Nitrocellulose, which is used to make gunpowder, and its raw material – cotton cellulose – are in short supply. A suitable raw material could be obtained from Finnish timber, but chemistry professors disagree over whether this is feasible.
According to information published by Yle (Finland's public broadcaster), there are hopes that Finnish cellulose could offer a solution to the shortage of artillery ammunition for Ukraine, which is defending itself against Russian aggression – so says an Yle article.
A suitable raw material could be made from Finnish timber. According to Yle, smokeless powder is produced, put simply, by treating cellulose with a mixture of nitric acid and sulphuric acid.
Professor of organic chemistry at the University of Helsinki Ilkka Kilpeläinen told Yle that Finland has sufficient expertise both in wood processing and in gunpowder manufacture. “Wood cellulose would probably need further processing, either by separating out the hemicellulose or by breaking down its molecule. The chemical process involved is fairly simple and well known,” says Ilkka Kilpeläinen.
Powder production is constrained by time and money
Jyväskylä University chemistry professor Raimo Alén told forest.fi that the idea of making gunpowder from wood, which could increase its added value, strikes him as highly topical. Even so, Alén advises caution, since by his estimates it would be difficult to reach an efficient level of production and would take a fair amount of time.
“It is hard to predict what will happen in the war in Ukraine, but in my view responding to an acute rise in demand for nitrocellulose by modifying [Finland's] industrial production does not look like a particularly realistic solution, or one that could be implemented quickly. There are many practical complications, finance among them.” Alén points out that, compared with wood cellulose, cotton cellulose is chemically very pure. Using wood cellulose would require additional processing stages to reach the necessary degree of purity, and the cost of those is hard to estimate.
“The average degree of polymerisation of cotton cellulose molecules [the number of chemically bonded glucose units] is quite high compared with dissolving pulp: for cotton the figure is about 15,000, for dissolving pulp about 500,” says Professor Alén.
The wood cellulose production process yields what is known as kraft pulp, or sulphate pulp, with a recovery rate of about 50%. In this technically demanding process, both the lignin that binds the fibres and various extractives are separated from the wood. Kraft pulp is widely used in papermaking, particularly for magazine paper, packaging board and corrugated board.
Kraft pulp contains 75-80% cellulose, which is suitable for making gunpowder, and 20-25% hemicellulose.
“Without further processing, kraft pulp is not suitable for producing nitrocellulose, although in theory the remaining hemicellulose could be separated out by acid hydrolysis or by using suitable enzymes,” says Professor Alén.
Powder from birch and spruce
Raimo Alén explains that gunpowder could also be made using the sulphite process, which is used to break down lignin and then to produce dissolving pulp. That would make it possible to use birch and spruce in gunpowder manufacture.
Dissolving pulp, which the textile industry uses to make viscose fibre, contains 90-96% cellulose on average. According to Alén, however, the sulphite process is not currently in use in Finland. Around 90% of world production is made using the so-called alkaline kraft process.
Alén estimates the additional demand for gunpowder in Finland at around 100-200 tonnes a year. “Securing the wood needed for that volume could pose problems even in the present situation,” he says, mentioning one interesting and possibly workable option: the dissolving pulp intended for gunpowder could be produced at Finnish-owned mills that use eucalyptus as their raw material. In that case the kraft process with prehydrolysis could be used.
The complex process of making gunpowder
Describing the production of smokeless powder, which is based on nitrocellulose and is used in ammunition, Raimo Alén stresses how complex the process is. The properties of the powder can be altered by adjusting particle size and composition. Smokeless powder undergoes deflagration rather than detonation. It is classified as a brisant, meaning that it has a shattering effect. An external impulse is needed to make it explode.
“The most important properties of a powder are its burning rate and, to some extent, its detonation velocity,” says the chemist. Detonation velocity is the time it takes for the explosion to propagate through the substance. Raimo Alén points out that the powder must be homogeneous and insensitive to changes in temperature, and it must not cause contamination. All of the above also imposes certain requirements on the raw materials.
“The production process, including control of the product's properties, as well as the financial factors involved in production, can only be discussed reliably and unambiguously by professionals who are actively involved in it and who have detailed information at their disposal. In Finland, powder is produced by the Nammo group, and its main raw material is most likely cotton-based nitrocellulose,” says Alén.
Nammo's brands include Vihtavuori and Lapua. Raimo Alén believes Nammo's output is probably in the region of 650 tonnes of powder a year. The company declined forest.fi's request for an interview, citing commercial confidentiality.
https://forest.fi/article/finnish-pulp-to-solve-shortage-of-ammunition-in-ukraine/#f4da1e95