Cyanoacrylates

by Vince Zeigenbein [Internet Article]

Tech Editor’s Note:
It turns out that there is a downside to the use of cyanoacrylate glues. Inhaling the fumes given off when the material polymerizes can sensitize someone. This can lead to an allergic or allergic-like reaction, resembling severe asthma, in which the lungs may even shut down. The specific allergic reaction to cyanoacrylate fumes may be what’s called, anaphylactic shock, which is a dire situation. Cyanoacrylate should never again be used by someone who has already had an allergic reaction to it; the result can be fatal. A positive ventilation system, dispersing the vapors away from yourself or anyone else, is vital in preventing any harm.

Cyanoacrylate glues are reactive monomers that chemically link (polymerize) when pressed into a thin film. The very thin layer of water moisture present on most surfaces acts as an alkali, or weak base, which is the catalyst that results in bonding. However, the presence of detectable amounts of water usually degrades the performance of cyanoacrylate glues.

The thinner variety of cyanoacrylate glues have a water-thin viscosity that wicks deep into joints by capillary action and cures in a matter of seconds. Surfaces to be bonded must be tight fitting and should be held together while you apply the cyanoacrylate glue around the edges of the seam. At the moment cyanoacrylates cure, they give off a vapor that can irritate the nose and eyes, so be prepared. Thin cyanoacrylate’s work well on balsa because they penetrate into the wood and form more than just a surface bond.

Tech Editor’s Note:
If cyanoacrylate fumes are allowed to mix with the atmosphere and be diluted, all negative effects cease. The point at which you become allergic to the fumes is highly individual and can happen without any warning. Best is to always ventilate!

The thicker form of cyanoacrylate glue has a higher viscosity for loose fitting joints in which the adhesives must bridge gaps. Normally the thicker cyanoacrylate is applied to one surface and then the parts are held tightly together for approximately 5 to 15 seconds. For large surface areas, including those with close-fitting joints such as lamination, this grade of cyanoacrylate glue should be used. To prevent premature curing, don’t spread the glue into a thin film layer. Lay down a serpentine bead about 1-inch separations on one surface, then assemble the parts letting the pressure spread the cyanoacrylate out.

The Cure Accelerator is a catalyst that works by allowing cyanoacrylates to quickly cure in thick layers. When a light mist of the accelerator is sprayed on the surface to be bonded, it dries almost instantly, but remains active for several minutes. Apply accelerator to the opposite surface, and the glue will set within a few seconds after the parts are held together.

To allow for more time for the parts to be positioned correctly, wait to spray the accelerator around the glue joints after joining. This will instantly hold the part in place while the rest of the cyanoacrylate cures normally. A bead of medium cyanoacrylate can be placed over a joint for reinforcement when sprayed with accelerator. When parts meet at right angles, lay a bead along both sides of the joint to form fillets that will buttress the joint when cured with the accelerator. The thick variety of cyanoacrylate glue is the best for most plastics, including GE’s Lexan. It is also the best choice for plastic model assembly. When used with the accelerator, it works better than nearly any putty for modifying or filling voids. It can be carved with a knife or razor blade and sanded and feathered to form a finish indistinguishable from plastic.

The thick cyanoacrylate bonds fiberglass, hardwood, metal, and rubber better than any other hobby adhesive. For gluing to the inside of the cloth-textured surfaces of fiberglass, scrape the area to be bonded with a razor blade or coarse sandpaper before using the cyanoacrylate.

With all cyanoacrylate glues, the closer the parts fit together, the stronger the bond. Always hold the bonding surfaces together as tightly as possible. Any rough spots on the mating surfaces should be smoothed out. Although cyanoacrylates will hold objects together with considerable strength in seconds, the full strength of the bond is not reached for several hours. Allow for this before subjecting parts to maximum stress. Also, cyanoacrylates are generally a little less brittle and have higher strength when they are allow to cure on their own.

Heat and moisture will decrease the shelf life of cyanoacrylate glues. Unopened bottles can be stored in a freezer or refrigerator, but allow them to reach room temperature before using. Keep your bottle in a cool place that won’t be exposed to direct sunlight and store away from bottles of accelerators. Q