Environment International 123 (2019) 476–485
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Environment International
journal homepage: www.elsevier.com/locate/envint
Characterization of particulate and gaseous pollutants emitted during
operation of a desktop 3D printer
T
⁎
Jianwei Gu , Michael Wensing, Erik Uhde, Tunga Salthammer
Fraunhofer WKI, Department of Material Analysis and Indoor Chemistry, Bienroder Weg 54E, 38108 Braunschweig, Germany
A R T I C LE I N FO
A B S T R A C T
Handling Editor: Xavier Querol
The emission of ultrafine particles (UFP) and gaseous pollutants from 3D printing has been increasingly gaining
attention in recent years due to potential health risks. The physical and chemical properties of the emitted
particulate matter, however, remain unclear. In this study, we characterized these particles with a focus on their
chemical composition and volatility, and measured the gaseous pollutants from desktop 3D printing in a standardized environmental test chamber. Eight types of filaments were tested, including ABS (acrylonitrile butadiene styrene), ASA (acrylonitrile styrene acrylate), HIPS (high impact polystyrene), PETG (polyethylene terephthalate glycol), and PCABS (polycarbonate & ABS). Particle size distribution (PSD), particle number
concentration (PNC), particle chemical composition and particle volatility were measured. In addition, volatile
and very volatile organic compounds (VOCs and VVOCs) emitted during 3D printing were analyzed. The specific
emission rates (SERs) for particles in the size range of 5.6 to 560 nm ranged from 2.0 × 109 (GLASS, a PETGbased filament) to 1.7 × 1011 (ASA) #/min. The particle SERs for ABS were (4.7 ± 1.1) × 1010 #/min. The
SERs for total volatile organic compounds (TVOC) varied from 0.2 μg/min (GLASS) to 40.5 μg/min (ULTRAT, an
ABS-based filament). Particles started to evaporate extensively from 150 °C. At 300 °C, only 25% of the particle
number remained with the size distribution mode peaked at 11 nm. The particles collected on the quartz filter
were mainly composed of semi-volatile organic compounds (SVOCs) associated with the plasticizers, flameretardants, antioxidants of the thermoplastics, and cyclosiloxanes which may be used as lubricants in the 3D
printer.
Keywords:
3D printing
Emission
Ultrafine particles
VOCs
SVOCs
Environmental test chamber
1. Introduction
Three-dimensional (3D) printing is gaining more and more popularity. A large number of 3D printers are available on the market and,
depending on the individual printer characteristics, widely used in
private homes, office environments and laboratories. Most of the
desktop 3D printers use the fused filament fabrication (FFF) technique.
Basically, thermoplastic filaments such as polylactic acid (PLA) and
acrylonitrile butadiene styrene (ABS) are fed to the extruder and melted
when passing the extruder nozzle under a variety of temperatures
(mostly in the range of 180–270 °C). The extruder applies the melted
filament on the object, building the object layer by layer. The filaments
harden after deposition on the object. It has been demonstrated that
industrial processing of thermoplastics (180–280 °C) leads to emissions
of both gases and particles (Unwin et al., 2013). Thermal treatment of
common filaments such as PLA, ABS, polyethylene terephthalate (PET)
and polyamide (PA) may cause unwanted emissions of volatile and
semi-volatile organic compounds (VOCs and SVOCs) (Wojtyła et al.,
⁎
2017). The growing use of 3D printers in private and occupational
spaces raises the question as to whether human exposure to emitted
substances may cause adverse health effects. In a recent study,
Gümperlein et al. (2018) exposed 26 healthy adults to particles and
VOCs from 3D printing (PLA and ABS). Acute effects on inflammatory
markers after short-term (1 h) exposure were not found, but slightly
increased exhaled nitric oxide, indisposition and odor nuisance could
be observed during ABS printing.
Since the first publication on desktop 3D printing emission by
Stephens et al. (2013), there have been several studies published on the
3D printing-related emissions of particles and/or gases. With regard to
particles, most of the studies focused on particle number concentrations
(PNC) or particle size distributions (PSD) (Azimi et al., 2016; Deng
et al., 2016; Floyd et al., 2017; Kim et al., 2015; Kwon et al., 2017;
Seeger et al., 2018; Stabile et al., 2017; Stefaniak et al., 2018; Stefaniak
et al., 2017; Steinle, 2016; Yi et al., 2016; Zhang et al., 2017; Zhou
et al., 2015). In several investigations, total volatile organic compounds
(TVOC) were addressed (Azimi et al., 2016; Floyd et al., 2017; Kim
Corresponding author.
E-mail address: jianwei.gu@wki.fraunhofer.de (J. Gu).
https://doi.org/10.1016/j.envint.2018.12.014
Received 15 October 2018; Received in revised form 30 November 2018; Accepted 5 December 2018
Available online 05 January 2019
0160-4120/ © 2018 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/BY-NC-ND/4.0/).
Environment International 123 (2019) 476–485
J. Gu et al.
et al., 2015; Mendes et al., 2017; Stefaniak et al., 2017; Steinle, 2016).
So far, studies assessing the individual VOCs have been published by
Azimi et al. (2016), Floyd et al. (2017) and Stefaniak et al. (2017), in
which they determined that the type of emitted VOCs was driven by the
filament types.
The previous studies focused mostly on the widely used filaments
PLA and ABS. As far as other thermoplastic materials are concerned, the
information is limited. Polyamide (Nylon) was studied by Zhang et al.
