Thursday, April 23, 2009

Plastic Glue and Adhesive

I thought I would blog a little about plastic glue (plastic adhesives) to help sort out the mystery of using adhesives and plastics. There's really some basic element to cover first. That's whether the plastic material you want to glue or bond CAN be solvent glued.

So let's take a test and see if the plastic can be glued. There a large group of plastics that CANNOT be solvent glued. They included polyethylene, polypropylene, teflon, acetal (Delrin), and Nylon (and some other exotic plastics).
A quick test is to take a solvent like acetone (nail polish remover) or MEK (hazardous stuff) and put a little dab on the material. If it gets tacky, you can glue it. If it does nothing, you need to use mechanical fastening or adhesive tape. There is a special treatment for Teflon to allow epoxy glues to adhere (called "etched teflon").

Water jugs, plastic gas tanks, plastic water tanks (RV's) are mostly HDPE (high density polyethylene) and can only be hot air welded. They are generally white in color. They are "waxy" and slick on the surface. Your 1 gallon milk container is HDPE. The bottome of your snowboard or ski is UHMW and cannot be solvent glued. Soda bottles are made of PETG which is difficult to solvent bond.

PVC (normally gray in color) CAN be solvent glued. PVC is used in sprinkler pipes (along with ABS). And PVC comes in CLEAR - think vinyl windows, think synthetic leather and upholstery.

Here's a list of adhesives by material type to explain further about the plastics that CAN be solvent glued... keep in mind that a "water thin" solvent adhesive needs the pieces to fit together perfectly and has a short working time - whereas a "bodied" adhesive allows some gaps to be filled and has a longer working time. ALL ADHESIVES REQUIRE 24 HOURS TO CURE AND ARE STRONGER IN 48 HOURS. Some adhesives have a 20-30 minute setting time and seem strong enough to move. They are not. I always tell people to wait overnight before testing the bond. The first 24 hours usually cures to about 85% of ultimate bond strength. The next 24 hours goes to about 90% with a couple more days to full strength. Just thought you might want to know.

Repairing a Crack in Plexiglass? Click on this link - I wrote about that elsewhere in this blog. (Repairing Plexiglass acrylic sheet and Lexan Polycarbonate sheet are similar issues)

Plastic Adhesive and Glue Cross-Reference Guide (thanks to IPS for this chart)



Plexiglass Glue - Plexiglas is an acrylic based sheet - the actual solvent for Plexiglass is Acetone, but is not a good glue as it evaporates too quickly. The proper glues are either based on a Methylene Chloride solvent formula (WeldOn 3, 4, and 16) or have PMMA monomer in the mix (WeldOn 40). I have seen people mix in other chemicals such as Acetic Acid to "enhance" it. My recommendation is learn to use what's in the can as adding other chemicals that are pretty nasty, and potentially cancerous, isn't the wise course of action. When building a display case you would use Weld-On #4 - that gives you the clear bonded edges. When building a large aquarium of 3/4" thick plexiglas you would use Weld On #40. #40 requires experience as it is a 2-part adhesive and 30 minute working time. It is almost as strong as the sheet itself.

ABS Plastic Glue - ABS is a styrene based plastic - very widely used in automotive and electronics industries. Could have a textured finish or not. Test with acetone to see if it gets tacky. ABS is a high impact material but can still crack and break. There are water thin solvents and milky bodied adhesives. Since ABS is always a solid color, it's easy to work with.

PVC Vinyl Glue
- PVC could be a medium gray color or clear. It can be rigid or flexible. It could even be a foam sheet (hard or soft). Confused? Hmmm. The gray is easy. The clear is easy. But foam? Yes - sign makers use a foamed PVC sheet (called Sintra, Celtec, Komatex, etc) that is widely available and comes in white, black and a rainbow of colors. Backpackers use a soft PVC foam sheet to sleep on. Sign Banners are typically PVC based material. Convertible windows, air matresses, inflatable pool toys are mostly flexible PVC based. There are water thin and bodied glues. As in other materials, the water thin are great for matching parts. For everything else, a bodied adhesive is required.


