A team of Swedish researchers is proposing poplar as an alternative to cotton. Their research aims at replacing cotton fibre for textiles with fibre for textiles from fast-growing poplars. Today, worldwide there are 34.5 million hectares of arable land fit for food crops currently devoted to cotton cultivation.
By substituting cotton fibres with poplar fibres, the researchers aim at reducing the demand for cotton fibres for textiles, and consequently reducing the need for cotton plantations.
The primary benefit would be freeing-up millions of hectares of land currently devoted to cotton cultivation, that could be used for food crops, since poplar can be planted in marginal lands which are not apt for food crops.
The researchers are also studying a new extraction method for producing bio-oils that can be used to produce fuel from poplar wood: the entire tree would become useful.
Another advantage of this solution would be its contribution to the fight against climate change by increasing the dynamics of atmospheric carbon storage, allowed by the growth of poplars, as the researchers noted in the journal Joule.
Producing a ton of cotton requires 2,955 m3 of water. Growing cotton requires the use of large quantities of fertilisers and other treatment products which, when disposed of in the soil, cause eutrophication downstream.
Organically grown cotton, which uses less or no chemicals, is a solution, but it currently accounts for only 1% of global cotton production and, with lower yields, requires more land to produce.
This is partly the reason why there is a growing demand for more durable fibres such as viscose and lyocell, which are produced from wood cellulose. Poplars, which are fast-growing trees, are an interesting source of cellulose in several respects.
The aim of the research was to determine whether poplar fibres can substitute cotton for textile purposes while saving resources and optimising the use of arable land.
The method and the results
They began by analysing the available uncultivated ‘marginal’ land in Northern Europe that is suitable for poplar cultivation, focusing on countries within the Baltic Sea region, which includes parts of Sweden, Poland, Germany, Lithuania, Latvia, Estonia, Russia. and Denmark.
“Marginal” lands are those that are not designated as forest land and may be inaccessible or low-yielding due to their sandy soils and therefore not suitable for agriculture.
In these countries, they identified 4.6 million hectares of available marginal land, just under 3% of the total land area, where poplars could be grown without competing with agriculture.
They then modelled how much biomass poplars could produce in this area. The clones investigated were SnowTiger and OP24. They also explored the potential of a more efficient extractive method called “reduced catalytic cracking” to convert wood pulp into fibres and yarns.
Through this process, oil can also be extracted as a by-product of the 50% of the wood that normally remains after processing the cellulose to obtain fibre. This oil can be used to produce biofuel.
Using the growth data of the two varieties investigated, the team calculated that, on the area of marginal lands in the Baltic Sea countries, these trees could generate 2.4 tonnes per hectare of fibrous pulp each year.
Although the researchers focused their analysis on the Baltic countries, they estimated that across Europe there are 43 million hectares of marginal land that could be filled with poplar plantations. This could free up large tracts of land used for growing cotton that could be converted into arable land for production of food.