their cyanoacrylate (crazy glue). I use their 401. It is also sold in the usual retail stores in a tiny combi pack, good for one or two small jobs. The solvent treats the surface of PP, PE, teflon, delrin, etc. To accept the adhesive. Works oretty good. I have forgotten the number if the primer but it aint cheap, either
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ReplyDeleteHeat welding is the best but if joining dissimilar plastics like ABS to Polypropylene for example some times a two step approach might work. You mechanically joint the two pieces first (bolts, screws, pegs etc. ) to keep the pieces together then use something applied before assembly to fill the gaps like ABS--PVC transition solvent.
ReplyDeleteFrom a pure gluing perspective a small test I did showed cyanoacrylate (crazy glue on roughened surface) had considerable holding power. Other people show mixing this with baking powder. This would give it bulk and perhaps work as a sealant.
August 29, 2016 at 5:55 AM
Another test showed Contact Cement worked even better than cyanoacrylate
ReplyDeleteI've heard Contact Cement doesn't hold up well under heat. 3M 17.6-fl oz Bonding Clear Multipurpose Adhesive would likely be a decent alternative
DeleteA DVD case made of PP cleaned with alcohol, cyanoacrylate (superglue) and a piece of plywood did not stick at all.
ReplyDeleteOk you need to change the surface energy, dyne (a measurement of that energy) with a silane, usually but there other ways these have quite the affinity to carbon and hydrgen atoms but not to itself, so the thickness of this coating is very important then apply the cynoactrylate adhesive with a soft brush this helps with silane thickness .The other ways are flame and corona/plasma treatment but due to the delicate nature of the process it is exceptionally difficult to do by hand on a one off basis and is usally reserved for automated processes Another way is to florinate the surface with florine gas but as this stuff is detrmental to most living things I would avoid trying this. Hope this helps with laying out the issues of poly propylenes, poly ethylenes and the rest of the polyolfin range This not so much a how to, but a why to.
ReplyDeleteHow can I repair a cracked (broken) basket from my Fellowes paper shredder? Manuf could not tell me the type of plastic used!
ReplyDeleteBest Test Rubber Cement Thinner is Hexane, available at better art supply stores.
ReplyDeleteThere should be letters molded into the plastic. Example(s) HDPE, PP of which you will be able to learn the type of used.
ReplyDeleteThe recycle code can tell you a lot, too. Mine is 5 - polypropylene.
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