Biobased lignin/polyamide filaments surface–modified with electrochemically produced graphene oxide to improve their thermal stabilisation behaviour as precursors for carbon fibre production

The thermal stability of melt-spun hydroxypropyl–modified lignin/polyamide (PA1010) 50:50 wt% blended precursor fibres, crucial for the thermal stabilisation stage in carbon fibre production, was enhanced by pre-treating the fibres with a graphene oxide (GO) suspension, synthesized via the modified Hummers method. This pre-treatment allowed the fibres to be subsequently thermally stabilised at a faster heating rate of 20 °C/min, compared to the typical 0.1–0.25 °C/min used for lignin-based fibres, thereby reducing overall thermal stabilisation time from 29 h to 2.5 h. The stabilised filaments were successfully carbonised at 950 °C, yielding coherent, void-free carbon fibres without inter-filament fusion. The tensile modulus of GO-treated filaments improved from 1.3 GPa to 2.3 GPa after thermal stabilisation. However, derived carbon fibres were brittle in nature. Various characterisation techniques, including DSC, TGA, FTIR, SEM-EDX, AFM, XPS, and tensile testing, were used to analyze the physico-chemical changes. DSC showed that GO improved the polycrystallinity of the precursor filaments and contributed to the formation of a three-dimensional cross-linked network during heat stabilisation, suppressing the PA melt endotherm. TGA confirmed that GO-treated filaments had higher char yields (∼40 %) than untreated fibres (∼30 %), further supporting GO-induced crosslinking reactions. FTIR, SEM-EDX, and AFM confirmed an even GO coating. A study of GO pre-treatment variables suggested that a reduction in GO concentration is required to reduce resulting carbon fibre brittleness at the expense of increased thermal stabilisation time.