KONA Powder and Particle Journal No. 41 (2024) 26–41/https://doi.org/10.14356/kona.2024012

Review Paper

Role of Powder Properties and Flowability in Polymer Selective
Laser Sintering—A Review †Xi Guo and Brij M. Moudgil *Department of Materials Science and Engineering, Center for Particulate and Surfactant Systems (CPaSS), University of Florida, USA

Polymer selective laser sintering (SLS) is an additive manufacturing
Final Part Properties
technology that involves the melting of a selected area of particles on
High Porosity
Low Porosity
the powder bed. A 3D component is then printed using layer-by-layer
sintering of the powder bed. SLS is considered one of the mostpromising technologies applicable to a variety of applications,
Powder Flowability
particularly for manufacturing customized design products with highPolymer melt
Polymer melt
geometric complexity, such as patient-specific designed implants,
Low Flowability
High Flowability
surgical tools. Currently, only a small number of polymers are available
that are suitable for SLS due to the complex multiple physicalInterparticle Forces
phenomena involved. Therefore, it is critical to develop new materials
in order to fully realize the potential of SLS technology for
manufacturing value-added customized products. For a given material,
Particle Properties
the quality of powder spreading in SLS plays a key role in printing
performance and is a precondition for new material development. The
aim of this review is to (1) present flowability characterization methods
suitable for SLS, (2) examine the influence of powder properties and flowability on laser–material interaction and the quality of the final
part, and (3) discuss the methods adopted in the literature to improve the quality of powder spreading.
Keywords: polymer selective laser sintering, powder property, flowability, powder packing

1. Introduction

Additive manufacturing (AM) is a group of solid
freeform fabrication methods used to build 3D objects
layer by layer based on computer-aided design files. The
layer-by-layer building process, which is the opposite of
traditional subtractive manufacturing, enables additive
manufacturing to create highly complex structures. AM
was introduced in the late 1980s (Ligon et al., 2017), primarily for building complex structure prototypes. With thedevelopment of technology, AM nowadays is capable ofbuilding products with various materials (polymers, metals, ceramics), processing desired properties and shapes.
The fundamental principle of AM process is to form
parts by joining materials together. In polymer additive
manufacturing, this is achieved through thermal reaction or
chemical reaction, or both. Current processes in polymer
AM include material extrusion, material jetting, powder
bed fusion, binder jetting, vat photopolymerization, andsheet lamination (ISO/ASTM, 2021). In selective laser
sintering (SLS), a laser is used to selectively melt or fuseparticles in the powder bed, layer by layer. SLS is one of
†

*

26

Received 25 July 2022; Accepted 22 September 2022
J-STAGE Advance published online 29 July 2023
Corresponding author: Brij M. Moudgil;
Add: Gainesville, FL 32611, USA
E-mail: bmoudgil@perc.ufl.edu
TEL: +1-352-846-1194 Fax: +1-352-846-1196

the most widely used AM technologies due to its high levelof accuracy, high productivity in manufacturing complex
structures, and good mechanical properties (Kruth et al.,
1998; Lupone et al., 2022).
To address the unmet needs in various industries, researchers have investigated the processability of several
polymers including Polyamides (PA) (Beitz et al., 2019;
Benedetti et al., 2019; Berretta et al., 2014; Drummer et al.,2010; Soe, 2012; Starr et al., 2011; Vasquez et al., 2011,2014), Polypropylene (Ituarte et al., 2018; Kleijnen et al.,2016, 2017; Tan et al., 2021; Wegner, 2016; Zhu et al.,2016), Polyetheretherketone (PEEK) (Benedetti et al.,2019; Berretta et al., 2014, 2016), Polyethylene (Drummer
et al., 2010), Polyoxymethylene (Drummer et al., 2010),
Poly-butylene terephthalate (Schmidt et al., 2016), Polyε-caprolactone (Williams et al., 2005), Polystyrene (Yan etal., 2011), Thermoplastic polyurethanes (Dadbakhsh et al.,2016; Vasquez et al., 2014; Verbelen et al., 2017; Yuan etal., 2017), Thermoplastic elastomers (Vasquez et al., 2014),
etc. However, it is worth noting that the SLS process currently has a limited number of commercially available
polymers. PA-related materials account for over 95 % of
the market (Goodridge and Ziegelmeier, 2017; Stansbury
and Idacavage, 2016). Semi-crystalline polymers such as
Polyamide 12 (PA12) are the material of choice in SLS for
the following reasons, (1) sharp melting peak to ensure
homogeneous melting, (2) large melting temperature (Tm)

Copyright © 2024 The Authors. Published by Hosokawa Powder Technology Foundation. This is an open
access article under the CC BY license (https://creativecommons.org/licenses/by/4.0/).

Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41

to degradation temperature (Td) window to enable fullmelting, (3) a rapid viscosity drop once the crystalline region disappears enabling rapid particle coalescence(Drummer et al., 2010). The limited material option is a
result of the high powder production cost, lower final partmechanical properties, and dimensional accuracy compared to the traditional manufacturing processes.
The physical phenomena involved in SLS include particle spreading and deposition, laser material interaction,polymer melting and coalescence, and polymer crystallization. Each phenomenon spans different time scales and has
a significant impact on the final product properties(Bierwisch et al., 2021; Lupone et al., 2022). An in-depth
understanding of these phenomena is the key to improving
the final part properties and expanding the suitability ofcommercial powders for SLS applications.
A SLS process schematic and a process temperature
profile are depicted in Fig. 1. The process temperature
profile is embedded in a semi-crystalline polymer differential scanning calorimetry (DSC) graph to provide a better
understanding of polymer heating and cooling behavior
during SLS.
The SLS process initiates with a preheating step. An inert gas is continuously purged into the printing chamberfrom this step and throughout the entire printing process.
As shown in Fig. 1 diagram A, the polymer powder on the
powder bed is preheated to a temperature below the polymer’s Tm. This temperature is defined as the printing temperature. The preheating step holds significant importancefor several reasons: (1) it stabilizes the temperature of theentire instrument, (2) it minimizes the energy required for
melting the polymer in the target area, (3) it reduces thetemperature gradient between the melt area and the chamber air to prevent curling (Soe, 2012). It should be notedthat during the preheating stage, since the bed temperature

Review Paperis close to the onset of melting temperature, the unmelted
powder may undergo physical and chemical changes after
printing (Goodridge et al., 2010; Kuehnlein et al., 2010)
and could reduce its reusability. The thermal properties andflowability of the polymer play essential roles in the preheating phase (Berretta et al., 2014; Drummer et al., 2010;
Tan et al., 2021; Verbelen et al., 2017).
The second phase is laser scanning (B in Fig. 1). Laser
scanning of the target area starts once the preheating temperature is stabilized. CO2 laser (10600 nm wavelength) is
the most common laser used in polymer SLS systems because of its high absorptance and low penetration depth in
the polymer (Jones, 2013). When the polymer molecular
structure interacts with the laser beam, which typically hasa size of 500 μm for a CO2 laser, heat is generated due tothe vibration of the polymer’s molecular structure. The
generated heat raises the temperature above the melting
point, but below the Td, as illustrated by point 2 in Fig. 1.
Upon heating, the polymer particles melt, resulting in viscous flow and coalescence. After laser scanning, the molten
area rapidly cools down to the printing temperature (point
3 in Fig. 1) (Greiner et al., 2019). Once the layer scanningis completed, the printing bed will move down one layer
and a new layer of powder is deposited on the printing bed
by a blade or roller. The laser scanning step is repeateduntil the designed part is fully printed (C in Fig. 1). During
the preheating phase as well as the later phases where there
is no polymer melting involved, powder deposition is primarily governed by powder–powder interactions (A1 in
Fig. 1). During the scanning phase, where there is polymer
melt on the top layer, powder deposition is mainly governed by powder–polymer melt interactions (B1 in Fig. 1).
Polymer flowability, optical properties, thermal properties,
and rheology are the main factors that impact the laser
scanning phase (Kruth et al., 2007; Laumer et al., 2016a;

Laser Beam

1

2

A

B

4

C

A1

Recoating Blade

Recoating Blade

B1

Heat Flow

Roller

3

4

1

2

D
3
Recoating on powder surface

Polymer melt

Recoating on melt surface

Fig. 1

Temperature

Polymer SLS process schematic.

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Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41

Verbelen et al., 2016, 2017; Vock et al., 2019a; Wudy et al.,2015).
After the completion of a printing job, the entire machine, including the printed parts, undergoes a gradualcooling process until it reaches room temperature. The
slow cooling process allows the polymer chains to form acrystalline structure (point 4 in Fig. 1). Polymer crystallization plays an essential role in this step (Drummer et al.,2019; Goodridge and Ziegelmeier, 2017; Verbelen et al.,2016).
Fig. 2 illustrates the interplay between operational parameters of the SLS process, particle properties and material properties. Powder properties such as size, shape, size
distribution, and surface roughness, not only determine its
flowability but also affect the thermal and optical propertiesof the powder bed (Bierwisch et al., 2021; Myers et al.,2015).
An in-depth understanding of powder flowability is essential for designing a successful SLS material and productdevelopment scheme. However, due to the specific spreading mechanism involved in SLS, it is challenging to directly apply existing knowledge from traditional particle
science research to SLS systems. The present review aims
to provide an overview of the role of powder properties,
particle deposition, and flowability characteristics in designing a successful SLS system. Experimental analysis,
characterization methods, and computational modeling arereviewed to provide the current state of polymer powderresearch. Although it is challenging to establish comprehensive quantitative correlations between powder properties, powder deposition, process parameters, and final partproperties, the review strives to enhance the understanding

Review Paperof the factors that influence the SLS powder deposition
process and ultimately establish the sciencebased guidelines for new material development rather than
the trial-and-error approaches currently practiced.

