| From: Woodie ® | 16/12/2001
16:10:56 |
| Subject: How does glue dry? | post id:
539779 |
| Is it a chemical reaction? or
evaporative? | |
| From: Zardoz ® | 8/21/01 7:51:34
PM |
| Subject: re: glue/adhesives | post id:
386693 |
| Your question refers to
poly[vinyl acetate] adhesive. The polymer is made by emulsion
polymerization from vinyl acetate, at room temperature in a water-based
emulsion, in the presence of an anionic surfactant (long-chain alkyl
sulfonate), a protective colloid (e.g. polyvinyl alcohol) and a
water-soluble radical initiator (potassium persulfate). The resulting
emulsion can be used directly as an adhesive (glue). The monomer, vinyl acetate, is made industrially from ethylene and lithium acetate in the presence of palladium and copper catalyst, at 80..150 deg. centigrade. There is no chemical bond formed. What happens is that (in the case of Elmer's glue and similar latex glues) the polymer + solvent fills in the surface pores (which is why they work best with porous materials). Then the solvent evaporates, leaving behind a polymer film which adheres to itself in the same way that strands of cooked spaghetti adhere to each other. The whole thing acts as a glue because the polymer has penetrated pores in the surface of each object, and when it hardens it doesn't want to come out! Think about paint, which has the same sort of polymer in it: have you ever "glued" something together with paint? painted a door or window shut? doesn't paint get "tacky" as it dries? (Incidentally, that's how they get teflon to stick to frying pans: they sandblast the metal surface, then coat it with they polymer. When it dries, the polymer has penetrated the surface and doesn't want to come out.) Other types of adhesives (epoxies and cyanoacrylates, for example) form the polymer in situ; this gives them greater penetrating power, because the small molecules can penetrate smaller pores before they link up into the polymer network. But in no case do you ever get a chemical bond between glue and substrate.  http://www.ananova.com/news/story/sm_377350.html?menu=news.quirkies http://www.madsci.org/posts/archives/apr2000/955665848.Ch.r.html | |
| From: Woodie ® | 16/12/2001
16:20:52 |
| Subject: re: How does glue dry? | post id:
539799 |
| why doesn't superglue stick to
the bottle? Surely superglue is "reactive" as it seems to "melt" plastics
when glueing them. | |
| From: The Bone Collector | 16/12/2001
16:27:21 |
| Subject: re: How does glue dry? | post id:
539807 |
| Glues or adhesives tend to work
in one of three basic ways: Some work by "drying" out (in fact the solvent evaporates, concentrating the chemicals). Some work by reacting chemically with the air (oxidation) to change the chemicals into adhesives. Then there are other types you may have used which need mixing in two parts (each part alone won't set). the bone collector | |
| From: spOOk ® | 16/12/2001
22:04:37 |
| Subject: re: How does glue dry? | post id:
540040 |
| I've heard that superglue only
dries in the absence of air... and that's why a new bottle is never
full. Other glues that come in one tube will be air-drying - evaporative. - PVA glue for example, and contact adhesives. But some are actually solvents - like those for PVA and other plastics. They effectively weld the two surfaces together, then the solvent evaporates. Then there are fillers which require a catalyst - like car body fillers and builder's bog. This is a chemical reaction - like a chain reaction. And epoxies - where you mix equal parts A to B. The last two chemical reactions produce quite a lot of heat as they harden. | |