PRODUCTION AND SEPARATION OF LYOCELL-CELLULOSE ACETATE KNITS

Cellulose acetate (CA) in its commercially by far most important form cellulose diacetate with a degree of substitution (DS) of around 2.5, has historically been relatively common in textile applications. It has been replaced by other textile fibers, of which polyethylene terephthalate (PET) is currently the most widely produced.

Several CA staple fibers have been produced by a non-textile specific process, dry spinning including a stuffer box. Fibers were produced on an industrial scale filter tow machine at selected settings. There appears to be only minor differences between the different CA staple fibers, apart from minor coloration and tenacity differences. As fiber titer increases, tenacity appears to increase and dye bath extraction decreases. Increased crimp results in increased dyeing of the fibers. From CA:LyoC yarns knit fabrics were produced without severe limitations. Therefore, the research hypothesis is confirmed and crimped fibers from filter tow machines can be used in textile applications. However, it seems that fine (< 3 dtex) secondary staple fibers, in the case of LyoC, are essential in mixed fibers in this process. Selective dissolution of CA in acetone, including separation of dispersion dyes from CA by selective CA-ethanol precipitation, was carried out as a recycling option. Overall, the separation efficacy in the simple laboratory experiment is close to 90 %.

Given the low toxicity, cost and good recoverability of acetone, the recycling process could be relevant in industrial applications where acetone recovery is close to 99 %. In the future better mixing of CA fibers, based on less fiber coalescence and intermingling from the production process, is expected to result in stronger yarns. Future improvements in staple fiber properties will make downstream processes simple, possibly faster and more cost-effective. Fiber titer matching and spin finishes are options for further comprehensive yarn adaptation. The problems in the processing and application of CA have to be counter-balanced by follow-up properties and costs. Due to its predominantly amorphous structure with low interpolymer forces and correspondingly low mechanical strength, it is more susceptible to mechanical disintegration in the environment. As the size of the material decreases, the available surface for microbial attack increases. Compared to PET, CA is much less persistent in the environment, does not or to a lesser extent enviro-accumulate, and helps to reduce fossil-based carbon enrichment of the atmosphere. This is without taking into account the energy used in the production process, which is being shifted to renewable sources globally. Consequently, despite its performance drawbacks, CA may be the more reasonable choice of material in textile applications. Especially when considering the true costs, including unquantifiable environmental costs of current fiber market shares.

Publication:

Wurm F, Schöb F, Moor T, Schweiß J, Leukel J, Pham T, Bechtold T (2025), Production and separation of knitted lyocell-cellulose acetate fabrics from crimped cellulose acetate fibers. Resour. Conserv. Recycl. 212:107959. https://doi.org/10.1016/j.resconrec.2024.107959