Glue

Recently I have been demolishing and taking down some internal walls; this was hard physical work and had me thinking.

When I remove a screw, I need to use similar amounts of energy to undo the screw that were used to tighten the screw.

When I built the framework I glued the wood together. This gluing took very little effort on my part, but a great deal of force to break.

Where did the glues energy come from?

Well I'll take a stab at your question here to see if I can provide you with an answer. When the PVA (Polyvinyl acetate, commonly used as Wood Glue) begins to dry it creates a bond between the two pieces of wood. This bond is fairly strong and is why it's ideal for holding together wood. The reason it takes so much force to break it is because of the bond the glue forms to the wood. Does that help answer your question?

reply to post by Poisson


Thank you for your reply Poisson.

But where does the energy come from to form the bond?
What energy gives it the strength?

Well, as I recall, it is an endothermic reaction, meaning it pulls in environmental energy to organize itself into a strong lattice structure. This is not a heavily pronounced reaction, but it is there. It is also why you don't want to try gluing in cold temps... there is less energy to pull from. You also want dry air, but that is because the solvent keeping the glue from curing needs dry air to evaporate into.

Hope this helps.

reply to post by lightchild


Atomic cohesiveness! Think in terms of chemical bonding on a molecular level, the glue forms a matrix of hardened cellular walls that form millions of tetrahedrons interlocked together with the wood fiber, the glues is actually stronger than the wood itself. The energy released is chemical from a semi solid to a gas.

Edit: Horn explained it better then I did, so there is your answer.

[edit on 20-9-2009 by Poisson]

It makes a bond between the 2 objects. What I find interesting is that we don't know how it makes a bond.