h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Another question courtesy of PaperKid: Why is glue sticky?

(To narrow it down, the only glues she's familiar with are plain white glue and glue sticks.)

Hi Amy and Faith,

There are lots and lots of different kinds of adhesives, because people like to stick all sorts of different things together - wood, plastic, rubber, metal, glass. Industrial adhesives tend to be very specific, and I won't even try to get into that here.

The trick of sticking things together is finding a substance that in some way resembles the thing you want to glue. Like sticks to like. If you want to bind paper to paper, you want to find something that resembles paper.

This is why starch works well as a glue for papier mache (aka paper mache). The starch in vegetable matter (corn, wheat, etc.) is very similar to the cellulose of paper. The starch molecules form nice long strings when you cook them, and can stick to the cellulose in paper very nicely. Incidentally, these same starch molecules also thicken gravy when you cook them.

Nowadays, school glue is a polyvinyl acetate product, which is a synthetic material having long chain molecules that are also very similar to cellulose (or starch) so they also stick paper together very nicely. (An advantage of the synthetic glue is it doesn't attract insects.)


Happy Nerd

That makes sense, though it'll be interesting trying to boil it down for a 5-year-old...

I think the horses they boil down for glue are generally a bit older than that.

Orcas,

I said polyvinyl acetate, not pony vinyl acetate.