2. Flowability overview

In SLS, the powder bed packing density is directly
linked to the achievable part density (Schmid et al., 2015).
Despite some applications where porous parts are desired(Yan et al., 2017), the main objective of powder depositionin SLS is to transfer the powder from a feed container to theprinting bed to form a homogenous and densely packed
layer. Therefore, a good flowing powder is a necessary
condition to constitute a suitable SLS material. Powder
flow properties and flowability are commonly used to evaluate the suitability of a powder for SLS. Additionally, thenewly deposited powder layer should exhibit uniform
thickness. According to Prescott et al. (2000), powder flow
properties are specific bulk characteristics and can be measured. Powder flow properties depend on the particle size
distribution, particle shape, surface morphology, density,
electrostatic charge, and environmental factors such astemperature and humidity. Powder flowability, on the other
hand, refers to the ability of a powder to flow in a desiredmanner in a specific piece of equipment (Prescott andBarnum, 2000), and depends on powder flow properties,
underlying surface layer morphology and spreading (recoating) mechanism. During recoating on top of the polymer melt scenario, the melt viscosity and surface tension of
the molten layer also impact the powder flowability.
From the force perspective, the flowability of SLS powder is influenced by inter-particle forces and external forces

Final Part Properties
Laser Parameters
Temperature
Layer Thickness

SLS Flowability

Layer Deposition

Rheological
Properties

Interparticle Force /Process Conditions
Temperature Layer Thickness
Humidity
Recoating Strategy
Gas flow

Powder
Properties

Particle Size Distribution
Shape
DensitySurface morphology

Fig. 2

28

Strength
Dimension
Porosity

Printing Parameters

Rheological
Properties

ThermalProperties

OpticalProperties

Melt Viscosity
Surface Tension

Heat Capacity
Conductivity
Latent Heat

Reflectance
AbsorptanceTransmittanceChemical Properties
Chemical Structure
Molecular Weight
Crystallization
Kinetics

Graphical representation of the relationships between material properties, printing parameters and final part properties.

Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41

Review Paper

2.1 Flowability characterization

due to mechanical interlocking and layer recoating. Van der
Waals force, electrostatic force, liquid bridge formation(capillary force), and gravity are the main inter-particle
forces between spherical particles (Suzuki, 2019). The vander Waals forces are based on electric dipoles of atoms andmolecules. Their magnitude depends on particle size, distance and surface characteristics/morphology (Schulze etal., 2008). Liquid bridge force is formed by the surface
tension of the liquid between particles. Considering that theprinting temperature of the majority of SLS semicrystalline polymers is above 100 °C and inert gas is commonly used, the liquid bridge force can be neglected.
Electrostatic forces are generated by different electric potentials of particle surfaces (Schulze et al., 2008). Triboelectric charging of polymer powder occurs when thepolymer particles come into contact with materials of different dielectric constants (e.g., a metal component)(Tanoue et al., 1999). Due to their low conductivity, it iscommon practice to allow polymer powder to remain undisturbed for at least 12 hours before printing to reduce/
dissipate any electrostatic charge generated during powder
preparation. However, triboelectric charging during powder deposition is inevitable. Although the charge build-up
between particles improves powder spreading by reducing
the attractive van der Waals force and liquid bridge forces,
it leads to low packing density (Hesse et al., 2019). Understanding the relationships between these different forces iscritical to explaining some of the flowability issues encountered in SLS.

During the material development stage, powder flowability needs to be characterized and optimized before
printing. Although the flowability characterization may not
represent the powder flow conditions in the SLS process
because of the different force and flow mechanisms employed, it can still provide a good indication of the powder
flow behavior. Table 1 gives an overview of the flowability
characterization methods that have been used in polymer
SLS research.

2.2 Flowability measurement techniques

The two most used methods are the angle of repose andHausner ratio measurement techniques. Although different
setups can be used to measure the angle of repose(Schwedes, 2003), the static angle of repose is widely used
in SLS (Berretta et al., 2014; Montón Zarazaga et al., 2022;
Tan et al., 2017). In the static angle of repose measurements, powder freely flows through a funnel onto a plate.
The angle between the developed pile and the plate is defined as angle of repose (Spierings et al., 2016). A small
angle of repose represents good flowability. The Hausnerratio is defined as the ratio between the tapped and loosebulk density of the powder. It describes powder compressibility and flowability. Geldart et al. (2006) found a linear
relationship between angle of repose and Hausner ratio.
Although being widely used in SLS (Arai et al., 2017,2019; Chatham et al., 2019; Schmid et al., 2013; Wegner,
2021; Ziegelmeier et al., 2015), the Hausner ratio wasfound to be inaccurate in predicting the flowability ofhigh-density polyethylene composite and polypropylene

Methods

Table 1 list of powder flowability characterization methods in polymer SLS.

Angle ofrepose(ASTM
D6393)

Hausner ratio(ASTM D748109) / Carr index(ASTM D6393)

Shear cell
(ASTM
D6773)

TensiletesterPowder rheometer (ASTM
D7891)

Revolution powder
analyzer

Modified film applicator

References

Parameters

camera▪Angle ofrepose▪ Hausner ratio▪ Carr index (C)- loose bulk
density- tapped bulk
density▪ Shearforce▪ Yield loci

▪ Adhesionforce▪ Basic flowability energy▪ Specific energy▪ Conditioned
bulk density▪ Avalanche angle▪ Surface fractal
volume▪ Expansion ratio▪ Degree of coverage▪ Packing density▪ Packing ratio(Berretta etal., 2014;
MontónZarazaga etal., 2022;
Tan et al.,2017)

(Arai et al., 2017, (Ruggi et
2019; Chatham et al., 2020a,al., 2019; Schmid 2020b)
et al., 2013, 2019;
Wegner, 2021;
Ziegelmeier etal., 2015)(Schmidt etal., 2014)(Ziegelmeier etal., 2013, 2015)(Amado et al., 2011;
Amado Becker, 2016;
Chatham et al., 2019;
Sassaman et al.,2022)

(Laumer et al., 2016b;
Van den Eynde et al.,2015; Van den Eynde
et al., 2017; Verbelen
et al., 2016)

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Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41

Review Paperof the most important indices of the rotating powder. The
flow of powder in this method is considered closer to SLS
process conditions than the other techniques (Spierings etal., 2016). The high temperature measurement capability ofthis method can provide more insights into powder flow
behaviors under SLS temperature conditions (Amado
Tapped Bulk Density  Loose Bulk Density
Carr Compressibility
100
Becker,2016).
Tapped Bulk Density
To provide a direct assessment of the powder flowability,(1)
Tapped Bulk Density  Loose Bulk Density
Carr Compressibility
100some researchers modified a film applicator into a powder
Tapped Bulk Density
spreader with a similar powder spreading mechanism as in
SLS (Laumer et al., 2016b; Verbelen et al., 2016; Van den
In addition to the Carr Compressibility, the measurement
Eynde et al., 2015). A basic powder spreader enables visualof (1)
Carr Angle of Repose is also described in the ASTM
observation of the spreading condition. Van den Eynde et
D6393 (2021) to test the flowability and floodability ofal. (2015) set up a powder bed plate on a balance so thatbulk
solidsusing
Carr
Indicesmethod.
1)
layer weight and packing density could be measured in situ
Tensile strength can also be used to measure SLS powto assess powder flowability. Furthermore, a powder
der flowability (Schmidt et al., 2014). This method requires
spreader with high-temperature capability (up to 140 °C)
a tensile tester and a smooth loose powder bed. The tensile
testing head is coated with jelly. The test starts with thewas developed (Van den Eynde et al., 2017). This modificatesting head in contact with the powder surface, the firsttion not only facilitated the characterization of powder forlayer of the powder in the container adheres to the jellyrecoating purposes but also allowed for the evaluation ofcoated testing head. When the powder container moves
melt surface recoating for low melting temperature polydownward, the force between the stamped powder layer
mers.
and the remaining powder is measured. The measured force
is a combination of gravity and adhesion force between the
2.3 Comparative features of various techniques
powder particles. This method provides a good insight into
With the availability of various characterization meththe fundamental interparticle force relationship. However,ods, it is important to understand their relationships, advantages, disadvantages, and differences. Ziegelmeier et al.
it is limited in indicating a suitable powder flow behavior.
(2013) compared cohesion, flowability and packing effiShear testers are commonly used to evaluate the powder
ciency of polymer powders with different characterization
flowability under well-defined shear conditions. Powder
methods—rotational revolution powder analyzer, powder
rheological properties like cohesive strength and wall fricrheometer and the Hausner Ratio technique. Different partion under shear can be measured in a shear tester to repreticle size distributions of a cryogenically ground polyuresent flowability. Ruggi et al. (2020a, 2020b) characterizedthane powder and standard PA12 were used to study the
SLS polymers with a modified high-temperature ring shear
effect of both particle size distributions and particle shape.
tester. Among different types of shear testers, ring shear
The revolution powder analyzer showed the best reproductesters not only provide homogeneous shear displacementible and reliable results under all experimental conditions(Schulze et al., 2008), but they also have the capability of
examined.
low normal stress measurements (Vock et al., 2019b). Although the force conditions in ring shear testers are closer
Krantz et al. (2009) investigated the relationship beto SLS printing conditions compared to other shear testers,
tween different characterization techniques using two difthe flow mechanism of the shear tester is different from thatferent formulations of powders with particle sizes ranging
encountered in SLS (Schmidt et al., 2019). Another characbetween 22 to 31 μm. Characterization methods included
terization method involving shear stress is the powder rheangle of repose, powder rheometer and revolution powderometer. It measures the resistance of a powder to flow
analyzer. A linear relationship between angle of repose andagainst an upward or downward rotating helix under differavalanche angle was discovered regardless of powder forent consolidation conditions. Under specific consolidation
mulation. This is because both techniques involve similarand shear conditions, the powder rheometer and shear cellforce conditions. Additionally, a linear relationship wasdata correlate well with each other (Freeman, 2007).
discovered between angle of repose and cohesion (powder
More recently, the rotational revolution powder analyzer
rheometer characterization index) for individual powder
has become more popular (Amado et al., 2011; Amado
types. However, the trend line for different powders did not
Becker, 2016; Chatham et al., 2019; Sassaman et al., 2022).
overlap because of the different forces encountered in the
It consists of a transparent rotating drum and a camera that
two techniques. The authors concluded that matching therecords the powder flow conditions in the drum. The
measured and process force conditions is critical for reliAvalanche angle, which is the maximum angle of the powable flowability characterization. Furthermore, they emder surface before an avalanche occurs, is considered one
phasized that utilizing multiple characterization techniques
composite materials (Laumer et al., 2016b). Anothermethod that is similar to Hausner ratio but less common in
SLS is the Carr index(C) (Schmid et al., 2019), which is theCarr Compressibility as referenced in ASTM D6393(2021) and can be expressed as,30

Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41

provides a more comprehensive understanding of powder
flowability compared to relying on a single techniquealone.
The above discussion highlights that each flowability
characterization technique focuses on examining powder
flowability from a specific perspective related to a particular flow mechanism. The modified film applicator simulates the SLS flow behavior; however, the setup is noteasily accessible. Therefore, it is important to obtain a better understanding of powder flowability by applying multiple flowability characterization techniques during the newmaterial development.

