Alternative sources of raw materials for fiber production
Any plant-based material can potentially serve as a source of cellulose to make dissolving pulp for fiber production. Lenzing has undertaken extensive research into many different alternative non-wood cellulose sources. In its research, Lenzing identifies promising new cellulose sources and carefully considers their availability, technical feasibility and economic scalability, as well as the overall ecological impact with respect to Lenzing’s climate targets and circularity approach.
Studies have been conducted on sources, including annual plants such as hemp, straw and bamboo. In general, annual plants have a higher growth rate per hectare than trees. Additionally, certain species have a higher cellulose content. Some of them are already available in large quantities, especially in the form of agricultural waste. This allows an attractive cellulose yield per hectare to be achieved; however, the feasibility of any alternative raw material has to be assessed on a case-by-case basis.
Based on current data, large-scale production of cellulose is still best conducted using wood from well-managed forests. The process for isolating cellulose from wood is well implemented and optimized regarding energy, chemicals and process steps. By-products can be extracted during pulp production and excess material is burned for heat and energy production, which does not necessarily apply for alternative cellulose sources.
As an innovative company, Lenzing aspires to find new solutions, and looks beyond the immediate horizon. Limited edition fibers made with pulp from alternative sources such as orange residues or hemp have been successfully produced in the past. Within the framework of the INGRAIN innovation alliance, a development project together with RWTH Aachen and other partners is ongoing. Furthermore, Lenzing is in dialog with manufacturers of pulp from alternative cellulose sources and is evaluating their suitability. Academic collaborations aim for even more exotic cellulose sources, such as macrophytes (aquatic plants growing in or near water), which are still at a very low level of technology readiness.
The development of other new sources of non-wood-based cellulose in the future will require targeted research into the ecological and economic aspects of industrial production as well as increased cooperation. A number of challenges need to be addressed and are described in more detail below.
Availability
Alternatives such as bamboo, straw, and various annual plants do not yet meet large-scale industry needs in terms of availability in the required quality and quantity. Many sources from annual plants are only available in the harvesting season and are difficult to store for year-round use. Despite specific benefits and high annual growth per hectare, the material is very bulky and more costly to transport.
Environmental sustainability
The conversion of forest to agricultural land for annual plants is a worldwide phenomenon that increases pressure on all kinds of forests.
Another important factor in the performance of annual plants is the management of the agricultural areas. Highly productive sites need far more fertilizers and pesticides than forests, causing other environmental issues. For example, the overall environmental profile of large-scale bamboo plantations is known to be unsatisfactory.
When considering processing, important factors that affect the environmental impact include energy consumption and the use of process chemicals in pulp production. They depend heavily on the actual process and vary significantly from one annual plant to the next.
Technical feasibility
Lenzing’s biorefinery process is optimized for certain wood species as raw material. This keeps quality and efficiency high and yields bioenergy as a by-product. Non-wood feedstocks certainly lead to less bioenergy, hence requiring additional energy sources and resulting in higher process emissions.
Annual plants contain more mineral components and organic substances that have to be removed to produce high-quality dissolving pulp. This purification process typically requires the use of aggressive chemicals and causes waste issues. It is a big challenge to develop technologies for these materials while maintaining product quality and ecological safety. On the other hand, in woody plants such as trees, these components are mainly concentrated in the bark, which is easily removed in the first stage of the process. For more information, please see the “Wood & pulp” focus paper.