Saul Kinderis wrote: > > One of the things to consider is whether you are looking at an adhesive bond > or a cohesive bond. In an adhesive bond, you are using a bonding agent and > it attaches to each of the materials in effect bridging them. While in a > cohesive bond the bonding agent causes the material to "flow" into the > other, much as welding causes to materials to "mix" and forms a direct bond. [snip] Good job, Saul, of illuminating what we technodweebs made obscure. The trick is in knowing when cohesion is possible, and with which solvent. And, the same goes for adhesion, and which adhesive can adhere to dissimilar materials. Sad to say, much of the time the an adhesive approach depends on mechanical adherence to one or both of the materials to be joined, because the adhesive does not bond chemically to the molecules in the material(s) to be joined. (Exception: successive layers of the same stuff before the surface becomes "inactive:" Weldwood Contact Cement, for example, is typically used in two layers, the first to make a mechanical bond to each material, and the succeeding layer to make an active surface on each material, which bonds to itself when the materials are joined. In my experience, most such joints fail in the mechanical part, delaminating from one or the other of the surfaces. Polyethylene-WWCC adherence almost always fails this way, but not until a "high" load (for the usual PE/minicell applications, anyway) is placed across the joint.) (Not connected to the Weldwood folks, just a satisfied user. This stuff does well in many "low-load" applications, and is considerably cheaper than many of the specialty adhesives sold for marine use. Use in a very well-ventilated area!) -- Dave Kruger Astoria, OR *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Mon Jul 12 1999 - 19:11:41 PDT
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