3. Role of powder properties

3.1 Particle size distribution (PSD)

To achieve high surface quality and printing accuracy,
smaller particle sizes are theoretically preferred. However,for fine powders, van der Waals forces are significantly
greater than gravity which causes powder agglomeration
issues leading to nonuniformity of layer thickness, andparticle packing inhomogeneity during flow (Krantz et al.,2009). While polydisperse powders can benefit particle
packing in free flow conditions (McGEARY, 1961), it isoften limited by polymer powder production methods.
From the laser material interactions perspective, a narrow
PSD is preferred to obtain homogeneous melting (Berretta
et al., 2014; Wegner, 2021). With the above considerations,a particle size range of 45 to 90 μm is usually preferred(Goodridge and Ziegelmeier, 2017), although some authors
have reported this range to be from 20 to 80 μm (Schmid etal., 2015; Vock et al., 2019b).
Beitz et al. (2019) sieved PA12 into three grades: PA12
Coarse (D50 = 56.80 μm), PA12 Original (D50 = 51.14 μm)
and PA12 Fine (D50 = 46.03 μm). All grades had an identical level of PSD span, which is defined as (D90 − D10)/D50.
The powders were characterized by Hausner ratio and used
for laser printing under the same conditions. The threegrades of PA12 showed no difference in either flowability
or surface roughness of the printed parts. However, it isimportant to note that this conclusion should be consideredvalid only within the particle size range examined in thisstudy. A larger difference in D50 could lead to different results.
As part of a flowability study by Van den Eynde et al.
(2015), standard PA12 powder with a mass-median diameter of 59 μm was compared with a smaller average particle
size PA12 (around 42 μm). The PSD span of standard PA12
(0.84) was higher than the smaller PA12 (0.58). A customized powder spreader setup that simulated the SLS spreading process was used to characterize flowability. The
smaller PA12 showed lower packing density. Compared to
the results from Beitz et al., it is inferred that the span of
PSD plays a vital role in flowability; with a similar PA12
particle size in both studies, a smaller span could result in

Review Paper

lower packing density.
It is noteworthy that the effect of PSD span has also beenreported in a review primarily focusing on ceramic andmetal powders (Vock et al., 2019b). With increasing PSD
span, the printed part density and surface quality increased,
but the mechanical properties decreased. This indicates thata higher PSD span improves particle packing and part
density, however, it can lead to inhomogeneous melting
and reduced mechanical properties. However, in a comparison between two commercially available PA12 powders,Schmid et al. (2017) suggested that powder with a smaller
span exhibits better flowability and high packing density.
Even though the different inter-particle forces could lead to
opposite results, more systematic studies are needed to
improve the understanding of the flow mechanism during
the polymer SLS process.
Multiple studies have been conducted to identify a suitable PSD for SLS. Ziegelmeier et al. (2015) compared theflowability and printability of thermoplastic polyurethane(TPU) and thermoplastic elastomer Duraform Flex (DF).
Except for the original particle size fraction, two additional
fractions were obtained by sieving out particles below
25 μm or 45 μm. The overall packing density, flowability,
printed part surface roughness, ultimate tensile strengthand the elongation at break were found to be higher with adecreasing number of fine particles. It was concluded thatthe gravitational forces increase with particle size, resulting
in reduced cohesiveness and improved flowability. Similarly, Schmid et al. (2015) compared two powders withsimilar volume distribution but different number distribution. The powder with a significant number of small particles (below 20 μm) failed the processability testing due toa higher ratio of cohesion to gravity forces.
On the contrary, other researchers reported the benefitsof small particles for powder flow. Verbelen et al. (2016)
compared PA6, PA11 and PA12 from different manufacturers with PA11 consisting of rough particles with sharpedges and a large fraction of smaller particles(D10 = 20.6 μm). Surprisingly, the rough PA11 had a higher
packing density. One of the reasons the authors concluded
was that the large fraction of smaller particles allowed
more efficient packing at the given layer thickness. Although no quantified values were reported, this study alongwith the previous two studies emphasized that a smaller
number of fine particles in the distribution promotes powder flow possibly due to the ball bearing effect, while anexcess number of fine particles hinders flow due to agglomeration.
It should be noted that the PSD directly impacts the SLS
printing results by changing the powder bed packing density. Indirectly, PSD changes the thermal and optical properties of the powder bed. The powder thermal conductivity
is significantly lower than the bulk because of the high porosity of powder beds (Gong et al., 2013). Sillani et al.

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reported a positive linear relationship between packing
density and thermal conductivity for several SLS polymer
powders (Sillani et al., 2021). The porosity also changes
powder optical properties which in turn affects the amountof heat energy generated by laser–material interaction. In
an infrared spectroscopy study, quantitative infrared directional–hemispherical reflectance spectra were obtained using a commercial integrating sphere (Myers et al., 2015).
The results suggested that the optical reflectivity drops withincreased particle size for most wavelengths. With a higher
optical reflectivity, higher laser energy is needed to compensate for the energy loss. Overall, the change of powder
optical reflectivity and thermal conductivity resulting fromthe PSD should be considered when selecting the laser
power and laser scanning rate for a given material.

3.2 The impact of Particle morphology

In free-flowing particle packing, particles with highroundness and low roughness exhibit reduced mechanicalinterlocking and increased packing density (German, 1989;
Hettiarachchi and Mampearachchi, 2020). Thus, particle
morphology is important for the SLS process as well
(Schmid et al., 2014; Van den Eynde et al., 2015; Verbelen
et al., 2016).
In the spreading study conducted by Van den Eynde et al.
(2015), medium roundness standard PA12, medium roundness PA12 with smoother edges, high roundness monodisperse Polystyrene (PS) and low roundness TPU werecompared with a customized powder spreader. The highroundness PS exhibited the highest packing density andlayer smoothness. Smoother edge PA12 had a higher packing density than the standard PA12. The low roundness
TPU had the lowest packing density and resulted in incomplete layers. Accordingly, the high roundness and low
roughness were emphasized as the optimal particle morphology conditions for SLS.
However, the high roundness and low roughness particles are not always available for SLS due to the limitationof polymer powder production methods. The current commercially available SLS powder is produced by three main
methods: co-extrusion of two non-compatible polymers,
precipitation of polymer solutions and cryogenic milling oflarge polymer granules. Co-extrusion methods produce
spherical and smoother particles. However, only limited
polymers can be produced by this method, one example is
Polypropylene from IRPD AG. The most popular potato
shape PA12 powders, such as PA2200 from EOS GmbH, isproduced by the precipitation method. Cryogenic milling
can process a wide range of polymers by milling below
glass transition temperatures. However, milled particles
result in irregular shapes and rough surfaces due to therandom mechanical force application during the size reduction process. Cryogenic milling also generates a large
amount of fine particles which reduces the powder flow-

32

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spherical particles

potato shape particles cryogenic milled particles

Fig. 3 Typical SLS powder particle shapes (Reprinted with permission
from AIP Conference Proceedings “open access”, Schmid et al., 2015).

aerosol inflow

N2
sintered
metal platesheath air
outletaerosol
outletheatingzones

Fig. 4 Schematic drawing of downer reactor (Reprinted with permission from Procedia Engineering “open access”, Sachs et al., 2015).

ability (Schmid et al., 2014). Some typical SLS powder
particle shapes are shown in Fig. 3.
In addition to the commercially available methods, multiple techniques have been developed in the literature to
improve flowability by generating high-roundness particles.
Berretta et al. (2014) found that virgin PEEK particles
did not yield a smooth powder bed during powder deposition. The powder was annealed at a temperature above its
glass transition temperature for 24 hours in an airventilated oven, left to cool down naturally and sieved. The
thermal treatment improved particle roundness and flowability significantly, ultimately enabling a smooth spreading within the printing system.
Downer reactor as shown in Fig. 4, which utilizes theeffect of the surface tension of the molten polymer, is commonly used to smooth irregular polymer particles (Sachs etal., 2015). Schmidt et al. (2014; 2016) demonstrated the

Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41

rounding process of polystyrene (PS) and polybutylene
terephthalate (PBT) powder and introduced a procedure to
generate spherical particles for SLS. The polymer microparticles were produced by wet grinding first. Then theparticle roundness was improved by passing them in aheated downer reactor. Finally, hydrophobic fumed silica
was mixed with the polymer powder to further improve theflowability by reducing the interparticle van der Waals
forces.

4. The impact of processing conditions

During layer deposition, factors such as layer thickness,spreading speed, spreading tool, and temperature are someof the important operational parameters that affect SLS
process performance. The impact of these process conditions has also been reported in the literature.

