What is the chemical force that makes common household glues work

There are a lot of forces at work but mostly chemical, both covalent and ionic.

Mechanical is also important as glue might penetrate when it is liquid.

The mechanical properties of the glue are also important particularly when bonding materials with considerably different mechanical properties.

Not a simple subject and I worked > What is the chemical force that makes common household glues work

Let's take the three most common types of household glue first:

1. Elmer's Glue (for example, wood to wood or paper to wood)
2. Crazy Glue (for example, plastic to plastic or steel to steel)
3. Shoe Goo (for example cloth to leather or rubber to cloth)

There's just no way that these three glues are "ionic" bonding with the wood, plastic, or cloth respectively. Just no way. There is no "outer layer" of electrons being shared in these cases.

Likewise with covalent bonding. It's just not happening.

I can't explain why though - but it's just not that type of bonding that is going on. What type of bonding "is" going on, I don't know though.

I suspect nobody knows, but that's why I asked - which is to find someone who knows what kind of bonding force is happening when two items are glued together.

the

Buit I thought that every atom has an "outer layer" of electrons. (Well maybe hydrogen's single electron is a degenerate "layer"!)

But I agree if "ionic" means electrostatic (like Na and Cl in salt) it seems unlikely...

Mike.

Hi Mike, I thank you for your opinion where I realize the extreme hazards of responding on something that, most likely, none of us actually know the answer to (least of all me).

Like you, I can't imagine that ionic bonding is going on here, although I will readily admit I only have the chemistry training that everyone has, which is, for ionic bonding, classically portrayed by the metal sodium and the non-metal chlorine.

This bonding is an electrostatic force between oppositely charged ions, anions and cations if you will, where the requirement is that both compounds be ionic.

Taking our three common household glues:

1. Elmers (paper to wood)
2. Crazy (plastic to plastic)
3. Goop (rubber to leather)

I can't imagine that any of those materials are ionic, whether they be paper, wood, plastic, rubber, or leather.

Can you?

If it's not ionic (which I can't imagine that it is), then we have covalent bonding, which is a more complex sharing of electrons between atoms.

How is covalent bonding going on with plastic to plastic cyanacrylate (crazy glue, Eastman Kodak 910) stuff?

The whole purpose of sharing electrons is to become more stable where, in the case of glueing two things together, stability isn't what's happening.

For example, when I glue rubber to leather, stability of either the rubber or the leather isn't the issue for the molecules. And yet, they're stuck together so "some" kind of force must exist.

But what is that force of glue?

Clearly there "is" a bonding force. But what is that bonding force?

Oh, it's happening. The SURFACES of wood, plastic, cloth have material-air interfaces, with some kind of loose chemical links (that would hold the material together, if you hadn't run out of material when you got to the surface...) which is loosely holding on to (maybe) oxygen or another interface layer of random stuff.

The glue first has to come into closer contact than that oxygen molecule, i.e. it has to wet the surface and displace the O2. It has to flow into contact, and either repel or dissolve the contaminants already present. Afterward, it has to solidify into something with tensile strength, or shear strength, enough to transfer force through the glue to the surface it bonds to.

Something like tin/lead solder joining metsls is EXACTLY covalent (metallic) bonding, but with more complex materials, there's just a lot of different kinds of bonds involved, Good glues, like soap, have hydrophobic and hydrophilic and all sorts of bondable molecular sites, but unlike soap, they also harden or stiffen after some time due to cooling, chemical restructuring, loss of solvent (vehicle).

None of these form bonds except maybe weak hydrogen bonds with the hydroxyls in wood and the glue. Makes it sort of a solvent situation where the glue penetrates the wood fibers, just like when you dye cotton and when dry is insoluble.

The other glues are in solvents and there is a little of like dissolves like going on allowing the glues to penetrate except for the metals. Metals often have oxide surfaces and there may be chemical interaction.

Shoe Goo is more of an adhesive with, again, like chemical contact to like with glue to rubber.

My experience was mainly with epoxies and Kevlar adhesion to rubber and plastics, even cement. All of these were chemical bonds.

The material sets harder than most glues, like contact adhesive or rubber/silicone glue.

Beside fast curing, the big advantage of CA glue is how it whets and penetrates into small gaps and pores in a materials before setting.

..... Phil

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So piss off then !!