Chemistry of Mighty Putty

Oh no… my shelf just broke! What should I do??

I should use mighty putty! Take a look below…

 

What is it?

Mighty Putty is a simple and useful chemical reaction that can be done by anyone! There’s no degree in chemical engineering required!  But how? How is it that everyone has the ability to complete a complex epoxy reaction in the palm of their hand? That’s where the chemistry comes in.

 

Where did it come from?

In the 1930s, a German firm called I.G. Farben Industries began researching epoxy reactions purely out of academic curiosity. They gained more fame as viable products in the 1950s after being introduced to North America by Jim Peters B.Sc., the founder of the company Industrial Formulators. His revolutionary experiments using Epoxy Reactions eventually lead the front for industrial applications of epoxide chemistry around the world.

The first U.S. scientist to work with this branch of science was  Dr. S.O. Greenlee, who discovered Epoxy Reactions soon after Peters. Over time, U.S. companies continued developing epoxy reactions until they were finally released to the public.

Today, a well-known example is advertised on TV as Mighty Putty. Mighty Putty’s quick spread throughout the U.S. has only added to the interest in this chemical reaction.

Yet even today, new experiments with Epoxy Reactions are still being performed. Anything could happen in the next few years.

 

How does it work?

To induce the reaction, the two parts of the Mighty Putty must be mixed together, and a multi-step reaction process begins.  Around the outside is the epoxy resin and on the inside lies the curing agent, or hardener. Pay close attention to these two terms throughout the following explanation.

 

The epoxy resin is composed of Bisphenol A (BPA) and epichlorohydrin (ECH). In part one of this two-part reaction, two epoxy groups are formed on the ends of the Bisphenol A compound as it begins mixing with the ECH. This produces a thick, glue-like product that can be molded and shaped to the user’s preferences. This is consistent with the malleable consistency of Mighty Putty as the user molds it into the desired shape.

 Reaction between Bisphenol A and epichlorohydrin, for more info click on the picture!

 

The second step involves setting or “curing” the reaction to make it strong. The hardening component in Mighty Putty, also known as the “curing agent” of an epoxy reaction, can only react with the initial reaction’s final product. The curing agent is composed of polyamines which are very similar to ammonia in structure, and are strongly alkaline.

Structure of polyamines. Note the three amine groups, as they become important in the later reaction.

 

The amine groups in the hardener react with the epoxy groups that were formed earlier in the first reaction to form a “cured” resin. This reaction is exothermic, and slowly cools to form an impressively strong substance.

The total cure time required for this reaction depends on the rate determining step.  In this case, the initial endothermic elementary step of the reaction between Bisphenol A and epichlorohydrin will determine the speed at which it goes to completion. Thus having a greater mass of epoxy resin – as seen around the outside of the Mighty Putty – can increase the speed of the reaction. This is also why the reaction is known to accelerate, as the heat from the second step begins to aid in the reaction of the initial step. By this same logic, the reaction slows down as the hardening agents overwhelm the mixture and the substance cools.

 

So why is it SO strong?

The strength of Mighty putty can also be explained through its chemistry. Epoxy resins are also known to be thermosetting materials. Thermosetting plastics can be cured and “set” to hold a particular form – the reaction for which was just explained. These reactions also form tightly linked cross-polymer structures.

This diagram shows the difference between polymer chains and cross-linked polymer chains.  The structure is much more connective and stable.

 

These structures explain the immense strength of the product, because bonds can be formed not just between and within molecules, but also across the polymer chains – which explains the name. In addition, strong polar bonds between the putty and its applied surface keep it locked in tight.

 

What else can Epoxy Reactions do?

Although Mighty Putty is a great example of epoxy reactions, that’s certainly not the only way they are can be applied. Epoxy reactions can also occur as a foam, liquid, and adhesive backing.

When used as a foam or liquid, cooling time is key.  These reactions can be more sensitive to surrounding environments and temperatures. The sharp scent of ammonia can also be dangerous to work with which is why this is mostly seen with professionals.  However, the end result is still a rather rigid yet lightweight material that can bond two surfaces together.

Otherwise, Epoxy Reactions are simply used as putty adhesives or some variation thereof. When used as an adhesive it can fix almost anything. Examples include creating a mug handle, fixing leaking pipes, and most importantly fixing that broken shelf!

 

Ready to buy it yet? 

         So maybe not everyone has a “broken shelf” to go fix, but the immensely useful applications that result from a simple chemical reaction are clear. And how can Mighty Putty have the strength to pull an entire truck?!  It’s all in the chemistry of epoxy reactions.  Just another way to show how the little things in life can end up being the most important.

 

Stay tuned for the next Chemistry of Infomercials blog post… coming soon!

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