(2017); multiple-filament types, including newly developed materials,
were tested in studies by Azimi et al. (2016), Stabile et al. (2017) and
Seeger et al. (2018).
Few studies tackled the physical and chemical properties of 3D
printing-emitted particles. The question of whether the particles are
solid or liquid is important with respect to health-related issues when
deposited in the human lung. Zhang et al. (2017) suggested that the
particles may be formed from the condensation of SVOCs. Vance et al.
(2017) hypothesized that particles are formed through degradation of
ABS polymer, probably involving semi-volatile compounds. From
measurements in test chambers and real rooms, Mendes et al. (2017)
concluded that the particles consist of high and low-volatility compounds; however, only PLA and ABS were considered in this study.
The chemical composition of particles is of vital importance for a
better understanding of the potential health impacts. It also helps to
determine the nature of particle sources and particle-generating processes. In the study by Vance et al. (2017), the Raman peaks of particles
during 3D printing with ABS corresponded to the benzene ring and the
carbon-nitrogen triple bond. Zontek et al. (2017) applied Fouriertransform infrared spectroscopy and found that isocyanic acid and ndecane are possible chemical components of condensed aerosols from
ABS 3D printing. Stefaniak et al. (2017) found chromium (Cr) and iron
(Fe) in 3D printing-emitted particles. Despite the above-mentioned
qualitative analyses, many details about the composition of 3D
printing-emitted particles still remain unknown.
Previous studies on 3D printer emission were usually carried out
under varying test conditions, in either room environments or chambers
of different setups. Furthermore, the calculation methods of emission
rates also differed. Consequently, the obtained emission rates from
these studies cannot be directly compared. From studies on laser printer
emissions (Schripp et al., 2009; Schripp et al., 2008), we understand
that it is important to use a standard test protocol (ISO/ICE 28360,
2015).
Realizing the gap in the knowledge of 3D printer emission behavior,
we designed a standardized experimental test chamber setup, aiming at
the determination of the physical and chemical properties of 3D
printing-emitted particles and the quantification of particle and VOC
emission rates using multiple types of filaments. Our results add another piece to the difficult puzzle of 3D printer emission characteristics.
Table 1
Tested filaments and the main chemical composition.
Filament trade name
Main composition
ABS
ULTRAT
ASA
HIPS
PETG
GLASS
PCABS
ESDa
Acrylonitrile butadiene styrene
Acrylonitrile butadiene styrene + 0–3% polycarbonate
Acrylonitrile styrene acrylate
High impact polystyrene
Polyethylene terephthalate glycol
80% PETG + 8–12% fiber glass filings
30–35% polycarbonate + 55–65% ABS
PETG + carbon-based conductive additives
a
A filament with electrostatic discharge (ESD) protection.
Fig. 1. Photos of the printed object (see also Moylan et al. (2012)).
with electrostatic protection.
In addition to the main polymers, filaments usually contain additives such as stabilizers, lubricants, mineral oils, antioxidants, and
colorants. However, no information on the specific substances and mass
fraction of these additives is provided by the manufacturer.
The object to be printed (shown in Fig. 1) in the study is a model
proposed by the National Institute for Standards and Technology (NIST)
for additive manufacturing (Moylan et al., 2012). This model has been
used in previous studies (Azimi et al., 2016). It has a square base and
some small structures on the top and on one side wall. The size of the
model is 10 cm × 10 cm × 1 cm. In order to keep the printing duration
to about 4 h, the model was printed at 90% of its original size. The
printing time, object weight, and printing speed are provided in Appendix A (Table A.1) to permit the calculation of emission yields.
2. Methods
2.1. 3D printer and filaments
2.2. Chamber measurement
Our study aimed at the comparison of thermoplastic materials by
use of the FFF technique. Therefore, all experiments were carried out
with the same desktop 3D printer (Model M200, Zortrax, Poland). The
printer has a single extruder, one heated plate, and sidewalls but no
cover on the top. It does not apply glue on the printing bed. It can print
an object with a maximum size of 20 cm × 20 cm × 20 cm. The 3D
printer supports several filaments. Table 1 shows the filaments that
have been tested in this study. These filaments were purchased from
Zortrax and 3Dmensionals/Pontialis GmbH. They are based on five
basic thermoplastics: ABS, ASA, HIPS, PETG and PCABS. They have
different properties and are used for different applications. According to
the manufacturer, ASA is for outdoor application due to its better resistance to UV radiation and humidity; PETG is resistant to salts, acids,
and alkaline; PCABS is durable and impact resistant; ESD is a material
The 3D printing was carried out in a 3 m3 stainless steel chamber
(self-built, Fraunhofer WKI, Germany). The chamber fulfills the ISO
16000-9 (2006) standard, in which diverse requirements, including the
chamber material, tightness, air supply, and air mixing efficiency, are
specified. The incoming chamber air was cleaned and filtered to remove
organic compounds and particles. The chamber air was set to 23 °C and
50% relative humidity. The air exchange rate was set to 1.0 h−1 or
1.5 h−1, depending on the total air volume drawn by the measuring
instruments and sampling devices. As a quality assurance measure, the
chamber background concentrations of VOCs and particle numbers
were measured. After the printing experiment was finished, the
chamber was cleaned by heating to 65 °C for 11 h at an air exchange
rate of 1.0 h−1.
Fig. 2 is a schematic of the chamber measurement setup. First, the
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Environment International 123 (2019) 476–485
J. Gu et al.
can be obtained through comparison of the two FMPS signals (see
Fig. 4).
