Carbon Fibre from Kraft Lignin
The aim of the project is to manufacture carbon fibre from black liquor lignin with the same quality as today’s raw material.
In today´s pulp and paper mills, the recovery boiler often becomes a bottle-neck for increasing the production. A new way of isolating lignin from kraft black liquor (lignoboost) makes it possible to increase the production of pulp and paper at the same time as a new raw material is formed (lignin). Lignin can be used as a biofuel or to make other chemicals and materials, i.e. carbon fibre. The advantages of using lignin as a raw material for carbon fibre production is that it is a cheap and renewable material that is easily available.
There are some requirements that have to be fulfilled to use lignin as a raw material for carbon fibre production; the ash content, <1000 ppm, no carbohydrates of polymeric size, able to soften without starting to decompose and low polydispersity.
Black liquor from spruce/pine, birch and eucalypt has been ultra-filtered through membranes with a cut-off of 5 and 15 kD. The lignin has been isolated by precipitation with carbon dioxide at pH 9 followed by filtering under pressure, washed at pH 2 with sulphuric acid and dried.
After isolation, the ash content was around 1 %. To be able to spin carbon fibre, the ash content must be lower than 1000 ppm (0,1%). To achieve that, the lignin was treated with an ion-exchanger.
Chemical and thermal analyses, which includes SEC (Size Exclusion Chromatography), Thioacidolysis, 31P-NMR, elemental analysis, DSC (Differential Scanning Calorimetry) and TGA (Thermal Gravimetric Analysis) has been performed.
At a later stage:
1. Add a plasticizer to the lignin and evaluate if the properties to become a raw material for carbon fibre production are improved.
2. Manufacture carbon fibre by spinning the lignin