Mechanical characterisation and fibre morphology analysis in ABS and short carbon fibre composites: influence of different polymer processing techniques

Polymer composites have attracted considerable interest due to their potential to enhance mechanical properties of polymers for advanced applications. Yet, challenges exist, including complex mechanical behaviour and poor affinity between reinforcement material and polymer matrix. This study investigates the influence of different processing methods on the mechanical properties of acrylonitrile butadiene styrene (ABS) reinforced with 15 wt% short carbon fibres (sCF), with a main focus on the fibre morphology. By analysing injection moulded (IM), fused filament fabricated (FFF) and compression moulded (CM) parts, this research aims to elucidate the relationship between the processing method, fibre orientation and mechanical properties. Improved affinity is achieved through nitric acid surface treatment. Scanning electron and optical microscopy are used to analyse the morphology, revealing insights into void presence and fibre roughness, length, distribution, and orientation. Additionally, mechanical properties are assessed through impact, tensile and flexural tests. Significant differences in morphology among ABS/sCF composites produced by different methods are revealed. Microscopy images show that in IM parts, fibres are highly aligned in the shear layer but exhibit a more varying orientation in the core, with minimal voids. FFF parts exhibit excellent sCF alignment but show voids between different layers, while CM parts display varying fibre orientations and small air inclusions. Test bars produced via IM demonstrate superior stiffness, tensile strength, and tensile strain at break, followed by FFF (which shows a very high impact strength), while CM parts exhibit the least favourable properties, partly due to their isotropic nature and random sCF orientation. These outcomes can be immediately linked to the resulting morphologies. The findings of this work highlight the critical role of processing methods and fibre morphology in determining the composite performance.