4.1 Layer thickness

For given powder flow characteristics, the desired printing layer thickness depends on different product requirements. A smaller layer thickness is desired to improve
printing resolution, but it is limited by the particle size
discussed in the previous section. On the other hand, alarger layer thickness reduces printing time. The decreased
printing time improves manufacturing efficiency and reduces overall cost. In general, the layer thickness in polymer SLS ranges from 80 to 150 μm. During the depositionof the subsequent layer, melting of the previous layer
causes shrinkage in the bed thickness. New powder needs
to form a smooth layer on top of the sintered bed. Static anddynamic wall effects are the other main mechanisms ofvoids formation during the sintering process (Chen et al.,2019). The static wall voids in SLS occur among particles,
printing bed and spreading tool due to the round shape of
the particles. On the other hand, dynamic wall voids arecaused by the arches formed between particles during the
spreading motion. In the scenario where particle size andshape cannot be modified to improve packing, increasing
the layer thickness can improve the packing density by reducing both the static and dynamic wall effects. Dechet etal. (2020) utilized a layer thickness of 1.5 times the D90,
corresponding to around 300 μm, in PLLA development.
Although this significantly thicker layer provided promising flowability, it compromised the printing resolution.

4.2 Spreading blade/roller

Blade and roller (counter-rotating with respect to theadvancement direction) are the most common powderspreading tools in SLS systems. The design and movementof the spreading tool also affect the powder packing condition.
Beitz et al. (2019) compared three blade geometries in
PA12 printing, including flat, round and sharp bottom. The
flat bottom blade shape resulted in the most uniform andReview Paper

dense powder bed due to the larger horizontal contact zone
between the blade and the powder bed.
Haeri et al. (2017) simulated the spreading tool and its
speed using discrete element simulation and validated thepredicted values with experimental results. The use of aroller produced better bed quality compared to the flat bottom blade because of the adequate contact of a roller, which
prevented particle dragging. It was also found that thelower roller translational speed produced better powder
bed quality compared to a higher speed. It should be notedthat non-spherical (rod-shaped) particles were used in thiswork which might not represent the spreading conditions ofspherical or potato shape particles.
Drummer et al. (2015) investigated the effect of spreading speed with both blade and roller systems. The reproducibility of three spreading speeds (125 mm/s, 250 mm/s,
500 mm/s) was analyzed. An optimal spreading speed of
250 mm/s was found independent of spreading tools. The
optimal speed was based on the curling phenomenon due tothe temperature gradient after laser scanning as shown in
Fig. 5. With a low speed, the long roller and molten areainteraction time led to significant cooling of the molten
area. Consequently, curling got worse and the warped layer
became stuck to the roller and failed to print. With highspeed, the varying compression force could shift theslightly curled section and fail the print.
Niino and Sato (2009) proposed a powder compaction
method by using a two-steps roller spreading technique asshown in Fig. 6. Compaction was carried out by using aroller of whose rotation speed was controlled independentof its traversing speed. After a traditional roller spreading
and layer formation, the powder bed moved up and an additional roller spreading step using the same roller was applied to compact the powder bed. This additional process
improved the packing density of the powder bed by a factorof 20 % and reduced residual porosity by 30 %.

V<

Fig. 5

V=

opt

opt

V>

opt

The effect of powder recoating speed on molten areas.

Fig. 6

Powder bed compacting step.

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Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41

4.3 Other in-process factors

In addition to the powder properties and layer spreadingmechanisms, there are other factors in the printing processthat also affect powder flowability. One of the most crucial
factors is the elevated temperature during the SLS process.
The effect of elevated temperature on the flowability isthreefold. (1) The polymer particles become softer thereby
introducing additional forces by changing contact area andfriction between particles during powder flow. (2) Humidity induces cohesive forces between the particles andstrongly affects the flow of powders (Rescaglio et al.,2017). For the polymer with a melting temperature above
100 °C, the moisture in the powder evaporates during printing and liquid bridge force gets minimized. Both changes
under the elevated temperature cannot be captured with themost powder flowability measurements. (3) The extended
long time under elevated temperatures causes changes in
the properties of unused powder, which affects its flowability during recycling.
Van den Eynde et al. (2017) examined PA12 flowability
under elevated temperatures with a customized powder
spreader. A slight increase in the packing condition wasobserved above the glass transition temperature, indicatingthat the softening of the polymer increased the powder
compressibility. Similarly, Amado et al. (2014) comparedPA12 and a co-polypropylene using a modified revolution
powder analyzer. The results showed PA12 has reduced
surface fractal and improved flowability when processtemperatures were above its glass transition temperature.
Ruggi et al. (2020a; 2020b) evaluated PA12 flowability
with a high-temperature annular shear cell. The followability was characterized using the “free-flowing range”
method (ASTM D6773). The results showed that the flowability improved from 25 °C to 100 °C, then reduced from
100 °C to 160 °C. The liquid bridges present at 25 °C were
proposed as the main limitation of the free flow. The flowability increased with reduced moisture from 25 °C to
100 °C. From 100 °C to 160 °C, powder became cohesive
towards close to melting temperature because the softened
polymer induced more contact points and contact area
which reduced the flowability.
In the earlier discussion of morphology, it was mentioned that PEEK flowability can be optimized by hightemperature annealing. However, high-temperatureannealing is not always desired. In a SLS print, most of thepowder is not melted. It is important to recycle the unmelted
powder to reduce the production cost (Dotchev and Yusoff,2009). The recycling process involves sieving and storing
the unmelted powder, which is then mixed with fresh powder for the next cycle of use. The purpose of powder mixing
is to neutralize the changes in the properties of used powderthat occur as a result of prolonged exposure to elevatedtemperatures. The mixing rate depends on the extent ofproperty change in the used powder, and not all the poly-

34

Review Paper

mers can be recycled (Dadbakhsh et al., 2017; Mwania etal., 2021). The change in the chemical structure, thermal
properties and rheology properties of the used polymer
have been well researched in the literature, especially for
PA12 (Dooher et al., 2021; Kuehnlein et al., 2010; Wudy etal., 2014). Mielicki et al. (2015) reported a higher PA12
particle shape deviation for particle size bigger than
100 μm and longer aging times. Dadbakhsh et al. (2017)
observed an increased cracking in used PA12 from scanning electron microscope images. The cracks might becaused by the evaporation of remaining alcohol and absorbed moisture and/or the subsequent expansion/
shrinkage steps of the process cycles. From the powder
flowability perspective, Wegner et al. (2014) reported reduced flowability of used polypropylene (PP) based on the
Hausner-ratio method. On the contrary, Yang et al. (2021)
reported an improved flowability of used PA12 based on
the powder rheometer measurement. The discrepancy inflowability results could be attributed to the different measurement methods employed, where the simulated forced
flow in a powder rheometer may yield different outcomescompared to free flow and tapped-based Hausner ratio
methods.
In our study, both new and used PA12 were evaluatedwith the Hausner-ratio method. As shown in Table 2, new
PA12 exhibits a lower Hausner-ratio compared to used
PA12, which suggested a reduced flowability of used PA12.
The used PA12, on the other hand, has a higher tapped
density. Comparing this with the higher flowability in thepreviously mentioned PA12 powder rheometer measurement results, there could be a similarity between the tapped
force during tapped density measurement and the simulated forced flow in the powder rheometer measurement.
Systematic studies of the triboelectric phenomena inpolymer SLS are rare. Recently, Hesse et al. (2019) investigated the triboelectric charge of fresh and used PA12. A
powder spreading setup with the electrostatic voltmeter
was used to compare both fresh and aged PA12. The electrostatic charge build-up of used PA12 was found to besignificantly higher than the fresh PA12. The degradationof an antistatic agent in the powder, or the electrical properties change due to the post-condensation were the reasonscited for the observation according to the author. This

Table 2 Hausner ratio of new and used PA12. The raw data on the
Hausner ratio is available publicly at https://doi.org/10.50931/data.
kona.23741511

Material

Loose bulk
density(g/cm3)

Tapped bulk
density(g/cm3)Hausner ratio

New PA12

0.44

0.51

1.15 ± 0.01

Used PA12

0.42

0.52

1.23 ± 0.02

Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41

finding is important for the analysis of powder flowability
and the development of powder recycling strategies.

5. Additives

Another approach to improve or modify material flow
properties is combining additives with established SLS
materials (Arai et al., 2018; Gulotty et al., 2013; Mousah,
2011; Sivadas et al., 2021; Tolochko et al., 2000; Yan et al.,2009; Yuan et al., 2019). Additives, especially hydrophobic
fumed silica, have been widely used as flow aids to improve powder flowability (Berretta et al., 2014; Laumer etal., 2013; Schmidt et al., 2014, 2016; Verbelen et al., 2016).
The presence of the flow aids reduces the interparticle vander Waals forces (Schmidt et al., 2014) and the effects ofelectrostatic charges (Lexow and Drummer, 2016).
Considering the significantly small particle size of flow
aids, they have a large surface-to-volume ratio, and only asmall percentage needs to be added to the polymer matrix.
The optimal amount of flow aids is of great interest.
Laumer et al. (2016b) investigated the effect of flow aids
content in high-density polyethylene (PE-HD, D50 = 57 μm)
and polypropylene (PP, D50 = 100 μm). Weight concentrations of 0.0 %, 0.1 %. 0.25 % and 1.0 % of nano-scaled
fumed silica were mixed with the polymer by dry mixing.
The Hausner ratio and degree of coverage were measured
to evaluate flowability. The degree of coverage measurement was done by a customized powder spreader. The results showed that the addition of fumed silica improved
overall flowability. However, the concertation effect differed between the two characterizations. The Hausner ratio
increased with increasing concentration, with 0.1 % as the
optimal concentration. On the other hand, in PE-HD degreeof coverage testing, saturation was observed at 0.25 % anddegree of coverage decreased above this concentration.
The proposed explanation was that the increased amount offumed silica after saturation caused the separation of fumed
silica and polymer particles, and/or the fumed silica agglomeration reduced flowability. On the contrary, no satu-

Fig. 7

Review Paper

ration was found in the PP system. The degree of coveragecontinuously increased with the increase in fumed silica
amount, which could be attributed to the different particle
sizes and inter-particle forces between the two polymers.
Similarly, Kleijnen et al. (2019) reported the effect offume silica concentration ranging from 0.005 % to 0.5 % ina PBT (D50 = 41.5 μm) powder system. Hausner ratio and arevolution powder analyzer were used to characterize theflowability. The results showed that the flowability did notchange below 0.01 wt%, increased from 0.01 wt% to
0.1 wt%, then reached a plateau. Additionally, SEM images
revealed that at 0.5 wt% of additive, the polymer surfaces
were fully covered and aggregates were formed, which
could justify the flowability plateau.

