Is Cellulose Flammable? (A 5-point guide)

This article will answer the following question: “Is Cellulose Flammable?”. We will reveal what cellulose is, where it comes from, what is it used in, and in which conditions it is considered flammable.

Is Cellulose Flammable?

Cellulose is normally considered combustible only, not flammable. Although, it depends on the other products that are part of the material. Some may enhance flammability, some will lower it. 

The same chemical compounds can create a flammable and a non-flammable material, depending on the physical properties that arise from the manufacturing.

What is cellulose?

Cellulose is the most abundant natural organic material. It’s harvested from green plants that can create fibers.

For example, 90% of cotton and 50% of wood are composed of cellulose. Hence why they’re so used in paper-making, and the fashion industry. 

The source of cellulose often comes from plants, including sources of wood, cotton, and hemp. It can also come from the recycling of paper.

Cellulose is the name of the molecule that’s a precursor to all the commercial applications under the name of cellulose. The molecule is a polymer made of thousands of glucose molecule units linked together.

Cellulose chemistry

Before we proceed to explain if cellulose can become flammable, let’s take a look at what cellulose looks like chemically.

Cellulose is an important structural component of green plant cells. 

Some animals such as ruminants and termites can digest plant cells and retrieve energy from them because they have microorganisms living in a symbiosis that allows them to do so. We humans can’t digest it, which is why we consider it a source of fibers, not energy.

But a cow can get fat by eating it.

The cellulose molecule has the formula (C6H10O5)n. The ‘n’ varies depending on the source of cellulose, it could be worth thousands. This is what a polymer is, a simple unit that repeats itself lots of times. Biopolymers like this receive the name carbohydrates.

As we said, cellulose is made of glucose, but not entirely. A glucose molecule has the formula C6H12O6. If you compare the two formulas it’s possible to see that the cellulose units are glucose molecules, minus a water (H2O) molecule.

This water is lost in the process of crafting cellulose by the plants.

Is cellulose a carbohydrate?

Yes. Cellulose is one of the many types of carbohydrates.

The word carbohydrates instantly make us think about foods that are bad for our diet. But wasn’t cellulose something plants have?

Well, a carbohydrate is a biomolecule that’s made from sugar units. These sugar binds to one another to form polymers (big molecules that are made from small units that repeat in a chain-like structure).

There are a few types of those units, and a few ways they can bond with each other. Cellulose and starch, for example, are molecules made from the same sugar unit, but that bond slightly differently.

One molecule of cellulose requires about 3000 units of sugar side-by-side to be crafted.

The pictures above are chemical representations of cellulose and starch molecules. Note how similar the molecules are. 

The different spacial configurations the structures above have is what separates herbivores from us.

In cellulose, the sugar units are bonded interleaving a standing and an upside-down sugar, while in the starch they are all standing. This may not look much, but it’s what separates a healthy meal from a caloric one.

In the digestion process, the polymers can’t be digested at once. They first need to be broken until reaching the size of their units.

We humans can only digest starch because we have enzymes that help break the polymer into smaller sugars. But the same enzymes can’t shatter cellulose, and that’s why we practically get no energy from eating lettuce, while potatoes can make us gain weight.

So, when we digest sugar, bread, or starch in any form, what our body do first is break the chemical bonds highlighted above, until reaching the size of those rings the molecules have.

Even though we don’t digest cellulose, it’s still very important to eat our greens because they serve other purposes in our body, are sources of vitamins, and help regulate and improve our digestion.

Cellulose’s important physical and chemical properties

  • Chemical formula: (C6H10O5)n;
  • Molar mass: 162.1406 g/mol (per glucose unit);
  • Appearance: white powder;
  • Density: 1.5 g/cm3;
  • Melting point: 260–270 °C; 500–518 °F;
  • Solubility in water: none;
  • Enthalpy of formation (room temperature): −963,000 kJ/mol;
  • Combustion enthalpy (room temperature): −2828,000 kJ/mol.

But what is fire?

Fire is what we see as the result of a combustion reaction. Combustion is just a specific form of oxidation. 

Not all oxidations are burnings, but all combustions are oxidations.

Fire takes place once oxygen reacts chemically with a source of fuel, and liberates energy that was trapped between the chemical bondings of fuel. Normally, this source is an organic compound. 

The heat of a combustion reaction breaks down the fuel molecules. The smaller molecules can then react more easily with oxygen, and liberate the energy within the fuel molecules.

This is the main reason why combustions are so intimately related to heat. The heat makes fuel molecules available to be burned.

In fuels, the carbon (C) was bonded with other carbons and hydrogens (H), but it is an opportunist that only cares about its stability, so he abandons hydrogen and marries oxygen forever (or until he finds an even better partner).

Most carbon bonds with two atoms of oxygen (O). This is the carbon dioxide molecule (CO2). Some eventually bond with only one oxygen, and those we name carbon monoxide, a highly toxic compound that will kill us certainly if we inhale enough of it.