For the determination of the particle chemical composition, particles were first sampled on quartz fiber filter using a total particle
sampler at a flow rate of 20 L/min for about 4 h during the 3D printing
period. Prior to sampling, the filters were baked at 300 °C for 5 h to
remove any semi-volatile compounds. After sampling, the filter samples
were stored at 4 °C until extraction. The filter samples were Soxhlet
extracted with 100 mL acetone for 2 h. The extracted solution was reduced to 10 mL by evaporation and further concentrated to 100 μL with
nitrogen gas. The concentrated extract was analyzed for organic compounds on a coupled gas chromatograph/mass spectrometry (GC/MS)
system (Agilent 7890A GC; 7975C MSD; J&W HP-5ms capillary column,
30 m, 0.25 mm i.d., 0.25 μm thickness). Before choosing the method, we
tried to sample particles on a quartz fiber filter followed by a polyurethane foam (PUF) cartridge as backup for SVOCs in the gas phase.
This method (filter + PUF) was not successful and was not adopted.
Discussions on methods determining the particle chemical composition
can be found in Section 3.3.
VOCs from 4 L of chamber air were sampled on stainless steel tubes
filled with Tenax® TA. In three measurements, VOCs were sampled
using Carbotrap® tubes in parallel with Tenax® TA tubes. Details can be
found in Section 3.3 and in Appendix A (Table A.2). The tubes were
analyzed on a GC/MS system (Agilent 7890A GC; 7975C MSD; J&W DB5ms capillary column, 60 m, 0.25 mm i.d., 0.25 μm thickness) after
thermal desorption (Markes TD-100). VVOCs from 4 L of chamber air
were sampled on stainless steel tubes filled with Carbograph 5TD and
analyzed by thermal desorption GC/MS (Agilent 7890A GC; 7975C
MSD; J&W DB-5ms capillary column, 60 m, 0.25 mm i.d., 0.25 μm
thickness). This analytical method has been developed by Schieweck
et al. (2018) and is suitable for the analysis of VVOCs between C3 and
C6. The sampling of VOCs and VVOCs during printing was duplicated.
Two tubes were sampled in parallel and analyzed.
Moreover, particles were collected on Whatman Nuclepore™ tracketched membrane filters made of polycarbonate (pore size 15 nm)
during 3D printing with ABS, PETG and GLASS. The samples were
coated with carbon and analyzed by Scanning Electron Microscopy
(SEM) (Zeiss LEO, Model 1530). However, the microscopic analysis did
not provide reliable results.
Fig. 2. Schematic of the 3D printing emission test in the chamber.
online particle measuring instruments (FMPS and OPS, descriptions are
provided in Section 2.3) were started. Then air samples were taken for
determining the chamber background concentrations of very volatile
and volatile organic compounds (see Salthammer (2016) for definitions
of VVOCs and VOCs). Second, the 3D printer was loaded into the
chamber, switched into stand-by mode. VVOC and VOC samples were
taken 1 h after loading. Third, when the 3D printing started, the particle
filter sampling started and lasted until the printing process was finished. VOCs were sampled 1 and 2 h after 3D printing started, respectively. VVOC sampling was carried out 1.5 h after 3D printing started.
Online particle measurement (FMPS and OPS) continued after the end
of the printing to determine the decay kinetics of the particle concentration. A detailed overview of the measurement and sampling time
is provided in Fig. A.1. A single test has been performed for each filament except ABS, for which different filament colors and printing
temperatures have been additionally tested (see Table 2).
2.3. Instruments and chemical analysis
The particle number size distribution (PNSD) was measured by a
Fast Mobility Particle Sizer (FMPS, model 3091, TSI Inc., USA) in the
size range of 5.6–560 nm and by an Optical Particle Sizer (OPS, model
3330, TSI Inc., USA) in the size range of 0.3–10 μm. Both instruments
can measure PNSD at a high time-resolution. A second FMPS was
connected downstream to a self-built thermo-denuder (TD), which is
designed for a maximum air flow of 10 L/min and can be heated
stepwise from room temperature to 300 °C. The PNSD after heating was
measured by the second FMPS. The information on particle volatility
Table 2
Overview of printing conditions, median PNCs, CMDa, and particle unit specific emission rates (SER)a during 3D printing with different filaments.
Filamentb_color
ABS_Blue
ABS_Green
ABS_Grey
ABS_Red
ABS_Red
ABS_Red_230
ABS_Red_240
ABS_Red_250
ABS_Red_260
ABS_White
ULTRAT_Ivory
ASA_Blue
PETG_Black
ESD_Black
GLASS_Transparent
HIPS_Yellow
PCABS_Ivory
Test roundc
2
2
2
2
1
2
2
2
2
1
2
2
1
2
1
1
1
Printing temp. (°C)
275
275
275
275
275
230
240
250
260
275
260
254
254
280
254
255
290
Printing bed temp. (°C)
PNC0.3–10μm (#/cm3)
PNC5.6–560nm (#/cm3)
Backgroundd
Printing
Backgroundd
2
1
3
2
0
3
4
2
4
3
4
11
3
6
0
1
0
16
17
18
20
22
1
1
2
5
15
14
45
27
1
149
61
56
241
163
213
219
10
166
323
266
212
169
173
220
48
168
12
103
3
80
80
80
80
80
80
80
80
80
80
80
90
30
70
30
80
105
CMD (nm)
Particle SER (#/min)
27
30
27
28
30
31
29
29
24
27
24
24
59
30
82
41
32
3.8 × 1010
4.3 × 1010
6.5 × 1010
4.1 × 1010
4.5 × 1010
4.2 × 109
8.3 × 109
2.3 × 1010
1.3 × 1011
2.9 × 1010
1.4 × 1011
1.7 × 1011
9.7 × 109
6.5 × 1010
2.0 × 109
3.3 × 109
7.3 × 1010
Printing
3.4 × 105
3.4 × 105
4.4 × 105
2.3 × 105
2.7 × 105
3.3 × 104
5.0 × 104
8.7 × 104
7.3 × 105
2.5 × 105
9.9 × 105
7.3 × 105
1.2 × 105
2.4 × 105
2.1 × 105
2.4 × 105
7.0 × 105
PNC0.3–10μm was measured by OPS for particles in the size range of 0.3–10 μm; the other particle parameters (PNC5.6–560nm, CMD and particle SER) were for
particles in the size range of 5.6–560 nm measured by FMPS.
