No Cure - Differential Scanning Calorimetry DSC

There are more sophisticated techniques to determine the extent of cure but these do require the use of specialised (and expensive) equipment. DSC is a thermo-analytical technique [2] in which the difference in the amount of heat required to increase the temperature of the sample of suspect uncured adhesive and a fully cured reference are measured as a function of temperature. Both the sample and reference are maintained at the same temperature throughout the experiment and DSC will detect any energy changes or heat capacity changes with great sensitivity and thus determine whether the test sample has fully cured. 

Sometimes cyanoacrylates will form a white powder adjacent to the bond line. This is known as blooming or sometimes frosting . This section explains the reason for blooming and suggests various options to eliminate it from the production line. Also included are general guidelines for troubleshooting an application. 

When excess adhesive has been applied, the surface-to-volume-of-adhesive ratio is too low and the moisture on the surface will be insufficient to neutralise the stabiliser in the adhesive. The cyanoacrylate vapour will escape and fuming will occur. Reduce the quantity of the adhesive by using fine-bore application nozzles and/or dispensing equipment. 

In the same way as excess adhesive can cause blooming, a slow cure may give a similar result. The cyanoacrylate at the periphery of the joint will search for available moisture from the surrounding air and may then cure as a white powder on the adjacent surface. A slow cure may be the result of excess adhesive but may also be caused by acidic deposits on the substrate. These acidic deposits can cancel out the neutralising effect of the initiators (moisture) and result in very slow polymerisation or in some cases inhibition of cure completely. 

Slow cure can also be overcome by using an activator (or accelerator). The activators increase the level of initiators on the surface to negate the stabiliser and thus increase the speed of polymerisation. UV-curing cyanoacrylates have also been used in applications to accelerate the cure speed and thus eliminate the possibility of blooming. 

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