What is the difference between cyanoacrylate and “superglue?”
Cyanoacrylate is the chemical term used to describe the main ingredient used in many modern instant adhesives. When cyanoacrylate
adhesives were introduced more than 30 years ago, their very fast setting properties and ability to bond to a wide variety of materials
led to them being widely described as “superglues.”
How do cyanoacrylate adhesives harden?
Cyanoacrylates are fast-setting adhesives which are kept liquid by the presence of dissolved stabilizers. These stabilizers are
neutralized by reacting with moisture on the surface of parts to be bonded, which then allows the liquid adhesive to harden (or cure) in a
matter of seconds. The speed at which the adhesive hardens will depend on the surface moisture (affected by the relative humidity in
the atmosphere) and also the gap between the parts (the smaller the gap, the faster the cure).
How do I use cyanoacrylate adhesives?
First, make sure that the parts to be bonded fit very closely together. Cyanoacrylates work best when there is little or no gap betw een
the parts – ideally less than 0.05 mm (larger gaps will require more time to cure). Apply a small drop (or narrow bead) onto one of the
surfaces to be bonded and lightly press the parts together in order to spread the adhesive to cover the mating surfaces. Avoid excessive
squeeze-out of adhesive by careful control of the quantity and the location of the applied adhesive. Maintain this pressure until the
adhesive has set (between 10 and 60 seconds, depending on the parts and conditions). The parts can now be handled but note that the
adhesive continues to increase in strength for the next 12 to 24 hours.
Do I need to clean the surfaces of my parts before bonding?
For optimum results with any adhesive, it is recommended that surfaces are clean and free from surface contamination such as dust or
loose particles. Wiping the surfaces with an organic solvent (e.g., acetone) or appropriate water-based cleaner will help remove oils and
greases that could reduce the strength of the final assembly. Always check the suitability of the proposed cleaning solvent before
application.
What’s the difference between “fixture time” and “cure time?”
Fixture time is the time required for the bond to reach enough strength that the assembly can be handled without compromising the
long-term performance of the adhesive. On a laboratory scale, fixture time is equivalent to the time required for 25 mm-wide lap shears
bonded with a 12 mm overlap to support a 3 kg weight in shear mode for at least 5 seconds (this equates to a shear strength of 0.1
N/mm 2). For cyanoacrylates this time is usually measured in seconds. Cure time is usually defined as the time required for the adhesive
to reach its highest bond strength. For cyanoacrylates this is typically 24 to 72 hours. Both of these measurements will depend on the
gap between the parts and the relative humidity.
What is the characteristic odor that I can smell? Is it harmful?
In its liquid form, cyanoacrylate adhesive contains a monomer that can evaporate into the atmosphere, giving a characteristic sweet
odor. The monomer may cause some irritation to sensitive membranes in the eyes, nose and throat. Th is risk of irritation can be
minimized by using cyanoacrylates in well-ventilated areas. A small percentage of the population can become sensitized to
cyanoacrylate fumes after repeated exposure – where necessary, refer to the Material Safety Data Sheet or seek medical advice. Once
fully cured, the cyanoacrylate forms an inert plastic which is not harmful.
What is “blooming” and how do I prevent it?
“Blooming” describes a white powdery material that is sometimes observed on parts that have been assembled using cyanoacrylate
adhesives. Blooming occurs when cyanoacrylate monomer evaporates from the surface of the liquid adhesive and reacts with moisture
in the surrounding environment or on adjacent surfaces and cures, leaving behind a white residue. The effect is most noticeable on
black parts where an excess quantity of adhesive has been applied or when parts have been stored in a sealed container before the
adhesive has fully cured. (Interesting fact: this behavior is actually used by detectives to find fingerprints at crime scenes).
There are several ways to prevent blooming:
a) by minimizing the time that any adhesive may remain liquid (when monomer can escape). This can be achieved by avoiding excess
adhesive – especially after squeeze-out – and ensuring that the assembly conditions are optimized (minimum gap and adequate relative
humidity (>30% RH)
b) by providing good ventilation over the assembly or storage area to allow any airborne monomer to be removed from the bonded parts
c) avoid sealing any parts until the full cure has been achieved
How do I separate my rapidly bonded fingers?
Cyanoacrylate adhesives bond skin very rapidly because of its high moisture content. An easy way to separate bonded fingers and skin
is to apply a peel ing force to the bond line by simply rolling a pen or pencil through the bond joint. You could also try warm water and
soap. Avoid trying to force the fingers apart by excessive force as this may tear the skin.
How should I store my cyanoacrylate?
For the best shelf life results, it is recommended to store unopened bottles of cyanoacrylate in a refrigerator between 5⁰ and 8⁰ Celsius
(41⁰ and 46⁰ Fahrenheit). Once the bottle is opened, it is best to store it at room temperature as storing in the refrigerator will cause any
moisture contamination to condense and prematurely cure the adhesive.
What types of solvents/chemicals attack cyanoacrylates?
In general, cyanoacrylate adhesives resist non-polar solvents (e.g., motor oil, ether and toluene) very well but demonstrate poor
resistance to strong polar solvents (e.g., caustic, acetic acid, acetone, etc.)
What is the maximum temperature cyanoacrylates can withstand?
Cyanoacrylates are remarkably versatile adhesives that can bond a wide variety of materials to form strong and permanent bond s.
However, there are some basic limitations based on the properties of the cured resin. Cyanoacrylat es are thermoplastic materials which
mean they soften at elevated temperatures and eventually melt. For long-term exposure, a maximum temperature of 80 oC (176⁰F) is
recommended ‒ although depending on the materials being bonded and the joint de sign, it may be possible to survive short-term
exposures up to 120 oC (248⁰ F).
Will cyanoacrylates bond any material?
Cyanoacrylates are not recommended for use on glass. When used to bond glass, the strength is initially high but degrades dramatically
over time. A permanent bonded joint cannot be achieved when bonding substrates involving glass. Cyanoacrylates require some very
low-energy materials (such as PTFE, polyethylene or polypropylene) to be surface-treated by plasma-etching or corona discharge prior
to bonding.
What factors affect the speed of cure?
Cyanoacrylate adhesives are acid-stabilized, single-component adhesives that react rapidly at room temperature when in contact with
moisture between close-fitting surfaces. The speed of cure is dependent on three main factors:
(i)
The gap between the parts. Ideally the gap should be less than 0.05 mm for optimum performance.
(ii)
The relative humidity: The presence of surface moisture is required to trigger the curing reaction. Ideally, humidity
should be between 40% and 60%.
(iii)
The nature of the substrate: Some materials are naturally acidic, which means that the stabilizer is not neutralized.
These materials (such as paper, wood and leather) may be slow to cure. Surface insensitive grades (such as SICOMET
102) are specially formulated to overcome this effect and should be selected for bonding these materials.
Is the speed of cure affected by the ambient conditions or temperature of the parts?
The curing of cyanoacrylates, like most chemical reactions, can be affected by the reaction temperature (the higher the temperature, the
faster the cure). However, surface moisture is necessary to initiate the curing of cyanoacrylates. Since moisture can be driven off the
surface of the parts during heating, the cure speed of cyanoacrylate adhesives is not particularly sensitive to the temperature of the
parts.