b
ABS-based filaments include ABS and ULTRAT; The PETG-based filaments include PETG, ESD and GLASS.
c
The air exchange rate was set to 1.0 h−1 in test round 1 and 1.5 h−1 in test round 2.
d
Chamber background PNCs were calculated after 3D printer was loaded and before 3D printing started.
a
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J. Gu et al.
ABS_Red_260 °C, and ESD_Black), PNC0.3–10μm during printing were
very low (lower than the background level), indicating few particles
being emitted in the size range of 0.3–10 μm.
The particle SERs in Table 2 were calculated for particles in the size
range of 5.6–560 nm. The observed particle SERs ranged from
2.0 × 109 (GLASS) to 1.7 × 1011 (ASA) #/min, covering a range of
nearly two magnitudes. The mean particle emission when printing ABS
at the default temperature was (4.7 ± 1.1) × 1010 (mean ± standard
deviation) #/min. High particle SERs were found during printing with
ASA (blue), ULTRAT (ivory), ESD (black) and PCABS (ivory). Printing
with GLASS (transparent), HIPS (yellow), and PETG (black) was associated with lower particle SERs. The particle emissions for the ABS_Red
filament were evaluated under different printing temperatures. In addition to the default printing temperature of 275 °C for ABS, we measured particle emission at four different temperatures of 230 °C, 240 °C,
250 °C and 260 °C, respectively. Particle SERs for ABS decreased with
lower extruding temperatures from 260 to 230 °C. This is consistent
with other studies on the relationship between particle emission and 3D
printer extruder temperatures (Zhang et al., 2017), and the association
of particle emission with fuser temperature on laser printers (Wensing
et al., 2009b).
The particle SERs for ABS reported by previous studies were in a
wide range of 2.4 × 108 to 1.5 × 1012 #/min (Azimi et al., 2016; Floyd
et al., 2017; Kim et al., 2015; Seeger et al., 2018; Steinle, 2016;
Stephens et al., 2013; Vance et al., 2017; Zhang et al., 2017). The SERs
for ABS measured in this study are similar to those found by Azimi et al.
(2016) when printing the same NIST object (2–9 × 1010 #/min) and
Zhang et al. (2017) (interquartile range about 1 × 1010–1 × 1011 #/
min).
2.4. Calculation of emission rates
The air pollutant concentration in the chamber air is influenced by
the emission strength and the removal rate. A mass balance Eq. (1) can
be used to describe the change of the chamber concentration with time
dc (t )
= L·SER (t ) − k ·c (t ),
dt
(1)
where c(t) is the pollutant concentration at time t, L is the unit loading
factor in the chamber (m−3), SER(t) is the unit specific emission rate at
time t, and k is the total loss coefficient (h−1). When the concentration
reaches a steady state with dc(t)/dt = 0, Eq. (2) is obtained.
SER = k ·c (t )/ L
(2)
For the non-steady state condition with dc(t)/dt ≠ 0, SER(t) can be
calculated by the convolution Eq. (3) as described by Schripp et al.
(2009).
SER (t ) =
c (t ) − c (t − ∆t )·e−k ∆t
L·∆t·e−k ∆t
(3)
where Δt is the time interval between two adjacent measurements.
The total loss coefficient k for particles was obtained by exponential
fitting of the particle decay curve (for detailed description see Schripp
et al. (2011)). k includes all ways of particle losses including air exchange, particle losses on chamber wall, deposition and coagulation.
The VOCs, VVOCs, and TVOC (sum of total VOCs between C6 and
C16) emission rates were calculated using Eq. (2). We assumed that air
exchange is the only way for the loss of VOCs. The chamber is constructed from polished stainless steel, and the VOCs have a high recovery rate (> 80%, as required by ISO 16000-9 standard), indicating
that such an assumption is reasonable. The concentrations during the
warm-up phase after the 3D printer is loaded into the chamber were
subtracted from C(t). We used this simplified method because VOCs and
VVOCs were determined discontinuously, which requires a sampling
time of 32 min. TVOC concentrations at 1st and 2nd hour during
printing processing were close (the interquartile range of the relative
differences of the 1st and 2nd hour TVOC concentrations is 3.2–17.5%).
