GRETE developed novel superbase ionic liquids (ILs) that perform excellent in dissolution of wood pulps and are stable in conditions required for recycling of the solvent in the fibre production process. Furthermore, the target was to find ILs that can be synthesized economically from inexpensive and available starting materials and that can be safely used in the wood-to-textile value chain. During the project, three novel non-toxic superbase IL structures were synthetized with good properties for textile fibre spinning meaning good cellulose dissolution power and good stability for recycling.
Spinning of textile fibres from paper-grade pulp requires a pretreatment to enable preparation of a spinnable dope. The aim of the pretreatment step was to lower the degree of polymerization of cellulose in the pulp to enable subsequent pulp dissolution in high yield to enable a spinnable dope with high cellulose content. In GRETE, four pretreatments were tested and finally two of them, mild sulfuric acid pretreatment and enzymatic pretreatment with endoglucanase, were thoroughly analysed in textile fibre production. Two types of paper grade pulp, bleached eucalyptus kraft pulp from Portugal and bleached softwood kraft pulp from Finland, were used..
Chemical functionalisation of the final regenerated fibres was tested by developing chemical modifications for the pulp raw materials.
The GRETE project demonstrated successfully that textile fibres with good mechanical properties can be spun using pre-treated paper grade pulps from eucalyptus and softwood paper grade pulps. A dissolution method was developed where it was possible to avoid drying of the pulps after pretreatment, and dissolve wet pulps into novel superbase ionic liquid. In GRETE with the optimized dissolution and spinning procedures for high hemicellulose kraft pulps, it was possible to improve the fibre tenacity up to over 10 cN/dtex without impairing elongation (>10%). Additionally, it was shown that regenerated fibres from pretreated kraft pulps had comparable mechanical properties with fibres from dissolving grade pulp.
Chemical post-treatments were developed for regenerated textile fibres to enhance the performance of man-made cellulosic textile fibres.
In GRETE a novel hemicellulose characterization method based on immunolabelling of xylan was successfully developed for regenerated fibres and the results suggest that xylan is not only found from the surface of the regenerated fibres but is also distributed throughout the fibre structure.
Efficient recycling of the ionic liquid solvent is a prerequisite for an economically viable textile fibre process. The recovery and purification of superbase ionic liquids (IL) from the spinning bath using different approaches was evaluated. The results demonstrate that aqueous two-phase system separation method can be considered as a way to remove water. The results also showed that the liquid-liquid extraction method can be improved by using parallel structure, with both solvents showing similar efficiency.
Two of GRETE concepts showed higher profitability compared to the reference concept (Lyocell) suggesting that textile fibre production using ionic liquids and paper grade pulp can be economically viable.
Environmental impacts of the selected GRETE concepts were assessed by following a Cradle-to-Gate LCA approach using mass and energy balance data generated by the simulation model. The results of the assessment showed that a textile fibre production concept utilising eucalyptus paper grade pulp and ionic liquid as solvent led to the most competitive environmental performance. The GRETE concepts were analysed also from a social and socioeconomic perspective. The results showed that the same concept that was competitive from environmental perspective was also the most effective in terms of generating social value.
The GRETE project has resulted in 3 master theses, 5 peer revied publications, 3 manuscripts that are under review in peer-review journals. In addition to these papers, 5 more manuscripts are currently under preparation. These papers contain the scientific novelty of the project that spans from novel ionic liquid structures to the techno-economics of man-made cellulosic textile fibres. The partners have introduced the GRETE project in 51 onsite or online events, including 17 oral and 16 poster presentations that have been given based on GRETE results. Also, events targeted for the Stakeholder Group (SHG) have been organized.
