Manufacturing Pitch and Polyethylene Blends-Based Fibres as Potential Carbon Fibre Precursors

Abstract

The advantage of mesophase pitch-based carbon fibres is their high modulus, but pitch-based carbon fibres and precursors are very brittle. This paper reports the development of a unique manufacturing method using a blend of pitch and linear low-density polyethylene (LLDPE) from which it is possible to obtain precursors that are less brittle than neat pitch fibres. This study reports on the structure and properties of pitch and LLDPE blend precursors with LLDPE content ranging from 5 wt% to 20 wt%. Fibre microstructure was determined using scanning electron microscopy (SEM), which showed a two-phase region having distinct pitch fibre and LLDPE regions. Tensile testing of neat pitch fibres showed low strain to failure (brittle), but as the percentage of LLDPE was increased, the strain to failure and tensile strength both increased by a factor of more than 7. DSC characterisation of the melting/crystallization behaviour of LLDPE showed melting occurred around 120 °C to 124 °C, with crystallization between 99 °C and 103 °C. TGA measurements showed that for 5 wt%, 10 wt% LLDPE thermal stability was excellent to 800 °C. Blend pitch/LLDPE carbon fibres showed reduced brittleness combined with excellent thermal stability, and thus are a candidate as a potential precursor for pitch-based carbon fibre manufacturing.

Influence of High-Concentration LLDPE on the Manufacturing Process and Morphology of Pitch/LLDPE Fibres

“…As in our previous paper [39], we identified being brittle with low strain to failure, and the pitch fibre samples demonstrated such brittle behaviour. Increasing the wt% LLDPE in the blend increased the strain to failure, which was taken to mean that increasing the proportion of LLDPE in the fibres decreased brittleness.…”

“…The specimens were cut into 50 mm lengths. The specimens were mounted end-on for the vertical image and for surface features laid horizontally on aluminium stubs, for more details see [39].…”

“…The stress limit of extruded neat LLDPE is typically about 40 MPa, and the typical strain will be about 0.8 which suggests that the LLDPE component in LLDPE/MP fibres has an important load-bearing role, and toughens the material [39]. Figure 5 shows that boosting the wt% LLDPE in relatively brittle LLDPE/MP fibres can be significant.…”

“…However, their industrial application would greatly increase if they could be manufactured at a Aldosari et al, (2020) have reviewed the possibility of achieving these desired objectives and showed that, despite relevant research being at an early stage, they could be achieved by using a PE/pitch blend to produce CF precursors with improved ductility [11]. In our previous work, we showed the feasibility of mixing LLDPE/pitch as a possible precursor for the manufacture of CFs [39]. That work was limited to a narrow LLDPE/MP range, from 0 to 20 wt% LLDPE, with a corresponding range from 100 to 80 wt% MP.…”

“…The optimum precursor fibre can potentially overcome the issue of the high level of the brittleness of pitch fibres for future high-performance CF manufacturing. As this research is a direct continuation of our previously published work, the same equipment was used and the reader may refer to [39] for details.…”