3.1.1. Particle size distribution
Each 3D printing job lasted for about 4 h. The particle number size
distribution (PNSD) for particles in the size range of 5.6–560 nm during
printing with ABS_Red and ASA_Blue is shown in Fig. 3. The PNC increased (~1 min) before printing started, presumably due to the
heating of the residual filament in the extrusion nozzle. The PNC then
increased rapidly when the printing process began. The PNC decreased
after 3 h but increased again about 30 min before the printing was
finished. The growth in size of particles was observed at the beginning
of the printing phase. For ABS, the initial PNSD peaked at 11 nm, and
increased to about 30 nm within 20 min. The PNSD then remained
stable until the 3rd printing hour. Similar observations were obtained
for the other filaments including ASA, ESD, PCABS, HIPS, PETG and
GLASS. The median PNC (5.6–560 nm) and the particle count median
diameter (CMD) during printing are shown in Table 2. CMD was about
or < 30 nm for most printing jobs and filament types except for PETG
(59 nm), GLASS (82 nm) and HIPS (41 nm).
3.1.3. Chemical composition
Table 3 shows the quantified organic compounds collected on
quartz fiber filters during 3D printing. There are four compounds, caprolactam, 4-tert-butylphenol, 2,4-di-tert-butylphenol and DEP, which
can be grouped as VOCs. The other compounds are SVOCs. In the
chamber blank sample, trace amounts of n-octyl ether, DiBP, TPPO, and
methyl palmitate were detected. DEP, DnBP and DiBP are typical
plasticizers; TCEP, TPPO and TDTBP are flame retardants; Irganox 1076
is an antioxidant. Bisphenol A is a monomer of polycarbonate. It could
also be used as a stabilizing additive, which may explain its presence in
ABS and ASA. Most of the printing-related compounds appeared in low
concentrations of < 100 ng/m3. Irganox 1076 was detected during
printing with three filaments (PCABS, ABS, and ASA) and the concentrations were the highest compared with other substances.
In addition to the substances listed in Table 3, several cyclosiloxanes, including tetradecamethylcycloheptasiloxane (D7) and hexadecamethylcyclooctasiloxane (D8) were identified but not quantified
in the quartz fiber filter samples. We also observed increased cyclosiloxane (D3–D6) concentrations in the VOC samples (Tenax® TA) when
the 3D printer was turned on (not printing) and the printing bed was
automatically heated to 55 °C. See Section 3.2 for details. These cyclosiloxanes may be used as lubricants in the mechanical components of
the 3D printer, thereby being released when the printing bed is heated.
The particle sampling was carried out using a total particle sampler,
the particle mass size distribution can be estimated from the particle
number size distribution measurements (by FMPS and OPS), assuming
particles are spherical and have a density of 1.0 g/cm3. We found that
the particle mass was mainly distributed in the size range of
40–200 nm. Very little mass was distributed above 1 μm.
3.1.2. Particle emission rates
Median PNCs during printing and background PNCs before 3D
printing started are shown in Table 2. PNC5.6–560nm during printing
increased greatly compared with background concentrations.
PNC0.3–10μm during printing were in the range of 1–149 #/cm3. In
several tests (ABS_Red_230 °C, ABS_Red_240 °C, ABS_Red_250 °C,
3.1.4. Particle volatility
The particle volatility was studied by measuring PNSD using a FMPS
after the particles passed through a thermo-denuder (TD), which was
heated stepwise from room temperature to 300 °C. The temperature
increased by 50 °C in each step. In parallel, another FMPS measured the
PNSD at room temperature. Due to technical issues, complete results
3. Results and discussions
3.1. Release of particles
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Fig. 3. Development of PNSD during 3D printing with ABS_Red (a) and ASA_Blue (b). Note the scales are different for (a) and (b).
particle size and number concentrations gradually decreased with the
increase of temperature. A considerable decrease in particle size and
number was observed at 150 °C (TD temperature at 100 °C was
skipped). The major particle mode changed from 60–70 nm at 23 °C to
34–39 nm at 150 °C, 29 nm at 200 °C, and 11 nm at 250 °C and 300 °C.
At 250 °C, almost all particles > 60 nm had disappeared. For particles
emitted from printing with ABS, particle sizes and concentrations
changed little at 100 °C. Visible decrease in particles > 50 nm started
could only be obtained for HIPS, ABS, and PETG (up to 250 °C).
Fig. 4 shows the PNC measured by FMPS 1 and FMPS 2 coupled with
TD during 3D printing with HIPS (Fig. 4a), ABS (Fig. 4b) and PETG
(Fig. 4c). PNC decreased at increased TD temperatures. Fig. 5 shows the
change of PNSD when the aerosol was thermally stressed (Fig. 5a, c, e),
and the volatility of peak mode particles (Fig. 5b, d, f). PNSD in counter
plot is shown in Appendix A (Fig. A.2).
With respect to particles emitted from 3D printing with HIPS, the
Table 3
Concentrations of organic compounds (ng/m3)a in chamber air collected on quartz fiber filter during 3D printing with several filaments.
Substance
Caprolactam
4-tert-Butylphenol
2,4-Di-tert-butylphenol
Diethyl phthalate (DEP)
n-Octyl ether
Lauryl acrylate
Tris-(2-chloroethyl)-phosphate (TCEP)
Diisobutyl phthalate (DiBP)
Methyl palmitate
Di-n-butyl phthalate (DnBP)
Bisphenol A
Triphenylphosphine oxide (TPPO)
Tris(2,4-di-tert-butylphenyl) phosphate (TDTBP)
Irganox 1076
a
b
Chamber blankb
PCABS Ivory
ABS Red
HIPS Red
PETG Black
ASA Blue
6
22
59
33
28
19
39
30
17
12
8
31
19
70
63
26
79
17
143
46
936
17
41
25
47
10
185
78
1043
Missing value means not detected or below detection limit.
