Material Extrusion of Wool Waste/Polycaprolactone with Improved Tensile Strength and Biodegradation

Abstract

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.

Tensile Properties of Natural Fibre-Reinforced FDM Filaments: A Short Review

“…However, even with a 100% infill, a lower strength was seen in the 3D-printed object compared to the respective filament [33]. Only in a series of studies, where filament properties were evaluated first [52], followed by the properties of printed objects with different printing parameters [42], a similar strength was seen in wool-reinforced PCL. This was attributed to the hydrophobic nature of the wool surface, which was claimed to be more compatible with PCL, thus promoting a uniform dispersion of filler in the matrix.…”

“…The extruded material is then lined up as per the pre-program onto a printing bed (base) on a layer-by-layer basis [51]. The printing temperature can be higher than the melting temperature of the thermoplastic to maintain a consistent flow of melts [42]. The printing bed temperature is also adjustable to synchronise the whole process of 3D printing.…”

“…This was attributed to the hydrophobic nature of the wool surface, which was claimed to be more compatible with PCL, thus promoting a uniform dispersion of filler in the matrix. This was noted that during the 3D printing, due to the use of a higher temperature (130 • C) than that of filament preparation (90 • C), the flowability of the polymer-matrix system was improved [42]. This could be a reason for better adhesion in the printed objects as well.…”

“…During 3D printing, a varied range of parameters are used, such as type of infill patterns, percentages of infill, and the variation of design in different layers. All of these influence the density [40], weight, and filament consumption [42]. Therefore, a 3D printed part is perceived as a complex architectural object, compared to a plain composition of filament.…”

Three-Dimensional Printing of Multifunctional Composites: Fabrication, Applications, and Biodegradability Assessment

“…The study was extended to 5 months of seawater testing, during which changes in the prints (dark spots) were visually observed. The changes depended on the amount of wool used and the thickness of its fibers, which may be due to the lower amount of cuticle in thicker wool, which is more susceptible to degradation [194]. The seawater tests have been extended to include biodegradation tests in a compost environment (for filaments).…”