But hydrogen, which is not dumb, also goes straight to other oxygen molecules. From this bonding, water (H2O) is the result.

Because carbon dioxide and water are very simple and stable molecules, they don’t react with oxygen again, so it’s impossible that the reaction turns the other way around spontaneously. 

Although, this is exactly what plants do. They simply take carbon dioxide, water (and other minor compounds) from the atmosphere, and craft sugars that will have many functions for the plant. 

One of them is the creation of cellulose, which we humans harvest for many uses. Once we dispose of a piece of paper, for example, nature will eventually decompose it until the form of carbon dioxide, and the cycle is restarted once again.

But of course, nothing is forever. Energy is lost during these cycles. Even if plants were 100% efficient, the second law of thermodynamics says that there exists one thing called entropy, a form of energy that’s always lost and can’t be recovered directly.

But thanks to the sun, there’s always a source of energy being irradiated towards our planet. This energy is used during photosynthesis by the plants and allows the cycle to be restarted constantly. 

Cellulose flammability

Knowing what cellulose is made of and how fires happen, now we can distinguish if cellulose might be a fire hazard or not.

Can cellulose ignite? Will it catch fire? 

Well, yes. Cotton is 90% made of cellulose, and you can easily set it on fire using a lighter. 

At the same time, most cellulose things we come across are cellulose-based, for them to become flammable or not, it depends on the other percentage of things that compose the material. Some may enhance flammability, some will diminish.

Cellulose molecules are very sparse in the cotton structure, which makes them easy to burn. Since cellulose molecules themselves are combustible, any powdery or fluffy form of cellulose will be considered flammable, unless there are other fire-retardants mixed.

Is cellulose a fire hazard?

Although cellulose itself is considered combustible and flammable under some circumstances, cellulose is not the only compound found in materials.

Cellulose-based fibers vary considerably in their mechanical, physical, and chemical properties. The chemical composition of a cellulose-based fiber depends on its source.

Cellulose fibers can pose a fire risk, but we can’t know for sure unless we check the flammability trials the manufacturer had done. 

Normally, companies make all the necessary research into the flammability of their products, compiling existing data and providing some new more.

This information is then expressed in a Safety Data Sheet (SDS), a document that can normally be found online. It also has information such as health hazards, and environmental dangers.

Conclusion

Cellulose molecules are combustible. Some cellulose materials are considered flammable and some are not, it depends on the source of the fibers. 

Although, there are many more non-flammable materials because it’s easy to craft cellulose compounds using flame-retardant ingredients together. But a cellulose-based compound can always burn if enough heat and/or flames are provided to it.

Frequently Asked Questions (FAQS): Is Cellulose Flammable?

What materials contain cellulose?

The following table presents sources of cellulose fibers, which part of the plants it’s gotten from, and how much cellulose percentage by weight it has.

Is cellulose a polysaccharide?

Yes. Cellulose is a polysaccharide, a type of carbohydrate made from glucose-like units.

Amylose is made from the same ingredients, but the glycoside bond is different, so their properties are very similar.

Is cellulose insulation flammable?

It depends. Cellulose insulation is combustible and can catch fire, but only if it has the right conditions to do so. 

Cellulose insulation formulas often have fire-retardant ingredients added, lowering the fire hazard, but the material can always burn if in contact with a source of flames or intense heat.

Citations

Mettler, M. S., Vlachos, D. G., & Dauenhauer, P. J. (2012). Top ten fundamental challenges of biomass pyrolysis for biofuels. Energy & Environmental Science, 5(7), 7797. doi:10.1039/c2ee21679e

https://www.cpsc.gov/Newsroom/News-Releases/1977/Tips-For-Consumers-Insulating-Their-Homes

Lewin, M., & Basch, A. (1978). Structure, Pyrolysis, and Flammability of Cellulose. Flame – Retardant Polymeric Materials, 1–41. doi:10.1007/978-1-4684-6973-8_1

Hernandez, Cécile & Rosa, D.. (2016). Extraction of cellulose nanowhiskers: natural fibers source, methodology, and application. 

https://commonchemistry.cas.org/detail?cas_rn=9004-34-6
https://www.khanacademy.org/science/ap-biology/chemistry-of-life/properties-structure-and-function-of-biological-macromolecules/a/carbohydrates#:~:text=Cellulose%20is%20made%20of%20glucose,gives%20it%20very%20different%20properties.
https://en.wikipedia.org/wiki/Cellulose
https://www.ebi.ac.uk/chembl/compound_report_card/CHEMBL2109009/
https://en.wikipedia.org/wiki/Glucose
https://pubchem.ncbi.nlm.nih.gov/compound/14055602
https://commonchemistry.cas.org/detail?cas_rn=9004-34-6

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