Cyanoacrylate time systems

The adhesive is put under pressure and the dispense valve is opened for a certain time to provide the correct quantity of adhesive (see Figure 10.15). Since the cyanoacrylate contacts the pressurised air, the dryness of the air is important and an air filter on the mains air line is recommended. A pressure/time system is best suited for cyanoacrylates up to a viscosity of 5,000 mPa-s, i.e., self levelling products. 

Cyanoacrylate (Histoacryl) is a tissue adhesive used in duraplasty. The sites at which it is used should be carefully chosen. Cyanoacrylates are also in use for embolization of arteriovenous malformations in the brain. The risk of this procedure is the creation of pulmonary emboli after acrylate glue injection, particularly when delivery systems without flow arrest are used in high-flow vascular brain lesions. Techniques using acetic acid to delay polymerization time and sandwich techniques, in which glue is pushed with dextrose, appear to be more likely to cause this complication (1). 

Since bases are catalysts for the curing reaction and acids are stabilizers for the cyanoacrylates, the pH value of the surface will control the cure speed. Surfaces that tend to be acidic will cure slowly compared to a neutral surface, which in turn will cure more slowly than an alkaline surface. In most applications the objective is to speed the cure therefore, all the commercially available activators are weak bases dissolved in a volatile carrier. Applying an activator to a surface places a layer of the weak base in position to initiate the cure. Since they are stronger bases than moisture, they are able to neutralize the stabilizer systems in the adhesive more effectively, and thus they can tolerate larger gaps than would be possible with moisture alone. In general, the fixturing time is 10 times faster with activator than without it. Even with activator, the effect of the gap is clear (see Table 4). 

Typically, objects to be treated are left in an enclosed chamber in the presence of a small quantity of cyanoacrylate ester that is generally heated to aid evaporation (Figure 3). The objects are removed when sufficient fingerprint detail is observed. More recently, vacuum cyanoacrylate systems have been developed that are purported to give better fingerprint detail within a shorter period of time. 

The setting times for reactive adhesives vary from a few seconds with Cyanoacrylate adhesives to several hours for a typical DIY epoxide cured at room temperature. For a given reactive system, the setting time can be varied by a large factor by changing the temperature and/or catalyst. 

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