Table 2.

A summary of different particle reinforcements into polymer matrices. HDPE—high-density polypropylene; LDPE—low-density polypropylene; β-TCP—beta tricalcium phosphate.

Process	Matrix + Particle	Property Evaluation	Remarks	Ref
DLP	Acrylic based resin + microdiamond powder	The heat transfer rate was improved with 30 wt.% filler (30% of the time required compared to the pure matrix to reach the same temperature when heated), decreased thermal expansion coefficient, and decreased wettability.	More suitable for high temperature applications. High material costs may limit commercial use.	[131]
FDM	ABS + TiO2	Addition of 5 wt.% filler showed ~13.3% improvement in the tensile strength and ~11.6% improvement in the tensile modulus.	A smoother surface finish can be achieved by reducing voids which leads to better and consistent mechanical properties.	[112]
FDM	ABS + stainless steel particles	The tensile strength decreased slightly with the addition of stainless-steel particles. Specific heat increased to ~0.1 J/(g K) from ~0.05 J/(g K) (pure ABS) at constant pressure and at 200 °C.	Finer particles tend to disperse well. Defects and voids become dominant beyond a certain percentage of the particles which results in the decreased mechanical properties.	[121]
FDM	ABS + Al and ZnO2	Failure strain was increased by 80% for ABS/ZnO2 and 108% for ABS/Al.	The addition of metal and metallic powder did not change the melt flow properties significantly.	[130]
FDM	ABS + Cu and Fe	The tensile modulus increased by adding 10 wt.% of Cu (~930.2 MPa) and 30 wt.% of Fe (~978.5 MPa). However, the tensile strength was decreased by adding fillers. The thermal expansion coefficient of the composite with 50 wt.% Cu was decreased by 30% while thermal conductivity increased by 41%.	Strength reduces with the incorporation of fillers in the composite. The addition of Cu in the composite resulted in less distortion in the printed parts.	[132]
FDM	ABS + BaTiO3	Improvement of relative permeability was achieved by 260% at 35 vol.% while a 53% decrease in flexural strength was reported at 30 vol.%.	Inhomogeneous particle distribution may cause premature mechanical failure. Proper adhesion of the printed parts to the bed becomes challenging at higher vol.% of fillers (above 45%).	[133]
FDM	LDPE + Al2O3	The compressive strength was improved by 7%.	Better surface finish and dimensional accuracy can be achieved with Al2O3 addition into the polyethylene matrix.	[122]
FDM	HDPE + fly-ash cenosphere	Density was decreased and the tensile modulus was improved (2.6 times of HDPE filament), but fracture strain was decreased by about 40%.	Better quality of the printed parts can be achieved by optimizing the layer thickness, speed of the printer, print temperature, and cooling condition.	[127,128]
FDM	Nylon + Fe	Thermal conductivity increased by increasing vol.% and particle size of Fe.	The metal fillers form conductive particle chains in the matrix.	[134]
FDM	PA 12 + zirconia and β-TCP	The printed composites with 40 wt.% filler reported a tensile modulus of 995 MPa compared to that of pure PA 12 (~906 MPa). Tensile and flexural strengths decreased with increasing filler content.	Zirconia and β-TCP do not melt with the matrix during printing because of their high melting point. Agglomeration of the filler may cause clogging.	[135]
SLA	Epoxy resin + FeO	Printed parts with a layer thickness of less than 80 µm showed consistent mechanical properties. However, part thickness higher than 100 µm resulted in irregular properties.	SLA is a slow printing process. Therefore, micro particle-sized fillers must remain uniformly dispersed in the matrix for an extended period.	[136]
SLS	PA 11 + glass bead	The tensile modulus was improved with increasing vol.% of glass bead (~900 MPa for 10%, ~1250 MPa for 20%, and ~1750 MPa for 30%). The stiffness increased, but elongation at break was reduced.	The melting depth of the composite in SLS is crucial for successive layer adhesion. Printing settings should be optimized for different vol.% of glass beads.	[137]