Model Forum / Radio Controlled / Air Models / June 2004

oops! You are correct! My mistake.

In my experience, a 'kickered' CA joint is crumbly and nearly useless
for mechanical strength.  Bill(oc)

So would gently blowing on a joint speed up the setting by virtue of
the moisture in your breath??

 

Moisture initiates cure but other substances can also cause cure to happen.

The basic way CA's work is that they contain an acid inhibitor which
prevents the homopolymerization reaction from occuring in storage. When the
CA contacts a substrate with surface moisture present, the moisture reacts
with the acid inhibitor and neutralizes it - thereby removing the "shackles"
from the CA molecules and they then immediately begin their cure reaction.
The amount of stabilizer in CA is tiny and can be measured in parts per
million, therefore very little moisture is needed to permit polymerization.

Where kicker becomes necessary is on surfaces devoid or nearly devoid of
moisture, and on surfaces that are acidic in nature - wood and paper are
good examples of the latter. Acidic surfaces inhibit cure just as the built
in stabilizer does. Therefore on these types of materials, cure may be
delayed or inhibited depending on their pH level and moisture content. On
the other hand, surfaces that are alkaline (pH > 7) promote cure. Thus as
some folks advocate, baking soda accelerates cure as it is alkaline.
However, every time I have tried it the results were absolutely terrible in
comparison. I use nothing but real kickers, and hold to the opinion that
cheaping out on CA catalyst is a waste of time on a model worth several
hundred dollars and that needs quality glue joints to survive.

CA in plastic bottles has a life span - moisture slowly permeates these
containers, just like it does to plastic fuel jugs. This is why I do not
advocate placing bottles of CA back in the fridge after opening them the
first time, and why I recommend allowing them to come up to room temp before
opening when first removed - atmospheric moisture will condense on the
inside of the bottle and on the surface of the CA much more when it is cold.

While moisture does indeed initiate the cure reaction through neutralization
of the inhibitor, you really have to be careful not to add too much -
otherwise you end up with a lot of trapped moisture and this can result in
mediocre properties in the end. Too much surface moisture, while certainly
allowing rapid cure, can cause havoc at the interface between the adhesive
and the substrates. Basically, instead of bonding to the substrate the
adhesive can be prevented from doing so by a film of water. That's not good.

CA kickers are an aromatic amine, and yes Shannon they are a true catalyst.
They do not participate in the actual polymerization reaction, rather they
promote it by neutralizing the inhibitor. Because so little of it is
required (generally about 98% of these kickers is volatile solvents) the
final bond integrity is very good, WHEN properly applied. Dousing the parts
in kicker is a great way to cause such a rapid reaction that the exotherm
causes blooming, with the end result a wad of weak brittle foam and very
little useful adhesive actually bonding the substrates. You don't want to
trap solvent in the CA matrix, so don't marinate the parts then immediately
bond them - either lightly surface spritz them (LIGHTLY, and from a few
inches) or else pre-treat one surface, then let it sit for a moment for the
solvents to evaporate. As I mentioned in another post, the catalyst remains
active for a while - on porous substrates several minutes.

Like many things, kickers, whether commercial (yea) or homebrew (boo), are
best used with care and in moderation. Just because the adhesive cures
doesn't necessarily mean you achieved the best bond that was possible.

Mike D.

Talking about kicker, is there any stuff out there that doesn´t stink so
badly and so long after application? I´d be a happy customer in a blink.

In the winter I hardly ever use any kicker because that smell seems to stick
to anything nearby. In the summer I do the spraying outside leaving the part
outside until the worst smell is gone, still the part will smell after a
long time. I don´t spray a lot, just a light spray from a reasonable
distance of the part.