Foto: autor

CHEMISTRY

Text: Josef Blažek

JOSEF BLAŽEK

Instant, Epoxy and Dispersion Adhesives

To continue our discussion on modelling chemistry and

tips for beginners (and maybe advanced modellers will

find out something new, too), we will look at more types

of adhesives that are commonly used in the hobby.

We will then focus on cyanoacrylate (CA)

glues, their accessories, epoxy adhesives and

dispersive type glues. We will discuss their

differences and their composition, how they work,

and their properties that make them suitable for

different situations. We’ll demonstrate specific

glue types, with products from Bolt due to their

wide range of products and popularity among

modellers. However, the characteristics we will

be discussing are applicable to products from

other manufacturers as well.

CYANOACRYLATE GLUES

These are also known as instant glue and often

shortened to CA, and as the name implies,

these are rapid curing systems that harden on

contact with the bonding surfaces. Practical

applications of these types of adhesives are far

and wide, to include such materials as plastics,

glass, metal, fabric, paper and wood. Bonded

materials can be dissimilar. They can easily

be obtained from hardware and hobby stores

42

INFO Eduard

Vítěz mezinárodních IPMS soutěží v kategorii Master a několikanásobný mistr ČR.

Autor článků v mezinárodních časopisech

s celosvětovým dosahem (Military Illustrated

Modeller, Cocardes International, ModellFan,

Modelář). Spoluautor modelářského startupu

Plastic Invasion.

and pretty much any place that caters to the

handyman. To begin, we’ll discuss the principle

on which these glues work. They are based on an

unstable compound, which in this case is ethyl

cyanoacrylate. The compound reacts with water

(or moisture in the air) to quickly harden. To get

a little more technical, the chemical reaction

with water leads to reactive sites at the end of

the molecular chains. These reactive sites then

connect to each other under the influence of the

ongoing reaction, which leads to the formation

of a dense network of interconnected molecules.

This process is actually visible to the naked

eye. If there is a sufficient quantity of the glue

applied, the gradual hardening can be observed

until the adhesives has hardened as a whole.

On the contrary, if we spread a small amount of

glue, the whole process of gradual solidification

is extremely dynamic, which is caused by the

rapid penetration of moisture from the air

(that is, water) into the glue. This penetration

of moisture into the glue fundamentally affects

the speed of setting, which, from a modeler’s

perspective, explains why open containers of

glue gradually set (moisture penetrates the glue

after initial opening and consequent initiation of

the reaction).

STORAGE AND SHELF LIFE

OF CA GLUES

There are a lot of myths in the modelling

community about how to store and how not

to store instant glues in order to extend their

life. Unopened adhesives have an extended

shelf life due to the protective gas filling,

but this does not mean that their shelf life is

infinite. In general, higher storage temperature,

higher exposure to UV radiation (light) and

higher humidity always have negative effects

on the overall life of cyanoacrylate adhesives.

To give a specific example illustrating the idea

of the dynamics of the shortening of the shelf

life, when storing instant glues at an ambient

temperature of about 30 degrees Celsius,

the shelf life will be shortened by some 60 to

April 2023