6. White spot

Besides the lack of a comprehensive understanding of
powder flow mechanisms discussed in the previous sections, there are two other major areas that require further
investigation.
Most of the existing powder flowability studies wereconducted to improve particle packing. However, there aresituations where a low packing density can be advantageous, such as when reducing printing time or achieving a
porous product is desired. According to Beer-Lambert law,
the laser intensity along with the powder depth as it transmits into a media decays exponentially (Osmanlic et al.,2018; Xin et al., 2017). A low particle packing density allows for a slow decay of the laser, which leads to deeper
melting depth compared to a high powder packing density
bed as shown in Fig. 7. A larger layer thickness can be
employed in this condition which reduces the overall printing time. However, there are two potential penalties forprinting with a low packing density. First, the high laser
scattering caused by low packing density could lead to issues with printed part dimension, such as over-sintering.
Second, extremely high melting depth could result in highsurface temperatures, potentially leading to polymer

Laser–powder interaction under different packing densities (Reprinted with permission from Polymers “open access”, Osmanlic et al., 2018).

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Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41

Review Paper

Table 3 The effect of powder properties and process conditions on SLS–other polymers.
SLS process
Factors
Powderproperty- PSD

Optimal range+ Span+ D50+ Fine particles

Powderproperty- Morphology

Recoating

Process
conditions

Particle
additives

Flowability

Layer smoothness+ Roundness

High roundness(Berretta et al.,2014; Haeri etal., 2017; Van
den Eynde etal., 2015)+ Roughness

Low roughness(Van den Eynde
et al., 2015)+ Layerthickness

1. Detailed
design ofexperimentto find out
the optimal
PSD

0 (PA12) (Beitz etal., 2019)+ (PA12) (Vanden Eynde etal., 2015)

0 Surface roughness (PA12) (Beitz
et al., 2019)− (TPU, TPE)
(Ziegelmeier et al.,
2015)
− (Schmid et al.,2015)

− (TPU, TPE)
(Ziegelmeier etal., 2015)+ (PA11, PA12)(Verbelen et al.,2016)

− Tensile strength(TPU, TPE)
(Ziegelmeier et al.,2015)
− Surface roughness (TPU, TPE)
(Ziegelmeier et al.,2015)
0 Shore hardness(TPU, TPE)
(Ziegelmeier et al.,2015)

2. Improved
polymer
powderproduction
methods+ (PEEK) (Berretta
et al., 2014)+ (Haeri et al., 2017)+ (PA12) (Vanden Eynde etal., 2015)+ (Haeri et al.,2017)
+ (PA12) (Vanden Eynde etal., 2015)− (PA12) (Vanden Eynde etal., 2015)+ Blade flatness

Flat (Beitz etal., 2019)+ (PA12) (Beitz
et al., 2019)+ Roller insteadof blade

Roller (Haeri etal., 2017)+ (Haeri et al.,2017)

+ Recoating
speed

250 mm/s(Drummer etal., 2015)− (Simulation)(Haeri et al.,2017)+− (PA12)(Drummer etal., 2015)+ (PA12) (Amado etal., 2014)+− (PA12) (Ruggi etal., 2020a, 2020b)+ ReuseFresh Powder(Wegner andÜnlü, 2016)+ Concentration

0.25 wt%
Fumed silica in
HDPE, 1 wt.%
Fumed silica in
PP (Laumer etal., 2016b)
0.1 wt% Fumed
silica in PBT(Kleijnen et al.,2019)

Researchneeds− Homogeneous
melting [49]+ (PLLA) (Dechet etal., 2020)+ (HDPE, PP)(Laumer et al., 2016b)+ Temperature

SLS printed part
(Caused byflowability change)+ (PA12) (Vanden Eynde etal., 2015)− (PA12)(Schmid et al.,2017)

45 to 90 μm(Goodridge andZiegelmeier,2017).
20 to 80 μm(Schmid et al.,2015; Vock etal., 2019b)(General guild
line, No
experimental
data support)

Packing density+ (PA12) (Beitz
et al., 2019)

3. Lowpackingdensity andlarge layer
thickness
scenario
4. Powder–polymer melt
recoatingscenario+ (PA12) (Vanden Eynde etal., 2017)
5. Aging
effect on
powderpropertychange indifferent
polymersystems− (PP) (Wegner andÜnlü, 2016)+ (PA12) (Yang etal., 2021)+− (Fumed
silica in HDPE,
PP) (Laumer etal., 2016b)(Fumed silica in
PBT) (Kleijnen
et al., 2019)“+” denotes a positive effect with an increased factor, “−” a negative effect with an increased factor, “0” for no effect. “+−” denotes a
positive, then a negative effect with an increased factor. “()” denoted the polymer used in the cited work.

36

Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41

degradation. The detailed impact of packing density, layer
thickness and laser parameters on polymer coalescence is
not yet well understood and requires further systematic investigations.
Although studies have been conducted on the relationship between powder flow conditions and printed partproperties, there remains a significant knowledge gap regarding powder–polymer melt recoating, as shown in
Fig. 1 diagram B1. This fundamentally differs from thewidely investigated powder flow behavior on flat powder
surfaces, which is a significantly different environment
than the relatively uneven polymer melt surfaces in realsystems. From a powder flowability perspective, most researchers have analyzed the flowability based on a designated single-layer thickness. However, the layer thickness
would be different after melting. The powder packing density is about 40–50 % (Van den Eynde et al., 2015). During
melting, the powder layer sinks due to the filling of gaps
between particles. This phenomenon leads to powder layerheight changes for the next powder deposition. In the caseof metal SLS, this powder layer height is 4–5 times thedesigned layer thickness (Wischeropp et al., 2019). The
dramatic increase in the layer thickness could change powder flow behavior. Furthermore, Mielicki et al. (2015) discovered that the temperature of the polymer melt, 10
seconds after laser exposure, is close to the printing temperature, indicating that the polymer is in a viscous flow
undercooling stage during the next layer powder deposition. Powder deposition on a surface under viscous flow
conditions encounters different force conditions compared
to deposition on a cooled solid surface. From a polymer
rheology perspective, most of the research has focused on
the polymer melt coalescence (Haworth et al., 2013;
Mielicki et al., 2012), except for a study by Wudy et al.
(2015) who investigated the effect of different polymer
melt surface tension conditions on the powder bed formation. The opposite scenario, where powder flows on thepolymer melt, remains unexplored.

7. Conclusion and future perspectives

Polymer selective laser sintering is a powder-based additive manufacturing technology. In this paper, we have presented a review focusing on one of the most important
aspects of SLS: powder flowability. The powder flowability determines layer packing and the final printed partproperties. Besides a brief discussion of the powder flowability characterization methods used in polymer SLS, theprimary objective of the review was to provide a better
understanding of the powder flow mechanism during theprinting process. The powder properties such as PSD andparticle morphology play important roles in flowability.
The effect of powder properties and process conditions
on SLS process performance, based on the literature citedin this review, is summarized in Table 3. Some factors ex-

Review Paper

hibit contradictory effects when viewed from different
perspectives., e.g., PSD span improves packing but results
in inhomogeneous melting. There is also a delta between
the findings for polymer and metal/ceramic regarding theeffect of PSD as discussed in the previous section. The
current research on polymer SLS is constrained by thelimited variety of powder properties options i.e., availability of spherical, and smooth particles with controllable
particle sizes. It is essential to improve existing polymer
powder production methods and develop new methods sothat the desired powder properties criteria for optimal printing conditions can be developed.
As discussed in the above sections, all material properties contribute to a successful SLS print. Regarding thepowder properties and flowability:• A smooth powder layer formation is the precondition of
the layer-by-layer process. It is influenced by powder
flowability, morphology and process conditions. The useof an optimal PSD (45–90 μm or 20–80 μm), highroundness particles or an appropriate concentration offlow aids often leads to an acceptable layer formation.
• The powder packing density is influenced by the same
factors as powder flowability and can be improved byutilizing an appropriate PSD, high roundness particles
and an optimal concentration of flow aids. The packing
density affects the thermal and optical properties of thepowder bed, which cause a direct impact on the laser–material interaction as shown in Fig. 7. By tuning laserparameters, process conditions and adding absorption
intensifiers (Laumer et al., 2013), successful print properties can be achieved even with powder beds that have
low packing densities.
In addition to experimental studies, simulations andmodeling efforts are needed to provide further insights todevelop meaningful guidelines for achieving optimal powder properties and successful process performance.
Considering that PA and its composites account for 95 %of the SLS polymer commercial market, there is a need todevelop other polymers to meet diverse product property
requirements and expand the range of SLS applications.
The current understanding of polymer processing phenomena, including flowability, is primarily based on PA12. As acommon approach, investigating the printing mechanismof PA12 and using it as a basis for developing guidelines
for new materials is often employed. Without the development of universally quantified criteria for powder/material
properties, the trial-and-error method will continue to be
the most common approach for new material developmentin the industry. It is also critical to expand the investigationof other polymers, from feasibility tests to fundamental
failure mode analysis, to gain a deeper understanding of the
SLS process.

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Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41

Data Availability Statement

The raw data on Polyamide 12 Hausner ratio is available
publicly in J-STAGE Data (https://doi.org/10.50931/data.
kona.23741511).

Acknowledgments

The authors acknowledge the financial support of the
National Science Foundation Center of Particulate andSurfactant Science (CPaSS) and the industry members(NSF Award #1362060). Any opinions, findings, and conclusions or recommendations expressed in this material arethose of the authors and do not necessarily reflect the viewsof the National Science Foundation or the CPaSS industry
members.

