Hello to the group,
There has been a recent thread on CA and I thought some of you may like
a bit of background information on CA and it properties.
Cyanoacrylates, A Brief Overview:
Monofunctional 2-cyanoacrylates were first patented in 1949, but the
first viable production process did not evolve until 1954. In the early
1950's, scientists at Eastman Kodak were working on thermal
polymerization and discovered the rapid room-temperature cure and
excellent adhesion properties of 2-cyanoacrylates, quite by accident.
While working on a freshly prepared monomer, the scientists discovered
that the glass prisms of the refractometer has become tightly bonded.
Extensive work thereafter, found that many different types of substrates
bonded in the same manner. Subsequently in 1958, Eastman 910 debued, the
first in a large family of 2-cyanoacrylate ester adhesives.
2-cyanoacrylates polymers spontaneously form (via an anionic/radical
mechanisms) when their liquid precursors, or monomers are placed between
two closely fitting surfaces. The great utility of these adhesives
arises from the electron-withdrawing character of the groups adjacent to
the polymerizable double bond.
The high reactivity (cure rate) and their polar nature, enables the
polymers to adhere quite tenaciously to a wide variety of substrates.
Low humidity and/or acidic groups on the substrate surface will slow or
inhibit the cure reaction. To extend the usable shelf life, free-radical
stabilizers such as quinones or hindered phenols are used.
Methyl, Ethyl, Butyl, Allyl and Methoxyethyl esters are available with
various setting characteristics and rheological properties. However, the
Methyl and Ethyl esters dominate the commercial industrial market. The
vinyl structure of 2-cyanoacrylates makes them prone to spontaneous
polymerization. The chain propagation can be initiated by ionic or
The rate of polymerization depends on temperature, humidity, light and
the presence of accelerators, like peroxides or bases. In addition to
polymerization, 2-cyanoacrylates undergo reactions typical of vinyl
compounds, such as addition.
2-cyanoacrylates can be manufactured by many different methods. The base
monomers are too thin for convenient use, so thickeners, stabilizers or
property-modifying additives may be added. The viscosity's are available
from wicking grades (water thin) to thixotropic gels that range from
20,000 to 50,000 mPa*s for large gaps.
The acrid odour of 2-cyanoacrylates, can be effectively mitigated by the
substitution of an alkoxyalkyl ester side chain, for the normal alkyl
group. Products so modified, are practically odour free, but are
slightly less effective as adhesives.
The basic method to manufacture 2-cyanoacrylate esters involves
preparation via the Knoevenagel condensation reaction (the corresponding
alkyl cyanoacetate reacts with formaldehyde in the presence of a basic
catalyst, to form a low molecular weight polymer). The resulting polymer
slurry is acidified and the water is removed.
The polymer is then cracked and redistilled at high temperatures onto a
suitable stabilizer combination to prevent repolymerization. Protonic or
Lewis acids are typically used in combination with small amounts of a
Although the methods and processes have continually changed and evolved
over the years, this is the standard method to manufacture these esters.
One recent and significant advancement in the manufacturing process is a
continuous process where the condensation is carried out in an extruder.
By-products are then removed in a degassing zone and the molten polymer
(mixed with stabilizers), is cracked to yield a raw monomer.
Recent advances have lead to flexible 2-cyanoacrylate formulas, which
remain somewhat flexible when cured. These types of esters are
particularly useful to turners when bonding dissimilar materials like
stone/metal and wood. The dissimilar expansion and contraction rates of
these materials, can cause subsequent failure of the bond when using
traditional cyanoacrylates that feature non-flexible, or brittle bonds.
If you would like to learn more about CA's, look for my extensive
article on 2-cyanoacrylate adhesives, which will be published in
"Woodturning" magazine early next year. Happy holidays and best wishes
for a safe and prosperous new year!
Letting the chips fly...
Steven D. Russell
Eurowood Werks Woodturning Studio
The Woodlands, Texas
Website coming soon!