Cellulose nitration converts some of the hydroxyl groups on cellulose into nitrate groups using a mixture of nitric and sulfuric acids, and the degree of nitration decides the product: lightly nitrated cellulose can be plasticised into celluloid, while heavily nitrated cellulose is guncotton, an explosive. The chemistry, history and hazard are explained below with deliberately no acid proportions, temperatures, quantities or procedure, because the margin between the two products is narrow and the wrong side of it is an explosive.
Part of Plastics and Polymers
Cellulose nitration is the acid treatment of cotton or wood-pulp cellulose that turns it into cellulose nitrate, the basis of celluloid, lacquer and guncotton.
One Reaction, Two Very Different Products
Cellulose is a long chain of glucose units, and each unit carries three hydroxyl (–OH) groups. Nitration replaces some of them with nitrate (–ONO₂) groups, giving cellulose nitrate. The more hydroxyls replaced, the higher the nitrogen content of the product, and nitrogen content is how the grades are told apart.
The figures below are from general knowledge and not from the corpus; treat them as orders of magnitude only. Celluloid and lacquer grades sit at roughly 11% nitrogen, and guncotton at about 13% and above, with a theoretical ceiling a little over 14%. A difference of two percentage points in nitrogen is the gap between a billiard ball and an explosive. The cellulose still looks like cotton; it burns, with no smoke.
The Acids Are A Cause Of Harm Before The Cellulose Is
The nitrating agent is made by combining nitric acid with sulfuric acid. Nitric Acid and Sulfuric Acid describe each one; the nitric acid article notes it is the only common mineral acid that reliably nitrates organic compounds. Both are corrosive, nitric acid can ignite combustibles, and the fumes are toxic and can injure the lungs after a delay. See Nitrating Mixture for what makes the mix dangerous.
A Short History
The reaction was found in the 1830s and 1840s. Christian Schönbein described guncotton in 1846 (recalled). Guncotton proved dangerous to make and store: an early guncotton factory at Faversham in England exploded in 1847, killing 21 people (recalled; treat the details as unverified). Frederick Abel’s work in the 1860s on pulping the fibre and washing it thoroughly made guncotton far more stable (recalled). Alexander Parkes and then John and Isaiah Hyatt used less-nitrated material, softened with a plasticiser, to make a moldable plastic. That is celluloid: see Celluloid.
Where This Article Stops, And Why
This article gives no acid ratios, no temperatures, no times, no quantities and no procedure. That is a deliberate editorial limit, not an oversight. The reasons are these:
- The window is narrow. Plastic-grade and explosive-grade product differ by a small change in degree of nitration, and which one you get depends on the strength of the acids, the water in them, the temperature and the time.
- Controlling it takes measurement. It needs acid strengths known and held to tolerance, temperature held down against a reaction that generates heat, and washing thorough enough to remove every trace of acid. Without them the reaction can overheat, release brown nitrogen oxide fumes and run away.
- A bad batch can fail slowly. Product that is not washed free of acid decomposes by itself and can ignite later, in storage. Film stores and archives have burned this way. See Celluloid Safety.
- A published recipe cannot be supervised. A written procedure goes to anyone, in any state of preparation. The risk falls on the maker, and the product is an explosive.
A reader who has finished this page should understand why celluloid mattered, what the chemistry is, and why its makers took the risks they did. They should not be able to make it from this page, and are not meant to.
What To Do Instead
- Salvage celluloid from old goods, and handle it with the care in Celluloid Safety.
- Use plastics that do not need nitration: casein, Bakelite and shellac (see Bioplastics).
- For coatings, use shellac or Bakelite varnish instead of nitrocellulose lacquer: Lacquers and Coatings.
Common Mistakes
- Treating nitration as a plastics step like any other — it makes an explosive precursor.
- Believing a plant fibre product is benign — nitrated cotton burns without smoke.
- Assuming a washed product is stable — washing is a critical step, not a rinse.
Strong acids, toxic fume, explosive product
Nitration involves concentrated nitric and sulfuric acids that burn skin and can blind, brown nitrogen oxide fume that can injure the lungs after hours, and a product that becomes an explosive if over-nitrated and a fire and decomposition hazard even when it is not. This page is not a procedure and must not be used as one.
What’s Next
- Learn next: Nitrating Mixture — why two acids, and the hazard of mixing them
- Combine with: Nitration Process — what has to be controlled, and what fails