References

Amado A., Schmid M., Levy G., Wegener K., Advances in SLS powder
characterization, 22nd Annual International Solid Freeform Fabrication Symposium, (2011) 438–452. DOI: 10.26153/tsw/15306
Amado A., Schmid M., Wegener K., Flowability of SLS powders at elevated temperature, Swiss Institute of Technology, ETH Zürich, 2014.
DOI: 10.3929/ethz-a-010057815
Amado Becker A.F., Characterization and prediction of SLS processability of polymer powders with respect to powder flow and part warpage, Doctoral Thesis, ETH-Zürich, 2016. DOI: 10.3929/ethz-a010657585
Arai S., Tsunoda S., Kawamura R., Kuboyama K., Ougizawa T., Comparison of crystallization characteristics and mechanical properties ofpoly(butylene terephthalate) processed by laser sintering and injection molding, Materials & Design, 113 (2017) 214–222. DOI:
10.1016/j.matdes.2016.10.028
Arai S., Tsunoda S., Yamaguchi A., Ougizawa T., Effects of short-glassfiber content on material and part properties of poly(butylene
terephthalate) processed by selective laser sintering, Additive Manufacturing, 21 (2018) 683–693. DOI: 10.1016/j.addma.2018.04.019
Arai S., Tsunoda S., Yamaguchi A., Ougizawa T., Characterization offlame-retardant poly(butylene terephthalate) processed by laser sintering, Optics & Laser Technology, 117 (2019) 94–104. DOI:
10.1016/j.optlastec.2019.04.006
ASTM D6393, Standard Test Method for Bulk Solids Characterization by
Carr Indices, ASTM International, 2021. DOI: 10.1520/d6393_
d6393m-21
Beitz S., Uerlich R., Bokelmann T., Diener A., Vietor T., Kwade A.,
Influence of powder deposition on powder bed and specimen properties, Materials, 12 (2019) 297. DOI: 10.3390/ma12020297
Benedetti L., Brulé B., Decreamer N., Evans K.E., Ghita O., Shrinkage
behaviour of semi-crystalline polymers in laser sintering: PEKK and
PA12, Materials & Design, 181 (2019) 107906. DOI: 10.1016/j.
matdes.2019.107906
Berretta S., Evans K.E., Ghita O.R., Predicting processing parameters inhigh temperature laser sintering (HT-LS) from powder properties,
Materials and Design, 105 (2016) 301–314. DOI: 10.1016/j.matdes.
2016.04.097
Berretta S., Ghita O., Evans K.E., Morphology of polymeric powders in
Laser Sintering (LS): from Polyamide to new PEEK powders, European Polymer Journal, 59 (2014) 218–229. DOI: 10.1016/j.
eurpolymj.2014.08.004
Bierwisch C., Mohseni-Mofidi S., Dietemann B., Grünewald M., Rudloff
J., Lang M., Universal process diagrams for laser sintering of polymers, Materials & Design, 199 (2021) 109432. DOI: 10.1016/j.
matdes.2020.109432

38

Review Paper

Chatham C.A., Long T.E., Williams C.B., Powder bed fusion of poly(phenylene sulfide) at bed temperatures significantly below melting,
Additive Manufacturing, 28 (2019) 506–516. DOI: 10.1016/j.
addma.2019.05.025
Chen H., Wei Q., Zhang Y., Chen F., Shi Y., Yan W., Powder-spreadingmechanisms in powder-bed-based additive manufacturing: experiments and computational modeling, Acta Materialia, 179 (2019)
158–171. DOI: 10.1016/j.actamat.2019.08.030
Dadbakhsh S., Verbelen L., Vandeputte T., Strobbe D., Van Puyvelde P.,
Kruth J.P., Effect of powder size and shape on the SLS processability
and mechanical properties of a TPU elastomer, Physics Procedia, 83(2016) 971–980. DOI: 10.1016/j.phpro.2016.08.102
Dadbakhsh S., Verbelen L., Verkinderen O., Strobbe D., Effect of PA12
powder reuse on coalescence behaviour and microstructure of SLS
parts, European Polymer Journal, 92 (2017) 250–262. DOI:
10.1016/j.eurpolymj.2017.05.014
Dechet M.A., Demina A., Römling L., Gómez Bonilla J.S., Lanyi F.J.,
Schubert D.W., Bück A., Peukert W., Schmidt J., Development ofpoly(L-lactide) (PLLA) microspheres precipitated from triacetin for
application in powder bed fusion of polymers, Additive Manufacturing, 32 (2020) 100966. DOI: 10.1016/j.addma.2019.100966
Dooher T., Archer E., Walls T., McIlhagger A., Dixon D., Ageing of laser
sintered glass-filled Polyamide 12 (PA12) parts at elevated temperature and humidity, Polymers and Polymer Composites, 12 (2021)
1–11. DOI: 10.1177/09673911211027127
Dotchev K., Yusoff W., Recycling of polyamide 12 based powders in thelaser sintering process, Rapid Prototyping Journal, 15 (2009) 192–203. DOI: 10.1108/13552540910960299
Drummer D., Drexler M., Wudy K., Density of laser molten polymer parts
as function of powder coating process during additive manufacturing, Procedia Engineering, 102 (2015) 1908–1917. DOI: 10.1016/j.
proeng.2015.01.331
Drummer D., Greiner S., Zhao M., Wudy K., A novel approach for understanding laser sintering of polymers, Additive Manufacturing, 27(2019) 379–388. DOI: 10.1016/j.addma.2019.03.012
Drummer D., Rietzel D., Kühnlein F., Development of a characterization
approach for the sintering behavior of new thermoplastics for selective laser sintering, Physics Procedia, 5 (2010) 533–542. DOI:
10.1016/j.phpro.2010.08.081
Freeman R., Measuring the flow properties of consolidated, conditioned
and aerated powders—a comparative study using a powder rheometer and a rotational shear cell, Powder Technology, 174 (2007)
25–33. DOI: 10.1016/j.powtec.2006.10.016
Geldart D., Abdullah E.C., Hassanpour A., Nwoke L.C., Wouters I.,
Characterization of powder flowability using measurement of angleof repose, China Particuology, 4 (2006) 104–107. DOI: 10.1016/
s1672-2515(07)60247-4
German R.M., Particle Packing Characteristics, Metal Powder Industry,
1989, ISBN: 9780918404831. DOI: 10.1016/0032-5910(90)80071-6
Gong X., Cheng B., Price S., Chou K., Powder-bed electron-beammelting additive manufacturing: powder characterization, processsimulation and metrology, ASME District Early Career TechnicalConference, ASME Early Career Technical Journal, (2013) 59–66.
Goodridge R., Ziegelmeier S., Powder bed fusion of polymers, Laser
Additive Manufacturing: Materials, Design, Technologies, andApplications, (2017) 181–204. DOI: 10.1016/B978-0-08-1004333.00007-5
Goodridge R.D., Hague R.J.M., Tuck C.J., Effect of long-term ageing on
the tensile properties of a polyamide 12 laser sintering material,
Polymer Testing, 29 (2010) 483–493. DOI: 10.1016/j.
polymertesting.2010.02.009
Greiner S., Wudy K., Wörz A., Drummer D., Thermographic investigationof laser-induced temperature fields in selective laser beam melting ofpolymers, Optics and Laser Technology, 109 (2019) 569–576. DOI:
10.1016/j.optlastec.2018.08.010

Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41
Gulotty R., Castellino M., Jagdale P., Tagliaferro A., Balandin A.A.,
Effects of functionalization on thermal properties of single-wall andmulti-wall carbon nanotube-polymer nanocomposites, ACS Nano, 7(2013) 5114–5121. DOI: 10.1021/nn400726g
Haeri S., Wang Y., Ghita O., Sun J., Discrete element simulation andexperimental study of powder spreading process in additive manufacturing, Powder Technology, 306 (2017) 45–54. DOI: 10.1016/j.
powtec.2016.11.002
Haworth B., Hopkinson N., Hitt D., Zhong X., Shear viscosity measurements on Polyamide-12 polymers for laser sintering, Rapid Prototyping Journal, 19 (2013) 28–36. DOI: 10.1108/13552541311292709
Hesse N., Dechet M.A., Bonilla J.S.G., Lübbert C., Roth S., Bück A.,
Schmidt J., Peukert W., Analysis of tribo-charging during powder
spreading in selective laser sintering: assessment of polyamide 12
powder ageing effects on charging behavior, Polymers, 11 (2019)609. DOI: 10.3390/polym11040609
Hettiarachchi C., Mampearachchi W.K., Effect of surface texture, size
ratio and large particle volume fraction on packing density of binary
spherical mixtures, Granular Matter, 22 (2020) 1–13. DOI: 10.1007/
s10035-019-0978-3
ISO/ASTM 52900:2021, Additive manufacturing—General principles—
Fundamentals and vocabulary, 2021. <https://www.iso.org/standard/
74514.html> accessed 20042023
Ituarte I.F., Wiikinkoski O., Jansson A., Additive manufacturing of polypropylene: a screening design of experiment using laser-based powder bed fusion, Polymers, 10 (2018) 1293. DOI: 10.3390/
polym10121293
Jones I., Laser welding of plastics, in: Katayama S. (Ed.) Handbook ofLaser Welding Technologies, Woodhead Publishing, 2013, pp. 280301e, ISBN: 9780857092649. DOI: 10.1533/9780857098771.2.280
Kleijnen R.G., Schmid M., Wegener K., Nucleation and impact modification of polypropylene laser sintered parts, AIP Conference Proceedings, 1779 (2016) 100004-1–5. DOI: 10.1063/1.4965572
Kleijnen R.G., Schmid M., Wegener K., Impact of flow aid on the flowability and coalescence of polymer laser sintering powder, 2019
International Solid Freeform Fabrication Symposium, (2019) 806–
817. DOI: 10.26153/tsw/17317
Kleijnen R.G., Sesseg J.P.W., Schmid M., Wegener K., Insights into thedevelopment of a short-fiber reinforced polypropylene for laser sintering, AIP Conference Proceedings, 1914 (2017) 190002. DOI:
10.1063/1.5016791
Krantz M., Zhang H., Zhu J., Characterization of powder flow: static anddynamic testing, Powder Technology, 194 (2009) 239–245. DOI:
10.1016/j.powtec.2009.05.001
Kruth J.P., Leu M.C., Nakagawa T., Progress in additive manufacturing
and rapid prototyping, CIRP Annals—Manufacturing Technology,
47 (1998) 525–540. DOI: 10.1016/s0007-8506(07)63240-5
Kruth J.P., Levy G., Klocke F., Childs T.H.C., Consolidation phenomena
in laser and powder-bed based layered manufacturing, CIRP
Annals—Manufacturing Technology, 56 (2007) 730–759. DOI:
10.1016/j.cirp.2007.10.004
Kuehnlein F., Drummer D., Rietzel D., Seefried A., Degradation behavior
and material properties of PA12-plastic powders processed by powder based additive manufacturing technologies, Annals of DAAAM
and Proceedings of the International DAAAM Symposium, 21(2010) 1547–1548. ISBN 9783901509735.
Laumer T., Stichel T., Nagulin K., Schmidt M., Optical analysis of polymer powder materials for Selective Laser Sintering, Polymer Testing,56 (2016a) 207–213. DOI: 10.1016/j.polymertesting.2016.10.010
Laumer T., Stichel T., Raths M., Schmidt M., Analysis of the influence ofdifferent flowability on part characteristics regarding the simultaneous laser beam melting of polymers, Physics Procedia, 83 (2016b)
937–946. DOI: 10.1016/j.phpro.2016.08.098
Laumer T., Stichel T., Sachs M., Amend P., Schmidt M., Qualification andmodification of new polymer powders for laser beam melting using

