Adhesives
Adhesives bind our wounds, repair our mistakes, and help attach that gold star to a job well done.
Credit: iStock
There are many methods of fastening two materials together: a button and a buttonhole work fine to close a jacket, wooden dowels will peg a chair or even the walls of a cabin. But when a bond is needed, especially between two different materials, such as skin and a Bandaid, then adhesives do the best job.
Another benefit of adhesives is they join two surfaces without adding significant weight to the overall product, which is especially useful for fragile and fine applications such as repairing broken ceramics, paper, or musical instruments. Adhesives are often highly specialized chemical compounds, created through different processes, to achieve different purposes.
White glue, one of the most familiar adhesives, works through the principle of solvent evaporation. Part of the class of drying adhesives, these substances harden as the solvent leaves through vaporization. Adhesives for woodworking or for dealing with fabric also create bonds between materials after the solvent evaporates; these materials specifically contain the polymer polyvinylacetate.
The hot adhesives used in glue guns for numerous craft applications are thermoplastics. They are heated up to be runny, applied to the two surfaces to be joined, and upon cooling, they harden again to form the seal between the two materials.
Pressure sensitive adhesives work because they are soft enough to flow to make a connection to the second material, but they are also strong enough to resist stress to separate the two components. These materials span a broad range from permanent to removable. Permanent pressure sensitive adhesives are used for situations in which a label should not be removed, such as for safety information on power tools. In contrast, temporary pressure sensitive adhesives are designed to be removed at some future time, ideally without leaving any residue. Uses for these materials include masking tape, price tags, and items to be attached to the skin such as EKG electrodes, wound dressings, and athletic tape. Our ubiquitous Post-It® notes fall into this category as well.
Anyone who has ever gotten pine sap on his hands is familiar with the many adhesives found in nature as well. Starch-based glues are used extensively with corrugated cardboard as well as for putting up wallpaper, and animal glues remain the preferred adhesive used by luthiers, craftsmen who repair stringed instruments.
With the wide variety of adhesives, it is possible to find just the right solution for every sticky situation.
More information about adhesives is available at http://www.adhesives.org/Home.aspx
This topic was suggested by Harry Workman of Bloomfield, Conn.