Cyanoacrylates cure method

The cure method of the adhesive very often dictates the type of dispensing equipment to be used. Cyanoacrylates are extremely sensitive to moisture and so a clean dry air supply to the pressure pot is essential to ensure the adhesive does not thicken in the pot. 

For this study, 250 p-thick circular discs, each having a diameter of 15 mm, were prepared by pouring the cured cyanoacrylate into a plastic template submerged in a phosphate buffer solution at pH = 7.4 and 37°C. The cured discs were dried and their dry weight was determined. Weight was determined periodically after incubating in a phosphate buffer at 37°C and pH = 7.4. Using titis method, it was shown that MFC and V-200 lost 55 3% and 80 4% of their initial mass at 75 days. These results are consistent with the thesis that the oxalate polymer modifier accelerates the absorption rate of polymeric MFC. 

A common method of wire-tacking today is to use cyanoacrylate adhesive and primer. In this process, a drop of cyanoacrylate is placed on top of the wire to be tacked, followed by a drop of primer. The resulting wire-tack is usually serviceable in 5 - 15 seconds although several hours can be required for full cure. The usage of the wire tack, although limited by a lack of moisture, temperature and impact resistance, has been finding increasing application in the electrical industry. 

Cellulosic materials can be mechanically fastened by a number of methods. However, their rigidity and propensity to have internal molding stresses must be carefully considered. The adhesives commonly used are epoxies, urethanes, isocyanate-cured polyesters, nitrile-phenolic, and cyanoacrylate. Only cleaning is required prior to applying the adhesive. A recommended surface cleaner is isopropyl alcohol. Cellulosic plastics may contain plasticizers. The extent of plasticizer migration and the compatibility with the adhesive must be evaluated. Cellulosics can be stress cracked by uncured cyanoacrylate and acrylic adhesives. Any excess adhesive should be removed from the surface immediately. 

The first examples of thickened cyanoacrylate adhesives were described by Coover and Shearer in a U.S. Patent. The thickeners cited and claimed were polyalkyl cyanoacrylates, polyacrylates, polymethacrylates, cellulose nitrate, and cellulose organic acid esters, such as cellulose acetate butyrate. Several years later. Wicker and Shearer improved the process for thickening cyanoacrylates. Instead of adding the thickener directly to the monomer, the thickener was first dissolved in a volatile solvent and then added to the ester. The solvent was then vacuum stripped to give the thickened adhesive. The authors claimed that this process gave adhesives having better clarity, better storage stability, and faster cure speed than adhesives prepared by the older method. 

Surface preparation. Cyanoacrylate adhesives are very sensitive to surface preparation methods and surface contamination, owing to the nature of the cure and to the high polarity of cyanoacrylate monomers and polymers. 

Solvent cleaning with solvents such as isopropyl alcohol is generally a very acceptable cleaning method although it should be noted that sometimes these solvents can stress crack or craze some amorphous thermoplastics [7]. They can also remove all traces of moisture from the surface and this can slow down or even inhibit the cure of cyanoacrylates. 

After a dwell time of five seconds under the device, it can be seen in Figure 7.10 that the shear strength of the bond between the LPDE sample and cyanoacrylate adhesive increased 10-fold, and the shear strength of the bond between the LPDE sample and the light cure acrylic adhesive increased 40-fold. Subsequently, MIL-STD-883 Method 2011.7 was applied as a destructive bond pull test to evaluate bond strength and bond strength distribution of various surface contaminations after CO2 treatment. The apparatus used had an accuracy of 5% and performed at a 90° peel angle. 

An advantage of this method is that the whole wound can be covered, thereby largely suppressing secondary bleeding and the risk of infection. Cyanoacrylic acid butyl ester is normally preferred over the methyl and ethyl esters because it cures more slowly and the polymerization produces less heat. Cyanoacrylic also causes less tissue irritation. By and large, this adhesive is only used for relatively small wounds, and it is occasionally used in vascular surgery. 

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