silly question

[flying haggis]

How does glue "know" when to change from a liquid ie pva to a solid when you use it.

 

[sunnybob]

how does the sun know what time its supposed to rise each day?

answer to both questions... Because it does.

 

[Jacob]

I think it just guesses when it's out of the bottle. Or maybe it can read the instructions? It's obviously not as daft as it looks.

 

[SteveF]

evaporation I believe

Steve

 

[RogerP]

It dries (and glues) by evaporation of the water content. It can't evaporate in a sealed container but just see what happens in a half used container if you leave the lid off for an extended period.

 

[MusicMan]

Traditional glues were by evaporation. Modern glues are polymer-based, and work by (further) polymerisation. When initiated, the chain-like molecules extend and form longer chains, tangling up like a ball of wool and using up the free liquid in the process.

The initiation may be by a separate chemical (two-part epoxy) or by exposure to air, or by pressure (I think PVA is in this category), or by water (e.g. Gorilla glue).

They adhere to the surface because the surface is more stable with a layer of glue on it (in jargon, the surface energy is lowered). This happens whenever a liquid 'wets' a surface.

Keith

 

[sunnybob]

I still prefer my answer (lol)

 

[MusicMan]

Ah, Sunnybob a follower of fact-free debates? ;-)

Correction to my answer - there is a large evaporative part for ordinary or decorators PVA, until the resin particles are close enough to start to adhere to each other. There is also a cross-linking PVA that sets mostly by polymerisation. This might be 'yellow' PVA but I'm not sure.

Keith

 

[sunnybob]

Ah, Sunnybob a follower of fact-free debates?

You do me an honour sir.
I just thought it was funny, but I cant get any smileys on my reply box. (VBG)

 

[MusicMan]

Well, Sunnybob, in the end in science it always gets down to "because it does" !

Keith

 

[sunnybob]

What? No! I cant be right!
being right isnt funny!!!!!

 

[n0legs]

Would a monkey crossed with a fish be called a monkeyfish?

 

[Doug B]

Would a monkey crossed with a fish be called a monkeyfish?

Sounds more like a fishy-monkey :lol:

 

[Bm101]

*peers in to see whats happening. Sighs and goes to get (another) cider.

 

[monkeybiter]

Would a monkey crossed with a fish be called a monkeyfish?

Sounds more like a fishy-monkey :lol:

Is that what 'funky' means?