Alternative feedstocks for fiber production and how to test their suitability for different processes.
The mainstream raw material in pulp production is wood. The main reason for wood still being preferred over alternative raw materials are the fact that:
- Trees can be grown on poor land or in cold climates, where agriculture has a low carbon binding rate;
- Wood has high density, making long-distance transport possible;
- Low price and low demand for fertilizers and chemicals.
The main exception is bamboo, which, despite being technically a grass, is also converted into dissolving pulp in large volumes.
Often in agriculture, only the fruit, seeds or center part of the plant are utilized, and the rest is discarded as waste or utilized in low-value added applications. The discarded sections include but are not limited to bark, peels, leaves, hurds, branches, needles, and other lignocellulosic fractions. They are currently mainly utilized as animal bedding, mulching, bioenergy feedstock, or for compost, rather than being upgraded into high-value applications.
Worldwide efforts are being made to utilize these side streams into higher-value materials, such as dissolving pulp, which would create meaningful additional revenue and help improve the biosustainability of current industrial processes.
Dissolving pulp is a grade of pulp intended for use in man-made cellulosic fibers (MMCFs) and other cellulose derivatives. Several alternative raw materials have been already successfully used in pulp production. These include agricultural by‑products such as straw and bagasse, other non‑wood plants like hemp, and other forest sidestreams that have been previously underutilized.
Recycled textiles (post‑consumer garments, industrial textile waste, and pre‑consumer cutting scraps) have been recognized as a viable alternative feedstock for MMCF production. Their appeal comes from the high cellulose content in cotton-rich textiles, already existing global waste streams, decoupling of fiber production from land use and strong worldwide policies and brand pressure to reduce textile waste.
The MMCF market comprises two major product grades: viscose and lyocell, both value-added products with a growing demand. For ecological reasons, latest years have witnessed a clear shift away from viscose toward Lyocell and other next‑generation solvent systems. This is driven by the desire to reduce the environmental footprint associated with viscose production—particularly the use of carbon disulfide, sulfuric acid, and other chemicals, as well as the challenges of closed‑loop recovery in older viscose lines. Lyocell’s direct‑dissolution process, based on NMMO, enables higher solvent recovery rates, lower emissions, and a more favorable sustainability profile, making it increasingly attractive for both producers and brands.
However, the success rate of alternative feedstocks in viscose and lyocell is still widely variable, depending on the material sources, treatments, and recycling technologies. Nonetheless, several alternative feedstocks have moved beyond pilot scale and demonstrated commercial or near commercial success. The strongest examples comes from hemp, recycled cotton, agricultural residues, and bamboo. These have been successfully used in different end user products categories like apparel and fashion, home textiles, hygiene and nonwovens, packaging and paper, biocomposites for automotive and construction.
The conversion of alternative raw materials into dissolving pulp can be done with a combination of various pulping methods, mechanical separation, acid or base extraction or washing, depolymerization, bleaching with various methods and impurity removal. The exact methods combination depends on the raw material and desired pulp properties. There are three major grades of dissolving pulp: “viscose grade”, “Lyocell grade” and ”acetate grade” (for chemical derivatization).
To achieve the ideal yield and desired final product characteristics, the use of some alternative raw materials is still going through a lot of research and development. SciTech-service has a long track record in testing and developing pulping methods using alternative raw materials. We are specialized in helping customers to test and condition their raw material feedstock for MMCF use.
In the last 5 years, following the previously mentioned worldwide trend, SciTech acquired state of the art equipment that allows testing different samples’ suitability for lyocell process, which complements the already long available services in testing suitability of feedstocks for viscose process.
Using specific raw material characteristics, it is possible to estimate what would be the most suitable use for the raw material. For instance, the molar mass distribution of the produced dissolving pulp is a critical factor to determine the suitability to use in viscose and Lyocell process.
SciTech’s laboratories are fully equipped to test different raw material suitability to produce dissolving pulp and subsequently produce and analyze spinning solutions for Lyocell and viscose fibers.
In the well-established viscose process, dissolving pulp is converted into alkali cellulose followed by xanthation with carbon disulfide. One of the key quality parameters of the produced viscose spinning solution is the presence of undissolved material which, amongst other parameters, is reflected in the filterability of the spinning solution.
At SciTech laboratories an experienced team and wide range of equipment allow the customization of the well-established Treiber test. Which allows us to categorize, with a high degree of confidence, which dissolving pulp is not suitability for industrial scale viscose processes.
Lyocell spinning solution is produced by a thorough mix of an organic solvent and dissolving pulp, using a kneader system. A key quality parameter for Lyocell spinning solution is its viscosity and viscoelastic properties. A state-of-the-art rheometer allows the simulation of the shear stress experienced by the spinning dope, where the high viscosity spinning solution is pushed through several small orifices and drawn in an air gap to filaments.
Furthermore, SciTech possesses an extensive network of partners, which allow an even wider range of analytical services than the ones performed in in-house laboratories.
SciTech experts are also available to offer insight into pulping, pretreatment processes and MMCF related topics in the form of seminars or consulting sessions, including, amongst other, second opinion services to help customers determine the technoeconomic viability of certain processes.
In brief, SciTech has been successfully able to support the R&D efforts in finding the ideal method combination needed to optimize the use of alternative raw materials to be used in both viscose and Lyocell industrial scale processes.
If you would like to know more about this topic and the current offered services, SciTech experts will be glad to further discuss and support your journey into a more bio sustainable path.