| From: Chris W (Avatar) | 31/07/2001
14:14:31 |
| Subject: Contact Cement | post id:
365835 |
How does contact cement work? | |
| From: Zardoz ® | 31/07/2001
14:21:05 |
| Subject: re: Contact Cement | post id:
365844 |
| PRODUCT DESCRIPTION: A water
based contact adhesive, ready to apply directly from the can with no
further additions of liquid or powder. Cures or sets by
evaporation. COMPOSITIONS AND MATERIALS: One component, prepared formulation based on latex polymers, inert fillers, resins, surfactants, solvents, preservatives and other chemical additives. Safe and non-flammable. TECHNICAL DATA & more here http://www.super-tek.com/contact.htm" Water Based Contact Cement  | |
| From: Chris W (Avatar) | 31/07/2001
14:24:23 |
| Subject: re: Contact Cement | post id:
365849 |
| Not quite Lib. The idea behind contact cement is that you spread a thin layer on the two surfaces to be bonded. The layer is allowed to dry to the point of being tacky to the touch before the surfaces are pushed together. The surfaces then stick together exceptionally well. I don't know the chemistry. | |
| From: Zardoz ® | 31/07/2001
14:29:41 |
| Subject: re: Contact Cement | post id:
365861 |
| Contact Cement (Non-Flammable)
Material Safety Data Sheet Methyl Chloroform (1,1,1-Trichloroehane) (Sara Iii) http://www.biosci.ohio-state.edu/~jsmith/MSDS/3M%20CONTACT%20CEMENT.htm Material Safety Data Sheet | |
| From: Mjr | 31/07/2001
14:36:53 |
| Subject: re: Contact Cement | post id:
365872 |
| Question:
What chemical reaction takes place when the two halves of epoxy glue are
joined together? Answer: OK, this may not answer the question, but here goes. The McGraw-Hill encyclopedia of Science and Technology says that epoxy resin is a polyether resin formed by the polymerization of bisphenol A and epichlorohydrin. Past all the 10-dollar words, what that means is that the two halves of the glue are a resin (composed of relatively small molecules) and a catalyst (which initiates and speeds up the reaction). The reaction that happens involves the joining together of smaller molecules, plus reacting them with oxygen-containing compounds, to form a "polyether resin." This resin is nice and hard, and very stable. From http://www.newton.dep.anl.gov/askasci/chem99/chem99211.htm Not sure if that's what you're after though. Mjr (NUFAH) | |
| From: Zardoz ® | 31/07/2001
14:46:00 |
| Subject: re: Contact Cement | post id:
365882 |
| Rubber cement works by a
mechanism of cohesion [also called autohesion, or 'self-sticking-to-self]
but this is true both for the paper gluing example and the rubber gluing
example, provided there is cement on both pieces of paper. Cohesion occurs when the long polymer chains of the adhesive material are able to penetrate and mix with the polymer chains of the adherend [the substrate]. This process is also called 'interdigitation' in reference to the simile of fingers of opposite hands interlaced, as if in prayer. It is much harder to seperate hands with interlaced fingers than when the hands simply lay one on the other. When rubber cement is used to bond rubber to itself, the solvent in the cement swells the substrates somewhat and facilitates the interdigitation process. After the solvent evaporates, it is hard to distinguish just where the joint lies. The bonding force is not a chemical bond -- no bonds are made or broken; the strength of the bond is purely a physical phenomenon involving van der Walls and London forces between two intimately mixed and chemically similar non-polar hydrocarbon rubber molecules. Paper is a polar carbohydrate, however, and wouldn't be expected to have any physical attraction to rubber. But, as you note, paper is porous and allows an adhesive to penetrate into its internal structure. This happens with rubber cement [just as with Elmer's Glue] when the solvent evaporates, leaving only dry rubber behind physically wrapped around the fibers in the surface of the paper. When this dry rubber coating contacts another piece of plain paper, nothing happens, because the solvent that provides mobility to the adhesive is absent. But if another rubber coated piece of paper is encountered cohesion [autohesion, interdigitation] occurs rapidly and an adhesive bond is formed. Elmer's Glue is made from polyvinylacetate [the same as found in common latex wall paint] and is polar, which favors interaction and attraction to polar cellulose, and is much more rigid than rubber and has a higher tensile strength which is all manifested in stronger paper-to-paper bonds than rubber cement. http://www.madsci.org/posts/archives/may98/893193004.Ch.r.html | |