Filter sampling of the chamber blank was taken in a separate test (sampling for 4 h in the empty chamber).
480
20
19
16
107
41
101
24
92
12
8
23
55
30
59
26
80
18
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71
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Fig. 4. PNC during 3D printing with HIPS (a), ABS (b) and PETG (c), respectively, measured in parallel by FMPS 1 and FMPS 2 combined with thermo-denuder (TD)
under different temperatures. Dashed line indicates the ratio of PNC by FMPS 2 + TD: FMPS 1.
The particle volatility result agreed with the particle chemical
composition in that particles are composed of SVOCs. First, this provides additional evidence regarding the particle formation mechanism
of SVOC-involved nucleation and condensation, which has been hypothesized in previous studies (Vance et al., 2017; Zhang et al., 2017).
Second, proper sampling methods are needed to catch SVOCs that are
distributed in both gas and particle phases. Particles may also be lost
during certain analytical procedures such as SEM. Third, upon inhalation, particles emitted from 3D printing may have different clearance
pathways than solid nanoparticles or soot, due to differences of particle
solubility on lipids or in intracellular and extracellular fluid
(Oberdörster et al., 2005; Tantra et al., 2016). The toxicity of UFPs
emitted from 3D printing deserves more study.
at 150 °C. The particle mode around 30 nm decreased dramatically at
200 °C. The smallest particles, particles with a diameter of around
10 nm, however, showed little change even at 300 °C. For particles
emitted from printing with PETG, PNC decreased by 32%, 55% and
73% at 150 °C, 200 °C, and 250 °C, respectively. The peak mode particle
(70 nm) decreased by 87% at 150 °C. The major particle mode shifted
greatly, from 70 nm at room temperature to 34 nm at 150 °C, and to
11 nm at 250 °C.
The results show that particles started to evaporate at 150 °C. At
300 °C, about 25% of particles remained with the particle size mode of
11 nm. In this study, we stressed the bulk aerosol from chamber air in
the heated thermo-denuder and measured the particle size distribution
after heating. The method was similar to a study by Wensing et al.
(2009a), and different from some others (Mendes et al., 2017;
Morawska et al., 2009), in which mono-dispersed particles were selected by a DMA before heating. The choice was made due to the fact
that the FMPS does not select and scan particle sizes. However, the
thermo-denuder was designed for the working flow rate of 10 L/min,
which allows it to be used together with FMPS. The particle volatility
results are obtained specifically under this test condition.
We did not detect any particles using SEM analysis (results not
shown). One possible explanation is that the particles, which are mainly
composed of SVOCs, may evaporate under vacuum and the high-energy
electron beam in SEM analysis.
3.2. Release of VOCs
3.2.1. VOCs
Fig. 6 shows the VOC concentrations in the chamber air by Tenax®
TA before and during 3D printing with HIPS. Two chamber background
concentrations of VOCs were measured, the first one before the 3D
printer was loaded (empty chamber background) and the second one
after loading the printer (background with 3D printer loaded). The
empty chamber background has low concentrations of acetic acid.
When the printer was loaded into the chamber and powered on (stand481
Environment International 123 (2019) 476–485
J. Gu et al.
Fig. 5. PNSD during 3D printing with HIPS (a), ABS (c), and PETG (e) after passing through thermo-denuder (TD) under different temperatures, and the volatility of
the peak-mode particles emitted during 3D printing with HIPS (b), ABS (d) and PETG (f). The volatility is expressed as the fraction of particle number remaining after
passing through TD.
55 °C, thus facilitating the evaporation of volatile organics. However,
when the printer is loaded in the chamber and conditioned overnight,
only low concentrations of cyclosiloxanes are detected in the chamber
air. This again indicates that the cyclosiloxanes are emitted from the
heated bed during warm-up of an idling 3D printer, but to a lesser
extent by the 3D printing process.
Major VOC species emitted during 3D printing are summarized in
by, no printing), increased concentrations of cyclosiloxanes, including
hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4),
decamethylcyclopentasiloxane (D5) and dodecamethylcyclohexasiloxane (D6), were observed. Similar cyclosiloxane concentrations
were detected during the printing phase, which points towards the
printer case as the exclusive source of these substances. When the 3D
printer is powered on, the printing bed is heated automatically to about
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with higher concentrations during printing than background concentrations. Lower aldehydes (acetaldehyde, 2-propenal) were detected
often. Acrylonitrile was detected exclusively during tests with ABSbased filaments.
3.3. Considerations on measurement & chemical analysis
In this study, different methods for measuring the particulate and
gaseous pollutants were employed. Some were found to be successful,
while others showed limitations or failed. In the following, we therefore
discuss these measurement and analytical issues.
VOC sampling: VOCs were first sampled with Tenax® TA sorbent
tube. Substances including benzaldehyde and n-nonanal were detected
at low concentrations (a few μg/m3). These compounds could be
emitted from 3D printing but could also be the by-products of Tenax®
TA degradation, when reactive chemicals are present (Clausen and
Wolkoff, 1997; Klenø et al., 2002). To find out which source is responsible, we additionally carried out a comparison test using Carbotrap® tube, which has no degradation products of benzaldehyde and nnonanal. VOCs were sampled in parallel on Tenax® TA tubes and Carbotrap® tubes during 3D printing with ABS, HIPS and PCABS, respectively. The data are presented in Appendix A (see Table A.2). The
comparison shows that both Tenax® TA and Carbotrap® tubes detected
benzaldehyde and n-nonanal at the same levels, proving that Tenax® TA
is suitable for VOC sampling in this 3D printing emission experiment.
