Carbon fibers (CF) are a material with a composition of over 90% carbon, which has high mechanical properties and low density. This unique combination of properties makes it requirable in applications such as vehicles, aerospace, wind power, and space industries. Commercially made CF are made using the fossil raw material polyacrylonitrile (PAN). In order to make a more sustainable precursor fiber (PF), this project has focused on other raw materials; cellulose and lignin. The PFs were produced with a cellulose and lignin mixture (70:30 wt%). In order to make a more green production of PF, cold alkali system was used as the solution in conjunction with wet spinning with an acid:salt coagulation bath. The acid:salt baths used was the P system with phosphoric acid and ammonium dihydrogen phosphate (ADHP), and the S system with sulphuric acid and sodium sulphate with varying concentrations of both acid and salt. The objectives for this thesis was to evaluate the effect of the acid:salt coagulation bath composition, as well as the spin finish. This was done using tensile tests where Young’s modulus, strain to failure, and tensile strength (TS) were determined. The spin finish was evaluated using thermogravimetric analysis (TGA). The results showed that the P system had a significantly higher Youngs modulus and tensile strength compared to the S system, whilst the S system had a higher strain to failure. For the different concentrations of the S system, the tensile tests showed no significant difference between the concentrations. The fibers contained more phosphorus when ADHP was added to the spin finish, making them more flame retardant.

Användningen av cellulosa och lignin för prekursorfibrer (PF) för kolfibrer (CF) är ett mycket intressant forskningsområde på grund av den stora miljöpåverkan som dagens PF-fossilbaserade råvara PAN har. Denna avhandling fokuserar på att utveckla PF med ett kallt NaOH-upplösningssystem med cellulosakoncentrationer från 4,5 till 5,5 viktprocent med varierande massaviskositet och tillsats av lignin från 0-40 viktprocent jämfört med cellulosa. Koagulationssystemet som användes var ett fosforbaserat system med fosforsyra och ammoniumdivätefosfat (ADP) och tvätttiden ändrades för att undersöka påverkan på det slutliga oorganiska innehållet i PF. Effekten av tillsatt lignin och användning av en högre massaviskositet med en förändrad cellulosakoncentration undersöktes. Det som noterades av resultatet av dragegenskaperna och spinnbarheten hos dopen visar en viss trend som är att hög massaviskositet på 330 ml/g och hög ligninhalt på 40 viktprocent (i jämförelse med cellulosamängden i dopen) tycks uppvisa dålig spinnbarhet och svagare dragegenskaper. Användning av längre tvätttider under centrifugeringsprocessen resulterade i en lägre ask- och fosforhalt i PF. / The use of cellulose and lignin for precursor fibers (PFs) for carbon fibers (CFs) is a highly researched topic because of the large environmental impact that today’s PF raw material PAN which is fossil based. This thesis focuses of developing PFs with a cold NaOH dissolution system with cellulose concentrations ranging from 4.5 to 5.5 wt% with varying pulp viscosity and the addition of lignin ranging from 0-40 wt% in comparison to the cellulose. The coagulation system used was a phosphorus-based system with phosphoric acid and ammonium dihydrogen phosphate (ADP) and the washing time was altered to investigate the impact on the final inorganic content in the PF. The impact of the addition of lignin and using a higher pulp viscosity with an altered cellulose concentration is researched. What was noticed from the result of the tensile properties and the spinnability of the dope shows a certain trend which is that high pulp viscosity of 330 ml/g and a high lignin content of 40 wt% (in comparison to the cellulose amount in the dope) seems to present poor spinnability and weaker tensile properties. Using longer washing times during the spinning process resulted in a lower ash and phosphorus content in the PF.