Is spray adhesive flammable when dry?

This article will answer the following question: “Is spray adhesive flammable when dry?”. We will show what adhesives are made of and in which conditions spray adhesives become flammable when dry, or not.

Is spray adhesive flammable when dry?

It depends but, overall, spray adhesives are not flammable after they completely dried out. The part that sticks is a kind of polymer that’s normally not flammable. 

Also, fire-retardant additives can be added to the formula to prevent a fire from spreading, but it depends on every product. Spray adhesive products that possess fire retardancy properties will have this information available on the label.

What are adhesives?

Adhesives are products meant to bind two or more things together.

They can be made of natural or synthetic polymers. In general, an adhesive is a kind of plastic.

Adhesives can be classified by many methods such as dispensing method, application, and primary resin. It all depends on the manufacturer and the given application.

There are many kinds of adhesives because adhesion happens differently on every kind of surface because the chemistry of each thing in our world is unique.

Some adhesives are made specifically for some kinds of tasks and surfaces, but there are also those meant for many purposes.

The same kind of glue product can also have an aerosol version. Aerosols products can grant much easiness and readiness in the application of an adhesive, it dispenses the need for other tools and, generally, gets the job done in a single step.

Composition of adhesives

The ingredients of an adhesive must be incorporated together into a practical and workable formulation, which normally requires in-depth knowledge of science. But there are also simpler formulations that can be done in a DIY manner.

Adhesives are made of more or less 6 ingredients, which we will discuss briefly.

  • Primary Resins

Resins are the sealants that provide lots of chemical and physical characteristics to the product, including wettability, adhesion strength, thermal property, and chemical resistance. Resins can be thermosets, thermoplastics, or elastomeric.

  • Solvents

Solvents are volatile liquids or gases that can lower the viscosity of the primary resins, but also the formulation as a whole, making it easier to be applied. They are normally the most flammable constituents of adhesives.

  • Fillers

Normally fillers are not adhesive themselves, they are used to enhance or suppress characteristics of other ingredients, including mechanical strengths, thermal properties, adhesion performance, and conduciveness. Or to reduce costs.

  • Plasticizers

Are used to increase the workability, flexibility, or extensibility of a polymer. They can improve flame retardancy, electrical and corrosion resistance, and adjust mechanical properties, among many others.

  • Reinforcements

Reinforcements are mainly used to enhance mechanical properties.

  • Other additives

Added to adhesives to ease the process and improve some properties, like: antioxidant capacity, thermal stabilizers, UV stabilizers, polymer processing aids, slip additives, antifogging agents, and antistatic additives, among others.

Flame retardant additive materials can be added to adhesive formulations not only to suppress the fire in the adhesive itself but binded materials too.

The flame retardants can remove thermal energy from the substrate by dissipating the heat of a fire, or by participating in char formation as a heat barrier. 

Additives can promulgate flame retardancy by conduction, evaporation, mass dilution, or by participating in chemical reactions.

Adhesives chemistry

Now, before we proceed, we must discuss important scientific topics regarding flammability, chemical compounds, and fire.

The solvents used in spray adhesives are a type of organic compound named hydrocarbons. Most of them originate from crude oil.  

Chemically speaking, these compounds are entirely made of carbon and hydrogen. Their names are given according to the amount of carbon each molecule has. 

You can construct the molecule in your head bonding a carbon next to each other, and then adding hydrogens until each carbon makes four bonds.

source: http://www.chemistryland.com/ElementarySchool/BuildingBlocks/BuildingOrganic.htm

The more length a carbon chain has, the heavier each molecule is. In fact, at room temperature, a carbon chain with more than 4 carbons is already liquid. 

If we continue to imagine more carbons being added to it, the hydrocarbon will eventually become solid, like paraffin.

As you can see from the picture above, a burnable molecule can’t get more simple than a hydrocarbon. To understand why let’s take a look at how and why combustion happens.

Fires

Fire is nothing but a consequence of a chemical reaction. 

Combustion requires a hydrocarbon source, oxygen, and heat to sustain the reaction. 

As a result, carbon dioxide (CO2) and water(H2O) are produced, along with energy in the form of heat and light.

