Table 1.

A summary of different fiber reinforcements into polymer matrices using FDM. ABS—acrylonitrile butadiene styrene; CF—carbon fiber; GF—glass fiber; PA—polyamides; PEEK—polyetheretherketone; PLA—polylactic acid; PP—polypropylene.

Matrix + Fibers	Property Evaluation	Remarks	Ref
ABS + CF	Composite with higher fiber length (150 µm) showed better tensile properties. 5 wt.% to 7.5 wt.% of fiber content in the composite had the highest tensile strength of around 43 MPa.	The mechanical properties of the final parts can be achieved at an optimum nozzle temperature of the extruder (~220 °C).	[100]
ABS + short GF	Improvement in tensile strength (~58.60 MPa) at the expense of flexibility and handleability.	The addition of plasticizer and compatibilizer recovered flexibility and handleability to some extent.	[101]
PLA + continuous CF	Around 200% and 370% increase in tensile and bending modulus, respectively.	Continuous CF reduces strain at failure. Annealing can increase the crystalline behavior of the composite.	[96,102]
PLA + CF	Improvement of tensile strength by 225% (28 MPa for pure PLA, 80 MPa for CF + PLA, and 91 MPa for modified CF + PLA) and flexural strength increased by 194% (53 MPa for pure PLA, 59 MPa for CF + PLA, and 156 MPa for modified CF + PLA).	The use of a coupling agent (methylene diacrylate) improves the adhesion between the fiber and the matrix.	[103]
PA 12 + CF	277.8% improvement of thermal conductivity of the composite was reported compared to pure PA 12.	The addition of CF increases the Melt Viscosity Index thus reducing the flowability leading to clogging in the extruder.	[104]
PEEK + CF	Improvement in tensile strength from 95 MPa to 101 MPa and modulus from 3.79 GPa to 7.37 GPa. Bending and compressive properties were also improved.	PEEK-GF composite showed comparable mechanical properties with human cortical bones. Surface roughness is ideal for biocompatibility, cell adhesion, and spreading.	[105]
PP + GF	0° filament orientation showed the highest modulus (~1.23 GPa) and strength (~35 MPa). However, the addition of GF resulted in a decreased melt flow rate.	Higher printing temperatures can rescue the reduced melt flow rate. However, the higher printing temperature may lead to distortion and shrinkage of the printed parts.	[106]
PP + short GF	Tensile modulus was improved (~400 MPa compared to pure PP ~75 MPa). Lower flexibility and elongation at break were observed.	GF reduced the shrinkage significantly. First layer adhesion and distortion of parts can be addressed by using GF.	[107]
Nylon + CF, GF, Kevlar fiber	Increased tensile strength (6.3 folds) and flexural strength (5 folds). However, the creep properties decreased.	Fibers were not embedded in the filament but printed as layers in between the Nylon layers in the parts. CF reinforced Nylon composite showed the highest improvements in the tensile strength.	[108,109]
Nylon + CF, GF, and Kevlar fiber	For any given infill pattern, progressively higher fiber volume fraction resulted in higher fatigue life. 0° orientation of isotropic infill pattern resulted in the highest fatigue life.	The 0° fiber orientation leads to high stiffness. The 45° fiber orientation makes the parts ductile. The loads are carried by the matrix only when the fiber orientation is set at 90°.	[110,111]
ABS + jute fiber	The tensile modulus was increased by 1% in horizontal printing direction and decreased by 25% in vertical printing direction with the addition of 5 wt.% jute fiber. Tensile strength decreased around 9% in both directions.	Jute fibers introduced more porosity in the filament. Decomposition of jute is observed during extrusion because of high temperature.	[112]
PLA + flax and bamboo fibers	High length to width ratio (l/d) of the fibers leads to increased stiffness (up to 215%).	The rotational speed of the filament extruder influences the l/d of the fibers in the filament. A higher l/d ratio of fibers in the filament makes the surface rough.	[113]
PLA + jute yarn	Improvement in tensile modulus and strength were observed by ~157% and ~134%, respectively.	Impregnation of fibers into filaments during extrusion resulted in continuous fiber orientation.	[114]
PLA + wood	The density of the printed composite decreased. However, the tensile strength did not change significantly.	The addition of a very high percentage of wood makes the surface rough.	[115,116]
PP + hemp and harakeke fibers	Tensile modulus and strength increased with the increase of hemp and harakeke fibers within the filaments.	With the increasing fiber content, the net shrinkage is reduced.	[117]
PP + bamboo fibers	Less than 500 µm sized fibers demonstrated the highest tensile strength (15 MPa for 50 wt.% fiber).	Bamboo reinforced PP composites are lightweight and water resistant.	[118]