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Additive manufacturing (AM) through material extrusion (MEX) is becoming increasingly popular worldwide due to its simple, sustainable and safe technique of material preparation, with minimal waste generation. This user-friendly technique is currently extensively used in diverse industries and household applications. Recently, there has been increasing attention on polycaprolactone (PCL)-based composites in MEX due to their improved biodegradability. These composites can be printed at a lower temperature, making them more energy efficient compared to commercial filaments such as acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA). Although wool is the leading protein fibre in the world and can be more compatible with PCL due to its inherent hydrophobicity, the suitability of MEX using a wool/PCL combination has not been reported previously. In the current study, waste wool/PCL composite parts were printed using the MEX technique, and rheology, thermal and tensile properties, and morphology were analysed. The impact of wool loading (10% and 20%) was investigated in relation to different filling patterns (concentric, rectilinear and gyroid). Furthermore, the impact of fibre fineness on the final material produced through MEX was investigated for the first time using two types of wool fibres with diameters of 16 µm and 24 µm. The yield strength and modulus of PCL increased with the inclusion of 10% wool, although the elongation was reduced. The crystallinity of the composites was found to be reduced with wool inclusion, though the melting point of PCL remained mostly unchanged with 10% wool inclusion, indicating better compatibility. Good miscibility and uniform structure were observed with the inclusion of 10% wool, as evidenced by rheology and morphology analysis. The impact of fibre fineness was mostly minor, though wool/PCL composites showed improved thermal stability with finer diameter of wool fibres. The printed specimens exhibited an increasing rate of biodegradation in marine water, which was correlated to the amount of wool present. Overall, the results demonstrate the practical applicability of the wool/PCL composition in MEX for the preparation of varied objects, such as containers, toys and other household and industrial items. Using wool/PCL combinations as regular plastics would provide a significant environmental advantage over the non-degradable polymers that are currently used for these purposes. [ABSTRACT FROM AUTHOR]

3D printing is a popular technique for numerous applications from households to industrial purposes. Commercially available filaments for 3D printing are not eco-friendly, yet energy intensive due to their high extrusion temperature (200–220°C). Polycaprolactone (PCL) is increasingly proposed for 3D printing due to its biocompatibility and lower extrusion temperature, which is more sustainable, though is slow in actual biodegradation. Although PCL-blends are often proposed to promote the degradation, strong hydrophobicity of PCL leads to poor compatibility. This study, for the first time proposes waste wool/PCL filaments for 3D printing using a clean production method, to utilise the hydrophobicity of wool as an advantage with PCL interfaces. Micro-sized wool powders from waste wool fabrics of two fibre fineness (16 and 24 μm) were prepared with minimal in-process waste and then extruded completely with PCL using different ratios (10/90, 20/80 and 25/75 combination of wool/PCL) to produce the composite filaments. A uniform mixing in the composite structure was observed particularly with 10% of wool loading, also the biodegradation rate significantly increased, i.e., from 0.8% to 6.8–10.5% in 3 months. Filaments prepared with 10% and 20% wool showed an increased yield strength, while a finer diameter of initial fibre was found more influential in changing tensile, thermal, and crystalline properties. The reduction in crystallinity was found correlated to the increasing amount of wool, though interlayer spacing of PCL was unaltered and overall thermal stability improved. The filaments were found printable through a 0.4 mm nozzle using a desktop 3D printer at 80 mm/min speed. The findings suggested the possible use of the produced filaments for fabrication of varied products, such as containers for holding or packing, toys, and other common household objects or industrial tools. [Display omitted] • Clean production of Waste wool/Polycaprolactone filaments for 3D printing. • Utilisation of the hydrophobicity of wool as an advantage with PCL matrix. • Tensile strength and biodegradation were improved by wool addition. • Finer fibre was influential in tensile, thermal, and crystalline properties. [ABSTRACT FROM AUTHOR]