Cyanoacrylates Subject

Humans have developed strong skin reactions when rechallenged with the liquid. Allergic contact dermatitis has been reported in workers handling methacrylate sealants, including methyl methacrylate. In another report, five subjects were shown by bronchial provocation tests to have occupational asthma due to methyl methacrylate or cyanoacrylates. ... 

Cyanoacrylate adhesives are the most widespread type of adhesive that are applied today for glueing traumatized tissues. They have been subjected to long-term improvement by introducing different alkyl substituents and even fluorine atoms5,6). 

Different acrylate adhesives are differentiated depending on the conditions the decomposition of the C=C double bond is subjected to. The cyanoacrylate adhesives are the best known of this group. 

Cyanoacrylates have wide appeal as industrial product assembly adhesives because they rapidly form strong bonds on so many dissimilar materials. They are particularly useful in joining rigid, impervious substrates which will not be subjected to high heat, high impact, outdoor use, or long-term moisture exposure. They are also useful for bonding flexible adherends to... 

In selecting a cyanoacrylate for a particular application, one of the most important considerations is the environment or surroundings to which the adhesive will be subjected. 

Cyanoacrylates will bond skin tissue very rapidly, but bonded skin can usually be relatively easily prised apart by subjecting the adhesive to a peel action rather than direct tension. Hot soapy water will help as well as proprietary hand cleansers. It should never normally be necessary to have to resort to drastic measures such as surgery. 

Other nitrogen containing polymers which have been subjected to thermal decomposition studies include aromatic polyester imides containing 2,7-bis(4-aminobenzoyloxy) naphthalene groups [16], poly-4-vinylpyridine [17], poljmrethanes [18], polybutyl cyanoacrylate [19], and polypropyl acrylate [20]. 

The photochemistry of cyanoacrylates (Uvinal N-35) probably involves a charge-separated species that would be subjected to attaek by nucleophiles (water) and the addition of free radieals across the double bonds would result in the loss of the chromophore. 

The degree of tack-free cure is to some extent subjective and many of the later-generation UV adhesives will be less susceptible to the oxygen inhibition effect. UV cyanoacrylates and UV epoxies, for example, will give excellent tack-free finishes even under relatively low-intensity UVA lamps. 

Rigid adhesives (e.g., standard ethyl cyanoacrylates) are used for bonding assemblies when the joints can be designed to be subjected only to shear and normal static forces. If the application is subjected to peel stresses or impact loads, a toughened adhesive (e.g., epoxy, two-part acrylic or toughened cyanoacrylate) would be more suitable. 

When materials with different coefficients of thermal expansion (CTE) are joined, shear stresses result when the assembly is heated or cooled. Many engineering plastics have a CTE value in the range 80-100 x 10 mm/mm/°C but sometimes differences can occur. Eor example, liquid crystal polymer has a CTE of 10 x 10 mm/mm/°C, whereas acrylic has a CTE of 80 x 10 mm/mm/°C, and if these two substrates were to be bonded with a cyanoacrylate (CTE = 80 x 10 mm/mm/°C [5]) then the adhesive could be subjected to some quite severe stresses at the extreme operating temperature range. In this case a thicker bond line and more compliant or flexible adhesive (e.g., a flexible UV acrylic) may reduce problems. 

For example, polyethylene terephthalate (PET) plastic can be bonded with many different types of adhesives, including cyanoacrylates, UV acrylics and epoxies, and good strengths can be obtained on standard lap shear parts (1.6 mm thick). However, if thin films (<0.75 mm thick) of PET are to be bonded then it will be much easier to subject the adhesive to a peel load and the measured strength of the adhesive on the same grade of PET will be considerably lower. 

The ability of cyanoacrylates to resist attack from moisture when bonded to polymeric substrates can be most drastically tested by subjecting bonded assemblies to autoclaving. The autoclaving process combines the environmental stresses of high temperature, high-pressure and humidity. As such, it provides a good indicator of the ability of adhesives to withstand exposure to moisture. 

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