Review Paper

Ulbricht spheres, in: High Value Manufacturing: Advanced Researchin Virtual and Rapid Prototyping, 1st ed., CRC Press, 2013, pp.
255–260. ISBN: 9781138001374. DOI: 10.1201/b15961
Lexow M.M., Drummer D., New materials for SLS: the use of antistaticand flow agents, Journal of Powder Technology, 2016 (2016)
4101089. DOI: 10.1155/2016/4101089
Ligon S.C., Liska R., Stampfl J., Gurr M., Mülhaupt R., Polymers for 3D
printing and customized additive manufacturing, Chemical Reviews,
117 (2017) 10212–10290. DOI: 10.1021/acs.chemrev.7b00074
Lupone F., Padovano E., Casamento F., Badini C., Process phenomena
and material properties in selective laser sintering of polymers: a
review, Materials 2022, 15 (2021) 183. DOI: 10.3390/ma15010183
McGeary R.K., Mechanical packing of spherical particles, Journal of theAmerican Ceramic Society, 44 (1961) 513–522. DOI: 10.1111/j.
1151-2916.1961.tb13716.x
Mielicki C., Gronhoff B., Wortberg J., Effects of laser sintering processing
time and temperature on changes in polyamide 12 powder particle
size, shape and distribution, AIP Conference Proceedings, 1593
(2015) 728–731. DOI: 10.1063/1.4873880
Mielicki C., Wegner a, Gronhoff B., Wortberg J., Witt G., Prediction of
PA12 melt viscosity in laser sintering by a time and temperaturedependent rheological model, RTeJournal, 32 (2012). <https://rtejournal.de/document/2012_11> accessed 20012023.
Montón Zarazaga A., Abdelmoula M., Küçüktürk G., Maury F., Ferrato
M., Grossin D., Process parameters investigation for direct powder
bed selective laser processing of silicon carbide parts, Progress in
Additive Manufacturing, 7 (2022) 1307–1322. DOI: 10.1007/
s40964-022-00305-7
Mousah A., Effects of filler content and coupling agents on the mechanicalproperties and geometrical accuracy of selective laser sintered partsin glass bead-filled polyamide 12 composites, Thesis (Ph.D.), Cardiff
University, 2011, pp. 227–231. https://orca.cardiff.ac.uk/id/eprint/
11094
Mwania F.M., Maringa M., Van Der Walt J.G., A review of the techniques
used to characterize laser sintering of polymeric powders for use andre-use in additive manufacturing, Manufacturing Review, 8 (2021)
1–17. DOI: 10.1051/mfreview/2021012
Myers T.L., Brauer C.S., Su Y.-F., Blake T.A., Tonkyn R.G., Ertel A.B.,
Johnson T.J., Richardson R.L., Quantitative reflectance spectra ofsolid powders as a function of particle size, Applied Optics, 54(2015) 4863. DOI: 10.1364/ao.54.004863
Niino T., Sato K., Effect of powder compaction in plastic laser sinteringfabrication, 2009 International Solid Freeform Fabrication Symposium, (2009) 193–205. DOI: 10.26153/tsw/15100
Osmanlic F., Wudy K., Laumer T., Schmidt M., Drummer D., Körner C.,
Modeling of laser beam absorption in a polymer powder bed, Polymers, 10 (2018) 1–11. DOI: 10.3390/polym10070784
Prescott J., Barnum R.A., On powder flowability, Pharmaceutical Technology, 24(10) (2000) 60–84.
Rescaglio A., Schockmel J., Vandewalle N., Lumay G., Combined effectof moisture and electrostatic charges on powder flow, EPJ Web ofConferences, 140 (2017) 13009. DOI: 10.1051/epjconf/
201714013009
Ruggi D., Barrès C., Charmeau J.Y., Fulchiron R., Barletta D., Poletto M.,
A quantitative approach to assess high temperature flow properties of
a PA 12 powder for laser sintering, Additive Manufacturing, 33(2020a) 101143. DOI: 10.1016/j.addma.2020.101143
Ruggi D., Lupo M., Sofia D., Barrès C., Barletta D., Poletto M., Flowproperties of polymeric powders for selective laser sintering, Powder
Technology, 370 (2020b) 288–297. DOI: 10.1016/j.powtec.
2020.05.069
Sachs M., Schmidt J., Toni F., Blümel C., Winzer B., Peukert W., Wirth
K.E., Rounding of irregular polymer particles in a downer reactor,
Procedia Engineering, 102 (2015) 542–549. DOI: 10.1016/j.proeng.
2015.01.119

39

Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41
Sassaman D., Phillips T., Milroy C., Ide M., Beaman J., A method forpredicting powder flowability for selective laser sintering, JOM, 74(2022) 1102–1110. DOI: 10.1007/s11837-021-05050-w
Schmid M., Amado F., Levy G., Wegener K., Flowability of powders forselective laser sintering (SLS) investigated by round robin test, in:High Value Manufacturing: Advanced Research in Virtual and Rapid
Prototyping, 1st ed., CRC Press, 2013, pp. 95–99, ISBN:
9781138001374. DOI: 10.3929/ethz-a-010057806
Schmid M., Amado A., Wegener K., Materials perspective of polymers for
additive manufacturing with selective laser sintering, Journal of
Materials Research, 29 (2014) 1824–1832. DOI: 10.1557/jmr.
2014.138
Schmid M., Amado A., Wegener K., Polymer powders for selective laser
sintering (SLS), AIP Conference Proceedings, 1664 (2015) 1600091–5. DOI: 10.1063/1.4918516
Schmid M., Kleijnen R., Vetterli M., Wegener K., Influence of the originof polyamide 12 powder on the laser sintering process and laser sintered parts, Applied Sciences (Switzerland), 7 (2017) 462. DOI:
10.3390/app7050462
Schmidt J., Dechet M.A., Gómez Bonilla J.S., Hesse N., Bück A., Peukert
W., Characterization of polymer powders for selective laser sintering, 2019 International Solid Freeform Fabrication Symposium,(2019) 779–789. DOI: 10.26153/tsw/17314
Schmidt J., Sachs M., Blümel C., Winzer B., Toni F., Wirth K.E., Peukert
W., A novel process route for the production of spherical LBM
polymer powders with small size and good flowability, Powder
Technology, 261 (2014) 78–86. DOI: 10.1016/j.powtec.2014.04.003
Schmidt J., Sachs M., Fanselow S., Zhao M., Romeis S., Drummer D.,
Wirth K.E., Peukert W., Optimized polybutylene terephthalate powders for selective laser beam melting, Chemical Engineering Science,
156 (2016) 1–10. DOI: 10.1016/j.ces.2016.09.009
Schulze D., Powders and Bulk Solids: Behavior, Characterization, Storage and Flow, 1st ed., Springer Berlin, Heidelberg, 2008, ISSN:
9783540737674. DOI: 10.1007/978-3-540-73768-1
Schwedes J., Review on testers for measuring flow properties of bulk
solids, Granular Matter, 5 (2003) 1–43. DOI: 10.1007/s10035-0020124-4
Sillani F., de Gasparo F., Schmid M., Wegener K., Influence of packing
density and fillers on thermal conductivity of polymer powders for
additive manufacturing, International Journal of Advanced Manufacturing Technology, 117 (2021) 2049–2058. DOI: 10.1007/s00170021-07117-z
Sivadas B.O., Ashcroft I., Khlobystov A.N., Goodridge R.D., Laser sintering of polymer nanocomposites, Advanced Industrial and Engineering Polymer Research, 4 (2021) 277–300. DOI: 10.1016/j.
aiepr.2021.07.003
Soe S.P., Quantitative analysis on SLS part curling using EOS P700
machine, Journal of Materials Processing Technology, 212 (2012)
2433–2442. DOI: 10.1016/j.jmatprotec.2012.06.012
Spierings A.B., Voegtlin M., Bauer T., Wegener K., Powder flowability
characterisation methodology for powder-bed-based metal additive
manufacturing, Progress in Additive Manufacturing, 1 (2016) 9–20.
DOI: 10.1007/s40964-015-0001-4
Stansbury J.W., Idacavage M.J., 3D printing with polymers: challenges
among expanding options and opportunities, Dental Materials, 32(2016) 54–64. DOI: 10.1016/j.dental.2015.09.018
Starr T.L., Gornet T.J., Usher J.S., The effect of process conditions onmechanical properties of laser-sintered nylon, Rapid Prototyping
Journal, 17 (2011) 418–423. DOI: 10.1108/13552541111184143
Suzuki M., Chapter 3.5: Packing properties, in: Higashitani K., Makino,
H., and Matsusaka, S. (Eds.), Powder Technology Handbook, 4th ed.,CRC Press, 2019, pp.203–209, ISBN: 9781315184258. DOI:
10.1201/b22268
Tan L.J., Zhu W., Sagar K., Zhou K., Comparative study on the selective
laser sintering of polypropylene homopolymer and copolymer: pro-

