Is Polyurethane Adhesive Flammable?

This article will elucidate the following question: “Is Polyurethane Adhesive Flammable?” and other important questions regarding flammability, adhesives, and Chemistry.

Is Polyurethane Adhesive Flammable?

Well, it depends. Pure polyurethane is known for being highly flammable, but polyurethane adhesives can have fire-retardant compounds added to them. 

It is safer to assume that a polyurethane adhesive is flammable unless the fabricant has told otherwise.

What is Polyurethane?

Polyurethane (PUR) is a class of polymers (see the section below). It is produced from a wide range of materials and can create a really big list of construction materials. 

Polyurethane basic chemistry

Everything in the world is made of atoms if it has mass and could be weighted. When atoms bond with each other they create molecules. One very specific group of them we usually call Organic Molecules and an even more specific group is called polymers.

“Poly” stands for many, while “urethane” is a specific organic molecule. Polyurethane consists of a molecule (monomer) that’s bonded to another equal, creating a line. 

“Polymers” is just a name we give to a large group that can create a line like that.

PUR is therefore a repeated structure of a certain molecule. Most of its atoms are carbon and hydrogen, but many others can be present, especially if we are dealing with a material that has been processed a lot. 

As a consequence of this complexity, a wide variety of materials can be crafted, with tons of different technical features. 

The specific chemical and physical properties of every material must then be assessed individually.

But the more a component is chemically altered, the less it differs from what can be found naturally. Nature can then have a real hard time degrading such products, and that’s when pollution strikes.

Nowadays, biodegradable raw materials are constantly being tested so more sustainable (and cheaper) alternatives can be found.

How about its applications?

It can be found in liquid or solid form. 

One of the most common examples of PUR is a simple kitchen sponge. The foam filling used in upholstery, automotive seats, mattress, and roofs is also made of PUR. 

Shoe soles, clothing, watch-band wrapping, varnishes, skate, and rollerblading wheels, solid fuel, and many other things we haven’t invented yet are also made from this one class of plastics.

How do Polyurethane adhesives work?

Adhesives are basically meant to bond two or more surfaces together. There are many ways to do such a thing, but adhesives can distribute load stress more equally because there is a larger binding area that allows stress absorption to happen.

To successfully make a joint concise, the adhesive must be able to have some flexibility to sustain mechanical shocks, while still having a high cohesive strength so the glue doesn’t fall apart. 

PUR adhesives tend to be more flexible than epoxies, for example. They can bind different kinds of material together because of this flexibility.

When two materials are different, their characteristics and properties differ. One of the most important properties of solid materials is their thermal expansion. A good adhesive must be able to bond materials that have different tensioning from each side.

Back to the flammability problem

One of the most common flammability tests is the standard Bunsen burner test, which consists of putting a piece of what’s been tested into a (little) controlled flame. The physical and chemical alterations in the product are then noted.

Although it’s a well-known test, it can only satisfy some of the questions, since a fire can start in many scenarios (It’s important to say that if a licensed product claims to be fire-resistant, we should trust it).

Let’s imagine we can’t find official information, or that we can’t clarify which kind of  PUR we are dealing with, what should we do? 

But keep in mind the content of this article serves informational purposes only. You should always contact a qualified professional or authorities if you feel something could be wrong.

Fires

Fire is a chemical reaction that involves the consumption of a source of fuel in the presence of oxygen gas. The fuel is a hydrocarbon that can be burned if in a set of circumstances, where available oxygen is the most important.

Fire is the consequence of a chain reaction that liberates energy in the form of heat and light. The heat liberated can force more reactive oxygen to stay put, so the fire can grow even bigger as heat increases.

The products of such reactions are major water and carbon dioxide, but subproducts like toxic vapors, ashes, and gasses can also arise, especially when the burning is poorly controlled.

Several chemical reactions take place once a fire starts, and it depends a lot on the combustible constituents and other environmental properties. 

To prevent a fire from happening we should avoid three major ingredients that allow it to start: letting too much fuel disponible in one place, leaving oxygen available, and allowing the conditions that make a fire bigger once it starts.

Of course, if a construction material needs to be used extensively and there’s a chance that it’s flammable, the first ingredient mentioned above will always be present, and that is why avoiding the other two is so important.

Polyurethane adhesives flammability

Always consider that a less flammable product can still catch fire if the right conditions are allowed. Small but continuous sources of heat such as the sun can gradually evaporate some of the hydrocarbons. 

A vapor film can be formed, creating a condition that can easily ignite a little and start a chain combustion reaction, setting a bigger fire. 

As mentioned earlier, it’s really hard to determine if there’s a risk of a PUR adhesive getting caught on fire, because there are just too many formulations and scenarios to be understood before. We should always analyze the manufacturer data if available.

Examples:

Conclusion

Polyurethane adhesive can be flammable or not, it depends on the specific product. If there’s an indication in the label or from the manufacturer that it is not flammable, we must take their word for it if it’s a licensed product. 

If there’s not enough available information about the product it’s better to assume that it’s flammable and double your care over it. PUR adhesives can add fire-retardants, making it much safer, but it is better to be safe than sorry.

If you believe an installation may not be safe or be compromised it is better to call a verified professional to assess it and/or the authorities responsible.

Frequently asked questions (FAQS): is Polyurethane Adhesive Flammable?

The best answer is: that is possible. Let’s assume it is unless the manufacturer told otherwise.

Is construction adhesive flammable?

It depends on what is it made of. If it is organic solvent-based it’s very flammable. Specific research is required for each product.

Is polyurethane glue flammable?

Polyurethane glue is another term for polyurethane adhesive. It may light a fire, so be careful. The fabricants normally tell when the product is not flammable on the label.

Is Original Gorilla Glue flammable?

According to the fabricant, it’s not flammable but is toxic and irritating.

References

https://en.wikipedia.org/wiki/Polymer
https://en.wikipedia.org/wiki/Polyurethane#Applications

Burchardt, B. (2010). Advances in polyurethane structural adhesives. Advances in Structural Adhesive Bonding, 35–65. doi:10.1533/9781845698058.1.35 

Allen, K. W. (2003). Adhesion and Adhesives. Encyclopedia of Physical Science and Technology, 237–250. doi:10.1016/b0-12-227410-5/00012-0

https://www.gulfindustrialgroup.com/saaf/wp-content/uploads/2016/08/POLYURETHANE-ADHESIVE-40-1000-MSDS.pdf
https://buyat.ppg.com/rep_pafpainttools_files/Liquid%20Nails%20US/LN-950_DataSheet_FINAL.pdf

http://objects.eanixter.com/PD365568.PDF

https://multimedia.3m.com/mws/mediawebserver?mwsId=SSSSSuUn_zu8l00xlYtGNxmZnv70k17zHvu9lxtD7SSSSSS–
https://www.buildsite.com/pdf/dap/DAP-Premium-Polyurethane-Construction-Adhesive-Sealant-SDS-1875563.pdf
https://www.gorillatough.com/wp-content/uploads/SDS-Update_Original-Gorilla-Glue-v1.5.pdf

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