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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 3 - GreenLight (Cost effective lignin-based carbon fibres for innovative light-weight applications)

Teaser

Summary

The overall objectives of the GreenLight project are to demonstrate a new biobased, renewable and economically viable carbon fibre (CF) precursor, lignin, produced in Europe with European raw material and to develop conditions for its processing into CF and structural CF composites. The target is a cost-effective bio-based CF for use in reinforced composites delivering enough strength and stiffness properties for large-volume automotive applications. Todayâ€™s CF production is based on use of a petroleum-based raw material, PAN, which is costly due to the starting precursor and the process for turning it into CF. The automotive sector has identified a need for a cheaper lower-grade CF to meet the demands of components in normal consumer cars. Wood lignin, a by-product from kraft pulp mills, is a green, sustainable, new potential CF precursor. Successful lignin applications like CF will create new business opportunities and new jobs also in rural areas where the pulp mills are located. The development of lignin-based CF is still in laboratory scale and material properties meeting high-quality product demands is the main challenge. A new technology in commercial operation makes it possible to produce lignin with new properties, higher purity and with less impact on the pulp mill operation. The idea is to tailor kraft lignin properties already in the lignin separation and optimize the lignin for target automotive applications. Within the scope of the project it was demonstrated the continuous mulitifilament spinning of a 100% softwood lignin into high quality filaments. Based on the promising mechanical performances, lignin-based carbon fibre could have a potencial large-volume automotive application in manufacturing short fibre composites which have lower production cost and broad applications.

Work performed

Production of lignin filaments: Several lignins have been produced and evaluated for filament spinning using a small-scale monofilament apparatus. More than 100 kg of the selected parent lignin was produced. Thermal treatments were performed and multifilament spinning was investigated at up to the about 1000-filament scale.
Turning the lignin filaments into carbon fibres: Different methods for stabilisation such as UV irradiation, crosslinker addition and isothermal heating of the fibres were used to assist and facilitate stabilization. Pre-stabilization of fibers, at lower temperatures, showed the most promising results and reduced the main stabilization time significantly.
Surface chemistry and physical properties of the lignin-based carbon fibres were evaluated. Plasma treatment is a safe and effective method for improving fibre/matrix adhesion by adding surface functional groups on the fibre surface.
Process upscaling: Different pre-treated lignins were analysed regarding their potential large-scale spinning behaviour. With these results the plant setup, spinneret design, process parameters and winding conditions were adapted to the unique spinning behaviour of lignin.
Spinning trials were performed with all lignin samples in near-industrial scale. Continuous processing was possible on a standardised single screw extruding system without any gas inclusions which allows an easy scale-up to existing production plants. A new spinning concept was developed which allows continuous spinning and winding with automatic spool change. It is based on a spin-carrier where the outer envelope component can be removed in a continuous after-treatment process to gain a 100 % lignin precursor yarn. A 1000 filaments precursor yarn was produced. The stabilization of the precursor fibre could not be realized with existing commercially available stabilization ovens and alternative stabilization technologies needs to be further investigated.
Product application development: Fabrics, matrices and manufacturing methods for reference composites were selected. A suitable experimental methodology has been identified and tuned on the early stage fibres. The fibres were characterised with a single fibre tensile test. A car bracket-component and a back plate were selected as a benchmark reference for thermoplastic and thermoset demonstrator. The bracket was redesigned for composite manufacturing. The thermoset demonstrator has been designed from SMC production technique and with commercial material data. Both thermoset and thermoplastic composites have been manufactured. All the manufactured composites have been characterised via tensile, compression and short beam testing to determine the tensile and compression modulus and strength as well as the short beam strength. The results show that the lignin carbon fibre produced are performing in line with or better than previously presented in the literature. Computer simulations of the demonstrator with material data from all benchmark materials and the lignin carbon fibre have been carried out and show great weight saving potential by using lignin carbon fibre.
Techno-economic evaluation: A simulation model, integrating lignin extraction from a pulp mill, melt spinning and carbon fibre conversion, was developed for techno-economic evaluations of an up-scaled industrial process. The estimated production cost of the GreenLight carbon fibre (CF) was 12.6 EUR/kg (to be compared with cost estimates of PAN-based CF of ~16 EUR/kg). A sensitivity analysis showed a reduction in production cost, down to 6.5-7.1 EUR/kg, through cooperation with existing melt spinning and carbon fibre plants. The number of holes per spinneret in the melt spinning process has a significant impact on the total production cost.
The GreenLight process has a global warming potential (GWP) of 1.50 kg CO2eq/kg CF with production and use of chemicals as the main contributors. This number is 35 % lower than the GWP for glass fibre product

Final results

Our progress beyond the state of the art is that we have demonstrated the continuous multifilament spinning (up to 1000 filaments) of kraft lignin without additives. The tensile properties of the fibres are the highest reported for meltspun pure lignin-based carbon fibres.
A new spinning process for lignin was developed, which allows continuous spinning and winding with automatic spool change. An application for a patent is in progress. Overall the project succeeded in increasing the TRL level of precursor fiber production from 2-3 (Proof of concept) to TRL 5: the technology of precursor fiber production was validated in an industrially relevant environment.