Why does Superglue not work on plastic?

Many plastics like polyethylene are thermoplastics that can only be re-bonded by heat welding or re-melting of the two surfaces. Adhesive glues like Superglue or methyl methacrylates are great quick fix adhesives best suited for more porous surfaces than plastics. Slick plastics are very difficult at best to bond with liquid adhesives. There are exotic solvent based 2 part adhesives that will give an OK bond but don’t have high hopes for long term structural bonds.

cheaper to go buy more reading glasses

Why does the glue not set? It seems to stay in liquid form until you touch it with your finger when it automatically hardens.

@rojo Quick setting is the amazing quality of Crazy Glues…fast is not always better and if you want to truly know why cyanoacrylates are not the miracle glue in every situation…PM me.

Maybe I’m a nerd, but it wouldn’t bother me if yall had your discussion about cyanoacrylates here.

I use glue every now and then, mainly for fishing rods.

I’ve become a Gorilla Glue guy. Is there a better alternative, that isn’t like expensive, or military grade?

I used to work with a guy who used to help build supersonic aircraft. He said that because of the unique stresses that speed and maneuvering put on the aircraft, they couldn’t use bolts,or rivets. They used some secret glue ,that bonded metal to metal on a molecular level. Does that sound feasible?

It has to do with a property called “surface energy”, which affects the way liquids behave on the surfaces of various plastics.

On some, liquids tend to bead up; these are said to have low surface energy. Some low surface energy plastics include polyethylene and polypropylene. Adhesives applied to these have a hard time spreading out and conforming intimately to the plastic surface (which is what makes glue work).

High surface energy plastics will allow liquids to spread rather than bead up, so liquid glues get a more intimate contact. Some high surface energy plastics are polycarbonate and polyester. They’ll actually adhere pretty well with CA glues.

Super glue needs moisture to cure. If you apply it, then prevent moisture from reaching the adhesive, it will not cure. Same goes for most silicones.

Is this why it will sit on a surface indefinitely and suddenly congeal/set once it touches your finger @RocketGuy ?

Yep. Or you can blow on it with moist breath.

@rojo In most parts of the world you don’t have to blow on the adhesive as available humidity will usually cure moisture cure adhesive like Superglue and RTV Silicones and why they are so popular.