40

Review Paper

cessability, crystallization kinetics, crystal phases and mechanicalproperties, Additive Manufacturing, 37 (2021) 101610. DOI: 10.
1016/j.addma.2020.101610
Tan Y.-Q., Zheng J.-H., Gao W., Jiang S.-Q., Feng Yuntian, Zheng J., Gao
Á.W., Jiang Á.S., Feng Y, The effect of powder flowability in theselective laser sintering process, Proceedings of the 7th International
Conference on Discrete Element Methods, 188 (2017) 629–636.
DOI: 10.1007/978-981-10-1926-5_65
Tanoue K.I., Ema A., Masuda H., Effect of material transfer and work
hardening of metal surface on the current generated by impact ofparticles, Journal of Chemical Engineering of Japan, 32 (1999)
544–548. DOI: 10.1252/jcej.32.544
Tolochko N.K., Laoui T., Khlopkov Y.V., Mozzharov S.E., Titov V.I.,
Ignatiev M.B., Absorptance of powder materials suitable for laser
sintering, Rapid Prototyping Journal, 6 (2000) 155–160. DOI:
10.1108/13552540010337029
Van den Eynde M., Verbelen L., Van Puyvelde P., Assessing polymer
powder flow for the application of laser sintering, Powder Technology, 286 (2015) 151–155. DOI: 10.1016/j.powtec.2015.08.004
Van den Eynde M., Verbelen L., Van Puyvelde P., Influence of temperatureon the flowability of polymer powders in laser sintering, AIP Conference Proceedings, 1914 (2017) 190007-1–5. DOI: 10.1063/
1.5016796
Vasquez G.M., Majewski C.E., Haworth B., Hopkinson N., A targetedmaterial selection process for polymers in laser sintering, Additive
Manufacturing, 1 (2014) 127–138. DOI: 10.1016/j.addma.
2014.09.003
Vasquez M., Haworth B., Hopkinson N., Optimum sintering region for
laser sintered Nylon-12, Proceedings of the Institution of MechanicalEngineers, Part B: Journal of Engineering Manufacture, 225 (2011)
2240–2248. DOI: 10.1177/0954405411414994
Verbelen L., Dadbakhsh S., Van den Eynde M., Kruth J.P., Goderis B., Van
Puyvelde P., Characterization of polyamide powders for determination of laser sintering processability, European Polymer Journal, 75(2016) 163–174. DOI: 10.1016/j.eurpolymj.2015.12.014
Verbelen L., Dadbakhsh S., Van den Eynde M., Strobbe D., Kruth J.P.,
Goderis B., Van Puyvelde P., Analysis of the material properties
involved in laser sintering of thermoplastic polyurethane, Additive
Manufacturing, 15 (2017) 12–19. DOI: 10.1016/j.addma.2017.03.001
Vock S., Klöden B., Kirchner A., Weißgärber T., Kieback B., Powders for
powder bed fusion: a review, Progress in Additive Manufacturing, 4(2019a) 383–397. DOI: 10.1007/s40964-019-00078-6
Vock S., Klöden B., Kirchner A., Weißgärber T., Kieback B., Powders for
powder bed fusion: a review, Progress in Additive Manufacturing, 4(2019b) 383–397. DOI: 10.1007/s40964-019-00078-6
Wegner A., New polymer materials for the laser sintering process: polypropylene and others, Physics Procedia, 83 (2016) 1003–1012. DOI:
10.1016/j.phpro.2016.08.105
Wegner A., Introduction to powder bed fusion of polymers, Additive
Manufacturing, (2021) 33–75. DOI: 10.1016/B978-0-12-8184110.00011-2
Wegner A., Mielicki C., Grimm T., Gronhoff B., Witt G., Wortberg J.,
Determination of robust material qualities and processing conditions
for laser sintering of polyamide 12, Polymer Engineering and Science, 54 (2014) 1540–1554. DOI: 10.1002/pen.23696
Wegner A., Ünlü T., Powder life cycle analyses for a new polypropylene
laser sintering material, 2016 International Solid Freeform Fabrication Symposium, (2016) 834–846. https://hdl.handle.net/2152/89636
Williams J.M., Adewunmi A., Schek R.M., Flanagan C.L., Krebsbach
P.H., Feinberg S.E., Hollister S.J., Das S., Bone tissue engineering
using polycaprolactone scaffolds fabricated via selective laser
sintering, Biomaterials, 26 (2005) 4817–4827. DOI: 10.1016/
j.biomaterials.2004.11.057
Wischeropp T.M., Emmelmann C., Brandt M., Pateras A., Measurementof actual powder layer height and packing density in a single layer in

Xi Guo et al. / KONA Powder and Particle Journal No. 41 (2024) 26–41
selective laser melting, Additive Manufacturing, 28 (2019) 176–183.
DOI: 10.1016/j.addma.2019.04.019
Wudy K., Drummer D., Drexler M., Characterization of polymer materials and powders for selective laser melting, AIP Conference Proceedings, 1593 (2015) 702–707. DOI: 10.1063/1.4873875
Wudy K., Drummer D., Kühnlein F., Drexler M., Influence of degradation
behavior of polyamide 12 powders in laser sintering process on produced parts, AIP Conference Proceedings, 1593 (2014) 691–695.
DOI: 10.1063/1.4873873
Xin L., Boutaous M., Xin S., Siginer D.A., Multiphysical modeling of theheating phase in the polymer powder bed fusion process, Additive
Manufacturing, 18 (2017) 121–135. DOI: 10.1016/j.addma.2017.
10.006
Yan C., Shi Y., Hao L., Investigation into the differences in the selective
laser sintering between amorphous and semi-crystalline polymers,
International Polymer Processing, 26 (2011) 416–423. DOI:
10.3139/217.2452
Yan C.Z., Shi Y.S., Yang J.S., Xu L., Preparation and selective laser sintering of nylon-12-coated aluminum powders, Journal of Composite
Materials, 43 (2009) 1835–1851. DOI: 10.1177/0021998309340932
Yan M., Tian X., Peng G., Cao Y., Li D., Hierarchically porous materials
prepared by selective laser sintering, Materials and Design, 135(2017) 62–68. DOI: 10.1016/j.matdes.2017.09.015
Yang F., Schnuerch A., Chen X., Quantitative influences of successive
reuse on thermal decomposition, molecular evolution, and elemental

Review Paper

composition of polyamide 12 residues in selective laser sintering,International Journal of Advanced Manufacturing Technology, 115(2021) 3121–3138. DOI: 10.1007/S00170-021-07368-W/TABLES/7
Yuan S., Shen F., Bai J., Chua C.K., Wei J., Zhou K., 3D soft auxetic lattice structures fabricated by selective laser sintering: TPU powder
evaluation and process optimization, Materials & Design, 120 (2017)317–327. DOI: 10.1016/J.MATDES.2017.01.098
Yuan S., Shen F., Chua C.K., Zhou K., Polymeric composites for
powder-based additive manufacturing: materials and applications,
Progress in Polymer Science, 91 (2019) 141–168. DOI: 10.1016/j.
progpolymsci.2018.11.001
Zhu W., Yan C., Shi Yunsong, Wen S., Han C., Cai C., Liu J., Shi Yusheng,
Study on the selective laser sintering of a low-isotacticity polypropylene powder, Rapid Prototyping Journal, 22 (2016) 621–629. DOI:
10.1108/RPJ-02-2015-0014
Ziegelmeier S., Christou P., Wöllecke F., Tuck C., Goodridge R., Hague
R., Krampe E., Wintermantel E., An experimental study into theeffects of bulk and flow behaviour of laser sintering polymer powders
on resulting part properties, Journal of Materials Processing Technology, 215 (2015) 239–250. DOI: 10.1016/j.jmatprotec.2014.07.029
Ziegelmeier S., Wollecke F., Tuck C., Goodridge R., Hague R., Characterizing the bulk & flow behaviour of ls polymer powders, Solid
Freeform Fabrication Symposium, (2013) 354–367. DOI: 10.26153/
tsw/15437

Authors’ Short Biographies
Xi GuoXi Guo received his bachelor’s degree in process equipment and control engineering from the
Beijing University of Chemical Technology in 2014. He went to graduate school at the University of
Florida and received his master’s degree in mechanical engineering in 2016. Afterward, he worked
for Johnson and Johnson as a materials engineer. In 2022, he completed his doctoral degree under theadvisement of Dr. Brij M. Moudgil, Department of Materials Science and Engineering, University of
Florida. His current research focus is on polymer selective laser sintering.

Brij M. Moudgil
Dr. Brij M. Moudgil is a Distinguished Professor of Materials Science and Engineering at the
University of Florida. He received his B.E from the Indian Institute of Science, Bangalore, India, andhis M.S. and Eng.Sc.D. degrees from Columbia University, New York. His current research interests
are in surfactant and polymer adsorption, dispersion and aggregation of fine particles, adhesion, andremoval of microbes from surfaces, synthesis of functionalized nanoparticles, antiscaling and surfactant mediated corrosion inhibitors, photocatalytic degradation of hazardous microbes, and nanotoxicity. He has published more than 400 technical papers and has been awarded over 25 patents. He isa member of the U.S National Academy of Engineering.

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