Abstract
In general, the electro-spinning of lignin requires it to be functionalised and/or blended with synthetic or natural polymers. This paper reports on the use of solvent fractionated lignin-lignin blend to electro-spin BioChoice softwood Kraft lignin. The blend consisted of acetone-soluble and ethanol-soluble lignin in a binary solvent of acetone and DMSO. Solvent fractionation was used to purify lignin where the ash content was reduced in the soluble lignin fractions from 1.24 to ~ 0.1%. The corresponding value after conventional acid-washing in sulphuric acid was 0.34%. A custom-made electro-spinning apparatus was used to produce the nano-fibres. Heat treatment procedures were developed for drying the electro-spun fibres prior to oxidation and carbonisation; this was done to prevent fibre fusion. The lignin fibres were oxidised at 250 °C, carbonised at 1000 °C, 1200 °C and 1500 °C. The cross-section of the fibres was circular and they were observed to be void-free. The longitudinal sections showed that the fibres were not fused. Thus, this procedure demonstrated that solvent fractionated lignin can be electro-spun without using plasticisers or polymer blends using common laboratory solvents and subsequently carbonised to produce carbon fibres with a circular cross-section.
Highlights
Over the past decade, the use of naturally occurring biomaterials such as lignin and cellulose as an alternative precursor to polyacrylonitrile (PAN) for the production of carbon fibres has been studied extensively[1,2,3,4,5]
Since a linear relationship exists between the interaction parameter and temperature, lowering the temperature of the polymer solution in a controller manner will cause precipitation of the higher molar mass fractions in a manner that is similar to the non-solvent-based approach
This paper reports on the development of a method for electro-spinning a lignin/lignin blend, without using any additives
Summary
The use of naturally occurring biomaterials such as lignin and cellulose as an alternative precursor to polyacrylonitrile (PAN) for the production of carbon fibres has been studied extensively[1,2,3,4,5]. The relationship between the polymer chain length ( xn) and the critical polymer concentration (χ1c) at which phase separation will be observed is given b y27,28: Scientific Reports | (2021) 11:16237 This leads to the conclusion that if χ1 can be adjusted and controlled for a polydisperse polymer solution, appropriate processing conditions can be adjusted to enable a specified molar mass or fraction of the polymer to be precipitated. The concentration of the non-solvent can be increased progressively to achieve the fractionation of the polymer with a narrow molar mass distribution in each fraction[29,30]. Since a linear relationship exists between the interaction parameter and temperature, lowering the temperature of the polymer solution in a controller manner will cause precipitation of the higher molar mass fractions in a manner that is similar to the non-solvent-based approach. The source, type of lignin and the extraction procedures used influence its processability during fibre spinning[2,40]
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