When fuel is ignited, it doesn’t have much heat available right away. If you had ever lighted up a barbecue you probably saw that it takes some time for the fire to catch in the fuel. 

But once there are more flames, the fire can go on its own until a certain point. This is also the reason why we must take really good care of an initial fire.

When a fuel source is too much available, although, something a little different can happen. If the hydrocarbon molecules can react with oxygen too quickly, an explosion can occur. 

This simply means that the combustion took place in a small amount of time. But not all explosions require the combustion of a hydrocarbon, sometimes it happens because an unstable compound decomposes itself naturally, without any oxygen.

Hydrocarbon gases can react more promptly because their molecules are simple and can interact quickly with oxygen. Since they’re in the form of gas, the molecules are very dispersed and are much more available to react at once. 

A canned gas is a liquefied gas. This means that lots of molecules are put in one place, and the danger of an explosion grows even bigger.

When a tin containing gas is used, although, the gas escapes and suddenly the molecules become sparse. 

This is why the fabricants often state that their product must be applied with good ventilation of the installations. This way the fire hazard extinguishes quickly.

The biggest threat when it comes to adhesive sprays and aerosols is their solvents. The glue and other compounds that remain after the application are normally combustible at best, but not flammable.

What does adhesion mean?

Only in the last 100 years, people have started formalizing how two things can be glued together. No single explanation can successfully explain how so different things can be attached together. 

Many physical and chemical explanations had been developed ever since. We’d like to point out six of them: 

  • Mechanical Interlocking, 
  • Adsorption, 
  • Chemical, 
  • Diffusion, 
  • Electrostatic, 
  • and Weak boundary layers.

Spray adhesives have just too many types of adhesion, making it impossible to discuss all of them. 

Cured adhesives flammability

Although, we can say that the adhesives, after being cured, are less flammable than if they had dried without adhering to anything. This is because adhesion is a stable chemical interaction.

The glue molecules appreciate being cured because they lose energy by doing so, which is a synonym of stability in chemistry.

As we discussed, adhesive molecules are polymers. These molecules have long carbon chains that can’t be broken easily (remember that combustion happens by shredding organic molecules and adding oxygen to them until there’s only CO2 left).

When the polymer is participating in adhesion, the bonding between the glue and the surfaces must be undone as well, so only then the molecules are available to interact with oxygen.

This is how adhesives are not considered flammable normally.

But make no mistake: The cure of an adhesive may take longer than we can assume by the touch.

Conclusion

It’s not likely that a spray adhesive will remain flammable after the solvents dried out completely. Besides, adhesives can be mixed with other additives that promulgate fire-retardancy. Adhesives are normally polymers that, alone, present low flammability.

Always read and follow the instructions on the label.

Frequently Asked Questions (FAQS): Is spray adhesive flammable when dry?

Is spray adhesive toxic?

All spray adhesives are toxic if inhaled or ingested. Some may be toxic when in contact with the skin as well.

Before the adhesive cures, toxic vapors, gases, and fumes may arise, so good ventilation is always required in the application of any spray adhesive.

After the product dries, its toxicity reduces but is still present. The overall toxicity of cured adhesives depends on their ingredients.

To correctly assess how toxic a certain label of spray adhesive is, specific safety information must be sought. To do so, google the trading name of the adhesive followed by the words “safety data sheet” (SDS).

SDS are documents that possess all the required safety information for a given product and are made according to the context the product will be applied.

Is spray adhesive waterproof?

It depends on every product, only a few are. If the compound is waterproof, this information will surely be available on the label.

is spray adhesive glue?

In essence, a spray adhesive is a low viscosity glue dispensed from an aerosol can. Glue is the name we give for anything that will bind two or more materials together, it can be a synonym for adhesive.

Citations

Kim, H.-J., Lim, D.-H., Hwang, H.-D., & Lee, B.-H. (2011). Composition of Adhesives. Handbook of Adhesion Technology, 291–314. doi:10.1007/978-3-642-01169-6_13 

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

SAUNDERS, Keith J. Organic polymer chemistry: an introduction to the organic chemistry of adhesives, fibers, paints, plastics and rubbers. Springer Science & Business Media, 2012.

https://en.wikipedia.org/wiki/Neanderthal
https://en.wikipedia.org/wiki/Polymer

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