Particle chemical composition: Because particles emitted from 3D
printing are likely to consist of semi-volatile substances, the constituents can be found in both particle and gas phases. In this study, we
initially tried to sample particles using a quartz fiber filter, and a PUF
cartridge as backup for SVOCs in the gas phase. This method was not
successful because of the high background of PUF, which interferes
heavily with the chemical characterization. Consequently, particles
were sampled on quartz fiber filter only. This approach works better
due to the low background in the quartz fiber filter. However, although
a proportion of SVOCs in the particle phase could be lost due to evaporation during the sampling period (negative bias, blow-off), and some
part of the SVOCs in the gas phase might condense on the filter (positive
bias), it was regarded as a priority of this study to first identify the
chemicals. A more accurate quantification could be done by coupling a
denuder (for SVOC vapor) – quartz fiber filter (for particulate SVOCs) low background backup foam (for evaporated particulate SVOCs).
Another difficulty in obtaining the particle chemical composition is
the low concentration and the limitation of the air sampling volume.
For SVOCs at very low concentrations (shown in Table 3), a high sample
volume is preferred but is difficult to achieve in a chamber experiment.
Firstly, the sample flow rate is limited by the chamber size and air
exchange rate. Secondly, the relatively short printing time restricts the
sampling time. Therefore, the use of a large sampling volume and the
smallest possible volume of the extraction is recommended.
Fig. 6. VOCs chamber air concentrations (using Tenax® TA tubes) before and
after loading the 3D printer, and during 3D printing with HIPS_Yellow. VOCs
were sampled by Tenax® TA tubes. The chamber air exchange rate was 1.0 h−1.
Table 4. The background concentrations (when the 3D printer is
loaded) have been subtracted when calculating the emission rates. The
TVOC emission rates, calculated as the sum of VOCs in C6–C16, are also
shown.
3D printing with PETG and GLASS was related with low TVOC
emission, while high emission rates were found for ULTRAT, ASA and
ABS. The most abundant VOC was styrene for most of the filaments
except PETG-based filaments (PETG, GLASS and ESD). In addition, for
the eight filaments, benzaldehyde (8 times), acetophenone (6 times),
ethylbenzene (5 times), toluene (5 times), and other C3-benzenes (5
times) were detected. VVOCs, including acrylonitrile (5 times) and
acetone (5 times) were also observed; however, their concentrations
may have been underestimated due to their low breakthrough volume
on Tenax® TA. Emissions of dodecamethylcyclohexasiloxane and/or
other siloxanes from ABS, HIPS and ASA were found, which may be
caused by the variations of siloxane concentrations between background and during printing rather than direct emissions from 3D
printing (see discussion above).
Filaments that have the same basic polymers may show different
VOC emission profiles: For instance, ABS and ULTRAT are mainly based
on ABS polymer, and while the main monomers styrene and acrylonitrile were often detected, both the TVOC emission rates and other major
VOCs differed. The printing temperatures of ABS and ULTRAT are also
different (275 °C vs. 260 °C). Therefore, no conclusion can be drawn as
to whether the subtle difference in the filament composition, the
printing temperatures, or other undefined factors are contributing to
the different VOC emissions. The same is found for PETG and ESD,
which are both PETG-based materials.
As previous studies mainly focused on PLA and ABS, few data are
available for comparison. Caution should also be exercised when
comparing the TVOC SERs with other studies, as the experiment conditions could be different. The SERs for ABS obtained in this study
(about 15 μg/min) was in the range of 10–68 μg/min reported by Azimi
et al. (2016), Floyd et al. (2017), Stefaniak et al. (2017) and Steinle
(2016). The SER for HIPS in this study was 6.8 μg/min; in comparison,
33 and 46.9 ± 0.5 μg/min were reported from 3D printing with HIPS
by Azimi et al. (2016) and Floyd et al. (2017), respectively. The SER for
PCABS in this study (9.1 μg/min) was lower than the 65.9 ± 0.3 μg/
min found by Floyd et al. (2017).
4. Conclusions
In this study, we measured and characterized the particles and organic compounds emitted from a desktop 3D printer in an environmental test chamber. High PNCs (in the size range of 5.6–560 nm) in
the chamber were measured during 3D printing. The emitted particles
from most filaments have CMD around or < 30 nm, except two PETGbased filaments (59, 82 nm) and HIPS (41 nm). The particle emission
rates varied from 2.0 × 109 #/min (GLASS, a PETG-based filament) to
1.7 × 1011 #/min (ASA). The chemical composition of particles collected on the quartz fiber filter was analyzed. Most of the quantified
chemicals are SVOCs, mainly ingredients of the thermoplastics, including the monomer caprolactam, phthalates, flame retardants and
stabilizers. Cyclosiloxanes (D3–D6 in VOC samples and D7–D8 in particle filter samples) were detected as well. It is evident that D3–D6 were
emitted during the heating of the printing bed. Particle volatility was
3.2.2. VVOCs
Table 5 shows the concentrations of VVOCs sampled by Carbograph
tubes and the emission rates during 3D printing. Only a few VVOCs
were detected, mainly lower aldehydes, alcohols, and acrylonitrile,
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Table 4
VOC emission rates (μg/min)a during 3D printing with different filaments.
