Pulp could be processed into raw material for gunpowder, according to the Finnish Broadcasting Company Yle. Professors of chemistry disagree about the feasibility of this.
Finnish pulp is hoped to provide a solution to the shortage of artillery ammunition in Ukraine, as it defends itself against the aggression by Russia, according to a news article by Yle.
Nitrocellulose, used to make gunpowder, and its raw material cotton-based pulp are in short supply. A corresponding raw material might be processed from Finnish timber. According to Yle, in simple terms, smokeless powder is made by treating cellulose with a mixture of nitric and sulphuric acids.
Speaking to Yle, Ilkka Kilpeläinen, Professor of Organic Chemistry at the University of Helsinki, says that there is sufficient know-how in Finland in both wood processing and the manufacturing of gunpowder.
’It may be that the wood-based cellulose ought to be further processed, maybe by removing hemicellulose or breaking up the molecule. This type of chemistry is, however, fairly straightforward and well known,’ says Kilpeläinen.
Production of gunpowder constrained by both time and money
Speaking to forest.fi, Raimo Alén, Professor of Chemistry at the University of Jyväskylä, says he finds the idea of wood-based gunpowder highly topical and something that would increase the added value of wood. However, he advises caution. In his estimate, achieving effective production levels would be difficult and take quite a lot of time.
’It’s hard to predict what will happen in the war against Ukraine, but in my opinion, to respond to the acute increase in the need for nitrocellulose by means of modifying [Finnish] industrial production doesn’t seem a very realistic or rapidly implementable option.’
There are many practical complications, such as money. Alén points out that compared to wood-based cellulose, cotton-based cellulose is chemically extremely pure. Using wood-based cellulose would require more processing stages to achieve the necessary purity, and the cost of this is difficult to estimate.
’The average degree of polymerization [the number of glucose units bound together chemically] of cotton-based cellulose molecules is quite high, compared to dissolving pulp: for cotton, the figure is about 15,000, as against about 500 for dissolving pulp,’ says Alén.
The kraft, or sulfate, process of manufacturing wood pulp produces kraft pulp at a recovery rate of about 50 percent. In the technically sophisticated process, both the lignin that binds the fibres together and various extractives are removed from wood. Kraft pulp is widely used in manufacturing paper, especially grades used for magazines, packaging paperboard and corrugated paperboard.
Kraft pulp contains 75–80 percent of cellulose suitable for making gunpowder. 20–25 percent consists of hemicellulose.
’Without further processing, kraft pulp is not suitable for making nitrocellulose, though in theory, the remaining hemicellulose could be removed by acid hydrolysis or by using suitable enzymes,’ Alén considers.
Gunpowder out of birch and spruce
Alén explains that gunpowder could also be made in the acidic sulphite process used to defiber wood, followed by the manufacture of dissolving pulp. This would allow gunpowder to be made from birch and spruce.
The dissolving pulp used in textile industry to manufacture viscose fibre contains 90–96 percent of cellulose on average. According to Alén, however, the acidic sulphite process is not in use in Finland at the moment. About 90 percent of the global production is based on what is called the alkaline kraft process.
Alén estimates that the additional demand for gunpowder in Finland is about 100–200 tonnes per year.
’Procuring the timber required for this volume could also create problems in today’s situation.’
Alén does mention one interesting and perhaps feasible option: the dissolving pulp for gunpowder could be produced in mills in Finnish ownership that use the rapidly growing eucalyptus as raw material. The method used here could be a kraft process with pre-hydrolysis.
Complicated process to make gunpowder
Describing the manufacturing of smokeless powder based on nitrocellulose and used in ammunition, Alén says it is a complicated process. The properties of gunpowder can be modified by adjusting the particle size and composition. Smokeless powder undergoes deflagration instead of detonation. It is classified as brisant, which means it has a shattering effect. To explode, it requires an external impulse.
’The key properties of powder include its rate of combustion and, to some extent, also its speed of detonation,’ says Alén.
The speed of detonation refers to the time taken for the explosion to travel through a substance.
Alén reminds that powder must be homogeneous and not sensitive to temperature changes, and it may not produce fouling. All this poses certain requirements on the raw materials.
’The manufacturing process, including, among other things, the controlling of product properties, as well as the financial factors related to the manufacturing, can only be discussed reliably and unambiguously by professionals who are actively involved in the process and in possession of detailed information. In Finland, powder is made by the Nammo group, and their main raw material is probably cotton-based nitrocellulose,’ Alén says.
Nammo’s brands include Vihtavuori and Lapua. Alén cautiously estimates Nammo’s production volume to be about 650 tonnes of powder. The company declined the request for interview by forest.fi, citing business secrecy.
