When Super Glue Doesn’t Save the Day

broken-3d-figureSince we’ve been solving scientific problems in the community for years, our friends now know to turn to us to solve their everyday science struggles. In the past, it’s related to white work vans and titanium dioxide. Most recently, a 3D-printed Star Trek action figure was the subject of scrutiny.

A friend of the Polymer Solutions team broke his beloved figure between the body and head piece.

Thinking of a quick fix, he reached for cyanoacrylate–better known as Super Glue. He got the glue out, added some to the plastic pieces, and pressed them together. To his surprise (and dismay), this most “super” of glues didn’t work at all!

Much like permanent marker, Super Glue isn’t perfect. It doesn’t work for every application. There are instances where it is ineffective at bonding surfaces and in some cases, it’s cost prohibitive to buy and use in bulk. Just like how some solvents don’t work to dissolve certain materials, some adhesives don’t work for certain applications either.

To understand a little bit about the different kinds of adhesives and why superglue doesn’t work for everything, we need to understand the different ways adhesives stick things together. Some materials bond chemically, when materials are joined together to form a different material, as a byproduct of the chemical reaction. Others are chemically “softened”, allowing the adhesive to bond to the newly softened substance once it cures. Another way, and the one we we’ll focus on, is a physical adhesion:

Physical “Lock and Key” Adhesion

In woodworking, a dovetail joins two pieces of wood together. This is a great way to explain this type of adhesion. White glues, like Elmer’s glue for instance, work this way. When they are put on a substance, the glue seeps into all the little imperfections on the materials–into tiny cracks and pores. After that, solvent evaporation occurs. The solvent in Elmer’s glue is water. When evaporation occurs, the “glue” solidifies and forms a bond. Just like a dovetail, these connections hold the two materials together.

Cyanoacrylate works in a similar way, through a process called anionic polymerization. Cyanoacrylate actually bonds into a durable mesh structure that hardens to form a very strong, rigid bond. Isn’t that cool!?

Hearing how amazing cyanoacrylate is begs the question: why doesn’t cyanoacrylate work for everything? Sometimes the materials you want to adhere to simply don’t provide the right conditions. Since cyanoacrylate falls under the physical “lock and key” method of adhesion, non-porous surfaces don’t really work well. That’s why some adhesives–like cyanoacrylate–don’t work well on some plastics and other materials like glass.

All that doesn’t mean it isn’t a great adhesive–it is! It’s fast-drying, adheres tightly to many surfaces, and is widely available. One great example of cyanoacrylate being a perfect adhesive for a particular use is in integrated circuits. In this application, a quick-drying and strong adhesive is needed and cyanoacrylate shines in the context of this application. There just isn’t a single adhesive that’s perfect for everything application–there is no one size fits all approach.

So how did we fix the figurine after all?

broken-figureThe fix was two-fold. First, we inserted a pin into the top and bottom parts of the broken plastic. Then, we adhered the pin in place with epoxy. Epoxy is a great example of an adhesive that is bonded chemically. It comes in two parts: a resin and a hardener. When the two parts react, they form a bond that is both strong and relatively quick-drying.

This fix involved a little extra work to adhere the two parts of a simple figurine together. For our friend, who is a die-hard Star Trek fan, this adhesive solution allowed his beloved figurine to be restored. Although this was a fairly straightforward example, it is a great lesson in the kinds of things we test and work with here at Polymer Solutions each and every day. When you think beyond the surface and inquire about the world around you, simple things become quite interesting!