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Materials Science in Additive Manufacturing Natural composite filaments for 3D-Print

Figure 6. Detailed outline of the filament fabrication process through the twin-screw extruder device

to offer better features in terms of mixing capabilities, foregoing challenges and for consideration in filament-
temperature control, and throughput efficiency. Some based material in AM, most natural fibers would,
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of the commonly used extruders for filament fabrication therefore require further treatment modification so as to
include the Wellzoom desktop single-screw extruder improve their surface adhesion with the polymer matrix.
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and the HAAKE Mini CTW Micro-Conical Twin Screw Natural fibers are thus subjected to a pre-processing stage
Compounder. 67 consisting of chemical or thermal treatment modifications,
which is an indispensable stage in the fabrication of
As reported in several studies, a filament diameter of
1.75 mm was considered when extruding the biofilament filament material from natural fiber-reinforced polymer
composites. Typical pre-processing stages, which could
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material, which also corresponds to the standard filament have a direct impact on the characteristics and usability of
diameter used in FDM printers. 68,69 Moreover, the 1.75 mm the final filament material, include sieving of fibers, drying,
filament was mainly considered for further investigation and mixing methods. For instance, drying methods and
as reported in previous studies, as they tend to provide surface treatment have been reported to promote good
finer details and better print quality overall. Besides, the adhesion between natural fibers and polymer matrix
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1.75 mm-sized filament, which offers better compatibility in the NFRC mix, thereby enhancing their mechanical
with small-sized nozzles, was found to be less susceptible properties. 73
to breakage given their enhanced flexibility in contrast
to large-diameter filaments. In the fabrication process of To further enhance the properties of natural fiber-
wood flour-PLA filament, a two-stage extrusion process reinforced composite filaments (NFRCFs), additives
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was considered whereby a twin-screw extruder was used are generally considered. Typically used additives for
in the first place for pelleting followed by a single-screw this purpose can be classified in terms of compatibilizer,
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extruder which was used for extrusion molding to generate plasticizer, and toughening agent. The addition of
the 1.75 mm in diameter filament material. In another plasticizer in the composite mix for filament formation, for
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study, a two-stage extrusion process, consisting of a single instance, was found to result in a notable improvement in
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screw and corotating meshing twin-screw extruders, was their interfacial bonding. The inclusion of plasticizer was
also considered in the filament formation involving PLA thus found to improve printing parameters such as layer
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and biodegradable plasticizer. The extrusion temperature adhesion and surface finish. In another study, the addition
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of FDM filaments, which can vary over a wide range of plasticizer to polymeric filament was found to be beneficial
of temperatures ranging between 160°C and 230°C, is to 3D-printed products as it had a positive impact on their
dependent on the properties of the source material from thermal properties and shape stability, hence reducing the
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which the filament is derived. 72 warping effect. In one investigation, the use of glycerol as
a plasticizer in wood flour-PLA filament was found to be
3.1. Pre-processing of fibers and addition of most suited for extrusion processing of composite filaments
plasticizer for filament fabrication as they exhibited a higher melt index. 71
In the AM process, the final strength of printed components Besides their noteworthy contribution to the
largely depends on the characteristics of the filament improvement of printing parameters, the inclusion
material. Similar to the fabrication of conventional natural of plasticizers in NFRCFs was found to significantly
fiber composites, the utilization of natural fibers in the enhance their mechanical characteristics. On the other
fabrication of filament material poses common challenges, hand, another plasticizer, namely tributyl citrate (TBC),
namely incompatibility with the polymer matrix, was found to enhance the mechanical properties, water
susceptibility to moisture absorption, and inhomogeneous absorption, and thermal stability of the wood flour-PLA
distribution of fibers among others. 61,73,74 To address the filament despite resulting in an inferior melt index. In
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Volume 4 Issue 1 (2025) 7 doi: 10.36922/msam.8533