Substance
ABS Red
ULTRAT Transparent
b
2-Propenal
Acetoneb
Acrylonitrileb
Acetic acid
Hexane
Benzene
Cyclohexane
2-Methylhexane
n-Butanol
3-Methylhexane
Trichloroethene
Methyl methacrylate
Toluene
n-Butyl acetate
4-Vinylcyclohexene
Ethylbenzene
m,p-Xylene
Styrene
o-Xylene
Nitrogenous substance or siloxanec,d
Benzaldehyde
Phenol
α-Methylstyrene
Benzonitrile
Octanal
2-Ethyl-1-hexanol
Aldehydec,d
Acetophenone
2-Phenyl-2-propanol
n-Nonanal
Dioxanec,d
1-Dodecene
Benzoic acid
2-Phenylpropenalc
3,6-Dimethyl-1,4-dioxane-2,5-dionec
n-Decanal
1,5-Dimethyltetralinc
4-tert-Butylphenol
Dodecamethylcyclohexasiloxane
Dodecanal
4-Phenylbutyronitrilec
Quinolinec
2-Isopropenylindolizinec
4-Phenylcyclohexene
Carboxylic acid esterd,e
2,4-Di-tert-butylphenol
Naphthalenecarbonitrilee
Sum other iso/cycloalkanesd
Sum other siloxanesd
Sum other C3-benzenesd
Sum other sesquiterpenesd
Sum VOC (C6–C16)
ASA Blue
HIPS Yellow
PETG Black
GLASS Transparent
PCABS Ivory
ESD Black
0.1
0.2
0.1
0.7
0.4
0.1
0.4
0.2
0.3
0.04
0.1
0.3
0.1
0.2
0.1
0.2
0.2
0.2
0.2
0.2
1.1
0.2
0.3
0.1
0.4
0.1
0.3
3.9
0.6
0.2
0.5
0.7
0.1
0.1
0.1
0.3
0.9
0.1
0.2
0.4
0.1
2.1
0.4
4.8
0.2
6.4
0.2
0.8
0.1
0.8
1.4
0.1
26.3
0.1
1.7
0.2
0.2
0.1
0.1
0.2
0.8
1.6
0.1
0.5
4.8
1.3
0.2
0.5
0.1
0.5
0.8
0.1
3.0
0.1
0.1
0.2
0.2
0.1
0.4
0.5
0.3
0.1
0.1
0.1
0.1
0.1
0.2
0.1
0.1
0.3
0.1
0.3
0.9
0.2
0.1
0.2
0.3
0.3
0.2
0.2
0.2
0.3
0.3
0.3
3.0
0.4
0.2
0.03
0.1
0.2
0.4
1.6
0.8
0.1
0.1
0.5
0.2
0.1
0.3
0.2
0.04
0.1
0.1
0.1
0.3
0.6
1.2
0.2
0.1
0.2
0.5
15.3
40.5
0.2
0.1
0.3
0.5
0.3
0.6
0.5
0.5
0.2
0.2
17.3
6.8
0.6
0.2
0.5
0.2
0.2
0.1
0.1
9.1
4.4
a
Missing value means not detected or below detection limit.
VVOCs measured with Tenax® TA.
c
Quantified using toluene as reference.
d
Exact isomer cannot be determined, instead, the type of substances is given.
e
Quantified using methyl dodecanoate as reference.
b
cyclosiloxanes. Our data, which supplement results from previous studies, lead to the conclusion that, regarding particulate and gaseous
emissions, 3D printing technology and the chemical composition of filaments still need to be optimized.
evaluated by heating the aerosol and measuring the particle size distribution. Emitted particles are volatile, and start to evaporate from
150 °C.
The results show large variations of VOC emission rates from different filaments: the total VOC (C6–C16) emission rates ranged from
0.2 μg/min (GLASS, a PETG-based filament) to 40.5 μg/min (ULTRAT,
an ABS-based filament). Styrene was the major VOC, followed by other
substances including benzaldehyde and ethylbenzene. VVOCs were also
sampled and only a few substances (e.g. acetaldehyde and 2-propanal,
acrylonitrile, and alcohol) were detected at low concentrations. To the
best of our knowledge, we have demonstrated for the first time that the
particles emitted from a desktop 3D printer are semi-volatile and are
composed of SVOCs which are mainly thermoplastic additives and
Acknowledgement
This work is supported by Fraunhofer WKI internal funding. We
would like to thank Alexander Omelan and Deniz Varol for the chemical
analysis of particle filter samples.
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Table 5
VVOC chamber air concentrationsa and emission rates during 3D printing.
Filament
Substance
Concentration (μg/m3)
Background
ASA_Blue
ESD_Black
ULTRAT_Ivory
ABS_Gray
ABS_Green
ABS_Blue
a
b
Acetaldehyde
n-Butanol
Butaneb
2-Propenal
Acrylonitrileb
Ethanol
2-Propenal
Acetone
Acrylonitrileb
Acetaldehyde
2-Propenal
8
1
3
<1
4
<1
<1
<1
<1
7
<1
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Emission rates
(μg/min)
1.5 h after
printing
19
5
5
4.5
22
2.5
4
5.5
2
12
4
0.8
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Chamber air exchange rate of 1.5 h−1.
Quantified using toluene as reference.
Declarations of interest
None.
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.envint.2018.12.014.
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