Electro-spinning and characterisation of neat lignin fibres

Jassi, Rohit Jordi (2025). Electro-spinning and characterisation of neat lignin fibres. University of Birmingham. Ph.D.

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Abstract

Lignin is a complex and abundant biopolymer, which is often fractionated, functionalised, and/or blended with synthetic or natural polymers to facilitate its processing into fibres via wet, melt, or electro-spinning methods. These traditional processes are typically complicated and involve multiple steps, limiting the scalability and economic feasibility of lignin fibre production. This study explores a novel approach to electro-spin neat BioChoice softwood Kraft lignin using a single-solvent, dimethyl sulfoxide (DMSO), aiming to simplify the process and enhance fibre uniformity.

Previous attempts to electro-spin lignin using DMSO alone, resulted mainly in electro-spraying rather than continuous fibre formation, underscoring the need to optimise solution properties and spinning conditions. In this study, thermal treatment was used to modify the lignin solution characteristics, enabling the successful electro-spinning of neat lignin in DMSO without the need for additives or co-polymers. Therefore, this work investigated whether refluxing lignin in DMSO at specified temperatures could produce a solution with suitable molecular properties, such as increased molecular weight and chain entanglement for effective fibre formation.

To test this hypothesis, neat lignin in DMSO was refluxed at temperatures of 80, 100, 120, 140, and 160 °C under a nitrogen atmosphere. The solutions and corresponding electro-spun fibres were then characterised using nuclear magnetic resonance (NMR), Fourier-transform infrared spectroscopy (FTIR), electrical conductivity, and viscosity measurements to determine their suitability for electro-spinning. Electro-spinning was conducted at 55 °C using a custom-designed rig, followed by drying the fibres at 100 °C for 4 hours in a vacuum oven to remove residual solvent.

The electro-spun fibres were analysed using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and image analysis to assess their thermal properties, stability, and morphology respectively. The results indicated that unfused fibres with circular cross-sections were obtained when the lignin was refluxed at 120, 140, and 160 °C, supporting the research hypothesis that elevated reflux temperatures prior to electro-spinning increased the molecular weight and provide adequate chain entanglement for fibre formation. This hypothesis is supported by the gel permeation chromatography (GPC) analysis, which demonstrated that vacuum drying lignin at elevated temperatures resulted in increased molecular weight and polydispersity. This trend is attributed to thermal-induced reactions, which enhance molecular chain entanglement. These changes improve the rheological properties of lignin solutions, facilitating more stable electro-spinning and successful fibre formation. The resulting electro-spun lignin fibres were successfully thermostabilised and carbonised, yielding continuous carbon fibre mats suitable for further structural and morphological analysis.

This study demonstrates a novel and simplified method for electro-spinning neat lignin using a single-solvent system, potentially revolutionising the production of lignin-based fibres by reducing the need for extensive chemical modifications and co-polymer blending. The findings highlight the efficacy of DMSO in facilitating high-quality lignin fibre formation, aligning with green chemistry principles and paving the way for more sustainable and cost-effective lignin utilisation.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):