Multipurpose Glue - I call this group of adhesives the "sticky" ones - they tend to STICK the plastics together rather than chemically solvent weld. A contact adhesive like IPS 1829 will stick 2 flat faces of materials together rather well. A "structural" adhesive like IPS WeldOn #10 is a 2 part mix - and the adhesive itself becomes structure. It's white so it's usually used behind the material where it's hidden. WeldOn #40 is also a structural adhesive and is CLEAR. It seamlessly bonds Plexiglass and is great for bonding different plastics together. #40 requires some patience learning how to mix and apply. As always, try a test part before going forward with the real deal.

Lexan Polycarbonate Glue - Polycarbonate is a bit more sensitive to solvent adhesives, so a fast drying glue like Weld On #3 is a great choice. There is a new specialty adhesive, IPS #55, that requires a special application gun. For industrial users, this baby delivers a high strength liquid that is superior to all the other glues available.


Styrene Glue - styrenes are very sensitive to solvent adhesives. Most of the styrene product that is being solvent glued is a solid color (not clear) and either is a quick shot for tight fitting parts, or you need the bodied adhesive for filling gaps (or extra working time).

Polyethylene Adhesives & Glue - The fact is that the group of olefins (polyethylene based plastics), which include LDPE, HDPE, and UHMW, are so chemical resistant that modern science has not invented a solvent glue to bond these plastics. Of course, such properties are why these plastics exist and perform their job so well. You might even note that the solvent applicators and most chemical containers are made from polyethylenes.

All is not lost - You do have some choices!

1. Mechanical fasteners - screws, nuts and bolts and the like - you may have to recess the hole or deeper countersink based on the application.

2. Pressure Sensitive Adhesive applied to 1 surface. For the thinner sheets of UHMW - called "Slick Strips" - you can peel and stick a variety of thicknesses and widths from .010" to .125" thick,

3. Contact Adhesives - IPS Weld On adhesive #1829 - it STICKS but the bond is limited as it would be with ALL solvent based contact adhesives. There are a wide variety of solvent based contact adhesives available nationwide.

4. Double Sided Tape - OK, I know you didn't want to hear this, but for some of you, laying down a few strips may do the job. There are 2 kinds of tape. Double Sided Foam Tape is a permanent adhesive good for non-smooth surfaces. "Killer Red Tape" is a thin 0.015" thick acrylic adhesive transfer tape perfect for SMOOTH surface applications. Thicker tape is available such as the line of 3M VHB tape.

5. Hot Air Welding - the way LDPE and HDPE tanks and trays are built is by hot air welding the pieces together. Similar to metal welding, but at lower temperatures, a welding rod is melted into the sheet joint to make a strong bond. The materials must be the same - you cannot effectively join dis-similar materials.

Whew. Ok - I will probably have to keep expanding this post - it's a BIG subject area.

8 comments:

  1. This article is very helpful to understand the properties of various adhesive and the relation between adhesives and substrates,

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  2. 3M makes a great "epoxy" 2 part adhesive for HDPE (high density polyethylene) 3M DP 8010 it holds strong under most conditions. When we tried a sample I was skeptical as polyethylenes don't bond well, but after curing we couldn't get the parts to separate (we kicked the crap out of our samples)I was impressed, the only draw back is the cost. It costs approx. $175.00 to set up with the special gun, tips, plunger etc. but this stuff works. I've been doing this fabrication stuff for 30 plus years and I know what it takes to get this stuff to stick, and it is usually screws. Greg Salmans, Plastic Sales So. Inc.

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  3. Good news! I am going to break out a cartridge of WeldOn 45 structural adhesive and do some testing on HDPE. The high cost of a cartridge has kept me from experimenting. I think there is a huge market for consumer packaging of a polyethylene glue in a little 2 part system.

    Keep posted...

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  4. Hi, Plastic Genius. I'm very keen in knowning the result for your finding, is it possible to let me know the outcome.
    Thank you.

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  5. informative. learning about how adhesive works and is made is important somehow. This could help us in choosing the right adhesive for the right job/project.

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  6. The use of plastic bonding adhesive are primary joining technology has become a popular way to bond all type of material parts.

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  7. I have a lifetime shed made of HDPE I would like put sheet foam insulation inside it. What would you suggest the attach the sheet foam to the ceiling and inside walls?

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  8. 3M Spray Adhesive #77 will work great ( or any spray adhesive)

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